Structural Loads and Procedures

(1)The scope of this Part shall be as described in Subsection 1.3.3. of Division A.

(1)Words that appear in italics in this Part are defined in Article 1.4.1.2. 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., 4.1.3.5. and 4.1.3.6.

(3)All permanent and temporary structural members, including the 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)Reserved.

(5)Precautions shall be taken during all phases 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 following categories of loads, specified loads and effects shall be taken into consideration in the design of a building and its structural members and connections: D dead load – a permanent load due to the weight of building components, as specified in Subsection 4.1.4., E earthquake load and effects – a rare load due to an earthquake, as specified in Subsection 4.1.8., H a permanent load due to lateral earth pressure, including groundwater, L live load – a variable load due to intended use and occupancy (including loads due to cranes and the pressure of liquids in containers), as specified in Subsection 4.1.5., LXC live load exclusive of crane loads, C live load due to cranes including self weight, Cd self weight of all cranes positioned for maximum effects, C7 crane bumper impact load, P permanent effects caused by pre-stress, S variable load due to snow, including ice and associated rain, as specified in Article 4.1.6.2., or due to rain, as specified in Article 4.1.6.4., T effects due to contraction, expansion, or deflection caused by temperature changes, shrinkage, moisture changes, creep, ground settlement, or a combination thereof, and W wind load – a variable load due to wind, as specified in Subsection 4.1.7., where

• (a) 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,
• (b) permanent load is a load that changes very little once it has been applied to the structure, except during repair,
• (c) variable load is a load that frequently changes in magnitude, direction or location, and
• (d) 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., 4.1.7. and 4.1.8., buildings shall be assigned an Importance Category based on intended use and occupancy, in accordance with Table 4.1.2.1.

(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 Subsection, 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) means those loads defined in Article 4.1.2.1.,
• (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., 4.1.7. and 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.(2), the counteracting factored dead load—0.9D in load combination cases 2, 3 and 4 and 1.0D in load combination case 5 in Table 4.1.3.2.-A, and 0.9D in load combination cases 1 to 5 and 1.0D in load combination case 6 in 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 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 m, 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 cases 5 of Table 4.1.3.2.-A and 6 of Table 4.1.3.2.-B includes horizontal earth pressure due to earthquake determined in accordance with Sentence 4.1.8.16.(7).

(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.

(1)A building and its structural components, including connections, shall be checked for fatigue failure under the effect of 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.

(2)The effect of service loads on the serviceability limit states shall be determined in accordance with this Article and the load combinations listed in Table 4.1.3.4., the applicable combination being that which results in the most critical effect.

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

(4)Deflections calculated for load types P, T and H, if present, with load factors of 1.0 shall be included with the calculated deflections due to principal loads.

(5)The determination of the deflection shall consider the following:

• (a) for materials that result in increased deformations over time under sustained loads, the deflection calculation shall consider the portion of live load, L, that is sustained over time, Ls, and the portion that is transitory, Lt, and
• (b) the calculated deflection due to dead load, D, and sustained live load, Ls, shall be increased by a creep factor as specified in the standards listed in Section 4.3. to obtain the additional long-term deflection.

(6)The determination of the long-term settlement of foundations shall consider the following:

• (a) for foundation soil types that result in increased settlement over time under sustained loads, the additional long-term settlements shall be determined for the portion of live load, L, that is sustained over time, Ls, and the portion that is transitory, Lt, and
• (b) the additional long-term settlements due to dead load, D, and sustained live loads, Ls, shall be calculated from the foundation soil properties provided by a qualified professional geotechnical engineer.

(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 floor vibrations caused by resonance with operating machinery or equipment are anticipated, dynamic analysis of the floor system shall be carried out.

(3)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.

(4)A building susceptible to lateral vibration under wind load shall be designed in accordance with Article 4.1.7.1. 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 soil, superimposed earth, plants and trees.

