en Optimal design Optimal design پژوهشي Research This paper presents a new model updating approach for structural damage localization and quantification. Based on the Modal Assurance Criterion (MAC), a new damage-sensitive cost function is introduced by employing the main diagonal and anti-diagonal members of the calculated Generalized Flexibility Matrix (GFM) for the monitored structure and its analytical model. Then, the cost function is solved by Democratic Particle Swarm Optimization (DPSO) algorithm to achieve the optimal solution of the problem lead to damage identification. DPSO is a modified version of standard PSO algorithm which is developed for presenting a fast speed evolutionary optimization strategy. The applicability of the method is demonstrated by studying three numerical examples which consists of a ten-story shear frame, a plane steel truss and a plane steel frame. Several challenges such as the efficiency of the DPSO algorithm in comparison with other evolutionary optimization approaches for solving the inverse problem, impacts of random noise in input data on the reliability of the presented method, and effects of the number of available modal data for damage identification, are studied. The obtained results reveal good, robust and stable performance of the presented method for structural damage identification using only the first several modes’ data. damage detection, modal data, generalized flexibility matrix (GFM), modal assurance criterion (MAC), democratic particle swarm optimization (DPSO). 445 464 http://ijoce.iust.ac.ir/browse.php?a_code=A-10-66-78&slc_lang=en&sid=1 G. Ghodrati Amiri 18003194753284600869 18003194753284600869 Yes A. Zare Hosseinzadeh 18003194753284600870 18003194753284600870 No S. A. Seyed Razzaghi 18003194753284600871 18003194753284600871 No