This paper presents an experimental and nonlinear finite-element analysis (NLFEA) results of circular short reinforced concrete (RC) columns confined externally with carbon fiber-reinforced polymers (CFRP) subjected to pure axial loading. The experimental program involves the fabrication and testing of 55 specimens wrapped with different number and configuration of CFRP sheet layers in the transverse and longitudinal directions. In addition, the columns were modeled using NLFEA. After reasonable validation of NLFEA with the experimental test results of companion columns and available technical literature results, NLFEA was expanded to provide a parametric study of 96 columns that correlates the ultimate axial stress of CFRP-confined RC columns to unconfined strength of concrete ( fco ) , the volumetric ratio of CFRP ( ρf ) , and the size effect. Results indicated that the ultimate capacity and ductility increase with the increase in volumetric ratio of CFRP ( ρf ) and unconfined strength of concrete ( fco...

Incorporating discontinuous structural synthetic fibers in general enhances the performance of concrete and increases its durability by minimizing its potential to cracking and providing crack arresting mechanism. Synthetic fibers are non-corrosive, alkali resistant, simple to apply, and added in small quantities due to their low density; thus, a substantial number of uniformly distributed fibers are added. In this research, an experimental program was undertaken to investigate the shear behavior of lightweight concrete beams containing discontinuous structural synthetic fibers. The studied parameters include fiber content and shear reinforcement. The tests were conducted under four-point loading in a simply supported span of 0.85 m. The beams were divided into three groups based on shear reinforcement. Group 1 was designed without shear reinforcement, Group 2 with closed vertical stirrups placed at d/4 spacing (where d is the effective depth), and Group 3 with closed vertical stirrups placed at d/2 spacing. Each group contains four identical specimens except in terms of the fiber content: 0, 3, 5, and 7 kg/m ³ equivalent to fiber volume fractions of 0%, 0.33%, 0.55%, and 0.77%, respectively. The experimental results showed that the discontinuous structural synthetic fibers improve the ultimate shear strength, ductility, stiffness, and toughness of lightweight concrete beams significantly. Therefore, design codes are encouraged to consider their contribution to shear strength and revise the maximum stirrups spacing when discontinuous structural synthetic fibers are used. The results also showed that addition of discontinuous structural synthetic fibers reduces the crack width of lightweight reinforced concrete beams. The effectiveness of the discontinuous structural synthetic fibers decreases as the stirrups spacing decreases.

This paper investigated the impact of room temperature, cyclic ponding salt water (15%), hot water of 65°C, and rapid freeze and thaw cycles for three years on the flexural behavior of reinforced concrete beams strengthened with different configuration of CFRP composites. Totally sixteen RC beams were casted and tested as simply supported load as four point loading with a shear span to a depth ratio of 2.25. The investigated parameters includes mode of failure, ultimate load and corresponding deflection, yielding load and corresponding deflection, stiffness, steel strain, concrete strain, and CFRP strain. Based on tested results, the environment conditions had no effect (No separation or debonding) on the bond strength between CFRP composites and tension side of concrete. After applying the load, the inelastic deformation was shown in concrete which leads to yielding of main steel reinforcement and then compression failure of tested beams. In addition, the strengthened beams indicated a reduction in flexural stiffness and enhancement in the ductility of the member through. Finally, the increasing of number of layers (CFRP bonded area) had a strong impact on concrete by shelter concrete from environmental consequences and undesirable effect on the CFRP-concrete bond performance.