Performance-based Seismic Failure Mode Identification And Muti-objective Optimization For Steel Frame Structures

In the recent two decades, with the rapid development of the construction industry, a large number of tall building structures have been built in China. However, China is located at the convergent boundaries of two worst seismic zones, and the earthquake disaster is very serious. Previous earthquakes have demonstrated that the collapse of building structures is the primary cause for casualty and economic loss. Therefore, for the high-rise building structures under large earthquakes, the study on failure process and failure modes identification and optimization is of great theoretical significance and engineering value to improve structural seismic performance and delay or prevent structural failure. In this paper, performance-based seismic failure mode identification and optimization for steel frame structures are studied. Primary research contents are summarized as follows:(1) Two performance indices, damage index and hysteretic energy dissipation index, are defined in this paper, and based on the incremental dynamic analysis (IDA) method, the performance-based structural failure mode identification method for steel frame structures is proposed. The multi-objective optimization method of structural failure modes is developed using two performance indices as the objective function and the section dimension of members as the variables. As a numerical example, a20-story benchmark steel frame structure is analyzed to identify and optimize its failure modes under various earthquakes. Results indicate that the failure modes of structure under the most unfavorable earthquake can be effectively identified through the performance-based identification method using the damage and hysteretic energy dissipation indices as evaluation functions, and the seismic behaviors of structure can be significantly improved by the performance-based multi-objective optimization method.(2) According to the distribution of inter-story drift ratios when the structure is in the state of failure, seismic failure modes of the frame structure under different earthquake records are classified in this paper. A probability-based seismic failure mode identification method is proposed to establish the structural failure probability formula under different failure modes, and then, the structural safety margin under different failure modes is evaluated. As a numerical example, a20-story benchmark steel frame structure is analyzed based on Open Sees platform. Results indicate that structural failure modes can be reasonably classified according to the damage states of key floors, and the occurrence probability of different failure modes can be effectively distinguished by the probability-based seismic failure modes identification method.(3) The section importance coefficients under different failure modes are calculated through the section damage index of components when the structure is in the state of failure, and the objective functions of failure modes multi-objective optimization is established with the considering of component importance coefficient. The most unfavorable ground motion is selected as the optimization input by the defined parameter EDR, which is the ratio of the hysteretic energy dissipation to damage. As a numerical example, a20-story benchmark steel frame structure is analyzed to optimize its failure modes. Results indicate that the seismic performance under different ground motions can be evaluated well by the parameter EDR. The section dimensions can be well distributed, the structural cost can be reduced, and the structural damage is decreased while the energy dissipation capacity is significantly improved by the performance-based multi-objective optimization method with the considering of section importance coefficient.