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(1) A building and its structural components shall be designed to have sufficient strength and stability so that the factored resistance, ΦR, is greater than or equal to the effect of factored loads, which shall be determined in accordance with Sentence (2). (2) Except as provided in Sentence (3), the effect of factored loads for a building or structural component shall be determined in accordance with the requirements of this Article and the following load combination cases, the applicable combination being that which results in the most critical effect:
(a) for load cases without crane loads, the load combinations listed in Table 4.1.3.2.A., and
(b) for load cases with crane loads, the load combinations listed in Table 4.1.3.2.B. (3) Other load combinations that must also be considered are the principal loads acting with the companion loads taken as zero. (4) Where the effects due to lateral earth pressure, H, restraint effects from pre-stress, P, and imposed deformation, T, affect the structural safety, they shall be taken into account in the calculations, with load factors of 1.5, 1.0 and 1.25 assigned to H, P and T respectively. (5) Except as provided in Sentence 4.1.8.16. (1), the counteracting factored dead load, 0.9D in load combination cases 2, 3 and 4 and 1.0D in load combination case 5 of Table 4.1.3.2.A. and 0.9D in load combination cases 1 to 5 and 1.0D in load combination case 6 of Table 4.1.3.2.B., shall be used when the dead load acts to resist overturning, uplift, sliding, failure due to stress reversal, and to determine anchorage requirements and the factored resistance of members. (6) The principal-load factor 1.5 for live loads, L in Table 4.1.3.2.A. and LXC in Table 4.1.3.2.B. may be reduced to 1.25 for liquids in tanks. (7) The companion-load factor for live loads, L in Table 4.1.3.2.A. and LXC in Table 4.1.3.2.B. shall be increased by 0.5 for storage areas and for equipment areas and service rooms referred to in Table 4.1.5.3. (8) Except as provided in Sentence (9), the load factor 1.25 for dead load, D, for soil, superimposed earth, plants and trees given in Tables 4.1.3.2.A. and 4.1.3.2.B. shall be increased to 1.5, except that when the soil depth exceeds 1.2 m, the factor may be reduced to 1 + 0.6/hs but not less than 1.25, where hs is the depth of soil in metres supported by the structure. (9) A principal-load factor of 1.5 shall be applied to the weight of saturated soil used in load combination case 1 of Table 4.1.3.2.A. (10) Earthquake load, E, in load combination case 5 of Table 4.1.3.2.A. and case 6 of Table 4.1.3.2.B. includes horizontal earth pressure due to earthquake determined in accordance with Sentence 4.1.8.16. (4). (11) Provision shall be made to ensure adequate stability of the structure as a whole and adequate lateral, torsional and local stability of all structural parts. (12) Sway effects produced by vertical loads acting on the structure in its displaced configuration shall be taken into account in the design of buildings and their structural members.
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(1) Except as required by Clause (2)(b), structures with a Type 6 irregularity, Discontinuity in Capacity – Weak Storey, as described in Table 4.1.8.6., are not permitted unless IEFaSa(0.2) is less than 0.2 and the forces used for design of the SFRS are multiplied by RdRo. (2) Post-disaster buildings shall,
(a) not have any irregularities conforming to Types 1, 3, 4, 5, 7 and 9 as described in Table 4.1.8.6., in cases where IEFaSa(0.2) is equal to or greater than 0.35,
(b) not have a Type 6 irregularity as described in Table 4.1.8.6.,
(c) have an SFRS with an Rd of 2.0 or greater, and
(d) have no storey with a lateral stiffness that is less than that of the storey above it. (3) For buildings having fundamental lateral periods, Ta, of 1.0 s or greater and where IEFvSa(1.0) is greater than 0.25, shear walls that are other than wood-based and form part of the SFRS shall be continuous from their top to the foundation and shall not have irregularities of Type 4 or 5 as described in Table 4.1.8.6. (4) For buildings constructed with more than 4 storeys of continuous wood construction and where IEFaSa(0.2) is equal to or greater than 0.35, timber SFRS of shear walls with wood-based panels, braced frames or moment-resisting frames as defined in Table 4.1.8.9. within the continuous wood construction shall not have irregularities of Type 4 or 5 as described in Table 4.1.8.6.
