International Concrete Abstracts Portal

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.

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.

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.

PC members reinforced with FRP as tendons show brittle failure regardless of the failure mode. The authors' objective was to improve the ductility of PC members reinforced with FRP as tendons. First, the compressive properties of concrete confined with FRP as transverse reinforcement was investigated. Major improvement can be made in the stress-strain relationship of concrete laterally reinforced with FRP, and the concrete members can be given ductility characteristics similar to those of steel-reinforced members by confining the concrete with FRP. Secondly, several PC members reinforced with FRP as tendons and transverse reinforcement were tested and investigated. It was found that marked improvements could be made in the ductility of PC members with FRP tendons by confining the part of concrete subjected to flexural compression with FRP and forcing the members to undergo flexural compression compression failure. 235-493

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.