Steel Buildings in Europe

Part 2: Concept Design 2 - 40 buckling is based on the length between out-of-plane restraints – usually the roof purlins or other members. 5. Select the tension chord member. The critical design case is likely to be an uplift case, when the lower chord is in compression. The out-of-plane buckling is likely to be critical. It is common to provide a dedicated system of bracing at the level of the bottom chord, to provide restraint in the reversal load combination. This additional bracing is not provided at every node of the truss, but as required to balance the tension resistance with the compression resistance. 6. Choose internal members, whilst ensuring the connections are not complicated. 7. Check truss deflections. 4.5 Rigid frame trusses The structures described in Sections 4.1 and 4.4 are stabilised by bracing in each orthogonal direction. It is possible to stabilise the frames in-plane, by making the truss continuous with the columns. Both chords are fixed to the columns (i.e. no slip connection). The connections within the truss and to the columns may be pinned. The frame becomes similar to a portal frame. For this form of frame, the analysis is generally completed using software. Particular attention must be paid to column design, because the in-plane buckling length is usually much larger than the physical length of the member. 4.6 Connections Truss connections are either bolted or welded to the chord members, either directly to the chord, or via gusset plates, as shown in Figure 4.6. 3 Figure 4.6 Truss connections Trusses will generally be prefabricated in the workshop, and splices maybe required on site. In addition to splices in the chords, the internal member at the splice position will also require a site connection. Splices may be detailed with cover plates, or as “end plate” type connections, as shown in Figure 4.7.