Study On Parameter Sensitivity Of Fully Floating Space Frame Single Tower Cable-stayed Bridge

In recent years,with the rapid development of social economy,people’s demand for roads,bridges and other transportation infrastructure is increasing.In order to adapt to various complex natural environment and engineering geological problems,the selection of bridge structure system is diversified.For the construction of cable-stayed bridges in high-intensity areas or areas with seismic requirements,a full-floating support system is preferred.Taking into account the mechanical behavior of the structure and the needs of landscape design,the full-floating system single-tower cablestayed bridge often uses a space framecable tower.The main girder of this kind of cable-stayed bridge is not supported at the cable tower,so that the main girder is in a fully suspended state to facilitate earthquake resistance and energy dissipation.Moreover,the space frame cable tower can adapt to the longitudinal stiffness requirements of the cable tower for the longitudinal swing of the main girder.Because the main girder of space frame tower cable-stayed bridge with full floating system is in the state of full suspension,its mechanical behavior is not easy to grasp.The force of space frame tower is complex,and its static and dynamic mechanical behavior is different from that of the conventional cable tower.The sensitivity of bridge design parameters and t the law of influence on the structural mechanics behavior needs indepth analysis.In view of this,this paper uses a full-floating system space frame tower cable-stayed bridge as the engineering support,uses finite element analysis software Midas/Civil to establish a full bridge finite element model,carries out static and dynamic mechanical behavior analysis of the bridge,and discussed the parameter sensitivity of the full floating space frame single tower cable-stayed bridge.The main research contents and conclusions are as follows:(1)Summarizing the research status of the full-floating system space frame tower steel-concrete composite girder cable-stayed bridge and the actual engineering construction,the structural characteristics,basic mechanical characteristics and existing problems of this type of cable-stayed bridge are sorted out,and the research content of the thesis is clarified.(2)Based on the characteristics of the engineering structure,the finite element software is used to establish a numerical model of the fish-bone girder of the full bridge,and the boundary conditions and load conditions of the model are simulated in detail;the influence of the wind resistance of the decorative component on the top of thecable tower is analyzed.,The results show that the wind resistance of Taodou has little effect on thecable tower,and the component does not directly participate in the structural force,the numerical model can only consider the Taodou’s own weight.(3)Considering that the bridge is constructed with support,based on the one-time bridge model,the influence laws of environmental temperature,concrete shrinkage and creep,cable force,second-stage dead load and other parameters on the internal force and deformation of the structure are analyzed,and the static sensitivity parameters of the bridge are obtained.The analysis shows that the deformation of main girder in the range of 1/4 to 1/3 span is sensitive to temperature,shrinkage and creep,cable force and second-stage dead load of main girder.The stress sensitive parts of main girder are mainly concentrated in the support,mid-span and 1/3 span of the main girder.The structural deformation and internal forces are more sensitive to temperature effects and concrete shrinkage and creep effect,while the cable force and the second-stage dead load only have significant effects on the main girder deformation and internal force.(4)A single-tower cable-stayed bridge with a semi-floating system and an equivalent portal-shapedcable tower is established to study the influence of the supporting system and the form of the cable tower on the mechanical behavior of the structure.The results show that: the full-floating system is a more flexible structure than the semi-floating system;the sensitivity of internal force and deformation of the full floating system cable-stayed bridge to temperature effect,shrinkage and creep effect,cable force,and second-stage dead load is lower than that of the semi floating system;the frame tower belongs to a spatially high-order statically indeterminate structure,which greatly improves the lateral rigidity of the tower,disperses the internal force of the tower structure,and improves the adaptability of the tower structure.(5)Based on the sensitivity analysis of static behavior,the influence of parameters such as main girder supporting system,main girder stiffness,second-stage dead load,and cable force on natural vibration characteristics is discussed.Research shows that the cable force has little effect on the natural vibration characteristics of the structure;the rigidity of the main girder and its own weight mainly affect the fundamental frequency of the structure,but have no significant effect on the mode shape of the structure;after the full-floating support system is converted to a semi-floating system,The overall rigidity of the structure is significantly improved.The first-order mode of the semi-floating system is the main girder longitudinally floating,vertical bending +vertical bending of the main tower,compared with the first-order mode of the full floating system main girder longitudinal floating + vertical bending,The integrity of the semi-floating system tower girder is significantly enhanced.(6)Based on the analysis of the natural vibration characteristics of the structure,the influence of the supporting system on the seismic response of the structure is studied,and the influence of the viscous damper on the natural vibration characteristics and seismic response of the cable-stayed bridge is analyzed.The seismic time history analysis shows that :only the longitudinal bridge displacement of the main girder and the top of the tower of the full floating system is greater than that of the semi-floating system,the bending moment and shearing force of the tower foot,and the mid-span bending moment and shearing force of the main girder are less than those of the semifloating system.After the cable-stayed bridge is installed with dampers,the fundamental frequency of the structure increases from 0.38 Hz to 0.76 Hz,and the first-order formation changes from longitudinal floating of the main girder + vertical bending to transverse bending,which significantly increases the longitudinal restraint of the main beam and improves the structural stiffness.The dampers have a great influence on the dynamic response of the structure.Except that the dampers increase the torque of the tower foot,the rest of the seismic response of the cable tower and the main girder is in a downward trend,and anti-seismic effect is remarkable,of which the tower foot torque is affected the most,with the maximum amplitude of 278.4%,and the tower foot bending moment is least affected,with the maximum amplitude of 1.12%.The seismic response of the main girder is generally more affected by the damper than the cable tower.