SUMMARYThe Asymmetric Friction Connection (AFC) remains elastic during moderate earthquake shaking but slides and dissipates energy through friction during severe earthquake shaking. The sliding friction forces developed are dependent on the clamping force in the connection which is provided by fully tensioned bolts which pass through slotted holes. During sliding these bolts are subject to moment and shear as well as axial force. Moment-shear-axial force interaction reduces the clamping axial force on the sliding interfaces thereby reducing the sliding shear resistance (V ss ). Two methods to evaluate the moment-shear-axial force interaction have been proposed so that the sliding shear strength can be quantified, but as yet, these methods are not robust. This paper describes the results of 60 tests undertaken to improve the two methods, namely the moment-shear-axial force bolt model and the effective coefficient of friction method, for AFCs with high hardness steel shims. The bolts were M16 to M30 bolts and cleat thicknesses ranged from 12 mm to 25 mm. It is shown that either method may be used in design as the results obtained are similar.

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The Sliding Hinge Joint with Asymmetric Friction Connectors (SHJ), to give its full name, is a semi-rigid moment resisting joint used between the beams and columns of a moment-resisting steel frame and also at the column base between the column and the ground. It’s performance is intended to be as follows: 1) On completion of construction, rigid under serviceability limit state conditions, 2) During a severe earthquake, allowing controlled rotation between the column and the beam or foundation on designated friction sliding planes within the connection, then 3) Returning to its rigid in-service condition at the end of the severe shaking with the building returning to its pre-earthquake position (self-centering). During its development and proof of concept through large scale testing, the initial results showed that the SHJ as originally designed and detailed performs 1) and 2) very well, but the bolts in the friction sliding planes loose much of their original installed bolt tension during significant sliding, lowering the level at which rotation within the joint will occur post severe earthquake. A concerted research programme of component testing, analytical model development and numerical modelling in recent years has developed solutions to the bolt tension loss issue as well as enhanced the joint’s performance to deliver dependable self-centering capability for the building. This work marks the final steps towards developing an optimum low damage seismic-resisting steel moment frame system. This paper presents key findings from the research work and general recommendations for the optimum performing sliding hinge joint.