Concrete-empty Testing And The Mechanical Property Influence Of CFST Arch Bridge Cause By Concretes Empty

In the last20years, concrete filled steel tube (hereafter abbreviatedas CFST arch bridge has been vigorously developing in our country, and morethan300large CFST arch bridges have been built in China. According to?relevant data, connection void is prevalent in today s CFST arch bridges,which will be a hidden danger for construction of CFST arch bridges. Voidof CFST arch bridges is a common but complicated engineering problem, andthis paper mainly studies the following problems:①Disengagingmechanism. The author divides void problems into thefirst class void and the second class void, and also believes that the mainfactors affecting the first class void are quality of the core concrete,structure of pipe flange and stiffening ring, and pumping constructiontechnology, etc. which can be solved by improving the constructiontechnology； based on the cylinder theory, after analyzing the influence ofaxial load, temperature load and shrinkage and creep of concrete on thesecond class void, the author believes that temperature load and shrinkageand creep are the main factors causing the second class void.②Quantitativedetection of the void. The author, after learning thelaws of ultrasonic propagation, studies the propagation path and time ofultrasonic waves at different defects. Based on the qualitative detection,calculation formulas are deduced from travel time of the first wave ofcentral void, concrete subsidence void, and debonding void, etc. whoseapplicable conditions have been deeply studied;when conditions are not met,mobile probe symmetry detection can be used. Finally, feasibility andaccuracy of the above mentioned methods have been verified via model test,scale test and engineering experiment of Hejiang Yangtze River Bridge No.1，which is valuable for guiding later detection of CFST arch bridges.③Effectsof the void on mechanical performance of CFST arch bridges.The author first analyzes the confinement of steel tube to concrete, andmakes a research in the basic mechanical performance of CFST； Throughtheoretical analysis and model experiment, studies the influence of voidon the mechanical performance of CSFT, that the sectional area of ferruleeffect and the core concrete of concrete filled steel tubular cavity can reduce the decrease of the bearing capacity.(4)Void prevention measures. According to the mechanism of void and effects of void on the mechanical performance, the author puts forward some relevant prevention and reinforcement measures. The author believes that the first Class void can be prevented by improving the pumping technology and using high-performance micro-expansive concrete. As for the second class void, the cohesive force of steel tube and concrete can be strengthened by applying inner flange, stiffening ring and patter-steel plate in the internal wall to avoid Debonding and relative slippage; the effect of temperature load can be reduced by using steel products with a low linear expansion coefficient or by covering The steel tube with thermal insulation material. If a void is detected in a bridge, secondary grouting is helpful for reinforcement.China is still in the stage of a large-scale construction of infrastructure, and CFST arch bridge has a broad prospect. The research findings of this paper have great practical meanings for the void of concrete filled steel tubular structure.