(2)In areas of a building for which partitions are shown on the drawings, the weight of partitions referred to in Clause (1)(c) shall be taken as the actual weight of such partitions.

(3)In areas of a building for which partitions are not shown on the drawings, the weight of partitions referred to in Clause (1)(c) shall be a partition weight allowance determined from the anticipated weight and position of the partitions, but shall not be less than 1 kPa over the area of floor being considered.

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

(5)Where the partition weight allowance referred to in Sentence (3) is counteractive to other loads, it 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 to other loads, 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 either the uniformly distributed load patterns listed in Article 4.1.5.3., the loads due to the intended use and occupancy, or the concentrated loads listed in Article 4.1.5.9., whichever produces the most critical effect.

(2)For buildings in the Low Importance Category as described in Table 4.1.2.1., 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., 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.

(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 either 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 effect.

(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 and exterior areas accessible to vehicular traffic shall be designed

• (a) for the appropriate load combination listed in Sentence 4.1.3.2.(2) with a live load, L, consisting of either a uniformly distributed live load as specified in Table 4.1.5.3. or a concentrated live load as listed in Table 4.1.5.9., whichever produces the most critical effect, and a companion snow load, S, as prescribed in Subsection 4.1.6., but with the companion-load factor reduced to 0.2, and
• (b) such that the load combination in Clause (a) is not less than the snow and rain loads prescribed in Subsection 4.1.6. with the live load taken as zero.

(5)Roof parking decks that are used for the long-term storage of vehicles shall be designed for the appropriate load combination listed in Sentence 4.1.3.2.(2) with a live load, L, consisting of either a uniformly distributed live load as specified in Table 4.1.5.3. or a concentrated live load as listed in Table 4.1.5.9., whichever produces the most critical effect, and a snow load, S, as prescribed in Subsection 4.1.6.

(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)One- and two-way floor slabs shall have no reduction for tributary area applied to live load.

(2)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.

(3)Where a structural member supports a tributary area of a floor or a roof, or a combination thereof, 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 5.0 + A / where A is the tributary area in square metres for this type of use and occupancy.

(4)Where a structural member supports a tributary area of a floor or a roof, or a combination thereof, that is greater than 20 m2 and used for any use or occupancy other than those indicated in Sentences (2) and (3), the specified live load due to use and occupancy is the load specified in Article 4.1.5.3. multiplied by 3.0 + 9.8 / B where B is the tributary area in square metres for this type of use and occupancy.

(5)Where the specified live load for a floor is reduced in accordance with Sentence (3) or (4), the structural drawings shall indicate that a live load reduction factor for tributary area has been applied and which structural elements are impacted by this factor.

(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 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.

(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.

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

(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 0.75 m, 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 horizontal specified live 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) 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 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 horizontal specified live 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 horizontal specified live load of 0.5 kN applied outward over an area of 100 mm by 100 mm located at any point on 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 horizontal 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 specified live loads required in Sentence (3) need not be considered to act simultaneously with the loads provided for in Sentences (1), (2), (6) and (7).

(6)The minimum specified live 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 specified live load provided for in Sentences (1), (3) and (7).

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

• (a) 0.9 kN applied at any point and in any direction for all handrails, and
• (b) 0.7 kN/m applied in any direction for 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 required 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 Subsection 4.1.5. 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 1.1.3., Cb = basic roof snow load factor in Sentence (2), Cw = wind exposure factor in Sentences (3) and (4), Cs = slope factor in Sentences (5) to (7), Ca = accumulation factor in Sentence (8), and Sr = 1-in-50-year associated rain load, in kPa, determined in accordance with Subsection 1.1.3., but not greater than Ss(CbCwCsCa).

