| The famous bridge expert,Professor zhou Nianxian,believes that "the difficulty of designing for 100m arch bridge or for 1000m arch bridge involves few differential,while the difficulty of construction is tremendously different",which shows the construction technology is crucial to the construction of a super-large span arch bridge.Concrete-filled steel tube arch bridge,by its advanced construction technology of assembly of light steel tube arch ribs prior to core concrete pouring,thus making it possible for a longer span on arch bridge.However,by span lengthening,especially when it spans over 500m,the problem of long construction period,obvious Error Accumulation Effect,long segments,gigantic dimensions,complexity of welding effect etc.enables obstacles to emerge in precision of arch ribs fabrication,assembly and construction controlling.Besides,threats to the structure safety also consist of mega concrete pouring,long pumping distance,concrete distribution in-tube to the top the rib,incompatibility.Nonetheless,as the development of national transportation network,it is unchangeable trend that natural moat change thoroughfare,by the advantage of structure,the concrete-filled steel tube arch bridge is the ideal bridge to be built over gorges and gully.Therefore,a series of problems remain to be solved during the construction process of super-large span concrete-filled steel tube arch bridge for the purpose of implement of national strategic development,innovation of arch bridge key construction technology,consolidation of China in arch bridge construction.In this paper,based on the world’s largest span concrete-filled steel tube arch bridge,namely Hejiang Changjiang River 1st Bridge(spans 530m)construction project,the key calculation theory and controlling method involved in its construction are studied,and the main research results are as follows:1.Due to the large welds would definitely cause complicated impact on ribs’linear fabrication and bring high risks when super-large CFST arch bridge’s ribs are being fabricated,the delicate data based on element birth and death technology simulates the process of dynamic butt welding in segments,which leads to the symmetrical and asymmetrical welding in comparative analysis on distribution patterns of welding residual stress and deformation in butt weld and heat affected zone of super large steel tube,and to reach the conclusion that the mechanism on how welding defect affects structure performance,symmetrical welding is superior to that of asymmetrical,the welding defect causes the largest deformation of the closure parts of the arch rib in addition of changes on structure stress distribution.Based on the distribution characteristics of welding defects,the "2+1" high-precision horizontal coupling manufacturing technology of arch ribs is proposed not only to solve the problem of precision of large steel arch ribs but also to play a guidance role in similar projects.2.Focusing on the reality of unfavorable geological conditions and guarantee of linear integrity of rib ring after closure under designed closure temperature circumstance,we present an arch rib assembly linear correction method for closure under the non-designed closure temperature circumstance,deduce an elevation adjustment calculation of segment pre-elevation and arch rib assembly joints.Facing the problem of multiple constraint conditions,inconformity cable force distribution in invariable cable calculation by traditional separation of buckle and anchor,we provide an "optimal procedure,controllable consequence" one-off cable stretching improved calculation.For the buckle and anchor combination process and static force deformation compatibility condition,we deduce the calculation for cable force from single saddle and dual saddle which under the influence of considering foundation(tower)anti-push rigidity and elastic support,optimize the detail for traditional bidirection cable saddle structure and new type scattered dual turning cable saddle to solve the problem of combination of limit on traditional cable saddle’s radius and friction waste.Thus create a complete super-large span CFST arch rib assembly control method,which has been applied to the construction of Hejiang Changjiang River 1st Bridge.3.For the potential errors during the super-large span CFST arch rib fabrication and assembly on site,we analyzed the calculation method of arc length variation caused by temperature change,weld shrinkage and fabrication error,based on the geometric continuity characteristics of the arch rib under the condition of zero stress,the influence law of installation errors at different positions and the number of arch rib segments on the elevation and linear shape of the arch rib is deduced,what’s more,the key part of the arch rib installation segment elevation error control is clarified.For cantilever construction for joint cannot stick and cushion plate of the measures,based on the segmental coordinate geometry relationship,this paper derived the segment between the cushion plate of the coordinate correction formula,and expounds the tangent assembled,segmental coordinates correction in the implementation methods of fem,the mat plug plate was calculated by an example of cable force,main arch,the linear and the influence law of internal force,In view of the arch rib with super-large span CFST lattice configuration,the coordinate correction formula of the arch rib during tangential assembly is derived,and the coordinate correction method for the installation of the arch rib segment with oblique abdominals is proposed.4.For cable hoisting system method applied in 500 m class CFST arch bridge which comes across difficulties such as large,heavy lifting,high cable tower and problems like poor stability,complex environment,from the force performance,installation accuracy and offset control difficulty and so on the feasibility of the system compares the existing cable-buckle connection,thus has been clear about the " truly combination of cable and buckle " on super-large span CFST arch bridge,in the form of deviation control technology and research and development the tower.Based on the balance equations of forward and backward cable and wheel elements,the geometric non-linear finite element model of cable was constructed,and the nonlinear cable and wheel element method was developed.The slewing beam spreader is developed to carry out the lifting and turning on the arch rib,which solves the problem that the transport vessel in the rapid-current section cannot parking in the horizontal river,and ensures the robustness and economy of the cable hoisting and assembly system of CFST arch bridge of over 500m class.5.Through the combination of theoretical analysis,numerical simulation and experimental study,the causes of void of concrete-filled steel tube arch bridge is studied Experimental research by glass tube concrete pouring,it is clarified that the in-tube air is a major cause to incompatibility during construction stage,therefore we raise the auxiliary vacuum infusion technology,and through contrast tests,we concluded that under the vacuum circumstance,the way of air discharge revealed the working mechanism of vacuum assisted pouring and verified the feasibility of vacuum assisted pouring improves the compactness of concrete of the pipe.The research and development of "vacuum-assisted pouring method of concrete in large concrete-filled steel tube structure" and the corresponding "vacuum-assisted pouring system",has realized the whole process of three-stage continuous pumping construction of concrete filled steel tube arch bridge of 500m class,ensuring the compactness of concrete.In view of the problem that concrete shrinkage in tube leads to later emptying,the technology of "zero-shrinking concrete+vacuum-assisted pouring" is put forward and successfully practiced to solve the long time incompatibility problem of concrete-filled steel tube arch bridge. |
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