The objective of this paper is to provide and verify simplified models that predict the longitudinal stresses that develop in C-section purlins in uplift The paper covers the simple case of flexural stress, where the force has to be applied at the shear center or the section braced in both flanges, up through the more complex problem of bending where movement of the tension flange alone is restricted, as commonly found in purlin-sheeting systems. Winter's model for predicting the normal stresses developed due to direct torsion is reviewed, verified, and then extended to cover the case of a bending member with tension flange restraint alone. The impact of considering the combined longitudinal stresses, in determining the elastic stability behavior is highlighted. Strength predictions of typical C-section purlins are provided for existing AISI methods and a newly proposed extension to the Direct Strength Method.
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