Optimization Of Tower Span Ratio And Cable-free Zone Length Of Railway Extradosed Cable-stayed Bridge

In the past ten years,as a new type of bridge,the extradosed cable-stayed bridge,which is built on the basis of continuous girder bridge and conventional cable-stayed bridge,has some mechanics characteristics of two kinds of bridge structures,including the "stiff" of continuous girder bridge and the "flexible" of conventional cable-stayed bridges.It has good advantages on the structural performance and economic aspects,especially,it has a very large competitiveness when the span of bridge is between the 200 m and 300 m.The extradosedcable-stayed bridge is currently used in highway bridges,and its research parameters such as design parameters,stress characteristics,and earthquake resistance are relatively mature;and such bridges are being gradually promoted on railway bridges.Both are designed due to their different design requirements.There must be differences in parameters and forces;therefore,this article would like to take this analysis.On the basis of collecting,analyzing and summarizing some relevant domestic and foreign data,it takes the Xinjiang Kalasuke bridge as the engineering background and analyzes the related parameters and seismic response of the bridge in this article.The main related work and results are as follows:(1)Without changing other parameters,eight tower height models of the bridge were established under the premise of only changing the height of the non cable area of the bridge tower,and it optimized the cable-stayed forces of all the tower height models by the bending energy method in this article.And the main girder,the tower foot bending moment,the main beam stress,the tower foot stress and the total cable quantity were chosen as the objective functions and the ratio of the bridge tower to the bridge span were chosen as the independent variable.It fitted by curves with the independent variable and the five objective functions which are dependent variables respectively and analyzed all objective functions comprehensively.And the whole bridge mechanics characteristics and the optimum tower height after the tower height was changed are obtained under the comprehensive condition.The analysis results show that under the above conditions,the optimum tower span ratio is about 0.138.(2)Without changing the other parameters,six kinds of the length of non cable area of the tower foot finite element model were established to optimize the cable force under the premise of only changing the number of cable and unchanging the tension cable stiffness.The six kings of variables which have large influence on the length of the non cable area of the tower foot,including the maximum negative bending moment of the main beam at the tower foot,the bending moment at the middle span of the mid-span,the bending moment at the middle span of the side span,the deflection at the quarter span of the mid-span,the stress at thequarter span of the mid-span,and the total amount of the cable,were chosen as the objective functions.And the ratio of the length of the non cable area at the tower foot to the main span was chosen as the independent variables.It fitted by curves with the independent variable and the six objective functions which are dependent variables respectively and analyzed all objective functions comprehensively.And the optimum length of the non cable area at the tower foot is obtained under the comprehensive condition.The analysis results show that under the above conditions,the ratio of the length of optimal cable root to midspan is 0.12 to0.16.(3)Without changing the other parameters,six kinds of the length of non cable area in the mid-span and the side span finite element model were established to optimize the cable force under the premise of only changing the number of cable and unchanging the tension cable stiffness.The six kings of variables which have large influence on the length of the non cable area in the mid-span and the side span,including the maximum negative bending moment of the main beam at the tower foot,the bending moment at the middle span of the mid-span,the bending moment at the middle span of the side span,the absolute value of deflection near the middle span of the mid-span,the stress at the quarter span of the mid-span,and the total amount of the cable,were chosen as the objective functions.And the ratio of the length of the non cable area in the mid-span to the main span was chosen as the independent variable.It fitted by curves with the independent variable and the six objective functions which are dependent variables respectively and analyzed all objective functions comprehensively.And the optimum length of the non cable area in the mid-span and the side span is obtained under the comprehensive condition.The results show that under the above conditions,the ratio of the length of the optimal midspan to the midspan is 0.17-0.22.(4)In order to study the mechanical performance of the full-bridge after the tower height was changed under the earthquake,the optimum tower height obtained in the above study and the original design tower height were simultaneously conducted to response spectrum and time-history seismic analysis,and the dynamic characteristics and seismic response of the two kinds of tower height were calculated,Analysis of the aseismic performance of the optimized tower after optimization.