International Concrete Abstracts Portal

This paper presents the results of an experimental investigation on the response of continuous reinforced concrete (RC) beams with shear deficiencies, strengthened with externally bonded carbon fiber reinforced polymer (CFRP) sheets. The experimental program consisted of nine full-scale, two-span, continuous beams with rectangular cross section. The tested beams were grouped into three series. Three beams, one from each series, were not strengthened and taken as reference beams, whereas, six beams were strengthened using different schemes. The variables investigated in this study included the amount of steel shear reinforcement, amount of CFRP, wrapping schemes, and 900/00 ply combination. The experimental results indicated that the contribution of externally bonded CFRP to the shear capacity of continuous RC beams is significant and is dependent on the tested variables. In addition, the test results were used to validate shear design algorithms. The proposed algorithms show good correlation with the test results and provided conservative estimates

In this study, it was investigated experimentally that flexural performance of RC beam reinforced by using CFRP sheet which has separation of CFRP sheet caused by secular degradation or substandard execution. The specimens were RC beams with several conditions of CFRP sheet separating at bending span and strengthening methods by CFRP sheet at anchorage. The bending test of RC beams and the adhesion test of CFRP sheet were performed. The strength of RC beam was improved by CFRP sheet strengthening in comparison with conventional RC beam and estimated by existing methods. The adhesive strength between CFRP sheet and concrete at the anchorage zone were 1.12-2.53 MPa, which were same value as tensile concrete strength and enough. When separation occurred between CFRP sheet and concrete at bending span of RC beams, the flexural behavior of RC beams, especially about strain or stress distribution of CFRP sheet, was influenced by methods of anchorage and characteristic property of concrete at the anchorage zone. And it was confirmed no effects of preventing the progress of crack in this case. We could say that it was necessary to pay attention in case of using CFRP sheet for repairing RC member deteriorated by rebar corrosion or crack.

The research on seismic retrofit of RC members using continuous fiber sheets is rapidly advancing in Japan. These research activities have been accelerated since the Hanshin-Awaji Earthquake, 1995 because this retrofitting technique has an advantage due to lightweight, flexibility, non-welding, and easy handling in construction works. The most preferable retrofitting technique for the existing building being in use is jacketing RC columns with carbon or aramid fiber sheets because of the advantage above. Recently many results of the research on short column with spandrel wall, columns with wing wall, beams with slab (T shaped beam), earthquake resisting wall have been reported in Japan. This paper introduces, first of all, these experimental research results in detail and the seismic retrofitting effects by the continuous fiber sheets are comprehensively evaluated. Flexural capacity, shear capacity and the improvement of ductility are discussed to evaluate the effect of reinforcement of continuous fiber sheets. Then, methods for evaluating the seismic retrofit of regular columns with continuous fiber sheets are described. A basic idea of the evaluation method proposed for a regular column is shown, and the problems which should be examined are extracted and explained about these effects. As the summary, the problems which should be solved, research direction and prospect are pointed out for the future research on seismic retrofit by continuous fiber sheets. Research needs for establishment of a design method when various members are reinforced by continuous fiber sheets in the future are also discussed.

Fiber Reinforced Polymer (FRP) composites are a very promising alternative to the use of traditional materials and methods in the repair and strengthening of under-designed or deteriorating structures. While most results indicate that strengthening with FRP is very effective, the wide variety of testing techniques used among researchers makes it very difficult to compare results. Objectives of this research were to gain a broader understanding of FRP’s effects on the failure modes and performance of reinforced concrete beams, to investigate a variety of strengthening schemes, and to validate current design methods used for shear and flexural strengthening of reinforced concrete members. This was achieved by comparing a variety of FRP systems under similar conditions. The seventy-one specimens tested exhibited a variety of failure modes depending on the strengthening scheme, thickness of the laminates, and material (carbon or glass fibers). The beam failure modes showed strong dependency on the FRP thickness. As the thickness of the composite laminate increased, debonding or concrete shear failure dominated. The effectiveness of FRP reinforcement was studied as a function of FRP rigidity and the effective strains developed in the fibers.

Current design methods for predicting deflections and crack widths at service load in concrete structures reinforced with steel bars may not be necessarily applicable in those reinforced with fiber reinforced polymer (FRP) bars. In this paper, methods for predicting deflections and crack widths and spacing of glass fiber reinforced polymer (GFRP) reinforced concrete beams were proposed. In order to use the effective moment of inertia for concrete beams reinforced with FRP bars, the effect of reinforcement ratios and elastic modulus of the FRP reinforcement were incorporated in Branson’s equation. This paper also presents a new equation to predict crack width. Six concrete beams reinforced with different GFRP reinforcement ratios were tested. Deflections and crack widths were measured and compared with those obtained by the proposed models. The comparison between the experimental results and those predicted was in good agreement.