(4.1) For buildings where IEFaSa(0.2) is equal to or greater than 0.35 or IEFvSa(1.0) is equal to or greater than 0.2 that are constructed with more than 4 storeys of continuous wood construction, timber SFRSs consisting of moderately ductile or limited ductility cross-laminated timber shear walls, platform-type construction, as defined in Table 4.1.8.9., within the continuous wood construction shall not have Type 4, 5, 6, 8, or 9 irregularities as described in Table 4.1.8.6. (5) The ratio, α, for Type 9 irregularity as described in Table 4.1.8.6. shall be determined independently for each orthogonal direction using the following equation:
𝛼 = QG / Qy
where,
QG =gravity-induced lateral demand on the SFRS at the critical level of the yielding system, and
Qy =the resistance of the yielding mechanism required to resist the minimum earthquake loads, which need not be taken less than Ro multiplied by the minimum lateral earthquake force as determined in Article 4.1.8.11. or 4.1.8.12, as appropriate. (6) For buildings with a Type 9 irregularity as described in Table 4.1.8.6. and where IEFaSa(0.2) is equal to or greater than 0.5, deflections determined in accordance with Article 4.1.8.13. shall be multiplied by 1.2. (7) Structures where the value of α, as determined in accordance with Sentence (5), exceeds twice the limits in Table 4.1.8.6. for a Type 9 irregularity, and where IEFaSa(0.2) is equal to or greater than 0.5 are not permitted unless determined to be acceptable based on non-linear dynamic analysis studies.
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(1) The static loading due to earthquake motion shall be determined according to the procedures given in this Article. (2) Except as provided in Sentence (12), the minimum lateral earthquake force, V, shall be calculated using the following formula:
V = S (Ta) MvIEW/ (RdRo)
except,
(a) for walls, coupled walls and wall-frame systems, V shall not be less than,
[[FORCE_FORMULA]] S (4.0) Mv IEW/ (RdRo) (b) for moment-resisting frames, braced frames and other systems, V shall not be less than,
[[FORCE_FORMULA]] S (2.0) Mv IEW/ (RdRo) (c) for buildings located on a site other than Class F and having an SFRS with an Rd equal to or greater than 1.5, V need not be greater than the larger of,
[[FORCE_FORMULA]] (2/3) · S(0.2) · I_E · W / (R_d R_o)
and
[[FORCE_FORMULA]] S (0.5) IEW/ (RdRo)
(3) Except as provided in Sentence (4), the fundamental lateral period, Ta, in the direction under consideration in Sentence (2) shall be determined as,
(a) for moment-resisting frames that resist 100% of the required lateral forces and where the frame is not enclosed by or adjoined by more rigid elements that would tend to prevent the frame from resisting lateral forces, and where hn is in metres,
(i) 0.085 (hn)3/4 for steel moment frames,
(ii) 0.075 (hn)3/4 for concrete moment frames, or
(iii) 0.1 N for other moment frames,
(b) 0.025 hn for braced frames where hn is in metres,
(c) 0.05 (hn)3/4 for shear wall and other structures where hn is in metres, or
(d) other established methods of mechanics using a structural model that complies with the requirements of Sentence 4.1.8.3. (8), except that,
(i) for moment-resisting frames, Ta shall not be taken greater than 1.5 times that determined in Clause (a),
(ii) for braced frames, Ta shall not be taken greater than 2.0 times that determined in Clause (b),
(iii) for shear wall structures, Ta shall not be taken greater than 2.0 times that determined in Clause (c),
(iv) for other structures, Ta shall not be taken greater than that determined in Clause (c), and
(v) for the purpose of calculating the deflections, the period without the upper limit specified in Subclauses (d)(i) to (iv) may be used, except that, for walls, coupled walls and wall-frame systems, Ta shall not exceed 4.0 s, and for moment-resisting frames, braced frames, and other systems, Ta shall not exceed 2.0 s. (4) For single-storey buildings with steel deck or wood roof diaphragms, the fundamental lateral period, Ta, in the direction under consideration is permitted to be taken as,
