Hollow Flange Research Articles

Recent innovations in cold-formed tubular sections

Cold-formed tubular sections are widely used in many modern steel structures. Two innovative cold-formed sections have been introduced to the Australian building industry. They are the 'in-line' galvanized rectangular hollow section (RHS) tubes and the hollow flange beams (HFB). They offer significant advantages but at the same time provide challenges to designers because of their special characteristics. The application, manufacturing, advantages and characteristics of these two sections are described.

Buckling Experiments on Hollow Flange Beams with Web Stiffeners

The hollow flange beam (HFB) is a new cold-formed and resistance-welded section developed in Australia. Due to its unique geometry comprising two stiff triangular flanges and a slender web, the HFB is susceptible to a lateral-distortional buckling mode of failure involving web distortion. Investigation using finite-element analyses showed that the use of transverse web plate stiffeners effectively eliminated lateral-distortional buckling of HFBs and thus any associated reduction in flexural capacity. A detailed experimental investigation was then carried out to validate the results from the finite-element analysis and to improve the stiffener configuration further. This led to the development of a special stiffener that is screw-fastened to the flanges on alternate sides of the web. This paper presents the details of the experimental investigation, the results, and the final stiffener arrangement whereas the details of the finite-element analyses are presented in a companion paper.

Finite-Element Analysis of Hollow Flange Beams with Web Stiffeners

A new cold-formed and resistance-welded section known as the hollow flange beam (HFB) has been developed recently in Australia. In contrast to the common lateral-torsional buckling mode of I-beams, this unique section comprising two stiff triangular flanges and a slender web is susceptible to a lateral-distortional buckling mode of failure involving lateral deflection, twist, and cross-section change due to web distortion. This lateral-distortional buckling behavior has been shown to cause significant reduction of the available flexural capacity of HFBs. An investigation using finite-element analyses and large-scale experiments was carried out into the use of transverse web plate stiffeners to improve the lateral buckling capacity of HFBs. This paper presents the details of the finite-element model and analytical results. The experimental procedure and results are outlined in a companion paper.

Lateral-Distortional Buckling of Hollow Flange Beams

While the flanges of cold-formed hollow flange beams (HFBs) are very stiff torsionally, their webs are comparatively flexible, and may allow web distortion effects to reduce their resistances to lateral buckling. There is no simple formulation for predicting the effects of web distortion on the lateral buckling of HFBs. As a result, structural designers are unable either to check or to extend the available elastic buckling predictions; thus code writers are not able to provide explicit formulations for the effects of distortion. The conversion from elastic buckling to strength for HFBs is also questionable, since cold-formed beams have different stress-strain curves, residual stresses, and geometrical imperfections from those of hot-formed beams. This paper deals with these problems, first by finding a simple but sufficiently accurate closed-form solution for the effects of distortion on the elastic lateral buckling of simply supported HFBs in uniform bending, and then by developing an advanced theoretical method of predicting the effects of the stress-strain curve, residual stresses, and geometrical imperfections on the strengths of HFBs that fail by lateral-distortional buckling. Such a method allows the development of a conversion from elastic buckling to strength, which is appropriate for HFBs. The use of this conversion together with the simple approximation developed here for elastic lateral-distortional buckling provides a rational basis for the lateral buckling design of unbraced HFBs.

Branch plate to reinforced HSS connections in tension and compression

The tension and compression zones of moment plate connections were studied separately by testing branch plate and hollow structural section connections under each type of loading. Square hollow section flanges were reinforced by doubler plates fillet-welded all around. The results from 13 specimens tested in tension indicate that branch plate to reinforcing plate width ratio is an important parameter in joint behaviour. The dominant failure mode was punching shear of the reinforcing plate. The importance of reinforcing plate and HSS wall thicknesses was apparent from the results of 13 specimens tested in the compression series. The capacities of specimens in all but one test in this series were limited by failure of the HSS webs. Key words: hollow structural sections, W-shape, columns, beams, connections, experimental, design, steel.

A Proposed Skirtlike, Hollow Flange Design for Self-Locking Hex Nuts.

Continued experimentation with photoelastic simulations confirmed that our proposed hollow flange design for hex nuts is as effective against loosening by vibration as against loosening due to uneven load distribution by virtue of distributing the load evenly on the symmetrical periphery of the flange through raising the fulcrum point on the threads away from the bearing surfaces of the nut and its seat.