Steel Buildings in Europe

Part 2: Concept Design 2 - 7 Table 1.2 Efficient portal frame design Most Efficient Less Efficient Analysis using elastic-plastic software Elastic analysis Cladding considered to restrain the flange of the purlins and side rails Purlins and side rails unrestrained Purlins and side rails used to restrain both flanges of the hot-rolled steelwork The inside flange of the hot rolled steelwork is unrestrained Nominal base stiffness utilised Nominal base stiffness ignored The reasons for choosing simple beam structures, portal frames or trusses are shown in Table 1.3. Table 1.3 Comparison of basic structural forms for single storey buildings Simple beam Portal frame Truss Advantages Simple design Long span Very long spans possible Designed to be stable in-plane Heavy loads may be carried Member sizes and haunches may be optimised for efficiency Modest deflection Disadvantages Relatively short span Software required for efficient design Generally more expensive fabrication Bracing needed for in-plane stability Limited to relatively light vertical loading, and modest cranes to avoid excessive deflections Generally bracing is used for in-plane stability No economy due to continuity 1.3.1 Cladding types The main types of roofing and wall cladding used in single storey buildings are described as follows: Roofing  ‘Built-up’ or double layer roofing spanning between secondary members such as purlins.  Composite panels (also known as sandwich panels) spanning between purlins.  Deep decking spanning between main frames, supporting insulation, with an external metal sheet or waterproof membrane. Walls  Sheeting, orientated vertically and supported on side rails.  Sheeting or structural liner trays spanning horizontally between columns.  Composite or sandwich panels spanning horizontally between columns, eliminating side rails.  Metallic cassette panels supported by side rails.