On the relevance of incorporating bar slip, bar buckling and low-cycle fatigue effects in seismic fragility assessment of RC bridge piers

Abstract

The paper reports the results of a numerical investigation on the relevance of including bar slip, bar buckling and low-cycle fatigue in seismic fragility assessment of RC bridge piers. The numerical study is completed on a series of well-confined circular RC bridge column with different configurations where the main variables included are the longitudinal reinforcement ratio, the axial load ratio, the spiral reinforcement ratio and the aspect ratio. Moreover, calculations are performed in several options, namely: (i) Model considering perfect bond (ii) Model considering perfect bond + buckling + fatigue (iii) Model incorporating bar slip only (iv) Model incorporating bar slip + buckling and (v) Model incorporating bar slip + buckling + fatigue. The significance of each individual or combined effect is assessed through comparison of the results from two calculation options. The response of the RC bridge is firstly evaluated through cyclic and monotonic analyses giving indication whether its inherent individual or combined effects should be explicitly considered or if it may be neglected in the probabilistic risk assessment analyses. By considering the main conclusions of the preliminary sensitivity study, the fragility curves are the developed using the Performance-Based Earthquake Engineering (PBEE) methodology. The sensitivity of results to the modelling strategy are discussed in terms of (i) the inelastic seismic demands under strong ground motions using the incremental dynamic analysis (IDA) and (ii) the relative vulnerability developed using probabilistic demand models (PSDM) extracted from the results of the IDA analyses. Based on these studies recommendations are made for the development of reliable and efficient modelling strategy when evaluating the performance of RC bridge piers for use in PBEE.