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.
