Steel Buildings in Europe

Part 1: Architect’s Guide 1 - 23 may be exposed in the completed structure, which may increase the fabrication costs if, for example, hollow sections are used for the members. The span/depth ratio for flat trusses is typically 15 to 20 for spans up to 100 m. Trusses are usually planar and will generally require bracing of some form to provide stability. As an alternative, three-dimensional trusses can be created, as shown in cross section in Figure 3.18 and illustrated in Figure 3.19. This form of truss is generally expensive to fabricate, because of the complex intersections of the internal members. The span/depth ratio for three-dimensional trusses is typically 16 to 20 for spans over 50 m. Triangular truss (with circular hollow sections) Triangular truss (with rectangular hollow sections) Figure 3.18 Three dimensional triangular trusses Figure 3.19 Three-dimensional trusses supporting a roof 3.1.3 Cable stayed roofs In a cable-stayed structure, tensile members (wire ropes or bars) are provided to give intermediate support to members such as roof beams, thus allowing those members to be reduced in size. The stays need to be supported by columns or masts and those members need to be anchored or braced with other stays. The bracing arrangement is usually very conspicuous and the aesthetics