Available Sizes and Shapes

Cold-formed C and Z purlins are the workhorses of the industry. Configurations of these members have originated at the bending press they represent the two basic ways to bend a sheet of metal into a section with a web and two flanges. Light-gage purlins of 8 to 12 in in depth can span 25 to 30 ft, and even more, depending on the loading, material thickness, and deflection criteria. Purlin spacing is dictated by the load-carrying capacity of the roof panels; a 5-ft spacing is common. Appendix B includes section properties for purlin sizes offered by some manufacturers.

Cold-formed purlins are normally made of high-strength steel. Uncoated cold-formed members, still in the majority, usually conform to ASTM A 570 or A 607. Occasionally, galvanized purlins are provided. The old designation for galvanized members, ASTM A 446, has been replaced with a new ASTM Standard Specification A 653.7 The new standard includes the designations of zinc coating, G60 and G90, which used to be a part of a separate standard, ASTM A 525. (The latter has been replaced by ASTM A 924, which now covers all kinds of metal coatings applied by a hot-dip process.) For the products of structural quality (SQ), three grades 33, 40, and 80 are available, corresponding to the old grades A, C, and E of ASTM A 446. For example, ASTM A 653 SQ grade 40 with coating designation G60 takes the place of the old ASTM A 446 grade C...