ANALYSIS OF THE CYCLIC INELASTIC RESPONSE OF BRACED STEEL STRUCTURES (BUCKLING, INELASTIC)

This research report presents a state-of-the-art model for inelastic response analysis of braced steel structures. This model achieves realism and efficiency by combining analytical formulations describing plastic hinge behavior with empirical formulae developed based on a study of experimental data. As such it is suitable for studying the inelastic cyclic behavior of individual elements as well as the dynamic response of relatively large structural systems.; The brace is idealized as a pin-ended member with a plastic hinge located at its midspan. The plastic state of the plastic hinge is defined by a specified interaction curve relating axial force and plastic hinge moment. The plastic axial and rotational deformations at the plastic hinge are defined based on the flow rule. Based on these assumptions, analytical expressions for the axial force versus axial deformation behavior of the brace are derived as a solution of the basic beam-column equation. While these expressions form the basis of the new model, several empirical behavioral characteristics are implemented in this modeling in order to achieve better representation of observed cyclic inelastic behavior. These empirical characteristics include: the variation of the tangent modulus of elasticity during cycles, the gradual plastification process of the plastic hinge, etc.; Verification of the new model is performed on the basis of quasi-static analyses of individual struts and dynamic response analyses of a three-story X-braced steel frame. The inclusion of the empirical characteristics has achieved a refined representation of hysteresis loops for braces. Furthermore, it has become clear that the new model is able to accurately simulate the cyclic inelastic behavior of steel braces and is efficiently applicable to dynamic analyses of braced frame structures.; The model is applied to the study of the design of a real sized six-story K-braced steel building frame. From this study, it has become clear that the braces' slenderness ratio, buckling strength, and material properties have a great influence on the performance of the braced frame. The brace model permits the influence of the parameters on structural behavior to be easily assessed.