Part 4 — Structural Design

(1) The scope of this Part shall be as described in Subsection 1.1.2. of Division A.

(1) Buildings and their structural members and connections including formwork and falsework shall be designed to have sufficient structural capacity and structural integrity to safely and effectively resist all loads, effects of loads and influences that may reasonably be expected, having regard to the expected service life of buildings, and shall in any case satisfy the requirements of this Section.

(2) Buildings and their structural members shall be designed for serviceability, in accordance with Articles 4.1.3.4. to 4.1.3.6.

(3) All permanent and temporary structural members, including formwork and falsework of a building, shall be protected against loads exceeding the specified loads during the construction period except when, as verified by analysis or test, temporary overloading of a structural member would result in no impairment of that member or any other member.

(4) Precautions shall be taken during all stages of construction to ensure that the building is not damaged or distorted due to loads applied during construction.

(1) Except as provided in Sentence (2), buildings and their structural members shall be designed in conformance with the procedures and practices provided in this Part.

(2) Provided the design is carried out by a person especially qualified in the specific methods applied and provided the design demonstrates a level of safety and performance in accordance with the requirements of this Part, buildings and their structural components falling within the scope of this Part that are not amenable to analysis using a generally established theory may be designed by,

(a) evaluation of a full-scale structure or a prototype by a loading test, or

(b) studies of model analogues.

(1) Except as provided in Article 4.1.2.2., the categories of loads, specified loads and effects set out in Table 4.1.2.1.A. shall be taken into consideration in the design of a building and its structural members and connections.

Table 4.1.2.1.A. Categories of Loads, Specified Loads and Effects

**Forming Part of Sentence 4.1.2.1.(1)**

(1) Load means the imposed deformations (i.e., deflections, displacements or motions that induce deformations and forces in the structure), forces and pressures applied to the building structure.

(2) Permanent load is a load that changes very little once it has been applied to the structure, except during repair.

(3) Variable load is a load that frequently changes in magnitude, direction or location.

(4) Rare load is a load that occurs infrequently and for a short time only.

(2) Minimum specified values of the loads described in Sentence (1), as set forth in Subsections 4.1.4. to 4.1.8., shall be increased to account for dynamic effects where applicable.

(3) For the purpose of determining specified loads S, W or E in Subsections 4.1.6. to 4.1.8., buildings shall be assigned an Importance Category based on intended use and occupancy, in accordance with Table 4.1.2.1.B.

Table 4.1.2.1.B. Importance Categories for Buildings

**Forming Part of Sentence 4.1.2.1.(3)**

(1) Where a building or structural member can be expected to be subjected to loads, forces or other effects not listed in Article 4.1.2.1., such effects shall be taken into account in the design based on the most appropriate information available.

(1) In this Part, the term,

(a) "limit states" means those conditions of a building structure that result in the building ceasing to fulfill the function for which it was designed. (Those limit states concerning safety are called ultimate limit states (ULS) and include exceeding the load-carrying capacity, overturning, sliding and fracture; those limit states that restrict the intended use and occupancy of the building are called serviceability limit states (SLS) and include deflection, vibration, permanent deformation and local structural damage such as cracking; and those limit states that represent failure under repeated loading are called fatigue limit states),

(b) "specified loads (C, D, E, H, L, P, S, T and W)" mean those loads set out in Table 4.1.2.1.A.,

(c) "principal load" means the specified variable load or rare load that dominates in a given load combination,

(d) "companion load" means a specified variable load that accompanies the principal load in a given load combination,

(e) "service load" means a specified load used for the evaluation of a serviceability limit state,

(f) "principal-load factor" means a factor applied to the principal load in a load combination to account for the variability of the load and load pattern and the analysis of its effects,

(g) "companion-load factor" means a factor that, when applied to a companion load in the load combination, gives the probable magnitude of a companion load acting simultaneously with the factored principal load,

(h) "importance factor, I," means a factor applied in Subsections 4.1.6. to 4.1.8. to obtain the specified load and take into account the consequences of failure as related to the limit state and the use and occupancy of the building,

(i) "factored load" means the product of a specified load and its principal-load factor or companion-load factor,

(j) "effects" refers to forces, moments, deformations or vibrations that occur in the structure,

(k) "nominal resistance, R," of a member, connection or structure, is based on the geometry and on the specified properties of the structural materials,

(l) "resistance factor, Φ," means a factor applied to a specified material property or to the resistance of a member, connection or structure, and that, for the limit state under consideration, takes into account the variability of dimensions and material properties, workmanship, type of failure and uncertainty in the prediction of resistance, and

(m) "factored resistance, ΦR," means the product of nominal resistance and the applicable resistance factor.

(1) A building and its structural components shall be designed to have sufficient strength and stability so that the factored resistance, ΦR, is greater than or equal to the effect of factored loads, which shall be determined in accordance with Sentence (2).

(2) Except as provided in Sentence (3), the effect of factored loads for a building or structural component shall be determined in accordance with the requirements of this Article and the following load combination cases, the applicable combination being that which results in the most critical effect:

(a) for load cases without crane loads, the load combinations listed in Table 4.1.3.2.A., and

(b) for load cases with crane loads, the load combinations listed in Table 4.1.3.2.B.

(3) Other load combinations that must also be considered are the principal loads acting with the companion loads taken as zero.

(4) Where the effects due to lateral earth pressure, H, restraint effects from pre-stress, P, and imposed deformation, T, affect the structural safety, they shall be taken into account in the calculations, with load factors of 1.5, 1.0 and 1.25 assigned to H, P and T respectively.

(5) Except as provided in Sentence 4.1.8.16.(1), the counteracting factored dead load, 0.9D in load combination cases 2, 3 and 4 and 1.0D in load combination case 5 of Table 4.1.3.2.A. and 0.9D in load combination cases 1 to 5 and 1.0D in load combination case 6 of Table 4.1.3.2.B., shall be used when the dead load acts to resist overturning, uplift, sliding, failure due to stress reversal, and to determine anchorage requirements and the factored resistance of members.

(6) The principal-load factor 1.5 for live loads, L in Table 4.1.3.2.A. and LXC in Table 4.1.3.2.B. may be reduced to 1.25 for liquids in tanks.

(7) The companion-load factor for live loads, L in Table 4.1.3.2.A. and LXC in Table 4.1.3.2.B. shall be increased by 0.5 for storage areas and for equipment areas and service rooms referred to in Table 4.1.5.3.

(8) Except as provided in Sentence (9), the load factor 1.25 for dead load, D, for soil, superimposed earth, plants and trees given in Tables 4.1.3.2.A. and 4.1.3.2.B. shall be increased to 1.5, except that when the soil depth exceeds 1.2 m, the factor may be reduced to 1 + 0.6/hs but not less than 1.25, where hs is the depth of soil in metres supported by the structure.

(9) A principal-load factor of 1.5 shall be applied to the weight of saturated soil used in load combination case 1 of Table 4.1.3.2.A.

(10) Earthquake load, E, in load combination case 5 of Table 4.1.3.2.A. and case 6 of Table 4.1.3.2.B. includes horizontal earth pressure due to earthquake determined in accordance with Sentence 4.1.8.16.(4).

(11) Provision shall be made to ensure adequate stability of the structure as a whole and adequate lateral, torsional and local stability of all structural parts.

(12) Sway effects produced by vertical loads acting on the structure in its displaced configuration shall be taken into account in the design of buildings and their structural members.

**Forming Part of Sentences 4.1.3.2.(2) and (5) to (10)**

(1) See Sentences 4.1.3.2.(2), (3) and (4).

(2) See Sentence 4.1.3.2.(9).

(3) See Sentence 4.1.3.2.(8).

(4) See Sentence 4.1.3.2.(5).

(5) See Sentence 4.1.3.2.(6).

(6) See Article 4.1.5.5.

(7) See Sentence 4.1.3.2.(7).

(8) See Sentence 4.1.3.2.(10).

**Forming Part of Sentences 4.1.3.2.(2), (5) to (8) and (10)**

(1) See Sentences 4.1.3.2.(2) to (4).

(2) See Sentence 4.1.3.2.(8).

(3) See Sentence 4.1.3.2.(5).

(4) See Article 4.1.5.5.

(5) See Sentence 4.1.3.2.(6).

(6) See Sentence 4.1.3.2.(7).

(7) Side thrust due to cranes need not be combined with full wind load.

(8) See Sentence 4.1.3.2.(10).

(1) A building and its structural components, including connections, shall be checked for fatigue failure under the effect of the cyclical loads, as required in the standards listed in Section 4.3.

(2) Where vibration effects, such as resonance and fatigue resulting from machinery and equipment, are likely to be significant, a dynamic analysis shall be carried out.

(1) A building and its structural components shall be checked for serviceability limit states as defined in Clause 4.1.3.1.(1)(a) under the effect of service loads for serviceability criteria specified or recommended in Articles 4.1.3.5. and 4.1.3.6. and in the standards listed in Section 4.3.

(1) In proportioning structural members to limit serviceability problems resulting from deflections, consideration shall be given to,

(a) the intended use of the building or member,

(b) limiting damage to non-structural members made of materials whose physical properties are known at the time of design,

(c) limiting damage to the structure itself, and

(d) creep, shrinkage, temperature changes and prestress.

(2) The lateral deflection of buildings due to service wind and gravity loads shall be checked to ensure that structural elements and non-structural elements, whose nature is known at the time the structural design is carried out, will not be damaged.

(3) Except as provided in Sentence (4), the total drift per storey under service wind and gravity loads shall not exceed 1/500 of the storey height unless other drift limits are specified in the design standards referenced in Section 4.3.

(4) The deflection limits required in Sentence (3) do not apply to industrial buildings or sheds if experience has proven that greater movement will have no significant adverse effects on the strength and function of the building.

(5) The building structure shall be designed for lateral deflection due to E, in accordance with Article 4.1.8.13.

(1) Floor systems susceptible to vibration shall be designed so that vibrations will have no significant adverse effects on the intended occupancy of the building.

(2) Where the fundamental vibration frequency of a structural system supporting an assembly occupancy used for rhythmic activities, such as dancing, concerts, jumping exercises or gymnastics, is less than 6 Hz, the effects of resonance shall be investigated by means of a dynamic analysis.

(3) A building susceptible to lateral vibration under wind load shall be designed in accordance with Article 4.1.7.2. so that the vibrations will have no significant adverse effects on the intended use and occupancy of the building.

(1) The specified dead load for a structural member consists of,

(a) the weight of the member itself,

(b) the weight of all materials of construction incorporated into the building to be supported permanently by the member,

(c) the weight of partitions,

(d) the weight of permanent equipment, and

(e) the vertical load due to earth, plants and trees.

(2) Except as provided in Sentence (5), in areas of a building where partitions other than permanent partitions are shown on the drawings, or where partitions might be added in the future, allowance shall be made for the weight of such partitions.

(3) The partition weight allowance in Sentence (2) shall be determined from the actual or anticipated weight of the partitions placed in any probable position, but shall be not less than 1 kPa over the area of floor being considered.

(4) Partition loads used in design shall be shown on the drawings.

(5) In cases where the dead load of the partition is counteractive, the load allowances referred to in Sentences (2) and (3) shall not be included in the design calculations.

(6) Except for structures where the dead load of soil is part of the load-resisting system, where the dead load due to soil, superimposed earth, plants and trees is counteractive, it shall not be included in the design calculations.

(1) Except as provided in Sentence (2), the specified live load on an area of floor or roof depends on the intended use and occupancy, and shall not be less than whichever of the following loads produces the most critical effect:

(a) the uniformly distributed load patterns listed in Article 4.1.5.3.,

(b) the loads due to the intended use and occupancy, or

(c) the concentrated loads listed in Article 4.1.5.9.

(2) For buildings in the Low Importance Category as described in Table 4.1.2.1.B., a factor of 0.8 may be applied to the live load.

(1) Except as provided in Sentence (2), where the use of an area of floor or roof is not provided for in Article 4.1.5.3., the specified live loads due to the use and occupancy of the area shall be determined from an analysis of the loads resulting from the weight of,

(a) the probable assembly of persons,

(b) the probable accumulation of equipment and furnishings, and

(c) the probable storage of materials.

(2) For buildings in the Low Importance Category as described in Table 4.1.2.1.B., a factor of 0.8 may be applied to the live load.

(1) The uniformly distributed live load shall be not less than the value listed in Table 4.1.5.3., which may be reduced as provided in Article 4.1.5.8., applied uniformly over the entire area, or on any portions of the area, whichever produces the most critical effects in the members concerned.

Table 4.1.5.3. Specified Uniformly Distributed Live Loads on an Area of Floor or Roof

**Forming Part of Sentence 4.1.5.3.(1)**

(1) See Article 4.1.5.6.

(2) See Article 4.1.5.4.

(3) See Sentence 4.1.5.1.(1).

(4) See Article 4.1.5.5.

(1) The following shall be designed to carry not less than the specified load required for the occupancy they serve, provided they cannot be used by an assembly of people as a viewing area:

(a) corridors, lobbies and aisles not more than 1 200 mm wide,

(b) all corridors above the first storey of residential areas of apartments, hotels and motels, and

(c) interior balconies and mezzanines.

(1) Exterior areas accessible to vehicular traffic shall be designed for their intended use, including the weight of firefighting equipment, but not for less than the snow and rain loads prescribed in Subsection 4.1.6.

(2) Except as provided in Sentences (3) and (4), roofs shall be designed for the uniform live loads specified in Table 4.1.5.3., the concentrated live loads listed in Table 4.1.5.9., or the snow and rain loads prescribed in Subsection 4.1.6., whichever produces the most critical effects in the members concerned.

(3) Exterior areas accessible to pedestrian traffic, but not vehicular traffic, shall be designed for their intended use, but not for less than the greater of,

(a) the live load prescribed for assembly areas in Table 4.1.5.3., or

(b) the snow and rain loads prescribed in Subsection 4.1.6.

(4) Roof parking decks shall be designed for the uniformly distributed live loads specified in Table 4.1.5.3., the concentrated live loads listed in Table 4.1.5.9., or the roof snow load, whichever produces the most critical effect in the members concerned.

(1) The minimum specified live load listed in Table 4.1.5.3. for dining areas may be reduced to 2.4 kPa for areas in buildings that are being converted to dining areas, provided that the floor area does not exceed 100 m² and the dining area will not be used for other assembly purposes, including dancing.

(1) Where an area of floor or roof is intended for 2 or more occupancies at different times, the value to be used from Table 4.1.5.3. shall be the greatest value for any of the occupancies concerned.

(1) An area used for assembly occupancies designed for a live load of less than 4.8 kPa and roofs designed for the minimum loading specified in Table 4.1.5.3. shall have no reduction for tributary area.

(2) Where a structural member supports a tributary area of a floor or a roof, or a combination of them, that is greater than 80 m² and either used for assembly occupancies designed for a live load of 4.8 kPa or more, or used for storage, manufacturing, retail stores, garages or as a footbridge, the specified live load due to use and occupancy is the load specified in Article 4.1.5.3. multiplied by,

0.5 +

where,

"A" is the tributary area in square metres for this type of use and occupancy.

(3) Where a structural member supports a tributary area of a floor or a roof or a combination of them, that is greater than 20 m² and used for any use or occupancy other than assembly occupancies and those indicated in Sentences (1) and (2), the specified live load due to use and occupancy, is the load specified in Article 4.1.5.3. multiplied by,

0.3 +

where,

"B" is the tributary area in square metres for this type of use and occupancy.

(4) Where the specified live load for a floor is reduced in accordance with Sentence (2) or (3), the structural drawings shall indicate that a live load reduction factor for tributary area has been applied.

(1) The specified live load due to possible concentrations of load resulting from the use of an area of floor or roof shall not be less than that listed in Table 4.1.5.9. applied over the loaded area noted in Table 4.1.5.9. and located so as to cause maximum effects, except that for occupancies not listed in Table 4.1.5.9., the concentrations of load shall be determined in accordance with Article 4.1.5.2.

Table 4.1.5.9. Specified Concentrated Live Loads on an Area of Floor or Roof

**Forming Part of Sentence 4.1.5.9.(1)**

(1) The floor assembly and other structural elements that support fixed seats in any building used for assembly occupancies accommodating large numbers of people at one time, such as grandstands, stadia and theatre balconies, shall be designed to resist a horizontal force equal to not less than 0.3 kN for each metre length of seats acting parallel to each row of seats, and not less than 0.15 kN for each metre length of seats acting at right angles to each row of seats, based on the assumption that these forces are acting independently of each other.

(1) The minimum specified load due to equipment, machinery or other objects that may produce impact shall be the sum of the weight of the equipment or machinery and its maximum lifting capacity, multiplied by an appropriate factor listed in Table 4.1.5.11.

Table 4.1.5.11. Factors for the Calculation of Impact Loads

**Forming Part of Sentence 4.1.5.11.(1)**

(1) See ASME A17.1 / CSA B44, "Safety Code for Elevators and Escalators."

(2) Crane-supporting structures shall be designed for the appropriate load combinations listed in Article 4.1.3.2.

(3) Crane runway structures shall be designed to resist a horizontal force applied normal to the top of the rails equal to not less than 20% of the sum of the weights of the lifted load and the crane trolley, excluding other parts of the crane.

(4) The force described in Sentence (3) shall be equally distributed on each side of the runway and shall be assumed to act in either direction.

(5) Crane runway structures shall be designed to resist a horizontal force applied parallel to the top of the rails equal to not less than 10% of the maximum wheel loads of the crane.

(1) Bleacher seats shall be designed for a uniformly distributed live load of 1.75 kN for each linear metre or for a concentrated load of 2.2 kN distributed over a length of 750 mm, whichever produces the most critical effect on the supporting members.

(2) Bleachers shall be checked by the erector after erection to ensure that all structural members, including bracing specified in the design, have been installed.

(3) Telescopic bleachers shall be provided with locking devices to ensure stability while in use.

