A study of FRP wrapped reinforced concrete columns

Fiber-Reinforced Plastics (FRP) have received significant attention for use in civil infrastructure due to their unique properties, such as the high strength-to-weight ratio and stiffness-to-weight ratio, corrosion and fatigue resistance, and tailorability. It is well known that FRP wraps increase the load-carrying capacity and the ductility of reinforced concrete columns. However, the behavior of FRP wrapped RC columns is not yet fully understood, and the design code is still not available at this time. This study is intended as a step towards improving this status. A stress-strain model for FRP wrapped concrete is proposed, which is subsequently used in the development of the moment-curvature relations for FRP wrapped RC column sections. A comparison of the proposed FRP wrapped concrete stress-strain model to the available test results shows good agreement. It has also been found that based on the moment-curvature relations, the value of the balanced moment of the cross section for the FRP wrapped RC column greatly differs from the value of the maximum moment of the cross section because of the effect of the confinement provided by the FRP wraps. This implies that the balanced moment of the cross section for FRP wrapped RC columns can not be considered as a critical point in the interaction diagram. An analysis of the FRP wrapped RC beam-columns for calculating the ultimate strength based on the Newmark\u27s method is developed and implemented in a computer program. The theoretical solutions of the column curves obtained by the developed program are verified with existing experimental results. A good agreement is achieved. Sensitivity studies are also carried out in this study to investigate the effects of design parameters on the ultimate strength of the FRP wrapped RC beam-columns. The parameters used in the study are the unconfined concrete strength, the steel ratio, the thickness of the FRP wraps, and the section diameter. The enhancement in ultimate strength due to the confinement provided by the FRP wraps is also confirmed in this study. Simple interaction equations are developed to provide a simplified and practical tool to evaluate the ultimate strength of the FRP wrapped RC beam-columns. The assumption of elastic-perfectly plastic moment-curvature relationship is made, and the concept of average flow moment is adopted in the derivation of these equations. A comparison between the solutions obtained by the proposed simple interaction equations and by the theoretical analysis indicates that the proposed simple interaction equations for predicting the ultimate strength are simple and reliable. Finally, a step-by-step design procedure is developed, and an example is given to illustrate the use of the procedure. This design procedure provides engineers with simple guidelines for calculating the ultimate strength and for the design of FRP wrapped RC columns