عنوان مقاله [English]
Environmental conditions and uncertainty in materials and service loads cause operational defects in structures. Detection of damage at the earliest stages can increase the life expectancy of structures and also prevent occurrence of disaster. So, structural health monitoring has been of interest over the last decades.Among the various methods for damage detection, vibrating response processing is one of the best and most efficient methods. Structural health monitoring systems are set up in such a way that the natural and forced vibrations can be investigated. So, by using reliable monitoring systems, structural behavior can be controlled in various stages of onstruction r peration.Occurrence of damage in a structure causes changes in its dynamic characteristics, such as its natural frequencies and mode shapes. Comparison of frequencies and mode shapes or mode shape curvature under various conditions can be used for health monitoring. For minor damage situations, direct comparison of modal parameters is not very useful. Instead, evaluation of mode shape curvature can be considered.In this paper, in order to detect damage in the connections of a moment resistant frame, a method based on analysis of the free vibration response of a frame, using Hilbert-Huang transform, is presented. In this methodology, natural frequencies and mode shapes of the frame are predicted by processing the acceleration response of the structure. Variation of the mode shape curvature is considered as damage index. This method is tested on the numerical model of a 2D concrete frame and a 3D steel frame as a benchmark. Different damage scenarios, such as single and multiple defects of beam-to-column connections, are investigated. Results show that the presented method is reliable for operation monitoring of connections in moment resistant frames by considering the low number of mode shapes, and its high accuracy in damage detection.