Evaluation of a Substitute Structure Method to Estimate Seismic Displacement Demand in Piers and Wharves

Abstract

This paper compares seismic displacement from the MOTEMS and the ASCE/COPRI 61-14 substitute structure method (SSM) with results from the nonlinear response history analysis (NLRHA). It is found that the SSM is biased toward overpredicting displacement demand for short-period systems and under-predicting displacement demand for long-period systems. The overprediction was found to be excessive for very-short period systems (i.e., systems with periods shorter than the period at which the design spectrum transitions from linearly increasing spectral acceleration to constant spectral acceleration). It is recommended that the SSM not be used for such systems. It is also recommended that the SSM not be used for long-period systems (i.e., systems with periods longer than the period at which the design spectrum transitions from constant spectral acceleration to constant spectral velocity), where it underpredicts displacement demand and may lead to unconservative design. The SSM provides reasonable results (within 20% of results from NLRHA) for systems with periods in the constant spectral acceleration region of the design spectrum.