Study On The Seismic Design Of Bridge Joints

The performance of a bridge joint interacted with a pier and a crossbeam with the representative formation in China under outside force was studied, as well as the factors influenced the ultimate strength, based on the philosophy of capacity design.An analysis used finite-element method on the performance of components in an experiment was performed, using the theoretical stress-strain model for confined concrete propossed by J. B. Mander. The analysis results coincided the results of the experiment quit well. Based on the results of the analysis, another analysis was performed on a frame with the representative formation of bridge joint in China. The moment on the bottom section of the pier was largest in the sections of the frame with the increasing of the lateral displacement. And this section would yield first. After that, the stress of the transversal reinforcement would increase to yield with the increasing of the lateral displacement, as well as the moment on the top section of the pier. Then the stiffness of the joint decreased and the constrain on the top section of the pier weakened. This resulted in the re-distribution of the internal force in the frame, which led to the faster increasing of the lateral displacement. It's adverse to the seismic performance of the frame. Joints with adequate amount of transversal reinforcement in the core region had better performance because the concrete was confined better. And the transversal reinforcement could prevent the development of the fracture and the stiffness decreasing rapidly. For the prestressed concrete bridge, the prestressing reinforcement in the crossbeam could harden the joint stiffness and avoid rapid softening of the constrain on the top section of the pier on one hand. Thereby the seismic performance of the frame was improved. On the other hand, the prestressing reinforcement could resist the shear force thereafter the amount of crowd reinforcement was cut down, and it's more convenient for construction. The shore between the pier and crossbeam extended the joint region and hardened the stiffness of the joint so that the seismic performance of the frame was improved. The stiffness ratio of the pier and the crossbeam influence the ultimate strength of the joint quite much. The closer the ratio to 1, the lower the joint ultimate strength was, and the faster the joint stiffness weakened. In the conditions of the pier and crossbeam were constructed in box formation and the joint was solid, the joint ultimate strength and stiffness was higher comparatively, and the lateral seismic performance was improved.