Study On Seismic-resistant Behaviors Of Pier And Analytic-model Subjected To Variational Axial Force

Pier is an important vertical load-bearing structure and lateral force resisting members in the bridge structures, its seismic performance may affect the security of the whole bridge structure. So far, many researchers have finished much study on the seismic performance of steel and concrete bridge piers subjected to constant axial force. The results show that the axial force will influence significantly the seismic performance and seismic response of bridge piers. However, the study on variational axial force is still defective. In order to clarify the influence of variational axial force on the seismic performance and seismic response of bridge piers, the fiber model which can consider the variational axial force and the traditional lumped plastic hinge model were used to carry out numerical analysis. The following work were finished:1) Using lumped plastic hinge model and the fiber model to analyze the seismic response of reinforced concrete piers subjected to constant axial force. The difference of seismic response between the two models were compared, and discussed the influence of axial compression ratio, reinforcement ratio, stirrup ratio and the length of plastic hinge.2) Taking a continuous rigid frame reinforced concrete bridge as an example, the lumped plastic hinge model and fiber model were established, the variational law of the axial force in the earthquake were investigated, the difference of seismic response between the two models were compared, the reasons for the differences were analyzed, discussed the influence of axial force variation, the vertical earthquake and near-field earthquake on seismic response of piers, and the influence of varational axial force on the seismic response of unequal height pier were also analyzed.3) Steel bridge pier shell element model is established using the finite element analysis software Abaqus, Horizontal monotonically increasing load and cyclic loading subjected to constant axial force were analyzed. Seismic performance of steel pier subjected to different axial compression ratio were discussed, the influence of varying axial force on the seismic performance of steel piers were discussed preliminarily.the main conclusions are as follows:1) In the condition of constant axial force, only when the pier achieve the strong nonlinearity, the maximum displacement of hinge model and fiber model will emerge great difference, but the maximum bending moment is similar.2) The influence of variational axial force on the maximum displacement and the maximum bending moment of pier is indistinctive, but the effect on unequal heigh pier is significant. Therefore, the effect of variational axial force should be considered when analyzing the seismic response of unequal heigh pier.3) Variational axial force has a great influence on the seismic performance of steel bridge piers, the hysteresis curve is unasymmetry under horizontal loading subjected variational axial force, with the enlargement of the axial compression ratio range, the asymmetric degree increase. The bearing capacity of bridge pier in reverse loading is greater than the positive loading, the ultimate compressive strain is influenced by the varational axial force, during the seismic analysis of steel pier, the variational axial force should be considered.