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

• (a) be determined as follows: (i) Cb = 0.8 for lc ≤ (Cw/2), and (ii) Cb = 1/Cw [1 −(1 −0.8Cw) exp (−lcCw/2 −70)] for lc > (70/Cw2) where lc = characteristic length of the upper or lower roof, defined as 2w-w²/l, in m, w = smaller plan dimension of the roof, in m, and l = larger plan dimension of the roof, in m, or
• (b) conform to Table 4.1.6.2.-B, using linear interpolation for intermediate values of lc Cw2.
• (c) be taken as equal to 1 for any roof structure with a mean height of less than 1 + Ss/γ, in m, above grade, where γ is the specific weight of snow determined in accordance with Article 4.1.6.13.

(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., the wind exposure factor, Cw, given in Sentence (3) may be reduced to 0.75 for rural areas only, or to 0.5 for exposed areas north of the treeline, where

• (a) the building is exposed on all sides to wind over open terrain as defined in Clause 4.1.7.3.(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 in m, 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 where the roof slope, α, is equal to or less than 15°,
• (b) (60° − α)/45° where α is greater than 15° but not greater than 60°, and
• (c) 0 where α exceeds 60°.

(7)Unless otherwise stated 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 gable, arch or curved roofs and domes, as prescribed in Articles 4.1.6.9. and 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 given in Sentence 4.1.6.2.(1), distributed over the entire loaded area.

(2)In addition to the distribution mentioned in Sentence (1), flat roofs and shed roofs, gable roofs of 15° slope or less, and arch 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 the accumulation factor 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 1.1.3. 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 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 as secondary drainage systems 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 1.1.3. or a depth of rainwater equal to 30 mm above the bottom 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, and the accumulation factor, Ca, shall be determined as follows: 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: xd = 5 CbSs/γ (Ca0 −1) where γ = specific weight of snow as specified in Article 4.1.6.13.

(3)Except as provided in Sentence (4), the value of Ca0 for each of Cases I, II and III shall be the lesser of Ca0 = β γh/CbSs and Ca0 = F/Cb 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 F = 0.35β√γ(lcs −5hp′)/Ss + Cb, but F ≤5 for Cws = 1.0 where Cws = value for Cw applicable to the source of drifting, lcs = characteristic length of the source area for drifting, defined as, lcs = 2ws − ws2/ls, 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 hp′ = hp −(0.8Ss/γ), but 0 ≤ hp′ ≤(lcs/5) 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)Where h ≥ 5 m, the value of Ca0 for Case I is permitted to be taken as Ca0 = (25 − h)(F/Cb −1) + 1 for 5 m ≤h ≤25 m, and Ca0 = 1 for h > 25 m

(5)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 Sentences (3) and (4) and Figure 4.1.6.5.-B.

(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 for the lower roof can be ignored, 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, 0.67 γh/CbSs and γl0/7.5CbSs + 1, and
• (b) xd shall be taken as the lesser of 3.35h and (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 the higher of the two loads shall be applied where the drifts overlap as shown in Figure 4.1.6.8.-B.

(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 β > 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 + β/20, where 15° ≤ β ≤ 20°, and (ii) 1.25, where 20° < β ≤ 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 (See Figure 4.1.6.10.-A), the load cases provided in Sentences (3) to (7) shall also be considered.

(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.

(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 presented in Sentences (2) and (3) shall be considered to account for sliding, creeping and movement of meltwater.

(2)For Case II (See Figure 4.1.6.12.), the accumulation factor, Ca, shall be calculated as follows: Ca = 1/Cb for 0 < x ≤ b/4, and Ca = 0.5/Cb for b/4 < x ≤ b 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 in question.

(3)For Case III (See Figure 4.1.6.12.), Ca shall be calculated as follows: Ca = 1.5/Cb for 0 < x ≤ b/8, and Ca = 0.5/Cb for b/8 < x ≤ b where x, b = as specified in Sentence (2).

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

(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 CAN/CSA-S37, "Antennas, towers, and antenna-supporting structures."

(1)Where solar panels are installed on a roof, the snow loads, S, shall be determined in accordance with Sentences (2) to (6) or with the requirements for roofs without solar panels, whichever produces the most critical effect.

