Secondary framing system is mainly purlin and girt of Z or C shapes of various sizes. In Pre-Engineered buildings normally cold form Z sections are used for secondary framing to achieve high strength and lower weight. Typically cold form members used for roof are called purlin and for wall it is called as girt however profile for the both in general is same. Sometime C section is also used in place of Z. Purlin/Girts are the members which transfers forces and moments from one frame to another frame for overall stability of the building structure and it all acts as framing system for weather covering sheeting purpose. For all practical purpose these members are spaced at an interval of about 1.5 m which can vary and placed perpendicular to the direction of rafter.
Pre-Engineered steel building system offer various type of steel framing system for various economic module and options as per functional need and aesthetic choices.
Some standard frame options are as under:
Typical purlin and girt connections are shown below for better understanding:
Rafter to purlins and girts are always connected using 4.4 grade bolts assembly with the help of L-shape cleats and these are always overlapped by at least 300 mm at each frame location. In addition flange angle is also used to connect purlin and bottom flange of the rafter to provide better restraining to rafter for economy reason.
Purlins are also used for various services support such as electrical lines, fans, air lines, false ceiling support etc. after adequately designed for desired load purpose.