Research On Key Issues In Construction Monitoring Of Long-span Asymmetric Suspension Bridge

In recent years,China’s transportation construction has developed rapidly,and the level of bridge construction is also in the leading position in the world,and more and more iconic bridges have also been built.According to the characteristics of China’s topography and landforms,some asymmetrical suspension bridges with side spans appear,which increase the difficulty of construction and calculation.Therefore,in order to explore the characteristics of the asymmetrical suspension bridge,supplement and improve on the basis of previous studies,this article relies on the construction process of the asymmetrical suspension bridge under construction-Zhaoyun Bridge,combined with finite element analysis software and programming The software carried out detailed analysis and research on the three key issues of the calculation of the unstressed length of the main cable,the calculation of the tension of the anchor span cable strands and the formulation of the steel box girder lifting scheme during the construction monitoring of an asymmetric suspension bridge.The main research contents and research results of this article are:(1)The history of suspension bridges and the evolution of calculation theory are briefly described,and the types and characteristics of asymmetric suspension bridges are summarized.The theory and calculation methods of suspension bridge structure analysis are briefly reviewed.(2)The calculation formula of the unstressed length of the main cable is derived based on the segmented catenary theory,the geometric models of the main cable saddle and the loose cable saddle are established,and the correction formulas of the unstressed length of the main cable strands at different layer heights are derived.Using the spatial coordinate conversion method,the local coordinates of the main cable in the anchor span area are converted into a unified coordinate system,and the correction formula for the length of the main cable anchorage area without stress is derived.For the cable strands with different layer heights in other sections of the main cable,the cable strand fold line model is established to derive the unstressed length correction formula for the different layer heights of the other sections of the main cable.Analyze the influence of different elastic modulus,area change,cable strand weight and temperature on the unstressed length of the main cable and fit the influence curve.Through engineering examples,Matlab programming is used to iterate out the coordinates of the tangent point and fit the position map of the tangent point of the loose cable saddle.The comparison of the values proves the correctness of the correction formula of the unstressed length of the main cables proposed in this paper.(3)According to the structural characteristics of the loose cable saddle and the anchor span,the mechanical model of the loose cable saddle is established,and the calculation formula of the anchor span tension of the swing shaft type loose cable saddle and the temperature influence formula of the anchor span tension are derived.A simplified model of a single cable strand in the saddle groove is established,the anti-slip safety factor formula of the single cable strand is derived using Euler’s formula,the tension of the anchor span cable strand is calculated through an engineering example,and the loose cable is calculated using the principle of equal tension of the anchor span The timing of releasing the temporary restraint of the saddle,and taking the relative slip of the loose cable saddle and cable strand as the control condition,calculate the temperature control range of the tension force of the anchor span.(4)Analyze the stress state of the main tower during the lifting of the steel box girder of the asymmetric suspension bridge,clarify the control index of the deviation of the main tower,and give the determination method of the lifting scheme of the asymmetric suspension bridge.Combined with the design hoisting schemes of the engineering examples,two other hoisting schemes were drawn up,and the three hoisting schemes were subjected to construction and formal simulation calculations.The main tower deflection change rule and swing history of each scheme were analyzed,and corresponding thrusting schemes were formulated.Then carry out the simulation calculation of the formal installation with the addition of pushing conditions.According to the control index of the main tower deflection,the first scheme is determined as a reasonable lifting scheme,and the correctness of this scheme is verified by comparison and analysis with the measured data.