Research On Application Of Generalized Lite Formula In Design Of Long-Span Concrete Arch Bridge

Concrete arch bridges are favored by bridge engineers at home and abroad for their large span capacity,multiple construction methods and low maintenance costs in the later stage.In order to improve the stress state of the arch ring,the section of large-span concrete arch bridge is usually in the form of variable height,such as a 600 m grade concrete arch bridge being built and Beipanjiang Bridge on Shanghai-Kunming highspeed railway,or the section with equal height,variable top and bottom plate thickness.At present,the commonly used methods for calculating the height of arch ring are cosine formula,parabola and Lite formula.The cosine formula is applicable to middle and small span arch bridges.The parabola is that the height of the remaining sections changes according to the set parabola after determining the height of the arch crown and the arch foot.The Lite formula takes the coefficient of arch thickness as a linear change.However,theoretical analysis shows that the phenomenon of excessive bending moment of arch foot will be encountered in extra-long span arch bridges.Therefore,on the basis of Lite’s formula,this paper changes the ratio of moment of inertia to parabolic change,and then puts forward a new calculation method of variable section height of arch ring,which is applied to the design of long-span concrete arch bridge.The main research contents include:(1)This paper analyzes the suitable span of the existing calculation method of variable section height of arch ring,and gives the calculation formula of high-order parabola according to the linear variation law of arch ring height,studies the influence of different times of parabola on the change of arch ring height,and analyzes the influence of Lite formula and different times of parabola on the static characteristics,dynamic characteristics and stability of 400 m span arch bridge based on 400 m trial design of concrete arch bridge,Provide a reasonable value for the number of parabolas when calculating the height of a section using higher-order parabolas,as well as the problems with traditional Ritter’s formula.(2)The arch thickness coefficient in traditional Lite formula is changed from linear change to parabolic change.Then the general Lite formula is derived and analyzed.β The number of parabola,ratio of rise to span,arch axis coefficient,the change of inertia moment for the thickness of roof and bottom plate in the arch foot area and the change of inertia moment for the thickness of roof and bottom plate in the arch foot area are considered,and the influence of the change of inertia moment for the thickness of roof and bottom plate in the arch foot area on the change of section height is neglected.Establish differences β Finite element model of parabola number is used to analyze the influence on mechanical behavior,stiffness,stability,dynamic characteristics and economy of 400 m span arch bridge under constant load only.β Reasonable suggestions for value determination.(3)The adaptability of the generalized Lite formula is further studied for concrete arch bridges with 200 m span,400 m span and 600 m span.For 200 m span bridges,the influence of the generalized Lite formula on the mechanical behavior,dynamic characteristics,stability and economy of the main arch under the change of section with equal height and thickness(constant arch height,change of thickness of roof and floor)is studied.The rationality of the height variation rule of the generalized Lite formula is verified by comparing a 600 m variable section arch bridge with the original design.Finally,the span range applicable to the generalized Lite formula is given by synthesizing the variation trend of internal force and stability of the main arch under different spans.