Omid BAHAR - Assistant Professor, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran
Masoud DARYOUSHI - Msc Graduate, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran

Direct extracting matrices of a building is of major interest of a practical engineers. In this paper a method based on the stochastich subspace state-space identification has been proposed to identify stiffness matrix of structures.Only the output data is used. Once the state matrix of a system is identified by using of a similarity transformation it transforms from discrete time general form to the continuous time classical form of mass-spring-damper systems. Then, with known mass matrix the stiffness and damping matrices are simply in hand by multiplying each corresponding block by mass matrix.The proposed method is applied on a three-story two-dimansional shear frame. Once a model has been identified, a seismic assessment under Tabas earthquake excitation are examined and their responses are compared with the concern original model responses. The results show that this method is capable to be an appropriate tool for extracting main matrices of structures.

System Identification, Stiffness Matrix, Stochastic Subspace Identification, SSI