The Seismic Input Energy Estimation Method Of Superhigh Bridge Tower Under Long-period Ground Motions

As the key node of the transportation network,the importance of long-span bridges is selfevident,and the seismic response of long-period structures such as long-span bridges under long-period ground motions is obvious.With the continuous development of seismic design theory,more and more attention has been paid to energy-based seismic analysis methods.On the basis of the existing researches,the method of estimating the seismic input energy of the super-high bridge tower under long-period ground motions is proposed,which provides a useful reference for the seismic design and performance evaluation of the long-span bridge.The main contents include:(1)Compared with the ordinary ground motions,the difference of characteristics between long-period and ordinary ground motions is studied.The indentification approach of the former is developed.The 175 long-period ground motion records in total are collected according to different site types to establish the long-period ground motion record database.(2)With the help of nonlinear response spectrum analysis program,the energy response spectrum of long-period ground motions is calculated.Parametric analysis is carried out on ground motion characteristics(earthquake magnitude,site type,PGA,fault projection distance,PGV/PGA,effective duration,mechanism)and structural dynamic parameters(restoring force model,damping ratio,post-yield stiffness ratio,ductility ratio),providing the foundation for the establishment of the energy design spectrum of long-period ground motions.(3)Taking the long-period ground motion record database as the sample input,long-period ground motion energy response spectrum of different site types is statistically analyzed,and the energy design spectrum of the elastic SDOF system is fitted.To study the effects of structural damping ratio and ductility ratio on long-period ground motion input energy spectrum values and peaks,the input energy design spectrum of elastoplastic SDOF system is obtained by the adjustment of the energy input spectrum of elastic SDOF system.The results obtained by this method are verified with the elastoplastic energy response spectrum calculated by the nonlinear response spectrum analysis program.(4)A method of estimating the seismic input energy of the super-high bridge tower under long-period ground motions is proposed,and the calculation of this method is used in an engineering case.The calculation results of this method are verified by the nonlinear timehistory analysis.