Experimental Study of the Unified Structural Behavior of Pull-Through and Pull-Out Failures in a Crest-Fixed Trapezoidal Roof–Purlin Connection

This study presents an experimental investigation into the unified structural behavior governing pull-through (PT) and pull-out (PO) failures in crest-fixed trapezoidal roof–purlin connections. The experimental program comprised a total of 49 tests, including repeat tests, conducted on 24 different combinations of trapezoidal profiled roof sheets and C-purlins connected through crest-fastened self-drilling screws. The study varied key parameters such as roof sheet thickness, purlin thickness, material properties, and screw type. Their combined effect was evaluated using an integrated small-scale test setup designed to simulate wind-uplift loading capable of inducing both pull-out and pull-through failures. Two primary failure modes were identified: pull-through failure (Type 1 and Type 2) and pull-out failure. A nondimensional parameter, denoted as ψ , was observed to act as a transition index, with ψ > 3 marking the shift from pull-out to pull-through governing behavior. The three-dimensional digital image correlation (3D-DIC) technique was employed to capture strain contours and out-of-plane displacements around the screw head and purlin flange, providing enhanced insight into the localized deformation mechanisms. Comparisons with existing design codal provisions and previously proposed literature based equations for pull-through and pull-out revealed notable inconsistencies, particularly in the prediction of pull-through capacity of mild and high strength roof sheet. Based on the experimental findings, a revised design equation is proposed to improve the accuracy of pull-through capacity. A reliability analysis was subsequently performed to evaluate the adequacy of the proposed formulation.