International Concrete Abstracts Portal

The use of Fiber-reinforced polymer (FRP) composite materials in new construction and repair of concrete structures has been growing rapidly in recent years. FRP provides options and benefits not available using traditional materials. The promise of FRP materials lies in their high-strength, lightweight, noncorrosive, nonconducting, and nonmagnetic properties. ACI Committee 440 has published several guides providing recommendations for the use of FRP materials based on available test data, technical reports, and field applications. The aim of these document is to help practitioners implement FRP technology while providing testimony that design and construction with FRP materials systems is rapidly moving from emerging to mainstream technology.

An experimental study was conducted to determine the transfer length of prestressed Glass Fiber Reinforced Polymer bars. This paper is a part of a broad program that studies the long-term behaviour of GFRP prestressed concrete beams. 16 GFRP prestressed concrete beams were cast in this study. The parameters included were; prestressing level; 300 MPa (44 ksi) and 500 MPa (73 ksi), concrete compressive strength; 30 MPa (4440 psi) and 70 MPa (10000 psi), and the GFRP bar diameter;12Φ (No. 4) and 16Φ (No.5). Accurate estimation of the transfer length is necessary for elastic stress calculations at the service limit state and for the shear design of prestressed members. Strain gauges were used to measure strains on the GFRP bars and DEMEC gauges were used to measure the concrete surface strains at the level of the prestressed GFRP bar to determine the transfer length. The transfer length of 16Φ (No.5) GFRP bars in concrete with compressive strength of 30 MPa (4440 psi) was found to be about 17 db, and 14 db for prestressing levels of 500 MPa (73 ksi) and 300 MPa (44 ksi), respectively. The measured transfer length values were used to improve the transfer length estimates provided by the ACI 440.4 R-04 equation by calibrating the material coefficient factor (αt) used in the ACI equation.

Strength and fatigue testing were conducted on concrete specimens strengthened with three different epoxy systems. These specimens were conditioned in elevated water baths, subjected to fatigue loading, then tested for strength. For all three systems, the bond strength of a single conditioned specimen was at least 90 percent of the bond strength of three samples that had been fatigued but not conditioned in elevated water baths. Because of the limited data the results are anecdotal and only preliminary findings can be drawn from this work.

The development of fiber composite materials (FRPs) and their application to structural elements as externally bonded reinforcement is an effective means to increase the strength of existing bridge girders in flexure, shear and torsion. Despite the high strength of FRP materials, premature debonding of the FRP from the concrete substrate typically occurs well before the ultimate tensile strength of the material is reached. Recent research has found that the introduction of end anchorage systems such as bidirectional fiber patch anchors has been found to counteract the end peeling and interfacial shear stresses that occur at fiber ends, resulting in much higher material utilisation prior to debond. However, all of the research conducted on patch anchors to date has been based on near-end supported single shear pull tests and the performance of patch anchors when applied to large-scale beams remains to be investigated. The paper presents a finite element analysis of a large-scale bulb T beam which was calibrated using experimental results from the literature. The calibrated model was later modified by the addition of FRP shear strengthening and the inclusion of bidirectional fiber patch anchors which were found to significantly enhance the maximum laminate strains attained prior to beam failure.

Experimental and analytical investigation into the performance of a special bond system was conducted on small-scale mixed-mode bending (MMB) specimens for implementation in a full-scale hybrid bridge deck system. Full-depth threaded Glass Fiber Reinforced Polymer (GFRP) rods, as a proposed replacement for commonly used GFRP shear studs, in conjunction with an epoxy bonded coarse silica sand aggregate layer, were used at the bond interface between a pultruded GFRP plate and cast-in-place Ultra-High Performance Concrete (UHPC). Findings show that the presence of the threaded GFRP rods increased the strength of the system up to 250% while utilizing 25% of the rod capacity. The full potential of full-depth threaded GFRP rods for bond and crack control can be explored in greater detail in future studies, including the application of nut tightening forces to increase initial clamping forces at the bond interface.