Research On Behavior Of Hydraulic Pre-stressed Concrete-filled Steel Tubes Columns Under Axial Compression

Along with the technical and economical development, the application of concrete-filled steel tubes structure in engineering practice is more and more extensive. Concrete-filled steel tubes make full use of the advantages of steel and concrete materials, with high bearing capacity, good plasticity and toughness, convenient construction, good economic effect and so on. The steel tube and concrete with different deformation characteristics, ordinary concrete filled steel tube in normal use stage, the synergistic effect of steel tube and core concrete play is not good. The core concrete is not in the three dimension stress state, restriction of steel tube concrete filled steel tube on ordinary concrete core has not been brought into full play. This paper presents a new pre-stressed method is applied in the initial stage of the concrete filled steel tube pre-stressed concrete core in the whole work phase are subject to the restriction of steel tube in three to confining pressure state, thus improving the mechanical properties of concrete filled steel tubes. The method of hydraulic pre-stressed can be applied to the concrete filled steel tube, which can be applied to the concrete filled steel tube, and the obtained value is stable and reliable. In this paper, the experimental and theoretical analysis is made on the stress behavior of the concrete filled steel tubular short columns under hydraulic pressure. The main research contents are as follows:(1) Independent design and manufacture of hydraulic prestressed steel pipe and pressure device. The feasibility analysis test of hydraulic prestressed concrete filled steel tube is carried out.Independent design and production of hydraulic prestressed steel pipe can endure 10 MPa hydraulic prestressed, and to charge effect is good, the stress loss is smaller, meets the requirements of the tests; by pressurizing device and pipe connections, can realize active quantitative applied hydraulic prestressed; water instead of concrete filled steel tube, adopts hydraulic applying prestress method, the experimental research on the feasibility of prestressed steel pipes of the hydraulic; comparison of the experiment results and theoretical analysis to verify the feasibility and reliability of the hydraulic prestressed concrete filled steel tubular and the whole device.(2) The axial compression tests of six concrete filled steel tubular short columns and two common steel tubular short columns were carried out, and the mechanical properties of steel tubular short columns under different hydraulic conditions were studied. The results show that hydraulic prestress can improve concrete filled steel tubular short column axial pressure of mechanical properties, the normal use stage enhance the stiffness and cracking of concrete core has good delay and better play the mechanical properties of concrete filled steel tubular.(3) The experimental research on prestress loss of 6 hydraulic prestressed concrete filled steel tube is carried out. The results show that under the condition of non special facilities, the prestress loss is less than 20%, which verifies the reliability of the whole set of equipment.(4) Fiber model method, establish the basic assumption and sets up the hydraulic prestressed concrete filled steel tubular numerical model, the preparation of the hydraulic prestressed concrete short column axial compression process analysis program, and the experimental results were in good agreement. In-depth analysis of the steel pipe should be force changes in the whole process, the core concrete should force changes in the whole process and steel tube and the core concrete between each other under the action of hoop stress changes in the whole process, the more deeply reveals the hydraulic prestressed concrete in uniaxial compression and working mechanism.