(a) 0.05 (hn)3/4 + 0.004 L for shear walls,
(b) 0.035 hn + 0.004 L for steel moment frames and steel braced frames, or
(c) the value obtained from methods of mechanics using a structural model that complies with the requirements of Sentence 4.1.8.3. (8), except that Ta shall not be greater than 1.5 times the value determined in Clause (a) or (b), as applicable,
where L is the shortest length of the diaphragm, in m, between adjacent vertical elements of the SFRS in the direction perpendicular to the direction under consideration. (5) The weight, W, of the building shall be calculated using the formula,
[[FORCE_FORMULA]] W = Σ_{i=1}^{n} W_i
(6) The higher mode factor, Mv, and its associated base overturning moment reduction factor, J, shall conform to Tables 4.1.8.11.A. to 4.1.8.11.E. (7) The total lateral seismic force, V, shall be distributed such that a portion, Ft, shall be assumed to be concentrated at the top of the building, where Ft, is equal to 0.07 TaV but need not exceed 0.25 V and may be considered as zero, where the fundamental lateral period, Ta, does not exceed 0.7 s; the remainder, V - Ft, shall be distributed along the height of the building, including the top level, in accordance with the formula,
F_x = (V − F_t) · W_x · h_x / (Σ_{i=1}^{n} W_i h_i)
(8) The structure shall be designed to resist overturning effects caused by the earthquake forces determined in Sentence (7) and the overturning moment at level x, Mx, shall be determined using the formula,
M_x = J_x · Σ_{i=x}^{n} F_i (h_i − h_x)
where,
Jx =1.0 for hx ≥ 0.6hn, and
Jx =J + (1- J)(hx / 0.6hn) for hx,< 0.6hn
where,
J =base overturning moment reduction factor conforming to Table 4.1.8.11. (9) Torsional effects that are concurrent with the effects of the forces mentioned in Sentence (7) and are caused by the simultaneous actions of the following torsional moments shall be considered in the design of the structure according to Sentence (11):
(a) torsional moments introduced by eccentricity between the centres of mass and resistance and their dynamic amplification, and
(b) torsional moments due to accidental eccentricities. (10) Torsional sensitivity shall be determined by calculating the ratio Bx for each level x according to the following equation for each orthogonal direction determined independently:
[[FORCE_FORMULA]] Bx = δmax / δave
where,
B =maximum of all values of Bx in both orthogonal directions, except that the Bx for one-storey penthouses with a weight less than 10% of the level below need not be considered,
δmax =maximum storey displacement at the extreme points of the structure, at level x in the direction of the earthquake induced by the equivalent static forces acting at distances ± 0.10 Dnx from the centres of mass at each floor, and
δave =average of the displacements at the extreme points of the structure at level x produced by the above-mentioned forces. (11) Torsional effects shall be accounted for as follows:
(a) for a building with B ≤1.7 or where IEFaSa(0.2) is less than 0.35, by applying torsional moments about a vertical axis at each level throughout the building, derived for each of the following load cases considered separately,
(i) Tx = Fx(ex + 0.10 Dnx), and
(ii) Tx = Fx(ex – 0.10 Dnx)
where Fx is the lateral force at each level determined according to Sentence (6) and where each element of the building is designed for the most severe effect of the above load cases, or
(b) for a building with B >1.7, in cases where IEFaSa(0.2) is equal to or greater than 0.35, by a Dynamic Analysis Procedure as specified in Article 4.1.8.12. (12) Where the fundamental lateral period, Ta, is determined in accordance with Clause (3)(d) and the building is constructed with more than 4 storeys of continuous wood construction and has a timber SFRS consisting of shear walls with wood-based panels, braced frames or moment-resisting frames as defined in Table 4.1.8.9., the lateral earthquake force, V, as determined in accordance with Sentence (2) shall be multiplied by 1.2 but need not exceed the value determined by using Clause (2)(c).
