The maximum spacing of the trusses is at 3000 mm c/cįor continuous purlins, minimum depth of section (preliminary guide) = L/45 Permanent action γ G = 1.35 (unfavourable) Partial Factor for loads (BS EN 1990 NA 2.2.3.2 Table NA.A1.2(B)) Furthermore, if manual analysis is employed to analyse a truss loaded in such a manner, such secondary stresses may not be captured especially if nominally pinned connections are assumed.Ĭold formed Z (Zed) and C (channel) sections are normally specified for roof purlins in steel structures (see their form in image below). By implication, purlins should ideally be placed at the nodes of trusses and not on the members themselves so as not to induce secondary bending and shear forces in the members of the truss.
The spacing of roof purlins on rafters usually calls for careful arrangement, in the sense that it should follow the nodal pattern of the supporting trusses. Arrangement of Roof Purlinsīy default, purlin sections assume the slope of the roof they are supporting. This article will be focusing on design of steel purlin using cold formed sections. Therefore, a purlin should be adequately strong to withstand the loads it will encounter during its design life, and should not sag in an obvious manner thereby giving the roof sheeting an undulating and/or unpleasant appearance. during maintenance services and repairs), and environmental loads (e.g. In their design life, purlins are subjected to dead load (e.g self weight of sheeting materials and accessories), live load (e.g.
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