Effects of Prying Forces on the Hysteretic Behaviour of Asymmetric Friction Connections (AFCs)

Asymmetric Friction Connections (AFCs) are used to dissipate seismic energy. The AFC hysteresis loop shape has been described as rectangular. However, recently, testing of AFCs with long slotted plates (i.e., 200 mm slot length), showed the hysteresis loop is trapezoidal. This paper proposes an AFC sliding mechanism that explains such trapezoidal hysteresis loop shape. A simple AFC elastic model performed in MASTAN 2 was used to verify the proposed mechanism. It is shown the trapezoidal hysteresis loop shape is produced by prying forces developed between the slotted and fixed plates and at the AFC clamped zone. While in some areas of the AFC clamped zone, the prying forces move the fixed and slotted plates apart, in other areas of the AFC clamped zone, they increase the interface force between these plates. As a net result of this mechanism, the friction resistance of the AFC increases. The proposed mechanism agrees well with experimental data for AFCs with Bisalloy 500 shims.