International Concrete Abstracts Portal

Part 1 of this study concluded that reinforcing bar stress intensity can be reduced, thereby confirming the possibility of strengthening. In Part 2, CFRP is bonded by various methods on the lower faces of reinforced concrete slabs. To determine bonding methods in detail, CFRP is studied with respect to the confirmation test and strengthening design methods. Strengthening design and measurement plans are then made for reinforced concrete slabs on an existing bridge. In strengthening design, the main reinforcing bars are strengthened with three to five layers. It is confirmed that the reinforcing bar tensile stress intensity is reduced around 120 to 130 MPa. CFRP may be used as a strengthening material for reinforced concrete slabs. Measurements will be conducted in 1993. Bending resistance will be confirmed directly during existing bridge strengthening operations.

Reinforced concrete slabs on steel girder bridges on the Tokyo Metropolitan Expressway are generally strengthened by installing additional stringers or attaching steel plates. However, it is difficult to apply such methods to strengthening work in confined box girders or where there are obstructions. Carbon FRP plates (CFRP) have been selected as strengthening materials for their applicability to strengthening work in confined spaces, and because they can be bonded in lattice forms, allowing for bonding condition inspection on the lower faces of the slabs. The aim of CFRP strengthening is to reduce the reinforcing bar stress caused by excessive wheel loads. In Part 1, investigations are conducted on CFRP applicability to strengthening work through static loading and work efficiency tests. Reinforcing bar tensile stress intensity was reduced by 38 to 56 percent of the unstrengthened specimen. The loads at which the tensile stress intensity is 140 MPa (allowable reinforcing bar load) are around 1.3 times that of an unstrengthened specimen. It can be concluded from the preceding that reinforcing bar stress intensity can be reduced, confirming the possibility of strengthening.

An experimental study of rehabilitation methods was investigated using artificially damaged concrete beams. The rehabilitation consisted of strengthening the damaged concrete beams by external post-tensioning, and some beams were not only externally prestressed but were also specially injected with epoxy resin to repair several sizes of cracks. Static as well as fatigue tests for three-point bending were conducted to investigate the effect of these rehabilitation methods. Fatigue tests of PRC strengthened by external cable were conducted at 2 million cycles, with a stress level of 33 percent of the ultimate static beam strength and cable tension force of 34 percent of tensile strength. From these test results, the static behavior of deformation and ultimate strength of the rehabilitated beams were confirmed as reasonably upgraded and strengthened by the proposed method. The results indicate that the deflection and ultimate strength of beams for the yield stage can be estimated by theoretical calculation. For the plastic hinge formation stage, deflection and ultimate strength were also evaluated by theoretical calculation. The change in beam rigidity was found to differ insignificantly before and after fatigue tests. In the same manner, ultimate bending strength of beams before and after fatigue tests was nearly the same. As a result of measuring the ratio of loss in the tension force of aramid rope, values of approximately 10 percent were obtained for all three stress states.

The characteristics of CFCC, including mechanical properties, fatigue, relaxation, and anticorrosive properties, are described. Examples of actual bridges in which CFCC has been used as a reinforcement are shown. In summarizing the investigation of these characteristics and the results of such tests as adhesion with concrete, antifatigue characteristics, antialkali characteristics, relaxation, and temperature cycle tests, it was confirmed that CFCC is a material suitable for tension applications in PC bridges.

The authors had the opportunity to apply partially prestressed concrete (PPC) members reinforced and prestressed with braided aramid fiber bars to an actual structure. The PPC members were used as beams for an upper foundation of a seismic base-isolated story. The PPC beams were precast, pretensioned, prestressed concrete members reinforced with braided aramid fiber bars manufactured by braiding aramid fibers and epoxy resin impregnation. Braided aramid fibers were used as main reinforcement, prestressing tendons, and transverse reinforcement of the PPC beams. Design, fabrication, and construction of the beams are reported. Full-scale flexural tests were also conducted to insure the safety margins of the beams. Two specimens were prepared using aramid fiber bars and carbon fiber bars, with cross sections similar to the actual beams. The flexural capacity of the beam at rupture of tendons shows good agreement with the calculated capacity, which uses the average tensile strength of the bars. Full-scale fire-resistance tests were also conducted on two specimens with the same cross sections as the specimens for the flexural tests, although the design did not require fire resistance of the beams because of their use in the foundation. From the test results, the beams were considered to resist fire for about 2 hr.

