Steel Buildings in Europe

Part 8: Building Envelope 8 - 27 1 Double-span purlin 2 Penultimate support 3 Rafter 4 Sleeve Figure 4.6 Double-span lengths – non sleeved system Double-span lengths - sleeved system In double-span sleeved systems, the double-span lengths are staggered and sleeves are provided at alternate supports (Figure 4.7). Sleeves are provided to every purlin at the penultimate support to ensure semi continuity. A double span sleeved system has a slightly higher capacity than the double-span non-sleeved system and has the advantages of semi continuity at all sleeve positions. This system is limited to bay sizes less than 8 m, for reasons of transport and erection. Heavier purlins can be provided in the end bays, if necessary. 1 Sleeved double-span purlin 2 Sleeve Figure 4.7 Double span lengths - sleeved system 4.1.3 The use of anti-sag rods for purlins Anti-sag rods are small rods or angles that are bolted or clipped between the purlins. A typical arrangement is shown in Figure 4.8; other systems are also available. When used, they are commonly placed either at mid-span or at third points along the purlin and serve the following functions:  They provide restraint to the purlins against lateral-torsional buckling under wind uplift conditions