Evaluating the Effect of Welding Defect on Seismic Collapse Capacity of Steel Moment Resisting Frames

The seismic collapse of the building is a performance level in which the amount of human and financial damage reaches its maximum, so this event can be the most unfortunate accident in the construction industry. During strong earthquakes in different parts of the world, a more accurate assessment of the seismic collapse of structures and its prevention is one of the important challenges of structural engineers. In this way, any type of cut in the geometric or physical structure of the weld is called "discontinuity" when its value exceeds the specified limit. It is considered a "defect". There is a possibility of defects in the welding connections of steel structures. According to the seismic standards, the weld must be free of any defects and during an earthquake, weld failure should not occur. In this paper, the presence of defects in welding of beams-to-columns of the steel moment resisting frame (SMRF) connection is investigated for 4-story SMRF probabilistically by incremental dynamic analysis (IDA) and fragility curves under 7 far-fault earthquake records by two scenarios. Also, the influence of stiffness and strength deterioration is assumed according to the experimental results of the models. For this purpose, a normal distribution is used to consider the welding defect. Scenario I related to the removal of the connection of beam-to-column on the first story and scenario II was defined as the sudden removal of all the connections of the beams to columns of the first story. In the case of defects in welded connections, the results of this research showed that the important role of the quality of welding connection in seismic collapse capacity of structures. As an example, at the probability level of 50%, the seismic collapse capacity of the mentioned SMRF without defects in beam-to-column connection is 3.2g and the seismic collapse capacity of this SMRF has been obtained by applying probabilistic failure strains of 16%, 50% and 84% equal to 2.3g, 2.8g and 3.0g, respectively.