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(1) Except as provided in Articles 4.1.8.19. and 4.1.8.21., the Dynamic Analysis Procedure shall be in accordance with one of the following methods:
(a) Linear Dynamic Analysis by either the Modal Response Spectrum Method or the Numerical Integration Linear Time History Method using a structural model that complies with the requirements of Sentence 4.1.8.3. (8), or
(b) Non-linear Dynamic Analysis, in which case a special study shall be performed. (2) The spectral acceleration values used in the Modal Response Spectrum Method shall be the design spectral acceleration values, S(T), defined in Sentence 4.1.8.4. (7). (3) The ground motion histories used in the Numerical Integration Linear Time History Method shall be compatible with a response spectrum constructed from the design spectral acceleration values, S(T), defined in Sentence 4.1.8.4. (7). (4) The effects of accidental torsional moments acting concurrently with the lateral earthquake forces that cause them shall be accounted for by the following methods:
(a) the static effects of torsional moments due to (± 0.10 Dnx)Fx at each level x, where Fx is either determined from the elastic dynamic analysis or determined from Sentence 4.1.8.11. (7) multiplied by RdRo/IE, shall be combined with the effects determined by dynamic analysis, or
(b) if B, as defined in Sentence 4.1.8.11. (10), is less than 1.7, it is permitted to use a three-dimensional dynamic analysis with the centres of mass shifted by a distance of – 0.05 Dnx and + 0.05 Dnx. (5) Except as provided in Sentence (6), the design elastic base shear, Ved, is equal to the elastic base shear, Ve, obtained from a Linear Dynamic Analysis. (6) For structures located on sites other than Class F that have an SFRS with Rd equal to or greater than 1.5, the elastic base shear obtained from a Linear Dynamic Analysis may be multiplied by the larger of the following factors to obtain the design elastic base shear, Ved:
[[FORCE_FORMULA]] 2S(0.2)/3S(Ta) ≤ 1.0
and
[[FORCE_FORMULA]] S(0.5) / S(Ta) ≤ 1.0
(7) The design elastic base shear, Ved, shall be multiplied by the importance factor, IE, as determined in Article 4.1.8.5., and shall be divided by RdRo, as determined in Article 4.1.8.9., to obtain the design base shear, Vd. (8) Except as required by Sentence (9) or (12), if the base shear, Vd, obtained in Sentence (7) is less than 80% of the lateral earthquake design force, V, of Article 4.1.8.11., Vd shall be taken as 0.8 V. (9) For irregular structures requiring dynamic analysis in accordance with Article 4.1.8.7., Vd shall be taken as the larger of the Vd determined in Sentence (7) and 100% of V. (10) Except as required by Sentence (11), the values of elastic storey shears, storey forces, member forces, and deflections obtained from the Linear Dynamic Analysis, including the effect of accidental torsion determined in Sentence (4), shall be multiplied by Vd/Ve to determine their design values, where Vd is the base shear. (11) For the purpose of calculating deflections, it is permitted to use a value for V based on the value for Ta determined in Clause 4.1.8.11. (3)(d) to obtain Vd in Sentences (8) and (9). (12) For buildings constructed with more than 4 storeys of continuous wood construction, having a timber SFRS consisting of shear walls with wood-based panels, braced frames or moment-resisting frames as defined in Table 4.1.8.9., and whose fundamental lateral period, Ta, is determined in accordance with Clause 4.1.8.11. (3)(d), the design base shear, Vd, shall be taken as the larger value of Vd determined in accordance with Sentence (7) and 100% of V.
