With the continuous development of the ductility capacity concept for seismic design of bridges, the ductility capacity of many existing bridges does not meet the requirements of the current code for seismic performance because of the low reinforcement ratio and reinforcement corrosion of reinforced concrete (RC) piers. Because of their superior mechanical properties and low price, basalt fibre-reinforced polymer (BFRP) sheets have potential application in the seismic retrofits field of existing bridges. To study the seismic strengthening effect of RC pier columns, scaled specimens with standard reinforcement ratios, with low reinforcement ratios according to the past code and with corroded reinforcements, were designed and manufactured and then wrapped and pasted with BFRP sheets on the plastic hinge areas. Pseudostatic tests were conducted to verify the seismic performance of the strengthened and unstrengthened specimens. Experimental results showed that the ultimate flexural capacity, deformation capacity, and energy dissipation capacity of strengthened RC pier columns were superior. Especially for strengthened specimens with low reinforcement ratios or corrosion reinforcement, their seismic performance could rival than that of columns with standard reinforcement ratios, which showed the advantage of BFRP sheets in the seismic retrofitting of existing bridge piers.

Piers, abutments and bearings of viaducts may suffer severe damage during earthquakes, so it's not insufficient to evaluate the seismic vulnerability of a bridge system only by plastic hinge curvature, which is adopted in seismic design guidelines. In this paper, the seismic vulnerability evaluation of a viaduct is conducted by incremental dynamic analysis under 30 near-fault ground motions, which are selected from PEER database. Then several damage measures are recommended to make an overall estimation for the seismic vulnerability of the viaduct, including plastic hinge curvature, shear failure and sliding displacement failure of bearings and pounding force between abutments and the girder. The analysis results show that the transversal seismic excitations may lead to more severe damage than the longitudinal ground motions. No matter in which direction the ground motions are inputted, the bearings' seismic vulnerability resulted by shear force or sliding displacement is higher than the plastic hinge of piers, which indicates that the seismic vulnerability of the bridge system is determined by the bearings to an extent. As a result, bearings should be designed according to both static and seismic analyses to guarantee the safety during earthquakes.

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