Part 4 — Structural Design

Section 4.1. Structural Loads and Procedures

4.1.1. General

4.1.1.1. Scope

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

4.1.1.2. Definitions

1. Words that appear in italics in this Part are defined in Article 1.4.1.2. of Division A.

4.1.1.3. Design Requirements

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. (See Note A-4.1.1.3.(1))
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. (See Note A-4.1.1.3.(2))
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.

4.1.1.4. Reserved

4.1.1.5. Design Basis

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,
   1. evaluation of a full-scale structure or a prototype by a loading test, or
   2. studies of model analogues.
      (See Note A-4.1.1.5.(2))

4.1.2. Specified Loads and Effects

4.1.2.1. Loads and Effects (See Note A-4.1.2.1.)

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:

where

1. load means the imposed deformations (i.e. deflections, displacements or motions that induce deformations and forces in the structure), forces and pressures applied to the building structure,
2. permanent load is a load that changes very little once it has been applied to the structure, except during repair,
3. variable load is a load that frequently changes in magnitude, direction or location, and
4. rare load is a load that occurs infrequently and for a short time only.

2. Minimum specified values of the loads described in Sentence (1), as set forth in Subsections 4.1.4. to 4.1.8., shall be increased to account for dynamic effects where applicable.
3. For the purpose of determining specified loads S, W or E in Subsections 4.1.6., 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. (See Note A-4.1.2.1.(3))

Table 4.1.2.1. Importance Categories for Buildings

Forming Part of Sentence 4.1.2.1.(3)

Notes to Table 4.1.2.1.

1. See Note A-Table 4.1.2.1.

4.1.2.2. Loads Not Listed

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. (See Note A-4.1.2.2.(1))

4.1.3. Limit States Design (See Note A-4.1.3.)

4.1.3.1. Definitions

1. In this Subsection, the term,
   1. "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),
   2. "specified loads" (C, D, E, H, L, P, S, T and W) means those loads defined in Article 4.1.2.1.,
   3. "principal load" means the specified variable load or rare load that dominates in a given load combination,
   4. "companion load" means a specified variable load that accompanies the principal load in a given load combination,
   5. "service load" means a specified load used for the evaluation of a serviceability limit state,
   6. "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,
   7. "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,
   8. "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,
   9. "factored load" means the product of a specified load and its principal-load factor or companion-load factor,
   10. "effects" refers to forces, moments, deformations or vibrations that occur in the structure,
   11. "nominal resistance, R," of a member, connection or structure, is based on the geometry and on the specified properties of the structural materials,
   12. "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
   13. "factored resistance, $\Phi R$ ," means the product of nominal resistance and the applicable resistance factor.

4.1.3.2. Strength and Stability

1. A building and its structural components shall be designed to have sufficient strength and stability so that the factored resistance, $\Phi R$ , 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:
   1. for load cases without crane loads, the load combinations listed in Table 4.1.3.2.-A, and
   2. for load cases with crane loads, the load combinations listed in Table 4.1.3.2.-B. (See Note A-4.1.3.2.(2))
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. (See Note A-4.1.3.2.(4))
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. (See Note A-4.1.3.2.(5))
6. The principal-load factor 1.5 for live loads L in Table 4.1.3.2.-A and $L_{XC}$ in Table 4.1.3.2.-B may be reduced to 1.25 for liquids in tanks.

Table 4.1.3.2.-A — Load Combinations Without Crane Loads for Ultimate Limit States

Forming Part of Sentences 4.1.3.2.(2), (5) to (10) and 4.2.4.1.(3)

Notes to Table 4.1.3.2.-A:

1. See Sentences 4.1.3.2.(2) to (4).
2. See Sentence 4.1.3.2.(9).
3. See Sentence 4.1.3.2.(8).
4. See Sentence 4.1.3.2.(5).
5. See Sentence 4.1.3.2.(6).
6. See Article 4.1.5.5.
7. See Sentence 4.1.3.2.(7).
8. See Sentence 4.1.3.2.(10).

Table 4.1.3.2.-B — Load Combinations With Crane Loads for Ultimate Limit States

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

Notes to Table 4.1.3.2.-B:

1. See Sentences 4.1.3.2.(2) to (4).
2. See Sentence 4.1.3.2.(8).
3. See Sentence 4.1.3.2.(5).
4. See Article 4.1.5.5.
5. See Sentence 4.1.3.2.(6).
6. See Sentence 4.1.3.2.(7).
7. Side thrust due to cranes need not be combined with full wind load.
8. See Sentence 4.1.3.2.(10).

7. The companion-load factor for live loads L in Table 4.1.3.2.-A and $L_{XC}$ 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 $1+0.6/h_s$ but not less than 1.25, where $h_s$ 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.

4.1.3.3. Fatigue

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. (See Note A-4.1.3.3.(1))
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. (See Note A-4.1.3.3.(2))

4.1.3.4. Serviceability

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. (See Note A-4.1.3.4.(1))
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:
   1. 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
   2. 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:
   1. 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, L_s, and the portion that is transitory, L_t, and
   2. the additional long-term settlements due to dead load, $D$ , and sustained live loads, $L_s$ , shall be calculated from the foundation soil properties provided by a qualified professional geotechnical engineer.

Table 4.1.3.4. — Loads and Load Combinations for Serviceability

Forming Part of Sentence 4.1.3.4.(2)

Notes to Table 4.1.3.4.:

1. The calculated deflection due to dead load, D, is permitted to be excluded where specified in the standards listed in Section 4.3.
2. The companion load factor of 0.35 for live load, L, shall be increased to 0.5 for storage areas, equipment areas and service rooms.
3. The calculated immediate deflection due to dead load, D, is permitted to be excluded where specified in the standards listed in Section 4.3.
4. L_s = sustained portion of the live load, L.
5. L_t = transitory portion of the live load, L.
6. See Note A-Table 4.1.3.4.

4.1.3.5. Deflection

1. In proportioning structural members to limit serviceability problems resulting from deflections, consideration shall be given to
   1. the intended use of the building or member,
   2. limiting damage to non-structural members made of materials whose physical properties are known at the time of design,
   3. limiting damage to the structure itself, and
   4. creep, shrinkage, temperature changes and prestress.

(See Note A-4.1.3.5.(1))

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. (See Note A-4.1.3.5.(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.

4.1.3.6. Vibration

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. (See Note A-4.1.3.6.(1))
2. Where floor vibrations caused by resonance with operating machinery or equipment are anticipated, dynamic analysis of the floor system shall be carried out. (See Note A-4.1.3.6.(2))
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. (See Note A-4.1.3.6.(3))
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. (See Note A-4.1.3.6.(4))

4.1.4. Dead Loads

4.1.4.1. Dead Loads

1. The specified dead load for a structural member consists of,
   1. the weight of the member itself,
   2. the weight of all materials of construction incorporated into the building to be supported permanently by the member,
   3. the weight of partitions,
   4. the weight of permanent equipment, and
   5. 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. (See Note A-4.1.4.1.(2))
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. (See Note A-4.1.4.1.(3))
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. (See Note A-4.1.4.1.(6))

4.1.5. Live Loads Due to Use and Occupancy

4.1.5.1. Loads Due to Use of Floors and Roofs

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. (See Note A-4.1.5.1.(1))
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.

4.1.5.2. Uses Not Stipulated

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,
   1. the probable assembly of persons,
   2. the probable accumulation of equipment and furnishings, and
   3. 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.

4.1.5.3. Full and Partial Loading

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

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

Forming Part of Sentence 4.1.5.3.(1)

Notes to Table 4.1.5.3.:

1. See Note A-Table 4.1.5.3.
2. See Article 4.1.5.6.
3. See Article 4.1.5.4.
4. See Sentence 4.1.5.1.(1).
5. See Article 4.1.5.5.

4.1.5.4. Loads for Occupancy Served

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:
   1. corridors, lobbies and aisles not more than 1,200 mm wide,
   2. all corridors above the first storey of residential areas of apartments, hotels and motels, and
   3. interior balconies and mezzanines.

4.1.5.5. Loads on Exterior Areas (See Note A-4.1.5.5.)

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,
   1. the live load prescribed for assembly areas in Table 4.1.5.3., or
   2. 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
   1. 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
   2. 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.

4.1.5.6. Loads for Dining Areas

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.

4.1.5.7. More Than One Occupancy

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.

4.1.5.8. Variation With Tributary Area (See Note A-4.1.5.8.)

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

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

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

4. Where the specified live load for a floor is reduced in accordance with Sentence (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.

4.1.5.9. Concentrated Loads

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.

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

Forming Part of Sentence 4.1.5.9.(1)

Notes to Table 4.1.5.9.:

1. See Note A-Table 4.1.5.9.

4.1.5.10. Sway Forces in Assembly Occupancies

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.

4.1.5.11. Crane-Supporting Structures and Impact of Machinery and Equipment (See Note A-4.1.5.11.)

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.

Table 4.1.5.11. Factors for the Calculation of Impact Loads

Forming Part of Sentence 4.1.5.11.(1)

Notes to Table 4.1.5.11.:

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

3. Crane runway structures shall be designed to resist a horizontal force applied normal to the top of the rails equal to not less than 20% of the sum of the weights of the lifted load and the crane trolley (excluding other parts of the crane).
4. The force described in Sentence (3) shall be equally distributed on each side of the runway and shall be assumed to act in either direction.
5. Crane runway structures shall be designed to resist a horizontal force applied parallel to the top of the rails equal to not less than 10% of the maximum wheel loads of the crane.

4.1.5.12. Bleachers

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.

4.1.5.13. Helicopter Landing Areas

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).

