BUCKLING BEHAVIOR OF H-SHAPED BEAM WITH CONTINUOUS RESTRAINT INSTALLED TRANSVERSE STIFFENERS AND METHOD FOR DECIDING STIFFENING POSITION

Abstract

 Transverse stiffeners are effective for lateral buckling of H-shaped steel beams with continuous restraint on the upper flange because of constraining the deformation of the cross-section of beam members. There are, however, few studies on the additional stiffening effect of stiffeners on continuously restrained beam members, and the position to install stiffener is not clear. Therefore, the purpose of this paper is to evaluate the buckling strength of H-shaped beam members with continuous restraint and installed transverse stiffeners — furthermore, the position where stiffeners should be installed is investigated.

 In this study, the elastic buckling strength is calculated by the theoretical analysis using the energy method, and from these numerical simulations, the relationship between the geometric shape of the beam members and the stiffening effect is clarified. Also, the evaluating equation for lateral buckling strength is established by using the numerical simulation results. Moreover, the numerical analyses based on the finite element method are performed. The classification of the collapse mode, the maximum strength and the plastic deformation capacity are examined.

 From this research, the following are found.

 1) The stiffening effect (i.e., the increase of lateral buckling strength) is more effective at a position where the deformation of lateral buckling of the beam members without stiffeners is significant. In the case of stiffeners are installed at only one place on beam members, the stiffening effect increases as the moment gradient becomes large and the compressive region of the lower flange becomes narrow. Also, the cross-sections which have a large effect on the restraining upper flange are hard to deform due to lateral buckling, so the stiffening effect is also hard to increase.

 2) New evaluating index λ_cr was proposed. By using new index λ_cr, it is possible to evaluate the stiffening effects regardless of the cross-sectional shape. By means of the new index, moreover, the equation (3.4), which evaluates the elastic buckling strength of the H-shaped beam members with continuous restraint installed transverse stiffeners, has been proposed.

 3) Optimum stiffening position L_S^* is defined as the position where maximizes the stiffening effects. The equations evaluating optimum stiffening position and the maximum stiffening effect are derived by approximating.

 4) The elastic buckling strength of H-shaped beam members with continuous restraint and installed transverse stiffeners can be calculated based on equation (3.4). When the coupled buckling occurs, however, a slight reduction in the buckling strength should be considered. Especially in the case of the stiffening position is near the end of the beam members, the buckling strength is significantly reduced.

 5) The classification of the collapse mode is possible by means of the generalized slenderness ratio λ_b, which is modified by the evaluating formula (3.4) for the lateral buckling strength. Furthermore, the evaluations of the maximum strength and the plastic deformation capacity are also possible by means of the generalized slenderness ratio λ_b.