Effect of loading rate on the pull-through capacities of cold-formed steel roof battens

Localised connection failure is the main shortcoming of cold-formed steel roofing systems subjected to high wind suction loads. Pull-through failure in the vicinity of roof batten to rafter connection is the major connection failure observed during recent high wind events. Both static and fatigue pull-through failures occur based on the type of wind loads (static or cyclic loads). The loading rate to be used in the static and cyclic pull-through failure tests is a moot point as the wind loading frequency can vary during wind events such as storms and cyclones. Therefore, it is necessary to understand the effect of wind loading frequency/rate on the pull-through failures of steel roof battens. This paper investigates the influence of loading rate on both static and fatigue pull-through capacities of steel roof battens by means of a series of static and cyclic tests conducted at various loading rates/frequencies. Initially, tests were conducted on roof battens made of two steel grades (G300 and G550) and two thicknesses (0.8 and 1 mm). The results showed a significant improvement in the pull-through capacities during tests using higher loading rates. They also showed that the current static and cyclic pull-through design rules/guidelines do not include the effect of loading rate. Secondly, to understand the influence of loading rate on the pull-through capacity of battens, the effect of loading rate on the mechanical properties of steels was investigated using 40 tensile coupon tests. The effect of loading rate on both the tensile strength of steel used and the pull-through capacity of roof batten was then compared. Using the results of comparison, the reasons for the increase in the static pull-through capacity of roof battens with loading rate are discussed and, a recommendation is made in relation to the loading rate to be used with the new Low High Low (LHL) cyclic test. This paper presents the details and results of this study.