Numerical Evaluation And Experimental Study Of Seismic Performance For Reinforced Concrete Bridge Piers

Investigations of recent earthquake disasters develope bridge seismic technologies, as a result, the main bridge seismic design codes in the world have adopted ductility design method. Performance based bridge seismic design method is current research focus, of which understanding of nonlinear seismic response and damage mechanism of bridge system is the key component. At first, the main documentations in this field are summarized and analyzed in this dissertation. Then feasibility and precision for simplified plastic hinge model and inelastic fiber beam-column element to calculate integral and local seismic damage performance parameters are studied. At last a shaking table test is designed and implementd to understand and compare the seismic performance and damage mechanism of RC bridge pier specimens designed by current seismic code, by displacement based seismic design method or likely to occur flexure-shear failure.The main work of the study are:1. A computer program for numerical simulation and seismic damage evaluation of RC bridge piers subjected to cyclic loading—DLUT-RC is developed. The main functions of the program are hysteretic analysis of RC bridge piers and calculation of seismic performance indices from experimental or computing results. Two kinds of analysis models are employed in the program: simplified plastic hinge model and inelastic fiber beam-column element. P-A effects caused by variant test devices are considered in plastic hinge model. Fiber element includes stiffness-based element and flexibility-based element, in which material nonlinearity, geometry nonlinearity and bond slip effect of anchoring steel in joint are accounted for. Chang-Mander models for steel and concrete strain-stress relationship are employed, which reflect material mechanical property subjected to cyclic loading precisely. A new plastic hinge model is suggested, in which mechanics-based effective plastic hinge length is adopted and an experiment static formula based on strain suggested by Lehman is used to account for bond slip of steel in joint.2. The matching between seismic response analysis models and seismic performance indices for RC bridge piers is studied. Simplified plastic hinge model and fiber element are employed to compute damage evaluation indices of 5 bridge pier specimens by Lehman, such as section curvature, residual displacement, strain amplitude of steel and concrete, low cycle fatigue damage index of longitudinal steel etc. Comparison between experimental and simulating results is made, and it is concluded that the computed hysteretic curves and residual displacements by both models fit experiment results very well. With regard to plastic hinge model, limit curvature and longitudinal steel strain amplitude approximate experiment data, but the limit curvature is less than experiment whenλ≥8, which causes a dangerous design. With regard to fiber element model, section curvature and longitudinal steel strain amplitude calculated with stiffness-based element fit the experiment very well by proper dividing element. Low cycle fatigue damage indices of longitudinal steel computed by flexibility-based element are greater than that by stiffness-based element. Both models underestimate concrete compressive strain amplitudes when bridge piers fail, but fiber element is a little better than simplified plastic hinge model. According to the study of the dissertation, compressive strain of concrete and low cycle fatigue damage index of longitudinal steel are unfit for seismic performance indices of reinforced concrete bridge piers.3. Shaking table tests for RC bridge piers with ductile flexural damage model and with brittle flexure-shear damage model are studied. 8 RC bridge pier specimens are designed and fabricated by current seismic design code, by displacement-based seismic design method, and with low lateral reinforcement ratio and with low shear span ratio respectively for shaking table test. Damage states, displacement ductility and energy dissipation are compared to access their seismic performance. It is concluded that the specimens designed by displacement-based seismic design method have the equivalent seismic performance with those designed by current seismic design code, but the former can anticipate the seismic performance of bridge piers, reduce longitudinal steel amount by increasing lateral reinforcement and approach anticipated ductility. It is also shown that displacement ductility response of low shear span bridge piers is hige, and energy dissipation is low, which should be paid much attention to in bridge seismic design.