Purlins and Girts are Secondary Framing members used to support roof and walls panels. In addition to supporting sheeting/cladding systems, secondary framing also provide lateral bracing to main framing components and hence increasing their load carrying capacity.
Secondary members have two other functions: they act as struts that help in resisting part of the longitudinal loads that are applied on the building such as wind and earthquake loads, and they provide lateral bracing to the compression flanges for the main frame members thereby increasing frame capacity.
Purlins, girts and eave struts are designed in accordance with the American Iron and Steel Institute (AISI), “Cold-Framed Steel Design Manual”
Purlins are bolted to the top flanges of rafters and to each other at purlin laps buy means of machine bolts conforming to DIN 933 Grade or 4.6 or equivalent.
Roofs and Wall panels are laid perpendicular to the roof purlins and wall girts, respectively.
Purlins and Girts: are roll formed z sections or c sections.They are supported on columns, rafters or building walls.
C-sections: serve the same purposes as purlins and Girts but are better for smaller buildings
Eave struts: These are formed parallel to the roof slope, and are located along the side wall. Their purpose is to join the roof brace rods and wall brace rods
Open web Trusses: These are long span load carrying trusses suitable for direct support of floors and roof decks in the buildings. The system consists of crimped angles welded to the top and bottom chords.
Cable Bracing: a high strength to hold down a building in certain areas.