EVALUATION OF THE EFFECT OF CONFINEMENT V/S JACKETING ON CONCRETE STRENGTH

Abstract

In order to estimate the flexural behavior of reinforced concrete members, the stress—strain behavior of the constituent materials must be well established. The behavior of confined concrete is important to the designer in order to determine the quantity of the confining steel required in reinforced concrete column sections to achieve the ultimate curvatures required in seismic design for ductility. Previous research has established that retrofitting RC (reinforced concrete) columns with FRP (fiber reinforced polymer) jackets is an effective means of providing external confinement to the column cross section. In an effort to further FRP jacketing technology, this study focused on the confinement effectiveness of FRP jackets for square and circular type RC columns. Total 156 columns were tested to failure in axial compression. Variables investigated include Cross section shape (square and circular), Transverse Reinforcement ratio (spacing varied from 75 to 300 mm) and Number of FRP layers (from 0 to 4 layers). Unconfined specimens were included in the testing for reference. The stress strain behavior of these specimens was studied. For both square and circular specimens there is increase in ultimate stress and ultimate strain as number of layers goes on increasing and transverse reinforcement spacing goes on decreasing. This proved for FRP jacketing confinement due to FRP and transverse reinforcement both affects the stress strain behavior significantly As for as section shape is considered circular section effectively confined than square section. The confined model is proposed on the basis of the observations derived from experimental results for ultimate strength and strain- gain of confined concrete as a function of lateral pressure induced due to FRP and transverse reinforcement. This model is compared with earlier existing models. The agreement between the proposed model and existing models is observed.