Research And Application On Mechanical Properties Of Main Tower Of Super Long Span Suspension Bridge

The development of suspension bridges has a long history and has made great strides in the development of super-kilometer bridges,and as the span of suspension bridges increases,the height of the main tower increases,and the construction difficulties it faces become more and more prominent.As most of the main towers of mega-span suspension bridges in China are reinforced concrete structures and hollow box sections,the upper and lower crossbeams have a large volume of cast-in-place concrete,so in the process of construction,each section of the tower column is prone to deviate from the design line due to the increasing self-weight load,which can seriously lead to concrete cracking due to excessive tensile stress at the root of the tower column.Crossbeam as a structure connecting the two sides of the tower column,its construction process directly affects the final alignment and stress of the tower state,especially the crossbeam to take a layered casting program,need to avoid excessive temporary prestress tension value will be pulled apart.During construction,the daily temperature change will make the temperature difference between the inner and outer wall of the tower column box,forming a certain temperature difference stress,which may lead to excessive local stress to produce concrete cracks.In this paper,relying on the example of Nanjing Xianxin Road river crossing main tower project,finite element model is established to simulate the construction process of the main tower,optimize the temporary cross bracing arrangement scheme,conduct the force analysis of the cross beam structure in the construction stage,and study the influence law of temperature field changes on the mechanical properties of the main tower under each moment.The main work and research results are as follows:(1)In order to properly offset the line deviation and additional internal forces generated by the self-weight and construction load of the tower column during construction,the setting schemes of 3,4 and 5 temporary cross braces are determined,the spatial rod system model of the main tower is established,the shape-finding analysis of the main tower structure based on the temporary cross brace system is carried out to balance the magnitude of the internal forces in each section so that the main tower achieves a reasonable line state,and the internal forces of each temporary cross brace under each scheme are extracted The initial pre-topping force of the temporary cross brace was determined.(2)Establish a solid finite element model of the main tower,add the initial pre-topping force to the solid model,and analyze the effect of different options of temporary cross bracing on the stress of the root section of the tower column and the effect on the alignment of the tower column in each section during the construction of the main tower.Through comparative analysis,the optimal number of active temporary cross bracing for the main tower was determined to be 5.(3)The force analysis of the upper and lower crossbeams during the construction of the main tower was carried out,and the effects of the crossbeam concrete layered casting on the bracing,the effects of the upper and lower crossbeam concrete falling at one time and layered casting on the crossbeam structure,the effects of the prestressing tension value on the first and second layer structure of the lower crossbeam,and the relationship between the prestressing tension and the age of the crossbeam were studied.The results show that the crossbeam can share part of the load for the subsequent concrete casting after forming a certain stiffness,and the layered casting process is better than the single drop process.It is more appropriate to tension the prestressing beam after the concrete age reaches 5d.(4)The temperature field effect analysis of the main tower structure was carried out to determine the calculation parameters of the main tower temperature field,including environmental parameters,atmospheric and solar radiation parameters,concrete thermal parameters and convective heat transfer parameters.The effect of solar insolation temperature on the main tower during 24 hours is studied.The temperature difference between the inner and outer walls of the tower column and its change law are analyzed,and the temperature stress generated in the tower wall under the most unfavorable temperature difference is calculated,and the results show that the maximum tensile stress will be generated in the inner side of the tower wall under the positive temperature difference,and in the negative temperature difference,the maximum tensile stress will be generated in the outer side of the tower wall.In order to further study the effect of annual temperature change on the mechanical properties of the main tower,the overall temperature rise and fall of 10℃,20℃ four working conditions,the analysis of the tower column section stress and deflection change law,the results show that the tower wall and the lower beam,the first to the fifth temporary cross brace and the upper beam intersection of the location will produce a large local stress concentration,and affect the trend of the tower column deflection change.