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The seismic hazard caused by ground shaking is defined for any Seismic Hazard Level using approved 5% damped response spectrum ordinates for short (0.2 s) and long (1 s) periods, in the direction of maximum horizontal response. QuakeManager computes the design short-period spectral response acceleration parameter, SXS, and the design long-period response acceleration parameter, SX1, as follows:
•SXS = FaSS .......... Eq (2-1)
•SX1 = FvS1 .......... Eq (2-2)
where Fa and Fv are site coefficients determined respectively from tables below, based on the site class and the values of the response acceleration parameters SS and S1 for the selected return period.
Table: Site Coefficient Fa (ASCE/SEI 41-13)
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Table: Site Coefficient Fv (ASCE/SEI 41-13)
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If the site soil class data is unavailable or insufficient, site class ""D" may b taken as the default site class. However, if evidences of soft clays characteristics are available, then site class "E" may be taken as the default site class.
General Response Spectrum
QuakeManager develops the response spectrum similarly to Section 11.4.6 of ASCE 7 (Sa v/s T) but with replacing SDS and SD1 with SXS/B1 and SX1/B1 respectively. For T<T0, QuakeManaher evaluates Sa by interpolating between 0.4SXS and SXS/B1 between 0 and T0 where B1 = 4÷[5.6 - ln100β] and β is the effective viscous damping. Figure below illustrates how QuakeManager develops the spectra:
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where:
•T0 = 0.2 (SDS ÷ SD1)
•TS = (SDS ÷ SD1)
•TL = long-period transition period (s)
•B1 = 4/[5.6 − ln(100β)]
General Vertical Response Spectrum
According to section 2.4.1.7.2:
If a vertical response spectrum is required for analysis, it may be developed by taking two-thirds of the maximum horizontal spectral ordinate, at each period, obtained for the horizontal response spectrum or by alternative rational procedures.
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