Site Factors and Site Categories in Seismic Codes

Abstract

The overall objective of the task reported was to provide a detailed evaluation and assessment of the site coefficients contained in the 1994 NEHRP provisions for the seismic design of buildings in light of data provided by recent strong motion records obtained during the 1994 Northridge and 1995 Kobe earthquakes. It was found that site coefficients back-calculated from recordings of the Northridge earthquake validated the 1994 NEHRP values quite well. These site coefficients reflect a broad consensus of the geotechnical engineering and earth science communities and constitute a significant improvement over provisions contained in older codes and specifications. The authors recommend that the current AASHTO "Standard Specifications for Highway Bridges" and AASHTO "LRFD Bridge Design Specifications" be upgraded to be consistent with the 1994 and 1997 NEHRP and 1997 UBC provisions for site categories and coefficients.