Exploratory study on the applicability of the capacity spectrum method on bridge pile groups

Abstract

The paper presents a feasibility study on the Capacity Spectrum Method (CSM) (widely used in structural design), applied on Soil-Structure Interaction (SSI) systems. A bridge pier founded on two distinct Reinforced Concrete (RC) pile groups, is employed as an illustrative example. Finite Element (FE) models are used to perform (monotonic and cyclic) static pushover and nonlinear time-history analyses. The CSM method predicts the seismic performance of the studied system by comparing the capacity to the demand diagram. The first corresponds to the monotonic pushover analysis, while the latter is the combined acceleration-displacement elastic spectrum of each input motion. The intersection of the two curves represents the expected performance point. Iterations, required to account for increased damping of the SSI system, are possible using the results of the cyclic pushover analyses. The predictions of the CSM method are comparatively assessed to the results of nonlinear FE time-history analysis and are shown to be in good agreement. Thus, the application of the CSM for the design of bridges on pile groups is considered promising. Allowing for parametric investigations, such an approach can contribute towards performance-based design, as an alternative to the computationally demanding time-history analyses.