Research On Nonlinear Seismic Response Of Bridge Structures (Friction Force At Moveable Supports·Restrainer·Nonlinearity Of Foundation)

The research on the nonlinear seismic response is of great significance to the seismic analysis and design of the bridge structures. The bridge structure can be destroyed at different locations under the strong earthquake. Correspondingly, the analysis method and model are also different. Precise analysis of nonlinear seismic response of bridge structure is quite complicated because of various nonlinearities. So, the simplified mathematical model is usually adopted for the nonlinear analysis. Based on the research results obtained by others, some key technical issues on nonlinear analysis of bridge structures under strong motion are comprehensive analyzed. The corresponding finite elements and nonlinear finite model are put forward, which are used in the analysis of the effect of the nonlinearity on the integral seismic-resistant performance of the bridge structure. The studies and results in this dissertation are summarized as follows:(1) The nonlinear computing model for the bridge structure, the general constitutive relationship, and the nonlinear dynamic equations and its solutions are summarized. Three models for elastic-plastic beam element are discussed. And the element flexibility matrix considering the length of plastic hinge for the elastic-plastic beam element is also introduced. The moment-curvature hysteretic model for the reinforced concrete pier is presented. A computer program is compiled and a linear method is also introduced to analyze the moment-curvature curve.(2) A "friction and contact" element for the support is introduced to take into account the effect of the friction force at movable supports and the influence of the bearing dynamic vertical resistance force on the bearing horizontal friction force. A finite element model for a continuous bridge with "friction and contact" elements is created. With this model, the effects of the friction force at movable supports and vertical excitation on seismic-resistant performance of continuous bridges are analyzed. And the effects of the supports parameters such as friction coefficient and initial stiffness, etc on the seismic response are also discussed according to the finite element analysis results. It shows that the friction force at the movable supports and vertical excitation needs to be taken into account for the study of the seismic-resistance performance of continuous bridges in some cases.(3) The finite element that considering the friction nonlinearity at the movable support and the contact and material nonlinearity at the restrainer is put forward. And its stiffness and hysteretic curve are also derived. The finite element model considering the nonlinearity of the supports and restrainer and pier is established to study the nonlinear seismic response of the bridge structure. The study on the interaction among the friction force at movable supports and contact and material nonlinearity at restrainer, and elasto-plasticity at pier is performed. The effect of initial gap and stiffness of the restrainer on the nonlinear seismic response is also discussed. And the effective methods to reduce the seismic response of the fixed pier are discussed.(4) The nonlinear Winkler soil spring model is improved and the hysteretic features for the nonlinear compression soil spring are presented. The improved model takes into account the contact and material nonlinearity of soil around piles. Based on the current finite element models for the pile foundation bridges, an improved nonlinear finite model for the seismic analysis of pile foundation bridges is put forward, which include the horizontal contact and material nonlinearity of the soil on each side of the pile, the vertical friction nonlinearity between the soil and piles, and the nonlinear compression and uplift features of the soil at pile bottom. This model also takes the elasto-plastic characteristics of piers and piles into account. The static pushover experiment under cyclic loads for a pile foundation pier approved that results of this model match that of the experiment.(5) The improved distributed spring finite element model of the pile foundation pier is used in a bridge project. The feasibility of the time-history analysis is discussed. And the nonlinear effect of pile foundation on the seismic response of the pier and pile is analyzed. The hysteric curves of the horizontal shear force-linear displacement and that of the moment-angular displacement at the bottom of pile cap are summarized. The results show that the curve is spindle-shaped or pinched spindle-shaped. The simplified centralized spring model is put forward in which the Clough spring model is used to simulate the influence of the soil-pile interaction on the superstructure. The comparison results indicate that the results of the simplified centralized Clough spring model and the distributed spring model are similar.(6) For bridges whose weak points are not apparent and every part can be destroyed in the strong earthquake, an integral nonlinear finite element model, which takes the nonlinear pile-soil-structure interaction into account, is put forward. The model includes the nonlinearity of the supports, piers, piles and soil. The nonlinear interaction among different parts is discussed based on the results. The nonlinear seismic response of the moment-curvatures at the pier bottom and the linear and angular displacement at the bottom of the pile cap, and beam displacement are also studied.