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(1) The increased displacements of the structure resulting from foundation movement shall be shown to be within acceptable limits for both the SFRS and the structural framing elements not considered to be part of the SFRS. (2) Except as provided in Sentences (3) and (4), foundations shall be designed to have factored shear and overturning resistances greater than the lateral load capacity of the SFRS. (3) The shear and overturning resistances of the foundation determined using a bearing stress equal to 1.5 times the factored bearing strength of the soil or rock and all other resistances equal to 1.3 times the factored resistances need not exceed the design forces determined in Sentence 4.1.8.7. (1) using RdRo = 1.0 except that the factor of 1.3 shall not apply to the portion of the resistance to uplift or overturning resulting from gravity loads. (4) A foundation is permitted to have a factored overturning resistance less than the lateral load overturning capacity of the supported SFRS, provided the following requirements are met:
(a) neither the foundation nor the supported SFRS are constrained against rotation, and
(b) the design overturning moment of the foundation is,
(i) not less than 75% of the overturning capacity of the supported SFRS, and
(ii) not less than that determined in Sentence 4.1.8.7. (1) using RdRo = 2.0. (5) The design of foundations shall be such that they are capable of transferring earthquake loads and effects between the building and the ground without exceeding the capacities of the soil and rock. (6) In cases where IEFaSa(0.2) is equal to or greater than 0.35, the following requirements shall be satisfied:
(a) piles or pile caps, drilled piers, and caissons shall be interconnected by continuous ties in no fewer than two directions,
(b) piles, drilled piers, and caissons shall be embedded a minimum of 100 mm into the pile cap or structure, and
(c) piles, drilled piers, and caissons, other than wood piles, shall be connected to the pile cap or structure for a minimum tension force equal to 0.15 times the factored compression load on the pile. (7) At sites where IEFaSa(0.2) is equal to or greater than 0.35, basement walls shall be designed to resist earthquake lateral pressures from backfill or natural ground. (8) At sites where IEFaSa(0.2) is greater than 0.75, the following requirements shall be satisfied:
(a) piles, drilled piers, or caissons shall be designed and detailed to accommodate cyclic inelastic behaviour when the design moment in the element due to earthquake effects is greater than 75% of its moment capacity, and
(b) spread footings founded on soil defined as Site Class E or F shall be interconnected by continuous ties in no fewer than two directions. (9) Each segment of a tie between elements that is required by Clause (6)(a) or (8)(b) shall be designed to carry by tension or compression a horizontal force at least equal to the greatest factored pile cap or column vertical load in the elements it connects, multiplied by a factor of 0.10 IEFaSa(0.2), unless it can be demonstrated that equivalent restraints can be provided by other means. (10) The potential for liquefaction of the soil and its consequences, such as significant ground displacement and loss of soil strength and stiffness, shall be evaluated based on the ground motion parameters referenced in Subsection 1.1.2., as modified by Article 4.1.8.4., and shall be taken into account in the design of the structure and its foundations.
