Research On Hysteretic Behavior Of Corroded Reinforced Concrete Column Under Sesmic Load

As the corrosion of steel bar is conducted in reinforced concrete(RC) column, the decrease of the cross-sectional area and the deterioration of the mechanical property of steel bar, as well the change of the bond strength between steel bar and surrounding concrete are approached. Meanwhile the dilation of corrosion products leads to concrete cover cracking. All the results concerned above influence the flexural strength, the shear strength and the deformability of corroded RC column. Under seismic load the performance of corroded RC column will certainly be very complicated. In the present dissertation, the hysteretic behavior of corroded RC column under seismic load is studied. The major works in the dissertation are as follows(1) Based on the hysteretic behavior of corroded RC column under combined axial compressive load, bending moment and shear force, a series of experiments are designed. Corrosion ratio and axial load ratio are considered as major factors by pseudo-static testing method. The rules of hysteretic loop, skeleton curve, circular stiffness, ductility and energy dissipation of corroded RC columns are obtained. The three components of total lateral deformation, which are bending deformation, shear deformation and anchorage slip displacement, are derived.(2) The bond-slip constitutive model between corroded rebar and surrounding concrete in anchorage area under reversed cyclic loading is proposed by analytical method, and the damage of the concrete within the ribs of rebar is considered in the model. The model can be used to calculate the anchorage slip deformation of corroded RC columns.(3) Three polyline load-bending deformation model for corroded RC column under compressive-flexural-shear load is established, which is made up of bending cracking load and corresponding bending deformation, yield load and corresponding bending deformation, as well limiting flexural load(flexural strength) and corresponding bending deformation. According to the degradation of the bond strength between corroded rebar and surrounding concrete, the bending deformation of corroded RC column after cracking can be described by a linear interpolation between perfectly bonded column and completely unbonded column. Proposed load-bending deformation model has also been verified by bending deformation component which is derived from the total experimentallateral deformation.(4) Three polyline load-shear deformation model for corroded RC column under compressive-flexural-shear load is established, which is made up of flexture-shear inclined cracking load and corresponding shear deformation, yield load and corresponding shear deformation, as well limiting shear load(shear strength) and corresponding shear deformation. Based on an existing model for RC beam in literature, a modified flexure–shear inclined cracking load model under axial load for corroded RC column is established. According to accepted beam-arch action and tension-shear critical model for concrete, a shear strength model of corroded RC column is proposed. Based on the published shear deformation model of perfectly bonded column at yield state, a new shear deformation model of corroded RC column is set up. Proposed load-shear deformation model has been verified by shear deformation component derived from the total experimental lateral deformation.(5) According to the experimental data of the present dissertation,the formulas for modified ductility factor and modified unloading stiffness for corroded RC column are proposed.(6) Combined with above concerned models, a hysteretic model for corroded RC column under seismic load is set up and can be described as follows:(1) Skeleton curve of hysteretic model is made of two parts, one part is the section before peak point and another part is the section after peak point.(2) The deformation of the section before peak point is formed by the linear superpositions of bending deformation, shear deformation and anchorage slip displacement. Meanwhile, the section after peak point can be determined by the modified ductility factor model.(3) Unloading stiffness is decided by the modified unloading stiffness model and reloading stiffness follows the rule which is accessed to the historic peak point. The new hysteretic model is verified by the experimental data and the errors are mainly within 20%, which shows that the model is viable in practice.