International Concrete Abstracts Portal

Lateral confinement of concrete members by means of spirally wrapping fiber-reinforced-plastic (FRP) composites onto the concrete surface may increase compressive strength and ultimate strain (pseudo-ductility). It may also provide a mechanism for shear resistance, and inhibit longitudinal steel reinforcement buckling. Lateral confinement of concrete members as a strengthening/repair technology is expected to have an impact in the rehabilitation/renovation of buildings and infrastructure. Structures that have been damaged, or need to comply with new code requirements, or are subjected to more severe usage are the primary targets. In this project, an experimental and analytical study of concrete strengthened with FRP lateral confinement I conducted using compression cylinders (300 and 600 mm in length) and l/4 scale column-type specimens. The latter specimens have a circular cross section and given longitudinal/transverse steel reinforcement characteristics. Column-type specimens are subjected to cyclic flexure with and without axial compression. When an aramid FRP tape is used as the lateral reinforcement, the variables are tape area and spiral pitch. In the case of filament winding with glass fiber, the thickness of the FRP shell is varied. The limited experimental results obtained at this stage of the research program indicate that lateral confinement significantly increases compressive strength and pseudoductility under uniaxial compression.

This paper reports on the effects of improvement in flexural characteristics and deformability(ductility) when using unbonded CFRP(Carbon Fiber Reinforced Plastic) tendons in prestressed concrete (PC) beams and bending fatigue characteristics of bonded type PC beams with CFRP tendons. Based on the results of flexural loading experiments, with PC beams using unbonded CFRP tendons, failure modes shifted from CFRP tendons rupture type to concrete crushing type. while deformation at the ultimate stage was also changed greatly for the better. It was also succeeded in ascertaining that effective prestressing force, and tensile reinforcement quantity and variety are influential as factors increasing deformability at the ultimate stage. Further, as the result of bending fatigue tests of bonded type PC beams with CFRP tendons, it was confirmed that reduction in ultimate flexural loads of bonded type PC beams due to repetitive loading was not seen and bending fatigue properties were favorable.

The use of fiber reinforced plastic reinforcement in reinforced and prestressed concrete structures is gaining increased attention. This paper describes the results of a preliminary experimental program in which strands made of carbon fiber composites (trade name CFCC - Carbon Fiber Composite Cable) were used as pretensioning reinforcement in two partially prestressed concrete T beams. The beams were ten foot in length and 12 inches in depth and contained, in addition to the carbon fiber strands, conventional reinforcing bars Experience gained with the stressing, anchoring, and releasing of CFCC strands is described. Relevant test results regarding load-deflection response, curvature, stress-increase in the reinforcement with increased load, cracking and crack widths, and failure modes are reported, and compared to results obtained from similar tests using prestressing steel strands. The load deflection response of beams prestressed with CFCC strands showed generally a trilinear ascending branch with decreasing slope up to maximum load. Deflections and crack widths were generally small but increased rapidly upon yielding of the non-prestressed steel reinforcement. The post-peak response was characterized by rapid step-wise decrease in load due to successive failures of the CFCC strands, and stabilization at about the load-carrying capacity of the remaining steel reinforcing bars. The presence of reinforcing bars helped the beams sustain large deflections before crushing of the concrete in the compression zone. Analytical predictions of the load-deflection response using a nonlinear analysis method were used and led to reasonable agreement with experimental results.

An investigation of the behavior of concrete slabs reinforced with pultruded FRP (fiber-reinforced plastic) gratings is described. Data from tests on small-scale and full-scale slab specimens obtained from three different experimental programs, beginning in September of 1989, are reviewed. Particular attention is paid to the description of failure modes, crack patterns, flexural stiffness, and shear response of the slabs. Analytical methods, based on those developed for steel reinforced concrete slabs, used to obtain predictions of the ultimate strengths and the flexural stiffnesses of the slabs, are described. Comparisons between experimental data and theoretical predictions are presented.

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.