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Increasing the strength and stiffness of cold-formed hollow flange

Section Moment Capacity of a New Cold-Formed Hollow Flange Channel Section

The details of the investigation into the lateral distortional buckling behavior of LiteSteel beam (LSB) sections that included the development and validation of a finite element model are discussed. The results show that the current design recommendations are not suitable for LSB sections.

Finite Element Analysis and Design of LiteSteel Beam Sections

In structures, steel members are primarily chosen according to the properties of their cross-sections. Hot-rolled sections, such as the universal beam and channel, are efficient in bending, as the majority of the material is located away from the neutral axis of the section, but are torsionally weak, and have low resistance to flexural-torsional buckling. Hollow structural sections (HSS) are extremely stiff torsionally compared to open sections, but the distribution of the steel cross-section relative to its neutral axis is not as efficient as that of open sections. Between early 1990 and mid 1995, Palmer Tube Mills Pty Ltd (PTM), now known as Smorgon Steel Tube Mills (SSTM) developed and refined a technique to roll-form steel strip and produce two simultaneous electrical resistance welds. This development resulted in the 'Dogbone' Hollow Flange Beam (HFB) as shown in Figure 1a, which was the world's first cold rolled, fully Dual Resistance Welded (DRW) structural beam, formed from a single high strength steel strip. The revolutionary cross sectional shape of the HFB had some unique failure modes such as flexural distortional buckling and bearing capacity failure. Research was required to investigate these failure modes before these sections could be used efficiently and safely. This research included analytical, experimental and numerical studies (Hancock et al (1994), Sully et al (1994), Pi and Trahair (1997), Avery et al (2000)). SSTM has recently introduced a new shape using this technology, the hollow flange channel, known as the LiteSteel Beam (LSB), as shown in Figure 1b. This paper forms part of a project to investigate the behaviour of LSB.

Bearing Tests of LiteSteel Beams (LSB)

Cold-formed steel beam sections remain an economic structural option in many applications given the cost & other advantages in their manufacture, efficiencies in section properties and material properties, and ease of handling, fabrication and connections - all relative to hot-rolled steel. However, they have not commonly been associated with high-load beam applications due to potential for localised instability in open sections necessitating additional stiffening elements or substitution by heavier sections. The development of hollow-flange sections has raised the upper limit of bending performance for cold-formed steel members and now recent innovation in relatively simple, high-capacity moment connections has further added to the suitability of these for high-load applications as a competitive alternative to hot-rolled sections. Case study details are given for an application of hollow-flange Long Span Beam in portal frame construction to be sited in Region D cyclonic conditions, including performance testing of innovative moment connections. Other developing applications include high-efficiency fabricated trusses, structural plan bracing, and fixed-ended purlin connections. These developments have largely been the result of critical engineering study of design and construction aspects in the use of steel to maximise the structural performance while minimising the construction limitations typically associated with steel.

Geoff Fletche

Papers

Engineering Advances in Cold-Formed Steel Hollow-Flange Long Span Beams