Cleat Angle Behavior in C-Shaped Purlin-to-Rafter Connections: Experimental Study and Design Considerations

This research examines the pull-through failure behavior of cold-formed steel (CFS) C-shaped purlin-to-rafter connections using a cleat angle. A total of 72 tests were performed to evaluate the influence of cross-sectional parameters, including cleat angle leg length, purlin thickness, cleat angle thickness, and screw head diameter. The experimental study employed a small-scale test setup to closely replicate loading conditions of the wind uplift forces. A full-field measurement technique, namely three-dimensional digital image correlation (3D-DIC) was used to capture strain contours and understand the failure mechanisms for the observed failure modes. Three distinct failure modes were identified: a rupture-type pull-through failure in the cleat angle; a bearing-type pull-through failure in the cleat angle accompanied by tearing failure in the web of the purlin; and a bearing-type pull-through failure in the cleat angle accompanied by shank failure of the screw. These failure modes varied according to the thickness of the cleat angle (tc), the thickness of the purlin (tp), the ultimate tensile strength of the material (fu), and the screw head diameter (dw). The results of the study concluded that existing design guidelines were unconservative in predicting the pull-through capacity. Therefore, a modified design equation to predict the pull-through capacity of cleat angles in C-shaped purlin-to-rafter screw connection is suggested. Additionally, guidelines to calculate the initial elastic stiffness of CFS C-shaped purlin-to-rafter screw connections using cleat angles are presented. Furthermore, a reliability analysis was conducted to propose appropriate resistance and safety factors for the suggested design equation.