The Study Of Torsional Behavior Of Carbon Fiber Sheet Strengthened RC Column

The column is one of important structural components among frame structures; it assumes the role bearing the loading from the building floor and above the beam. Due to the earthquake, the destruction of the column makes the whole structure lose bearing capacity and collapse, seriously damaging people's life and possession security. When the earthquake is coming, the column will take not only bending and shear, sometimes also torque; during the earthquake, wave can cause the action of earthquake power in both two directions of X-axis and Y-axis of building structure, which can be imitated by structural design soft wares, for example, PKPM; If there are floors with unevenly distributed quality, especially the above quality is much more than the below one, the torsion phenomena will be more obvious. Besides, the structure form is irregular and the quality center is away from axis, the torsion destruction is also caused.CFRP is a new reinforcing material with the characters of being highly strength, light in quality, anti-erosion and anti-fatigue. Anti-pull ability of CFRP in filament direction is very high, even up to 8-18times steel bar and it is mainly used to produce carbon fiber plate, carbon fiber bar, carbon fiber strip, carbon fiber cable, carbon fiber fabric, such as carbon fiber sheet; this thesis is to use carbon fiber to reinforcement and concrete columns and test its torsional behavior. According to the code of torsional behavior, in the test, I have preproducted the six columns, designed the different test parameters, namely, different length and different axial compression, and different layers of carbon fiber reinforcement; in this experiment, this text MTS electro-hydraulic loading device, hydraulic jack, steel beam, screw bars, steel fixture, steel pad plate and wheel are used to be combined into a reverse wheel loading device for loading on the six components; based on the imposed force and measured displacement, drawing the stress - strain curve (stress-strain curves), and according to its full extent, analyzed the reinforced columns ductility, ultimate load, displacement. By monitoring the strain gauges posted on the inside of strengthening column, I studied the strain by the internal fixture and established a mathematical model. I used ANSYS finite element analysis software to make a quasi-static analysis of the studied reinforcement columns and compared results with the experimental results.By experiments, it comes to that under the bending, shear and torsion complex stress, concrete columns of the same carbon fiber reinforced layers under different axial compression ratio, the greater axial compression ratio is, the better the torsional behavior properties are; the firmer the joint point between the top of column and steel arm beam and the closer the surface of the shear destruction is to the bottom of the column, and the more full hysteresis loop is, stronger energy dissipation is, better ductility is; the study of concrete columns of the same carbon fiber reinforced layers under different axial compression ratio concluded that the more layers of carbon fiber reinforcement are, the stronger the anti-torsion is, the more the joint point of columns needs to be reinforced; the test also obtained if the column's upper and lower joint points have the same reinforcement forms and reinforcement amount, then the damage by torsion must occur at the bottom of the column complex stress area, when the column is reinforced for torsion, the more reinforcement must be focused on the column root; through the study of the torsional behavior properties of two sets of concrete columns with different lengths, it came to that the shorter the length of column is, the higher the loading power is after being reinforced; the longer the length of the column is ultimate loading capacity became weak, but strength reinforced by the more high, the longer the ultimate bearing capacity of pillars weakened, but the greater the ultimate torsion angle is, the more obvious the damage phenomenon is, the better the ductility. In test, there is sudden fracture phenomena of the carbon fiber in middle of column angle and the bottom of the column; from carbon fiber strain data collected from the experiments, when components were being destructed, great changes happened to CFRP, indicating CFRP plays a significant role in the torsional behavior of component. By monitoring strain of steel bar in columns, it shows in the pure torsion region at the top of column, the longgitudinal steel bar in the four corners inside column play a significant role in torsional behavior, a shorter set reinforces the above and below vertical bars and is contrary to the stirrup strain, when longgitudinal steel bar becomes small, the stirrup strain is big, and longgitudinal steel bar becomes rather big, the stirrup strain is very small; the longer set has the rather same changes to the above and below steel bar strain; This phenomenon shows that the longer the column is, the better collaboration between the steel bar and concrete. By monitoring the strain of carbon fiber, it is observed that when the destructive interface is coming to bond stress gauge, there is great development to the strain of carbon fiber; by modified compression field theory, strain compatibility equation and force balance equation can be gotten, constitutive relations were established, and the strain at the crack was checked. The calculation equation obtained by the above modeling analysis can calculate torsional loading capacity of combined action of bending-shear-torsion rectangle section of steel concrete reinforced by carbon fiber sheet; through the comparison of the calculated result and test one, it is concluded that the torsion analysis of the reinforced column by using modified compression field theory is a feasible approach.At present, domestic and foreign researches pay much attention to the properties of carbon fiber filaments'high tensile strength in the direction of fiber silk and using carbon fiber materials on the beam, column bending, shear strengthening, while less attention to torsion reinforcing study of beam and column.When the earthquake occurs, torsions that can be ignored always happen to building structure, especially uneven distribution and disaccord between center of an area and center of gravity under the complex earthquake power. Therefore, the torsion test research of concrete components wrapped with carbon fiber has very magnificent significance to the application of the practical project and enrichment of study theories. According to the trial conclusion I think that the node part between beam and column in structure is always a weak link, so special attention should be paid to it in strengthening structure, especially the weakness of node fully wrapped with carbon fiber sheet is more apparent, hence the node part should be heavily strengthened, and observed from strengthening scale, the reinforcement at the bottom of the column must be greater than at the top of it.