Wave Method for System Identification and Health Monitoring of Buildings – Extension to Fitting Timoshenko Beam Model

A significant new development of the wave method for structural system identification and heath monitoring of buildings is presented. Previously, shear beam models were fitted, and changes in the identified equivalent shear wave velocities were monitored. These models are more appropriate for frame structures, which deform predominantly in shear. In this study, it is demonstrated, for the first time, that the method can be extended to fitting more complex models. As a first step, Timoshenko beam model is fitted, which accounts for bending deformation and rotary inertia, and is more appropriate for shear wall structures than the shear beam model. The model material parameters are estimated by minimizing the least squares (LSQ) error between the model and observed impulse response functions (IRF) over a time window, the IRFs representing the propagation of a pulse radiated from a virtual source. The Levenberg-Merquardt method for nonlinear LSQ estimation is employed. The initial values of the unknown parameters are estimated from the first two apparent frequencies of vibration. However, the fit is performed over a frequency band that excludes the first mode of vibration, which is the one most affected by SSI, in order to minimize the effects of soil-structure interaction (SSI). A major complexity in the nature of wave propagation in Timoshenko beam, in comparison to shear beam, is the wave dispersion due to bending deformation. The identification is demonstrated on the NS and EW responses of Millikan library, a 9-story RC frame/shear wall structure in Pasadena, CA. It is concluded that the waveform inversion algorithm of the wave method for structural system identification of buildings can be extended to fitting dispersive models, such as Timoshenko beam model. PhD Candidate, Dept. of Civil Eng., University of Southern California, Los Angeles, CA 90089, Email: [email protected] Research Professor, Dept. of Civil Eng., University of Southern California, Los Angeles, CA 90089, Email: [email protected] Ebrahimian M., Todorovska M.I., Wave method for system identification and health monitoring of buildings – extension to fitting Timoshenko beam model, Proceedings of the 10th National Conference in Earthquake Engineering, Earthquake Engineering Research Institute, Anchorage, AK,2014. DOI: 10.4231/D3NV99B46 Tenth U.S. National Conference on Earthquake Engineering Frontiers of Earthquake Engineering July 21-25, 2014 Anchorage, Alaska 10NCEE Wave Method for System Identification and Health Monitoring of Buildings – Extension to Fitting Timoshenko Beam Model M. Ebrahimian and M. I. Todorovska