| As a perfect composite structure system,the steel truss girder and flexible arch bridge takes full account of the structural performance characteristics of girder and arch.Not only the span ability of the structure has been increased,but also the mechanical properties of materials has been taken full use when the load is subjected.At the same time,the construction efficiency is improved due to the generally adopted method of manufacturing the rods in the factory and assembling that on site.There must be errors between the actual bridge state and the design state during the construction process due to various factors,and these errors will accumulate gradually with the construction process.Those errors will eventually lead to a large difference between the actual state of the bridge and the ideal design state after finishing the construction,and even endanger the structural safety.Thus,the construction control of large-span steel truss girder and flexible arch bridge has received increasing attention.This paper uses the construction of Yinchuan airport Yellow River long-span continuous steel truss girder and flexible arch bridge as the engineering background.Combing long-span bridge construction control theory,finite element calculation model and field measurement results,the key problems encountered during the construction control of the bridge were studied and solved.While providing technical support for the successful completion of the project,the construction experience of this type of bridge has also been accumulated.The main research work covers the following aspects:(1)Firstly,the history of the development of steel bridges are reviewed and summarized.The classification and mechanical characteristics of steel truss arch bridges are introduced;The significance and importance of bridge construction control and the theory of long-span bridge construction control are summarized;The construction method and monitoring scheme of the steel truss girder flexible arch bridge studied in this paper are described in detail.(2)According to the concrete construction process of the bridge,the calculation formula of the installation line shape in the cantilever assembly process was derived based on the initial displacement method,and the calculation results of the formula was used to guide the construction on site.The linear precision control in the assembly process was studied from severeal aspects,such as the elevation of the temporary pier support point,the quality of positioning pinning and the assembly error of the bar.In view of the phenomenon that the elevation of the nodes was too low occurred during the actual erection of the bridge,the adjustment measure of lifting the cantilever end after replacing the punching pin was proposed aftre analyzing the causes of the error(3)Based on the wind tunnel test results of the hanger,the static wind responses of flexible arch during the assembly process were calculated and analyzed,and the most unfavorable conditions during the construction process were grasped.The results show that the stress of the flexible arch member exceeds the upper limit of the allowable stress of the material under the action of wind load and self-weight.In order to avoid the phenomenon of instability of the flexible arch,two types of wind resistance measures,the internal cable method and the external cable method,have been proposed and optimized in combination with the characteristics of the structure and the actual conditions on the site.The internal cable method is optimized from two aspects of the location and quantity of the cable arrangement,which effectively improves the wind resistance performance of the flexible arch.(4)Combined with the calculation results of the finite element model and the measured results,the change of the shape of the closure under different temperature was discussed and the appropriate closing time was determined.In view of the phenomenon that the arch can not be closed naturally,a lifting scheme is proposed through calculation and analysis.Analyze the changes of measured stress and the theoretically calculated stress of some members during the closing process.(5)The change of the internal force of the members caused by the height difference of the fulcrum was analyzed and discussed.The results show that the maximum stress of the full-bridge members is within the permissible force range of the material under the most unfavorable load condition that happened in the process of falling beams.The height difference between the same piers is the focus of construction control.The line shape and the measurement results of stress after the completion of the falling beam shows that the construction control is effective. |
