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Confinement modeling in rectangular concrete columns with external FRP and internal steel

Recently, the need to increase the strength of reinforced concrete structures has become the dilemma that all civil engineers are eager to overcome. Of the many proposed solutions, fiber-reinforced polymer (FRP) material has attracted attention due to its superb properties such as high strength-to-weight ratio, high energy absorption and excellent corrosion resistance. FRP wrapping of concrete columns is done to enhance the ultimate strength due to the confinement effect, which is normally induced by steel ties. The existence of the two confinement systems changes the nature of the problem, thus necessitating specialized nonlinear analysis to obtain the column’s ultimate capacity. In this research, a model to estimate the combined behavior of the two systems is proposed. The calculation of the effective lateral pressure is based on Lam and Teng model and Mander model for FRP wraps and steel ties, respectively. The proposed model introduces load eccentricity as a parameter that affects the compression zone, and in turn the level of confinement engagement. Full confinement corresponds to zero eccentricity, while unconfined behavior corresponds to infinite eccentricity. The model then generates curves for eccentricities within these boundaries. Generalization of the moment of area approach is utilized based on proportional loading, finite layer procedure and the secant stiffness approach, to achieve equilibrium points up to failure.

Author(s):

Ahmed Al-Rahmani    
Kansas State University
United States

Hayder Rasheed    
Kansas State University
United States