International Concrete Abstracts Portal

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.

In concrete pretensioned with nonmetallic fiber reinforced plastic reinforcement (FRPR), the Hoyer effect leads to high splitting stresses due to confinement of radial deformations of bars or strands in the transfer zone. Incompatible linear temperature expansion can aggravate the splitting stresses. Bond in the transfer zone is heavily influenced by the confined radial expansion, as demonstrated by tests with bars in lightweight concrete. Very short transfer lengths (80 mm) have been measured. Three calculation approaches for splitting stresses are presented: the elasto-plastic, concrete deformation, and fracture energy approaches. The elasto-plastic model has been checked using a discrete element model that includes tensile softening of concrete. The presented formulas are confirmed by several tests on pretensioned prisms.

A comprehensive research program to investigate the suitability of a fiber reinforced plastic (FRP) for reinforced concrete is described. The investigation focuses on highway bridge decks and barrier walls. In determining the research needs, careful consideration has been given to the loads and environments to which highway bridges are subjected in northern North America. Short-term tension, creep, fatigue, and durability tests are being carried out on FRP specimens in the first phase of a three-phase program. Tests completed so far indicate a small yet noticeable change in strength and stiffness of FRP with change in temperature; small creep strain rates have been computed after 175 days of sustained loading, with satisfactory fatigue behavior under a tensile load cycling between 10 and 30 percent of the tensile strength.

FRP tensile elements exhibit the so-called creep rupture phenomenon when subjected to a high axial tensile stress. For this reason, the time of endurance until fracture that is dependent on the level of the permanent stress is the relation to be derived experimentally. The creep rupture phenomenon exists principally for all structural materials. However, experiments prove that for prestressing steel it is of no practical relevance: the usual permanent steel stresses that are in the range of 75 percent of characteristic tensile strength can be borne indefinitely without fracture or strength loss. However, this is not the case for FRP, whose stress rupture behavior is also influenced markedly by the micro-environment around the element and is dependent on the type of fiber and matrix employed. Paper presents an outline of the results known so far, the experimental techniques, methods of statistical evaluation, and forecast of the long-term behavior of specific FRP elements. It is shown that the characteristic stress rupture line is the essential basis for the derivation of the admissible permanent prestress of FRP tensile elements.