Reduction of seismic input motion through adjusting contact length of foundation side walls to surrounding medium

Abstract

SummaryThis study reviews possibilities of reducing the ordinates of foundation input motion by dictating partial contact of foundation side walls to surroundings. Here, the foundation is considered as a strip embedded inclusion with variable contact length to nearby medium. A newly proposed net input motion that replaced horizontal and rotational input motions with a single horizontal history is considered as the controlling record to explore the partial contact effects. The analysis is done in two stages using finite element method. First, in frequency domain, kinematic transfer functions are examined. Then iso‐valued spectral representation of seismic input modifications, on account of incomplete contact factor, is explored. The results show that for contact length of about half of the foundation depth, response spectra reach the lowest values with respect to other ratios of contact length. At last, as a sample, the input motion at different levels of main pier of San Francisco Bay Bridge is investigated. Three states of full, partial, and zero contact of foundation perimeter to nearby medium are considered, and total acceleration, total displacement, and relative displacements are reported. The results show the beneficial effect of partial contact to reduce the intensity of foundation input motion.