Steel Buildings in Europe

Part 8: Building Envelope 8 - 23 3.8.2 Deflections The cladding must be capable of carrying the specified design loads without deflecting excessively, if the other performance requirements such as weathertightness, airtightness and durability are to be achieved. The predicted deflections are normally calculated for the unfactored variable actions only. Loading at the construction stage is not normally included in the serviceability load cases and is not normally considered when specifying cladding systems. However, care must be taken on site to avoid excessive local deflections, especially those caused by concentrated loads such as foot traffic or stacked materials on roof liner sheets, as these could result in permanent damage to the cladding. Typical deflection limits imposed on the cladding are dependent on the loading regime considered (imposed load only or permanent plus imposed loading), the location (wall or roof) of the structural component and whether a brittle material is present. Deflection limits may be specified by National regulations. Common deflection limits are:  Span/150 for wall cladding, spanning between secondary steelwork  Span/200 for roof cladding, spanning between purlins  Span/180 for purlins or side rails. 3.8.3 Use of safe load tables The manufacturers of profiled metal sheeting and insulated panels provide safe load tables for their products, which may be used either to select a suitable profile or, where the profile has already been chosen, to determine the maximum permissible purlin spacing. It is important to note that the load tables often assume that the loading is uniformly distributed and that safe working loads are usually specified. If in doubt, specifiers should seek guidance from the cladding manufacturers.