Study On Gradation Criterion Of Seismic Damage And Seismic Behavior Of Girder Overpasses

Girder overpasses are the main structural system of urban overpasses and the key structure of the urban transportation system. If these bridges get damaged in an earthquake, great direct and indirect economic loss will be caused. Domestic and foreign researchers have studied on seismic damage modes and mechanisms of bridges. However, these modes and mechanisms vary in different structural systems of bridges. Thus, seismic damage of the girder overpasses still needs further study. In this paper, available criterions and provisions of China and other countries are collected and discussed, and a new gradation criterion of earthquake damage which is applicable for girder overpasses is presented. The dynamic characteristics and the seismic response of the girder overpasses are also studied in the paper. The main research work includes:1. Based on the investigation data of the girder bridge damages in several domestic and foreign large earthquakes, the seismic damage phenomena are categorized and the reasons are analyzed. The influence of some factors on the bridge damage is analyzed, such as seismic intensity, construction time, structural system and post-earthquake secondary geological disasters. The enlightenment in influence factors on seismic damage and damage mechanism of the girder overpasses is obtained.2. Domestic and foreign existed gradation criterions of earthquake damage to bridge engineering are collected and discussed. By adopting the methods of contrastive analysis, induction and summarization, the characteristics of different criterions and provisions are summarized from the aspects of gradation characteristic, phenomenon description and gradation characteristic of traffic capacity. The application of different criterions and provisions is also discussed. Combining structural characteristics and the earthquake damage characteristics of girder overpasses, the damage gradation criterions of structural members are established. With the damage degree of the structural members, the extent of functional incapacitation, the difficulty of repairing and the effect of bridge damage on the traffic after earthquake as main factors, a new gradation criterion of earthquake damage which is applicable for girder overpasses is presented.3. In order to study the dynamic characteristics of the girder overpasses, the site vibration testing data of 19 overpasses are collected and analyzed. The natural frequency of the girder overpasses is preliminarily summarized. Three finite element models of a girder overpass in Harbin according to different treatment methods of the movable supports are established using the ANSYS program. The calculation results of their dynamic characteristics and testing results are compared and analyzed. 4. The seismic response of the example bridge is analyzed with excitation of EL- Centro, Taft, and Tianjin waves. The influence of the friction force at the movable supports on the seismic response is studied.