(1) Helicopter landing areas on roofs shall be constructed in conformance with the requirements for heliports contained in Part III of the Canadian Aviation Regulations made under the Aeronautics Act (Canada).

(1) The minimum specified horizontal load applied outward at the minimum required height of every required guard shall be,

(a) 3.0 kN/m for open viewing stands without fixed seats and for means of egress in grandstands, stadia, bleachers and arenas,

(b) a concentrated load of 1.0 kN applied at any point so as to produce the most critical effect, for access ways to equipment platforms, contiguous stairs and similar areas where the gathering of many people is improbable, and

(c) 0.75 kN/m or a concentrated load of 1.0 kN applied at any point so as to produce the most critical effect, whichever governs for locations other than those described in Clauses (a) and (b).

(2) The minimum specified horizontal load applied inward at the minimum required height of every required guard shall be half that specified in Sentence (1).

(3) Individual elements within the guard, including solid panels and pickets, shall be designed for a load of 0.5 kN applied outward over an area of 100 mm by 100 mm located at any point in the element or elements so as to produce the most critical effect.

(4) The size of the opening between any two adjacent vertical elements within a guard shall not exceed the limits required by Part 3 when each of these elements is subjected to a specified live load of 0.1 kN applied in opposite directions in the in-plane direction of the guard so as to produce the most critical effect.

(5) The loads required in Sentence (3) need not be considered to act simultaneously with the loads provided for in Sentences (1), (2) and (6).

(6) The minimum specified load applied vertically at the top of every required guard shall be 1.5 kN/m and need not be considered to act simultaneously with the horizontal load provided for in Sentence (1).

(7) Handrails and their supports shall be designed and constructed to withstand the following loads, which need not be considered to act simultaneously:

(a) a concentrated load not less than 0.9 kN applied at any point and in any direction for all handrails, and

(b) a uniform load not less than 0.7 kN/m applied in any direction to handrails not located within dwelling units.

(1) Vehicle guardrails shall be designed for a concentrated load of 22 kN applied horizontally outward at any point 500 mm above the floor surface so as to produce the most critical effect.

(2) The loads described in Sentence (1) need not be considered to act simultaneously with the loads provided for in Article 4.1.5.14.

(1) Where the floor elevation on one side of a wall, including a wall around a shaft, is more than 600 mm higher than the elevation of the floor or ground on the other side, the wall shall be designed to resist the appropriate outward lateral design loads prescribed elsewhere in this Subsection or 0.5 kPa acting outward, whichever produces the more critical effect.

(1) Firewalls shall be designed to resist the maximum effect due to,

(a) the appropriate lateral design loads prescribed elsewhere in this Section, or

(b) a factored lateral load of 0.5 kPa under fire conditions, as described in Sentence (2).

(2) Under fire conditions, where the fire-resistance rating of the structure is less than that of the firewall,

(a) lateral support shall be assumed to be provided by the structure on one side only, or

(b) another structural support system capable of resisting the loads imposed by a fire on either side of the firewall shall be provided.

(1) The specified load on a roof or any other building surface subject to snow and associated rain shall be the snow load specified in Article 4.1.6.2., or the rain load specified in Article 4.1.6.4., whichever produces the more critical effect.

(1) The specified load, S, due to snow and associated rain accumulation on a roof or any other building surface subject to snow accumulation shall be calculated from the formula,

S = Is [Ss (CbCwCsCa) + Sr]

where,

Is = importance factor for snow load as provided in Table 4.1.6.2.A.,

Ss = 1-in-50-year ground snow load, in kPa, determined in accordance with Subsection 1.1.2.,

Cb = basic roof snow load factor in Sentence (2),

Cw = wind exposure factor in Sentences (3) and (4),

Cs = slope factor in Sentences (5), (6) and (7),

Ca = accumulation factor in Sentence (8), and

Sr = 1-in-50-year associated rain load, in kPa, determined in accordance with Subsection 1.1.2., but not greater than Ss(CbCwCsCa).

**Forming Part of Sentence 4.1.6.2.(1)**

(2) The basic roof snow load factor, Cb, shall be,

(a) for , 0.8, and

(b) for ,

(i) calculated using the following formula:

where,

lc = characteristic length of the upper or lower roof, defined as 2w-w²/l, in metres,

w = smaller plan dimension of the roof, in metres, and

l = larger plan dimension of the roof, in metres, or

(ii) determined in accordance with Table 4.1.6.2.B., using linear interpolation for intermediate values of

**Forming Part of Sentence 4.1.6.2.(2)**

(3) Except as provided for in Sentence (4), the wind exposure factor, Cw, shall be 1.0.

(4) For buildings in the Low and Normal Importance Categories as set out in Table 4.1.2.1.B., the wind exposure factor given in Sentence (3) may be reduced to 0.75 in rural areas, or to 0.5 in exposed areas north of the treeline, where,

(a) the building is exposed on all sides to wind over open terrain as defined in Clause 4.1.7.1.(5)(a) , and is expected to remain so during its life,

(b) the area of roof under consideration is exposed to the wind on all sides with no significant obstructions on the roof, such as parapet walls, within a distance of at least 10 times the difference between the height of the obstruction and CbCwSs/γ metres, where γ is the unit weight of snow on roofs as specified in Article 4.1.6.13., and

(c) the loading does not involve the accumulation of snow due to drifting from adjacent surfaces.

(5) Except as provided for in Sentences (6) and (7), the slope factor, Cs, shall be,

(a) 1.0 where the roof slope, α, is equal to or less than 30°,

(b) (70° - α)/40° where α is greater than 30° but not greater than 70°, and

(c) 0 where α exceeds 70°.

(6) The slope factor, Cs, for unobstructed slippery roofs where snow and ice can slide completely off the roof shall be,

(a) 1.0 when the roof slope, α, is equal to or less than 15°,

(b) (60° - α)/45° when α is greater than 15°, but not greater than 60°, and

(c) 0 when α exceeds 60°.

(7) Except as otherwise provided in this Subsection, the slope factor, Cs, shall be 1.0 when used in conjunction with accumulation factors for increased snow loads.

(8) The accumulation factor, Ca, shall be 1.0, which corresponds to the uniform snow load case, except that where appropriate for the shape of the roof, it shall be assigned other values that account for,

(a) increased non-uniform snow loads due to snow drifting onto a roof that is at a level lower than other parts of the same building or at a level lower than another building within 5 m of it horizontally, as prescribed in Articles 4.1.6.5., 4.1.6.6. and 4.1.6.8.,

(b) increased non-uniform snow loads on areas adjacent to roof projections, such as penthouses, large chimneys and equipment, as prescribed in Articles 4.1.6.7. and 4.1.6.8.,

(c) non-uniform snow loads on,

(i) gable roofs, as prescribed in Article 4.1.6.9., and

(ii) arched roofs, curved roofs and domes, as prescribed in Article 4.1.6.10.,

(d) increased snow or ice loads due to snow sliding, as prescribed in Article 4.1.6.11.,

(e) increased snow loads in roof valleys, as prescribed in Article 4.1.6.12., and

(f) increased snow or ice loads due to meltwater draining from adjacent building elements and roof projections.

(9) For shapes not addressed in Sentence (8), Ca corresponding to the non-uniform snow load case shall be established based on applicable field observations, special analyses including local climatic effects, appropriate model tests or a combination of these methods.

(1) A roof or other building surface and its structural members subject to loads due to snow accumulation shall be designed for the specified load in Sentence 4.1.6.2.(1), distributed over the entire loaded area.

(2) In addition to the distribution in Sentence (1), flat roofs and shed roofs, gable roofs of 15° slope or less, and arched or curved roofs shall be designed for the specified uniform snow load indicated in Sentence 4.1.6.2.(1), which shall be calculated using Ca = 1.0, distributed on any one portion of the loaded area, and half of this load on the remainder of the loaded area, in such a way as to produce the most critical effects on the member concerned.

(1) Except as provided in Sentence (4), the specified load, S, due to the accumulation of rainwater on a surface whose position, shape and deflection under load make such an accumulation possible, is that resulting from the one-day rainfall determined in conformance with Subsection 1.1.2. and applied over the horizontal projection of the surface and all tributary surfaces.

(2) The provisions of Sentence (1) apply whether or not the surface is provided with a means of drainage, such as rainwater leaders.

(3) Except as provided for in Sentence 4.1.6.2.(1), loads due to rain need not be considered to act simultaneously with loads due to snow.

(4) Where scuppers are provided and where the position, shape and deflection of the loaded surface make an accumulation of rainwater possible, the loads due to rain shall be the lesser of either the one-day rainfall determined in conformance with Subsection 1.1.2. or a depth of rainwater equal to 30 mm above the level of the scuppers, applied over the horizontal projection of the surface and tributary areas.

(1) The drifting load of snow on a roof adjacent to a higher roof shall be taken as trapezoidal, as shown in Figure 4.1.6.5.A., where the accumulation factor, Ca, is,

Ca = Ca0 - (Ca0 - 1)(x/xd), for 0 ≤ x ≤ xd

or

Ca = 1.0, for x > xd

where,

Ca0 = peak value of Ca at x = 0 as specified in Sentences (3) and (4) and as shown in Figure 4.1.6.5.A.,

x = distance from roof step as shown in Figure 4.1.6.5.A., and

xd = length of drift as specified in Sentence (2) and as shown in Figure 4.1.6.5.A.

(2) The length of the drift, xd, shall be calculated as follows:

where,

γ = specific weight of snow as specified in Article 4.1.6.13.

(3) The value of Ca0 for each of Cases I, II and III shall be the lesser of,

where,

β = 1.0 for Case I and 0.67 for Cases II and III,

h = difference in elevation between the lower roof surface and the top of the parapet on the upper roof as shown in Figure 4.1.6.5.A., and

where,

Cws = value for Cw applicable to the source of drifting,

lcs = the characteristic length of the source area for drifting, defined as , where ws and ls are respectively the shorter and longer dimensions of the relevant source areas for snow drifting shown in Figure 4.1.6.5.B. for Cases I, II and III, and

where,

hp = height of the roof perimeter parapet of the source area, to be taken as zero unless all the roof edges of the source area have parapets.

(4) The value of Ca0 shall be the highest of Cases I, II and III, considering the different roof source areas for drifting snow, as specified in Sentence (3) and Figure 4.1.6.5.B.

Figure 4.1.6.5.A. Snow Load Factors for Lower Level Roofs

**Forming Part of Sentences 4.1.6.5.(1) and (3) and 4.1.6.6.(1)**

(1) If a > 5 m or h ≤ 0.8Ss/γ, drifting from the higher roof need not be considered.

(2) For lower roofs with parapets, Cs = 1.0, otherwise it varies as a function of slope α as defined in Sentences 4.1.6.2.(5) and (6).

Figure 4.1.6.5.B. Snow Load Cases I, II and III for Lower Level Roofs

**Forming Part of Sentences 4.1.6.5.(3) and (4)**

(1) Where the roof of one building is separated by a distance, a, from an adjacent building with a higher roof as shown in Figure 4.1.6.5.A., the influence of the adjacent building on the value of the accumulation factor, Ca, for the lower roof shall be determined as follows:

(a) if a > 5 m, the influence of the adjacent building on Ca need not be considered, and

(b) if a ≤ 5 m, Ca for the lower roof shall be calculated in accordance with Article 4.1.6.5. for values of x ≥ a.

(1) Except as provided in Sentences (2) and (3), the accumulation factor, Ca, for areas adjacent to roof-mounted vertical projections shall be calculated in accordance with Sentence 4.1.6.5.(1) using the following values for the peak accumulation factor, Ca0, and the drift length, xd:

(a) Ca0 shall be taken as the lesser of,

(b) xd shall be taken as the lesser of,

(i) 3.35h, and

(ii) (2/3)l0,

where,

h = height of the projection, and

l0 = longest horizontal dimension of the projection.

(2) Ca is permitted to be calculated in accordance with Article 4.1.6.5. for larger projections.

(3) Where the longest horizontal dimension of the roof projection, l0, is less than 3 m, the drift surcharge adjacent to the projection need not be considered.

(1) The drift loads on the lower level roof against the two faces of an outside corner of an upper level roof or roof obstruction shall be extended radially around the corner as shown in Figure 4.1.6.8.A. and may be taken as the least severe of the drift loads lying against the two faces of the corner.

(2) The drift loads on the lower level roof against the two faces of an inside corner of an upper level roof or a parapet shall be calculated for each face and applied as far as the bisector of the corner angle as shown in Figure 4.1.6.8.B.

Figure 4.1.6.8.A. Snow Load at Outside Corner

**Forming Part of Sentence 4.1.6.8.(1)**

Figure 4.1.6.8.B. Snow Load at Inside Corner

**Forming Part of Sentence 4.1.6.8.(2)**

(1) For all gable roofs, the full and partial load cases defined in Article 4.1.6.3. shall be considered.

(2) For gable roofs with a slope of a > 15°, the unbalanced load case shall also be considered by setting the values of the accumulation factor, Ca, as follows:

(a) on the upwind side of the roof peak, Ca shall be taken as 0, and

(b) on the downwind side of the roof peak, Ca shall be taken as,

(i) 0.25 + a/20, where 15° ≤ a ≤ 20°, and

(ii) 1.25, where 20° < a ≤ 90°.

(3) For all gable roofs, the slope factor, Cs, shall be as prescribed in Sentences 4.1.6.2.(5) and (6).

(4) For all gable roofs, the wind exposure factor, Cw, shall be,

(a) as prescribed in Sentences 4.1.6.2.(3) and (4) for the full and partial load cases, and

(b) 1.0 for the unbalanced load case referred to in Sentence (2).

(1) For all arch roofs, curved roofs and domes, the full and partial load cases defined in Article 4.1.6.3. shall be considered.

(2) For arch roofs, curved roofs and domes with rise-to-span ratio h/b > 0.05 as shown in Figure 4.1.6.10.A., the load cases provided in Sentences (3) to (7) shall also be considered.

(3) For arch roofs with a slope at the edge αe ≤ 30° as shown in Figure 4.1.6.10.A. and as described in Table 4.1.6.10., Ca shall be,

(a) taken as 0 on the upwind side of the peak, and

(b) on the downwind side of the peak, taken as,

where,

x = horizontal distance from the roof peak,

h = height of arch, and

b = width of arch.

Figure 4.1.6.10.A. Accumulation Factors for Arch Roofs and Curved Roofs(1)

**Forming Part of Sentences 4.1.6.10.(2) to (4)**

(1) Refer to Table 4.1.6.10. for applicable values of Cw and Sentences 4.1.6.2.(5) and (6) for applicable values of Cs.

Table 4.1.6.10. Load Cases for Arch Roofs, Curved Roofs and Domes

**Forming Part of Sentences 4.1.6.10.(3), (4) and (9)**

(4) For arch roofs with slope at the edge αe > 30° as shown in Figure 4.1.6.10.A. and as described in Table 4.1.6.10., Ca, shall be,

(a) taken as 0 on the upwind side of the peak, and

(b) on the downwind side of the peak,

(i) for the part of the roof between the peak and point where the slope α = 30°, taken as,

and

where,

x, h, b = as specified in Sentence (2), and

x30 = value of x where the slope α = 30°, and

(ii) for the part of the roof where the slope α >30°, taken as,

(5) Except as provided in Sentence (6), Ca for curved roofs shall be determined in accordance with the requirements for arch roofs stated in Sentences (3) and (4).

(6) Where the slope, α, of a curved roof at its peak is greater than 10°, Ca shall be determined in accordance with the requirements for gable roofs described in Article 4.1.6.9. using a slope equal to the mean slope of the curved roof.

(7) For domes of circular plan form as shown in Figure 4.1.6.10.B., Ca shall,

(a) along the central axis parallel to the wind, vary in the same way as for an arch roof with the same rise-to-span ratio, h/b, and

(b) off this axis, vary according to,

where,

Ca(x,y) = value of Ca at location (x,y),

Ca(x,0) = value of Ca on the central axis parallel to the wind,

x = distance along the central axis parallel to the wind,

y = horizontal coordinate normal to the x direction, and

r = radius of dome.

Figure 4.1.6.10.B. Unbalanced Snow Accumulation Factor on a Circular Dome(1),(2)

**Forming Part of Sentence 4.1.6.10.(7)**

(1) Refer to Table 4.1.6.10. for applicable values of Cw and Sentences 4.1.6.2.(5) and (6) for applicable values of Cs.

(2) Refer to Sentences 4.1.6.10.(3) and (4) for the calculation of Ca(x,0).

(8) For all arch roofs, curved roofs and domes, the slope factor, Cs, shall be as prescribed in Sentences 4.1.6.2.(5) and (6).

(9) For all arch roofs, curved roofs and domes, the wind exposure factor, Cw, shall be as prescribed in Table 4.1.6.10.

(1) Except as provided in Sentence (2), where an upper roof, or part thereof, slopes downwards with a slope α > 0 towards a lower roof, the snow load, S, on the lower roof, determined in accordance with Articles 4.1.6.2. and 4.1.6.5., shall be augmented in accordance with Sentence (3) to account for the additional load resulting from sliding snow.

(2) Sentence (1) need not apply where,

(a) snow from the upper roof is prevented from sliding by a parapet or other effective means, or

(b) the upper roof is not considered slippery and has a slope less than 20°.

(3) The total weight of additional snow resulting from sliding shall be taken as half the total weight of snow resulting from the uniform load case prescribed in Article 4.1.6.2. with,

(a) the accumulation factor Ca = 1.0 for the relevant part of the upper roof,

(b) the slope factor, Cs, based on the slope of the lower roof, as prescribed in Sentences 4.1.6.2.(5) and (6), and

(c) the sliding snow distributed on the lower roof such that it is a maximum for x = 0 and decreases linearly to 0 at x = xd, as shown in Figure 4.1.6.11., where x and xd are as defined in Article 4.1.6.5.