(2)For the purposes of this Article, solar panels shall be classified as

• (a) Parallel Flush, where the panels are installed parallel to the roof surface with their upper surface less than or equal to CbCwSs/γ above the roof surface,
• (b) Parallel Raised, where the panels are installed parallel to the roof surface with their upper surface greater than CbCwSs/γ above the roof surface, or
• (c) Tilted, where the panels are installed at an angle to the roof surface with their highest edge greater than CbCwSs/γ above the roof surface.

(3)For sloped roofs with solar panels, the snow loads, S, shall be determined in accordance with the requirements for roofs without solar panels, except that the slope factor, Cs, shall be

• (a) taken as 1.0 for roof areas extending upslope from the downslope edge of a panel or array of panels at an angle of 45° from each side edge of the panel or array, and
• (b) as specified in Sentences 4.1.6.2.(5) to (7) for all other roof areas.

(4)For sloped roofs with Parallel Flush solar panels, the snow loads, S, shall be determined in accordance with the requirements for roofs without solar panels, except that

• (a) Cs shall be determined in accordance with Sentence (3),
• (b) where the gap width, wg, between the panels along the roof slope is greater than or equal to the panel width, wp, along the roof slope, the accumulation factor, Ca, shall be taken as (i) 0.0 for the panels, (ii) 2.0 for roof areas within a distance of wp downslope from a downslope panel edge, and (iii) 1.0 for all other roof areas, and
• (c) where the gap width, wg, between the panels along the roof slope is less than the panel width, wp, along the roof slope, Ca shall be taken as (i) 0.0 for panel areas within a distance of wg downslope from an upslope panel edge, (ii) 1.0 for other panel areas, (iii) 2.0 for roof areas in gaps between the panels, and (iv) 1.0 for all other roof areas.

(5)For roofs with Parallel Raised solar panels, the snow loads, S, shall be determined in accordance with the requirements for roofs without solar panels, except that

• (a) where the roof is flat, Ca shall be taken as (i) 1.0 for the panels, (ii) 1.0 for roof areas not under the panels, (iii) 1.0 for roof areas under the panels within a distance of min (2hg,2wg) from a panel edge, where hg is the gap height between the lower surface of the panels and the roof surface, and wg is the gap width between the panels, and (iv) 0.0 for other roof areas under the panels, and
• (b) where the roof is sloped, the snow loads, S, derived from Clause (a) shall be used, except that (i) Cs shall be determined in accordance with Sentence (3), (ii) S shall be taken as 0.0 on the panels, and (iii) S for all roof areas shall be taken as the sum of S on the panels, as derived from Subclause (a)(i) and shifted by a distance of wp downslope onto the roof, where wp is the panel width along the roof slope, and S on the roof areas, as derived from Subclauses (a)(ii) to (a)(iv).

(6)For flat roofs with Tilted solar panels, the snow loads, S, shall be determined in accordance with the requirements for roofs without solar panels, except that

• (a) Ca shall be taken as 0.0 for the panels,
• (b) Ca shall be taken as 1.0 for roof areas beyond a distance of 5(h – CbCwSs/γ) from the lowest edge of the panels, where h is the height of the highest edge of the panels above the roof surface,
• (c) except as provided in Clauses (d) and (e), for roof areas within a distance of 5(h – CbCwSs/γ) from the lowest edge of the panels, Ca shall be taken as (i) 1.25 for (hg – CbCwSs/γ) ≤ 0.3 m, where hg is the gap height between the lowest edge of the panels and the roof surface, (ii) 1.294 – 0.1471(hg – CbCwSs/γ) for 0.3 < (hg – CbCwSs/γ) ≤ 2.0 m, and (iii) 1.0 for (hg – CbCwSs/γ) > 2.0 m,
• (d) except as provided in Clause (e), Ca shall be taken as 2.0 for roof areas within a distance of wph beyond the lowest edge of the panels, where wph is the horizontal projection of the panel width, wp, along the sloped panel edges, and
• (e) where the panels, panel supports or back plates obstruct snow from sliding under the panels, the load of the increased volume of snow in the gaps between the panels shall be considered to be uniformly distributed.

