Study On Seismic Performance Of Damaged RC Columns Strengthened With Aramid Fiber Laminate

Taken as an important bearing constructional component of the bridge structure，columnhas been simultaneously found lack and degradation of bearing capacity，which will make itdifficult to bear the earthquake load. The urgent need to reinforce the column has thus beenwitnessed on account of the problems of insufficient bearing capacity, poor ductility as wellas other issues of the existing column structure. Fiber reinforced polymer （FRP） sheet hasbeen widely used in engineering structure because of its characteristics of high strength, gooddurability and convenient construction. What is more, FRP shares the advantages of beingable to improve the shear bearing capacity on inclined section and ductility effectively.Aramid fiber laminate （AFL）, a new type FRP sheet invented by our research group, is usedto strengthen RC column in this paper. Experiments and theoretical analyses had been exertedto anti-seismic capacity of RC columns strengthened with AFL. The main research contentsand conclusions are as follows:（1） Quasi static seismic experiment of impaired RC columns strengthened with AFL.Based on the testing load-displacement curve of non-damaged and non-strengthening columns,three initial damage levels were defined according to secant stiffness. Twelve columns werepre-damaged with three different specific levels. Six non-damaged and twelve damagedcolumns were strengthened with AFL by three different spiral spacing （0,5,10cm）. Specialdevice was set up and quasi static seismic experiments were carried out successfully.（2） The shear capacity on inclined section of RC column strengthened with AFL.Based on the failure models of damaged columns strengthened with AFL, truss-arch theorywas revised to calculate the shear capacity by considering strength reduction coefficient ofAFL and strength reduction coefficient of stirrup and concrete. The result shows thestrengthening method by AFL can improve the shear capacity of column, and computingresults fit with the experimental values well.（3） Study on the ductility of damaged RC columns strengthened with AFL. Thedisplacement ductility coefficient of strengthened damaged column has been proposed. Theinitial damage level as parameter was taken to build a theoretical formula of displacementductility coefficient and strong-shear weak-bending coefficient. The relationship betweenhysteretic energy dissipation coefficient and yield strength coefficient has been obtained withthe application of the energy balance theory. The relation expression about displacementductility coefficient and the yield strength coefficient was also given in this paper. The results show the strengthening method with AFL can improve the ductility of the column and thefeasible of calculation method is proven by the coincidence of the theoretical results and theexperimental values.（4） The research on damage model of damaged columns strengthened with AFL.Based on the failure character of specimen, Park-Ang damage model was revised byconsidering the total stirrup characteristic value and the initial damage level as the parameters.Experimental column damage model was then proposed and inspected by collecting thesuitable experimental data from the relative research. Results show the model expressed in thepaper can describe the damaged condition and predict damage limit better than Park-Angmodel, which have more widespread applicability.