Evaluation and Calibration of Load Deformation Models for Concrete Walls

December 30, 2009
Publication: Thomas T.C. Hsu Symposium: Shear and Torsion in Concrete Structures: ACI SP-265 p 171-198
Author(s): Lowes L. Oyen, Paul E. Lehman D.

Abstract: Recent advances in computational capabilities, both hardware and software, have made nonlinear analysis a viable tool for seismic structural engineering. To fully realize the potential of this tool, however, engineers require nonlinear models and modeling recommendations that have been validated using extensive experimental data sets. For reinforced concrete beams and columns that exhibit primarily flexural response, beam-column elements with fiber-type cross section models have been shown to simulate well observed response. While these types of models are used commonly in practice for design of concrete wall buildings, a comprehensive evaluation of these models for simulating wall response has not been accomplished. Thus, as part of an ongoing study funded by NSF through the NEES program, an investigation of the accuracy of these models for simulating concrete wall response was undertaken. A data set comprising 60 planar wall tests was assembled and used to evaluate the accuracy with which critical response parameters could be predicted. The force-based beam-column element formulations available in the OpenSees platform were used with a standard fiber-typecross section model that simulates flexureaxial load interaction. A MATLAB code was created to facilitate the evaluation process. Results of the evaluation showed that the basic model over-predicted stiffness and under-predicted critical displacements, and an enhanced model was developed that includes a bar-slip model at the base of the wall and an effective, elastic shear stiffness.|The enhanced model was calibrated using the data set, and the MATLAB-based code and MATLAB optimization toolbox were used to find an optimal shear stiffness. For three representative walls, the response history simulated using the enhanced beamcolumn element was compared with that simulated using the Response 2000 and VecTor2 analysis programs. The results of this study show that the enhanced beamcolumn element is appropriate for use in simulating the response of concrete walls with a range of design parameters.