Rotational restraint of cold-formed Z-purlins given by the trapezoidal sheeting with additional stiffening ribs

The Eurocode 3-1-3 [1] provisions, according to which the rotational restraint of a cold-formed Z-purlin given by the sheeting has to be determined, set out guidelines for the first-generation trapezoidal sheets only in strictly defined cases, and for the second-generation sheets there are no guidelines at all. In the experimental tests presented in this paper, values of stiffness CD were determined in the case where trapezoidal sheeting with additional stiffening ribs in the middle of each trough was used. Then, the obtained values were confirmed by numerical simulations. The cases when fasteners are located in each trough next to the intermediate stiffener (the 1+1 arrangement) or near the trapezoidal sheeting webs in every second trough (the 2+0 arrangement) were analyzed. Values of stiffness CD obtained from the experiments were also compared with CD values obtained on the basis of the Eurocode 3-1-3 provisions. As a result of the analyses carried out, several changes to the Eurocode 3-1-3 provisions were proposed. Values of the rotational coefficient C100 for cases not covered by Eurocode 3-1-3 were presented and, in addition, a modification of this coefficient for the 1+1 fastener arrangement under gravity loading was proposed.