Influence of Bidirectional Near-Fault Excitations on RC Bridge Piers

Abstract

Lateral load-resisting structural members, such as piers, are often analyzed under one component base excitation. The influence of bidirectional shaking is accounted for by using a simplified 30% rule. During seismic shaking, piers are often subjected to bidirectional ground motion, which leads to a complex combination of biaxial moments. In this backdrop, a RC bridge pier has been analyzed under a set of bidirectionally applied near-field motions with forward directivity (FD) and fling-step characteristics. Bidirectional interaction under near-fault motion is observed to substantially amplify damage, particularly for a stiff system (30% and 45%–50% under FD and fling motions, respectively). A complex combination of bidirectional load paths may have also contributed to increased vulnerability. Additional studies have shown that pulses with fling-step characteristics may often be more detrimental than FD, at least for the first mode-dominated systems. The roles of important ground-motion parameters, such as Arias intensity, mean period, and significant duration, that regulate this interaction effect are discussed. Using energetic length and mean period as characteristic linear and time dimensions, a self-similar response scenario has emerged even when degradation, complex loading patterns under bidirectional shaking, and record-to-record variability coexisted. Geometric nonlinearity in the presence of an axial force may have intensified the interaction effect, as revealed through a sample code-designed pier.