Seismic behaviour of symmetric friction connections for steel buildings

Abstract

Steel frames are increasingly common in seismic zones. However, they can also benefit from supplemental damping systems to reduce expensive sacrificial damage and increase performance. Quasi – static testing of 16 symmetric friction connections (SFCs) was undertaken using slotted plates of Grade 300 Steel, and steel shims with Brinell hardnesses from 150 to 500BH. Shim materials were Grade 300 Steel, Bisalloy 80, Bisalloy 400 and Bisalloy 500. SFC hysteretic behaviour is shown to depend on the hardness ratio, ρ, which is ratio of the nominal hardness of the shims to the hardness of the slotted plate. Unstable hysteresis loops, and an unpredictable SFC strength occurred for ρ = 1.0. The SFC hysteresis loop stability factor and strength predictability increased as ρ increased. An almost perfectly rectangular, and very stable, hysteresis loop was found for ρ = 3.3. SFC strength degradation between test runs, after testing and cooling, reduced as ρ increased. Bolt tension increased as SFCs were cyclically loaded, and the increments in bolt tension reduced as ρ increased. The magnitude of this increase was maximum for ρ = 1.0, where the bolt tension increased up to the bolt ultimate tensile load. Sliding surfaces degraded, and this degradation reduced as ρ increased. Sliding surfaces degraded significantly by an abrasive sliding mechanism for 1.0 ≤ ρ ≤ 1.7, and they degraded slightly by an adhesive sliding mechanism for ρ ≥ 2.7. A simple model for quantifying the average, maximum, and minimum SFC strength is proposed based on the experimental results. The proposed SFC strength model predicts the experimental results with an accuracy of 85% − 100%.