Seismic behaviour of rockable bridges on soil under multi-directional excitations

Allowing footings to rock has been used as a low-damage seismic design, e.g., the 315 m long Rangitikei Viaduct in New Zealand that can rock at all pier supports. With rocking capability, the bridge has experienced more than ten thousand earthquakes without damage. However, most existing studies on rockable bridges only consider one-directional excitations, even though in earthquakes bridges always experience multi-directional ground excitations. This research aims to experimentally investigate the effect of three-directional excitations and soil support on bridge rocking through large-scale shake table experiments. The results from one- and two-directional horizontal excitations were also investigated to elucidate the bridge behaviour. To reveal the influence of flexible support, the result of a rocking bridge on soil support is compared with that of a rigid base support. The result shows that neglecting multi-directional excitation can underestimate the development of footing rocking, bending moments, and girder rotations. The consequence of soil deformation for the bridge rocking is more pronounced when three-directional excitations are considered.