Metal Building Roof Purlin Line Strength by Computation

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A computation-based method for metal building purlin and girt design is introduced using the AISI S100-16 North American Specification for the Design of Cold-Formed Steel Structural Members. Purlin section properties, span length, material properties, and boundary conditions, including bracing connectivity to exterior screw-fastened or standing seam panels, are defined. Flexure, shear, and torsional strengths are calculated along the line. The capacity of the roof or wall system is determined by applying a gravity or uplift load until a strength limit state is reached. For uplift loads, buckling deformation of the purlin free flange between intermediate bridging is considered. The calculations are performed with an open-source software package called StructuresKit.jl written in the Julia computing language. Predicted strengths from the calculation method are compared to the experimentally determined strengths from 49 simple span Cee and Zee wall girt line uplift pressure box tests, some of which were constructed with rigid board insulation.