The Research On Construction Control Of The Large Span Steel Truss Girder

Incremental launching method originated in the 60’s of last century,mainly used in the early stage of small and medium span concrete beam bridge.And it was rapidly and widely applied because of the construction covers an area of small,little impact on the surrounding environment,as well as the bridge across the deep ravine,urban viaduct,the superiority of flyover.With the development of technology,equipment and the theory of computation,incremental launching construction method used to expand the scope,which will inevitably bring about some new problem which has not appeared in the previous construction process,also to pushing the structure in construction safety,quality and economic aspects put forward higher requirements.In this paper,pushing several key problems in construction are analyzed,which provides reference for the design and construction of similar bridge.The modeling analysis of the incremental launching of the side span of the Bidu high-speed north Panjiang bridge is using a formal analysis method,with the large-scale finite element analysis software Midas / civil.The analysis of the steel truss girder’s force characteristics in incremental launching method,are pushing construction in each stage of structure stress,deformation,and parameters of the theoretical value,to ensure the construction of safe and efficient.It’s an important solid theoretical support.The related calculation results show that the internal force and deformation of the steel truss girder are in the state of constant change,and the change range is large.The positive and negative direction of the bottom chord stress changed with the change of structure system.When the beam across a bridge span,throwing the guide front beam enters the incremental launching span section to the front of the main beam arrived in the front fulcrum.In this process,the maximum value of bearing load is located in the first pivot position of the rear of incremental launching cross section.By using the method of mechanical analysis,the internal force of the main beam nd the support reaction force in the all stages of incremental launching method were analyzed,and the expression was obtained.The influence of design parameters(length,stiffness and weight load)on the internal force and support reaction of the main beam is analyzed,computing the method of calculating the parameters of the guide beam in the construction of the roof.And draw a conclusion: when the front of guide beam reaches the front supporting point of incremental launching span,the reaction force and moment value are the maximum value in the process.It’s the most adverse condition.With continuous beam span number increased,the influence coefficient of the moment at the support,which throw the front incremental launching span to the middle span tends to a constant.When the span of the middle span to incremental launching span is larger than 3,it can be assumed that the beam of the supporting point is assumed to be a beam with fixed at both ends.And the effect of the bending moment on the intermediate support can be neglected.In order to ensure that the value of the rear of the incremental launching span is close to the value of the maximum cantilever state after the completion of incremental launching,the ratio of the weight load of the guide beam and the line load of the main beam should be controlled below 0.17,And the guide beam and girder stiffness ratio should be controlled at about 0.2.Discussing on the monitoring of steel truss girder Incremental launching method control method,content and process monitoring,the result of incremental launching of the side span of the Bidu high-speed North Panjiang bridge pushing results was analyzed.The results of finite element calculation results and field monitoring measurement were compared.The comparison shows that,in and after the process of the incremental launching method,the shape and force of the main girder of the steel truss girder,the reaction force of the temporary pier and the deflection of the front of the guide beam are all in line with the requirements and the construction effect is satisfactory,providing a guarantee for the construction quality of the subsequent stages of the cable-stayed bridge,but also proving that this control method is scientific and reasonable.