Study On Vertical Stiffness And Temperature Deformation Of Overlength Girder Of Multi Tower Cable Stayed Bridge

Since this century,although the multi tower cable-stayed bridge is more and more used by bridge designers,there are two inherent problems in the multi tower cable-stayed bridge which have been restricted by its widespread use.The two natural problems are that the overall vertical stiffness of multi tower cable-stayed bridge is low and the super long girder is greatly affected by temperature.This paper has carried out a series of research on the above two problems respectively.The main contents of this paper are as follows:(1)This paper collects the design data of more than 80 conventional multi-tower cable-stayed Bridges built,under construction or planned to be built at home and abroad,as well as the multi-tower cable-stayed Bridges in the form of short towers.According to the collected data,the parameters and information of the bridge,such as the ratio of edge to middle span,the ratio of height to span,the stiffening method and the structural system used in the data are analyzed.(2)Based on the principle of deformation coordination,the vertical bearing stiffness of side tower and middle tara cable of multi-tower cable-stayed bridge was deduced.In the derivation process,different structural systems were considered: consolidation of tower and beam,separation system of pier and tower,floating system,semi-floating system and rigid frame system,which was no longer simply considered as a whole of pier and tower.At the same time,different values of equivalent vertical stiffness of main girder are considered,instead of simply assuming that main girder is simply supported in each span.(3)Based on the law revealed by the cable support stiffness formula,a stiffening method for vertical stiffness of multi-tower cable-stayed bridge is proposed,which makes full use of the stiffness of side tower and side span.The layout method is that the number of side tara cables is more than the number of middle tara cables.Taking a three-pylon cable-stayed bridge as an example,it is found that the vertical displacement of the main girder and the deflection of the middle tower and the bending moment at the consolidation of the middle tower can be improved by increasing the number of side tower cables and decreasing the number of middle tara cables at the same time.The influence of side tower stiffness and middle tower stiffness on the overall vertical stiffness of multi-tower cablestayed bridge under the new stiffening method is analyzed.(4)Structural effects of different systems of four-tower low-pylon cable-stayed Bridges and three-tower conventional cable-stayed Bridges under temperature load are analyzed by changing the pylon anti-push stiffness.Based on the principle of deformation coordination,the anti-push stiffness formulas of side towers in different systems with the action of cable springs are derived.Based on the formulas,the internal forces and longitudinal displacements of main girders of three-tower rigid cable-stayed Bridges under the action of temperature at key positions are optimized.Finally,combined with the vertical stiffness index and temperature effect,the four-tower low-tower cablestayed bridge and the conventional three-tower cable-stayed bridge are analyzed.