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Elastomeric pad bearings are widely applied in short-to medium-span girder bridges in China, with the superstructure restrained by reinforced concrete (RC) shear keys in the transverse direction. Field investigations after 2008 Wenchuan earthquake reveal that bearing systems had suffered the most serious damage, such as span falling, bearing displaced, and shear key failure, while the piers and foundations underwent minor damage. As part of a major study on damage mechanism and displacement control method for short-to medium-span bridges suffered in Wenchuan earthquake, a 1:4 scale, two-span bridge model supported on elastomeric pad bearings were recently tested on shake tables at Tongji University, Shanghai. The bridge model was subjected to increasing levels of four seismic excitations possessing different spectralA c c e p t e d M a n u s c r i p t Downloaded by [RMIT University Library] at 04:19 30 June 20162 characteristics. Two restraint systems with and without the restraint of RC shear keys were tested. A comprehensive analytical modeling of the test systems was also performed using OpenSees. The experimental results confirmed that for the typical bridges on elastomeric pad bearings without RC shear keys, the sliding effect of the elastomeric pad bearings plays an important role in isolation of ground motions and, however, lead to lager bearing displacement that consequently increases the seismic risk of fall of span, especially under earthquakes that contain significant mid-period contents or velocity pulse components. It is suggested from the test results that RC shear keys should be elaborately designed in order to achieve a balance between isolation efficiency and bearing displacement. Good correlation between the analytical and the experimental data indicates that the analytical models for the bearing and RC shear key as well as other modeling assumptions were appropriate.

The present study aims to elucidate the anisotropic characteristics in material responses for crystallographic nickel substrates with (001), (011) and (111) surface orientations during nanoindentation. Molecular dynamic simulation is applied to compensate for the experimental limitation of nanoindentation, particularly for pure nickel substrates. Defect nucleation and evolution in Ni single crystal of these three crystal orientations was examined. Hardness and Young's modulus are also extracted in different orientations. The Young's modulus of (111) crystallographic orientation is the largest, while that of (001) surface is the smallest. The sensitivity of the yield point for face centred cubic crystals depends on the crystallographic orientation. The (001) crystallographic orientation reaches the yield point first, while the (111) crystallographic orientation is the most difficult in which to achieve yield. Using a visualisation method of centrosymmetry parameter, the homogeneous nucleation and early evolution of dislocations were investigated, deepening understanding of incipient plasticity at the atomic scale. The present results suggest that defect nucleation and evolution are the root of curve jitter. The indentation depth of the elastic–plastic transition point varies in the different crystallographic orientation models, and appears latest in the (111) model. The strain energy of the substrate exerted by the tip is stored by the formation of homogeneous nucleation and is dissipated by the dislocation slide in the {111} glide plane. The three nickel substrates with different crystallographic orientations exhibit different forms of dislocation propagation.

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