Presenting a New Model to Evaluate Damaged Steel Structures after an Earthquake with the Aim of Managing Emergency Conditions

In general, determining the seismic behaviour of a building damaged by an earthquake is a difficult and complex task. This issue is important and practical in today's world because demolishing of all the buildings damaged by the earthquake is very expensive and time-consuming. For this purpose, in the first step of the reconstruction of an earthquake-stricken city, it should be determined which buildings are useable and safe, which buildings are repairable, and which ones should be demolished. The repairability, destructibility or usability and safety of a damaged building is effective when the seismic behaviour of that building can be determined after the damage. To determine the seismic behaviour of the building damaged by the earthquake, some methods have been presented by other researchers. However, most of these methods need to spend a lot of time to check the behaviour of the structure. The purpose of this research is to provide a new analytical method for the seismic evaluation of steel moment frame structures damaged in an earthquake, which can determine the force-displacement curve of a steel structure for different levels of damage. Also, in this research, with the benefit of SPO2IDA's approximate analysis, a method for classifying damaged structures based on the percentage of damages has been presented. For this purpose, a three-story steel moment frame structure was subjected to nonlinear static analysis in OpenSEES Software. Then, using the proposed method to analyse the damaged structure and considering the cyclic deterioration of the damaged members and elements by modifying the behaviour curves of the structure, non-linear static analysis curves were extracted for different levels of damage. In the method of cyclic deterioration of damaged elements, based on the amount of rotation or deformation occurred in the member during the earthquake, the performance curve of the member changes in such a way that these changes include stiffness, resistance and ductility. According to the initial back-bone curve, four levels of damage were meant for the damaged structures, and each of these damage levels is dependent on the amount of reduction in resistance that occurred in the initial back-bone curve of the structure.Also, using the SPO2IDA method, the approximate curves obtained from incremental dynamic analysis were extracted for the analysed structure. Then, by using these curves, the proposed procedure was evaluated in order to classify the structures after the earthquake. At the end, the results of this method are compared with the methods proposed by others in each step, and the crucial differences in response are fully explained. It was shown that at different performance levels, by not considering the effects of cyclic distortion, between 30% and 50% of the structure's capacity will be estimated higher. According to the obtained results, in the event of an aftershock with a magnitude close to the main shock, it can be concluded that not considering the cyclic distortion in the behaviour of the damaged members and elements can lead to many mistakes in decision and classification of the structures which result to irreparable consequences.