Design of Steel Beams in Cantilever-Suspended-Span Construction

Abstract

In cantilever-suspended-span construction, secondary framing members such as open-web steel joists are likely to enhance markedly the stability of the beams that support them. Properly made joist-beam connections enable the joists to provide both lateral and torsional restraints to the beam top flange at discrete locations. This restraint, in turn, is transmitted through the web to the bottom flange of the beam, which is in compression in negative moment regions. Therefore, the buckling modes are generally characterized by the occurrence of web distortion. Current design procedures for this very common form of construction are inadequate as they do not consider web distortion and the beneficial effect of torsional restraint. They may also neglect the detrimental effect of the height of load application above the shear center. This results in an inaccurate assessment of the lateral-torsional buckling resistance. A finite-element model, corroborated by tests, is used to develop a simplified design procedure for these beams.