Impact of Clip Connection and Insulation Thickness on Bracing of Purlins in Standing Seam Roof Systems

The flexural strength of purlins in standing seam roof systems is highly dependent upon the extent to which the sheathing provides lateral and torsional restraint. Typical models to predict the restraint provided by the sheathing assume that the plane of lateral resistance occurs at the top flange of the purlin. In reality, depending on the configuration of the clip and the amount of insulation located between the purlin and the clip, the plane of lateral resistance and corresponding center of rotation shifts above the top flange. This distance, referred to as the effective standoff, is important to evaluate the effectiveness of the sheathing to brace the purlin. A series of 25 tests is performed on a variety of clip, panel, seam and insulation configurations to determine both the effective standoff and rotational stiffness of the panel-clip connections. Test results are reported and recommendations are provided to estimate the effective standoff for use in models to evaluate the effectiveness of the sheathing to brace the purlin. The implications of the effective standoff in the evaluation of purlin bracing are discussed through a parametric comparison of standing seam systems.

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