Figure 4.1.6.11. Snow Distribution on Lower Roof with Sloped Upper Roof

**Forming Part of Sentence 4.1.6.11.(3)**

(1) For valleys in curved or sloped roofs with a slope α >10°, in addition to the full and partial load cases defined in Article 4.1.6.3., the non-uniform load Cases II and III described in Sentences (2) and (3) shall be considered to account for sliding, creeping and movement of meltwater.

(2) For Case II as shown in Figure 4.1.6.12., the accumulation factor, Ca, shall be calculated as follows:

where,

x = horizontal distance from the bottom of the valley, and

b = twice the horizontal distance between the bottom of the valley and the peak of the roof surface under consideration.

(3) For Case III as shown in Figure 4.1.6.12., Ca shall be calculated as follows:

where,

x, b = as specified in Sentence (2).

Figure 4.1.6.12. Snow Loads in Valleys of Sloped or Curved Roofs(1),(2)

**Forming Part of Sentences 4.1.6.12.(2) and (3)**

(1) Cw = 1.0, as specified in Sentence 4.1.6.2.(3).

(2) Cs = 1.0, as specified in Sentence 4.1.6.2.(7).

(1) For the purposes of calculating snow loads in drifts, the specific weight of snow, γ, shall be taken as the lesser of 4.0 kN/m3 and 0.43SS + 2.2 kN/m3.

(1) Snow removal by mechanical, thermal, manual or other means shall not be used as a rationale to reduce design snow loads.

(1) For lattice structures connected to the building, and other building components or appurtenances involving small width elements subject to significant ice accretion, the weight of ice accretion and the effective area presented to wind shall be as prescribed in CSA S37, "Antennas, Towers, and Antenna-Supporting Structures".

(1) The specified wind loads for a building and its components shall be determined using the Static, Dynamic or Wind Tunnel Procedure as provided in Sentences (2) to (5).

(2) For the design of buildings that are not classified as dynamically sensitive in accordance with Sentence 4.1.7.2.(1), one of the following procedures shall be used to determine the specified wind loads:

(a) the Static Procedure described in Article 4.1.7.3.,

(b) the Dynamic Procedure described in Article 4.1.7.8., or

(c) the Wind Tunnel Procedure described in Article 4.1.7.12.

(3) For the design of buildings that are classified as dynamically sensitive in accordance with Sentence 4.1.7.2.(2), one of the following procedures shall be used to determine the specified wind loads:

(a) the Dynamic Procedure described in Article 4.1.7.8., or

(b) the Wind Tunnel Procedure described in Article 4.1.7.12.

(4) For the design of buildings that may be subject to wake buffeting or channelling effects from nearby buildings, or that are classified as very dynamically sensitive in accordance with Sentence 4.1.7.2.(3), the Wind Tunnel Procedure described in Article 4.1.7.12. shall be used to determine the specified wind loads.

(5) For the design of cladding and secondary structural members, one of the following procedures shall be used to determine the specified wind loads:

(a) the Static Procedure described in Article 4.1.7.3., or

(b) the Wind Tunnel Procedure described in Article 4.1.7.12.

(6) Computational fluid dynamics shall not be used to determine the specified wind loads for a building and its components.

(1) Except as provided in Sentences (2) and (3), a building is permitted to be classified as not dynamically sensitive.

(2) A building shall be classified as dynamically sensitive if,

(a) its lowest natural frequency is less than 1 Hz and greater than 0.25 Hz,

(b) its height is greater than 60 m, or

(c) its height is greater than 4 times its minimum effective width considering all wind directions, where the effective width, w, of a building shall be taken as,

where,

the summations are over the height of the building for a given wind direction,

hi = the height above grade to level i, and

wi = the width normal to the wind direction at height hi.

(3) A building shall be classified as very dynamically sensitive if,

(a) its lowest natural frequency is less than or equal to 0.25 Hz, or

(b) its height is more than 6 times its minimum effective width, where the minimum effective width is determined in accordance with Clause (2)(c).

(1) The specified external pressure or suction due to wind on part or all of a surface of a building shall be calculated using the following formula:

p = IwqCeCtCgCp

where,

p = specified external pressure acting statically and in a direction normal to the surface, considered positive when the pressure acts towards the surface and negative when it acts away from the surface,

Iw = importance factor for wind load, as provided in Table 4.1.7.3.,

q = reference velocity pressure, as provided in Sentence (4),

Ce = exposure factor, as provided in Sentences (5) and (7),

Ct = topographic factor, as provided in Article 4.1.7.4.,

Cg = gust effect factor, as provided in Sentence (8), and

Cp = external pressure coefficient, as provided in Articles 4.1.7.5. and 4.1.7.6.

Table 4.1.7.3. Importance Factor for Wind Load, IW

**Forming Part of Sentence 4.1.7.3.(1)**

(2) The net wind load for the building as a whole shall be the algebraic difference of the loads on the windward and the leeward surfaces, and in some cases may be calculated as the sum of the products of the external pressures or suctions and the areas of the surfaces over which they are averaged as provided in Sentence (1).

(3) The net specified pressure due to wind on part or all of a surface of a building shall be the algebraic difference, such as to produce the most critical effect, of the external pressure or suction calculated in accordance with Sentence (1) and the specified internal pressure or suction due to wind calculated as follows:

pi = IwqCeiCtCgiCpi

where,

pi = specified internal pressure acting statically and in a direction normal to the surface, either as a pressure directed toward the surface or as a suction directed away from the surface,

Iw = importance factor for wind load, as defined in Sentence (1)

q = reference velocity pressure, as defined in Sentence (1)

Cei = exposure factor for internal pressure, as provided in Sentence (7),

Ct = topographic factor, as defined in Sentence (1),

Cgi = internal gust effect factor, as provided in Sentence (10), and

Cpi = internal pressure coefficient, as provided in Article 4.1.7.7.

(4) The reference velocity pressure, q, shall be the appropriate value determined in conformance with Subsection 1.1.2. based on a probability of being exceeded in any one year of 1-in-50.

(5) The exposure factor Ce, shall be based on the reference height, h, determined in accordance with Sentence (6) for the surface or part of the surface under consideration and shall be,

(a) (h/10)0.2 but not less than 0.9 for open terrain, where open terrain is level terrain with only scattered buildings, trees or other obstructions, open water or shorelines thereof,

(b) 0.7(h/12)0.3 but not less than 0.7 for rough terrain, where rough terrain is suburban, urban or wooded terrain extending upwind from the building uninterrupted for at least 1 km or 20 times the height of the building, whichever is greater, or

(c) an intermediate value between the two exposures defined in Clauses (a) and (b) in cases where the site is less than 1 km or 20 times the height of the building from a change in terrain conditions, whichever is greater, provided an appropriate interpolation method is used.

(6) The reference height, h, shall be determined as follows:

(a) for buildings with height less than or equal to 20 m and less than the smaller plan dimension, h shall be the mid-height of the roof above grade, but shall not be less than 6 m,

(b) for other buildings, h shall be,

(i) the actual height above grade of the point on the windward wall for which external pressures are being calculated,

(ii) the mid-height of the roof for pressures on surfaces parallel to the wind direction, and

(iii) the mid-height of the building for pressures on the leeward wall, and

(c) for any structural element exposed to wind, h shall be the mid-height of the element above the ground.

(7) The exposure factor for internal pressure, Cei, shall be determined as follows:

(a) for buildings whose height is greater than 20 m and that have a dominant opening, Cei shall be equal to the exposure factor for external pressures, Ce, calculated at the mid-height of the dominant opening, and

(b) for other buildings, Cei shall be the same as the exposure factor for external pressures, Ce, calculated for a reference height, h, equal to the mid-height of the building or 6 m, whichever is greater.

(8) Except as provided in Sentences (9) and 4.1.7.6.(1), the gust effect factor, Cg, shall be one of the following values:

(a) 2.0 for the building as a whole and main structural members, or

(b) 2.5 for external pressures and suctions on secondary structural members including cladding.

(9) For cases where Cg and Cp are combined into a single product, CpCg, as provided in Article 4.1.7.6., the values Cp and Cg need not be independently specified.

(10) The internal gust effect factor, Cgi, shall be 2.0, except it is permitted to be calculated using the following equation for large structures enclosing a single large unpartitioned volume that does not have numerous overhead doors or openings:

where,

V0 = internal volume in m3, and

A = total area of all exterior openings of the volume in m2.

(1) Except as provided in Sentence (2), the topographic factor, Ct, shall be taken as 1.0.

(2) For buildings on hills or escarpments with slope, Hh/(2Lh), greater than 0.1 as shown in Figure 4.1.7.4., the topographic factor, Ct, shall be calculated as follows:

where,

where,

ΔSmax = applicable values from Table 4.1.7.4.,

x = horizontal distance from the peak of the hill or escarpment,

Lh = horizontal distance upwind from the peak to the point where the ground surface lies at half the height of the hill or escarpment, or 2Hh where Hh is the height of the hill or escarpment, whichever is greater,

z = height above ground, and

k and α = applicable constants from Table 4.1.7.4. based on shape of hill or escarpment.

Figure 4.1.7.4. Speed-up of Mean Velocity on a Hill or Escarpment(1)

**Forming Part of Sentence 4.1.7.4.(2)**

(1) V(z) = wind speed.

Table 4.1.7.4. Parameters for Maximum Speed-up Over Hills and Escarpments

**Forming Part of Sentence 4.1.7.4.(2)**

(1) For Hh/Lh > 0.5, assume Hh/Lh = 0.5 and substitute 2 Hh for Lh in the equation for ΔS.

(1) Applicable values of external pressure coefficients, Cp, are provided in,

(a) Sentences (2) to (5), and

(b) Article 4.1.7.6. for certain shapes of low buildings.

(2) For the design of the main structural system, the value of Cp shall be established as follows, where H is the height of the building and D is the width of the building parallel to the wind direction:

(a) on the windward face,

Cp = 0.6 for H/D < 0.25

= 0.27(H/D + 2) for 0.25 ≤ H/D < 1.0

= 0.8 for H/D ≥ 1.0,

(b) on the leeward face,

Cp = -0.3 for H/D < 0.25

= -0.27(H/D + 0.88) for 0.25 ≤ H/D < 1.0

= -0.5 for H/D ≥ 1.0, and

(c) on the walls parallel to the wind, Cp = -0.7.

(3) For the design of roofs, the value of Cp shall be established as follows, where x is the distance from the upwind edge of the roof:

(a) for H/D ≥ 1.0, Cp = -1.0, and

(b) for H/D <1.0,

Cp = -1.0 for x ≤ H

= -0.5 for x > H

(4) For the design of the cladding and of secondary structural elements supporting the cladding, the value of Cp shall be established as follows, where W and D are the widths of the building:

(a) on walls, Cp shall be taken as ±0.9, except that within a distance equal to the larger of 0.1D and 0.1W from a building corner the negative value of Cp shall be taken as -1.2,

(b) on walls where vertical ribs deeper than 1 m are placed on the facade, Cp shall be taken as ±0.9, except that within a distance equal to the larger of 0.2D and 0.2W from a building corner the negative value of Cp shall be taken as -1.4, and

(c) on roofs, Cp shall be taken as -1.0, except that,

(i) within a distance equal to the larger of 0.1D and 0.1W from a roof edge, Cp shall be taken as -1.5,

(ii) in a zone that is within a distance equal to the larger of 0.2D and 0.2W from a roof corner, Cp shall be taken as -2.3 but is permitted to be taken as -2.0 for roofs with perimeter parapets that are higher than 1 m, and

(iii) on lower levels of flat stepped roofs, positive pressure coefficients established for the walls of the steps apply for a distance b as shown in Figure 4.1.7.6.D.

(5) For the design of balcony guards, the internal pressure coefficient, Cpi, shall be taken as zero and the value of Cp shall be taken as ±0.9, except that within a distance equal to the larger of 0.1D and 0.1W from a building corner, Cp shall be taken as ±1.2.

(1) For the design of buildings with a height, H, that is less than or equal to 20 m and less than the smaller plan dimension, the values of the product of the pressure coefficient and gust factor, CpCg, provided in Sentences (2) to (9) are permitted to be used.

(2) For the design of the main structural system of the building, which is affected by wind pressures on more than one surface, the values of CpCg are provided in Figure 4.1.7.6.A.

(3) For the design of individual walls and wall cladding, the values of CpCg are provided in Figure 4.1.7.6.B.

(4) For the design of roofs with a slope less than or equal to 7o, the values of CpCg are provided in Figure 4.1.7.6.C.

(5) For the design of flat roofs with steps in elevation, the values of CpCg are provided in Figure 4.1.7.6.D.

(6) For the design of gabled or hipped, single-ridge roofs with slope greater than 7o, the values of CpCg are provided in Figure 4.1.7.6.E.

(7) For the design of gabled, multi-ridge roofs, the values of CpCg are provided in,

(a) Figure 4.1.7.6.C. for roofs with slope less than or equal to 10o, and

(b) Figure 4.1.7.6.F. for roofs with slope greater than 10o.

(8) For monosloped roofs, the values of CpCg are provided in,

(a) Figure 4.1.7.6.C. for roofs with a slope less than or equal to 3o, and

(b) Figure 4.1.7.6.G. for roofs with a slope greater than 3o and less than or equal to 30o.

(9) For sawtooth roofs, the values of CpCg are provided in,

(a) Figure 4.1.7.6.C. for roofs with a slope less than or equal to 10o, and

(b) Figure 4.1.7.6.H. for roofs with a slope greater than 10o.

Figure 4.1.7.6.A. External Peak Values of CpCg for Primary Structural Actions Arising from Wind Load Acting Simultaneously on All Surfaces of Low Buildings, H ≤20 m(1),(2),(3),(4)

**Forming Part of Sentence 4.1.7.6.(2)**

(1) The building shall be designed for all wind directions. Each corner shall be considered in turn as the windward corner shown in the Figure. For all roof slopes, Load Case A and Load Case B are required as two separate loading conditions to generate the wind actions, including torsion, to be resisted by the structural system.

(2) For values of roof slope not shown, the coefficient, CpCg, may be interpolated linearly.

(3) Positive coefficients denote forces toward the surface, whereas negative coefficients denote forces away from the surface.

(4) For the design of foundations, exclusive of anchorages to the frame, only 70% of the effective load is to be considered.

(5) The reference height, h, for pressures is the mid-height of the roof or 6 m, whichever is greater. The eave height, H, may be substituted for the mid-height of the roof if the roof slope is less than 7o.

(6) End-zone width, y, is the greater of 6 m or 2z, where z is the width of the gable-wall end zone defined for Load Case B. Alternatively, for buildings with frames, y may be the distance between the end and the first interior frame.

(7) End-zone width, z, is the lesser of 10% of the least horizontal dimension and 40% of height, H, but not less than 4% of the least horizontal dimension or 1 m.

(8) For B/H > 5 in Load Case A, the listed negative coefficients on surfaces 2 and 2E shall only be applied on an area whose width is 2.5H measured from the windward eave. The pressures on the remainder of the windward roof may be reduced to the pressures for the leeward roof.

Figure 4.1.7.6.B. External Peak Values of CpCg on Individual Walls for the Design of Cladding and Secondary Structural Members(1),(2),(3),(4),(5)

**Forming Part of Sentence 4.1.7.6.(3)**

(1) These coefficients apply for any roof slope, α.

(2) End-zone width, z, is the lesser of 10% of the least horizontal dimension and 40% of height, H, but not less than 4% of the least horizontal dimension or 1 m.

(3) Combinations of exterior and interior pressures shall be evaluated to obtain the most severe loading.

(4) Positive coefficients denote forces toward the surface, whereas negative coefficients denote forces away from the surface. Each structural element shall be designed to withstand forces of both signs.

(5) Pressure coefficients generally apply for facades with architectural features; however, where vertical ribs deeper than 1 m are placed on a facade, a local CpCg of -2.8 applies to zone e.

Figure 4.1.7.6.C. External Peak Values of CpCg on Roofs with a Slope of 7o or Less for the Design of Structural Components and Cladding(3),(4),(5)

**Forming Part of Sentences 4.1.7.6.(4), (7), (8), and (9)**

(1) Coefficients for overhung roofs have the prefix "o" and refer to the same roof areas as referred to by the corresponding symbol without a prefix. They include contributions from both upper and lower surfaces. In the case of overhangs, the walls are inboard of the roof outline.

(2) s and r apply to both roofs and upper surfaces of canopies.

(3) End-zone width, z, is the lesser of 10% of the least horizontal dimension and 40% of height, H, but not less than 4% of the least horizontal dimension or 1 m.

(4) Combinations of exterior and interior pressures shall be evaluated to obtain the most severe loading.

(5) Positive coefficients denote forces toward the surface, whereas negative coefficients denote forces away from the surface. Each structural element shall be designed to withstand forces of both signs.

(6) For calculating the uplift forces on tributary areas larger than 100 m2 on unobstructed nearly-flat roofs with low parapets, and where the centre of the tributary area is at least twice the height of the building from the nearest edge, the value of CpCg may be reduced from -1.5 to -1.1 at x/H = 2 and further reduced linearly to -0.6 at x/H = 5, where x is the distance to the nearest edge and H is the height of the building.

(7) For roofs having a perimeter parapet with a height of 1 m or greater, the corner coefficients CpCg for tributary areas less than 1 m2 can be reduced from -5.4 to -4.4.

Figure 4.1.7.6.D. External Peak Values of CpCg for the Design of the Structural Components and Cladding of Buildings with Stepped Roofs(1),(2)

**Forming Part of Sentences 4.1.7.5.(4) and 4.1.7.6.(5)**

(1) The zone designations, pressure-gust coefficients and Notes to Figure 4.1.7.6.C. apply on both the upper and lower levels of flat stepped roofs, except that on the lower levels, positive pressure-gust coefficients equal to those in Figure 4.1.7.6.B. for walls apply for a distance, b, where b is equal to 1.5h1 but not greater than 30 m. For all walls in Figure 4.1.7.6.D., zone designations and pressure coefficients provided for walls in Figure 4.1.7.6.B. apply.

