A measure for multiple bends and shear damage of RC rigid-frame bridge tall piers: application to seismic fragility analysis

Abstract

Abstract The reinforced-concrete (RC) rigid-frame bridges with tall hollow piers were widely constructed in Southwestern China with many seismic activities. For such bridges, the seismic damages would be underestimated because of the tall piers’ multiple bends caused by their high-mode shapes that can be activated under earthquakes. Moreover, the seismic damage assessment can be incorrect if we ignore the tall piers’ shear damages caused by their vastly weakened sectional areas and multiple bends. With this respect, this paper presents a fragility analysis for such bridges. A novel seismic damage measure (piecewise drift ratio, PDR) involving shear effects and multiple bends is proposed and experimentally validated. Damage states congruent to the PDR are provided by statistically acquiring from the 40 existing tests of hollow piers. A finite element (FE) model of an RC rigid-frame bridge with two tall piers was established and adequately calibrated based on the model-updating hybrid tests. To provide more comprehensive assessments of the damage measures and the seismic fragility, the ground motions were selected and divided into four categories by identifying their first two frequencies and their amplitude ratio. Both the 5% damped spectral acceleration of the fundamental period (Sa(T1, 5%)) and the peak ground acceleration (PGA) are adopted as the demand parameter to develop the seismic demand models (PSDMs). Results show the effectiveness of the proposed PDR, provide the more adverse types of ground motions, and reveal the high exceedance probability of the complete damage state of tall piers.