International Concrete Abstracts Portal

Fiber-reinforced polymer (FRP) composite materials have been proposed for use in lieu of steel for prestressing applications. The use of FRP 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. In 2005, ACI Committee 440, Fiber Reinforced Polymer Reinforcement, published ACI 440.4R-04, “Prestressing Concrete Structures with FRP Tendons,” as one of several guides in ACI’s Emerging Technology Series to provide recommendation for the use of FRP materials based on available test data, technical reports, and limited field applications. The aim of this 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. In addition to this publication, ACI Committee 440 organized a special technical session entitled “Case Histories and Use of FRP for Prestressing Applications” at the ACI Fall 2006 Convention in Denver, Colorado, on November 8, 2006. The session provided a worldwide state-of-the-art forum for researchers, civil/structural engineers, contractors, consultants, practitioners, and regulatory authorities to exchange recent advances in both research and practice. The technical papers presented at the session and published in this volume included the most recent analytical and experimental research work as well as selected field applications, design, and construction guidelines. The session was well attended, and generated substantial technical discussion and exchange of new technology. This Special Publication consists of 10 papers, some of which were presented in the special session sponsored by ACI Committee 440 at the ACI Fall 2006 Convention. Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-245

Fiber reinforced polymer (FRP) composites have been widely used as externally bonded reinforcements to strengthen or rehabilitate deteriorated concrete structures. However, premature debonding failure due to the limitation of bond at the FRP-concrete interface is often encountered which limits FRP material potential for flexural strength increase. To minimize debonding failures and mechanical damage such as vehicular traffic and impact, etc., near surface mounted (NSM) FRP technology has emerged as another structural rehabilitation method. This study aims at evaluating a new strengthening using prestressed NSM carbon fiber reinforced polymer (CFRP) tendons. Although NSM FRP tendons are less susceptible to debonding than externally bonded FRP laminates, the load-carrying capacity of RC structures with NSM reinforcements is still likely to be governed by "premature" debonding failure. An experimental program with design variables such as prestress level and bonding agents was carried out to study the strengthening performance in terms of stiffness, cracking behavior and load-carrying capacity. The experimental results are presented and discussed in this paper. Experimentally validated bonding method is also proposed in this study.

The monotonic flexural performance of reinforced concrete beams strengthened with external post-tensioned CFRP tendons was investigated. Variables include straight and double draped tendon profiles, and two post-tensioning conditions: at service load (50% of the yielding capacity - in-service beam) or after overloading to twice the steel reinforcement yield strain (overloaded beam). The beams were tested to failure in four-point bending. Experimental results indicated that the tendon profiles investigated did not affect the beam behavior. Overloading of the beam prior to post-tensioning had a significant effect on the deflection capacity of the beam, with a slight effect on the yield and ultimate capacities. A strain reduction approach, developed previously for unbonded steel tendons, was extended to model the beam behavior. The loading history of the beam prior to strengthening was explicitly accounted for in the model. The analytical predictions showed good agreement with the experimental values.

Strengthening of concrete structures with fibre reinforced polymer materials has today grown to be a widely used method over most parts of the world. As a way of higher utilization of the FRP (Fibre Reinforced Polymers) prestressing has proved to be beneficial. Most of the research done with prestressing Carbon Fibre Reinforced Polymers (CFRP) for strengthening has been with surface bonded plates. However, in this paper a presentation is given where CFRP quadratic rods are bonded in the concrete cover in sawed grooves and then immediately prestressed. Testing has, proven this to be an advantageous way of bonding CFRP to the concrete. There is also a tendency that the shear forces between the CFRP and the concrete are transferred more efficiently compared to surface bonded plates and sheets. In the tests performed, no mechanical device has been used to keep the prestress during testing, which then means that the adhesive has to transfer all shear stresses to the concrete. These tests have then been compared with concrete beams strengthened with prestressed external steel and CFRP tendons and similar load carrying capacity has been obtained.

Use of non-metallic (FRP) reinforcements provides a promising alternative in order to avoid corrosion in reinforced concrete. By applying non-metallic (FRP) reinforcements there is no ferrous material to corrode in reinforced concrete. This paper reviews experiences with Carbon Fiber Reinforced Polymers (CFRP) for precast prestressed concrete girders. An experimental program was completed at the Budapest University of Technology and Economics, Faculty of Civil Engineering to study service behavior of precast concrete beams prestressed with CFRP tendons in terms of both load vs. deflection responses and cracking behavior. In this paper deflection control is presented with an introduction of a new simplified method and discussion of pivot hysteresis behavior under cyclic loading.