عنوان مقاله [English]
Damage occurrence in all structural systems and their critical components is inevitable during their lifetime. Damage detection in structures is necessary for structural health monitoring, which can increase the safety. If the damage is identifiable in a way, damaged elements can be repaired or replaced and it can prevent the overall failure of the structure. Most of the damage identification methods are concentrated on detecting damage in structural members without considering damage at their connections that most have been seen. Beam to column connections of moment frames play an important role in their performance, because the performance of the structure mainly depends on the stiffness of the connections. Joint damage will change the stiffness of the structure, mass, and damping leading to a change in dynamic responses, such as displacement and acceleration. This principle can be used as a way to detect damage in connections. In this article, an optimization-based method for joint damage identification of moment frames subjected to an impact load is introduced. Spring model based connection simulation is used with flexible elements (springs), and converts the rigid joint to the semi-rigid one. Firstly, the beam-to-column connection in a steel moment frame structure is modeled by a zero length rotational spring at the end of the beam element. For each connection, an end-fixity factor is specified. This parameter has a zero value for a theoretically-pinned joint and a value of one for the theoretically-rigid one. The damage severity in any connection was defined as the reduction of the end fixity factor. Then, the problem of joint damage detection is transformed into a standard optimization problem. An objective function is defined using the acceleration of damaged structure and that of an analytical model obtained via the Newmark procedure. The optimization problem is solved by an improved differential evolution algorithm (IDEA) for determining the location and severity of the joint damage. Two numerical examples are considered to assess the performance of the proposed method and to check the effectiveness of sensor placement in damage detection. The results demonstrate the high efficiency of the proposed method for detecting the location and severity of joint damage, considering noise effects. Besides, an inappropriate location of sensors causes some errors in damage detection procedure, and the method cannot easily identify the damage.