International Concrete Abstracts Portal

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.

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.

Grid-shaped FRP reinforcement has been developed to prevent deterioration of concrete structures owing to corrosion of reinforcement. This reinforcement is made of high-strength continuous fibers impregnated with resin and formed into a grid shape to insure bond with concrete. When this development was carried out, joint research and development with some universities as well as a Japanese technological development project was conducted to clarify fundamental properties of this reinforcement and structural behavior of reinforced concrete members. Applications of this reinforcement to actual structures began with such civil engineering structures as tunnels, LPG tanks, etc. In Japan, applications of advanced composite materials to building structures require governmental approval. Therefore, to apply this reinforcement to precast concrete curtain walls, heat-resistance and fire-resistance tests were conducted to obtain the approval of the Minister of Construction. This is the first time that FRP reinforcement was used in Japanese building structures. Application of this reinforcement to box-framed reinforced concrete structures will be considered next.

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.

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.