×This report presents the results of a numerical investigation into the behaviour of welded steel tubular truss at elevated temperatures. The purpose is to assess whether the current method of calculating truss member limiting temperature, based on considering each individual truss member and using the member force from ambient temperature analysis, is suitable. Finite Element (FE) simulations were carried out for Circular Hollow Section (CHS) trusses using the commercial Finite Element software ABAQUS v6.10-1[1]. The FE simulation model had been validated against available fire test results on trusses. The simulated trusses were subjected to constant mechanical loads and then increasing temperatures until failure. The elevated temperature stress-strain curves were based on Eurocode EN-1993-1-2 [2]. Initial geometrical imperfections were included, based on the lowest buckling mode from eigenvalue analysis.The numerical parametric study examined the effects of truss type, joint type, truss span-to-depth ratio, critical member slenderness, applied load ratio, number of brace members, initial imperfection and thermal elongation on critical temperatures of the critical truss members. These critical temperatures were then compared with the member-based critical temperatures, which were numerically calculated using ABAQUS but using the member forces obtained from ambient temperature structural analysis as would be the case in the current design method. The results of the numerical parametric study indicate that due to truss undergoing large displacements at elevated temperatures, some truss members (compression brace members near the truss centre) experience large increases in member forces. Therefore, when calculating the member critical temperatures, it would not be safe to use the member forces from the ambient temperature structural analysis. Using the ambient temperature member force may overestimate the truss member critical temperature (based on truss analysis) by 100oC. Finally, this report proposes and validates an analytical method to take into consideration the additional compression force due to large truss displacement. This is based on assuming a maximum truss displacement of span over 30.

×Circular and rectangular hollow sections are used as structural elements of bridges, buildings, crane constructions and onshore- and offshore-wind energy plants. In many cases, joints of these constructions are welded. This facilitates a direct transfer of section forces and moments between the connected structural elements.For both economical and aesthetical reasons, elements for stiffening joints, gusset plates, flange plates, etc. are not used in many cases. The load bearing capacity of an unstiffened joint depends mainly on geometrical and material parameters. The ultimate brace load-bearing capacity also depends on axial chord stresses. Already in the 1960’s, studies on the influence of chord pre-loading on the brace load capacity were published. The results of these early studies have been that compressive chord stresses reduce the load-bearing capacity of the joint. For tensile chord stresses, it was supposed that these stresses only lead to an insignificant reduction of the ultimate brace load-bearing capacity due to stabilisation of the chord wall by tensile stresses. However, no limitations of chord deformation in the ultimate and serviceability limit state were considered at that time. More recent studies, which also consider different deformation criteria, indicate that there is a limitation of joint strength (due to governing deformation aspects) when the chord stresses although not as severe as for compressive stresses.

×This report presents a review of connection design focusing on methods which are already “pre-approved” (acceptable to code), for use by engineers in steel-framed structures, using hollow sections and subject to seismic loading. This is intended to illustrate the limited options currently available to structural engineers.The survey predominantly covers European and North American design solutions, but the latter is also heavily influenced by Japanese practice. The scope covers both braced frame connections (utilizing hollow sections for at least the bracing members) and un-braced frame connections (utilizing hollow section columns), the latter including both rigid and semi-rigid beam-to-hollow section column connections. Dissipative and non-dissipative connection types are considered, where appropriate. Emphasis is placed on connection concepts and principles, rather than detailed formulae, but reference is given to sources for further details. Areas in which there is a paucity of established design guidance are noted and the report concludes with recommendations for further research and development on specific types of connections to hollow sections, subject to seismic loading.

×Circular and rectangular hollow sections are used as load-bearing elements of bridges, buildings, crane constructions and onshore- and offshore-wind energy plants. In many cases joints of these constructions are welded, this enables a direct transfer of section forces and moments between the connected structural elements.Both for economical and aesthetical reasons, in many cases no elements for stiffening of joints, gusset plates, flange plates, etc. are used. The load bearing capacity of an unstiffened joint depends mainly on geometrical and material parameters. The ultimate brace load bearing capacity also depends on axial chord stresses. Already in the 1960’s, studies on the influence of chord pre-loading on the brace load capacity were published. The results of these early studies have been that compressive chord stresses reduce the load bearing capacity of the joint. For tensile chord stresses the belief has been that these stresses only lead to an insignificant reduction of the ultimate brace load bearing capacity due to stabilization of the chord wall by tensile stresses. However, no limitations of chord deformation in the ultimate and serviceability limit state were considered at that time. More recent studies, which also consider different deformation criteria, indicate that there exists a reduction of joint strength when subjected to tensile chord stresses although not as severe as for compressive stresses.