Earthquake Damage Mechanism And Damage Control Method For RC Bridge Bents

A lot of bridge bents were severely damaged in Loma Prieta earthquake, Kobe earthquake, WenChuan earthquake, and ChiChi earthquake, indicating the seismic vulnerability of the bridge bents. To study the seismic damage mechanism of the bents and develop new damage control method for the bents, a series of numerical analysis model for reinforced concrete (RC) bridge piers based on the OpenSees platform were built, in which the flexural, shear and bond-slip deformations were included. And the accuracy of these models was verified by comparison with test results. Then, the seismic damage control method for the bents is proposed by using ductile tie beam and Buckling Restrained Brace (BRB), and the behavior of the bents with ductile tie beam and BRB were studied. The main work and conclusions are summarized as follows:1. To investigate the longitudinal bond-slip deformation on the behavior of RC bridge piers, eight models were built based on OpenSees platform. The nonlinear beam-column element, zero-length rotational spring element and zero-length shear spring element were used to model flexural, bond-slip and shear deformation, respectively. The simulated hysteretic curves, flexural, bond-slip, shear deformations, initial stiffness and residual displacement of the pier were compared with test results. It is found that the simulated hysteretic curves, each displacement component, initial stiffness and residual displacement of the pier agreed well with test results. The longitudinal bond-slip deformation could account for 20%-50% of the total lateral displacement, and could not be neglected in the analysis model.2. To study uncertainty parameters on residual displacement simulation of the bridge piers, fiber model for RC bridge piers was built by OpenSees platform, which considered flexural deformations and bond-slip deformations. Key parameters are determined according to the test and specimen design, and dynamic time history analysis was carried out. Sensitivity analysis for residual displacement simulation was conducted by changing uncertainty parameters in OpenSees. Analysis results were compared with test results. It is found that uncertainty parameters have obvious effect on the maximum value of residual displacement in multiple earthquake waves. The simulated residual displacement agreed well with test results by adjusting uncertainty parameters.3. To investigate the seismic behavior of high strength concrete (HSC) columns with high strength stirrups (HSS), test results of 22 HSC columns with HSS were compared with the Elwood deformation model for normal strength concrete (NSC) column with normal strength stirrups (NSS). And the applicability of Elwood shear failure surface to HSC columns using HSS was verified.6 HSC columns with HSS appeared flexure-shear failure mode were modeled by OpenSees. The simulated hysteretic curves were compared with test results. It is found that the simulated hysteretic curves agree well with test results. Improved flexure-shear model has a high accuracy for HSC column with HSS in strength, stiffness degradation and residual displacement simulation.4. To improve the seismic behavior of bridge bents in the transverse direction and reduce the seismic damage to bridge piers, a new seismic design method by using ductile tie beam and the design details were proposed. The seismic analysis models for the bents with and without tie beam were built, and the seismic behavior of the bents was investigated by quasi-static and incremental dynamic analysis (IDA). It is found that the transverse strength and stiffness of the bents would be improved by the ductile tie beam, which will yielding before the pier and the seismic energy is consumed by the plastic hinge in the beam, the yielding damage of the pier would by delayed and the deformation demand of the bent would be decreased.5. To investigate the effect of the ductile tie beam and BRB on seismic behavior of the bridge bents, design method to improve the seismic behavior of the bridge bents by using BRB was proposed. The seismic analysis models for the bents with and without BRB were built. Then, quasi-static analysis and incremental dynamic analysis for the bents were conducted. It is found that the length of the BRB core is the key influencing factor for the yield sequence of the bridge bent. The properly designed BRB would yield before the bent and dissipate most of the seismic energy through hysteretic behavior of the BRB while avoiding damage to the bent, and the seismic performance of the bents would be improved.