(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 the Seismic Category is SC1 and the forces used for design of the SFRS are multiplied by RdRo.

(2)Post-disaster buildings shall

• (a) not have Type 1, 3, 4, 5, 7, 9 or 10 irregularities as described in Table 4.1.8.6., where the Seismic Category is SC3 or SC4,
• (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,
• (d) where they are constructed with concrete or masonry shear walls, have no storey with a lateral stiffness that is less than that of the storey above it, and
• (e) where they are constructed with other types of SFRS, have no storey for which the interstorey deflection under lateral earthquake forces divided by the interstorey height, hs, is greater than that of the storey above it.

(3)High Importance Category buildings shall

• (a) not have Type 1, 3, 4, 5, 7, 9 or 10 irregularities as described in Table 4.1.8.6., where the Seismic Category is SC4,
• (b) not have a Type 6 irregularity as described in Table 4.1.8.6.,
• (c) have an SFRS with an Rd of at least (i) 2.0 where the Seismic Category is SC4, and (ii) 1.5 otherwise,
• (d) where they are constructed with concrete or masonry shear walls, have no storey with a lateral stiffness that is less than that of the storey above it, and
• (e) where they are constructed with other types of SFRS, have no storey for which the interstorey deflection under lateral earthquake forces divided by the interstorey height, hs, is greater than that of the storey above it.

(4)Where the fundamental lateral period, Ta, is greater than or equal to 1.0 s and IES(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 Type 4 or 5 irregularities as described in Table 4.1.8.6.

(5)For buildings in Seismic Category SC3 or SC4 that are constructed with more than 4 storeys of continuous wood construction, timber SFRSs consisting of shear walls with wood-based panels or of braced or moment-resisting frames as defined in Table 4.1.8.9. within the continuous wood construction shall not have Type 4 or 5 irregularities as described in Table 4.1.8.6.

(6)For buildings in Seismic Category SC3 or SC4 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, 9 or 10 irregularities as described in Table 4.1.8.6.

(7)The ratio α for a 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 earthquake loads, which need not be taken as less than Ro multiplied by the specified lateral earthquake force as determined in Article 4.1.8.11. or 4.1.8.12., as appropriate.

(8)For buildings with a Type 9 irregularity as described in Table 4.1.8.6. and where IES(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.

(9)For buildings where the value of α, as determined in accordance with Sentence (7), exceeds twice the appropriate limit specified in Table 4.1.8.6. for a Type 9 irregularity and where IES(0.2) is equal to or greater than 0.5, a Non-linear Dynamic Analysis of the structure shall be carried out in accordance with Article 4.1.8.12. and the following criteria:

• (a) the analysis shall account for the effects of the vertical response of the building mass,
• (b) the analysis shall account for the effects of the vertical response of building components that undergo a vertical displacement when displaced laterally,
• (c) the analysis shall use vertical ground motion time histories that are compatible with horizontal ground motion time histories scaled to the target response spectrum and that are applied concurrently with the horizontal ground motion time histories,
• (d) the largest interstorey deflection at any level of the building as determined from the analysis shall not be greater than 60% of the appropriate limit stated in Sentence 4.1.8.13.(3), and
• (e) the results of an analysis using the ground motion time histories in Clause (c) multiplied by 1.5 shall satisfy the non-linear acceptance criteria.

(10)The design of buildings in Seismic Category SC3 or SC4 with a Type 10 irregularity as described in Table 4.1.8.6. shall satisfy the following requirements:

• (a) the structure shall be designed to resist the additional earthquake forces due to the vertical accelerations of the mass supported by inclined vertical members, and
• (b) the effects of the horizontal and vertical movements of inclined vertical members, while undergoing earthquake-induced deformations, on the floor systems they support shall be considered in the design of the building and accounted for in the application of Sentence 4.1.8.3.(5).

