(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 (See Note A-4.1.8.12.(1)(a))
(b)
Non-linear Dynamic Analysis, in which case a special study shall be performed. (See Note A-4.1.8.12.(1)(b))
(2)
The spectral acceleration values used in the Modal Response Spectrum Method shall be the design spectral acceleration values, S(T), defined in Sentence 4.1.8.4.(6).
(3)
The ground motion time histories used in the Numerical Integration Linear Time History Method shall be compatible with a response spectrum constructed from the design spectral acceleration values, S(T), defined in Sentence 4.1.8.4.(6). (See Note A-4.1.8.12.(3).)
(4)
The effects of accidental torsional moments acting concurrently with the lateral earthquake forces that cause them shall be accounted for by the following methods:
(a)
the static effects of torsional moments due to (±0.10Dnx)Fx at each level x, where Fx is either determined from the elastic dynamic analysis or determined from Sentence 4.1.8.11.(7) multiplied by Rd Ro /IE, shall be combined with the effects determined by dynamic analysis, or (See Note A-4.1.8.12.(4)(a))
(b)
if B, as defined in Sentence 4.1.8.11.(10), is less than 1.7, it is permitted to use a three-dimensional dynamic analysis with the centres of mass shifted by a distance of −0.05Dnx and +0.05Dnx.
(5)
Except as provided in Sentence (6), the adjusted elastic base shear, Ved, shall be equal to the elastic base shear, Ve, obtained from a Linear Dynamic Analysis.
(6)
For structures located on a site designated as other than XF that have an SFRS with Rd equal to or greater than 1.5, the elastic base shear obtained from a Linear Dynamic Analysis may be multiplied by the larger of the following factors to obtain the design elastic base shear, Ved:
(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 Rd Ro, as determined in Article 4.1.8.9., to obtain the design base shear, Vd.
(8)
Except as required by Sentence (9) or (12), if the base shear, Vd, obtained in Sentence (7), is less than 80% of the lateral earthquake design force, V, of Article 4.1.8.11., Vd shall be taken as 0.8V.
(9)
For irregular structures requiring dynamic analysis in accordance with Article 4.1.8.7., Vd shall be taken as the larger of Vd, determined in Sentence (7), and 100% of V.
(10)
Except as required by Sentence (11), the values of elastic storey shears, storey forces, member forces, and deflections obtained from the Linear Dynamic Analysis, including the effect of accidental torsion determined in Sentence (4), shall be multiplied by Vd /Ve to determine their design values, where Vd is the base shear.
(11)
For the purpose of calculating deflections, it is permitted to use a value of V based on the value of Ta determined in Clause 4.1.8.11.(3)(d) to obtain Vd in Sentences (8) and (9).
(12)
For buildings constructed with more than 4 storeys of continuous wood construction, having a timber SFRS consisting of shear walls with wood-based panels or braced or moment-resisting frames as defined in Table 4.1.8.9., and whose fundamental lateral period, Ta, is determined in accordance with Clause 4.1.8.11.(3)(d), the design base shear, Vd, shall be taken as the larger of Vd, determined in Sentence (7), and 100% of V. (See Note A-4.1.8.10.(5) and (6))