Construction Mechanics Analysis Of Large Span Continuous Steel Truss Cable-stayed Bridge

The long span steel truss cable-stayed bridge is one of the most popular bridges due to its advantages of strong bearing capacity,large overall stiffness and light deadweight.The long-span steel truss girder cable-stayed bridge belongs to the high-order statically indeterminate structure,the construction method and procedure are complicated.The risk of accidents in the construction process is high.It is very important to ensure the safety of the bridge during construction.Therefore it is necessary to carry out in-depth analysis of construction mechanics.Taking Yancheng grand bridge on Xuzhou-Yancheng high-speed railway as the research object,many mechanical problems are systematically studied in bridge construction from three aspects: calculation of construction stage,temporary restraint measures of tower beam under large cantilever state,forced closure technology.The main research contents include the following aspects:(1)Firstly,a three-dimensional finite element model of the whole bridge is established by means of structure mechanics analysis software,and the linear shape of the main girder and the cable force are analyzed under double control to verify the reliability of the model.Secondly,the normal bridge construction stage is analyzed by non-stress state control method.The reasonable control state of target is selected.The non-stress cable length value is found as tension control values of the construction process.The displacement response of the main girder in the forming state is verified to be closed with the displacement response of the target in the control state.In each construction stage,the internal force,displacement and support response of the bridge structure accord with the mechanical characteristics of the structure and meet the requirements of construction safety.Finally,the comparison between the state of construction stage and the primary stage shows that the state of construction stage is reasonable and feasible.(2)Based on the study of temporary limit measures for large cantilever state of long span continuous steel truss cable-stayed bridge,the problem of degree of constraint freedom between tower and beam is discussed from the point of view of mechanics.Through in-depth comparative analysis of three feasible longitudinal limit measures,the optimal longitudinal limit measures are determined as the rigid rod +10mm long circular hole measures.Based on the characteristics of the bridge structure design,it is determined that the transverse limit measure of the whole bridge is to set side block bracket and cushion stone at the lower beam.At the same time,the longitudinal limit calculation model based on the gap element and the simplified transverse limit model are established to analyze the force safety of the limit device.(3)Aiming at the construction scheme of cantilevered mid-span closure for the main girder of the cable-stayed bridge with large continuous steel truss beams,a fast and forced mid-span closure method for the structure is proposed.Firstly,according to the characteristics,difficulties and control conditions of the closure,the sensitivity analysis of the closure displacement of the steel truss beam is carried out by means of the simulation technology,which provides a theoretical basis for the corrective measures.Secondly,a control method of constrained release of tower beam is proposed.With the influence of measured temperature change on the opening distance of closure,the calculation formula of critical closing operation temperature is derived.The reasonable closure operating temperature range is determined,and the optimization and implementation of closure scheme are guided.Finally,with the help of monitoring means,the measured and calculated values of the pre-and post-closure states are compared and analyzed to verify that the post-closure state is reasonable and controllable.