Reduction of Seismic Acceleration Parameters for Temporary Bridge Design

Abstract

No prevailing method is currently available for reducing the seismic response acceleration parameters PGA, SS, and S1 from the probabilistic seismic hazard values used for permanent bridge design to levels suitable for temporary bridge design. A method of spectral reduction using spectral reduction factors was proposed to reduce the previously published spectral response acceleration parameters, the peak ground acceleration (PGA), the short-period response acceleration coefficient (Ss), and the long-period response acceleration coefficient (S1), from the 1,-year return period used for permanent bridge design to a return period suitable for temporary bridge design. The proposed spectral reduction factors are the ratios of the return period used for the seismic design of a permanent bridge to the return period used for the seismic design of a temporary bridge. Spectral ratios were obtained for each of the three seismic response acceleration coefficients for 1 locations around the United States. The examination of the short- and long-period response acceleration coefficients are presented in this paper. As a result of this examination, two spectral reduction factors for the seismic design of temporary bridges were proposed: one spectral reduction factor, of 2.5, to reduce each PGA, SS, and S1 parameter for the western United States, and one spectral reduction factor, of 3.75, to reduce each PGA, SS, and S1 parameter for the central and eastern United States.