Seismic Pounding Analysis And Performance Evaluation Of Urban Bridges

Urban bridges, which are of high construction cost, are the key projects of modern traffic network. If one urban bridge is damaged during earthquake, transportation paralysis will occur immediately, causing huge economic loss. What's more, the damaged bridges will be also very difficult to repair or be reconstructed. Therefore, research topics such as the earthquake-resistant design and damage prevention of urban bridges have been drew great attention all over the world. It has been observed from several modern major earthquakes that most serious damages of the urban bridges in earthquakes were caused by pounding destruction and falling beams. Therefore, in this thesis, a systematic study on seismic pounding analysis and performance evalution of urban bridges are carried out. Practical methods of seismic pounding prevention design and seismic performance evalution of urban bridges are proposed for improving the seismic safety of urban bridges. The primary research work and achievements in this dissertation are included as follows.(1) The formulae to calculate the critical safe distance between adjacent beams to avoid pounding during an earthquake are established. Based on the random vibration theory and pseudo excitation method, the influences of ground motion spatial effect and the soil-foundation interaction on the critical safe distance between adjacent beams to avoid pounding on the viaduct in the urban expressway are analyzed, and the formula to calculate the critical safe distance is deduced. For the interchange curved bridge, a large number of numerical simulations are carried out to study the influences of the different input direction of the ground motion, the curvature radius and the period ratio of the adjacent beam on the critical safe distance between adjacent beams to avoid pounding, based on which a simplified formula to calculate the critical safe distance between adjacent beams are put forward.(2) The formulae to calculate the critical safe distance between the pier and the beam to avoid pounding for urban bridges during an earthquake are proposed. The pounding between the pier and the beam for urban bridges can be classified into three types. The first type is the pounding between the upper straight layer and the lower straight layer; the second type is the pounding between the upper straight bridge and the lower curved bridge; the third type is the pounding between two curved bridges. Through a large number of numerical simulations, the influences of the different input direction of the ground motion, the curvature radius and the period ratio of the beam on the critical safe distance between piers and beams are analyzed. The formulae to calculate the critical safe distance between the pier and the beam to avoid pounding are derived through the regression analysis.(3) The pounding response of the adjacent beams or the pier and beam on urban bridges under high-intensity earthquake are investigated. Based on an example large urban bridge, which is part of Tianjin expressway, the pounding response feature of the curved girder bridges under is high-intensity earthquake studied, as well as the influencing regularities of the different input direction of the ground motion. The influence of the pounding response on the displacement of supports and the column's bending moment and shear is also studied. Furthermore, the control effect on the pounding response of urban bridges through installing viscous damper at the possible pounding part is studied. Accordingly, some applicable engineering measures for avoiding pounding between adjacent beams or the pier and beam are proposed.(4) A procedure for seismic performance evaluation of urban bridges is proposed in three levels, i.e. pier cross section level, pier level and bridge level. In the pier cross section level, the influences of stirrup configuration and concrete strength on the section seismic performance are studied. And the evaluation formula of section seismic performance is deduced; in the pier level, the damage grade of bridge pier for horizontal seismic is analyzed and the evaluation process for pier's seismic performance was proposed through considering the different link ways between the bridge pier and the foundation or the upper structures. In the bridge level, a procedure for seismic performance evaluation of urban bridges was proposed based on the incremental dynamic analysis. The index of the ratio of lateral displacements is derived. The failure probability of bridge structure for different grade of horizontal seismic is also analyzed.