Comparison of the Seismic Design Procedures of ASCE 7-16 With Non-Ergodic Site Response Analyses

Date: 4/25/2019

Time: 04:15 PM

Room: Pine

In an effort to address a shortcoming of ASCE 7-10 related to equivalent lateral force and modal response spectrum procedures for design of long period buildings on soft-soil sites, ASCE 7-16 enforces new criteria for development of risk-targeted maximum rotated (MCE_R) and design earthquake (DE) response spectra to capture the missing long period amplification. These modifications include, but are not limited to, the following cases:

Modified site-speicfic analysis requirements for Site Classes D and E

Modified deterministic lower limit spectrum

Modified design acceleration parameters

The modifications are based on a series of ergodic site-specific deterministic seismic hazard analyses (SHA) and a limited number of probabilistic SHA as described in Kircher (2015). This study found that the shapes of the response spectra were not accurately represented by the shape of the design response spectrum of ASCE 7-10 Figure 11.4-1 for the following condition: (1) Site Class D where S₁>= 0.2; and (2) Site Class E where S_S>= 1.0 and/or S₁>= 0.2. Therefore, specturm adjustment factors developed by Kircher (2015) were implemented in Chapter 21 of ASCE 7-16 to adjust the previously underestimated spectral accelerations at long periods. These modifications are an interim solution until multi-period MCE_R and DE spectra directly incorporate site, basin, and other effects that influence the shape of the spectra.

We report results of SHA performed for multiple structures in the San Francisco Bay Area, using non-ergodic site response models as described in Stewart et al. (2017). These analyses replace global site amplification functions used in ground motion models with site-specific amplification functions derived from evaluation of local ground motion records and deep ground response analyses. Similar to Kircher (2015), results of our analyses confirm the shortcoming of ASCE 7-10 at long periods. However, our analyses indicate that modified guidelines of ASCE 7-16 sometimes overestimate spectral acceleration below the site period and underestimate it at higher periods.

Presenting Author: David P. Teague

Authors