| The serviceability of concrete column would be weakened in the conditions of freezing, thawing cycles in service and insufficient vibration during casting, which can result in partial deterioration of concrete columns. The inconspicuous deterioration in concrete would bring potential danger to the whole structures, and even led to serious accident in earthquake. With the development of modern measurement theory and technology, the partially deteriorated concrete existing in reinforced concrete(RC) columns can be detected easily by equipments so that the effectively retrofitting measures could be employed in time to avoid serious accident in earthquake. Fiber reinforced polymers(FRP), which has the advantages of high strength and anti-corrosion, has been widely used in retrofitting engineering recent years. The application of FRP on seismic rehabilitation has been studied by researchers through numbers of experimental and theoretical researches. Based on the existing researches, this paper mainly focuses on the seismic rehabilitation using CFRP on partially deteriorated RC columns by experiment, numerical simulation and theory analysis. According to the results, the influence of partially deteriorated concrete on the seismic behaviors of RC columns was investigated, and the validity of seismic rehabilitation using CFRP on the partially deteriorated column was verified. The method to estimate the demanded quantity of CFRP was proposed. The details of this dissertation are shown as following:(1) Firstly, the quasi-static experiments, including 1 partially deteriorated column with square section and control column with square section; 2 partially deteriorated columns with circular section; 1 control column with circular section and 3 CFRP retrofitted columns with circular section, were conducted. The experimental results showed that the carrying capacities and ductility of columns are weakened when the deteriorated concrete locates at the foot of columns,. Wrapping CFRP can not only effectively improve the ductility and energy dissipation, but also recover the carrying capacities and delay the stiffness degradation of partially deteriorated columns.(2) Secondly, the damage processes of 48 partially deteriorated columns, which retrofitted with CFRP were simulated combined with fiber finite element model, using FE code OpenSees, and the hysteresis loops of, were obtained. The influence of axial load ratio, slenderness ratio and CFRP thickness on the seismic behaviors were investigated.. The numerical results showed that the bearing capacity and ductility of CFRP retrofitting partially deteriorated column increases with the increasing of CFRP thickness, decreases with the increasing of slenderness ratio and axial load ratio.(3) The experiment was simulated by 3D finite element model, using FE code ABAQUS. The hysteresis loops, failure location and failure state of specimens were obtained which were compared with experimental ones to verify the validity. Then, the hysteresis loops and failure states of 42 specimens, with different deteriorated locations in concrete, were simulated. The influence of deteriorated concrete at different locations on the seismic behaviors of RC columns was investigated. The formula used to determine the failure location of partially deteriorated column was proposed. It was shown that the failure of partially deteriorated columns would occur in deteriorated concrete or at the footing of columns. The failure location is related to the deteriorated ratio, axial load ratio and deteriorated concrete location. The retrofitted effect of CFRP is related to the strength of deteriorated concrete, thickness and tensile strength of CFRP.(4) According to the measured stress-strain curves of FRP confined concrete in literatures, a new analysis-oriented model was proposed. The theory analysis was conducted subsequently based on plane cross-section assumption. The design-oriented axial model of FRP confined concrete, the design-oriented eccentric model of FRP confined concrete and the new model proposed in this dissertation were employed to predict the load-displacement curves of columns under eccentric loading condition. It was shown that the proposed model is accurate and simple in programming. The design-oriented eccentric model of FRP confined concrete is more effective in predicting the load-displacement curves of columns in the cases of larger axial load ratio, larger slenderness ratio, larger CFRP thickness and lower strength of confined concrete. |
