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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 section 11.4 of ASCE 7.
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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Figure: Spectra Development
where:
•T0 = 0.2 (SDS ÷ SD1)
•TS = (SDS ÷ SD1)
•TL = long-period transition period (s)
•B1 = 4/[5.6 − ln(100β)]
Based on the Section 2.4, Site-Specific Spectra may be performed in the following conditions:
1.The structure is located on Site Class "E" with mapped spectral response acceleration at short periods (SXS) exceeding 2.0
2.The structure is located on Site Class "F"
3.The BSE-2N or BSE-1N hazard parameters are determined and Section 11.4.7 of ASCE 7 requires that site-specific ground motion procedure be used to determine the MCER parameters.
Additionally, if SS < 0.2 for a structure located on Site Class "F", engineers can utilize a Site Class "E" soil profile without performing site-specific spectra.
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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