4.1.5.14. Loads on Guards and Handrails (See Note A-4.1.5.14. and A-4.1.5.15.(1))

1. The minimum horizontal specified live load applied outward at the minimum required height of every required guard shall be
   1. 3.0 kN/m for open viewing stands without fixed seats and for means of egress in grandstands, stadia, bleachers and arenas,
   2. 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
   3. 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:
   1. 0.9 kN applied at any point and in any direction for all handrails, and
   2. 0.7 kN/m applied in any direction for handrails not located within dwelling units.

4.1.5.15. Loads on Vehicle Guardrails

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. (See Note A-4.1.5.14. and A-4.1.5.15.(1))
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.

4.1.5.16. Loads on Walls Acting As Guards

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.

4.1.5.17. Firewalls (See Note A-4.1.5.17.)

1. Firewalls shall be designed to resist the maximum effect due to,
   1. the appropriate lateral design loads prescribed elsewhere in this Section, or
   2. 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,
   1. lateral support shall be assumed to be provided by the structure on one side only, or
   2. another structural support system capable of resisting the loads imposed by a fire on either side of the firewall shall be provided.

4.1.6. Loads Due to Snow and Rain

4.1.6.1. Specified Load Due to Rain or to Snow and Associated Rain

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. (See Note A-4.1.6.1.(1))

4.1.6.2. Specified Snow Load (See Note A-4.1.6.2.)

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,

where

• $I_s$ = importance factor for snow load as provided in Table 4.1.6.2.-A,
• S_s = 1-in-50-year ground snow load, in kPa, determined in accordance with Subsection 1.1.3.,
• $C_b$ = basic roof snow load factor in Sentence (2),
• $C_w$ = wind exposure factor in Sentences (3) and (4),
• $C_s$ = slope factor in Sentences (5) to (7),
• $C_a$ = accumulation factor in Sentence (8), and
• $S_r$ = 1-in-50-year associated rain load, in kPa, determined in accordance with Subsection 1.1.3., but not greater than $S_s\left(C_b{C}_w{C}_s{C}_a\right)$.

Table 4.1.6.2.-A Importance Factor for Snow Load, Is

Forming Part of Sentence 4.1.6.2.(1)

2. The basic roof snow load factor, C_b, shall
   1. be determined as follows:
      1. C sub b equals zero point eight.$$C_b=0.8$$

         for $l_c\le \left(\frac{70}{C_w^2}\right)$ .

      2. C sub b equals one over C sub w times the bracket quantity: one minus the quantity one minus zero point eight times C sub w, multiplied by e to the power of the quantity negative L sub c times C sub w squared minus seventy, divided by one hundred.$$C_{\mathrm{rm}b}=\frac{1}{C_{\mathrm{rm}w}}[1-(1-0.8C_{\mathrm{rm}w}\left)\exp \right(-\frac{l_{\mathrm{rm}c}{C}_{\mathrm{rm}w}^2-70}{100}\left)\right]$$

         for $l_c>\left(\frac{70}{C_w^2}\right)$ .

   2. conform to Table 4.1.6.2.-B, using linear interpolation for intermediate values of l_c C_w².
   3. be taken as equal to 1 for any roof structure with a mean height of less than 1 + S_s / γ, in m, above grade, where γ is the specific weight of snow determined in accordance with Article 4.1.6.13.   
      (See Note A-4.1.6.2.)

3. Except as provided for in Sentence (4), the wind exposure factor, C_w, 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, C_w, 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
   1. 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,
   2. 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 $C_b{C}_w{S}_s/\gamma$ in m, where $\gamma$ is the unit weight of snow on roofs as specified in Article 4.1.6.13., and
   3. 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, C_s, shall be,
   1. 1.0 where the roof slope, $\alpha$ , is equal to or less than 30°,
   2. $({70}^{°}-\alpha )/{40}^{°}$ where $\alpha$ is greater than 30° but not greater than 70°, and
   3. 0 where $\alpha$ exceeds 70°.
6. The slope factor, $C_s$ , for unobstructed slippery roofs where snow and ice can slide completely off the roof shall be
   1. 1.0 where the roof slope, $\alpha$ , is equal to or less than 15°,
   2. $({60}^{°}-\alpha )/{45}^{°}$ where $\alpha$ is greater than ${15}^{°}$ but not greater than ${60}^{°}$ , and
   3. 0 where $\alpha$ exceeds ${60}^{°}$ .
7. Unless otherwise stated in this Subsection, the slope factor, $C_s$ , shall be 1.0 when used in conjunction with accumulation factors for increased snow loads.

Table 4.1.6.2.-B — Basic Roof Snow Load Factor for l_c > (70/C_w²)

Forming Part of Sentence 4.1.6.2.(2) 

8. The accumulation factor, $C_a$ , 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,
   1. 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.,
   2. 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.
   3. 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.,
   4. increased snow or ice loads due to snow sliding as prescribed in Article 4.1.6.11.,
   5. increased snow loads in roof valleys, as prescribed in Article 4.1.6.12., and
   6. increased snow or ice loads due to meltwater draining from adjacent building elements and roof projections.
9. For shapes not addressed in Sentence (8), C_a 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.

4.1.6.3. Full and Partial Loading

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 $C_a=1.0$ , 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. (See Note A-4.1.6.3.(2))

4.1.6.4. Specified Rain Load

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. (See Note A-4.1.6.4.(1))
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. (See Note A-4.1.6.4.(3))
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.

4.1.6.5. Multi-Level Roofs

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, $C_a$ , shall be determined as follows:

or

where

• $C_{a0}$ = peak value of $C_a$ 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
• $x_d$ = length of drift as specified in Sentence (2) and as shown in Figure 4.1.6.5.-A.

Notes to Figure 4.1.6.5.-A:

1. If a > 5 m or h $\le$ 0.8 S_s/ $\gamma$ , drifting from the higher roof need not be considered.
2. If h ≥ 5 m, the value of C_a0 for Case I is permitted to be determined in accordance with Sentence 4.1.6.5.(4).

Table 4.1.6.5.-A Wind Exposure, Slope and Accumulation Factors in Figure 4.1.6.5.-A

Forming Part of Sentence 4.1.6.5.(1)

Notes to Table 4.1.6.5.-A:

1. For lower roofs with parapets, C_s = 1.0; otherwise, C_s varies as a function of slope, α, as defined in Sentences 4.1.6.2.(5) and (6).
2. The length of the drift, $x_d$ , shall be calculated as follows:

where

• $\gamma$ = specific weight of snow as specified in Article 4.1.6.13.

3. Except as provided in Sentence (4), the value of C_a0 for each of Cases I, II and III shall be the lesser of

and

where

• $\beta =1.0$ 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

, but $F\le 5$ for $C_{ws}=1.0$

where

• $C_{ws}$ = value for $C_w$ applicable to the source of drifting,
• $l_{cs}=\text{characteristic length of the source area for drifting, defined as,}{l}_{cs}=2w_s-\frac{w_s^2}{l_s},\text{where}{w}_s\text{and}{l}_s\text{are}$ 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

, but $0\le h{\text{'}}_p\le \left(\frac{l_{cs}}{5}\right)$

where

• $h_p$ = 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 $h\ge 5$ m, the value of $C_{a0}$ for Case I is permitted to be taken as

5. The value of $C_{a0}$ 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.

Figure 4.1.6.5.-B — Snow Load Cases I, II and III for Lower Level Roofs — Forming Part of Sentences 4.1.6.5.(1), (3) and (5), and Table 4.1.6.5.-B

Figure 4.1.6.5.-B Snow Load Cases I, II and III for Lower Level Roofs Forming Part of Sentences 4.1.6.5.(1), (3) and (5), and Table 4.1.6.5.-B

4.1.6.5.-B — Parameters for Snow Load Cases in Figure 4.1.6.5.-B

Forming Part of Sentences 4.1.6.5.(1), (3) and (5)

4.1.6.6. Horizontal Gap Between a Roof and a Higher Roof

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, $C_a$ , for the lower roof shall be determined as follows:
   1. if a > 5 m, the influence of the adjacent building on $C_a$ for the lower roof can be ignored, and
   2. if $a\le 5$ m, $C_a$ for the lower roof shall be calculated in accordance with Article 4.1.6.5. for values of $x\ge a$ .

4.1.6.7. Areas Adjacent to Roof Projections

1. Except as provided in Sentences (2) and (3), the accumulation factor, $C_a$ , 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, $C_{a0}$ , and the drift length, $x_d$ :
   1. $C_{a0}$ shall be taken as the lesser of,
   2. $x_d$ shall be taken as the lesser of 3.35 h and $(2/3)l_0$ , where h = height of the projection, and $l_0=longest$ horizontal dimension of the projection. (See Note A-4.1.6.7.(1))

and $\frac{\gamma l_0}{7.5C_h{S}_s}+1$ , and

2. C_a is permitted to be calculated in accordance with Article 4.1.6.5. for larger projections. (See Note A-4.1.6.7.(2))
3. Where the longest horizontal dimension of the roof projection, $l_0$ , is less than 3 m, the drift surcharge adjacent to the projection need not be considered.

4.1.6.8. Snow Drift at Corners

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.

4.1.6.9. Gable Roofs (See Note A-4.1.6.9.)

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 $\alpha >{15}^{°}$ , the unbalanced load case shall also be considered by setting the values of the accumulation factor, $C_a$ , as follows:
   1. on the upwind side of the roof peak, Ca shall be taken as 0, and
   2. on the downwind side of the roof peak, $C_a$ shall be taken as
      1. $0.25+\alpha /20$ , where ${15}^{°}\le \alpha \le {20}^{°}$ , and
      2. 1.25, where  .
3. For all gable roofs, the slope factor, C_s, shall be as prescribed in Sentences 4.1.6.2.(5) and (6).
4. For all gable roofs, the wind exposure factor, $C_w$ , shall be
   1. as prescribed in Sentences 4.1.6.2.(3) and (4) for the full and partial load cases, and
   2. 1.0 for the unbalanced load case referred to in Sentence (2).