Aramid FRP rods, a composite of reinforced aramid fibers, are corrosion-free and used in various fields. Aramid FRP rods have been gaining attention for their use in prestressed concrete tendons. They have high tensile strength and excellent resistance. They are manufactured from aramid fibers and vinylester resin using a pultrusion process. The physical properties of aramid FRP rods were determined experimentally. Use of aramid FRP rods as prestressed concrete tendons requires a high-bond performance with grout or concrete, and a special anchoring system also had to be developed. Studies carried out in response to these requirements enabled the authors to conclude that aramid rods could make viable prestressed concrete tendons. A pretensioned road bridge (L = 12.5 m), a post-tensioned road bridge (L = 25.0 m); a ground anchor, and a prestressed concrete berth were constructed using aramid FRP rods.

A 30-ft span, 17-ft wide bridge was constructed in Rapid City, South Dakota, in the summer of 1991 to demonstrate the application of graphite and fiberglass cables for prestressing bridge decks. This bridge was designed by consultants and built by local contractors with the technology developed at the South Dakota School of Mines and Technology. Paper deals with the construction phase, testing, and monitoring of the bridge from September, 1991 to December, 1992. Post-tensioning bonded method was used for prestressing the bridge deck in the transverse direction, whereas nonprestressed reinforced reinforcement was used in the longitudinal direction as distributors. The slab thickness was 7 in. and was supported by three longitudinal girders. One-third of the bridge was prestressed with S-2 glass cables, while the second one-third was prestressed with graphite cables and the last one-third was prestressed with steel cables. Special anchorages were used for prestressing the cables. Electrical and slip gages were used to monitor the stresses in the cable and deck. After the bridge deck was constructed, it was loaded for static and dynamic loading before it was opened for traffic. Paper addresses the test methods and quality control for bridge cables, including the design guidelines for using new materials for the bridge decks. The actual test data for the bridge was compared with the design data and found very comparable in this project. This bridge project demonstrates the feasibility of using advanced composite cables for prestressing bridge decks. The information gained through the design, construction, and monitoring of this bridge will help provide guidelines for the design and construction of future bridges.

In reinforced concrete pavements, dowel bars are typically used to transfer the load across the transverse joint from one pavement slab into the adjoining slab. Steel dowels have been used almost exclusively in these applications in the past. Because the bars cross construction joints, they are particularly susceptible to corrosion from the salts used for ice control. Corrosion can cause the dowel bar to fail or to freeze in the joint, resulting in pavement distress. As a solution to this problem, it would appear to be practical to fabricate the dowels from a material which is more resistant to corrosion from roadway salts than is steel. This paper presents the initial results from an investigation into the feasibility of substituting fiberglass reinforced plastic (FRP) dowel bars for steel bars in reinforced concrete pavements. FRP dowels are compared with steel dowels, both theoretically using a Friberg analysis and also experimentally through laboratory tests with scaled model slabs. It is concluded that the use of FRP dowels is feasible, provided that dowel diameters are increased approximately 20 to 30 percent.

An experimental investigation was conducted to study the shear performance of concrete beams with bar-shaped FRP reinforcement. The 35 half-scale beams were subjected to monotonically increased shear force up to ultimate capacity. The principal variables were type and reinforcement ratio of stirrup and concrete strength. The beams with FRP stirrups failed due to either breaking of the curved stirrup sections or crushing of a diagonal strut. The former failure mode was excessively brittle and more undesirable than the latter. The ultimate shear capacity increased with increasing the content of FRP stirrup, and was not so remarkably affected by the type of stirrup, although the FRP stirrups without yielding did not so effectively carry the shear force as conventional steel stirrups. Under the same stirrups, the shear capacity of the beams flexurally reinforced with FRP bars was smaller than that of the beams with steel bars. Further, it was observed that the ultimate shear capacity of beams with FRP stirrups can be fairly well estimated by substituting the tensile strength of curved sections of stirrup for the yield strength in Arakawa's formula.

An experimental program consisting of three series of tests was conducted to investigate the bond performance of concrete members reinforced with FRP bars. First, a simple bond test was performed using several types of FRP bars. This test was carried out by pulling out a single bar located near the surface of the concrete block. The test objectives were to evaluate the bond splitting strength of FRP reinforced concrete without lateral reinforcement and to establish a standard test method for bond splitting. Test results show that the bond splitting strength can be estimated using the ratio of lug height to diameter of FRP bars. In the second test, a bond splitting test was conducted on cantilever-type specimens. These were modeled to exhibit a stress condition similar to an actual structure. The test objectives were to study the results of the simple bond test and evaluate the increment of the bond splitting strength caused by lateral reinforcement. From the test results, the tendency of the bond splitting strength without lateral reinforcement is equal to that obtained from the first test. The increment of the strength caused by lateral reinforcement can be evaluated in terms of its percentage and elastic modulus. Finally, an antisymmetrical loading test for actual beams reinforced with FRP bars was carried out. The bond performance obtained for the longitudinal bars shows a good correlation with the results obtained from the former two tests.