Lateral buckling of roof purlins with diaphragm restraints

The roof sheeting connected to metal roof purlins may provide effective restraints against lateral buckling. One important restraining action is that where the sheeting acts as a diaphragm so that its in plane shear stiffness opposes minor axis rotation of the purlin. The effectiveness of diaphragm restraints depends not only on their stiffness but also on their height above the shear centre axis of the purlin. Another important influence on the resistance to lateral buckling is the height of the load above the shear centre. In this paper the effects of bending moment distribution, cross section geometry, load height, and restraint stiffness and height on the elastic lateral buckling of uniform purlins are investigated by using a finite element computer program for the analysis of the lateral buckling of continuously restrained beam columns. (A)