Formation Cause Analysis And Structure Improvement Research On Steel Pipe Cracking Of Concrete-Filled-Stteel-Tube Arch Bridge

The concrete-filled-steel-tube arch bridges are a new technology of the bridge construction development and a kind of quite ideal structural style of the great span arch bridge in our country recent years. The dumbbell-shaped concrete-filled-steel-tube arch bridges will occur crack accident accidnetal because of inappropriate construction during the construction procedure of filling concrete into the web spaces of concrete filled steel tubular dumbbell arch ribs. In view of the pipe cracking accident when filling concrete into the web spaces of concrete filled steel tubular dumbbell arch ribs, we analyse the formation cause of steel pipe cracking of concrete-filled-stteel-tube arch bridge and research formation improvement plan of arch rib section.Firstly, the plane finite element models are established to analyse the stress of CFST dumbbell-shaped cross-section of arch rib caused by the pressure of fresh concrete. Diffrent construction order and cases are considered. Calculation results show that the great stess which will take place in the connection points of steel webs and the steel tubes under the fresh concrete pressure are the main cause of the cracking accidents in construction. The filling order of the concrete to the three spaces will influence the sresses in the cross-sections. The stesses will be the smallest one in this order that the two tubes are filled with concrete at first and then the web space. The stresses will be the largest one in the order that the web space is filled with concrete at the first.Through plane finite element model computation analysis result, the web plate and the steel pipe interface point stress value is very big, the web plate under the concrete pressure function will produce the serious external displacement, it will fracture and cause the cracking accidents by the tension at the steel pipe and the web plate attachment and welded joint. This time web plate stressful condition does not belong to the line elastic scope and the result according to the line elastic supposition is not able to reflect the actual situation, therefore we should apply space finite element procedure to analyse relations among steel web plate stress, the distortion and concrete pressure by pumping, analyzed according to elasticity, the ideal elastoplasticity and hardening elastoplasticity of the steel, the analysis result will be closer to actual stress condition of the structure. Calculation results show that pouring concrete into two steel tube firstly and pouring concrete into the abdominal cavity finally is the best plan of arch rib concrete's irrigation of steel tubular dumbbell arch ribs among the irrigation order; But the section stress is most disadvantageous when pouring concrete into the abdominal cavity firstly and pouring concrete into two steel tube finally, Therefore we should avoid using this plan as far as possible in the construction. About formation improvement plan of arch rib section, we should apply the spatial finite element method to analyse this problem, in which the steel elastoplastic behabior is also taken into account, such as, steel bars is used to connect the two web places, steel bars is used to connect the upper steel tube and the bottom steel tube and the web space of the rib is divided into several spaces, The results and conclusions will have implications for the design and construction of similar arch bridges.