Slack free connections to improve seismic behavior of tension-only braces: An experimental and analytical study

A passive mechanical device, called Slack Free Connection (SFC), is introduced by which hysteretic behavior of tension-only braces (TOBs) would be greatly improved in terms of energy dissipation capability. SFC has a mono-directional behavior such that it provides no constraint for the attached TOB under compression. As a result, the TOB can slide itself into the SFC experiencing no compressive force and subsequently no buckling or slackness. On the other hand, when the TOB tends to experience positive elongation, SFC locks itself and the attached TOB can carry tensile loads. This self-tensioning mechanism makes the TOB to be always taut during load reversals such that during the carried out tests, no buckling was observed for super-slender braces with slenderness of 765. Quasi-static cyclic tests as well as numerical simulations revealed that SFC can completely remove pinching from hysteretic behavior of the TOBs and significantly improve their energy dissipation capability. The energy dissipation would be provided through the tensile yielding of the TOB while the SFC would remain elastic. Finally, a tunable post-yield stiffness is proposed for the TOB-SFC system using a Wire Rope Brace (WRB) in parallel with the TOB-SFC system. Based on parametric studies conducted in this paper, even a minor positive post-yield stiffness can greatly reduce residual displacements as another benefit of the proposed system.