4.1.6.10. Arch Roofs, Curved Roofs and Domes

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.
3. For arch roofs with a slope at the edge ${\alpha }_e\le {30}^{°}$ (See Figure 4.1.6.10.-A and Table 4.1.6.10.), $C_a$ shall be
   1. taken as 0 on the upwind side of the peak, and
   2. on the downwind side of the peak, taken as

for  and

for $\frac{h}{b}>0.12$

where

• x = horizontal distance from the roof peak,
• h = height of arch, and
• b = width of arch.

Notes to Figure 4.1.6.10.-A:

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

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

Forming Part of Sentences 4.1.6.10.(1) and (3), 4.1.6.11.(1) and 4.1.6.12.(1)

4. For arch roofs with a slope at the edge ${\alpha }_e>{30}^{°}$ (See Figure 4.1.6.10.-A and Table 4.1.6.10.), $C_a$ shall be
   1. taken as 0 on the upwind side of the peak, and
   2. on the downwind side of the peak,
      1. for the part of the roof between the peak and point where the slope $\alpha ={30}^{°}$ , taken as,

for  , and

where

• x, h, b = as specified in Sentence (2), and $x_{30}$ = value of x where the slope $\alpha ={30}^{°}$ , and

2. for the part of the roof where the slope $\alpha >{30}^{°}$ , taken as,

for  , and

for $\frac{h}{b}>0.12$

5. Except as provided in Sentence (6), $C_a$ for curved roofs shall be determined in accordance with the requirements for arch roofs stated in Sentences (3) and (4).
6. Where the slope, $\alpha$ , of a curved roof at its peak is greater than 10°, $C_a$ shall be determined in accordance with the requirements for gable roofs stated in Article 4.1.6.9. using a slope equal to the mean slope of the curved roof.
7. For domes of circular plan form (see Figure 4.1.6.10.-B), C_a shall
   1. along the central axis parallel to the wind, vary in the same way as for an arch roof with the same rise-to-span ratio, h/b, and
   2. off this axis, vary according to

where

• $C_a(x,y)$ = value of $C_a$ at location (x,y),
• $C_a(x,0)$ = value of $C_a$ on the central axis parallel to the wind,
• x = distance along the central axis parallel to the wind,
• y = horizontal coordinate normal to the x direction, and
• r = radius of dome.

Notes to Figure 4.1.6.10.-B:

1. Refer to Table 4.1.6.10. for applicable values of C_w and Sentences 4.1.6.2.(5) and (6) for applicable values of C_s.
2. Refer to Sentences 4.1.6.10.(3) and (4) for the calculation of C_a(x,0).

8. For all arch roofs, curved roofs and domes, the slope factor, $C_s$ , shall be as prescribed in Sentences 4.1.6.2.(5) and (6).
9. For all arch roofs, curved roofs and domes, the wind exposure factor, C_w, shall be as prescribed in Table 4.1.6.10.

4.1.6.11. Snow Loads Due to Sliding

1. Except as provided in Sentence (2), where an upper roof, or part thereof, slopes downwards with a slope $\alpha >0$ 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
   1. snow from the upper roof is prevented from sliding by a parapet or other effective means, or
   2. 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
   1. the accumulation factor $C_a=1.0$ for the relevant part of the upper roof,
   2. the slope factor, C_s, based on the slope of the lower roof, as prescribed in Sentences 4.1.6.2.(5) and (6), and
   3. the sliding snow distributed on the lower roof such that it is a maximum for x = 0 and decreases linearly to 0 at $x=x_d$ , as shown in Figure 4.1.6.11., where x and $x_d$ are as defined in Article 4.1.6.5.

4.1.6.12. Valleys in Curved or Sloped Roofs

1. For valleys in curved or sloped roofs with a slope $\alpha >{10}^{°}$ , 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, C_a, shall be calculated as follows:

for  , and

for 

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.), C_a shall be calculated as follows:

for 

where

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

Notes to Figure 4.1.6.12.:

1. $C_w=1.0$ , as per Sentence 4.1.6.2.(3).
2. $C_s=1.0$ , as per Sentence 4.1.6.2.(7).

4.1.6.13. Specific Weight of Snow

1. For the purposes of calculating snow loads in drifts, the specific weight of snow, $\gamma$ , shall be taken as 4.0 kN/m³ or 0.43 S_S + 2.2 kN/m³, whichever is lesser.

4.1.6.14. Snow Removal

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

4.1.6.15. Ice Loading of Structures

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."

4.1.6.16. Roofs with Solar Panels (See Note A-4.1.6.16.)

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
   1. Parallel Flush, where the panels are installed parallel to the roof surface with their upper surface less than or equal to $C_b{C}_w{S}_s/\gamma$ above the roof surface,
   2. Parallel Raised, where the panels are installed parallel to the roof surface with their upper surface greater than $C_b{C}_w{S}_s/\gamma$ above the roof surface, or
   3. Tilted, where the panels are installed at an angle to the roof surface with their highest edge greater than C_bC_wS_s/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, $C_s$ , shall be
   1. 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
   2. as specified in Sentences 4.1.6.2.(5) to (7) for all other roof areas. (See Note A-4.1.6.16.(3))
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
   1. C_s shall be determined in accordance with Sentence (3),
   2. where the gap width, $w_g$ , between the panels along the roof slope is greater than or equal to the panel width, $w_p$ , along the roof slope, the accumulation factor, $C_a$ , shall be taken as
      1. 0.0 for the panels,
      2. 2.0 for roof areas within a distance of w_p downslope from a downslope panel edge, and
      3. 1.0 for all other roof areas, and (See Note A-4.1.6.16.(4)(b))
   3. where the gap width, $w_g$ , between the panels along the roof slope is less than the panel width, $w_p$ , along the roof slope, $C_a$ shall be taken as
      1. 0.0 for panel areas within a distance of w_g downslope from an upslope panel edge,
      2. 1.0 for other panel areas,
      3. 2.0 for roof areas in gaps between the panels, and
      4. 1.0 for all other roof areas. (See Note A-4.1.6.16.(4)(c))
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
   1. where the roof is flat, C_a shall be taken as
      1. 1.0 for the panels,
      2. 1.0 for roof areas not under the panels,
      3. 1.0 for roof areas under the panels within a distance of min (2 h_g,2 w_g) from a panel edge, where h_g is the gap height between the lower surface of the panels and the roof surface, and w_g is the gap width between the panels, and
      4. 0.0 for other roof areas under the panels, and
   2. where the roof is sloped, the snow loads, S, derived from Clause (a) shall be used, except that
      1. S shall be taken as 0.0 on the panels, and
      2. 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 $w_p$ downslope onto the roof, where $w_p$ is the panel width along the roof slope, and S on the roof areas, as derived from Subclauses (a)(ii) to (a)(iv).(See Note A-4.1.6.16.(5)(a) and (b))
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
   1. C_a shall be taken as 0.0 for the panels,
   2. $C_a$ shall be taken as 1.0 for roof areas beyond a distance of $5(h-C_b{C}_w{S}_s/\gamma )$ from the lowest edge of the panels, where h is the height of the highest edge of the panels above the roof surface,
   3. except as provided in Clauses (d) and (e), for roof areas within a distance of $5(h-C_b{C}_w{S}_s/\gamma )$ from the lowest edge of the panels, $C_a$ shall be taken as
      1. 1.25 for $(h_g-C_b{C}_w{S}_s/\gamma )\le 0.3$ m, where $h_g$ is the gap height between the lowest edge of the panels and the roof surface,
      2. $1.294-0.1471(h_g-C_b{C}_w{S}_s/\gamma )$ for  m, and
      3. 1.0 for $(h_g{C}_b{C}_w{S}_s/\gamma )>2.0\text{m}$ ,

(See Note A-4.1.6.16.(6)(c))

4. except as provided in Clause (e), Ca shall be taken as 2.0 for roof areas within a distance of $w_{ph}$ beyond the lowest edge of the panels, where $w_{ph}$ is the horizontal projection of the panel width, $w_p$ , along the sloped panel edges, and
5. 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.

(See Note A-4.1.6.16.(6))

4.1.7. Wind Load

4.1.7.1. Specified Wind Load

1. The specified wind loads for a building and its components shall be determined using the Static, Dynamic or Wind Tunnel Procedure as stated in Sentences (2) to (5).
2. For the design of buildings that are not dynamically sensitive, as defined in Sentence 4.1.7.2.(1), one of the following procedures shall be used to determine the specified wind loads:
   1. the Static Procedure described in Article 4.1.7.3.,
   2. the Dynamic Procedure described in Article 4.1.7.8., or
   3. the Wind Tunnel Procedure described in Article 4.1.7.14.
3. For the design of buildings that are dynamically sensitive, as defined in Sentence 4.1.7.2.(2), one of the following procedures shall be used to determine the specified wind loads:
   1. the Dynamic Procedure described in Article 4.1.7.8., or
   2. the Wind Tunnel Procedure described in Article 4.1.7.14.
4. For the design of buildings that may be subject to wake buffeting or channelling effects from nearby buildings, or that are very dynamically sensitive, as defined in Sentence 4.1.7.2.(3), the Wind Tunnel Procedure described in Article 4.1.7.14., shall be used to determine the specified wind loads.
5. For the design of cladding and secondary structural members, one of the following procedures shall be used to determine the specified wind loads:
   1. the Static Procedure described in Article 4.1.7.3., or
   2. the Wind Tunnel Procedure described in Article 4.1.7.14.
6. Computational fluid dynamics shall not be used to determine the specified wind loads for a building and its components. (See Note A-4.1.7.1.(6))

4.1.7.2. Classification of Buildings (See Note A-4.1.7.2.)

1. Except as provided in Sentences (2) and (3), a building is permitted to be classified as not dynamically sensitive.
2. A building shall be classified as dynamically sensitive if
   1. its lowest natural frequency is less than 1 Hz and greater than 0.25 Hz,
   2. its height is greater than 60 m, or
   3. its height is greater than 4 times its minimum effective width considering all wind directions, where the effective width, w, of a building shall be taken as,

where the summations are over the height of the building for a given wind direction, $h_i$ is the height above grade to level i, and $w_i$ is the width normal to the wind direction at height $h_i$ ; the minimum effective width is the lowest value of the effective width considering all wind directions.

