Nonlinear Seismic Response Reconstruction in Minimally Instrumented Buildings—Validation Using NEESWood Capstone Full-Scale Tests

Abstract

The authors present a methodology to reconstruct nonlinear seismic response and assess seismic performance of instrumented buildings subjected to earthquakes. The paper proposes the use of a nonlinear model-based state observer (NMBO) that combines global acceleration measurements and a nonlinear model of the building to estimate the complete dynamic response including displacements, velocity, acceleration and internal forces in all structural members. The proposed NMBO is designed to be realizable as a modified structural model of the building. The modified model consists of the original nonlinear model of the building with added grounded dampers placed at the accelerometer locations. The modified model is driven by corrective forces applied at the accelerometer locations and defined as the measured velocity response scaled by viscosity of the grounded dampers. The optimal viscosity of the added dampers is found by solving a matrix equation that yields the optimal dampers to minimize the estimation error. The response of the modified system to the corrective forces constitutes an estimate of the true response of the building. The fact that the proposed observer is realizable as a modified structural model makes it compatible and easy to implement in the environment of commercial structural analysis software and therefore amenable to implementation by practicing engineers. From the estimated dynamic response, engineering demand pa- rameters, such as inter-story drifts are obtained and compared with performance-based acceptance criteria to determine if the building meets the desired performance objective. The methodology is validated using seismic response measurements from the 2009 NEESWood Capstone full-scale tests.