Purlins, girts and eave struts are secondary structural members used to support the wall and roof panels. Purlins are used on the roof; girts are used on the walls and eave struts are used at the intersection of the sidewall and the roof.

Secondary members have two other functions:

• Act as struts that help in resisting part of the longitudinal loads that are applied on the building such as wind and earthquake loads
• Provide lateral bracing to the compression flanges of the main frame members thereby increasing frame capacity.