Preliminary Study On Analysis And Optimization Of Structural Failure Modes

The Performance-Based Earthquake Engineering (PBEE) inclding the theory and method of design, are issues paid extensive attentions by earthquake engineering academia and engineers at present. The main contents of PBEE include how to design structures reasonablly under seismic fortification levels to make them have the best seismic capacity, and reaching the desired performance objectives under earthquakes of different intensity to reduce the possible loss of life and property. Frequent occurrence of earthquakes in recent years, have showed that the structures under seismic design have better performance than the structures which are not seismic designed, but the former don't perform as well as expect. China's urban constructions have a huge amount with different types, and improving the seismic capacity of urban building is imminent nowadays. The structure's failure to withstand heavier ground motions is primarily caused by their unreasonable failure modes. Therefore, the optimization and control of failure modes for structures are the key issues of Performance-Based Earthquake Engineering.Structure self-control achieves its goal by improving the structure functions itself, and the essence is to optimize the performance of the structure by strengthening the local components, which is a special kind of passive control. Considering the optimization of failure modes based on OpenSees(Open System for Earthquake Engineering) platform, three approachs inclding Pushover analysis,IDA analysis and optimization criteria method are used to identify and optimize the failure modes for structure. The main contents of dissertation are as follows.(1) Structure has many failure modes, and the structural failure is caused by a few major failure modes. Pushover analysis can identify the main and the only failure mode, which solve the problem of multi-failure modes of structure. Also Pushover analysis with four kinds of typical lateral force will get four failure modes, which represent the typical damage of structures under earthquake. So we can make certain structural reinforcement to improve the failure modes according to the identified failure modes. Pushover analysis with its simplicity provides a good tool for the optimization of failure modes.(2) Structural failure under a single ground motion couldn't predict the possible damage of future earthquake, so Incremental Dynamic Analysis(IDA) and its diversity of ground motions, can provide a standard to some extent. We can select the severest ground motion, get the weakest failure mode and find some method to improve the structure. The IDA method can be used for the analysis of other specific structure, and also it's the most reliable method inspite of time-consuming because of many time history analyses.(3) Identification of failure modes and the joint probability are the core issues of structural system reliability theory which have some methods to identify the failure modes. This paper based on optimization criteria method study the process of optimization of failure modes for truss structure.The results show that the truss have fewer failure modes by controlling the some design parameters, and optimizing the first few components can increase the carrying capacity of the structure.