(2) Note (1) applies only when the following conditions are met: h1 ≥ 0.3H, h1 ≥ 3 m, and W1, W2, or W3 is greater than 0.25W but not greater than 0.75W.

Figure 4.1.7.6.E. External Peak Values of CpCg on Single-Span Gabled and Hipped Roofs with a Slope Greater than 7o for the Design of Structural Components and Cladding(1),(2),(3),(4),(5)

**Forming Part of Sentence 4.1.7.6.(6)**

(1) Coefficients for overhung roofs have the prefix "o" and refer to the same roof areas as referred to by the corresponding symbol without a prefix. They include contributions from both upper and lower surfaces.

(2) End-zone width, z, is the lesser of 10% of the least horizontal dimension and 40% of height, H, but not less than 4% of the least horizontal dimension or 1 m.

(3) Combinations of external and internal pressures shall be evaluated to obtain the most severe loading.

(4) Positive coefficients denote forces toward the surface, whereas negative coefficients denote forces away from the surface. Each structural element shall be designed to withstand forces of both signs.

(5) For hipped roofs with 7° < α ≤ 27°, edge/ridge strips and pressure-gust coefficients for ridges of gabled roofs apply along each hip.

Figure 4.1.7.6.F. External Peak Values of CpCg on Multi-Span Gabled (Folded) Roofs with a Slope Greater than 10o for the Design of Structural Components and Cladding(1),(2),(3),(4)

**Forming Part of Sentence 4.1.7.6.(7)**

(1) End-zone width, z, is the lesser of 10% of the least horizontal dimension and 40% of height, H, but not less than 4% of the least horizontal dimension or 1 m.

(2) Combinations of external and internal pressures shall be evaluated to obtain the most severe loading.

(3) Positive coefficients denote forces toward the surface, whereas negative coefficients denote forces away from the surface. Each structural element shall be designed to withstand forces of both signs.

(4) Where α ≤ 10°, the coefficients given in Figure 4.1.7.6.C. apply. Where α > 7°, use α = 7°.

Figure 4.1.7.6.G. External Peak Values of CpCg on Monoslope Roofs for the Design of Structural Components and Cladding(1),(2),(3),(4)

**Forming Part of Sentence 4.1.7.6.(8)**

(1) End-zone width, z, is the lesser of 10% of the least horizontal dimension and 40% of height, H, but not less than 4% of the least horizontal dimension or 1 m.

(2) Combinations of external and internal pressures shall be evaluated to obtain the most severe loading.

(3) Positive coefficients denote forces toward the surface, whereas negative coefficients denote forces away from the surface. Each structural element shall be designed to withstand forces of both signs.

(4) Where α ≤ 3°, the coefficients given in Figure 4.1.7.6.C. apply.

Figure 4.1.7.6.H. External Peak Values of CpCg on Sawtooth Roofs with a Slope Greater than 10˚ for the Design of Structural Components and Cladding(1),(2),(3),(4),(5)

**Forming Part of Sentence 4.1.7.6.(9)**

(1) End-zone width, z, is the lesser of 10% of the least horizontal dimension and 40% of height, H, but not less than 4% of the least horizontal dimension or 1 m.

(2) Combinations of external and internal pressures shall be evaluated to obtain the most severe loading.

(3) Positive coefficients denote forces toward the surface, whereas negative coefficients denote forces away from the surface. Each structural element shall be designed to withstand forces of both signs.

(4) Negative coefficients on corner zones of Span A differ from those on Spans B, C, and D.

(5) Where α ≤ 10°, the coefficients given in Figure 4.1.7.6.C. apply. Where α > 7°, use α = 7°.

(1) The internal pressure coefficient, Cpi, shall be as prescribed in Table 4.1.7.7.

Table 4.1.7.7. Internal Pressure Coefficients

**Forming Part of Sentence 4.1.7.7.(1)**

(1) For the application of the Dynamic Procedure, the provisions of Article 4.1.7.3. shall be followed, except that the exposure factor, Ce, shall be as prescribed in Sentences (2) and (3), and the gust effect factor, Cg, shall be as prescribed in Sentence (4), when determining the wind loads on the main structural system.

(2) For buildings in open terrain as described in Clause 4.1.7.3.(5)(a), the value of Ce for the design of the main structural system shall be calculated as follows:

Ce = (h/10)0.28, but 1.0 ≤ Ce ≤ 2.5

(3) For buildings in rough terrain as described in Clause 4.1.7.3.(5)(b), the value of Ce for the design of the main structural system shall be calculated as follows:

Ce = 0.5(h/12.7)0.5, but 0.5 ≤ Ce ≤ 2.5

(4) For the design of the main structural system, Cg shall be calculated as follows:

Cg = 1 + gp(δ/μ)

where,

gp = peak factor calculated as, and

,

where,

υ = average fluctuation rate calculated as ,

T = 3 600 s,

K = 0.08 for open terrain and 0.10 for rough terrain,

CeH = exposure factor evaluated at reference height h = H,

B = background turbulence factor, a function of w/H determined from Figure 4.1.7.8.,

s = size reduction factor calculated as ,

F = gust energy ratio calculated as , where x0 = (1 220 fn/VH), and

β = damping ratio, which shall be determined by a rational method or may be taken to be 0.01 for steel structures, 0.02 for concrete structures and 0.015 for composite structures,

where,

fnD = natural frequency of vibration of the building in the along-wind direction, in Hz,

fn = lowest natural frequency of the building, in Hz, as described in Sentences 4.1.7.2.(2) and (3),

H = height of the building,

w = effective width of windward face of the building calculated as , where wi = width normal to wind direction at height hi, and

VH = mean wind speed at the top of the structure, in m/s, calculated as ,

where,

= reference wind speed at a height of 10 m, in m/s, calculated as ,

where,

Iw = importance factor,

q = reference velocity pressure, in Pa, and

ϱ = air density = 1.2929 kg/m3.

Figure 4.1.7.8. Background Turbulence Factor, B

**Forming Part of Sentence 4.1.7.8.(4)**

(1) Except where the wind loads are derived from the combined CpCg values determined in accordance with Article 4.1.7.6., buildings and structural members shall be capable of withstanding the effects of,

(a) the full wind loads acting along each of the two principal horizontal axes considered separately,

(b) the wind loads as described in Clause (a) but with 100% of the load removed from any one portion of the area,

(c) the wind loads as described in Clause (a) but with both axes considered simultaneously at 75% of their full value, and

(d) the wind loads as described in Clause (c) but with 50% of these loads removed from any portion of the area.

(1) In the design of interior walls and partitions, due consideration shall be given to differences in air pressure on opposite sides of the wall or partition that may result from,

(a) pressure differences between the windward and leeward sides of a building,

(b) stack effects due to a difference in air temperature between the exterior and interior of the building, and

(c) air pressurization by the mechanical services of the building.

(1) The effects of wind loads on exterior ornamentations, equipment and appendages, including the increase in exposed area as a result of ice buildup as described in CSA S37, "Antennas, Towers, and Antenna-Supporting Structures", shall be considered in the structural design of the connections and the building.

(2) Where there are a number of similar components, the net increase in force is permitted to be based on the total area for all similar components as opposed to the summation of forces of individual elements.

(1) Except as provided in Sentences (2) and (3), wind tunnel tests on scale models to determine wind loads on buildings shall be conducted in accordance with ASCE/SEI 49, "Wind Tunnel Testing for Buildings and Other Structures".

(2) Where an adjacent building provides substantial sheltering effect, the wind loads for the main structural system shall be no lower than 80% of the loads determined from tests described in Sentence (1) with the effect of the sheltering building removed as applied to,

(a) the base shear force for buildings with ratio of height to minimum effective width, as described in Sentence 4.1.7.2.(2), less than or equal to 1.0, or

(b) the base moment for buildings with a ratio of height to minimum effective width greater than 1.0.

(3) For the design of cladding and secondary structural members, the exterior wind loads determined from the wind tunnel tests shall be no less onerous than those determined by analysis in accordance with Article 4.1.7.3. using the following assumptions:

(a) Cp = ±0.72 and Cg = 2.5, where the height of the building is greater than 20 m or greater than its minimum effective width, and

(b) CpCg = 80% of the values for zones w and r provided in Article 4.1.7.6., where the height of the building is less than or equal to 20 m and no greater than its minimum effective width.

(1) Except as permitted in Sentence (2), the deflections and specified loading due to earthquake motions shall be determined according to the requirements of Articles 4.1.8.2. to 4.1.8.22.

(2) Where IEFsSa(0.2) and IEFsSa(2.0) are less than 0.16 and 0.03 respectively, the deflections and specified loading due to earthquake motions are permitted to be determined in accordance with Sentences (3) to (15), where,

(a) IE is the earthquake importance factor and has a value of 0.8, 1.0, 1.3 and 1.5 for buildings of Low, Normal, High and Post-Disaster importance respectively,

(b) Fs is the site coefficient based on the average or su, as defined in Article 4.1.8.2., for the top 30 m of soil below the footings, pile caps or mat foundations and has a value of,

(i) 1.0 for rock sites or when or su > 100 kPa,

(ii) 1.6 when or 50 kPa ≤ su ≤ 100 kPa, and

(iii) 2.8 for all other cases, and

(c) Sa(T) is the 5% damped spectral response acceleration value for period T, determined in accordance with Subsection 1.1.2.

(3) The structure shall have a clearly defined,

(a) SFRS, as defined in Article 4.1.8.2., to resist the earthquake loads and their effects, and

(b) load path or paths that will transfer the inertial forces generated by the earthquake to the foundations and supporting ground.

(4) An unreinforced masonry SFRS shall not be permitted where,

(a) IE is greater than 1.0, or

(b) the height above grade is greater than or equal to 30 m.

(5) The height above grade of SFRS designed in accordance with CSA S136, "North American Specification for the Design of Cold-Formed Steel Structural Members", shall be less than 15 m.

(6) Earthquake forces shall be assumed to act horizontally and independently about any two orthogonal axes.

(7) The minimum lateral earthquake design force, Vs, at the base of the structure in the direction under consideration shall be calculated as follows:

Vs = Fs Sa(Ts) IE Wt / RS

where,

Sa(Ts) = value of Sa at Ts determined by linear interpolation between the value of Sa at 0.2 s, 0.5 s and 1.0 s, and

= Sa(0.2) for Ts ≤ 0.2 s,

Wt = sum of Wi over the height of the building, where Wi is defined in Article 4.1.8.2., and

Rs = 1.5 except Rs = 1.0 for structures where the storey strength is less than that in the storey above and for an unreinforced masonry SFRS,

where,

Ts = fundamental lateral period of vibration of the building, as defined in Article 4.1.8.2.,

= 0.085(hn)¾ for steel moment frames,

= 0.075(hn)¾ for concrete moment frames,

= 0.1 N for other moment frames,

= 0.025hn for braced frames, and

= 0.05(hn)¾ for shear walls and other structures,

where,

hn = height above the base, in m, as defined in Article 4.1.8.2.,

except that Vs shall not be less than FsSa(1.0)IEWt/Rs and, in cases where Rs = 1.5, Vs need not be greater than FsSa(0.5)IEWt/Rs.

(8) The total lateral earthquake design force, Vs, shall be distributed over the height of the building in accordance with the following formula:

where,

Fx = force applied through the centre of mass at level x,

Wx,Wi = portion of W that is located at or is assigned to level x or level i respectively, and

hx, hi = height, in m, above the base of level x and level i as described in Article 4.1.8.2.

(9) Accidental torsional effects applied concurrently with Fx shall be considered by applying torsional moments about the vertical axis at each level for each of the following cases considered separately:

(a) +0.1DnxFx, and

(b) -0.1DnxFx.

(10) Deflections obtained from a linear analysis shall include the effects of torsion and be multiplied by Rs/IE to get realistic values of expected deflections.

(11) The deflections described in Sentence (10) shall be used to calculate the largest interstorey deflection, which shall not exceed,

(a) 0.01hs for post-disaster buildings,

(b) 0.02hs for High Importance Category buildings, and

(c) 0.025hs for all other buildings,

where hs is the interstorey height as defined in Article 4.1.8.2.

(12) When earthquake forces are calculated using Rs = 1.5, the following elements in the SFRS shall have their design forces due to earthquake effects increased by 33%:

(a) diaphragms and their chords, connections, struts and collectors,

(b) tie downs in wood or drywall shear walls,

(c) connections and anchor bolts in steel- and wood-braced frames,

(d) connections in precast concrete, and

(e) connections in steel moment frames.

(13) Except as provided in Sentence (14), where cantilever parapet walls, other cantilever walls, exterior ornamentation and appendages, towers, chimneys or penthouses are connected to or form part of a building, they shall be designed, along with their connections, for a lateral force, Vsp, distributed according to the distribution of mass of the element and acting in the lateral direction that results in the most critical loading for design using the following equation:

Vsp = 0.1FsIEWp

where Wp is the weight of a portion of a structure as defined in Article 4.1.8.2.

(14) The value of Vsp shall be doubled for unreinforced masonry elements.

(15) Structures designed in accordance with this Article need not comply with the seismic requirements stated in the applicable design standard referenced in Section 4.3.

(1) In this Subsection,

Ar = response amplification factor to account for type of attachment of mechanical/electrical equipment, as defined in Sentence 4.1.8.18.(1),

Ax = amplification factor at level x to account for variation of response of mechanical/electrical equipment with elevation within the building, as defined in Sentence 4.1.8.18.(1),

Bx = ratio at level x used to determine torsional sensitivity, as defined in Sentence 4.1.8.11.(9),

B = maximum value of Bx, as defined in Sentence 4.1.8.11.(9),

Cp = seismic coefficient for mechanical/electrical equipment, as defined in Sentence 4.1.8.18.(1),

Dnx = plan dimension of the building at level x perpendicular to the direction of seismic loading being considered,

ex = distance measured perpendicular to the direction of earthquake loading between centre of mass and centre of rigidity at the level being considered,

Fa = site coefficient, as defined in Sentence 4.1.8.4.(7),

F(PGA) = site coefficient for PGA, as defined in Sentence 4.1.8.4.(5),

F(PGV) = site coefficient for PGV, as defined in Sentence 4.1.8.4.(5),

Fs = site coefficient, as defined in Sentence 4.1.8.1.(2),

F(T) = site coefficient for spectral acceleration, as defined in Sentence 4.1.8.4.(5),

Ft = portion of V to be concentrated at the top of the structure, as defined in Sentence 4.1.8.11.(6),

Fv = site coefficient, as defined in Sentence 4.1.8.4.(7),

Fx = lateral force applied to level x, as defined in Sentence 4.1.8.11.(6),

hi, hn, hx = the height above the base (i = 0) to level i, n, or x respectively, where the base of the structure is the level at which horizontal earthquake motions are considered to be imparted to the structure,

hs = interstorey height (hi - hi-1),

IE = earthquake importance factor of the structure, as described in Sentence 4.1.8.5.(1),

J = numerical reduction coefficient for base overturning moment, as defined in Sentence 4.1.8.11.(5),

JX = numerical reduction coefficient for overturning moment at level x, as defined in Sentence 4.1.8.11.(7),

Level i = any level in the building, i =1 for first level above the base,

Level n = level that is uppermost in the main portion of the structure,

Level x = level that is under design consideration,

Mv = factor to account for higher mode effect on base shear, as defined in Sentence 4.1.8.11.(5),

Mx = overturning moment at level x, as defined in Sentence 4.1.8.11.(7),

N = total number of storeys above exterior grade to level n,

= Average Standard Penetration Resistance for the top 30 m, corrected to a rod energy efficiency of 60% of the theoretical maximum,

PGA = Peak Ground Acceleration expressed as a ratio to gravitational acceleration, as defined in Sentence 4.1.8.4.(1),

PGAref = reference PGA for determining F(T), F(PGA) and F(PGV), as defined in Sentence 4.1.8.4.(4),

PGV = Peak Ground Velocity, in m/s, as defined in Sentence 4.1.8.4.(1),

PI = plasticity index for clays,

Rd = ductility-related force modification factor reflecting the capability of a structure to dissipate energy through reversed cyclic inelastic behaviour, as given in Article 4.1.8.9.,

Ro = overstrength-related force modification factor accounting for the dependable portion of reserve strength in a structure designed according to these provisions, as defined in Article 4.1.8.9.,

Rs = combined overstrength and ductility-related modification factor, as defined in Sentence 4.1.8.1.(7),

SP = horizontal force factor for part or portion of a building and its anchorage, as given in Sentence 4.1.8.18.(1),

S(T) = design spectral response acceleration, expressed as a ratio to gravitational acceleration, for a period of T, as defined in Sentence 4.1.8.4.(7),

Sa(T) = 5% damped spectral response acceleration, expressed as a ratio to gravitational acceleration, for a period of T, as defined in Sentence 4.1.8.4.(1),

SFRS = Seismic Force Resisting System(s) is that part of the structural system that has been considered in the design to provide the required resistance to the earthquake forces and effects defined in Subsection 4.1.8.,

su = average undrained shear strength in the top 30 m of soil,

T = period in seconds,

Ta = fundamental lateral period of vibration of the building or structure in seconds in the direction under consideration, as defined in Sentence 4.1.8.11.(3),

Ts = fundamental lateral period of vibration of the building or structure in seconds in the direction under consideration, as described in Sentence 4.1.8.1.(7),

Tx = floor torque at level x, as defined in Sentence 4.1.8.11.(10),

TDD = Total Design Displacement of any point in a seismically isolated structure, within or above the isolation system, obtained by calculating the mean + (IE × the standard deviation) of the peak horizontal displacements from all sets of ground motion histories analyzed, but not less than × the mean, where the peak horizontal displacement is based on the vector sum of the two orthogonal horizontal displacements considered for each time step,

V = lateral earthquake design force at the base of the structure, as determined by Article 4.1.8.11.,

Vd = lateral earthquake design force at the base of the structure, as determined by Article 4.1.8.12.,

Ve = lateral earthquake elastic force at the base of the structure, as determined by Article 4.1.8.12.,

Ved = lateral earthquake design elastic force at the base of the structure, as determined by Article 4.1.8.12.,

VP = lateral force on a part of the structure, as determined by Article 4.1.8.18.,

Vs = lateral earthquake design force at the base of the structure, as determined by Sentence 4.1.8.1.(7),

= average shear wave velocity in the top 30 m of soil or rock,

W = dead load, as defined in Article 4.1.4.1., except that the minimum partition load as defined in Sentence 4.1.4.1.(3) need not exceed 0.5 kPa, plus 25% of the design snow load specified in Subsection 4.1.6., plus 60% of the storage load for areas used for storage, except that storage garages need not be considered storage areas, and the full contents of any tanks,

Wi, Wx = portion of W that is located at or is assigned to level i or x respectively,

WP = weight of a part or portion of a structure, e.g., cladding, partitions and appendages,

Wt = sum of Wi over the height of the building,

δave = average displacement of the structure at level x, as defined in Sentence 4.1.8.11.(9), and

δmax = maximum displacement of the structure at level x, as defined in Sentence 4.1.8.11.(9).

