A HYSTERETIC MODEL FOR LATERALLY UNSUPPORTED H-SHAPED STEEL BEAMS CONSIDERING LOCAL AND LATERAL BUCKLING UNDER CYCLIC LOADING

Abstract

 Generally, steel frameworks are designed based on a beam-collapse principal that ensures a beam-to-column strength ratio that in the event of an earthquake distributes damage to each floor. Beams are important earthquake resistant members that dominate the seismic response of the entire structure. It is therefore important to clarify the performance of steel beams that are subjected to the seismic forces associated with repeated loads.

 We previously proposed hysteretic models to express the response to cyclic lateral torsional buckling of H-shaped beams with a large slenderness ratio λ_b.^1),2) In addition, we proposed a monotonic loading history model under a uniform bending moment (κ = -1.0) and a one-end bending moment (κ = 0.0) for beams with a small slenderness ratio, again under lateral torsional buckling.³⁾ However, to date, no monotonic loading history models has been developed for H-shaped beams subjected to an antisymmetric bending moment (κ = 1.0), or an associated cyclic loading hysteretic model.

 Therefore, the purpose of this study was to develop hysteretic models for H-shaped beams with a small slenderness ratio under cyclic loading for lateral torsional buckling that take into account coupling between local and lateral buckling. This buckling process is investigated using the finite element method (FEM). Based on the analytical results, hysteretic models for a H-shaped steel beam with a small slenderness ratio for lateral torsional buckling were formulated. These models consider the width-to-thickness ratio, the slenderness ratio, the stationary limit amplitude, the unloading stiffness, and the stiffness change point.

 The conclusions obtained in this study are as follows:

 1) Equations (19) and (20) were proposed as hysteretic models under monotonic loading based on the analysis results for H-shaped steel beams subjected to antisymmetric bending.

 2) Based on the above model and the results of a previous study,³⁾ a hysteretic model under cyclic loading composition rule is shown in Fig. 22.

 3) The applicable range for the hysteretic model under cyclic loading was found to be approximately 0.6≤ λ_b ≤0.7 (κ = -1.0), 0.4≤ λ_b ≤0.7 (κ = 0.0), 0.5≤ λ_b ≤0.9 (κ = 1.0).