Comparison of displacement coefficient method and capacity spectrum method with experimental results of RC columns

For the performance-based seismic design of buildings, both the displacement coefficient method used by FEMA-273 and the capacity spectrum method adopted by ATC-40 are non-linear static procedures. The pushover curves of structures need to be established during processing of these two methods. They are applied to evaluation and rehabilitation of existing structures. This paper is concerned with experimental studies on the accuracy of both methods. Through carrying out the pseudo-dynamic tests, cyclic loading tests and pushover tests on three reinforced concrete (RC) columns, the maximum inelastic deformation demands (target displacements) determined by the coefficient method of FEMA-273 and the capacity spectrum method of ATC-40 are compared. In addition, a modified capacity spectrum method which is based on the use of inelastic design response spectra is also included in this study. It is shown from the test specimens that the coefficient method overestimates the peak test displacements with an average error of +28% while the capacity spectrum method underestimates them with an average error of -20%. If the Kowalsky hysteretic damping model is used in the capacity spectrum method instead of the original damping model, the average errors become -11% by ignoring the effect of stiffness degrading and -1.2% by slightly including the effect of stiffness degrading. Furthermore, if the Newmark-Hall inelastic design spectrum is implemented in the capacity spectrum method instead of the elastic design spectrum, the average error decreases to -6.6% which undervalues, but is close to, the experimental results. Copyright (C) 2003 John Wiley Sons, Ltd.