Experimental investigation of alternative tie-rod solutions for stabilizing masonry façades

Historical masonry constructions often lack adequate connections between their façades and transverse structures, making them vulnerable to out-of-plane failures during earthquakes. Historically, tie rods have been used to prevent such failures and delivering a box-like behavior of masonry structures, essential for their seismic stability. The strength and the brittle or ductile behavior of tie rods are highly influential on the response of masonry façades. Preliminary experiments available in the literature have shown that tie rods may develop limited displacement capacity due to the threading necessary for their installation and tightening. The research investigates alternative solutions for tie rods, considering homogeneous or fuse-based setups. Homogenous tie rods are made either of carbon or stainless steel, with one or two nuts at each end. The effect of threading length is studied as well, up to fully threaded rods for carbon steel. Fuse-based setups have a plastic middle element, either of nylon or PEEK. Two diameters are considered in all setups. A total of 215 tests are performed. Threading the ends of homogenous steel rods reduces strength and ultimate strain, compared to a smooth rod. Increasing the threading length increases displacement capacity. Adding a nut has a small effect, but it may change the type of failure. Considering a fuse-based solution highly increases ultimate strain but dramatically reduces strength. The most promising solution resorts to fully threaded rods, balancing strength reduction and displacement capacity. However, the delivered displacement capacity is much smaller than usually assumed and might involve the revision of current equivalent-static design procedures.