Experimental Study On The Hysteretic Behavior Of Preloaded Concrete Columns With CFRP Confinement

Recently, the method of concrete structure restrengthened with fiber reinforced polymer sheet iswidely used in civil engineering. The Carbon fiber reinforced polymer(CFRP)is a new material with excellent performance. Researching on it has very important significance for constructional engineering. So far, many research activities have centered on the investigation of the mechanical behavior of CFRP-confined concrete columns and some substantial achievements have been already obtained. However, most part of those activities is aimed at CFRP-confined concrete columns without preloading. Study on the behavior of preloaded concrete columns with confinement is still at starting point. So, the effect of preloading stress on the behavior of CFRP-confinement concrete columns is not well known, and the components are reinforced in bearing certain load in practical engineering. Researchers did less experiment research on preloaded reinforced component. This paper deals with the application of CFRP for seismic strengthening for concrete rectangle columns, and simulates reinforcing column mainly in preloading stress.Firstly, it studies a common concrete column and six columns restrengthed with fiber-reinforced plastic(FRP)which have been wrapped CFRP sheets under low frequency alternate load. For accordance with the engineering practice, all the area from 0 to 500mm high of plastic hinge has been reinforced. The influence of the main parameters in the experiment are axial compressive ratio, the wrap layers of CFRP, preloading stress and stirrup ratio for the hysteretic performance of concrete column is studied. The paper has studied the questions such as characteristic of destroy, hysteretic curve, displacement ductility ratio, skeleton curve, energy consumption, degeneration of rigidity. The result indicates that strengthened with CFRP not only increase columns'ultimate strength but also improve the performance such as energy consumption, ductility and so on. This method has a great effect on the reinforced columns which have big axial compression ratio. Reinforced concrete columns in preloaded condition, the accumulation energy dissipation and ductility obtain improve signifcantly. Then, the paper studies the damage reinforce baseded on three concrete columns at nominal axial compression ratio of 0.75. The result indicates that reinforced pre-damage specimens could improve the sesmic performance better.The paper analysises the stress characteristics of rectangular columns confined by CFRP based on the theory of FRP constraint concrete. And Based on the test data, through the introduction of the so-called "residual strength" concept, in the Lam and Teng band for reinforcing directly the proposed binding CFRP rectangular column model based on "Concrete Structure Design Code (GB50010-2002)" of concrete column flexural capacity is calculated for the amendment, put forward CFRP reinforced concrete columns bound flexural capacity calculation.Finally, according to Yimin Li putting forward in accordance with the FRP reinforced concrete square columns directly meet the needs of seismic and ductility the formula for calculating the amount of fiber, combined with Lam and Teng's model, this article put forward CFRP reinforcement necessary to bring the volume bound set of formulas, providing reference for the design staff.