(1) The building shall be designed to meet the requirements of this Subsection and of the design standards referenced in Section 4.3.

(2) Structures shall be designed with a clearly defined load path, or paths, that will transfer the inertial forces generated in an earthquake to the supporting ground.

(3) The structure shall have a clearly defined Seismic Force Resisting System(s) (SFRS), as defined in Article 4.1.8.2.

(4) The SFRS shall be designed to resist 100% of the earthquake loads and their effects.

(5) All structural framing elements not considered to be part of the SFRS must be investigated and shown to behave elastically or to have sufficient non-linear capacity to support their gravity loads while undergoing earthquake-induced deformations calculated from the deflections determined in Article 4.1.8.13.

(6) Stiff elements that are not considered part of the SFRS, such as concrete, masonry, brick or pre-cast walls or panels, shall be,

(a) separated from all structural elements of the building such that no interaction takes place as the building undergoes deflections due to earthquake effects as calculated in this Subsection, or

(b) made part of the SFRS and satisfy the requirements of this Subsection.

(7) Stiffness imparted to the structure from elements not part of the SFRS, other than those described in Sentence (6), shall not be used to resist earthquake deflections but shall be accounted for,

(a) in calculating the period of the structure for determining forces if the added stiffness decreases the fundamental lateral period by more than 15%,

(b) in determining the irregularity of the structure, except the additional stiffness shall not be used to make an irregular SFRS regular or to reduce the effects of torsion, and

(c) in designing the SFRS if inclusion of the elements not part of the SFRS in the analysis has an adverse effect on the SFRS.

(8) Structural modelling shall be representative of the magnitude and spatial distribution of the mass of the building and of the stiffness of all elements of the SFRS, including stiff elements that are not separated in accordance with Sentence 4.1.8.3.(6), and shall account for,

(a) the effect of cracked sections in reinforced concrete and reinforced masonry elements,

(b) the effect of the finite size of members and joints,

(c) sway effects arising from the interaction of gravity loads with the displaced configuration of the structure, and

(d) other effects that influence the lateral stiffness of the building.

(1) The peak ground acceleration (PGA), peak ground velocity (PGV) and the 5% damped spectral response acceleration values, Sa(T), for the reference ground conditions (Site Class C in Table 4.1.8.4.A.) for periods T of 0.2 s, 0.5 s, 1.0 s, 2.0 s, 5.0 s and 10.0 s, shall be determined in accordance with Subsection 1.1.2. and are based on a 2% probability of exceedance in 50 years.

(2) Site classifications for ground shall conform to Table 4.1.8.4.A. and shall be determined using or, where is not known, using Sentence (3).

(3) If average shear wave velocity, , is not known, Site Class shall be determined from energy-corrected Average Standard Penetration Resistance, , or from soil average undrained shear strength, su, as noted in Table 4.1.8.4.A., and su being calculated based on rational analysis.

(4) For the purpose of determining the values of F(T) to be used in the calculation of design spectral acceleration, S(T), in Sentence (9), and the values of F(PGA) and F(PGV), the value of PGAref to be used with Tables 4.1.8.4.B. to 4.1.8.4.I. shall be taken as,

(a) 0.8 PGA, where the ratio Sa(0.2)/PGA < 2.0, and

(b) 1 PGA, in all other cases.

(5) The values of the site coefficient for design spectral acceleration at period T, F(T), and of similar coefficients F(PGA) and F(PGV) shall conform to Tables 4.1.8.4.B. to 4.1.8.4.I. using linear interpolation for intermediate values of PGAref.

(6) Site-specific evaluation is required to determine F(T), F(PGA) and F(PGV) for Site Class F.

(7) For all applications in Subsection 4.1.8., Fa = F(0.2) and Fv = F(1.0).

(8) For structures with a fundamental period of vibration equal to or less than 0.5 s that are built on liquefiable soils, Site Class and the corresponding values of F(T) may be determined as described in Tables 4.1.8.4.A., 4.1.8.4.B., and 4.1.8.4.C. by assuming that the soils are not liquefiable.

(9) The design spectral acceleration values of S(T) shall be determined as follows, using linear interpolation for intermediate values of T:

S(T) = F(0.2)Sa(0.2) or F(0.5)Sa(0.5), whichever is larger, for T ≤ 0.2 s

= F(0.5)Sa(0.5) for T = 0.5 s

= F(1.0)Sa(1.0) for T = 1.0 s

= F(2.0)Sa(2.0) for T = 2.0 s

= F(5.0)Sa(5.0) for T = 5.0 s

= F(10.0)Sa(10.0) for T ≥ 10.0 s

Table 4.1.8.4.A. Site Classification for Seismic Site Response

**Forming Part of Sentences 4.1.8.4.(1) to (3)**

(1) Site Classes A and B, hard rock and rock, are not to be used if there is more than 3 m of softer materials between the rock and the underside of footing or mat foundations. The appropriate Site Class for such cases is determined on the basis of the average properties of the total thickness of the softer materials.

(2) Where has been measured in-situ, the F(T) values for Site Class A derived from Tables 4.1.8.4.B. to 4.1.8.4.G. are permitted to be multiplied by the factor .

(3) Any profile with more than 3 m of soil with the following characteristics:

(a) plasticity index: PI > 20

(b) moisture content: w ≥ 40%, and

(c) undrained shear strength: su < 25 kPa.

(4) Other soils include:

(a) liquefiable soils, quick and highly sensitive clays, collapsible weakly cemented soils, and other soils susceptible to failure or collapse under seismic loading,

(b) peat and/or highly organic clays greater than 3 m in thickness,

(c) highly plastic clays (PI > 75) more than 8 m thick, and

(d) soft to medium stiff clays more than 30 m thick.

Table 4.1.8.4.B. Values of F(0.2) as a Function of Site Class and PGAref

**Forming Part of Sentences 4.1.8.4.(4) and (5)**

(1) See Sentence 4.1.8.4.(6)

Table 4.1.8.4.C. Values of F(0.5) as a Function of Site Class and PGAref

**Forming Part of Sentence 4.1.8.4.(4) and (5)**

(1) See Sentence 4.1.8.4.(6)

Table 4.1.8.4.D. Values of F(1.0) as a Function of Site Class and PGAref

**Forming Part of Sentences 4.1.8.4.(4) and (5)**

(1) See Sentence 4.1.8.4.(6)

Table 4.1.8.4.E. Values of F(2.0) as a Function of Site Class and PGAref

**Forming Part of Sentences 4.1.8.4.(4) and (5)**

(1) See Sentence 4.1.8.4.(6)

Table 4.1.8.4.F. Values of F(5.0) as a Function of Site Class and PGAref

**Forming Part of Sentences 4.1.8.4.(4) and (5)**

(1) See Sentence 4.1.8.4.(6)

Table 4.1.8.4.G. Values of F(10.0) as a Function of Site Class and PGAref

**Forming Part of Sentences 4.1.8.4.(4) and (5)**

(1) See Sentence 4.1.8.4.(6)

Table 4.1.8.4.H. Values of F(PGA) as a Function of Site Class and PGAref

**Forming Part of Sentences 4.1.8.4.(4) and (5)**

(1) See Sentence 4.1.8.4.(6)

Table 4.1.8.4.I. Values of F(PGV) as a Function of Site Class and PGAref

**Forming Part of Sentences 4.1.8.4.(4) and (5)**

(1) See Sentence 4.1.8.4.(6)

(1) The earthquake importance factor, IE, shall be determined according to Table 4.1.8.5.

Table 4.1.8.5. Importance Factor for Earthquake Loads and Effects, IE

**Forming Part of Sentence 4.1.8.5.(1)**

(1) See Article 4.1.8.13.

(1) Structures having any of the features listed in Table 4.1.8.6. shall be designated irregular.

(2) Structures not classified as irregular according to Sentence 4.1.8.6.(1) may be considered regular.

(3) Except as required by Article 4.1.8.10., in cases where IEFaSa(0.2) is equal to or greater than 0.35, structures designated as irregular must satisfy the provisions referenced in Table 4.1.8.6.

Table 4.1.8.6. Structural Irregularities(1)

**Forming Part of Sentence 4.1.8.6.(1)**

(1) One-storey penthouses with a weight of less than 10% of the level below need not be considered in the application of this Table.

(2) See Article 4.1.8.7.

(3) See Article 4.1.8.10.

(4) See Article 4.1.8.15.

(5) See Sentences 4.1.8.11.(9) and (10) and 4.1.8.12.(4).

(6) See Article 4.1.8.8.

(1) Analysis for design earthquake actions shall be carried out in accordance with the Dynamic Analysis Procedure described in Article 4.1.8.12., except that the Equivalent Static Force Procedure described in Article 4.1.8.11. may be used for structures that meet any of the following criteria:

(a) in cases where IEFaSa(0.2) is less than 0.35,

(b) regular structures that are less than 60 m in height and have a fundamental lateral period, Ta, less than 2 s in each of two orthogonal directions as defined in Article 4.1.8.8., or

(c) structures with structural irregularity, of Type 1, 2, 3, 4, 5, 6 or 8 as defined in Table 4.1.8.6., that are less than 20 m in height and have a fundamental lateral period, Ta, less than 0.5 s in each of two orthogonal directions as defined in Article 4.1.8.8.

(1) Earthquake forces shall be assumed to act in any horizontal direction, except that the following shall be considered to provide adequate design force levels in the structure:

(a) where components of the SFRS are oriented along a set of orthogonal axes, independent analyses about each of the principal axes of the structure shall be performed,

(b) where the components of the SFRS are not oriented along a set of orthogonal axes and IEFaSa(0.2) is less than 0.35, independent analyses about any two orthogonal axes is permitted, or

(c) where the components of the SFRS are not oriented along a set of orthogonal axes and IEFaSa(0.2) is equal to or greater than 0.35, analysis of the structure independently in any two orthogonal directions for 100% of the prescribed earthquake loads applied in one direction plus 30% of the prescribed earthquake loads in the perpendicular direction, with the combination requiring the greater element strength being used in the design.

(1) Except as provided in Sentence 4.1.8.20.(7), the values of Rd and Ro and the corresponding system restrictions shall conform to Table 4.1.8.9. and the requirements of this Subsection.

(2) When a particular value of Rd is required by this Article, the corresponding Ro shall be used.

(3) For combinations of different types of SFRS acting in the same direction in the same storey, RdRo shall be taken as the lowest value of RdRo corresponding to these systems.

(4) For vertical variations of RdRo, excluding rooftop structures not exceeding two storeys in height whose weight is less than the greater of 10% of W and 30% of Wi of the level below, the value of RdRo used in the design of any storey shall be less than or equal to the lowest value of RdRo used in the given direction for the storeys above, and the requirements of Sentence 4.1.8.15.(5) must be satisfied.

(5) If it can be demonstrated through testing, research and analysis that the seismic performance of a structural system is at least equivalent to one of the types of SFRS mentioned in Table 4.1.8.9., then such a structural system will qualify for values of Rd and Ro corresponding to the equivalent type in that Table.

Table 4.1.8.9. SFRS Ductility-Related Force Modification Factors, Rd, Overstrength-Related Force Modification Factors, Ro, and General Restrictions (1)

**Forming Part of Sentences 4.1.8 9.(1) and (5)**

(1) See Article 4.1.8.10.

(2) NP = system is not permitted.

NL = system is permitted and not limited in height as an SFRS; height may be limited in other Parts of this Code.

Numbers in Columns 4 to 8 are maximum height limits above grade in m.

The most stringent requirement governs.

(3) Higher design force levels are prescribed in CSA S16 for some heights of buildings.

(4) Frames limited to a maximum of 2 storeys.

(5) Frames limited to a maximum of 3 storeys.

(1) Except as required by Clause (2)(b), structures with a Type 6 irregularity, Discontinuity in Capacity - Weak Storey, as described in Table 4.1.8.6., are not permitted unless IEFaSa(0.2) is less than 0.2 and the forces used for design of the SFRS are multiplied by RdRo.

(2) Post-disaster buildings shall,

(a) not have any irregularities conforming to Types 1, 3, 4, 5, 7 and 9 as described in Table 4.1.8.6., in cases where IEFaSa(0.2) is equal to or greater than 0.35,

(b) not have a Type 6 irregularity as described in Table 4.1.8.6.,

(c) have an SFRS with an Rd of 2.0 or greater, and

(d) have no storey with a lateral stiffness that is less than that of the storey above it.

(3) For buildings having fundamental lateral periods, Ta, of 1.0 s or greater and where IEFvSa(1.0) is greater than 0.25, shear walls that are other than wood-based and form part of the SFRS shall be continuous from their top to the foundation and shall not have irregularities of Type 4 or 5 as described in Table 4.1.8.6.

(4) For buildings constructed with more than 4 storeys of continuous wood construction and where IEFaSa(0.2) is equal to or greater than 0.35, timber SFRS of shear walls with wood-based panels, braced frames or moment-resisting frames as defined in Table 4.1.8.9. within the continuous wood construction shall not have irregularities of Type 4 or 5 as described in Table 4.1.8.6.

(4.1) For buildings where IEFaSa(0.2) is equal to or greater than 0.35 or IEFvSa(1.0) is equal to or greater than 0.2 that are constructed with more than 4 storeys of continuous wood construction, timber SFRSs consisting of moderately ductile or limited ductility cross-laminated timber shear walls, platform-type construction, as defined in Table 4.1.8.9., within the continuous wood construction shall not have Type 4, 5, 6, 8, or 9 irregularities as described in Table 4.1.8.6.

(5) The ratio, α, for Type 9 irregularity as described in Table 4.1.8.6. shall be determined independently for each orthogonal direction using the following equation:

𝛼 = QG / Qy

where,

QG = gravity-induced lateral demand on the SFRS at the critical level of the yielding system, and

Qy = the resistance of the yielding mechanism required to resist the minimum earthquake loads, which need not be taken less than Ro multiplied by the minimum lateral earthquake force as determined in Article 4.1.8.11. or 4.1.8.12, as appropriate.

(6) For buildings with a Type 9 irregularity as described in Table 4.1.8.6. and where IEFaSa(0.2) is equal to or greater than 0.5, deflections determined in accordance with Article 4.1.8.13. shall be multiplied by 1.2.

(7) Structures where the value of α, as determined in accordance with Sentence (5), exceeds twice the limits in Table 4.1.8.6. for a Type 9 irregularity, and where IEFaSa(0.2) is equal to or greater than 0.5 are not permitted unless determined to be acceptable based on non-linear dynamic analysis studies.

(1) The static loading due to earthquake motion shall be determined according to the procedures given in this Article.

(2) Except as provided in Sentence (12), the minimum lateral earthquake force, V, shall be calculated using the following formula:

V = S (Ta) MvIEW/ (RdRo)

except,

(a) for walls, coupled walls and wall-frame systems, V shall not be less than,

S (4.0) Mv IEW/ (RdRo)

(b) for moment-resisting frames, braced frames and other systems, V shall not be less than,

S (2.0) Mv IEW/ (RdRo)

(c) for buildings located on a site other than Class F and having an SFRS with an Rd equal to or greater than 1.5, V need not be greater than the larger of,

and

S (0.5) IEW/ (RdRo)

(3) Except as provided in Sentence (4), the fundamental lateral period, Ta, in the direction under consideration in Sentence (2) shall be determined as,

(a) for moment-resisting frames that resist 100% of the required lateral forces and where the frame is not enclosed by or adjoined by more rigid elements that would tend to prevent the frame from resisting lateral forces, and where hn is in metres,

(i) 0.085 (hn)3/4 for steel moment frames,

(ii) 0.075 (hn)3/4 for concrete moment frames, or

(iii) 0.1 N for other moment frames,

(b) 0.025 hn for braced frames where hn is in metres,

(c) 0.05 (hn)3/4 for shear wall and other structures where hn is in metres, or

(d) other established methods of mechanics using a structural model that complies with the requirements of Sentence 4.1.8.3.(8), except that,

(i) for moment-resisting frames, Ta shall not be taken greater than 1.5 times that determined in Clause (a),

(ii) for braced frames, Ta shall not be taken greater than 2.0 times that determined in Clause (b),

(iii) for shear wall structures, Ta shall not be taken greater than 2.0 times that determined in Clause (c),

(iv) for other structures, Ta shall not be taken greater than that determined in Clause (c), and

(v) for the purpose of calculating the deflections, the period without the upper limit specified in Subclauses (d)(i) to (iv) may be used, except that, for walls, coupled walls and wall-frame systems, Ta shall not exceed 4.0 s, and for moment-resisting frames, braced frames, and other systems, Ta shall not exceed 2.0 s.