3. A building shall be classified as very dynamically sensitive if
   1. its lowest natural frequency is less than or equal to 0.25 Hz, or
   2. it contains a human occupancy, and its height is more than 6 times its minimum effective width as defined in Clause (2)(c).

4.1.7.3. Static Procedure

1. The specified external pressure or suction due to wind on part or all of a surface of a building shall be calculated as follows:

where

• p = specified external pressure acting statically and in a direction normal to the surface, considered positive when the pressure acts towards the surface and negative when it acts away from the surface,
• $I_w$ = importance factor for wind load, as provided in Table 4.1.7.3.,
• q = reference velocity pressure, as provided in Sentence (4),
• $C_e$ = exposure factor, as provided in Sentences (5) and (7),
• $C_t$ = topographic factor, as provided in Article 4.1.7.4.,
• $C_g$ = gust effect factor, as provided in Sentence (8), and
• $C_p$ = external pressure coefficient, as provided in Articles 4.1.7.5. and 4.1.7.6.

Table 4.1.7.3. Importance Factor for Wind Load, Iw

Forming Part of Sentences 4.1.7.3.(1) and 4.1.7.8.(4)

2. The net wind load for the building as a whole shall be the algebraic difference of the loads on the windward and leeward surfaces, and in some cases, may be calculated as the sum of the products of the external pressures or suctions and the areas of the surfaces over which they are averaged as provided in Sentence (1).
3. The net specified pressure due to wind on part or all of a surface of a building shall be the algebraic difference, such as to produce the most critical effect, of the external pressure or suction calculated in accordance with Sentence (1) and the specified internal pressure or suction due to wind calculated as follows:

where

• $p_i$ = specified internal pressure acting statically and in a direction normal to the surface, either as a pressure directed toward the surface or as a suction directed away from the surface,
• $I_w$ , q, $C_t$ = as defined in Sentence (1),
• $C_{ei}$ = exposure factor for internal pressure, as provided in Sentence (7),
• $C_{gi}$ = internal gust effect factor, as provided in Sentence (10), and
• $C_{pi}$ = internal pressure coefficient, as provided in Article 4.1.7.7.

4. The reference velocity pressure, q, shall be the appropriate value determined in conformance with Subsection 1.1.3. based on a probability of being exceeded in any one year of 1 in 50.
5. The exposure factor $C_e$ , shall be based on the reference height, h, determined in accordance with Sentence (6) for the surface or part of the surface under consideration and shall be
   1. (h/10)^0.2 but not less than 0.9 for open terrain, where open terrain is level terrain with only scattered buildings, trees or other obstructions, open water or shorelines thereof,
   2. 0.7(h/12)^0.3 but not less than 0.7 for rough terrain, where rough terrain is suburban, urban or wooded terrain extending upwind from the building uninterrupted for at least 1 km or 20 times the height of the building, whichever is greater, or
   3. an intermediate value between the two exposures defined in Clauses (a) and (b) in cases where the site is less than 1 km or 20 times the height of the building from a change in terrain conditions, whichever is greater, provided an appropriate interpolation method is used. (See Note A-4.1.7.3.(5)(c))
6. The reference height, h, shall be determined as follows:
   1. for buildings with height less than or equal to 20 m and less than the smaller plan dimension, h shall be the midheight of the roof above grade, but shall not be less than 6 m,
   2. for other buildings, h shall be,
      1. the actual height above grade of the point on the windward wall for which external pressures are being calculated,
      2. the mid-height of the roof for pressures on surfaces parallel to the wind direction, and
      3. the mid-height of the building for pressures on the leeward wall, and
   3. for any structural element exposed to wind, h shall be the mid-height of the element above the ground.
7. The exposure factor for internal pressure, C_ei, shall be determined as follows:
   1. for buildings whose height is greater than 20 m and that have a dominant opening, C_ei shall be equal to the exposure factor for external pressures, C_e, calculated at the mid-height of the dominant opening, and
   2. for other buildings, C_ei shall be the same as the exposure factor for external pressures, C_e, calculated for a reference height, h, equal to the mid-height of the building or 6 m, whichever is greater.
8. Except as provided in Sentences (9) and 4.1.7.6.(1), the gust effect factor, C_g, shall be one of the following values:
   1. 2.0 for the building as a whole and main structural members, or
   2. 2.5 for external pressures and suctions on secondary structural members including cladding.
9. For cases where $C_g$ and $C_p$ are combined into a single product, $C_g{C}_p$ , the values of $C_g$ and $C_p$ need not be independently specified. (See Article 4.1.7.6.)
10. The internal gust effect factor, $C_{gi}$ , shall be 2.0, except it is permitted to be calculated using the following equation for large structures enclosing a single large unpartitioned volume that does not have numerous overhead doors or openings:

where

• $V_0$ = internal volume in $m^3$ , and
• A = total area of all exterior openings of the volume in $m^2$ .

(See Note A-4.1.7.3.(10))

4.1.7.4. Topographic Factor

1. Except as provided in Sentence (2), the topographic factor, C_t, shall be taken as 1.0.
2. For buildings on hills or escarpments with slope, $H_h/{\left(2L_h\right)}^{}$ , greater than 0.1 (See Figure 4.1.7.4.), the topographic factor, $C_t$ , shall be calculated as follows:

where

where

• $\Delta S_{\text{max}}$ = applicable value from Table 4.1.7.4.,
• x = horizontal distance from the peak of the hill or escarpment,
• $L_h$ = horizontal distance upwind from the peak to the point where the ground surface lies at half the height of the hill or escarpment, or $2H_h$ (where $H_h$ is the height of the hill or escarpment), whichever is greater,
• Z =height above ground, and
• k and $\alpha =\text{applicable constants from <a href="\#table-caption-30">Table 4.1.7.4.</a>}$ based on shape of hill or escarpment.

Notes to Figure 4.1.7.4.:

1. V(z) = wind speed.

Table 4.1.7.4. Parameters for Maximum Speed-Up over Hills and Escarpments

Forming Part of Sentence 4.1.7.4.(2)

Notes to Table 4.1.7.4.:

1. For $H_h/L_h>0.5$ , assume $H_h/L_h=0.5$ and substitute $2H_h$ for $L_h$ in the equation for $\Delta S$ .

4.1.7.5. External Pressure Coefficients

1. Applicable values of external pressure coefficients, C_p, are provided in
   1. Sentences (2) to (9), and
   2. Article 4.1.7.6. for certain shapes of low buildings.
2. For the design of the main structural system, the value of $C_p$ shall be established as follows, where H is the height of the building and D is the width of the building parallel to the wind direction:
   1. on the windward face,

C subscript p equals 0.6 when H divided by D is less than 0.25, equals 0.27 times the quantity H divided by D plus 2 when H divided by D is greater than or equal to 0.25 and less than 1.0, and equals 0.8 when H divided by D is greater than or equal to 1.0 $$C_p=\left\{\begin{array}{c}0.6\text{for}H/D<0.25\\ 0.27(H/D+2)\text{for}0.25\le H/D<1.0\\ 0.8\text{for}H/D\ge 1.0\end{array}\right.$$

2. on the leeward face,

C subscript p equals negative 0.3 when H divided by D is less than 0.25, equals negative 0.27 times the quantity H divided by D plus 0.88 when H divided by D is greater than or equal to 0.25 and less than or equal to 1.0, and equals negative 0.5 when H divided by D is greater than or equal to 1.0 $$C_p=\left\{\begin{array}{c}-0.3\text{for}H/D<0.25\\ -0.27(H/D+0.88)\text{for}0.25\le H/D\le 1.0\\ -0.5\text{for}H/D\ge 1.0\end{array}\right.$$

3. on the walls parallel to the wind, $C_p=-0.7$ .

