Approach to the rotational stiffness of thin-walled cold-formed Z-profile purlins

For an economic design of main hall beams and frames, it is useful to consider the rotational stiffness from the roof structure. Until now, there is no adequate basis for the approach of cold formed roof purlins and their joint stiffness. Experimental tests and numerical analysis show that the joint stiffness of lightweight purlins is not negligible when considering the torsional stabilization effect. To determine this joint stiffness for thin-walled cold-formed Z-purlins, different profile heights and thicknesses were investigated. From the moment-rotation relation, the joint stiffness C-nu A,C-K can be determined as secant stiffness under consideration of non-linear deformations. Based on experimental tests, values for the joint stiffness of selected thin walled purlins have been made accessible, which can be used to determine the rotational stiffness according to the design codes. It was possible to show that the joint stiffness correlates with the stiffness of the individual components: hole bearing, shear bolt connection and deformation of the purlin support. To determine a general applicable formula, tests with a wider range of parameters have to be done.