STRUCTURAL CONTROL AND HEALTH MONITORING Struct. Control Health Monit. 2008; 15:958–973 Published online 23 October 2007 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/stc.229 Instantaneous damage detection of bridge structures and experimental verification Serdar Soyoz* ,y,z and Maria Q. Feng } Department of Civil and Environmental Engineering, University of California, Irvine, CA, U.S.A. SUMMARY An extended Kalman filtering (EKF) method was developed and applied to instantaneously identify elemental stiffness values of a structure during damaging seismic events based on vibration measurement. This method is capable of dealing with nonlinear as well as linear structural responses. Identification of the structural elemental stiffness enables location as well as quantification of structural damage. The instantaneous stiffness values during an event can provide highly useful information for post-event capacity estimation. In this study, a large-scale shaking table test of a three-bent concrete bridge model was performed in order to verify the proposed damage detection method. The bridge model was shaken to different damage levels by a sequence of earthquake motions with increasing intensities. The elemental stiffness values of the structure were instantaneously identified in real time during the damaging earthquake excitations using the EKF method. The identified stiffness degradations and their locations agreed well with the structural damage observed by visual inspection and strain measurements. More importantly, the seismic response accelerations analytically simulated using the instantaneous stiffness values thus identified agreed well with the measured accelerations, demonstrating the accuracy of the identified stiffness. This study presents an experimental verification of a structural damage detection method using a realistic bridge model subjected to realistic seismic damage. Copyright # 2007 John Wiley & Sons, Ltd. KEY WORDS: extended Kalman filter; seismic damage detection; instantaneous stiffness; shaking table test; bridge structure; vibration measurement 1. INTRODUCTION Sophisticated highway system in the United States is supported by tens of thousands of bridges and viaducts. Lack of information about the post-event structural integrity of these bridges can *Correspondence to: Serdar Soyoz, Department of Civil and Environmental Engineering, University of California, Irvine, CA, U.S.A. y E-mail: ssoyoz@uci.edu z Ph.D. Candidate. } Professor. Contract/grant sponsor: Caltrans; contract/grant number: 59A0311 Received 23 April 2007 Revised 10 August 2007 Accepted 24 August 2007 Copyright # 2007 John Wiley & Sons, Ltd.