Abstract:
Passive energy dissipaters, in the form of slip-friction connectors, are implemented in an experimental timber wall as hold-downs. Under an increasing and laterally applied force, rocking of the wall ensues when the slip-force in one or both of the connectors is obtained. The initial stages of this research focussed on developing a symmetric slipfriction connector that is both simple to fabricate and cost-effective. Previously, symmetric slip-friction connectors have relied on brass shims to enable stable sliding. However, experiments on symmetric connectors with abrasion resistant steel placed in direct contact with mild steel, reveals stable sliding with highly elastoplastic characteristics. This is provided the faying surfaces are in the clean mill scale condition (removal of mill scale and polishing of the faying surfaces is found to result in extremely erratic force-displacement behaviour). The need for brass shims, or indeed shims of any kind, is thus obviated. The new concept slip-friction connectors are implemented as hold-downs in an experimental wall of engineered lumber. The elastoplastic characteristics of the slipfriction connectors readily transfer to the wall, and a novel shear key arrangement facilitates re-centring during quasi-static reversed cyclic loading. The wall strength is readily adjusted through varying the preload in the bolts used to mobilise friction, and this preload is achieved and maintained through the use of stacked Belleville washers. The interaction of the slip-friction connectors with the shear key produces a rocking motion that is quite distinct from that of a free rocking block. An analytical procedure is developed in order to explore and describe this motion, and the influence of shear key placement on re-centring capability is clearly demonstrated. A tentative displacementbased design procedure is then proposed for multi-storey walls with slip-friction connectors, and an example structure numerically modelled. Under earthquake simulations, the example wall is found to emulate the response of an equivalent but idealised structure with a plastically deformable hinge at its base. Drifts typically remain within the intended limits, and residual displacements are small when gravity effects are considered. When compared with the response of comparable, but fully elastically responding structures, base shears and response accelerations are significantly reduced.