Centrifuge modelling of structures with oil dampers under seismic loading

Experimental research into the seismic performance of buildings with passive oil dampers has so far been restricted to large-scale testing of frames erected on laboratory shaking tables that ignore the foundation soil below. This simplification of the problem falls short of replicating dynamic soil-structure interaction that would occur in the field. This paper presents the first experimental attempt at utilising high gravity dynamic centrifuge testing to replicate the response of a damped building at a reduced model scale. The paper compares the dynamic response of two similar two-degree-of-freedom model sway frames, one control (bare) frame and one frame equipped with miniature oil dampers, both structures founded on shallow raft foundations in dry dense sand. The miniature oil dampers successfully mitigate floor accelerations, drifts, and storey shear forces in the damped frame with minor modification to the frame stiffness. For strong, near resonance motions, global rocking of the undamped frame associated with physical uplifting of the foundation from the soil surface and subsequent yielding of sand beneath has led to floor acceleration levels, which are comparable to those obtained in the damped building fitted with miniature oil dampers. Assessment of the instrumentation installed on the miniature oil dampers reveals a viscoelastic damper behaviour with a dependency on stroke magnitude and on velocity

Modelling the behaviour of large gravity wharf structure under the effects of earthquake-induced liquefaction

Gravity Wharf Structures are widely used worldwide to form shallow and deep water ports. They are large structures with a height of 25–50 m depending on the water depth. When these structures are to be sited on loose to medium dense sand, earthquake induced liquefaction settlements present a significant risk. This often requires expensive soil replacement or other ground improvement techniques. In this paper, the dynamic behaviour of these large structures that exert very high bearing pressures on the foundation soil was investigated for the first time. The level of settlements they can suffer due to soil liquefaction was investigated using dynamic centrifuge testing. It will be shown that the full liquefaction does not occur below the structure even when the free field soil fully liquefies during strong earthquakes. However there will be some stiffness degradation owing to excess pore pressure generation and consequent structural settlements. The level of these settlements are considered to be acceptable from a Service Limit State (SLS) perspective. In addition to this the hydro-dynamic pressures that act on the Gravity Wharf structure were also investigated