Flexural Strength of continuous-span Z-purlins with paired torsion braces using the Direct Strength Method

摘要

A procedure is presented to calculate the local and distortional flexural buckling strength of continuous span purlins with paired torsion braces using the Direct Strength Method. Displacement compatibility is utilized to determine the forces interacting between the purlin, the flexible diaphragm and the torsion braces. The biaxial bending and torsion effects caused by this interaction are superimposed, and the actual distribution of stresses within the cross section are calculated at critical locations along the span. With this distribution of stresses, a finite strip buckling analysis is performed to determine the local and distortional buckling strength. In current design practice, results from a simple span Base Test are extrapolated to multi-span systems using a constrained bending stress distribution. In previous work, a variation of the presented method was compared to simple span base test results with good correlation. In this paper, the simple span stresses are compared to the stresses of continuous span systems. Significant, although typically conservative differences in the stress distributions and, as a result the predicted flexural strength, are observed in the comparison between simple span and multi-span systems. Additionally, significant changes in the distribution of stresses are observed as roof slope effects are considered. Increases in the flexural strength with increasing roof slope are reported and compared to the strength predicted by the current base test method.