Effect of strain softening on the ultimate strength and stability of flexible frames.

Abstract

The principal role of any structural connection is to transfer forces safely between the various components meeting at that joint. Therefore, it is important for these connections to provide adequate structural strength to resist the loads and possess the necessary ductility to deform as the structure resists the loads. Local buckling or distortion of cross-section due to the complexities and irregularities in geometry of many types of connections of found to be a source of softening in the moment-rotation behavior of some kinds of connections and has an effect on the maximum load-carrying capacity of steel structures. In this study, a computer program is developed for the analysis of flexibly jointed frames. The connections are represented by nonlinear spring elements at the ends of members. An elastic-plastic hinge plane frame analysis including the effect of nonlinear connection behavior is presented to predict the ultimate load-carrying capacity of steel frames with sufficient accuracy. Members between plastic hinges are assumed to behave elastically. The nonlinear moment-rotation behavior of the connection is represented by a four parameters Richard model. The main objective of this study is to investigate the effect of connections with a strain softening behavior on the ultimate strength and stability of flexible frames. Further studies include the effect of connection flexibility on the drift of multi-story frames. The result of the analysis shows that the drift in multi-story frames can be reduced by increasing the stiffness of the connections used in the structure. Numerical studies of frames made using the developed computer program are presented. Observations regarding the effects of flexible connections on the strength and deflection of steel framed structures are discussed. The proposed analyses considering flexible joints using Richard model to represent the connection behavior were found to be simple and accurate.