Steel Buildings in Europe

Part 1: Architect’s Guide 1 - 13 Portal frames Portal frames typically use hot-rolled I-section beams and columns for the roof rafters and supporting columns, although cold formed sections may be adequate for small span structures. Portal frames come in a variety of different shapes and sizes, with flat and pitched roofs. A typical configuration is shown in Figure 3.1. The roof and wall cladding is supported on purlins and side rails that span between the portal frames. Bracing is not needed between every frame but is needed in at least one bay to transfer longitudinal forces (normal to the frames) to the side walls and thus to ground level. In some special design situations, the cladding can be used as the bracing – this is known as stressed skin design. The design of the cladding and the fixings to the supporting members will be assessed by the structural engineer. In most cases, bracing will be provided that does not rely on the sheeting. Figure 3.1 Typical structural configuration of a portal frame structure