*Co-chairs of the subcommittee that prepared this document. Note: The committee acknowledges the contribution of associate member Paul Kelley. ACI encourages the development and appropriate use of new and emerging technologies through the publication of the Emerging Technology Series. This series presents information and recommendations based on available test data, technical reports, limited experience with field applications, and the opinions of committee members. The presented information and recommendations, and their basis, may be less fully developed and tested than those for more mature technologies. This report identifies areas in which information is believed to be less fully developed, and describes research needs. The professional using this document should understand the limitations of this document and exercise judgment as to the appropriate application of this emerging technology.

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Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures

External bonding of steel plates has been used to strengthen deficient reinforced-concrete structures since the 1960s. In recent years, fiber-reinforced polymer (FRP) plates have been increasingly used to replace steel plates due to their superior properties. A key issue in the design of an effective retrofitting solution using externally bonded plates is the end anchorage strength. This paper first presents a review of current anchorage strength models for both FRP-to-concrete and steel-to-concrete bonded joints under shear. These models are then assessed with experimental data collected from the literature, revealing the deficiencies of all existing models. Finally, a new simple and rational model is proposed based on an existing fracture mechanics analysis and experimental observations. This new model not only matches experimental observations of bond strength closely, but also correctly predicts the effective bond length. The new model is thus suitable for practical application in the design of FRP-to-concrete as well as steel-to-concrete bonded joints.

Anchorage strength models for FRP and steel plates bonded to concrete

Full-range behavior of FRP-to-concrete bonded joints

Intermediate crack-induced debonding in RC beams and slabs

The behaviour of bond between FRP and concrete is a key factor controlling the behaviour of concrete structures strengthened with FRP composites. This article presents an experimental study on the bond shear strength between FRP and concrete using a near-end supported (NES) single-shear pull test. The test results are found to be in close agreement with the predictions of Chen and Teng's [J. Struct. Eng. 127(2001) 784] bond strength model, which mutually verifies the reliability of both the test method and the Chen and Teng model in general. The NES single-shear pull test, given its simplicity and reliability, is therefore a good candidate as a standard bond test. The test results also showed that Chen and Teng's [J. Struct. Eng. 127(2001) 784] bond strength model is slightly conservative when the FRP-to-concrete width ratios are at the two extremes, but this small weakness can be easily removed when more test results of good quality become available.

Experimental study on FRP-to-concrete bonded joints

In this study, the reinforced concrete (RC) beams are initially loaded to 85% of the ultimate flexural capacity and subsequently repaired with FRP (fiber reinforced plastic) plates, bonded to the soffit of the beam The plate thickness is varied to assess the premature failure initiated at the plate curtailment zone due to the high concentration of shear and peeling stresses Different repair and anchoring schemes were conducted in an effort to eliminate such failures and insure ductile behavior The results indicated that the flexural strength of the repaired beams is increased The ductile behavior of the repaired beams is inversely proportional to the plate thickness The use of an I-jacket plate provided a proper anchorage system and improved the ductility of beams repaired with plates of large thickness

Strengthening of Initially Loaded Reinforced Concrete Beams Using FRP Plates

Flexural behavior of reinforced concrete beams strengthened with ultra-high performance fiber reinforced concrete

Guidelines Toward the Design of Reinforced Concrete (RC) Beams with External Plates

This paper presents comprehensive data and their interpretation on the plate bonding repair technique in terms of effects of plate thickness and end anchorage on ductility, ultimate load, and mode of failure. Reinforced concrete (RC) beams were preloaded to 85 percent of their ultimate capacity and subsequently repaired by bonding steel plates of different thicknesses with and without end anchorages. Anchor bolts were used for end anchorages. The repaired beams showed higher strength than the original beams, provided the plates did not exceed a certain limiting thickness. Increasing the plate thickness changed the mode of failure of the repaired beams from flexural to premature failure, developed due to shear and/or tearing of the plate, causing a reduction in ductility. End anchorages to the bonded plates could not prevent the premature failure of the beams but improved ductility with decreasing significance as the plate thickness increased, and yielded a marginal improvement in ultimate strength. A procedure for designing the bonding plate to avoid premature failure is suggested.

Flexural behavior of precracked reinforced concrete beams strengthened externally by steel plates

The repair of cracks is a necessity, and a comparison between repair methods for reinforced concrete beams subjected to different levels of cracking was made experimentally. Four methods of repair were studied: epoxy injection; ferrocement; steel-plate bonding; and combined method of epoxy injection and ferrocement. Levels of damage studied range from beam cracking at service load to complete failure of the beams. Experimental data on strength and ductility characteristics of repaired beams were obtained and comparisons were made. Epoxy injection is shown to restore strength and ductility for all levels of damage studied while ferocement increases the strength and partially restores ductility, depending on the level of damage. The steel-plate bonding repair technique leads to an increse in strength, but concomitantly with considerable reduction in ductility of the repaired beams, regardless of the level of damage. The combined method of repair leads to both increase in strength and ductility. The increase in ductility will depend on the level of damage.

Mohammed H. Baluch

Papers

Strengthening of Initially Loaded Reinforced Concrete Beams Using FRP Plates

Flexural behavior of reinforced concrete beams strengthened with ultra-high performance fiber reinforced concrete

Guidelines Toward the Design of Reinforced Concrete (RC) Beams with External Plates

Flexural behavior of precracked reinforced concrete beams strengthened externally by steel plates

Repaired reinforced concrete beams