Effect On Rotational Ground Motions On Seismic Response Analysis Of Long-span Bridge Structure

Long-span bridges play an significant role in the traffic system,and is very important to our country and development of the economy.And our country is one of the most long-span bridges and the fastest building process.Thus,it is significantly meaningful to protect the long-span bridges' safety during the earthquake.This paper selected three groups of earthquake records,and calculated the corresponding rotational ground motion data by using the elastic wave theory,then the engineering characteristics of the components is analyzed,a three dimensional finite element model is built based on a real long-span bridge,the seismic response of the bridge under different load conditions is analyzed and the influence of rotational ground motion excitation is studied.The main content of this paper are:(1)The comparison of the different components of the ground motions show that the acceleration peak value and the waveforms are different for different earthquakes.The rocking accelerations waveforms are similar and have large difference with the torsional components.The frequency content of different ground motions is different,among the three translational components,the horizontal components have more low frequency than the vertical components,and the Fourier spectra decays more slow with the increasing frequency for the vertical components.Among the three rotational ground motions,the two rocking components have similar Fourier spectra and have more high frequencies than the torsional components.The rotational components contain more high frequencies than the translational components.(2)The difference between vertical and horizontal components is not uniform.The peak response spectra of the vertical components more likely appear in the lower period,and the amplification factor decays fast along with the increasing period.Among the rotational components,the amplification factor of the torsional components decays slow along with the increasing period.Compare to the translational components,the peak response spectra and classic period of the rotational components is smaller,this might cause negative influence for the stiff engineering structures.(3)For the long-span bridge structure,the peak response and its appearance time are different from the uniform ground excitation when considering the travelling wave effect.The time series of the force response are also different.With the increasing wave speed,the base force and top displacement become more close to the results under uniform ground excitation.For the long-span bridge structure,the travelling wave effect is complicated.Thus for such kind of important engineering structures,it becomes necessary to consider the multiple excitation effect during the seismic analysis and design.(4)The peak response and its appearance time are different under rotational ground excitation.The structural response of the long-span bridge increases with the decreasing wave speed,when the wave speed is increasing,the ratios between structural response under rotational and translational ground excitations decrease.(5)The appearance time of peak response and their phase are different under rotational and translational ground excitations,the time series differences of the structural response are not significant including rotational ground motions.The response of the long-span bridge structure could be positive when including rotational ground motions.Generally,the influences of the rotational ground excitations become more significant with the decreasing wave speed.Comparing to the response under translational ground motion alone,the transverse base shear and moment along the bridge increase significantly when including the rotational ground excitations.Thus the analysis results show that it is necessary to consider the potential influence of the rotational ground excitations for the high-pier long-span bridge structures.