The light steel inside a building.

In a steel-framed building the roof sheeting is carried on purlins spanning between the rafters of the main frames. Z purlins are lapped or sleeved over each rafter so they run continuous over several bays, while C purlins suit single spans, eaves and openings. Buyers specify the section depth, thickness and steel grade, commonly to AISI S100 and ASTM A653 in the US, EN 1993-1-3 and EN 10346 in Europe, and AS/NZS 4600 with AS 1397 steel in Australia.

Z Purlin and C Purlin carry the roof sheeting between the rafters. Sag Rods tie the purlins together at mid-span or third points so they stay straight and upright while the sheeting goes on. The main frames, cleats, roof sheeting and fixings come from the building supplier.

Wall cladding on a steel building hangs on horizontal members spanning between the columns, called girts in the US and side rails in the UK. They are the same cold-formed C and Z sections used in the roof, turned on their side and fixed to column cleats. Openings for doors and windows are framed with C sections.

C Purlin and Z Purlin carry the wall cladding between the columns and frame the openings. Sag Rods hang the girts from the eaves so they do not sag under their own weight and the cladding. Columns, cleats, cladding and fixings come from the building supplier.

Pipes, ducts and cable trays in a building are often carried on trapeze hangers: a length of strut channel hung level from the structure on two threaded rods. Several services can share one trapeze, and each is clamped to the channel. Buyers specify the channel profile, 41 x 41 mm or 41 x 21 mm (1-5/8 x 1-5/8 in or 1-5/8 x 13/16 in), its thickness, slotted or plain, and the finish.

Universal Strut Channel / ‘C’ Strut Channel is the trapeze bar. Accessories supply the channel nuts that grip the in-turned lips, the brackets and the clamps that fix the services to it. Threaded rod, anchors and the pipes, ducts and trays themselves come from other suppliers.

Strut channel is also bolted together into frames: wall supports for conduit, stands for plant and panels, cable ladder supports and small structures on roofs. The slotted channel lets fittings be moved and re-fixed on site without drilling or welding. Back-to-back channels make heavier posts and beams.

Universal Strut Channel / ‘C’ Strut Channel forms the posts, rails and cantilevers. Accessories provide the channel nuts, flat and angle plates, and brackets that join the lengths into a frame. Bolts, anchors and the supported equipment come from other suppliers.