Pounding Analysis And Seismic Performance Of Beam Bridge Based On The Phenomenological Model

Bridge is an important component of transportation network. In the past several decades, bridges have suffered catastrophic damage during the severe earthquake all over the world. Pounding is a typical earthquake-induced damage due to the difference of dynamic characteristics between the adj acent segments, non-uniform earthquakes and insufficience length of expansion joint. Pounding would cause the cracking, even unseated, of the bridge decks, and seriously threat the bridge safety. Understanding the pounding effect, effectively choosing the contact-element model and determining the corresponding model parameters are important issues for the seismic analysis of bridges with pounding effects under earthquake excitations. Therefore, this study investigates the pounding effect, pounding model and the corresponding parametric, and then seismic performance of bridges with pounding effects. The main research contents, method and finding are shown as follows.(1) A refined steel model of two-span girder bridge with difference dynamic characteristics was designed, a series of shaking table test was conducted including pounding effects under earthquake excitations. A method to indentify the parameters of the contact-element model was proposed based on the test data. The impact stiffness parameter was identified and compared with the theoretical impact stiffness. The effects of the impact stiffness on the dynamic responses of structure were also investigated. It is shown that the identified impact stiffness was seriously deviated from the theoretical impact stiffness when the accelerometer with lower frequency bandwidth was used to acquire the acceleration signal, the theory stiffness value of nolinear contact model is closer to experimental identificated results then the value of linear contact model. It is also verified the inconsistency between identified impact stiffness and theoretical impact stiffness in the openpublished literature. The reasons of difference in pounding stiffness between test identification and theory were analyzed, which are the discrepancy between the actual pounding state of bridge structure and premise assumption of contact model and the discrepancies and deficiency of testing technology.(2) Based on the wave theory and Hertz theory, the pounding of two straight bars is investigated. The wave equation of pounding bars with longitudinal constraint is established and analytical solution is obtained. Researh shows that the longitudinal constraint have little influence on the pounding effect. The main influence factors of the pounding are relative velocity before contact, bar length, form and size of contact surface. The relationships between the response of local and whole deck are analyzed by using the explicit finite element analysis software package of ANSYS/LS-DYNA. The difference of structural responses between uniform and non-uniform contact, and the effects of accelerometer frequency bandwidth on the accuracy of the test signal were analyzed. The analysis results indicated that structural responses with non-uniform contact are smaller than that with uniform contact. The analysis results further reveal the pounding phenomenon and the effect of signal acquisition system on the accuracy of the pounding test.(3). A phenomenological contact-element model based on the actual pounding phenomena was proposed according to the reality of non-uniform contact in the pounding process of bridge. The formula of the novel contact-element model and the corresponding paramtric determination method of the impact stiffness and damping are derived and established. The shaking table tests were conducted again with broadband frequency accelerometers. It is shown that using phenomenological contact-element model can predict structure pounding response effectively though analyzing and comparing the simulation results with the experimental results. The analysis results of test siginal acquired from the acoustic emission further verified the phenomenon that the actual contact surface during the pounding process was non-uniform contact.(4). Based on the Open Sees software package, finite element model of a bridge was established considering the nonlinear characteristics of the structure and pounding effects based on the proposed phenomenological contact-element model. Damage models and indexes of the structural components of bridge were analyzed and established. The seismic damage and fragility of the bridge with and without the pounding effects were investigated though Incremental Dynamic Analysis(IDA) method. The simulation results indicated that the pounding has tiny effects on the pier. However, it would significantly affect the abutment and bearing. Seimic-induce pounding decreases the bearing displacement, but increases the abutment displacement.