Research On The Key Problems Of Construction Control Of Through Type Steel Tube Truss Beam-Arch Composite Bridge With Single Cable Plane

Steel box beam-arch composite bridge has been widely used in modern bridge construction at home and abroad due to its beautiful design,large span capacity,small building height and good landscape effect.However,with the increasing span of the bridge,many problems in the construction process are exposed.In order to reduce errors caused by improper construction and avoid some uncertainties during construction as far as possible to ensure the safety of bridge structure,it is necessary to monitor and control the construction process on site.In combination with the construction control of a steel tube truss beam-arch composite bridge,the author studies some key problems in the construction control process,the main contents are as follows:(1)According to the structural characteristics of through-type single cable plane steel tube truss beam-arch composite bridge,the detailed construction control scheme is formulated,the simulation model considering the construction stage is established,and the deformation and stress of each component in each construction stage are analyzed.Through analysis of construction control data,it can be concluded that the linear control of main girder and arch rib is ideal,with maximum error not exceeding 2cm;the total cross section of arch rib is compressed when the bridge is completed,and its compressive stress is much less than that specified in specifications;and the short suspender cable force error on both sides is slightly larger,and the measured values of other hanger forces are basically in agreement with the theoretical values,with an error of no more than 5%.(2)The cable force of beam-arch composite bridge is determined by a drop frame method,rigid suspender method and the principle of minimum bend complex energy,and several methods are compared.With the restrained minimum energy method,the cable force of the completed bridge is optimized by establishing the optimization model and compiling the MATLAB program.Under the action of these cable forces,the deformation at the arch foot and the bending moment and deflection at the mid-span of the main girder are reduced.The adjustment values of hanger force after removal of temporary pier of main girder are determined by difference iteration method and influence matrix method respectively.By comparing the results of the two methods,it is found that the influence matrix method is better than the difference iteration method in accuracy and use.(3)In order to simplify the research on the mechanical performance of truss arch in the construction stage,the triangular section space truss arch is equivalent to beam element according to the principle of transverse deformation equivalence.By introducing the critical buckling load of circular arch,the three limb truss arch is determined.In this paper,the in-plane and out of plane equivalent flexural stiffness formulas of three limb truss arch considering shear deformation are proposed,and the rationality of the formulas is verified by finite element modeling..(4)Three equivalent methods of torsional stiffness of truss are summarized(displacement equivalent method,equivalent plate method based on the same shear stiffness,dynamic equivalent method based on the change of torsional frequency).The influence of span height ratio,chord member and web member stiffness ratio on the equivalent torsional stiffness of truss is analyzed,and the applicability of three methods to equivalent torsional stiffness of truss with different specifications is studied.Finally,the range of span height ratio and stiffness ratio which can make each method have higher equivalent accuracy is determined: when the span height ratio is between 8 ～ 18,the error of equivalent plate method is less than 5%,when the span height ratio is greater than 25,the dynamic equivalent method and displacement method are used When the stiffness ratio of chord and web members is less than 50,the three methods can get better equivalent effect,but the equivalent plate method is the best.(5)By simplifying the truss arch to beam element,the arch rib equivalent stiffness arch bridge model is established.After analyzing the stress of each component in the construction stage of the bridge,it is found that the stress characteristics of truss-arch bridge and arch rib equivalent stiffness arch bridge are similar.The axial force of the two models is basically the same in the whole construction stage,and the maximum error is 2.04%.Because of the different arch rib structure,there are some deviations in arch rib stress and suspender cable force.However,from the perspective of the whole bridge stress,this change has little effect on the mechanical performance of the whole bridge,which indicates that it is feasible to simplify the truss arch as beam element for the preliminary analysis of the construction stage of the beam-arch composite bridge.The research of this paper provides a reference for the optimization of suspension force and the simplified analysis and calculation of the structure in the construction control process of the same type of bridge in the future.