Investigation of a System Identification Methodology in the Context of the ASCE Benchmark Problem Hilmi Lus ¸ * , Raimondo Betti † , Jun Yu ‡ and Maurizio De Angelis § Abstract This article briefly presents the theory for a system identification and damage detection algo- rithm for linear systems, and discusses the effectiveness of such a methodology in the context of a benchmark problem that was proposed by the ASCE Task Group in Health Monitoring. The proposed approach has two well defined phases: (i) identification of a state space model using OKID, ERA, and a non-linear optimization approach based on sequential quadratic programming techniques, and (ii) identification of the second-order dynamic model parameters from the realized state space model. Structural changes (damage) are characterized by investigating the changes in the second-order parameters of the “reference” and “damaged” models. An extensive numeri- cal analysis, along with the underlying theory, is presented in order to assess the advantages and disadvantages of the proposed identification methodology. * Asst. Prof., Dept. of Civil Eng., Bo˘ gazic ¸i University, Bebek 80815 Istanbul, Turkey † Assoc. Prof.,Dept. of Civil Eng. and Eng. Mechanics, Columbia University, New York, NY, 10027 ‡ Grad. Stud., Dept. of Civil Eng. and Eng. Mechanics, Columbia University, New York, NY, 10027 § Asst. Prof., Dip. Ing. Strutt. e Geotecnica, Univ. di Roma “La Sapienza”, Rome, Italy 1