Fiber reinforced polymer (FRP) reinforcements, with their excellent mechanical and non-corrosive characteristics are being increasingly used as a replacement for conventional steel reinforcement. ACI 440.1R-06 equation for determining the development length of FRP bars is based on Glass FRP (GFRP) bars and may not be applicable for Carbon FRP (CFRP) bars. This paper presents the results of an experimental study on the flexural behavior, bond characteristics, and development length of concrete beams reinforced with CFRP bars. Twelve beams were fabricated and tested. All beams were tested up to failure using a four point bending regime. The results indicated that the average bond strength of CFRP bars in concrete is about 15% higher than those of GFRP bars at comparable concrete strength. The ACI 440.1R-06 over estimated the development length of the CFRP bars by slightly above 30%, while CAN/CSA-S6-06 equation was unconservative by 50%.

Seismic retrofitting of RC columns by external bonding of FRPs has been proven to be a cost-effective and simple technique in recent years. In this study, the ultimate drift capacity of FRP retrofitted columns were predicted by selecting design parameters as the ratios of confinement, axial load, longitudinal reinforcement and plastic damage with a database consisting flexure dominated RC columns with and without damage. The database consisted of 28 strengthened and 6 repaired specimens, representing typical deficient building columns with poor transverse reinforcement detailing, that were tested under cyclic displacement excursions and constant axial load. For the strengthened columns, a drift based design equation was proposed and this equation was modified regarding the damage amount and axial load level for the repaired columns. The deformation capacities were predicted with a good accuracy and the simplified design equations gave reliable results considering safe design regulations.

This paper deals with the shear strengthening of reinforced concrete (RC) beams using externally bonded (EB) fiber-reinforced polymers (FRP). The parameters that have the greatest influence on the shear behavior of RC members strengthened with EB FRP and the role of these parameters in current design codes are reviewed. The effect of transverse steel on the shear contribution of FRP was found significant and yet is not captured by any existing codes or guidelines. Therefore, a new design method is proposed, which considers the effect of transverse steel as well as to other influencing factors on the shear contribution of FRP (Vfrp). The accuracy of the proposed equations is verified by predicting the shear strength of experimentally tested RC beams using data collected from literature.

The behavior of seventeen RC beams strengthened with FRP laminates mechanically fastened to their tension soffits with concrete anchor bolts is presented. The beams were tested in four-point bending on a 7.5 foot (2286 mm) span. Bolt diameter and spacing and FRP strip length were varied. The beams exhibited increases in yield moment ranging from 12.5% to 46%, and increases in ultimate moment from 30% to 75%, while displacement ductility ratios were 75% of values from un-strengthened control beams. The number of fasteners in the shear span had a greater impact on ultimate strength than did FRP strip length. Terminating the FRP strips in regions of larger bending moment resulted in an unexpected change of failure mode from concrete compression to shear. Measured strains in the FRP were less than those calculated assuming fully bonded conditions.

Review of previous experiments on brittle R.C. columns through FRP jacketing illustrates that the efficiency of FRP jacketing in strengthening applications is superior to that which is observed when jacketing is used as a repair means. Actually, performance of the repair appears to be related to the state of damage along the anchorage or lap splice of primary reinforcement sustained in the initial phase and whether these defects have been corrected or not, by additional measures such as concrete replacement in cases of cracked cover or by epoxy injections along the damaged anchorages, prior to FRP jacketing. Surprisingly, this type of repair proves more effective in elements that have failed in a brittle manner rather than in cases that have undergone extensive yielding; the reason for that is that brittle failure along the member length occurs before the anchorage of the reinforcement has sustained excessive yield penetration, which cannot be avoided in ductile member behavior. This issue is explored systematically through evaluation of the collective experimental evidence from tests on columns repaired with FRP jacketing after having sustained damage under combined axial compression and cyclic lateral displacement reversals.