(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 specified 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), and
• (c) for buildings located on a site designated as other than XF and having an SFRS with an Rd equal to or greater than 1.5, V need not be greater than the larger of (2/3) S (0.2) IEW / (RdRo), 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 lateral earthquake 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) 0.1N for other moment frames,
• (b) 0.025hn for braced frames,
• (c) 0.05(hn)3/4 for shear wall and other structures, 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 as greater than 1.5 times that determined in Clause (a), (ii) for braced frames, Ta shall not be taken as greater than 2.0 times that determined in Clause (b), (iii) for shear wall structures, Ta shall not be taken as greater than 2.0 times that determined in Clause (c), (iv) for other structures, Ta shall not be taken as 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 (d)(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 + 0.004L for shear walls,
• (b) 0.035hn + 0.004L 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,

(5)The weight, W, of the building shall be calculated using the following formula: W = Σ(Wi)

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

(7)The specified lateral earthquake force, V, shall be distributed such that

• (a) a portion, Ft, is concentrated at the top of the building, where Ft is equal to 0.07TaV but need not exceed 0.25V and may be considered as zero where the fundamental lateral period, Ta, does not exceed 0.7 s, and
• (b) the remainder, V − Ft, is distributed along the height of the building, including the top level, in accordance with the following formula: Fx = (V – Ft) Wxhx / Σ(Wihi)

(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 following equation: Mx = J Σ(Fi(hi – hx)) 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 determined 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 forces determined in Sentence (7) 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 forces determined in Sentence (7).

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

• (a) for a building with B ≤ 1.7 or in Seismic Category SC1 or SC2, 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 determined in accordance with Sentence (7) 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 Seismic Category SC3 or SC4, 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 or of braced or moment-resisting frames as defined in Table 4.1.8.9., the specified lateral earthquake force, V, as determined in 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.(6).

(3)The ground motion time 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.(6).

(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 (±0.10Dnx)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 −0.05Dnx and +0.05Dnx.

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

(6)For structures located on a site designated as other than XF 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: (2/3)S (0.2) S(Ta) ≤1.0/ and S (0.5) S(Ta) ≤1/

(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 0.8V.

(9)For irregular structures requiring dynamic analysis in accordance with Article 4.1.8.7., Vd shall be taken as the larger of 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 of V based on the value of 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 or braced 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 of Vd, determined in 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 in Sentences 4.1.8.10.(8) 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 0.01hs for post-disaster buildings, 0.02hs for High Importance Category buildings, and 0.025hs 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 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 SFRSs, 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)Where the Seismic Category is SC3 or SC4, 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 that 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)Where the Seismic Category is SC3 or SC4, the following requirements shall be satisfied:

• (a) piles or pile caps, drilled piers, and caissons shall be interconnected by continuous ties in not less 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)Where the Seismic Category is SC3 or SC4, basement walls shall be designed to resist earthquake lateral pressures from backfill or natural ground.