(See Note A-4.1.7.5.(2) and (3))

3. For the design of roofs, the value of $C_p$ shall be established as follows, where x is the distance from the upwind edge of the roof:
   1. for H/D $\ge$ 1.0, $C_p=-1.0$ , and
   2. for H/D < 1.0,

(See Note A-4.1.7.5.(2) and (3))

4. For the design of the cladding and of secondary structural elements supporting the cladding, the value of $C_p$ shall be established as follows, where W and D are the widths of the building:
   1. on walls, $C_p$ shall be taken as $\pm 0.9$ , except that within a distance equal to the larger of 0.1D and 0.1 W from a building corner, the negative value of $C_p$ shall be taken as -1.2,
   2. on walls where vertical ribs deeper than 1 m are placed on the facade, $C_p$ shall be taken as $\pm 0.9$ , except that, within a distance equal to the larger of 0.2D and 0.2 W from a building corner, the negative value of $C_p$ shall be taken as -1.4, and
   3. on roofs, $C_p$ shall be taken as -1.0, except that
      1. within a distance equal to the larger of 0.1D and 0.1 W from a roof edge, $C_p$ shall be taken as -1.5,
      2. in a zone that is within a distance equal to the larger of 0.2D and 0.2 W from a roof corner, Cp shall be taken as -2.3 but is permitted to be taken as -2.0 for roofs with perimeter parapets that are higher than 1 m, and
      3. on lower levels of flat stepped roofs, positive pressure coefficients established for the walls of the steps apply for a distance b. (See Figure 4.1.7.6.-D for the definition of b)

(See Note A-4.1.7.5.(4))

5. Except as provided in Sentence (6), for the design of balcony guards, the internal pressure coefficient, $C_{pi}$ , shall be taken as zero and the value of $C_p$ shall be taken as $\pm 0.9$ , except that, within a distance equal to the larger of 0.1D and 0.1 W from a building corner, $C_p$ shall be taken as $\pm 1.2$ .
6. Where the top of the balcony guard is 2.0 m or less below the roof surface, the values of $C_p$ shall be taken as equal to those determined for parapets in Sentences (7) and (8).
7. To determine the contribution from parapets to the wind loads on the main structural system, the values of $C_p$ shall be taken as
   1. on the outer faces, equal to those on the walls below,
   2. on the inner face of the windward parapet, equal to that on the upwind edge of a roof surface at the level of the top of the parapet, and
   3. on the inner faces of the other parapets, zero.
8. For the structural design of parapets themselves, the values of $C_p$ shall be taken as equal to those specified in Sentence (7), except that the value of $C_p$ on the inner face of the leeward parapet shall be taken as equal to that on the outer face of the windward parapet.
9. For the design of cladding on parapets, the values of C_p shall be taken as
   1. on the outer vertical surfaces, equal to those on the cladding on the walls below, and
   2. on the inner and top surfaces, equal to those on the cladding of a roof surface at the level of the top of the parapet.

4.1.7.6. External Pressure Coefficients for Low Buildings

1. For the design of buildings with a height, H, that is less than or equal to 20 m and less than the smaller plan dimension, the values of the product of the pressure coefficient and gust factor, $C_g{C}_p$ , provided in Sentences (2) to (9) are permitted to be used.
2. For the design of the main structural system of the building, which is affected by wind pressures on more than one surface as shown in Figure 4.1.7.6.-A, the values of $C_g{C}_p$ are provided in Table 4.1.7.6.

Table 4.1.7.6. External Peak Values of C_gC_p in Figure 4.1.7.6.-A

Forming Part of Sentence 4.1.7.6.(2)

Notes to Table 4.1.7.6.:

1. For values of roof slope not shown, the coefficient C_gC_p can be interpolated linearly.
2. Positive coefficients denote forces toward the surface, whereas negative coefficients denote forces away from the surface.
3. For the design of individual walls and wall cladding, the values of $C_g{C}_p$ are provided in Figure 4.1.7.6.-B.
4. For the design of roofs with a slope less than or equal to $7^{°}$ , the values of $C_g{C}_p$ are provided in Figure 4.1.7.6.-C.
5. For the design of flat roofs with steps in elevation, the values of $C_g{C}_p$ are provided in Figure 4.1.7.6.-D.
6. For the design of gabled or hipped, single-ridge roofs with a slope greater than $7^{°}$ , the values of $C_g{C}_p$ are provided in Figure 4.1.7.6.-E.
7. For the design of gabled, multi-ridge roofs, the values of C_gC_p are provided in
   1. Figure 4.1.7.6.-C for roofs with a slope less than or equal to 10°, and
   2. Figure 4.1.7.6.-F for roofs with a slope greater than 10°.
8. For monosloped roofs, the values of C_gC_p are provided in
   1. Figure 4.1.7.6.-C for roofs with a slope less than or equal to 3°, and
   2. Figure 4.1.7.6.-G for roofs with a slope greater than 3° and less than or equal to 30°.
9. For sawtooth roofs, the values of C_gC_p are provided in
   1. Figure 4.1.7.6.-C for roofs with a slope less than or equal to 10°, and
   2. Figure 4.1.7.6.-H for roofs with a slope greater than 10°.
10. The wind loads on balcony guards on low buildings shall be as specified in Sentences 4.1.7.5.(5) and (6).
11. The wind loads on parapets on low buildings shall be as specified in Sentences 4.1.7.5.(7) to (9).

Notes to Figure 4.1.7.6.-A:

1. The building must be designed for all wind directions. Each corner must be considered in turn as the windward corner shown in the sketches. For all roof slopes, Load Case A and Load Case B are required as two separate loading conditions to generate the wind actions, including torsion, to be resisted by the structural system.
2. For the design of foundations, exclusive of anchorages to the frame, only 70% of the effective load is to be considered.
3. The reference height, h, for pressures is the mid-height of the roof or 6 m, whichever is greater. The eave height, H, may be substituted for the mid-height of the roof if the roof slope is less than 7°.
4. End-zone width y should be the greater of 6 m or 2z, where z is the width of the gable-wall end zone defined for Load Case B below. Alternatively, for buildings with frames, the end-zone width y may be the distance between the end and the first interior frame.
5. End-zone width z is the lesser of 10% of the least horizontal dimension and 40% of height, H, but not less than 4% of the least horizontal dimension or 1 m.
6. For B/H > 5 in Load Case A, the negative coefficients listed for surfaces 2 and 2E in Table 4.1.7.6. should only be applied on an area whose width is 2.5 H measured from the windward eave. The pressures on the remainder of the windward roof should be reduced to the pressures for the leeward roof.

Notes to Figure 4.1.7.6.-B:

1. These coefficients apply for any roof slope, $\alpha$ .
2. End-zone width z is the lesser of 10% of the least horizontal dimension and 40% of height, H, but not less than 4% of the least horizontal dimension or 1 m.
3. Combinations of external and internal pressures must be evaluated to obtain the most severe loading.
4. Positive coefficients denote forces toward the surface, whereas negative coefficients denote forces away from the surface. Each structural element must be designed to withstand forces of both signs.
5. Pressure coefficients generally apply for facades with architectural features; however, where vertical ribs deeper than 1 m are placed on a facade, a local C_gC_p of –2.8 applies to zone e.

Notes to Figure 4.1.7.6.-C:

1. Coefficients for overhung roofs have the prefix "o" and refer to the same roof areas as referred to by the corresponding symbol without a prefix. They include contributions from both upper and lower surfaces. In the case of overhangs, the walls are inboard of the roof outline.
2. s and r apply to both roofs and upper surfaces of canopies.
3. End-zone width z is the lesser of 10% of the least horizontal dimension and 40% of height, H, but not less than 4% of the least horizontal dimension or 1 m.
4. Combinations of external and internal pressures must be evaluated to obtain the most severe loading.
5. Positive coefficients denote forces toward the surface, whereas negative coefficients denote forces away from the surface. Each structural element must be designed to withstand forces of both signs.
6. For calculating the uplift forces on tributary areas larger than $100{\text{m}}^2$ on unobstructed nearly-flat roofs with low parapets, and where the centre of the tributary area is at least twice the height of the building from the nearest edge, the value of $C_g{C}_p$ may be reduced from -1.5 to -1.1 at x/H = 2 and further reduced linearly to -0.6 at x/H = 5, where x is the distance to the nearest edge and H is the height of the building.
7. For roofs having a perimeter parapet with a height of 1 m or greater, the corner coefficients $C_g{C}_p$ for tributary areas less than 1 m² can be reduced from -5.4 to -4.4.

Notes to Figure 4.1.7.6.-D:

1. The zone designations, pressure-gust coefficients and notes provided in Figure 4.1.7.6.-C apply on both the upper and lower levels of flat stepped roofs, except that on the lower levels, positive pressure-gust coefficients equal to those in Figure 4.1.7.6.-B for walls apply for a distance, b, where b is equal to 1.5 h₁ but not greater than 30 m. For all walls in Figure 4.1.7.6.-D, zone designations and pressure coefficients provided for walls in Figure 4.1.7.6.-B apply.
2. Note (1) above applies only when the following conditions are met: $h_1\ge 0.3H$ , $h_1\ge 3$ m, and $W_1$ , $W_2$ or $W_3$ is greater than 0.25 W but not greater than 0.75 W.

Notes to Figure 4.1.7.6.-E:

1. Coefficients for overhung roofs have the prefix "o" and refer to the same roof areas as referred to by the corresponding symbol without a prefix. They include contributions from both upper and lower surfaces.
2. End-zone width z is the lesser of 10% of the least horizontal dimension and 40% of height, H, but not less than 4% of the least horizontal dimension or 1 m.
3. Combinations of external and internal pressures must be evaluated to obtain the most severe loading.
4. Positive coefficients denote forces towards the surface, whereas negative coefficients denote forces away from the surface. Each structural element must be designed to withstand forces of both signs.
5. For hipped roofs with  , edge/ridge strips and pressure-gust coefficients for ridges of gabled roofs apply along each hip.

Notes to Figure 4.1.7.6.-F:

1. End-zone width z is the lesser of 10% of the least horizontal dimension and 40% of height, H, but not less than 4% of the least horizontal dimension or 1 m.
2. Combinations of external and internal pressures must be evaluated to obtain the most severe loading.
3. Positive coefficients denote forces towards the surface, whereas negative coefficients denote forces away from the surface. Each structural element must be designed to withstand forces of both signs.
4. For $\alpha \le {10}^{°}$ , the coefficients given in Figure 4.1.7.6.-C apply, but for cases where $\alpha >$ than 7°, use $\alpha =7^{°}$ .

