Site-Specific Seismic Ground Motion Analyses for Transportation Infrastructure in the New Madrid Seismic Zone.

摘要

Generic, code-based design procedures cannot account for the anticipated short-period attenuation and long-period amplification of earthquake ground motions in the deep, soft sediments of the Mississippi Embayment within the New Madrid Seismic Zone (NMSZ). As a result, generic, code-based seismic designs may lead to short-period structures being over-designed at a significant cost, and long-period structures being under-designed at a significant risk. For these reasons, AASHTO explicitly recommends site-specific ground motion response analyses for this part of the country. Most bridges constructed by the Arkansas State Highway and Transportation Department (AHTD) within the NMSZ are in the short-period range (i.e., 0.1-0.5 seconds), where site specific analyses can potentially allow engineers to reduce seismic design forces by up to 33% according to AASHTO guidelines. Site-specific ground motion response analyses have been conducted for an example bridge site in Blytheville, AR. Results from the site-specific analyses clearly show that the generic seismic design forces could have been reduced by the AASHTO-allowed 33% if these site-specific analyses had been performed prior to design. Similar results are expected for short-period bridges throughout Northeast Arkansas, where probabilistic seismic hazards are generally dominated by a single earthquake scenario and subsurface conditions are relatively homogenous.