Volume 8, Issue 8 (September 2011)
Influence of Edge Restraint on Clip Fastener Loads of Standing Seam Metal Roof Panels
This study investigates the effect of boundary conditions on the structural load paths within standing seam metal roof (SSMR) panel specimens subjected to uplift wind pressures. The objective is to determine the effect of boundary conditions (restrained or free) on observed load distributions among clip fasteners installed within a SSMR test specimen. Two roof specimens with instrumented clip fasteners were installed in a steel pressure chamber and subjected to static uplift pressures, while measuring panel deflection and clip fastener load distributions. The test specimen boundary conditions were modified in turn to represent field panel location (all free boundaries), gable panel (one restrained boundary, long dimension), eave panel (one restrained boundary, short dimension), and a corner panel (having two adjacent restrained boundaries). The load-displacement characteristics of the SSMR system were determined in a third specimen. The study found statistically significant differences in clip fastener loads, among the first three fastener rows away from the crosswise panel restraint, i.e., eave boundary condition. The gable boundary appeared to have less influence on load on the nearest fasteners. For the eave boundary condition, the measured load on the three exterior fasteners was about 40 % lower than the total fastener load on interior clips located just 3 m (10 ft) away. The results suggest why clip failures seldom occur in corner locations during uplift pressure tests. An empirical design method is proposed for predicting loads on clip fasteners installed near roof boundaries. More importantly, the design of SSMR roofing can be made more efficient, since it is shown that eave clip fasteners carry less than half the load of the interior fasteners, if other failure mechanisms (i.e., sheet tearing or boundary anchor failure) do not control the roof edge failures of installed SSMR.