Effect of near-fault ground motions on seismic response of deep basement walls

Abstract

The current state of practice for seismic design of basement walls in British Columbia is using the Mononobe-Okabe (M-O) method, which is based on the Peak Ground Acceleration (PGA). Preliminary results from a recent study of the authors show that the designed walls based on the M-O method with the code mandated PGA for Vancouver are too conservative. This conclusion was achieved by designing the basement wall for the earth pressures derived from the M-O method with different fraction of the code PGA, then subjecting the designed walls to ground motions matched to the UHS of Vancouver in a series of dynamic analyses, and monitoring the performance of the walls from results of the analyses. It was found that walls designed for the M-O pressures based on 50-60% PGA in Vancouver result in satisfactory performance in terms of moment, shear capacity, and drift ratio along the height of the wall, when subjected to ground motions with a 2% exceedance rate in 50 years. This conclusion was based on the use of far-fault motions for analysis. The objective of the present study is to check whether such walls would be safe when subjected to near-fault motions of approximately similar intensity.