Experimental testing of joints for seismic design of lightweight structures. Part 1. Screwed joints in straps

Connections in x-braced shear walls play a crucial role in the seismic performance of lightweight structures: they should be strong enough to allow energy dissipation via plastification of the diagonal straps. An extensive experimental research on tensile screwed joints between straps is reported here. Two dominant failure modes are identified: (1) tilting and net section failure (TCNSF) and (2) tilting, bearing and pull out (TCBC PO). The analysis in terms of strength and ductility shows that TCNSF joints are suitable for seismic design, because the straps yield before the connections fail. TCBCPO joints, on the contrary, are not suited because the connection fails before the straps can yield. The influence of various design parameters (strap thickness, number and diameter of screws, steel grade) in the failure mode is studied, and design criteria to induce a TC NSF response are given.