Notes to Figure 4.1.7.6.-G:

1. End-zone width, z, is the lesser of 10% of the least horizontal dimension and 40% of height, H, but not less than 4% of the least horizontal dimension or 1 m.
2. Combinations of external and internal pressures shall be evaluated to obtain the most severe loading.
3. Positive coefficients denote forces toward the surface, whereas negative coefficients denote forces away from the surface. Each structural element shall be designed to withstand forces of both signs.
4. Where $\alpha \le 3^{°}$ , the coefficients given in Figure 4.1.7.6.-C apply.

Notes to Figure 4.1.7.6.-H:

1. End-zone width z is the lesser of 10% of the least horizontal dimension and 40% of height, H, but not less than 4% of the least horizontal dimension or 1 m.
2. Combinations of external and internal pressures must be evaluated to obtain the most severe loading.
3. Positive coefficients denote forces towards the surface, whereas negative coefficients denote forces away from the surface. Each structural element must be designed to withstand forces of both signs.
4. Negative coefficients on the corner zones of Span A differ from those on Spans B, C and D.
5. For $\alpha \le {10}^{°}$ , the coefficients given in Figure 4.1.7.6.-C apply, but for cases where $\alpha >7^{°}$ , use $\alpha =7^{°}$ .

4.1.7.7. Internal Pressure Coefficient

1. The internal pressure coefficient, $C_{pi}$ , for buildings shall be as prescribed in Table 4.1.7.7.
2. The internal pressure coefficient, C_pi, for cladding on parapets shall be -0.70 to +0.70. (See Note A-4.1.7.7.(2))

Table 4.1.7.7. Internal Pressure Coefficients

Forming Part of Sentence 4.1.7.7.(1)

−0.15 to 0.0

4.1.7.8. Dynamic Procedure

1. For the application of the Dynamic Procedure, the provisions of Article 4.1.7.3. shall be followed, except that the exposure factor, C_e, shall be as prescribed in Sentences (2) and (3), and the gust effect factor, C_g, shall be as prescribed in Sentence (4), when determining the wind loads on the main structural system.
2. For buildings in open terrain, as defined in Clause 4.1.7.3.(5)(a), the value of $C_e$ for the design of the main structural system shall be calculated as follows:

(See Note A-4.1.7.8.(2) and (3))

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

(See Note A-4.1.7.8.(2) and (3))

4. For the design of the main structural system, C_g shall be calculated as follows:

where

, and

where

• $v=\text{average fluctuation rate calculated as}{f}_{nD}\sqrt{\frac{sF}{sF+\beta B}}$ ,
• T = 3600 s,
• K = 0.08 for open terrain and 0.10 for rough terrain,
• C_eH = exposure factor evaluated at reference height h = H,
• B = background turbulence factor, a function of w/H determined from Figure 4.1.7.8.,
• s = size reduction factor calculated as $\frac{\pi }{3}\left[\frac{1}{1+\frac{8f_{\text{nD}}H}{3V_{\text{H}}}}\right]\left[\frac{1}{1+\frac{10f_{\text{nD}}W}{V_{\text{H}}}}\right]$
• $F=\text{gust energy ratio calculated as}\frac{x_0^2}{(1+x_0^2)}\text{, where}{x}_0={(1220f_{nD}/V_H)\text{, and}}^{}$
• $\beta$ = damping ratio, which shall be determined by a rational method or may be taken to be 0.01 for steel structures, 0.02 for concrete structures and 0.015 for composite structures,

where

• f_nD = natural frequency of vibration of the building in the along-wind direction, in Hz,
• $f_n$ = lowest natural frequency of the building, in Hz, as described in Sentences 4.1.7.2.(2) and (3),
• H = height of the building,
• $w=\text{effective width of windward face of the}building\text{calculated as}\frac{\sum h_i{w}_i}{\sum h_i}$ , where $w_i=\text{width normal to wind direction at height}{h}_i$ , and
• $V_H$ = mean wind speed at the top of the structure, in m/s, calculated as $\overline{V}\sqrt{C_{eH}}$ ,

where

• $\overline{V}=\text{reference wind speed at a height of 10 <abbr title="metre">m</abbr>, in m/s, calculated as}\sqrt{\frac{2I_{W}q}{\rho }}$ ,

where

• $I_w$ = importance factor for wind load, as provided in Table 4.1.7.3.,
• q = reference velocity pressure, in Pa, and
• $\rho =\text{air density}=1.2929{\text{kg/m}}^3\mathrm{.}$

(See Note A-4.1.7.8.(4))

4.1.7.9. Full and Partial Wind Loading

1. Except where the wind loads are derived from the combined C_gC_p values determined in accordance with Article 4.1.7.6., buildings and structural members shall be capable of withstanding the effects of the following loads:
   1. the full wind loads acting along each of the 2 principal horizontal axes considered separately,
   2. 75% of the wind loads described in Clause (a) but offset from the central geometric axis of the building by 15% of its width normal to the direction of the force to produce the worst load effect,
   3. 75% of the wind loads described in Clause (a) but with both axes considered simultaneously, and
   4. 56% of the wind loads described in Clause (a) but with both axes considered simultaneously and offset from the central geometric axis of the building by 15% of its width normal to the direction of the force.

(See Note A-4.1.7.9.(1))

4.1.7.10. Interior Walls and Partitions

1. In the design of interior walls and partitions, due consideration shall be given to differences in air pressure on opposite sides of the wall or partition which may result from
   1. pressure differences between the windward and leeward sides of a building,
   2. stack effects due to a difference in air temperature between the exterior and interior of the building, and
   3. air pressurization by the mechanical services of the building.

4.1.7.11. Exterior Ornamentations, Equipment and Appendages (See Note A-4.1.7.11.)

1. The effects of wind loads on exterior ornamentations, equipment and appendages, including the increase in exposed area as a result of ice buildup as prescribed in CAN/CSA-S37, "Antennas, towers, and antenna-supporting structures," shall be considered in the structural design of the connections and the building.
2. Where there are a number of similar components, the net increase in force is permitted to be based on the total area for all similar components as opposed to the summation of forces of individual elements.

4.1.7.12. Attached Canopies on Low Buildings with a Height H ≤ 20 m

(See Note A-4.1.7.12.)

1. For the purposes of this Article, "attached canopy" shall mean a horizontal canopy with a maximum slope of 2% that is attached to a building wall at any height, h_c, above ground level.
2. The specified external wind pressure, p, and the specified net external wind pressure, $p_{net}$ , for attached canopies on exterior walls of low buildings with a height $H\le 20$ m shall be determined as follows:

, and

where

• p = specified external wind pressure acting statically and in a direction normal to the upper or lower surface of the canopy, considered positive when acting towards the surface and negative when acting away from the surface,
• $p_{net}$ = specified net external wind pressure acting statically on the canopy, considered positive when acting in a downward direction and negative when acting in an upward direction,
• $I_W$ , q, $C_e$ , $C_t$ = as defined in Sentence 4.1.7.3.(1),
• $C_g{C}_p$ = gust pressure coefficient on the upper or lower surface of the canopy, as given in Figure 4.1.7.12.-A, and
• ${\left(C_g{C}_p\right)}_{net}$ = net gust pressure coefficient on the canopy, considering simultaneous contributions from the upper and lower surfaces of the canopy, as given in Figure 4.1.7.12.-B.

Notes to Figure 4.1.7.12.-A:

1. The coefficients apply for any roof slope, a.
2. The reference height, h, is the mid-height of the roof or 6 m, whichever is greater.
3. Positive C_gC_p values denote forces acting towards the upper or lower surface of the canopy, whereas negative C_gC_p values denote forces acting away from the surface. Each structural element must be designed to resist both the positive and negative forces.

Notes to Figure 4.1.7.12.-B:

1. The coefficients apply for any roof slope, $\alpha$ .
2. The reference height, h, is the mid-height of the roof or 6 m, whichever is greater.
3. Positive ${\left(C_g{C}_p\right)}_{net}$ values denote net forces acting in a downward direction on the canopy, whereas negative ${\left(C_g{C}_p\right)}_{net}$ values denote net forces acting in an upward direction on the canopy. The canopy must be designed to resist both the positive and negative net forces.

4.1.7.13. Roof-Mounted Solar Panels on Buildings of Any Height (See Note A-4.1.7.13.)

1. Where solar panels are installed on a roof, the roof wind loads shall account for the wind loads on the solar panels, as determined in accordance with Sentences (2) to (7), or shall be determined in the same way as for the roof without solar panels, whichever approach results in the most critical effect.
2. For an array of solar panels where the panels are installed close and parallel to the roof surface with their upper surface not more than 250 mm above the roof surface and with gaps around the panels of not less than 6 mm, the net positive or negative pressure difference between the upper and lower surfaces of a panel or the array shall be calculated as follows:

where

• $I_W$ , q, $C_e$ , $C_t$ , $C_g$ , $C_p$ = as defined in Sentence 4.1.7.3.(1), determined in the same manner as for the roof cladding,
• E =edge factor, as provided in Sentence (4), and
• ${\gamma }_a$ = pressure equalization factor, as provided in Sentence (3).

3. The pressure equalization factor, ${\gamma }_a$ , in Sentence (2) shall be
   1. for a panel or an array where the panel chord length, L_p, is greater than 2 m or for a panel or an array that is within a distance of 2 h₂ from the roof edge or ridge, where h₂ is the height of the panel's highest point above the roof surface, taken as 1.0, and
   2. for other panels or arrays, determined from Figure 4.1.7.13.-A based on the area of the panel or array over which the wind load is being calculated.

