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January 3, 2025 <br />HWA Project No. 2021-159-21 <br />Geotechnical Engineering Report 14 HWA GEOSCIENCES INC. <br />Port Gardner Storage Facility <br />4.2 SEISMIC DESIGN CRITERIA <br />The structural resiliency of the existing and proposed structures and the site piping will be <br />evaluated using the 2021 International Building Code (IBC), which requires that above-grade <br />structures be designed for the inertial forces induced by a “Maximum Considered Earthquake” <br />(MCE), corresponding to an earthquake with a 2% probability of exceedance in 50 years <br />(approximately 2,475-year return period). <br />As part of the procedure to evaluate seismic forces, the 2021 IBC requires the evaluation of the <br />Seismic Site Class, which categorizes the site based upon the characteristics of the subsurface <br />profile extending to 100 feet below the proposed foundation. Based on the obtained SPT blow <br />counts noted in the boring logs and extrapolated to a depth of 100 feet, the site class classifies as <br />a Site Class “E” soil. However, due to the presence of potentially liquefiable soils, the site <br />qualifies as a Site Class “F” as defined in Table 20.3-1 of ASCE 07-16. The exception in Section <br />20.3.1 of ASCE 07-16 permits the Site Class to be determined in accordance with Section 20.3 <br />and the corresponding values of Fa and Fv determined from Tables 11.4-1 and 11.4-2, provided <br />the fundamental period of the building (T) is less than ½ second. In Section 11.4.8 of ASCE 7- <br />16, it is stated that a site-specific ground motions hazard analysis is required on sites with three <br />additional conditions: <br />1) Seismically isolated structures and structures with dampening systems on site with S1 <br />greater than or equal to 0.6. <br />2) Structures on Site Class E sites with Ss greater than or equal to 1.0. <br />3) Structures on Site Class D and E sites with S1 greater than or equal to 0.2. <br />Condition 1 should be determined by the project structural engineer but is assumed to not apply <br />to the proposed site improvements. Conditions 2 and 3 would necessitate performing a site- <br />specific ground motion hazard analysis on this site; however, three exceptions are provided, in <br />section 11.4.8 of ASCE 7-16, to determine seismic design parameters without performing a site- <br />specific ground motions hazard analysis. These exceptions are: <br />1) Structures on site Class E site with SS greater than or equal to 1.0, provided the site <br />coefficient Fa is taken to be equal to that of Site Class C. <br />2) Structures of Site Class D sites with S1 greater than or equal to 0.2, provided the <br />value of the seismic response coefficient (Cs) is determined by Eq 12.8-2 of ASCE 7- <br />16 for values of T ≤ 1.5Ts and taken as equal to 1.5 times the value computed in <br />accordance with either Equation 12.8-3 of ASCE 7-16 for TL ≥ T > 1.5Ts, or <br />Equation 12.8-4 of ASCE 7-16 for T > TL.