SECONDARY FRAMING SYSTEM

Secondary framing consists of elements which support the roof and wall sheeting and transfer load to primary framing system. In Pre-Engineered buildings normally cold formed Z sections are used for secondary framing to achieve high strength and lower weight. Secondary framing system is mainly Purlin and girt of Z or C shapes of various sizes. Typically cold formed members used for roof are called Purlin and for wall it is called as girt although profile for the both in general is same. Sometimes C section is also used in place of Z section. 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 are placed perpendicular to the direction of rafter. Wall Girts are cold-formed Z profiles, normally 100mm to 305mm deep manufactured out of 1.50 to 3.00mm thick steel. These are fixed to the outer flange of the sidewall columns.

Typical purlin and girt connections are shown above. 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 restrain to rafter for economical reasons.

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