Young Bong Kwon

Strength design curves for thin-walled sections undergoing distortional buckling

Abstract Certain types of cold-formed sections, notably those composed of high-strength steel, some decking sections and racking sections may undergo a mode of buckling called distortional in which edge and intermediate stiffeners are inadequate to prevent lateral movement of the flanges which they support. The existing design methods in current standards and specifications are often not adequate to account for distortional buckling. This paper describes proposed strength design curves for thin-walled sections undergoing distortional buckling. The design curves are based on testing and the test data base is included in the paper. The influence of local buckling on distortional buckling is also discussed.

Development of Cold-Formed Steel Portal Frames with PRY Sections

A series of column, beam, and connection tests for portal frames which consisted of closed cold-formed steel PRY sections as columns and rafters were carried out. Firstly the compressive and the flexural strengths of the PRY sections were investigated, and secondly the structural behavior of the connections including the moment-rotation relation, the yield and the ultimate moment capacities of the connections were studied. The connection test specimens consisted of column-base, column-to-rafter, and rafter-to-rafter connections. The main testing parameters of the connection tests were the thickness and the shape of mild steel connectors, which were important for the proposed attachment system of wall panels. The connection test results were compared with those achieved by using advanced analysis procedures. The semi-rigid connection concept was considered appropriate for the analyses of the portal frames using the secant stiffness of the connections, which were estimated from the measured moment-rotation curves of the connections tested. Simple formulae for the shear resistances of the screwed connections were also proposed after calibrated with test results. The performance of the portal frame with PRY sections was investigated through the full scale tests.

The Ultimate Strength of the Concrete-Filled Tubular (CFT) Section Columns

This paper describes design strength of concrete-filled tubular (CFT) section columns accounting for local buckling of steel skin. The local buckling has a negative effect on the ultimate compression strength based on the yield stress of steel skin and nominal compressive strength of in-filled concrete. A squash load formula for CFT stub columns is proposed to account for the post-local-buckling strength of steel skin. A compressive strength formula for filled-in concrete accounting for the confining effect of steel skin and strength ratio between filled-in concrete and steel skin is also proposed. The squash loads predicted by the proposed strength formula for the direct strength method were compared with the AISC (2010) and Eurocode4 (2004). The comparison showed that the squash load formula proposed can predict conservatively the squash load of circular and rectangular CFT columns with local buckling

Evaluation of the Fire Resistance of H-Section Steel Columns and Beams

Building fires can cause severe damages to not only human life but also building structures. Therefore, every nation requires a building regulation related to fire in aspect of safety of human and structural stability. The structural stability under fire condition can be evaluated by the fire test defined in each nation’s standard. However, the results from the test don’t satisfy the real situations of the building such as fire loads, opening size, loading and boundary condition of structural members, and etc. Meanwhile, performance based fire engineering design is regarded as an alternative evaluation method of fire. The fire engineering method has been regarded as a more rational method than the prescriptive method in terms of accuracy and cost efficiency. Recently, the limit temperature method is regarded as the easiest fire engineering method to evaluate the structural stability under fire. To make the backbone of a specification of limiting temperature method, limiting temperatures of various structural members are required. In this paper, in order to make a database of the limiting temperatures of H-section columns and beams, fire test programs with loading were conducted and the limiting temperatures and fire resistance were derived.

Flexural Tests on the H-Section Simple Beams with Local Buckling

This paper describes a series of flexural tests conducted on the H-section beams fabricated from SM490 plate of thickness 0.6mm with nominal yield stress 315 MPa. Flexural members with large width-to-thickness ratios in the flanges or the web may undergo local buckling before lateral-torsional buckling. The local buckling has a negative effect on the moment capacity based on the lateral-torsional buckling. Simple bending moment capacity formulas for flexural members were calibrated to the test results to account for interaction between local buckling and lateral-torsional buckling. The ultimate flexural strengths predicted by the proposed formulas for direct strength method were compared with the AISC (2005) and Eurocode3 (2003). The comparison showed that the moment formulas proposed can predict conservatively the bending moment capacity of H-section flexural members with local buckling.