Seismic Vulnerability Analysis For Bridge Structures With High Piers

In road transportation system bridges are the most critical structural component, due to its strategics, economic and aesthetic importance. The traffic will be badly hampered if there are damages in the bridge structure. Bridges provides fast access to ports and connects the cities, thus making the transportation network fast and efficient.With the economic globalization and rapid economic development in China, the need for more efficient and reliable transportation is required and bridges are the backbone of transportation system. A number of earthquakes with high magnitude occurred in our country in the last few years, thus causing a huge damage to the bridge structure, causing an adverse effect not only to transportation network but also to the relief work in case of disasters. Therefore, both in terms of economic consideration and from the people perspective, it is necessary to undertake a thorough research on seismic vulnerability analysis of bridges. The existing bridge seismic design specification applies only to the bridges whose piers’height is less than40m. For the bridges whose piers’height is larger than40m, there is no reasonable and effective seismic evaluation methods presently available. So the seismic vulnerability analysis of high pier bridges seems to be particularly important. In order to save the space in urban areas, where the land cost is very high, single column pier is widely used in viaduct. The second one is concrete continuous rigid frame bridge with high piers is a kind of irregular bridges, and it is widely used in highly irregular and unfavorable terrain, like mountains and valleys. So these two types of bridges were targeted for analysis. Some big earthquakes in China’s western provinces are caused by faults specially for the last one decade, and most of the bridges are constructed near the faults in western China, therefore it is inappropriate if vertical component of earthquake motion is ignore; furthermore, the three-dimensional study of the vulnerability after the earthquake is necessary. Keeping in view the above points in mind, the following work has been done:(1) The bridge seismic vulnerability analysis theory and method are introduced comprehensively. Those problems which need special attention and thorough investigation are further illustrated specially in detail.(2) The construction of fragility curves is presented and summarized. The selection of seismic waves, Moment-Curvature analysis, and the selection of the damage index are discussed in detail. Based on this a decision was made regarding the curvature ductility ratio which has broader applicability and therefore was used for the selection of damage index of seismic vulnerability analysis.(3) Seismic response analysis and seismic vulnerability analysis of regular bridge’s pier were performed by changing the height of its pier. It was found that with the presence of high-order vibration mode specially in piers with increasing pier’s height, the shape of pier-bottom’s curvature and the pier-top’s displacement tend to be inconsistent. With the increase of pier’s height, the earthquake damage probability increases initially and then decreases.(4) Seismic response analysis and seismic vulnerability analysis were performed along the longitudinal direction and transverse direction of concrete continuous rigid frame bridge with changing the height of its pier. After obtaining the vulnerability curves, it was revealed the core reason is the angle of the force and energy.(5) Bridge structural seismic vulnerability analysis under the action of three-dimensional seismic motion was briefly discussed, a new seismic fragility analysis method based on the theory of linear interpolation was proposed.