(4) For single-storey buildings with steel deck or wood roof diaphragms, the fundamental lateral period, Ta, in the direction under consideration is permitted to be taken as,

(a) 0.05 (hn)3/4 + 0.004 L for shear walls,

(b) 0.035 hn + 0.004 L for steel moment frames and steel braced frames, or

(c) the value obtained from methods of mechanics using a structural model that complies with the requirements of Sentence 4.1.8.3.(8), except that Ta shall not be greater than 1.5 times the value determined in Clause (a) or (b), as applicable,

where L is the shortest length of the diaphragm, in m, between adjacent vertical elements of the SFRS in the direction perpendicular to the direction under consideration.

(5) The weight, W, of the building shall be calculated using the formula,

(6) The higher mode factor, Mv, and its associated base overturning moment reduction factor, J, shall conform to Tables 4.1.8.11.A. to 4.1.8.11.E.

Table 4.1.8.11.A. Higher Mode Factor, Mv, and Base Overturning Reduction Factor, J(1)(2)(3)(4) for Moment-Resisting Frames

**Forming Part of Sentence 4.1.8.11.(6)**

(1) For intermediate values of the spectral ratio S(0.2)/S(5.0), Mv and J shall be obtained by linear interpolation.

(2) For intermediate values of the fundamental lateral period, Ta, S(Ta)Mv shall be obtained by linear interpolation using the values of Mv obtained in accordance with Note (1).

(3) For intermediate values of the fundamental lateral period, Ta, J shall be obtained by linear interpolation using the values of J obtained in accordance with Note (1).

(4) For a combination of different seismic force resisting systems (SFRS) not given in Table 4.1.8.11.A. that are in the same direction under consideration, use the highest Mv factor of all the SFRS and the corresponding value of J.

(5) For fundamental lateral periods, Ta, greater than 2.0 s, use the 2.0 s values obtained in accordance with Note (1). See Clause 4.1.8.11.(2)(b).

Table 4.1.8.11.B. Higher Mode Factor, Mv, and Base Overturning Reduction Factor, J(1)(2)(3)(4) for Coupled Walls(5)

**Forming Part of Sentence 4.1.8.11.(6)**

(1) For intermediate values of the spectral ratio S(0.2)/S(5.0), Mv and J shall be obtained by linear interpolation.

(2) For intermediate values of the fundamental lateral period, Ta, S(Ta)Mv shall be obtained by linear interpolation using the values of Mv obtained in accordance with Note (1).

(3) For intermediate values of the fundamental lateral period, Ta, J shall be obtained by linear interpolation using the values of J obtained in accordance with Note (1).

(4) For a combination of different seismic force resisting systems (SFRS) not given in Table 4.1.8.11.B. that are in the same direction under consideration, use the highest Mv factor of all the SFRS and the corresponding value of J.

(5) A "coupled" wall is a wall system with coupling beams, where at least 66% of the base overturning moment resisted by the wall system is carried by the axial tension and compression forces resulting from shear in the coupling beams.

(6) For fundamental lateral periods, Ta, greater than 4.0 s, use the 4.0 s values of S(Ta)Mv obtained by interpolation between 2.0 s and 5.0 s using the value of Mv obtained in accordance with Note (1). See Clause 4.1.8.11.(2)(a).

(7) For fundamental lateral periods, Ta, greater than 4.0 s, use the 4.0 s values of J obtained by interpolation between 2.0 s and 5.0 s using the value of J obtained in accordance with Note (1). See Clause 4.1.8.11.(2)(a).

Table 4.1.8.11.C. Higher Mode Factor, Mv, and Base Overturning Reduction Factor, J(1)(2)(3)(4) for Braced Frames

**Forming Part of Sentence 4.1.8.11.(5)**

(1) For intermediate values of the spectral ratio S(0.2)/S(5.0), Mv and J shall be obtained by linear interpolation.

(2) For intermediate values of the fundamental lateral period, Ta, S(Ta)Mv shall be obtained by linear interpolation using the values of Mv obtained in accordance with Note (1).

(3) For intermediate values of the fundamental lateral period, Ta, J shall be obtained by linear interpolation using the values of J obtained in accordance with Note (1).

(4) For a combination of different seismic force resisting systems (SFRS) not given in Table 4.1.8.11.C. that are in the same direction under consideration, use the highest Mv factor of all the SFRS and the corresponding value of J.

(5) For fundamental lateral periods, Ta, greater than 2.0 s, use the 2.0 s values obtained in accordance with Note (1). See Clause 4.1.8.11.(2)(b).

Table 4.1.8.11.D. Higher Mode Factor, Mv, and Base Overturning Reduction Factor, J(1)(2)(3)(4) for Walls, Wall Frame Systems

**Forming Part of Sentence 4.1.8.11.(5)**

(1) For intermediate values of the spectral ratio S(0.2)/S(5.0), Mv and J shall be obtained by linear interpolation.

(2) For intermediate values of the fundamental lateral period, Ta, S(Ta)Mv shall be obtained by linear interpolation using the values of Mv obtained in accordance with Note (1).

(3) For intermediate values of the fundamental lateral period, Ta, J shall be obtained by linear interpolation using the values of J obtained in accordance with Note (1).

(4) For a combination of different seismic force resisting systems (SFRS) not given in Table 4.1.8.11.D. that are in the same direction under consideration, use the highest Mv factor of all the SFRS and the corresponding value of J.

(5) For fundamental lateral periods, Ta, greater than 4.0 s, use the 4.0 s values of S(Ta)Mv obtained by interpolation between 2.0 s and 5.0 s using the value of Mv obtained in accordance with Note (1). See Clause 4.1.8.11.(2)(a).

(6) For fundamental lateral periods, Ta, greater than 4.0 s, use the 4.0 s values of J obtained by interpolation between 2.0 s and 5.0 s using the value of J obtained in accordance with Note (1). See Clause 4.1.8.11.(2)(a).

Table 4.1.8.11.E. Higher Mode Factor, Mv, and Base Overturning Reduction Factor, J(1)(2)(3)(4) for Other Systems

**Forming Part of Sentence 4.1.8.11.(5)**

(1) For intermediate values of the spectral ratio S(0.2)/S(5.0), Mv and J shall be obtained by linear interpolation.

(2) For intermediate values of the fundamental lateral period, Ta, S(Ta)Mv shall be obtained by linear interpolation using the values of Mv obtained in accordance with Note (1).

(3) For intermediate values of the fundamental lateral period, Ta, J shall be obtained by linear interpolation using the values of J obtained in accordance with Note (1).

(4) For a combination of different seismic force resisting systems (SFRS) not given in Table 4.1.8.11.E. that are in the same direction under consideration, use the highest Mv factor of all the SFRS and the corresponding value of J.

(5) For fundamental lateral periods, Ta, greater than 2.0 s, use the 2.0 s values obtained in accordance with Note (1). See Clause 4.1.8.11.(2)(b).

(7) The total lateral seismic force, V, shall be distributed such that a portion, Ft, shall be assumed to be concentrated at the top of the building, where Ft, is equal to 0.07 TaV but need not exceed 0.25 V and may be considered as zero, where the fundamental lateral period, Ta, does not exceed 0.7 s; the remainder, V - Ft, shall be distributed along the height of the building, including the top level, in accordance with the formula,

(8) The structure shall be designed to resist overturning effects caused by the earthquake forces determined in Sentence (7) and the overturning moment at level x, Mx, shall be determined using the formula,

where,

Jx = 1.0 for hx ≥ 0.6hn, and

Jx = J + (1- J)(hx / 0.6hn) for hx,< 0.6hn

where,

J = base overturning moment reduction factor conforming to Table 4.1.8.11.

(9) Torsional effects that are concurrent with the effects of the forces mentioned in Sentence (7) and are caused by the simultaneous actions of the following torsional moments shall be considered in the design of the structure according to Sentence (11):

(a) torsional moments introduced by eccentricity between the centres of mass and resistance and their dynamic amplification, and

(b) torsional moments due to accidental eccentricities.

(10) Torsional sensitivity shall be determined by calculating the ratio Bx for each level x according to the following equation for each orthogonal direction determined independently:

Bx = δmax / δave

where,

B = maximum of all values of Bx in both orthogonal directions, except that the Bx for one-storey penthouses with a weight less than 10% of the level below need not be considered,

δmax = maximum storey displacement at the extreme points of the structure, at level x in the direction of the earthquake induced by the equivalent static forces acting at distances ± 0.10 Dnx from the centres of mass at each floor, and

δave = average of the displacements at the extreme points of the structure at level x produced by the above-mentioned forces.

(11) Torsional effects shall be accounted for as follows:

(a) for a building with B ≤1.7 or where IEFaSa(0.2) is less than 0.35, by applying torsional moments about a vertical axis at each level throughout the building, derived for each of the following load cases considered separately,

(i) Tx = Fx(ex + 0.10 Dnx), and

(ii) Tx = Fx(ex - 0.10 Dnx)

where Fx is the lateral force at each level determined according to Sentence (6) and where each element of the building is designed for the most severe effect of the above load cases, or

(b) for a building with B >1.7, in cases where IEFaSa(0.2) is equal to or greater than 0.35, by a Dynamic Analysis Procedure as specified in Article 4.1.8.12.

(12) Where the fundamental lateral period, Ta, is determined in accordance with Clause (3)(d) and the building is constructed with more than 4 storeys of continuous wood construction and has a timber SFRS consisting of shear walls with wood-based panels, braced frames or moment-resisting frames as defined in Table 4.1.8.9., the lateral earthquake force, V, as determined in accordance with Sentence (2) shall be multiplied by 1.2 but need not exceed the value determined by using Clause (2)(c).

(1) Except as provided in Articles 4.1.8.19. and 4.1.8.21., the Dynamic Analysis Procedure shall be in accordance with one of the following methods:

(a) Linear Dynamic Analysis by either the Modal Response Spectrum Method or the Numerical Integration Linear Time History Method using a structural model that complies with the requirements of Sentence 4.1.8.3.(8), or

(b) Non-linear Dynamic Analysis, in which case a special study shall be performed.

(2) The spectral acceleration values used in the Modal Response Spectrum Method shall be the design spectral acceleration values, S(T), defined in Sentence 4.1.8.4.(7).

(3) The ground motion histories used in the Numerical Integration Linear Time History Method shall be compatible with a response spectrum constructed from the design spectral acceleration values, S(T), defined in Sentence 4.1.8.4.(7).

(4) The effects of accidental torsional moments acting concurrently with the lateral earthquake forces that cause them shall be accounted for by the following methods:

(a) the static effects of torsional moments due to (± 0.10 Dnx)Fx at each level x, where Fx is either determined from the elastic dynamic analysis or determined from Sentence 4.1.8.11.(7) multiplied by RdRo/IE, shall be combined with the effects determined by dynamic analysis, or

(b) if B, as defined in Sentence 4.1.8.11.(10), is less than 1.7, it is permitted to use a three-dimensional dynamic analysis with the centres of mass shifted by a distance of - 0.05 Dnx and + 0.05 Dnx.

(5) Except as provided in Sentence (6), the design elastic base shear, Ved, is equal to the elastic base shear, Ve, obtained from a Linear Dynamic Analysis.

(6) For structures located on sites other than Class F that have an SFRS with Rd equal to or greater than 1.5, the elastic base shear obtained from a Linear Dynamic Analysis may be multiplied by the larger of the following factors to obtain the design elastic base shear, Ved:

2S(0.2)/3S(Ta) ≤ 1.0

and

S(0.5) / S(Ta) ≤ 1.0

(7) The design elastic base shear, Ved, shall be multiplied by the importance factor, IE, as determined in Article 4.1.8.5., and shall be divided by RdRo, as determined in Article 4.1.8.9., to obtain the design base shear, Vd.

(8) Except as required by Sentence (9) or (12), if the base shear, Vd, obtained in Sentence (7) is less than 80% of the lateral earthquake design force, V, of Article 4.1.8.11., Vd shall be taken as 0.8 V.

(9) For irregular structures requiring dynamic analysis in accordance with Article 4.1.8.7., Vd shall be taken as the larger of the Vd determined in Sentence (7) and 100% of V.

(10) Except as required by Sentence (11), the values of elastic storey shears, storey forces, member forces, and deflections obtained from the Linear Dynamic Analysis, including the effect of accidental torsion determined in Sentence (4), shall be multiplied by Vd/Ve to determine their design values, where Vd is the base shear.

(11) For the purpose of calculating deflections, it is permitted to use a value for V based on the value for Ta determined in Clause 4.1.8.11.(3)(d) to obtain Vd in Sentences (8) and (9).

(12) For buildings constructed with more than 4 storeys of continuous wood construction, having a timber SFRS consisting of shear walls with wood-based panels, braced frames or moment-resisting frames as defined in Table 4.1.8.9., and whose fundamental lateral period, Ta, is determined in accordance with Clause 4.1.8.11.(3)(d), the design base shear, Vd, shall be taken as the larger value of Vd determined in accordance with Sentence (7) and 100% of V.

(1) Except as provided in Sentences (5) and (6), lateral deflections of a structure shall be calculated in accordance with the loads and requirements defined in this Subsection.

(2) Lateral deflections obtained from a linear elastic analysis using the methods given in Articles 4.1.8.11. and 4.1.8.12. and incorporating the effects of torsion, including accidental torsional moments, shall be multiplied by RdRo/IE and increased as required by Sentences 4.1.8.10.(6) and 4.1.8.16.(1) to give realistic values of anticipated deflections.

(3) Based on the lateral deflections calculated in Sentences (2), (5) and (6), the largest interstorey deflection at any level shall be limited to 0.01 hs for post-disaster buildings, 0.02 hs for High Importance Category buildings, and 0.025 hs for all other buildings.

(4) The deflections calculated in Sentence (2) shall be used to account for sway effects as required by Sentence 4.1.3.2.(12).

(5) The lateral deflections of a seismically isolated structure shall be calculated in accordance with Article 4.1.8.20.

(6) The lateral deflections of a structure with supplemental energy dissipation shall be calculated in accordance with Article 4.1.8.22.

(1) Adjacent structures shall be,

(a) separated by a distance equal to at least the square root of the sum of the squares of their individual deflections calculated in Sentence 4.1.8.13.(2), or

(b) connected to each other.

(2) The method of connection required in Sentence (1) shall take into account the mass, stiffness, strength, ductility and anticipated motion of the connected buildings and the character of the connection.

(3) Rigidly connected buildings shall be assumed to have the lowest RdRo value of the buildings connected.

(4) Buildings with non-rigid or energy-dissipating connections require special studies.

(1) Except as provided in Sentences (2) and (3), diaphragms, collectors, chords, struts and connections shall be designed so as not to yield, and the design shall account for the shape of the diaphragm, including openings, and for the forces generated in the diaphragm due to the following cases, whichever one governs:

(a) forces due to loads determined in Article 4.1.8.11. or 4.1.8.12. applied to the diaphragm are increased to reflect the lateral load capacity of the SFRS, plus forces in the diaphragm due to the transfer of forces between elements of the SFRS associated with the lateral load capacity of such elements and accounting for discontinuities and changes in stiffness in these elements, or

(b) a minimum force corresponding to the design-based shear divided by N for the diaphragm at level x.

(2) Steel deck roof diaphragms in buildings of less than 4 storeys or wood diaphragms that are designed and detailed according to the applicable referenced design standards to exhibit ductile behaviour shall meet the requirements of Sentence (1), except that they may yield and the forces shall be,

(a) for wood diaphragms acting in combination with vertical wood shear walls, equal to the lateral earthquake design force,

(b) for wood diaphragms acting in combination with other SFRS, not less than the force corresponding to RdRo = 2.0, and

(c) for steel deck roof diaphragms, not less than the force corresponding to RdRo = 2.0.

(3) Where diaphragms are designed in accordance with Sentence (2), the struts shall be designed in accordance with Clause (1)(a) and the collectors, chords and connections between the diaphragms and the vertical elements of the SFRS shall be designed for forces corresponding to the capacity of the diaphragms in accordance with the applicable CSA standards.

(4) For single-storey buildings with steel deck or wood roof diaphragms designed with a value of Rd greater than 1.5 and where the calculated maximum relative deflection, ΔD, of the diaphragm under lateral loads exceeds 50% of the average storey drift, ΔB, of the adjoining vertical elements of the SFRS, dynamic magnification of the inelastic response due to the in-plane diaphragm deformations shall be accounted for in the design as follows:

(a) the vertical elements of the SFRS shall be designed and detailed to any one of the following:

(i) to accommodate the anticipated magnified lateral deformations taken as RoRd (ΔB+ ΔD) - RoΔD,

(ii) to resist the forces magnified by Rd(1 + ΔD/ΔB)/( Rd + ΔD/ΔB), or

(iii) by a special study, and

(b) the roof diaphragm and chords shall be designed for in-plane shears and moments determined while taking into consideration the inelastic higher mode response of the structure.

(5) In cases where IEFaSa(0.2) is equal to or greater than 0.35, the elements supporting any discontinuous wall, column or braced frame shall be designed for the lateral load capacity of the components of the SFRS they support.

(6) Where structures have vertical variations of RdRo satisfying Sentence 4.1.8.9.(4), the elements of the SFRS below the level where the change in RdRo occurs shall be designed for the forces associated with the lateral load capacity of the SFRS above that level.

(7) Where earthquake effects can produce forces in a column or wall due to lateral loading along both orthogonal axes, account shall be taken of the effects of potential concurrent yielding of other elements framing into the column or wall from all directions at the level under consideration and as appropriate at other levels.

(8) The design forces associated with the lateral capacity of the SFRS need not exceed the forces determined in accordance with Sentence 4.1.8.7.(1) with RdRo taken as 1.0, unless otherwise provided by the applicable referenced design standards for elements, in which case the design forces associated with the lateral capacity of the SFRS need not exceed the forces determined in accordance with Sentence 4.1.8.7.(1) with RdRo taken as less than or equal to 1.3.

