Linear Control Of Phased-Formed Steel Truss Bridge Based On Arching Method Under Unstress State

Linear control is the key and difficult point in the whole construction process of phased forming bridge structure.At present,the construction methods such as subsection hoisting method and cantilever assembly method are mostly used for the stage forming bridge structures.These methods usually control the deflection of the structure in the construction process to make the structure reach the final bridge line shape.Because the deflection calculation is affected by the construction process,when the construction process is adjusted,the structural deflection will also change.At the same time,the deflection of the structure is also affected by the environment and the temporary construction load,and the linear control is difficult.In order to solve the above problems,the theory of the control of staged construction considering the unstressed state of the unit provides a theoretical basis.Based on no stress state of the arch since method calculating bridge construction control theory in stages of linear structure,the core content is calculated for each part of the structure of bar a stress free size,and strict control in the process of bar factory production precision,ensure construction by stages are the ultimate bridge into line with a bridge line match each other.Based on the engineering background of a three-span continuous steel truss bridge,a stress-free arching method suitable for specific interjoint structures is proposed in this paper.The stress-free lengths of each part of the rods are calculated and the sensitivity analysis of linear parameters is carried out.The main work of this paper is as follows:(1)The selection of linear control parameters for steel truss bridge is discussed,and the stress-free length of the element is determined as the linear control parameter of steel truss bridge.Based on the principle of minimum potential energy and the total column method,the mechanical equilibrium equation of the staged forming structure of the bar system is introduced,and the solving process of the mechanical equilibrium equation of the staged forming structure is illustrated with a numerical example.(2)Based on the mechanical equilibrium equation of the multi-stage forming structure、the stress-free arching method suitable for specific interjoint structure was proposed,and the stress-free length of each member of a steel truss bridge was calculated by taking the target forming line of a steel truss bridge as the known parameter input,so as to achieve the target setting of the pre-arching degree of the steel truss bridge.The results of pre-arching degree setting show that,compared with the traditional method of lifting and cooling,geometric method and other traditional methods,the proposed method can take into account the expansion of the upper chord and the bowstring in the process of steel truss girder arching,and will not cause secondary internal forces in the process of steel truss girder arching.Taking the stress-free length of the calculated members as the alignment control parameter during construction,the bridge span alignment automatically approximates the design objective into the bridge alignment,which verifies the reliability of the arch lifting method.(3)Furthermore,taking the reasonable alignment of the steel truss bridge as the control objective,the sensitivity analysis of the influencing factors of the alignment of the steel truss bridge was carried out based on the response surface method,and the influence degree of each factor was quantitatively evaluated by using the sensitive factors and the sensitive percentage.The structural response surface function(RSM)was fitted by Design-Exper data analysis software,and the structural alignment was modified by RSM.