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(1) The period of the isolated structure, determined using the post-yield stiffness of the isolation system in the horizontal direction under consideration, shall be greater than three times the period of the structure above the isolation interface calculated as a fixed base. (2) The isolation system shall be configured to produce a restoring force such that the lateral force at the TDD at the centre of mass of the isolated structure above the isolation interface is at least 0.025Wb greater than the lateral force at 50% of the TDD at the same location, in each horizontal direction, where Wb is the portion of W above the isolation interface. (3) The values of storey shears, storey forces, member forces, and deflections used in the design of all structural framing elements and components of the isolation system shall be obtained from analysis conforming to Sentence 4.1.8.19. (3) using one of the following values, whichever produces the most critical effect:
(a) mean plus IE times the standard deviation of the results of all Non-linear Dynamic Analyses, or
(b) √(I_E) times the mean of the results of all Non-linear Dynamic Analyses. (4) The force-deformation and damping characteristics of the isolation system used in the analysis and design of the seismically isolated structures shall be validated by testing at least two full-size specimens of each predominant type and size of isolator unit of the isolation system, which shall include,
(a) the individual isolator units,
(b) separate supplemental damping devices, if used, and
(c) separate sacrificial wind-restraint systems, if used. (5) The force-deformation characteristics and damping value of a representative sample of the isolator units installed in the building shall be validated by tests prior to their installation. (6) A diaphragm or horizontal structural elements shall provide continuity immediately above the isolation interface to transmit forces due to non-uniform ground motions from one part of the structure to another. (7) All structural framing elements shall be designed for the forces described in Sentence (3) with RdRo= 1.0, except,
(a) for structures with IE < 1.5, all the SFRS shall be detailed in accordance with the requirements for Rd ≥ 1.5 and the applicable referenced design standards, and
(b) for structures with IE = 1.5, all the SFRS shall be detailed in accordance with the requirements for Rd ≥ 2.0 and the applicable referenced design standards. (8) The height restrictions noted in Table 4.1.8.9. need not apply to seismically isolated structures. (9) All isolator units shall be,
(a) designed for the forces described in Sentence (3), and
(b) able to accommodate the TDD determined at the specific location of each isolator unit. (10) The isolation system, including a separate wind-restraint system if used, shall limit lateral displacement due to wind loads across the isolation interface to a value equal to that required for the least storey height in accordance with Sentence 4.1.3.5. (3).
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(1) The values of storey shears, storey forces, member forces, and deflections for the design of all structural framing elements and all supplemental energy dissipation devices shall be obtained from analysis conforming to Sentence 4.1.8.21. (4) using one of the following values, whichever produces the most critical effect:
(a) mean plus IE times the standard deviation of the results of all Non-linear Dynamic Analyses, or
(b) √(I_E) times the mean of the results of all Non-linear Dynamic Analyses. (2) The largest interstorey deflection at any level of the structure as determined in accordance with Sentence (1) shall conform to the limits stated in Sentence 4.1.8.13. (3). (3) The force-deformation and force-velocity characteristics of the supplemental energy dissipation devices used in the analysis and design of structures with supplemental energy dissipation systems shall be validated by testing at least two full-size specimens of each type of supplemental energy dissipation device. (4) The force-deformation and force-velocity characteristics and damping values of a representative sample of the supplemental energy dissipation devices installed in the building shall be validated by tests prior to their installation. (5) Elements of the supplemental energy dissipation system, except the supplemental energy dissipation devices themselves, shall be designed to remain elastic for the design loads. (6) All structural framing elements shall be designed,
(a) for an SFRS with Rd =1.0, using the forces referred to in Sentence (1) with RdRo = 1.0, except that the SFRS shall be detailed in accordance with the requirements for Rd ≥ 1.5 and the applicable referenced design standards, or
(b) for an SFRS with Rd > 1.0, using the forces referred to in Sentence (1) with RdRo = 1.0, except that the SFRS shall be detailed in accordance with the requirements for the selected Rd and the applicable referenced design standards. (7) Supplemental energy dissipation devices and other components of the supplemental energy dissipation system shall be designed in accordance with Sentence (1) with consideration of the following:
(a) low-cycle, large-displacement degradation due to seismic loads,
(b) high-cycle, small-displacement degradation due to wind, thermal, or other cyclic loads,
(c) forces or displacements due to gravity loads,
(d) adhesion of device parts due to corrosion or abrasion, biodegradation, moisture, or chemical exposure,
(e) exposure to environmental conditions, including, but not limited to, temperature, humidity, moisture, radiation (e.g., ultraviolet light), and reactive or corrosive substances (e.g., salt water),
(f) devices subject to failure due to low-cycle fatigue must resist wind forces without slip, movement, or inelastic cycling,
(g) the range of thermal conditions, device wear, manufacturing tolerances, and other effects that cause device properties to vary during the design life of the device, and
(h) connection points of devices must provide sufficient articulation to accommodate simultaneous longitudinal, lateral, and vertical displacements of the supplemental energy dissipation system. (8) Means of access for inspection and removal for replacement of all supplemental energy dissipation devices shall be provided.