Experimental investigation on the performance of roof tie-down straps in unreinforced masonry walls

Windstorms might lead to severe damage to houses when roof tie-down connections fail. One practice for securing a roof structure to unreinforced masonry walls is the use of tie-down straps, which consist of a thin, steel strap embedded into a brick-mortar interface at the internal leaf of unreinforced cavity walls. To date, very limited studies have been conducted on the performance of tie-down straps in unreinforced masonry walls. In this study, a total of 24 specimens were prepared to investigate the failure mechanisms and uplift capacities of tie-down straps. The effects of mortar grade, embedment depth and length, as well as the testing setup, were taken into consideration. It was found that increasing mortar grade and embedment length could increase the uplift capacities of straps by 41% and 22%, respectively, whilst increasing embedment depth has a limited effect on the uplift capacity of straps. Two new types of strap profiles were proposed: lipped and corrugated straps, which could lead to 81% and 59% higher uplift capacities, respectively, as compared to flat straps, indicating the strap profile has a significant effect on its uplift capacity. • First systematic tests of tie-down straps in unreinforced masonry wall. • The effects of various factors on its uplift capacity are examined. • New strap profiles are proposed and demonstrate enhanced performance. • Failure mechanisms of tie-down straps are revealed.