| Long-span single-tower cable-stayed bridge with hybrid beam combinesthe advantages of concrete beam and steel beam.It has the characteristics of strong spanning ability,high stability and beautiful shape,etc.,for which this type of bridge has been widely used in bridge construction in recent years.This thesis studies the dynamic characteristics,seismic performance and shock absorption measures of a long-span single-tower mixed beam cable-stayed bridge,yuekou hanjiang bridge,which has the largest span of single-tower freight railway in China.The main results are as follows:1、This study introduces the origin and development history of hybrid beam cable-stayed Bridges at home and abroad,summarizes the main characteristics of hybrid beam cable-stayed Bridges,and systematically expounds the research status of seismic performance and shock absorption measures of hybrid beam cable-stayed Bridges.The basic theory of seismic analysis of bridge structure and the seismic response analysis method of bridge are discussed.2、Based on the Midas/Civil software,a three dimensional finite element model of the bridge is established,the multiple Ritz vector method is adopted to calculate the natural frequency of the bridge and its dynamic characteristics has beed analisised.Many main design parameters,,such as the steel ratio,side span ratio,transverse wind resistance in the bearing,cross sectionarea of the stay cables,auxiliary piers,and weight of the long-span single tower hybrid girder cable-stayed bridge are studied.3、According to the site condition of this bridge and its anti-seismic design response spectra seismic which obtained from the code for seismic of railway bridges,artificial seismic waves were fitted as the input to dynamic time history curve.Then,the dynamic response spectrum method and the dynamic analysis method were used respectively to study the seismic response of this bridge in the combination of“longitudinal and vertical"and"horizontal and vertical"vibration conditions,the results of the two methods were compared.Finally,the traveling wave effect on seismic response analysis of the bridge is studied.4、A total of 49 conditions with different velocity indexαand damping coefficient C were modeled in this thesis.The damping effect of viscous damper with different parameter combinations was studied,and the influence of velocity index and damping coefficient on the damping effect was analyzed.To address the defects of the standard monkey algorithm,i.e.,the search redundancy and the easily plunged into local optimum in high dimensional search,an information sharing monkey algorithm based on distance matrix exchange mechanism is proposed in this study.The Kriging model was adopted to model the relationship between earthquake response of the bridge and the mechanical parameters of damper,and then the modified monkey algorithm is used to find the combination of viscous damper parameters with optimum damping effect.The result shows that the combination of speed index,α=0.27 and damping coefficient,C=2900kN·（m/s）-0.27 makes the best effect of damping energy dissipation and shock absorption.Finally,the concept of damping ratio is introduced to analyze the damping effect of the optimal parameter combination viscous damper. |
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