Research On Constitutive Relation Of Circular Tube Confined High Strength Concrete

High-strength concrete has been widely applied in structural engineering for its characteristic of high strength and good durability,but its obvious brittle property prevents its further promotion,especially in structures with seismic design. At present,closely spaced stirrup is used in reinforced high-strength concrete columns to assure ductility of structures, however,it also results in difficulty of concrete placement,and it can't provide a continuous and uniform confinement of concrete. Compared with closely spaced stirrups,high-strength concrete can be confined more efficiently by circular steel tube,and difficulty in construction is avoided simultaneously. Research on steel tube confined concrete at home and abroad mainly focused on the bearing capacity and seismic performance,but few research results were available about the deformation under compression and constitutive relationship. Following are the main research work:(1)The experiment of 18 circular steel tube confined concrete stub column specimens under axial compression was carried out. The main parameters are concrete strength(C40,C60 and C80)and diameter-to-thickness ratio of steel tube(100 and 130). Axial stress-strain curves of steel tube confined concrete, lateral deformation coefficient-axial stress curves and volumetric strain-axial strain curves were obtained. The failure mode,bearing capacity and ductility of specimens were analyzed. Inner micro cracks of concrete were also analyzed according to the experiment result base on the classical theory of development of micro cracks of concrete. Primary investigation of breakage mechanism of steel tube confined concrete was done by exploring the relationship between elastic or inelastic deformation and compression damage of concrete.(2)Basic on the existing experimental data of circular steel tubed concrete columns under axial compression,previous models of uniaxial stress-strain relationship of confined concrete were verified. Test results showed that previous models could predict the strength of steel tube confined concrete well,however,they couldn't predict the strain at peak stress correctly. Stress-strain model of steel tubed concrete was proposed according to the test results,and it could be applied in practical design.(3)Lateral deformation of circular steel tube confined high-strength concrete under axial compression was analyzed. Classical lateral strain-axial strain modelsof confined concrete were analyzed and compared with experimental results. Based on the proposed stress-strain model of circular steel tube confined high-strength concrete, and combined with a recent lateral strain model, the analytical model was established to predict the behavior of the circular steel tube confined high-strength concrete under axial compressive.