Experimental Studies on the Behavior of Connections, Before and After Sarpol-e Zahab Earthquake of November 12, 2017, Used in Steel Structures

This study is divided into two main parts. In the first part, the behavior of four groups of connections that arecommonly used in the construction of the country has been investigated, because of which their hysteresis behaviorhas been determined. In the second part, the behavior of connections damaged in Sarpol-e Zahab Earthquake hasbeen investigated, and finally the changes in the stiffness, strength and ductility parameters of the connectionsdamaged in the earthquake have been determined.Connections used in buildings may be categorized into rigid, semi-rigid or pinned-end connections. Theassumption of perfectly pin or rigid behavior for a connection may not always be reliable in the design of astructure; therefore, in this study, an attempt was made to investigate the real behavior of connections that arecommonly used in the country's constructions.In experimental studies, due to the existence of some limitations, assumptions are always considered that mayaffect the results of a test. Therefore, the best experiment is to determine the behavior of the members of a buildingafter an earthquake. One of the earthquakes that can be used to investigate the behavior of the members of a buildingis the Sarpol-e Zahab – Ezgeleh earthquake. Because the buildings built in the city of Sarpol-e Zahab were generallyafter the war between Iran and Iraq (1367-1359), which can represent engineering constructions in the country.Although several years have passed since the construction of these buildings, this type of connection is still commonin many constructions in Iran. For this purpose, in this research, the damages caused to this type of connections andtheir performance have been investigated.Based on field observations, the connections related to steel buildings in the earthquake-affected areas ofKermanshah province can be divided into four groups: 1- connection with top and bottom cover plates along withstiffeners; 2- simply supported seat angle connection with stiffener; 3- simply supported seat angle connection withstiffeners and shear plates; 4- like No. 2 or 3 together with gusset plate. In this study, in order to understand thebehavior of these connections during an earthquake, the experimental model of each group was made with full scale,and their moment-rotation curves were extracted under cyclic loading. Based on the results obtained from theexperimental studies, connections No. 1 and 4 of these groups were classified as rigid connection, and No. 2 and 3were evaluated as semi-rigid connection with brittle behavior.Another scope that has been addressed in this study is to determine the behavior of damaged connections in anearthquake. This issue, which is the result of observing the trend of the connection hysteresis curve during loading,makes it possible to determine the remaining capacity of the earthquake-damaged buildings. The remaining capacityof the damaged building is one of the important and crucial parameters in the decisions that to decide whether thebuilding should be repaired or demolished. For this purpose, the hysteresis curve of the tested connections has beeninvestigated and analyzed. As a result of these analyses, the curves that show the modifications in stiffness, strengthand ductility have been extracted for all four types of connections investigated in this study.Finally, two levels of damages were considered for each of the four connection groups. Then their performancecurves in each of the two levels of damages were presented along with the performance curve of the connectionwithout damage. The results of the studies showed that stiffness and ductility, unlike strength, are the parametersthat are most affected by the damage caused in the connections.