International Concrete Abstracts Portal

The use of non-metallic bridge deck reinforcement is of interest in regions where corrosion is a problem. A number of manufacturers have developed GFRP rebar for this application. Because the production of the material is relatively new, there is a great deal of variability among the products from different manufacturers. In addition, as the manufacturers continue to develop their own product, variations in GFRP from single manufacturers have been observed. The objective of this study was to investigate the bond between GFRP reinforcement and concrete using inverted half-beam specimen. The inverted half-beam specimen were designed to simulate the conditions likely to be found in a bridge deck (no transverse reinforcement and small concrete cover). Products from two different manufacturers were chosen for the study because of the widely varying characteristics of the product. One manufacturer produced reinforcement with surface deformations created by a helical wrap of glass fibers around the GFRP bar; the other manufacturer developed a ceramic coating that emulated the surface texture of a deformed steel bar. The two different bar types exhibited different bond behaviors. The bond for the bars with the ceramic deformations relied most heavily on mechanical interlock, as was evident from cracking patterns. The bond for the bars with the helical wrap deformations relied most heavily on friction. Both bar types demonstrated large variability for the bond specimen that failed in bar fracture, with some bar failure loads more than two standard deviations below the average bar tensile strength.

An experimental study on bond strength of Continuous Fiber Sheet (CFS) was conducted. Based on the experimental results the bond strength and various factors are clarified. Bond strength does not increase with bond length for bond length longer than 100 mm. As CFS stiffness increases, the maximum local and average bond stresses at delamination increase and CFS strain gradient decreases. CFS with a narrower width has a bond strength greater than that with a wider width. Non-uniform loading decreases the bond strength, however anchor steel plate with tensioned bolt increases it due to the bond between steel plate and CFS and confinement from the bolt. From the observed bond stress in CFS, the equation to predict the maximum local bond stress was proposed.

A two level parking facility formed the base of an apartment complex. The structural system incorporated a composite-steel deck for the upper level which provides bottom reinforcing for the structural slab. Other than Welded Wire Fabric (WWF), no top reinforcing was provided over the beams or girders. An inappropriate choice of construction for a parking deck due to the potential for corrosion from chloride contamination, the problem was compounded by inadequate reinforcing, poor drainage and no waterproofing. The result was a severely deteriorated deck. Slab cuts that would allow the installation of top reinforcing as required to develop the negative moment based on continuity were not feasible because the electrical conduit for the building was buried in the slab. Therefore, CFRP was used to save the existing structural system and minimize repair costs. Design concerns included load stress, shear strength and membrane integrity. Field testing was successfully conducted. The result was an innovative use of the material which decreased the severity and cost of repairs.

This paper presents the results of a pilot study to apply externally bonded CFRP sheets to strengthen a simple span reinforced concrete solid slab bridge. The objective was to remove the current load posting. This bridge is a load posted structure on a heavy truck route. Strengthening with CFRP sheets was accomplished in three days without traffic interruption. Preparation consisted of light sandblasting and no concrete repair. The University of Missouri at Rolla conducted the pilot study for the Missouri Department of Transportation. The testing procedure included the construction of two test beams, to simulate bridge deck performance with and without strengthening. Laboratory setup, instrumentation and test results of two full-scale test beams are presented. Field load tests of the bridge were performed by the University of Missouri at Columbia to verify the increase in flexural strength achieved with the application of externally bonded CFRP. The method used to instrument and field load test the bridge along with the subsequence load-deflection characteristics is presented. Comparisons are made between the analytical model, laboratory beam specimens strengthened with CFRP, and in situ field tests of the actual bridge before and after strengthening.

In-situ lateral load tests of reinforced concrete bridge bents were conducted to determine the strength and ductility of existing and retrofitted bents with Carbon Fiber Reinforced Polymer (CFRP) composites. The CFRP composite retrofit included three columns, the cap beam and the three cap beam-column joints. Existing design guidelines were used for retrofit of the columns with CFRP composites. New design guidelines were developed for retrofit of cap beam-column joints. The design of the CFRP composite retrofit was based on doubling the displacement ductility of the bent. The CFRP composite was able to strengthen the cap beam-column joints effectively for an increase in shear stresses of 35 percent. The bent retrofitted with the CFRP composite reached a system displacement ductility of 6.3 as compared to the bent in the as-is condition, which reached a ductility of 2.8. The peak lateral load capacity was increased by 16 percent.