(8)Where the Seismic Category is SC4, 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 designated as XV, where Vs30 is less than or equal to 180 m/s, XE or XF shall be interconnected by continuous ties in not less 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 0.1IES(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 1.1.3., 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 1.1.3. 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 specified lateral earthquake force, Vp, distributed according to the distribution of mass: Vp = 0.3S(0.2)IESpWp where S(0.2) = design spectral acceleration value at a period of 0.2 s, as defined in Sentence 4.1.8.4.(6), IE = earthquake 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 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 + 2hx/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 in Seismic Category SC1 or SC2, other than post-disaster buildings, seismically isolated buildings, and buildings with supplemental energy dissipation systems, 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 and 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) except as provided in Sentence (17), friction due to gravity loads shall not be considered to provide resistance to earthquake forces,
• (b) Rp for non-ductile connections, such as adhesives or power-actuated fasteners, shall be taken as 1.0,
• (c) Rp for shallow post-installed mechanical, post-installed adhesive, and cast-in-place anchors in concrete shall be 1.5, where shallow anchors are those with a ratio of embedment length to diameter of less than 8,
• (d) post-installed mechanical, drop-in and adhesive anchors in concrete shall be pre-qualified for seismic applications by cyclic load testing in accordance with (i) CSA A23.3, "Design of concrete structures," and (ii) ACI 355.2, "Qualification of Post-Installed Mechanical Anchors in Concrete (ACI 355.2-19) and Commentary," or ACI 355.4, "Qualification of Post-Installed Adhesive Anchors in Concrete (ACI 355.4-19) and Commentary," as applicable,
• (e) post-installed mechanical and adhesive anchors in masonry and post-installed mechanical anchors in structural steel shall be pre-qualified for seismic applications by cyclic tension load testing,
• (f) power-actuated fasteners shall not be used for cyclic tension loads,
• (g) 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
• (h) 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 pendent 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 (10) 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 Subsection 4.1.8.

(14)Except as provided in Sentence (15), the relative displacement of glass in glazing systems, Dfallout, shall be equal to the greater of

• (a) 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, or
• (b) 13 mm.

(15)Glass need not comply with Sentence (14), provided at least one of the following conditions is met:

• (a) the Seismic Category is SC1 or SC2,
• (b) the glass has sufficient clearance from its frame such that Dclear ≥ 1.25Dp calculated as follows: Dclear = 2C1(1 + hp C2 (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 = averages 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 non-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 structures with supplemental energy dissipation, elements and components of buildings described in Table 4.1.8.18. and their connections to the structure shall be designed for a specified lateral earthquake force, Vp, determined at each floor level as follows: Vp = SsedIE(Cp Ar Rp⁄)Wp where Ssed = peak spectral acceleration, Sa(T,X), in the period range of T = 0 s to T = 0.5 s determined from the mean 5%-damped floor spectral acceleration values by averaging the individual 5%-damped floor response spectra at the centroid of the floor area at that floor level determined using Non-linear Dynamic Analysis, and IE, Cp, Ar, Rp, Wp = as defined in Sentence (1).

(17)For a ballasted array of interconnected solar panels mounted on a roof, where IES(0.2) is less than or equal to 1.0, friction due to gravity loads is permitted to be considered to provide resistance to seismic forces, provided

• (a) the roof is not normally occupied,
• (b) the roof is surrounded by a parapet extending from the roof surface to not less than the greater of (i) 150 mm above the centre of mass of the array, and (ii) 400 mm above the roof surface,
• (c) the height of the centre of mass of the array above the roof surface is less than the lesser of (i) 900 mm, and (ii) one half of the smallest plan dimension of the supporting base of the array,
• (d) the roof slope at the location of the array is less than or equal to 3°,
• (e) the factored friction resistance calculated using the kinetic friction coefficient determined in accordance with Sentence (18) and a resistance factor of 0.7 is greater than or equal to the specified lateral earthquake force, Vp, on the array determined in accordance with Sentence (1) using values of Ar = 1.0, Ax = 3.0, Cp = 1.0, and Rp = 1.25,
• (f) the minimum clearance between the array and other arrays or fixed objects is the greater of (i) 225 mm, and (ii) 1 500(IES(0.2) − 0.4)2, in mm, and
• (g) the minimum clearance between the array and the roof parapet is the greater of (i) 450 mm, and (ii) 3 000(IES(0.2) − 0.4)2, in mm.

(18)For the purpose of Clause (17)(e), the kinetic friction coefficient shall be determined in accordance with ASTM G115, "Standard Guide for Measuring and Reporting Friction Coefficients," through experimental testing that

• (a) is carried out by an accredited laboratory on a full-scale array or a prototype of the array,
• (b) models the interface between the supporting base of the array and the roof surface, and
• (c) accounts for the adverse effects of anticipated climatic conditions on the friction resistance.

