"Nonlinear Analysis of Reinforced Concrete Frames under Cyclic Load Reversals"
by F.C. Filippou and A. Issa

Abstract: This study endeavors to develop improved analytical methods for predicting the nonlinear static and dynamic response of multistory reinforced concrete frames. This report is limited to the study of the static response.

A new approach in describing the nonlinear hysteretic behavior of reinforced concrete frame elements is proposed. This approach consists of isolating the basic mechanisms controlling the hysteretic behavior of girders and columns into individual subelements which are connected in series to form the girder or column superelement. Two particular subelement models are developed in this study: one describes the inelastic behavior along the girder accounting for the gradual spread of inelastic deformations at the girder ends, while the other models the fixed-end rotations that arise at the beam-column interface due to bond deterioration and slippage of reinforcing bars in the beam-column joint region. The properties of these elements can be derived from basic principles or refined finite element models.

Because several subelements are connected in series and each of these follows a different hysteretic rule, internal unbalanced moments might arise between these elements at any given load step. The implementation of the proposed superelement model thus requires the development of a numerical scheme which accounts for these unbalanced moments between subelements. Such a scheme is developed in this study within the framework of a special purpose analysis program for the nonlinear static and dynamic analysis of reinforced concrete moment-resisting frames.

To establish the validity of the proposed models correlation studies of analytical predictions with experimental evidence of the load-displacement response of beam-column subassemblages under static load reversals are conducted. The analytical predictions generally show excellent agreement with the experimental results.

The predictions of the proposed model are also compared with those of the widely used one-component model. The two models are compared by investigating the local and global response of simple structural subassemblages under cyclic load reversals. One of the key parameters of the one-component model, namely, the post-yield stiffness of the moment-rotation envelope curve is varied in these studies. It is concluded that the parameters of the one-component model can be adjusted to match reasonably well a given response. These parameters vary, however, with the type and history of loading as well as with the type of subassemblage. By contrast, the proposed model, while maintaining computational efficiency, is based on parameters which are directly connected with the physical properties of the structural elements and can be derived by well established rational methods.

If you are interested in a copy of this report, please contact the EERC Library at eerclib@shake.berkeley.edu or send e-mail to Professor Filippou