International Concrete Abstracts Portal

Extensive experimental verification has shown that the use of fiber-reinforced polymer (FRP) anchors in combination with externally bonded fiber-reinforced polymer composites increases the flexural capacity of existing Reinforced Concrete (RC) structures. Thus, a rational prediction model is introduced in this study so that the fiber splay anchors may be accurately designed for practical strengthening applications. Simplified structural mechanics principles are used to build this model for capacity prediction of a group of fiber splay anchors used for FRP flexural strengthening. Three existing test series utilizing fiber splay anchors to secure FRP-strengthened T-beams, block-scale, and one-way slabs were used to calibrate and verify the accuracy and applicability of the present model. The present model is shown to yield very accurate predictions when compared to the results of the block-scale specimen and eight different one-way slabs. The proposed model is also compared with the predictions of a design equation adapted from the case of channel shear connectors in composite concrete-steel construction. Results show a very promising correlation.

An experimental study was undertaken to assess the performance of shear-critical reinforced concrete (RC) beams strengthened with externally bonded carbon fiber-reinforced polymers (FRPs). Fifteen large-scale beam specimens were tested in reversed cyclic three-point loading to simulate a seismic event. Specimens were designed to fail in shear with three variations of internal transverse steel reinforcement. For each variation, specimens were strengthened with different FRP configurations: U-wrap strips, U-wrap sheets, closed wrap strips, and closed wrap sheets. Testing showed that FRP strengthening was effective at improving shear performance, which was not adversely affected by reversed cyclic loading prior to the occurrence of flexural yielding, even when transverse steel yielded. Design codes CAN/CSA S6-06 and ACI 440.2R-08 were found not to accurately predict the FRP shear contribution of the test specimens, particularly for closed wraps when the design strain limit of 0.4% was applied.

This research studies the interaction of concrete, steel stirrups, and external fiber-reinforced polymer (FRP) sheets in carrying shear loads in reinforced concrete (RC) beams. A total of eight 600 mm high T-beam tests are reported. Three types of FRP were applied externally to strengthen the web of the T-beams: uniaxial glass fiber; uniaxial carbon fiber; and triaxial glass fiber. The test results show that FRP reinforcement increases the maximum shear strengths from 77.4 to 117.3% over beams with no FRP. The magnitude of the increased shear capacity is dependent not only on the type of FRP, but also on the amount of internal shear reinforcement. The FRP strains were found to be uniformly distributed among the fibers crossing the concrete shear crack. This paper also presents a design model based on the failure mechanisms of the test specimens. Good agreement was obtained between test and predicted results by using the proposed model.

The present research studies the mutual effects between mechanical loading and corrosion of reinforcing steel, as well as their combined effect on serviceability (flexural deflection and residual loading capacity) of reinforced concrete beams. Beam specimens 10 x 15 x 117 cm in size were subjected to four-point bending at various loading levels (0 ~ 75% of the ultimate load) with different loading histories (previous loading and sustained loading). NaCl solution ponding was employed to accelerate the corrosion process. Half-cell potential and galvanized current measurements were taken to monitor time for corrosion initiation. After corrosion initiated, an external current was applied to some of the specimens to expedite corrosion propagation. Beam deflections were recorded throughout all of the tests. Residual flexural loading capacity of the beams was evaluated at the end of the experiment. The results indicate that loading history and loading level have significant effects on both corrosion initiation and the rate of corrosion propagation. The failure mode of the reinforced concrete beams appeared to shift from a shear failure of concrete to bond splitting as the degree of corrosion increased. The results suggest that for a rational service-life prediction of reinforced concrete structures, the influence of the service load on the structure performance should be considered in combination with environmental conditions and material proportions.

This paper summarizes all available previous shear tests on fiber reinforced concrete beams without stirrups, and presents the results from 11 large-scale beam element tests. The beams had an overall depth of 610 mm (effective depth of 560 mm), and were constructed with varying amounts of hooked steel fibers (0 to 1.5 percent by volume). Three specimens were subjected to axial tension in addition to shear and bending. Increasing the amount of fiber was found to reduce the crack widths and increase the shear strength, the maximum increase in shear strength being 117 percent. The 50-mm-long fiber resulted in similar shear strengths as an equal volume of 30-mm-long fiber, but considerably more ductility.