Interaction of Structural Model and Ground Motion Characteristics in Nonlinear Dynamic Analysis of RC Bridge Piers

Abstract eng:
The current performance-based seismic design philosophy of reinforced concrete (RC) structures relies on the proper detailing of plastic hinge regions where most of the inelastic deformations are expected to occur. The inelastic cyclic deformation in plastic hinge regions results in a significant tension and compression strain reversals. Unlike buildings where plastic hinges are designed to occur in beams, due to the nature of the structural system of bridges the plastic hinges are forced to occur in piers. As a result, they should be able to accommodate a significant inelastic deformation due to earthquake loading. One of the most common failure modes of RC bridge piers that has been observed in real earthquakes and experimental testing is the buckling of vertical reinforcement. This is then followed by either confined concrete crushing in compression and/or fracture of reinforcement in tension due to low-cycle high amplitude fatigue degradation. Earlier research resulted in the development of a novel nonlinear material model for reinforcing bars that accounts for the effect of inelastic buckling and low-cycle fatigue degradation of reinforcing bars. This paper discusses a new modelling technique that is able to predict the nonlinear cyclic response of bridge RC bridge piers up to complete collapse. This model has been validated and calibrated against experimental data. Three groups of ground motions are selected to represent the far field (FF), near field without pulse (NFWP) and near field pulse-like (NFPL) ground motions with a range of PGAs and durations. The response spectra of all ground motions are matched to the mean response spectrum of the far field ground motions group. Using the selected ground motions several incremental dynamic analyses (IDA) of a representative RC bridge piers with various fundamental periods (various heights) are conducted. Finally a comparison between the response of the structure using the new material model (accounting for both buckling and low-cycle fatigue) and the conventional material model for reinforcing steel (without buckling and any degradation) are made.

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