(1)For the purposes of this Article and Article 4.1.8.20., the following terms shall have the meanings stated herein:

• (a) "seismic isolation" is an alternative sei8mic 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 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) 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) 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 time 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.(6) for site designations XV, where Vs30 is greater than 360 m/s, XA, XB and XC, and (ii) a 5%-damped response spectrum based on a site-specific evaluation for site designations XV, where Vs30 is less than or equal to 360 m/s, XD, XE and XF, and
• (c) amplitude-scaled in an appropriate manner over the period range of 0.2T1 to 1.5T1, 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 results of all Non-linear Dynamic Analyses, or
• (b) √IE 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 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 SFRSs 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 SFRSs 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 meanings 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) 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 an 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 time 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.(6), and
• (c) amplitude-scaled in an appropriate manner over the period range of 0.2T1 to 1.5T1, 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) √IE 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 supplementary 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)All components of a supplemental energy dissipation device, except that portion of the device that dissipates energy, shall be designed to remain elastic.

(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)Buildings designed in accordance with Articles 4.1.8.19. to 4.1.8.22. need not comply with this Article.

(2)The design of post-disaster buildings in Seismic Category SC2, SC3 or SC4 shall be verified using 5%-damped spectral acceleration values based on a 5% probability of exceedance in 50 years and shall satisfy the following requirements:

• (a) the building shall be shown to behave elastically for a specified lateral earthquake force, V, determined in accordance with Sentence 4.1.8.11.(2) using IE = 1.0 and RdRo = 1.3,
• (b) the largest interstorey deflection at any level of the building, as determined in accordance with Sentence 4.1.8.13.(2) using IE = 1.0 and RdRo = 1.0, shall not exceed 0.005hs, and
• (c) the connections of elements and components of the building described in Table 4.1.8.18. with Rp > 1.5 shall be shown to behave elastically for a specified lateral earthquake force, Vp, determined in accordance with Sentence 4.1.8.18.(1) using Rp = 1.5.

(3)The design of High Importance Category buildings in Seismic Category SC3 or SC4 shall be verified using 5%-damped spectral acceleration values based on a 10% probability of exceedance in 50 years and shall satisfy the following requirements:

• (a) the building shall be shown to behave elastically for a specified lateral earthquake force, V, determined in accordance with Sentence 4.1.8.11.(2) using IE = 1.0 and RdRo = 1.3,
• (b) the largest interstorey deflection at any level of the building, as determined in accordance with Sentence 4.1.8.13.(2) using IE = 1.0 and RdRo = 1.0, shall not exceed 0.005hs, and
• (c) the connections of elements and components of the building described in Table 4.1.8.18. with Rp > 1.3 shall be shown to behave elastically for a specified lateral earthquake force, Vp, determined in accordance with Sentence 4.1.8.18.(1) using Rp = 1.3.

(4)For Normal Importance Category buildings in Seismic Category SC4 with a height above grade of more than 30 m, the structural framing elements not considered to be part of the SFRS shall be designed to behave elastically for a specified lateral earthquake force, V, determined in accordance with Sentence 4.1.8.11.(2) using spectral acceleration values based on a 10% probability of exceedance in 50 years and RdRo = 1.3.

(5)For the purposes of applying Sentences (2) to (4), torsional moments due to accidental eccentricities need not be considered if B, as determined in accordance with Sentence 4.1.8.11.(10), does not exceed 1.7.

(6)For the purposes of applying Sentences (2) to (4), elements of the SFRS and structural framing elements not considered to be part of the SFRS, when included in the analysis, shall be modeled in accordance with Sentence 4.1.8.3.(8) using elastic properties.

(7)All other requirements of Articles 4.1.8.2. to 4.1.8.18. shall be satisfied in meeting the additional requirements of this Article.