4. The edge factor, E, in Sentence (2) shall be taken as
   1. 1.5 within a distance of 1.5 L_p from an exposed edge of the array of solar panels, as defined in Sentence (5), and
   2. 1.0 elsewhere.
5. For the purposes of Clause (4)(a), an exposed edge of the array of solar panels shall be considered to occur
   1. where the distance to the next row of panels or the distance across a gap in the same row of panels exceeds 4 h₂ or 1.2 m, whichever is greater, or
   2. where the distance to the roof edge exceeds 4 h₂ or 1.2 m, whichever is greater, and exceeds 0.5 h, where h is the reference height of the roof.
6. For an array of solar panels mounted on a roof with a slope, $\alpha$ , less than or equal to $7^{°}$ , where the panels are tilted relative to the roof surface, have a chord length, $L_p$ , not greater than 2 m, and are installed such that the height of their lowest point above the roof surface, $h_1$ , is not greater than 0.6 m, the height of their highest point above the roof surface, $h_2$ , is not greater than 1.2 m, and their tilt angle relative to the roof surface, $\omega$ , is not greater than 35°, or where the panels are installed parallel to the roof surface with their upper surface greater than 250 mm above the roof surface and with gaps not less than 6 mm between the panels, the net positive or negative pressure difference between the upper and the lower surfaces of a panel or the array shall be calculated as follows:

where

• $I_W$ , q, $C_e$ , $C_t$ = as defined in Sentence 4.1.7.3.(1), determined in the same manner as for the roof cladding, and ${\left(C_g{C}_p\right)}_{net}$ = net gust pressure coefficient, as provided in Sentence (7).

7. The net gust pressure coefficient, ${\left(C_g{C}_p\right)}_{net}$ , in Sentence (6) shall be calculated as follows:

where

• ${\gamma }_p$ = parapet factor, determined as the lesser of 1.2 and (0.9 + h_pt/h),
• ${\gamma }_c$ = chord factor, determined as the greater of $(0.6+0.2L_p)$ and 0.8,
• E = as defined in Sentence (2), and
• (C_gC_p)_n = normalized gust pressure coefficient, determined from Figure 4.1.7.13.-B based on ω and A_N,

where

• $h_{pt}$ = height of the parapet above the roof surface, in m, h = reference height of the roof, in m,
• $L_p$ = panel chord length, in m,
• $\omega$ = panel tilt angle relative to the roof surface, and
• $A_N$ = normalized panel or array area, calculated as $A_N=\frac{1000A}{max(L_h^2,25)}$

where

• $A={\text{panel or array area over which the wind load is being calculated, in m}}^2$ , and
• $L_b$ = normalized building length, in m, determined as the lesser of $\left(0.4\sqrt{h{W}_L}\right)$ , h and $W_S$ ,

where

• W_L = longest horizontal dimension of the building, in m, and
• $W_S$ = smallest horizontal dimension of the building, in m.

Notes to Figure 4.1.7.13.-B:

1. H = height of the building.
2. h = reference height of the roof.
3. (C_gC_p)_n values are for both positive and negative values.
4. For panels with 5° < w < 15°, linear interpolation is permitted.

4.1.7.14. Wind Tunnel Procedure

1. Except as provided in Sentences (2) and (3), wind tunnel tests on scale models to determine wind loads on buildings shall be conducted in accordance with ASCE/SEI 49, "Wind Tunnel Testing for Buildings and Other Structures."
2. Where an adjacent building provides substantial sheltering effect, the wind loads for the main structural system shall be no lower than 80% of the loads determined from tests referred to in Sentence (1) with the effect of the sheltering building removed as applied to
   1. the base shear force for buildings with ratio of height to minimum effective width, as described in Sentence 4.1.7.2.(2), less than or equal to 1.0, or
   2. the base moment for buildings with a ratio of height to minimum effective width greater than 1.0.
3. For the design of cladding and secondary structural members, the exterior wind loads determined from the wind tunnel tests shall be no less onerous than those determined by analysis in accordance with Article 4.1.7.3. using the following assumptions:
   1. $C_g=2.5$ and $C_p=\pm 0.72$ , where the building's height is greater than 20 m or greater than its minimum effective width, and
   2. $C_g{C}_p=80\%$ of the values for zones w and r provided in Article 4.1.7.6., where the building's height is less than or equal to 20 m and no greater than its minimum effective width.

4.1.8. Earthquake Load and Effects

4.1.8.1. Analysis

1. Except as permitted in Sentence (2), the deflections and specified loading due to earthquake motions shall be determined according to the requirements of Articles 4.1.8.2. to 4.1.8.23.
2. Where $I_E{F}_s{S}_a(0.2,X_{450})$ and $I_E{F}_s{S}_a(2.0,X_{450})$ are less than 0.16 and 0.03 respectively, the deflections and specified loading due to earthquake motions are permitted to be determined in accordance with Sentences (3) to (15), where
   1. I_E is the earthquake importance factor and has a value of 0.8, 1.0, 1.3 and 1.5 for buildings in the Low, Normal, High and Post-disaster Importance Categories respectively,
   2. $F_s$ is the site coefficient based on the average ${\overline{N}}_{60}$ or ${\overline{s}}_u$ , as defined in Article 4.1.8.2., for the top 30 m of soil below the footings, pile caps or mat foundations and has a value of
      1. 1.0 for rock sites or when ${\overline{N}}_{60}>50$ or ${\overline{s}}_u>100$ kPa,
      2. 1.6 when $15\le {\overline{N}}_{60}\le 50$ or $50\text{kPa}\le {\overline{s}}_u\le 100\text{kPa}$ , and
      3. 2.8 for all other cases, and
   3. S_a(T, X₄₅₀) is the 5%-damped spectral acceleration value at period T for site designation X₄₅₀, as defined in Article 4.1.8.2., determined in accordance with Subsection 1.1.3. and corresponding to a 2% probability of exceedance in 50 years.
3. The structure shall have a clearly defined
   1. seismic force resisting system (SFRS) to resist the earthquake loads and their effects, and
   2. load path (or paths) that will transfer the inertial forces generated in an earthquake to the supporting ground.
4. An unreinforced masonry SFRS shall not be permitted where
   1. $I_E$ is greater than 1.0, or
   2. the height above grade is greater than or equal to 30 m.
5. The height above grade of an SFRS designed in accordance with CSA S136, "North American Specification for the Design of Cold-Formed Steel Structural Members (using the Appendix B provisions applicable to Canada)," shall be less than 15 m.
6. Earthquake forces shall be assumed to act horizontally and independently about any two orthogonal axes.
7. The specified lateral earthquake force, $V_s$ , at the base of the structure in the direction under consideration shall be calculated as follows:

where

• $S_a(T,X_{450})=\text{value of}{S}_a(T,X_{450})\text{determined by linear interpolation between the values of}{S}_a(0.2,X_{450}),S_a(0.5,X_{450})\text{and}{S}_a(1.0,X_{450}),$
• $=S_a(0.2,X_{450})$ for $T_s\le 0.2$ s, and
• $=S_a(1.0,X_{450})\text{for}{T}_s\ge 1.0\text{s},$
• $W=sumof{W}_i$ over the height of the building, where $W_i$ is defined in Article 4.1.8.2., and
• $R_s=1.5$ , except $R_s=1.0$ for structures where the storey strength is less than that in the storey above and for an unreinforced masonry SFRS,

where

• T_s = fundamental lateral period of vibration of the building, as defined in Article 4.1.8.2.,
• = $0.085\left(h_n\right)3/4$ for steel moment frames,
• = $0.075{\left(h_n\right)}^{3/4}$ for concrete moment frames,
• = 0.1N for other moment frames,
• $=0.025h_n$ for braced frames, and
• = $0.05{\left(h_n\right)}^{3/4}$ for shear walls and other structures,

where

• $h_n$ = height, in m, above the base to level n, as defined in Article 4.1.8.2., and
• N = total number of storeys above exterior grade to level n, as defined in Article 4.1.8.2.,

except that, in cases where $R_s=1.5$ , $V_s$ need not be greater than $F_s{S}_a{(0.5,X_{450})I_{E}W/R_s}^{}$ .

8. The total lateral earthquake design force, $V_s$ , shall be distributed over the height of the building in accordance with the following formula:

where

• $F_x$ = force applied through the centre of mass at level x,
• $W_x,W_i=\text{portion of}W\text{that is located at or is assigned to level}x\text{or i respectively, and}$
• $h_x$ , $h_i$ = height, in m, above the base to level x or i respectively, as defined in Article 4.1.8.2.

9. Accidental torsional effects applied concurrently with $F_x$ shall be considered by applying torsional moments about the vertical axis at each level for each of the following cases considered separately:
   1. $+0.1D_{nx}{F}_x$ , and
   2. $-0.1D_{nx}{F}_x$ .
10. Deflections obtained from a linear analysis shall include the effects of torsion and be multiplied by $R_s/I_E$ to get realistic values of expected deflections.
11. The deflections referred to in Sentence (10) shall be used to calculate the largest interstorey deflection, which shall not exceed
    1. 0.01 h_s for post-disaster buildings,
    2. 0.02 h_s for High Importance Category buildings, and
    3. $0.025h_s$ for all other buildings,

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

12. When earthquake forces are calculated using $R_s=1.5$ , the following elements in the SFRS shall have their design forces due to earthquake effects increased by 33%:
    1. diaphragms and their chords, connections, struts and collectors,
    2. tie downs in wood or drywall shear walls,
    3. connections and anchor bolts in steel- and wood-braced frames,
    4. connections in precast concrete, and
    5. connections in steel moment frames.
13. Except as provided in Sentence (14), where cantilever parapet walls, other cantilever walls, exterior ornamentation and appendages, towers, chimneys or penthouses are connected to or form part of a building, they shall be designed, along with their connections, for a lateral force, $V_{sp}$ , distributed according to the distribution of mass of the element and acting in the lateral direction that results in the most critical loading for design using the following equation:

where

• $W_p$ = weight of a portion of a structure as defined in Article 4.1.8.2.

