Enhancing Structural Dynamic Stability Using Two‐Stage Friction Connections (TFCs)

ABSTRACT Two‐stage friction connections (TFCs) are proposed as lateral force‐resisting components to enhance the stability of structures exhibiting negative postelastic stiffness under the P –Δ effect. A single point mass system composed of nonlinear springs, gap elements, and inherent damping, with varying ratios of initial sliding strength and length, is modelled. Time‐history analyses (THAs) are conducted to investigate the behaviour of the structural system with TFC, in comparison with the system using the single‐stage friction connection (SFC). Also, parameter studies are conducted considering different system postelastic stiffness ratios, r , considering initial strain hardening and P –Δ effects, T , and R . The displacement responses of a five‐storey braced frame structure using SFC and TFC braces are compared. It is shown that the hysteresis curves exhibit two sliding strengths, corresponding to the frictional resistances at each end of the TFC. The initial sliding length is determined by the bolt slot at the weak end, and the model shows good agreement with experimental results. THA of TFC systems indicated that reductions in peak and residual displacements, Δ p and Δ r , respectively, were most significant when r was negative, compared to the SFC systems. Displacements were lowest when the strength ratio, β , which is the ratio of initial sliding strength to the higher sliding strength, was in the range strength of 0.5–0.7, and when the gap ratio, α , which is the ratio of the bolt movement in the slot in one direction to the elastic displacement, was 0.2–0.6. Median Δ p and Δ r reductions were up to 41% and 77%, respectively. The postshaking bolt location at the initial sliding end was 45% of the one‐direction slot gap for the elastoplastic model, but 100% of this for significantly negative r . Lower r and larger R cause greater displacement reductions by using TFCs.