Steel Buildings in Europe

Part 8: Building Envelope 8 - 28  They provide restraint to the purlins in the construction condition (before the installation of the cladding)  They provide additional support to the down-slope component of the applied loads  They help to maintain the alignment of the purlins. The anti-sag rods are assisted in these functions by eaves beam struts and apex ties, both of which are also illustrated in Figure 4.8. 6 10 8 11 7 9 1 2 3 4 5 1 Purlin 2 Eaves beam 3 Column 4 Eaves beam 5 Column 6 Eaves beam strut 7 Purlin 8 Anti-sag ties (at 1/2 or 1/3 span) 9 Rafter 10 Apex tie 11 Rafter Figure 4.8 Typical anti-sag ties and eaves beam strut layout The need for anti-sag rods is dependent on a number of factors, including the chosen purlin section, the spacing between the purlins, the span of the purlins and the magnitude of the applied loads. Advice on this issue may be obtained from the purlin manufacturers’ technical literature. In some instances, the specifier may have a choice between the use of anti-sag rods or the selection of a heavier purlin that does not require intermediate restraint or support. There is clearly a trade-off between the cost of a heavier purlin section and the time (and corresponding cost) associated with the installation of additional components. Anti-sag rods only provide restraint at discrete locations along the span of the purlin. The purlins should only be considered to be ‘fully’ restrained under