(9) Foundations need not be designed to resist the lateral load overturning capacity of the SFRS, provided the design and the Rd and Ro for the type of SFRS used conform to Table 4.1.8.9. and the foundation is designed in accordance with Sentence 4.1.8.16.(4).

(10) Foundation displacements and rotations shall be considered as required by Sentence 4.1.8.16.(1).

(1) The increased displacements of the structure resulting from foundation movement shall be shown to be within acceptable limits for both the SFRS and the structural framing elements not considered to be part of the SFRS.

(2) Except as provided in Sentences (3) and (4), foundations shall be designed to have factored shear and overturning resistances greater than the lateral load capacity of the SFRS.

(3) The shear and overturning resistances of the foundation determined using a bearing stress equal to 1.5 times the factored bearing strength of the soil or rock and all other resistances equal to 1.3 times the factored resistances need not exceed the design forces determined in Sentence 4.1.8.7.(1) using RdRo = 1.0 except that the factor of 1.3 shall not apply to the portion of the resistance to uplift or overturning resulting from gravity loads.

(4) A foundation is permitted to have a factored overturning resistance less than the lateral load overturning capacity of the supported SFRS, provided the following requirements are met:

(a) neither the foundation nor the supported SFRS are constrained against rotation, and

(b) the design overturning moment of the foundation is,

(i) not less than 75% of the overturning capacity of the supported SFRS, and

(ii) not less than that determined in Sentence 4.1.8.7.(1) using RdRo = 2.0.

(5) The design of foundations shall be such that they are capable of transferring earthquake loads and effects between the building and the ground without exceeding the capacities of the soil and rock.

(6) In cases where IEFaSa(0.2) is equal to or greater than 0.35, the following requirements shall be satisfied:

(a) piles or pile caps, drilled piers, and caissons shall be interconnected by continuous ties in no fewer than two directions,

(b) piles, drilled piers, and caissons shall be embedded a minimum of 100 mm into the pile cap or structure, and

(c) piles, drilled piers, and caissons, other than wood piles, shall be connected to the pile cap or structure for a minimum tension force equal to 0.15 times the factored compression load on the pile.

(7) At sites where IEFaSa(0.2) is equal to or greater than 0.35, basement walls shall be designed to resist earthquake lateral pressures from backfill or natural ground.

(8) At sites where IEFaSa(0.2) is greater than 0.75, the following requirements shall be satisfied:

(a) piles, drilled piers, or caissons shall be designed and detailed to accommodate cyclic inelastic behaviour when the design moment in the element due to earthquake effects is greater than 75% of its moment capacity, and

(b) spread footings founded on soil defined as Site Class E or F shall be interconnected by continuous ties in no fewer than two directions.

(9) Each segment of a tie between elements that is required by Clause (6)(a) or (8)(b) shall be designed to carry by tension or compression a horizontal force at least equal to the greatest factored pile cap or column vertical load in the elements it connects, multiplied by a factor of 0.10 IEFaSa(0.2), unless it can be demonstrated that equivalent restraints can be provided by other means.

(10) The potential for liquefaction of the soil and its consequences, such as significant ground displacement and loss of soil strength and stiffness, shall be evaluated based on the ground motion parameters referenced in Subsection 1.1.2., as modified by Article 4.1.8.4., and shall be taken into account in the design of the structure and its foundations.

(1) The potential for slope instability and its consequences, such as slope displacement, shall be evaluated based on site-specific material properties and ground motion parameters referenced in Subsection 1.1.2., as modified by Article 4.1.8.4., and shall be taken into account in the design of the structure and its foundations.

(1) Except as provided in Sentences (2), (7) and (16), elements and components of buildings described in Table 4.1.8.18. and their connections to the structure shall be designed to accommodate the building deflections calculated in accordance with Article 4.1.8.13. and the element or component deflections calculated in accordance with Sentence (9), and shall be designed for a lateral force, VP, applied through the centre of mass of the element or component that is equal to:

Vp= 0.3FaSa(0.2) IESpWp

where,

Fa = as defined in Sentence 4.1.8.4.(7),

Sa(0.2) = spectral response acceleration value at 0.2 s, as defined in Sentence 4.1.8.4.(1),

IE = importance factor for the building, as defined in Article 4.1.8.5.,

Sp = CpArAx/Rp (the maximum value of Sp shall be taken as 4.0 and the minimum value of Sp shall be taken as 0.7), where,

Cp = element or component factor from Table 4.1.8.18.,

Ar = element or component force amplification factor from Table 4.1.8.18.,

Ax = height factor (1 + 2 hx / hn),

Rp = element or component response modification factor from Table 4.1.8.18., and

Wp = weight of the component or element.

(2) For buildings other than post-disaster buildings, seismically isolated buildings and buildings with supplemental energy dissipation systems, where IEFaSa(0.2) is less than 0.35, the requirements of Sentence (1) need not apply to Categories 6 through 22 of Table 4.1.8.18.

(3) For the purpose of applying Sentence (1) for Categories 11 and 12 of Table 4.1.8.18., elements or components shall be assumed to be flexible or flexibly connected unless it can be shown that the fundamental period of the element or component and its connection is less than or equal to 0.06 s, in which case the element or component is classified as being rigid or rigidly connected.

(4) The weight of access floors shall include the dead load of the access floor and the weight of permanent equipment, which shall not be taken as less than 25% of the floor live load.

(5) When the mass of a tank plus its contents or the mass of a flexible or flexibly connected piece of machinery, fixture or equipment is greater than 10% of the mass of the supporting floor, the lateral forces shall be determined by rational analysis.

(6) Forces shall be applied in the horizontal direction that results in the most critical loading for design, except for Category 6 of Table 4.1.8.18., where the forces shall be applied up and down vertically.

(7) Connections to the structure of elements and components listed in Table 4.1.8.18. shall be designed to support the component or element for gravity loads, shall conform to the requirements of Sentence (1), and shall also satisfy these additional requirements:

(a) friction due to gravity loads shall not be considered to provide resistance to seismic forces,

(b) Rp for non-ductile connections, such as adhesives or power actuated fasteners, shall be taken as 1.0,

(c) Rp for anchorage using shallow expansion, chemical, epoxy or cast-in place anchors shall be 1.5, where shallow anchors are those with a ratio of embedment length to diameter of less than 8,

(d) power-actuated fasteners and drop-in anchors shall not be used for tension loads,

(e) connections for non-structural elements or components of Category 1, 2 or 3 of Table 4.1.8.18. attached to the side of a building and above the first level above grade shall satisfy the following requirements:

(i) for connections where the body of the connection is ductile, the body shall be designed for values of CP, Ar and Rp given in Table 4.1.8.18., and all of the other parts of the connection, such as anchors, welds, bolts and inserts, shall be capable of developing 2.0 times the nominal yield resistance of the body of the connection, and

(ii) connections where the body of the connection is not ductile shall be designed for values of Cp=2.0, Rp =1.0 and Ar given in Table 4.1.8.18., and

(f) a ductile connection is one where the body of the connection is capable of dissipating energy through cyclic inelastic behaviour.

(8) Floors and roofs acting as diaphragms shall satisfy the requirements for diaphragms stated in Article 4.1.8.15.

(9) Lateral deflections of elements or components shall be based on the loads defined in Sentence (1) and lateral deflections obtained from an elastic analysis shall be multiplied by Rp/IE to give realistic values of the anticipated deflections.

(10) The elements or components shall be designed so as not to transfer to the structure any forces unaccounted for in the design, and rigid elements such as walls or panels shall satisfy the requirements of Sentence 4.1.8.3.(6).

(11) Seismic restraint for suspended equipment, pipes, ducts, electrical cable trays, etc. shall be designed to meet the force and displacement requirements of this Article and be constructed in a manner that will not subject hanger rods to bending.

(12) Isolated suspended equipment and components, such as pendant lights, may be designed as a pendulum system provided that adequate chains or cables capable of supporting 2.0 times the weight of the suspended component are provided and the deflection requirements of Sentence (11) are satisfied.

(13) Free-standing steel pallet storage racks are permitted to be designed to resist earthquake effects using rational analysis, provided the design achieves the minimum performance level required by this Subsection.

(14) Except as provided in Sentence (15), the relative displacement of glass in glazing systems, Dfallout , shall be equal to the greater of,

(a) 13 mm, or

(b) Dfallout ≥ 1.25IEDp ,

where,

Dfallout = relative displacement at which glass fallout occurs, and

Dp = relative earthquake displacement that the component must be designed to accommodate, calculated in accordance with Article 4.1.8.13. and applied over the height of the glass component.

(15) Glass need not comply with Sentence (14), provided at least one of the following conditions is met:

(a) IEFaSa(0.2) < 0.35,

(b) the glass has sufficient clearance from its frame such that Dclear ≥ 1.25 Dp calculated as follows:

Dclear= 2C1(1 +hpC2/(bpC1))

where,

Dclear = relative horizontal displacement measured over the height of the glass panel, which causes initial glass-to-frame contact,

C1= average of the clearances on both sides between the vertical glass edges and the frame,

hp = height of the rectangular glass panel,

C2= average of the top and bottom clearances between the horizontal glass edges and the frame, and

bp = width of the rectangular glass panel,

(c) the glass is fully tempered, monolithic, installed in a building that is not a post-disaster building, and no part of the glass is located more than 3 m above a walking surface, or

(d) the glass is annealed or heat-strengthened laminated glass in a single thickness with an interlayer no less than 0.76 mm and captured mechanically in a wall system glazing pocket with the perimeter secured to the frame by a wet, glazed, gunable, curing, elastomeric sealant perimeter bead of 13 mm minimum glass contact width.

(16) For a structure with supplemental energy dissipation, the following criteria shall apply:

(a) the value of Sa(0.2) used in Sentence (1) shall be determined from the mean 5% damped floor spectral acceleration values at 0.2 s by averaging the individual 5% damped floor spectra at the base of the structure determined using Non-Linear Dynamic Analysis, and

(b) the value of Fa used in Sentence (1) shall be 1.

Table 4.1.8.18. Elements of Structures and Non-structural Components and Equipment

**Forming Part of Sentences 4.1.8.18.(1), (2), (3), (6) and (7)**

(1) See Sentence 4.1.8.18.(8).

(2) See also ASME A17.1 / CSA B44, "Safety Code for Elevators and Escalators".

(3) See Sentence 4.1.8.18.(13).

(1) For the purposes of this Article and Article 4.1.8.20., the following terms shall have the meaning stated herein:

(a) "seismic isolation" is an alternative seismic design concept that consists of installing an isolation system with low horizontal stiffness, thereby substantially increasing the fundamental period of the structure,

(b) "isolation system" is a collection of structural elements at the level of the isolation interface that includes all individual isolator units, all structural elements that transfer force between elements of the isolation system, all connections to other structural elements, and may also include a wind-restraint system, energy-dissipation devices, and a displacement restraint system,

(c) "seismically isolated structure" includes the upper portion of the structure above the isolation system, the isolation system, and the portion of the structure below the isolation system,

(d) "isolator unit" is a structural element of the isolation system that permits large lateral deformations under lateral earthquake design forces and is characterized by vertical-load-carrying capability combined with increased horizontal flexibility and high vertical stiffness, energy dissipation (hysteretic or viscous), self-centering capability, and lateral restraint (sufficient elastic stiffness) under non-seismic service lateral loads,

(e) "isolation interface" is the boundary between the isolated upper portion of the structure above the isolation system and the lower portion of the structure below the isolation system, and

(f) "wind-restraint system" is the collection of structural elements of the isolation system that provides restraint of the seismically isolated structure for wind loads and is permitted to be either an integral part of the isolator units or a separate device.

(2) Every seismically isolated structure and every portion thereof shall be analyzed and designed in accordance with,

(a) the loads and requirements prescribed in this Article and Article 4.1.8.20.,

(b) other applicable requirements of this Subsection, and

(c) appropriate engineering principles and current engineering practice.

(3) For the analysis and modeling of the seismically isolated structure, the following criteria shall apply:

(a) three dimensional Non-linear Dynamic Analysis of the structure shall be performed in accordance with Article 4.1.8.12,

(b) unless verified from rational analysis, the inherent equivalent viscous damping - excluding the hysteretic damping provided by the isolation system or supplemental energy dissipation devices - used in the analysis shall not be taken as more than 2.5% of the critical damping at the significant modes of vibration,

(c) all individual isolator units shall be modeled with sufficient detail to account for their non-linear force-deformation characteristics, including effects of the relevant loads, and with consideration of variations in material properties over the design life of the structure, and

(d) except for elements of the isolation system, other components of the seismically isolated structure shall be modeled using elastic material properties in accordance with Sentence 4.1.8.3.(8).

(4) The ground motion histories used in Sentence (3) shall be,

(a) appropriately selected and scaled following good engineering practice,

(b) compatible with,

(i) a response spectrum derived from the design spectral acceleration values, S(T), defined in Sentence 4.1.8.4.(9) for ground conditions of Site Classes A, B and C, and

(ii) a 5% damped response spectrum based on a site-specific evaluation for ground conditions of Site Classes D, E and F, and

(c) amplitude-scaled in an appropriate manner over the period range of 0.2 T1 to 1.5 T1, where T1 is the period of the isolated structure determined using the post-yield stiffness of the isolation system in the horizontal direction under consideration, or the period specified in Sentence 4.1.8.20.(1) if the post-yield stiffness of the isolation system is not well defined.

(1) The period of the isolated structure, determined using the post-yield stiffness of the isolation system in the horizontal direction under consideration, shall be greater than three times the period of the structure above the isolation interface calculated as a fixed base.

(2) The isolation system shall be configured to produce a restoring force such that the lateral force at the TDD at the centre of mass of the isolated structure above the isolation interface is at least 0.025Wb greater than the lateral force at 50% of the TDD at the same location, in each horizontal direction, where Wb is the portion of W above the isolation interface.

(3) The values of storey shears, storey forces, member forces, and deflections used in the design of all structural framing elements and components of the isolation system shall be obtained from analysis conforming to Sentence 4.1.8.19.(3) using one of the following values, whichever produces the most critical effect:

(a) mean plus IE times the standard deviation of the results of all Non-linear Dynamic Analyses, or

(b) times the mean of the results of all Non-linear Dynamic Analyses.

(4) The force-deformation and damping characteristics of the isolation system used in the analysis and design of the seismically isolated structures shall be validated by testing at least two full-size specimens of each predominant type and size of isolator unit of the isolation system, which shall include,

(a) the individual isolator units,

(b) separate supplemental damping devices, if used, and

(c) separate sacrificial wind-restraint systems, if used.

(5) The force-deformation characteristics and damping value of a representative sample of the isolator units installed in the building shall be validated by tests prior to their installation.

(6) A diaphragm or horizontal structural elements shall provide continuity immediately above the isolation interface to transmit forces due to non-uniform ground motions from one part of the structure to another.

(7) All structural framing elements shall be designed for the forces described in Sentence (3) with RdRo= 1.0, except,

(a) for structures with IE < 1.5, all the SFRS shall be detailed in accordance with the requirements for Rd ≥ 1.5 and the applicable referenced design standards, and

(b) for structures with IE = 1.5, all the SFRS shall be detailed in accordance with the requirements for Rd ≥ 2.0 and the applicable referenced design standards.

(8) The height restrictions noted in Table 4.1.8.9. need not apply to seismically isolated structures.

(9) All isolator units shall be,

(a) designed for the forces described in Sentence (3), and

(b) able to accommodate the TDD determined at the specific location of each isolator unit.

(10) The isolation system, including a separate wind-restraint system if used, shall limit lateral displacement due to wind loads across the isolation interface to a value equal to that required for the least storey height in accordance with Sentence 4.1.3.5.(3).

(1) For the purposes of this Article and Article 4.1.8.22., the following terms shall have the meaning stated herein:

(a) "supplemental energy dissipation device" is a dedicated structural element of the supplemental energy dissipation system that dissipates energy due to relative motion of each of its ends or by alternative means, and includes all pins, bolts, gusset plates, brace extensions and other components required to connect it to the other elements of the structure; a device may be classified as either displacement-dependent or velocity-dependent, or a combination thereof, and may be configured to act in either a linear or non-linear manner, and

(b) "supplemental energy dissipation system" is a collection of energy dissipation devices installed in a structure that supplement the energy dissipation of the SFRS.

(2) Every structure with a supplemental energy dissipation system and every portion thereof shall be designed and constructed in accordance with,

(a) the loads and requirements prescribed in this Article and Article 4.1.8.22.,

(b) other applicable requirements of this Subsection, and

(c) appropriate engineering principles and current engineering practice.

(3) Where supplemental energy dissipation devices are used across the isolation interface of a seismically isolated structure, displacements, velocities, and accelerations shall be determined in accordance with Article 4.1.8.20.

(4) For the analysis and modeling of structures with supplemental energy dissipation devices, the following criteria shall apply:

(a) a three-dimensional Non-linear Dynamic Analysis of the structure shall be performed in accordance with Article 4.1.8.12.,

(b) for SFRS with Rd > 1.0, the non-linear hysteretic behaviour of the SFRS shall be explicitly - with sufficient detail - accounted for in the modeling and analysis of the structure,

(c) unless verified from rational analysis, the inherent equivalent viscous damping - excluding the damping provided by the supplemental energy dissipation devices - used in the analysis shall not be taken as more than 2.5% of the critical damping at the significant modes of vibration,

(d) all supplemental energy dissipation devices shall be modeled with sufficient detail to account for their non-linear force deformation characteristics, including effects of the relevant loads, and with consideration of variations in their properties over the design life of the structure, and

(e) except for the SFRS and elements of the supplemental energy dissipation system, other components of the structure shall be modeled using elastic material properties in accordance with Sentence 4.1.8.3.(8).

(5) The ground motion histories used in Sentence (4) shall be,

(a) appropriately selected and scaled following good engineering practice,

(b) compatible with a 5% damped response spectrum derived from the design spectral acceleration values, S(T), defined in Sentence 4.1.8.4.(9), and

(c) amplitude-scaled in an appropriate manner over the period range of 0.2 T1 to 1.5 T1, where T1 is the fundamental lateral period of the structure with the supplemental energy dissipation system.

