The overall objective of this paper is to establish the structural behavior of reinforced concrete (RC) beams strengthened with externally bonded carbon-fiber-reinforced plastic (CFRP) sheets. Four beams, three with bonded CFRP plates on the tension face, and two of which were provided with carefully designed external anchorages at the ends of the plates and along the span, were tested under four-point bending over a span of 4.8 m. The tests were carried out under displacement control. The beams were extensively instrumented to monitor strains, deflection, and curvature over the entire spectrum of loading to total failure, and to determine the structural response to load of the composite beams. The results show that bonding a CFRP plate on the tension face of a RC beam, without consideration of the end-anchorage stresses and the bond slip between the plate and the concrete substrate, can lead to significant degradation in the structural response of the plated beam. Carefully designed external anchorages, on the other hand, can lead to preservation of composite action to almost the failure load, increases in load capacity of up to 70%, substantial regain of structural ductility, and the transformation of a brittle failure to a more ductile failure.

Good structural design demands high quality experimental data and reliable modeling of the mechanical properties of the constituent materials. Although several theoretical models and much experimental data on the behavior of fiber-reinforced concrete in compression are available in published literature, there are considerable reservations on the general applicability of these models for design. This paper presents the results of tests in compression of steel fiber-reinforced concrete carried out according to standard procedures, and a critical evaluation of the models proposed to define the stress-strain behavior in compression. The tests reported were carried out on cylindrical specimens of plain and steel fiber-reinforced concrete with fiber volume of 1, 1.6, and 3%. To evaluate the reliability of the models available in literature, a critical comparative study was carried out between the experimental data and the various proposed theoretical stress-strain relationships. It is shown that while many of the models showed good agreement with test results from which the model equations were derived, there was no such good agreement when the models were applied to other published test data.

The objective of this study is to investigate the strength and ductility aspects of reinforced concrete (RC) beams strengthened with an externally bonded carbon fiber reinforced polymer (CFRP) laminate and to examine how such retrofitting affects strength, deflection, curvature, and energy, as exemplified by the area under the load-deflection curve of the strengthened composite beam. Three series of tests on eleven RC beams were carried out and their ultimate load capacities and ductilities evaluated. The variables in the experimental program were longitudinal steel ratio, volume of internal stirrups, and the location and configuration of external anchorages. The results show that both deflection and energy absorption are drastically reduced when beams are strengthened with bonded CFRP plates without external anchorages. Suitably designed and positioned external anchorages allow much of this lost ductility to be regained; however, even then the ductility of the strengthened beam cannot be restored to its original level. It is shown that definitions of ductility based on deflection and energy are able to give a good and rational representation of the physical aspects of ductility of RC beams strengthened with bonded CFRP laminates with or without external anchorages. The results show that the effects on ductility arising from strengthening existing RC beams with CFRP laminates cannot be ignored, even if it is not clear at this stage how to apply the concept of ductility indices and ductility ratios developed in this paper in design practice.