Experimental Study On Mechanical Property Of Microdilatancy Concrete Filled Steel Tube

Concrete filled steel tubular structure is a kind of composite structure which concrete isfilled into thin-wall steel tube. The fundamental of concrete filled steel tubular structure is thatthe core concrete is in compression stressed condition in trip-direction, steel tube acts as ahoop brake in the core concrete, so that it has higher compressive strength and better capacityof plastic deformation. Besides good mechanical property of high strength, light weight, goodductility, fatigue resistance, impact resistance and so on, concrete filled steel tubular structurealso has superior workability like saving both labor and money, light setting up and rapidconstruction which promotes the development of concrete-filled steel tubes arch bridge.The impact of creep can not be ignored for concrete filled steel tubular structure.Compared with normal concrete, because of trip-direction mechanical characteristic andbigger bearing capacity from concrete filled steel tube to its core concrete, the creep ofconcrete filled steel tube is more complex. The effect of creep on arch rib deflection, theincrement of steel tube stress, the reduction of concrete stress on will be very large. Concretefilled steel tube is a kind of composite material in principle of materials design, whilemicrodilatancy concrete filled steel tube is a new building material. As it has many excellentproperties, steel tube expansive concrete has been widely used in recent years. Creep ofconcrete has always been a hot and difficult problem that the studies, with no uniformconclusion about creep of concrete, are so few on creep of steel tube expansive concrete.Based on experiment, the present paper introduces general development situation ofconcrete-filled steel tubes arch bridge at home and abroad and the mechanical property ofconcrete filled tube. The key research questions, including the characteristics and mechanismof creep of concrete filled tube, the major influence factors of creep of concrete filled tube andthe effect of expanding agent on creep of concrete filled tube, bearing capacity, elasticoplasticdeformation and microstructure are studied. The conclusions are gotten binding experimentand theory as well as software simulation. Moderate expanding agent can increase the bearingcapacity of concrete filled steel tube. The microdilatancy action can make the core concretedenser. For bigger value of bearing capacity of concrete filled steel tube, the correspondingcreep is smaller. The longitudinal strain of concrete filled steel tube changes with differentparameter of expanding agent. The longitudinal strain reduces with the increase of theparameter of expanding agent within limits. Under repeated loading, the longitudinal elasticdeformation and plastic deformation of concrete filled steel tube change with the variations ofthe parameter of expanding agent. With the increase of the parameter of expanding agent, theplastic deformation of component is on a declining curve while its elastic deformation is onthe increase with certain limits. That is to say, the ductility of component of concrete filledsteel tube is enhanced and its fragility reduces. Based on comprehensive summing of the present paper, some questions on this issue forfurther study are proposed which provide references and examples for construction control ofconcrete-filled steel tubes arch bridge in future.