(1) The values of storey shears, storey forces, member forces, and deflections for the design of all structural framing elements and all supplemental energy dissipation devices shall be obtained from analysis conforming to Sentence 4.1.8.21.(4) using one of the following values, whichever produces the most critical effect:

(a) mean plus IE times the standard deviation of the results of all Non-linear Dynamic Analyses, or

(b) times the mean of the results of all Non-linear Dynamic Analyses.

(2) The largest interstorey deflection at any level of the structure as determined in accordance with Sentence (1) shall conform to the limits stated in Sentence 4.1.8.13.(3).

(3) The force-deformation and force-velocity characteristics of the supplemental energy dissipation devices used in the analysis and design of structures with supplemental energy dissipation systems shall be validated by testing at least two full-size specimens of each type of supplemental energy dissipation device.

(4) The force-deformation and force-velocity characteristics and damping values of a representative sample of the supplemental energy dissipation devices installed in the building shall be validated by tests prior to their installation.

(5) Elements of the supplemental energy dissipation system, except the supplemental energy dissipation devices themselves, shall be designed to remain elastic for the design loads.

(6) All structural framing elements shall be designed,

(a) for an SFRS with Rd =1.0, using the forces referred to in Sentence (1) with RdRo = 1.0, except that the SFRS shall be detailed in accordance with the requirements for Rd ≥ 1.5 and the applicable referenced design standards, or

(b) for an SFRS with Rd > 1.0, using the forces referred to in Sentence (1) with RdRo = 1.0, except that the SFRS shall be detailed in accordance with the requirements for the selected Rd and the applicable referenced design standards.

(7) Supplemental energy dissipation devices and other components of the supplemental energy dissipation system shall be designed in accordance with Sentence (1) with consideration of the following:

(a) low-cycle, large-displacement degradation due to seismic loads,

(b) high-cycle, small-displacement degradation due to wind, thermal, or other cyclic loads,

(c) forces or displacements due to gravity loads,

(d) adhesion of device parts due to corrosion or abrasion, biodegradation, moisture, or chemical exposure,

(e) exposure to environmental conditions, including, but not limited to, temperature, humidity, moisture, radiation (e.g., ultraviolet light), and reactive or corrosive substances (e.g., salt water),

(f) devices subject to failure due to low-cycle fatigue must resist wind forces without slip, movement, or inelastic cycling,

(g) the range of thermal conditions, device wear, manufacturing tolerances, and other effects that cause device properties to vary during the design life of the device, and

(h) connection points of devices must provide sufficient articulation to accommodate simultaneous longitudinal, lateral, and vertical displacements of the supplemental energy dissipation system.

(8) Means of access for inspection and removal for replacement of all supplemental energy dissipation devices shall be provided.

(1) This Section applies to excavations and foundation systems for buildings.

(1) A subsurface investigation, including groundwater conditions, shall be carried out, by or under the direction of a person having knowledge and experience in planning and executing such investigations to a degree appropriate for the building and its use, the ground and the surrounding site conditions.

(1) A field review shall be carried out by the designer or by another suitably qualified person to ascertain that the subsurface conditions are consistent with the design and that construction is carried out in accordance with the design and good engineering practice.

(2) The review required in Sentence (1) shall be carried out,

(a) on a continuous basis,

(i) during the construction of all deep foundation units with all pertinent information recorded for each foundation unit,

(ii) during the installation and removal of retaining structures and related backfilling operations, and

(iii) during the placement of engineered fills that are to be used to support the foundation units, and

(b) as required, unless otherwise directed by the chief building official,

(i) in the construction of all shallow foundation units, and

(ii) in excavating, dewatering and other related works.

(1) If during construction, the soil, rock or groundwater is found not to be of the type or in the condition used in design, and as indicated on the drawings, the design shall be reassessed by the designer.

(2) If during construction, climatic or any other conditions have changed the properties of the soil, rock or groundwater, the design shall be reassessed by the designer.

(1) Wood used in foundations or in support of soil or rock shall conform to the appropriate requirements of Subsection 4.3.1.

(1) Wood exposed to soil or air above the lowest anticipated groundwater table shall be treated with preservative in conformance with CAN/CSA-O80 Series, "Wood Preservation", and the requirements of the appropriate commodity standard as follows:

(a) CAN/CSA-O80.2, "Processing and Treatment",

(b) CAN/CSA-O80.3, "Preservative Formulations", or

(c) CSA O80.15, "Preservative Treatment of Wood for Building Foundation Systems, Basements, and Crawl Spaces by Pressure Processes".

(1) Plain or reinforced masonry used in foundations or in support of soil or rock shall conform to the requirements of Subsection 4.3.2.

(1) Where plain or reinforced masonry in foundations or in structures supporting soil or rock may be subject to conditions conducive to deterioration, protection shall be provided to prevent such deterioration.

(1) Plain, reinforced or prestressed concrete used in foundations or in support of soil or rock shall conform to the requirements of Subsection 4.3.3.

(1) Where concrete in foundations may be subject to chemical attack, it shall be treated in conformance with the requirements in CSA A23.1, "Concrete Materials and Methods of Concrete Construction".

(1) Steel used in foundations or in support of soil or rock shall conform with the appropriate requirements of Subsections 4.3.3. or 4.3.4., unless otherwise specified in this Section.

(1) Where steel piles are used in deep foundations and act as permanent load-carrying members, the steel shall conform with one of the following standards:

(a) ASTM A252, "Welded and Seamless Steel Pipe Piles",

(b) ASTM A283 / A283M, "Low and Intermediate Tensile Strength Carbon Steel Plates",

(c) ASTM A1008 / A1008M , "Steel, Sheet, Cold-Rolled, Carbon, Structural, High-Strength Low-Alloy, and High-Strength Low-Alloy with Improved Formability, Solution Hardened, and Bake Hardenable",

(d) ASTM A1011 / A1011M, "Steel, Sheet and Strip, Hot-Rolled, Carbon, Structural, High-Strength Low-Alloy, High-Strength Low-Alloy with Improved Formability, and Ultra-High Strength", or

(e) CSA G40.21, "Structural Quality Steel".

(1) Where high strength steel is used for tendons in anchor systems used for the permanent support of a foundation or in the erection of temporary support of soil or rock adjacent to an excavation, it shall conform with the requirements of CSA A23.1, "Concrete Materials and Methods of Concrete Construction".

(1) Where conditions are corrosive to steel, adequate protection of exposed steel shall be provided.

(1) The design of foundations, excavations and soil- and rock-retaining structures shall be based on a subsurface investigation carried out by a person competent in this field of work, and on any of the following:

(a) application of generally accepted geotechnical and civil engineering principles by a person especially qualified in this field of work as provided in this Section and other Sections of this Part,

(b) established local practice where such practice includes successful experience both with soils and rocks of similar type and condition and with a foundation or excavation of similar type, construction method, size and depth, or

(c) in situ testing of foundation units such as the load testing of piles, anchors or footings carried out by a person competent in this field of work.

(2) The foundations of a building shall be capable of resisting all the loads stipulated in Section 4.1., in accordance with limit states design in Subsection 4.1.3.

(3) For the purpose of the application of the load combinations given in Table 4.1.3.2.A., the geotechnical components of loads and the factored geotechnical resistances at ULS shall be determined by a suitably qualified and experienced person.

(4) Geotechnical components of service loads and geotechnical reactions for SLS shall be determined by a suitably qualified and experienced person.

(5) The foundation of a building shall be designed to satisfy SLS requirements within the limits that the building is designed to accommodate, including total settlement and differential settlement, heave, lateral movement, tilt or rotation.

(6) Communication, interaction and coordination between the designer and the person responsible for the geotechnical aspects of the project shall take place to a degree commensurate with the complexity and requirements of the project.

(1) A subsurface investigation shall be carried out to the depth and extent to which the building or excavation will significantly change the stress in the soil or rock, or to such a depth and extent as to provide all the necessary information for the design and construction of the excavation or the foundations.

(1) The identification and classification of soil, rock and groundwater and descriptions of their engineering and physical properties shall be in accordance with a widely accepted system.

(1) Except as permitted in Sentence (2), the bearing surface of a foundation shall be below the level of potential damage, including damage resulting from frost action, and the foundation shall be designed to prevent damage resulting from adfreezing and frost jacking.

(2) The bearing surface of a foundation need not be below the level of potential damage from frost where the foundation,

(a) is designed against frost action, or

(b) overlies material not susceptible to frost action.

(1) Where a foundation is to rest on, in or near sloping ground, this particular condition shall be provided for in the design.

(1) Where there is eccentricity or inclination of loading in foundation units, this effect shall be fully investigated and provided for in the design.

(1) Where dynamic loading conditions apply, the effects shall be assessed by a special investigation of these conditions and provided for in the design.

(1) Where a foundation or any part of a building is subject to hydrostatic uplift the effects shall be provided for in the design.

(1) Where proposed construction will result in a temporary or permanent change in the groundwater level, the effects of this change on adjacent buildings shall be fully investigated and provided for in the design.

(1) Where conditions of permafrost are encountered or proven to exist, the design of the foundation shall be based upon analysis of these conditions by a person especially qualified in that field of work.

(1) Where swelling or shrinking soils, in which movements resulting from moisture content changes may be sufficient to cause damage to a structure, are encountered or known to exist, such a condition shall be fully investigated and provided for in the design.

(1) Where rock that expands or deteriorates when subjected to unfavourable environmental conditions or to stress release is known to exist, this condition shall be fully investigated and provided for in the design.

(1) Buildings may be placed on fill if it can be shown by subsurface investigation that,

(a) the fill is or can be made capable of safely supporting the building,

(b) detrimental movement of the building or services leading to the building will not occur, and

(c) explosive gases can be controlled or do not exist.

(1) The structural design of the foundation of a building, the procedures and construction practices shall conform with the appropriate Sections of this Code unless otherwise specified in this Section.

(1) The design of excavations and of supports for the sides of excavations shall conform to the requirements of Subsection 4.2.4. and this Subsection.

(1) Every excavation shall be undertaken in such a manner as to prevent movement that would cause damage to adjacent buildings at all phases of construction.

(2) Material shall not be placed nor shall equipment be operated or placed in or adjacent to an excavation in a manner that may endanger the integrity of the excavation or its supports.

(1) The sides of an excavation in soil or rock shall be supported by a retaining structure conforming with the requirements of Articles 4.2.5.1. and 4.2.5.2., except as permitted in Article 4.2.5.4.

(1) The sides of an excavation in soil or rock may be unsupported where a design is prepared by a person especially qualified in this field of work in conformance with the requirements of Articles 4.2.5.1. and 4.2.5.2.

(1) Surface water, all groundwater, perched groundwater and in particular artesian groundwater shall be kept under control at all phases of excavation and construction.

(1) At all phases of excavation and construction, loss of ground due to water or any other cause shall be prevented.

(1) All sides of an excavation, supported and unsupported, shall be continuously maintained and protected from possible deterioration by construction activity or by the action of frost, rain and wind.

(1) Where an excavation is backfilled, the backfill shall be placed so as to,

(a) provide lateral support to the soil adjacent to the excavation, and

(b) prevent detrimental movements.

(2) The material used as backfill or fill supporting a footing, foundation or a floor on grade shall be of a type that is not subject to detrimental volume change with changes in moisture content and temperature.

(1) The design of shallow foundations shall be in conformance with the requirements of Subsection 4.2.4. and this Subsection.

(1) Where a shallow foundation is to be placed on soil or rock, the soil or rock shall be cleaned of loose and unsound material and shall be adequate to support the design load taking into account temperature, precipitation, construction activities and other factors that may lead to changes of the properties of soil or rock.

(1) Where a shallow foundation unit has not been placed or located as indicated on the drawings,

(a) the error shall be corrected, or

(b) the design of the foundation unit shall be recalculated for the altered conditions by the designer.

(1) Where a shallow foundation unit is damaged,

(a) it shall be repaired, or

(b) the design of the foundation unit shall be recalculated for the damaged condition by the designer.

(1) A deep foundation unit shall provide support for a building by transferring loads by end-bearing to a competent stratum at considerable depth below the structure, or by mobilizing resistance by adhesion or friction, or both, in the soil or rock in which it is placed.

(1) Deep foundation units shall be designed in conformance with Subsection 4.2.4. and this Subsection.

(2) Where deep foundation units are load tested, as required in Clause 4.2.4.1.(1)(c), the determination of the number and type of load test and the interpretation of the results shall be carried out by a person especially qualified in this field of work.

(3) The design of deep foundations shall be determined on the basis of geotechnical considerations taking into account,

(a) the method of installation,

(b) the degree of inspection,

(c) the spacing of foundation units and group effects,

(d) other requirements of this Subsection, and

(e) the appropriate structural requirements of Section 4.1. and Subsections 4.3.1., 4.3.3. and 4.3.4.

(4) The portion of a deep foundation unit permanently in contact with soil or rock shall be structurally designed as a laterally supported compression member.

(5) The portion of a deep foundation unit that is not permanently in contact with soil or rock shall be structurally designed as a laterally unsupported compression member.

(6) The structural design of prefabricated deep foundation units shall allow for all stresses resulting from driving, handling and testing.

(1) Permissible deviations from the design alignment and the location of the top of deep foundation units shall be determined by design analysis and shall be indicated on the drawings.

(1) Where a deep foundation unit has not been placed within the permissible deviations referred to in Article 4.2.7.3., the condition of the foundation shall be assessed by the designer.

(1) Deep foundation units shall be installed in such a manner as not to impair,

(a) the strength of the deep foundation units and the properties of the soil or rock on or in which they are placed beyond the calculated or anticipated limits,

(b) the integrity of previously installed deep foundation units, or

(c) the integrity of neighbouring buildings.

(1) Where inspection shows that a deep foundation unit is damaged or not consistent with design or good engineering practice,

(a) such a unit shall be reassessed by the designer, and

(b) any necessary changes shall be made and action taken as required.

(1) Where special foundation systems are used, such systems shall conform to Subsection 4.2.4. and Sentence 4.1.1.4.(2).

(1) Existing foundations may be used to support new or altered buildings provided they comply with all pertinent requirements of this Section.

(1) Buildings and their structural members made of wood shall conform to CSA O86, "Engineering Design in Wood".

(1) Glued-laminated members shall be fabricated in plants conforming to CSA O177, "Qualification Code for Manufacturers of Structural Glued-Laminated Timber".

(1) In areas known to be infested by termites, the requirements in Articles 9.3.2.9., 9.12.1.1. and 9.15.5.1. shall apply.

(1) Buildings and their structural members made of plain and reinforced masonry shall conform to CSA S304, "Design of Masonry Structures".

(1) Buildings and their structural members made of plain, reinforced or prestressed concrete shall conform to CSA A23.3, "Design of Concrete Structures".

(1) Buildings and their structural members made of structural steel shall conform to CSA S16, "Design of Steel Structures".

(1) Buildings and their structural members made of cold formed steel shall conform to CSA S136, "North American Specification for the Design of Cold-Formed Steel Structural Members".

(1) Steel building systems shall be manufactured by companies certified in accordance with the requirements of CSA A660, "Certification of Manufacturers of Steel Building Systems".

(1) Buildings and their structural members made of aluminum shall conform to CAN/CSA-S157 / S157.1, "Strength Design in Aluminum/Commentary on CSA S157-05, Strength Design in Aluminum", using the loads stipulated in Section 4.1., in accordance with limit states design in Subsection 4.1.3.

(1) Glass used in buildings shall be designed in conformance with,

(a) CAN/CGSB-12.20-M, "Structural Design of Glass for Buildings", using an adjustment factor on the wind load, W, of not less than 0.75, or

(b) ASTM E1300, "Determining Load Resistance of Glass in Buildings", using an adjustment factor on the wind load, W, of not less than 1.0.

(1) The structural design of air-supported structures shall conform to CSA S367, "Air-, Cable-, and Frame-Supported Membrane Structures" using the loads stipulated in Section 4.1., in accordance with limit states design in Subsection 4.1.3.

(1) Storage garages and repair garages shall be designed in conformance with CSA S413, "Parking Structures".

(1) Every retaining wall that is designated in Sentence 1.3.1.1.(1) of Division A shall be protected by guards on all open sides where the public has access to open space at the top of the retaining wall.

(1) Where suspended maintenance and window cleaning operations are intended to be carried out on the exterior of a building described in Article 1.1.2.2. of Division A, anchor systems shall be provided where any portion of the roof is more than 8 m above adjacent ground level.

(2) Except as provided in Sentence (3), the anchor systems in Sentence (1) shall be designed, installed and tested in conformance with CAN/CSA-Z91, "Health and Safety Code for Suspended Equipment Operations".

(3) Other anchor systems may be used where such systems provide an equal level of safety.

(4) The anchor system material shall be made of stainless steel, or other corrosion resistant base material, or from steel that is hot dipped galvanized, in accordance with CAN/CSA-G164-M, "Hot Dip Galvanizing of Irregularly Shaped Articles".

(1) Liquid manure storage tanks shall be constructed of steel, reinforced concrete or prestressed concrete.

(2) Liquid manure storage tank walls, bases and appurtenances, including piping for the conveyance of liquid manure and associated connections and joints, shall be designed and constructed to prevent leakage of contents.

(3) Concrete for liquid manure storage tanks shall,

(a) be made from HS or HSb cement,

(b) have a 28-day strength of at least 32 MPa, and

(c) have a water/cement materials ratio of not more than 0.45.

(4) Liquid manure storage tanks shall be placed on undisturbed soil free of any organic, deleterious and extraneous materials and capable of supporting the superimposed design loads from the tanks.

(5) Where granular fills are used between the bases of liquid manure storage tanks and the undisturbed soil, the granular fills shall be compacted to a Standard Proctor density of not less than 95%.