A measure for seismic multiple bends and shear damage patterns of RC rigid-frame bridge tall piers

Reinforced concrete (RC) rigid-frame bridges with tall hollow piers were widely constructed in Southwestern China, an earthquake-prone area. For such bridges, the seismic damages may be underestimated if multiple bends of tall piers are overlooked using a conventional damage measure such as the drift ratio. Moreover, the seismic damage assessment can be inaccurate if tall piers’ shear damages are ignored using the sectional curvature as a damage measure. Along these lines, this paper proposes a novel seismic damage measure, the piecewise drift ratio (PDR), involving both shear effects and multiple-bend deformations; it has been validated by hybrid tests and analyzed employing fragility curves. Damage state limits represented by the PDR are estimated through statistical analysis of the 40 existing tests of hollow piers. To validate the PDR, a finite element model of an RC rigid-frame bridge with two tall piers was established and adequately calibrated based on model-updating hybrid simulations. To comprehensively evaluate the PDR, ground motions were selected and grouped into four categories by identifying their first two-class nature frequency and their amplitude ratio; to determine fragility curves, both the spectral acceleration at the fundamental period with 5% damping, S_a(T₁, 5%), and the peak ground acceleration have been adopted as intensity measures. Results show the effectiveness of the proposed PDR, provide a more severe ground motion for assessment, and reveal the high exceedance probability of the complete damage state of tall piers under some potential seismic scenarios.