| Frequent occurrence of large earthquakes witnessed in recent years has brought the urgent need to reinforce RC columns those may be damaged due to being for long years out of repair. Fiber reinforced polymer(FRP) has gradually obtained its widely application as well as intensive study in the reinforcement of RC columns due to its high mechanical strength, convenient construction coupled with remarkable durability. However, most of the existing research were aiming at the reinforcement of RC columns without any damage while RC columns that needed to be strengthened in the practical engineering are often found damaged, so it may bring a certain security risk while the theories obtained from the untouched RC columns are applied to damaged RC columns. Therefore, it is necessary to take the initial damage degree of RC columns into consideration of the research on mechanical properties of RC columns strengthened with FRP.The study in this paper is the seismic behavior analysis of quantitative damaged RC columns strengthened with Aramid fiber laminate(AFL) and the main contents and conclusions are listed as follows:1) The quasi static test is utilized on untouched RC columns made in accordance with the Code for Design of Concrete, then the paper manufacture RC columns with different damage degrees according to the test data as well as the damage model of RC column by Park and Ang with reference to the existing related literature on degrees of damage of RC columns.2) Strengthening RC columns with damage degrees of 0, 0.23, 0.42, and 0.72 on 600 mm height above its bottom side with FRP specifically at gaps of 0mm, 50 mm, and 100 mm. What is more, another untouched RC column without reinforcement is set as the contrast specimen. Afterwards exerting quasi static tests on those specimens. The seismic behavior is assessed according to experimental data of each specimen such as failure mode, hysteretic curve, shear capacity, displacement ductility coefficient, skeleton curve, and FRP strain. It is shown that the failure mode of strengthened RC columns is improved on its ductility since it is changed from bending shear failure of no strengthen RC column to bending failure of strengthed RC columns and the plumpness of hysteretic curves are significantly enhanced as well as the shear capacity and ductility coefficient. It is also known from the experiment that the first RC crack emerges at the column bottom and continues to expand upward while maximum FRP strain appears at the column bottom and decreases with the increase RC column height as well as showing its positive correlation with the lateral displacement. Better reinforcement effect is realized with full package reinforcement relative to spacing reinforcement, and seismic behavior of RC column is greatly influenced by the pre-damage degree since a greater damage degree will result in worse seismic behavior. Yet even the seismic behavior of RC column with a damage degree of 0.72 strengthened by FRP is better than the untouched RC column without strengthen.3) The comparison of RC column shear capacity calculation results from existing calculation model and test results is firstly presented and the model with minimum error is selected to build the calculation formula of quantitative damaged RC column shear capacity, and the accuracy of the formula is tested and verified later with contrastive analysis with test data.4) The finite element model of FRP strengthening RC column is built with ANSYS and the whole quasi static tests process is simulated. The simulation result fits well with the test ones. Further parametric analysis is presented on the validated model, and the influence mechanism of axial pressure ratio, kinds of FRP, reinforcement thickness, height of reinforcement, and prestressed FRP on the seismic behavior of RC column are studied. A series of preliminary effective strengthening methods of FRP on RC column for further research and engineering practice reference is obtained. |
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