Study On SMA-sliding Lead Rubber Bearing System For Seismic Response Control Of Concrete Continuous Bridges

As the fundamental and long-term research focuses for seismic resistance and mitigation of engineering structures,seismic isolation device and its analytic model,design method for seismically isolated bridges(SIBs)have attracted much concern.In view of the widely employed concrete continuous bridges,the novel seismic isolation device,theoretical model and design method were investigated for continuous bridges against strong ground motions.The main research content and achieved conclusions are provided as follows:(1)Study on influence factors of seismic performance of LRBs for continuous bridges.The significant temperature-induced bearing movements have been observed in continuous bridges.The hysteretic behavior of the lead rubber bearing(LRB)is sensitive to ambient temperature,temperature-induced bearing deformation and lead core strength degradation(LSD).The joint effect of the three factors on the nonlinear responses of the SIBs was investigated,and the responses were compared with those of SIBs considering only the single factor.Results show that low temperature effect can introduce significant increase in base forces of the piers and reduction in preak displacement of the girder.The initial displacement and LSD can increase the peak displacement of the girder.(2)Numerical simulation and experimental validation of the hysteretic behavior of the sliding-LRB considering LSD.To improve the seismic performance of the LRB,a numerical study was conducted to investigate the compression-shear performance of the sliding-LRB considering LSD under cyclic loadings.The various loading conditions,e.g.,the vertical loading,displacement amplitude,loading frequency and times,were considered.Then,the numerical results were verified by the experiments.The hysteretic model of the sliding-LRB was achieved considering the different parameters.Results show that the numerical model can effectively track the hysteretic behavior of the sliding-LRB and provide reliable analytical model for optimal design of the sliding-LRB system in continuous bridges.(3)Parametric study on seismic performance of SIBs with sliding-LRBs.The hysteretic behavior of the sliding-LRB is sensitive to the friction coefficient and allowable sliding displacement.A parametric study was conducted to investigate the effect of the friction coefficient and allowable sliding displacement on the response of SIBs with sliding-LRBs.The optimal range of the friction coefficient for the optimum hysteretic behavior of sliding-LRB was determined.A solution using shape memory alloy(SMA)dampers to mitigate the residual displacement of the sliding-LRBs is suggested to improve the recentering capability of the sliding device.Results show that the base forces of the piers can be reduced when employing the optimum friction coefficient,while the peak displacement shows slightly increase.The residual displacement and peak displacement can be effectively reduced using the SMA dampers.Results can also provide reliable basis for designing the sliding-LRB system for continuous bridges.(4)Design method of the SMA-sliding lead rubber bearing(SSLRB)system for continuous bridges.To overcome the limitations of the conventional LRB,i.e.,the poor capability of the LRB to accommodate the temperature-induced movements and no reliable recentering force provided for the sliding device,incorporating SMA wires with the sliding-LRB,the SSLRB with self-centering capability and the corresponding parametric design method are proposed.The effectiveness and serviceability of the seismic design method were validated.Results show that the optimal parameters of the SSLRB system can be achieved by the proposed method,which can be selected to design the optimum parameters of the SSLRB system for continuous bridges.(5)Seismic performance of SIBs using proposed SSLRB design method: comparative study.To address the urgent limitations,e.g.,the low temperature-induced increase of the recentering demand for the sliding-LRB and degradation of the superelasticity for the widely used Ni Ti wires,incorporating the Cu Al Be wires and the sliding-LRB,the Cu Al Be-SLRB system is proposed for seismic mitigation of continuous bridges in cold regions,its effectiveness has been further validated and compared with those of the superelastic-friciton base isolator(SFBI)and SMA-based friction pendulum bearing(SMA-based FPB)systems.Results show that the Cu Al Be-SLRB system shows better response control efficiency in terms of reducing displacement responses and suppressing the base forces to nearly level corresponding to that of the sliding-LRB system.Compared with the SFBI and SMA-based FPB systems,the Cu Al Be-SLRB system also shows higher cost efficiency to promote its applications in bridges.