The first in our Glossary of Terms series. We aim to build this up into an exhaustive visual database of steel terms. First up is the portal frame ridge, or apex:

Purlin: A secondary structural member that transfers the load from roofing material to the primary structure.

Rafter: A primary steel roof member upon which the rest of the roof structure is supported, usually made up of Universal Beam sections.

Rafter Stay: A steel strut which connects the bottom flange of the rafter to the purlins, providing some restraint to lateral torsional buckling in the rafter.

Ridge Purlin: Name given to the purlins located nearest the roof ridge.

Purlin Cleet: Bracket welded to the rafter to which purlins are fixed. It is designed to limit rotation of the purlin.

Apex Haunch: Deepening of the rafter at the apex where bending moment is greater than what can be resisted by the rafter itself.

End Plate: A plate welded to the end of a steel member so that it may be connected to another member, usually by bolting.

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