14. The value of V_sp shall be doubled for unreinforced masonry elements.
15. Structures designed in accordance with this Article need not comply with the seismic requirements stated in the applicable design standard referenced in Section 4.3.

4.1.8.2. Notation

1. In this Subsection,

• $A_r$ = element or component force amplification factor to account for type of attachment, as defined in Sentence 4.1.8.18.(1),
• $A_x$ = height factor at level x to account for variation of response of an element or component with elevation within the building, as defined in Sentence 4.1.8.18.(1),
• $B_x$ = ratio at level x used to determine torsional sensitivity, as defined in Sentence 4.1.8.11.(10),
• $B$ = maximum value of $B_x$ , as defined in Sentence 4.1.8.11.(10),
• C_p = seismic coefficient for an element or component, as defined in Sentence 4.1.8.18.(1),
• D_nx = plan dimension of the building at level x perpendicular to the direction of seismic loading being considered,
• $e_x$ = distance measured perpendicular to the direction of earthquake loading between centre of mass and centre of rigidity at the level being considered, (See Note A-4.1.8.2.(1))
• F_a = acceleration-based site coefficient for application in standards referenced in Subsection 4.1.8., as defined in Sentence 4.1.8.4.(7),
• $F_s$ = site coefficient as defined in Sentence 4.1.8.1.(2) for application in Article 4.1.8.1.,
• $F_t$ = portion of V to be concentrated at the top of the structure, as defined in Sentence 4.1.8.11.(7),
• $F_v$ = velocity-based site coefficient for application in standards referenced in Subsection 4.1.8., as defined in Sentence 4.1.8.4.(7),
• $F_x$ = lateral force applied to level x, as defined in Sentence 4.1.8.11.(7),
• $h_i$ , $h_n$ , $h_x$ = height, in m, above the base (i = 0) to level i, n, or x respectively, where the base of the structure is the level at which horizontal earthquake motions are considered to be imparted to the structure,
• $h_s$ = interstorey height ( $h_i-h_{i-1}$ ),
• $I_E$ = earthquake importance factor of the structure, as described in Sentence 4.1.8.5.(1),
• J = numerical reduction coefficient for base overturning moment, as defined in Sentence 4.1.8.11.(6),
• $J_x$ = numerical reduction coefficient for overturning moment at level x, as defined in Sentence 4.1.8.11.(8),
• Level i = any level in the building, i = 1 for first level above the base,
• Level n = level that is uppermost in the main portion of the structure,
• Level x =level that is under design consideration,
• $M_v$ = factor to account for higher mode effects on base shear, as defined in Sentence 4.1.8.11.(6),
• $M_x$ = overturning moment at level x, as defined in Sentence 4.1.8.11.(8),
• N = total number of storeys above exterior grade to level n,
• $N_{60}$ = average standard penetration resistance, in blows per 0.3 m, in the top 30 m of soil, corrected to a rod energy efficiency of 60% of the theoretical maximum,
• PGA(X) = peak ground acceleration, expressed as a ratio to gravitational acceleration, for site designation X, as defined in Sentence 4.1.8.4.(1),
• PGV(X) = peak ground velocity, in m/s, for site designation X, as defined in Sentence 4.1.8.4.(1),
• PI = plasticity index for soil,
• R_d = ductility-related force modification factor reflecting the capability of a structure to dissipate energy through reversed cyclic inelastic behaviour, as defined in Article 4.1.8.9.,
• R_o = overstrength-related force modification factor accounting for the dependable portion of reserve strength in a structure designed according to these provisions, as defined in Article 4.1.8.9.,
• R_p = element or component response modification factor, as defined in Sentence 4.1.8.18.(1),
• R_s = combined overstrength and ductility-related modification factor, as defined in Sentence 4.1.8.1.(7), for application in Article 4.1.8.1.,
• $S_a(T,X)=5\%$ -damped spectral acceleration, expressed as a ratio to gravitational acceleration, at period T for site designation X, as defined in Sentence 4.1.8.4.(1),
• SC = Seismic Category assigned to a building based on its Importance Category and the design spectral acceleration values at periods of 0.2 s and 1.0 s, as defined in Article 4.1.8.5.,
• SFRS = seismic force resisting system, that part of the structural system that has been considered in the design to provide the required resistance to the earthquake forces and effects defined in Subsection 4.1.8.,
• $S_p$ = horizontal force factor for part or portion of a building and its anchorage, as given in Sentence 4.1.8.18.(1),
• S(T) = design spectral acceleration, expressed as a ratio to gravitational acceleration, at period T, as defined in Sentence 4.1.8.4.(6),
• ${\overline{S}}_{ij}$ = average undrained shear strength, in kPa, in the top 30 m of soil,
• T = period, in s,
• T_a = fundamental lateral period of vibration of the building or structure, in s, in the direction under consideration, as defined in Sentence 4.1.8.11.(3),
• TDD = total design displacement of any point in a seismically isolated structure, within or above the isolation system, obtained by calculating the mean + ( $I_E\times$ the standard deviation) of the peak horizontal displacements from all sets of ground motion time histories analyzed, but not less than $\sqrt{I_E\times }$ the mean, where the peak horizontal displacement is based on the vector sum of the two orthogonal horizontal displacements considered for each time step,
• $T_s$ = fundamental lateral period of vibration of the building or structure, in s, in the direction under consideration, as defined in Sentence 4.1.8.1.(7),
• $T_x$ = floor torque at level x, as defined in Sentence 4.1.8.11.(11),
• V = specified lateral earthquake force at the base of the structure, as determined in Article 4.1.8.11.,
• $V_d$ = specified lateral earthquake force at the base of the structure, as determined in Article 4.1.8.12.,
• V_e = lateral earthquake elastic force at the base of the structure, as determined in Article 4.1.8.12.,
• $V_{ed}$ = adjusted lateral earthquake elastic force at the base of the structure, as determined in Article 4.1.8.12.,
• V_p = specified lateral earthquake force on an element or component, as determined in Article 4.1.8.18.,
• $V_s$ = specified lateral earthquake force at the base of the structure, as determined in Sentence 4.1.8.1.(7), for application in Article 4.1.8.1.,
• $V_{s30}$ = average shear wave velocity, in m/s, in the top 30 m of soil or rock,
• W = specified dead load, as defined in Article 4.1.4.1., except that the minimum partition weight as defined in Sentence 4.1.4.1.(3) need not exceed 0.5 kPa, plus 25% of the specified snow load as defined in Subsection 4.1.6., plus 60% of the storage load for areas used for storage, except that storage garages need not be considered storage areas, and the full contents of any tanks, (See Note A-4.1.8.2.(1))
• $W_i$ , $W_x$ = portion of W that is located at or is assigned to level i or x respectively,
• W_p = weight of a part or portion of a structure, e.g., cladding, partitions and appendages,
• X =site designation, either $X_V$ or $X_S$ ,
• X_S = site designation in terms of Site Class, where S is the Site Class determined in accordance with Sentence 4.1.8.4.(3),
• $X_V$ = site designation in terms of $V_{s30}$ , where V is the $V_{s30}$ value calculated from in situ measurements of shear wave velocity,
• $X_{450}$ = site designation $X_V$ with $V_{s30}=450$ m/s,
• ${\delta }_{ave}$ = average displacement of the structure at level x, as defined in Sentence 4.1.8.11.(10), and
• ${\delta }_{\text{max}}$ = maximum displacement of the structure at level x, as defined in Sentence 4.1.8.11.(10).

4.1.8.3. General Requirements

1. The building shall be designed to meet the requirements of this Subsection and of the design standards referenced in Section 4.3.
2. Structures shall be designed with a clearly defined load path, or paths, that will transfer the inertial forces generated in an earthquake to the supporting ground.
3. The structure shall have a clearly defined SFRS, as defined in Article 4.1.8.2.
4. The SFRS shall be designed to resist 100% of the earthquake loads and their effects. (See Note A-4.1.8.3.(4))
5. All structural framing elements not considered to be part of the SFRS must be investigated and shown to behave elastically or to have sufficient non-linear capacity to support their gravity loads while undergoing earthquake-induced deformations calculated from the deflections determined in Article 4.1.8.13.
6. Stiff elements that are not considered part of the SFRS, such as concrete, masonry, brick or precast walls or panels, shall be
   1. separated from all structural elements of the building such that no interaction takes place as the building undergoes deflections due to earthquake effects as calculated in this Subsection, or
   2. made part of the SFRS and satisfy the requirements of this Subsection. (See Note A-4.1.8.3.(6))
7. Stiffness imparted to the structure from elements not part of the SFRS, other than those described in Sentence (6), shall not be used to resist earthquake deflections but shall be accounted for
   1. in calculating the period of the structure for determining forces if the added stiffness decreases the fundamental lateral period by more than 15%,
   2. in determining the irregularity of the structure, except the additional stiffness shall not be used to make an irregular SFRS regular or to reduce the effects of torsion, and (See Note A-4.1.8.3.(7)(b) and (c))
   3. in designing the SFRS if inclusion of the elements not part of the SFRS in the analysis has an adverse effect on the SFRS. (See Note A-4.1.8.3.(7)(b) and (c))
8. Structural modeling shall be representative of the magnitude and spatial distribution of the mass of the building and of the stiffness of all elements of the SFRS, including stiff elements that are not separated in accordance with Sentence 4.1.8.3.(6), and shall account for
   1. the effect of cracked sections in reinforced concrete and reinforced masonry elements,
   2. the effect of the finite size of members and joints,
   3. sway effects arising from the interaction of gravity loads with the displaced configuration of the structure, and
   4. other effects that influence the lateral stiffness of the building.