Study On Earthquake Mitigation Control Of Long-span Deck-arch Bridge

Long-span deck-arch bridge is a kind bridge which is prevalent in southwest China. However, the axial compressive ratio in the arch is high, the aseismic behavior is poor, and the traditional ductility designing method is unsuitable, so the current designing method is elastic design, which is very uneconomical. In this paper, in order to find a economical aseismic designing method, energy dissipation braces, which is commonly used in buildings, are installed in deck-arch bridges. Researches have carried out on some areas including the installing mode of damping braces, aseismic effect of arch bridges, multi-support seismic excitation of long-span arch bridges, the optimization of parameters of damping braces, and so on. Some works have finished in the following aspects:(1) The scheme of installing damping braces between the arch and the deck was put forward, and two methods of layout of damping braces were provided. In the example of Nimu Bridge, a FEM model of 3D beams is established by beam grid method, and mode analysis and time history analysis have been done. In the example of Nimu Bridge of damping braces, time history analysis with the model of nonlinear damping restoring force have been done. The comparison between Nimu Bridge with and without damping braces shows, the displacement within the arch plane have been controlled, and the effect of damping braces is obvious.(2) For some questions such as multi-support seismic excitation, structural optimization, many general FEM analysis software can not work conveniently. Therefore, adopting the object-oriented programming language of C++, a 3D FEM software 3DFIN based on Windows have been finished. The software has functions including damping brace element, non-proportional damping matrix, time history analysis of multi-support seismic excitation and optimization by genetic algorithms.(3) Some cases of multi-support seismic excitation analysis of traveling wave effect of a long-span deck-arch bridge have been done. According to the results, the responses in both top arch and quarter arch were larger than the results of consistent excitation. Further more, the longer the bridge is, the larger the effects of multi-support seismic excitation appear. Multi-support seismic excitation is a dispensable consideration in long-span bridges.(4) The sum of damping coefficient of all the damper braces is considered as a goal...