ELASTIC SHEAR BUCKLING STRENGTH OF L-SHAPED BEAM-TO-COLUMN JOINT PANELS COMPOSED WITH I-SHAPED MEMBERS

Abstract

 In factories and warehouses, I-shaped cross-section members are often employed for column and beam members, and an L-shaped joint panel (panel) is formed at a column-to-beam joint. Ordinary, the joint panels are restrained on their four sides by column and beam members; however, because a column and a beam member are connected only to adjacent sides, the behavior of the panels is assumed to be different.

 The current design procedure that allows the joint panels to yield under a destructive earthquake has been established in Japan because the joint panels have been proven to have large deformation capacity. On the other hand, the structural performance of the panels is not entirely explained. In particular, it is not clear that the influencing factors on the buckling strength. Therefore, it is important to clarify the structural performance of the panels in the current design procedure that allows the plasticization of the joint panels.

 The purpose of this study is to establish a buckling strength evaluation formula for the panels employed in steel structures such as factories and warehouses. It is essential to clarify the complex stress state and the buckling displacement function to establish the buckling strength evaluation formula. In this paper, only the panel web is extracted, the stresses acting on the panel web is expressed by Airy stress function, and the shear buckling coefficient is calculated based on the derived stress function by applying the energy method. Also, since a column and a beam are connected to the panels in two directions, the stress distribution changes depending on the load direction. As a result, the buckling strength of the panels changes depending on the load direction. Furthermore, the solution, evaluating the shear buckling strength considering the difference in the load direction, is proposed. Finally, reflecting these findings, a formula for evaluating the shear buckling coefficient is established. The validity of the evaluation formula is verified by comparing it with FE analysis results.

 

 The following are found.

 1) In the panel web, the boundary conditions of four sides can be regarded as fixed support conditions within the range of realistic width-to-thickness ratio, and the buckling at panel web is dominant.

 2) In the examination only for the panel web, the ratios of shear to bending α_b, α_c (index of the stress state of beam member, and column member) do not have an impact on the buckling strength. It is shown that the elastic buckling strength of the panel web is determined by the parameters related to the panel shape (section modulus ratio z_bw, z_cw and panel aspect ratio λ_p).

 3) It is shown that the distributed axial force acts on the panel web from the column and beam member, and this distributed axial force is evaluated with parameters related to the beam shape and the column shape.

 4) It is confirmed that the elastic buckling strength, which is calculated based on the energy method, is evaluated on the safe side by using the correlation curve between the distributed axial force, which is transmitted from a column and a beam member, and the shear buckling strength. The proposed evaluation formula can evaluate the elastic buckling strength accurately. Finally, the validity is confirmed by comparing eigenvalues obtained from FE analysis.