Shear key in a rocking timber shear wall with elasto-plastic behaviour

W. Y. Loo, P. Quenneville & N. Chouw

In an effort to develop a high-ductility/low-damage lateral-load resisting system, an experimental shear wall consisting of rigid LVL panels is fabricated and tested with slip-friction connectors acting as hold-downs. The slip-friction connectors are fabricated in such a way that their force-displacement behaviour can be described by close to an ideal elasto-plastic shape. With the application of an increasing racking force at a top-corner of the wall, the slip-force in the connectors is eventually attained – at which point sliding takes place and the wall corner displaces upwards. The wall thus displays a form of rocking behaviour, and this places a cap on the activated base shear. In order to resist this activated base shear, a new type of shear key is included at the bottom centre of the wall. The shear key consists of vertical steel plates welded to the foundation, placed on both sides of the wall, and with shear pins inserted through the plane of the wall, bearing directly against the edge of the plates. In order to facilitate rocking and to reduce the influence of the shear key on the force-displacement behaviour, the plates are sloped at a slight angle to the vertical. An equation is derived that quantifies the effect on the wall strength due to the interaction of the slip-friction connectors and the shear key. It is found that the predicted wall strengths align closely with the experimentally measured values. Furthermore, as expected, the hysteretic behaviour of the wall is highly elasto-plastic, and the strength of the wall can be readily ‘tuned’ through the use of Belleville washers in achieving and maintaining bolt preload. The wall readily descends at one end, while uplifting at the other end – and this indicates that it would likely have good re-centring ability under an actual earthquake. The results show the possibility of inherently brittle structures being made ductile through the application of a simple and cheap steel friction device.

TDJ 22-4

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