Innovative Repair Technique for RC Beams Predamaged in Shear
17 Jun 2013-Journal of Composites for Construction (American Society of Civil Engineers)-Vol. 17, Iss: 6, pp 04013005
TL;DR: In this paper, a temporary compressive force that was applied parallel to the beam depth in the cracking-shear zone was used to close all the existing shear cracks prior to the application of the CFRP-strengthening sheets.
Abstract: The one major practical difficulty associated with reinforced concrete (RC) structures strengthened with externally bonded (EB) carbon-fiber-reinforced polymer (CFRP) sheets is that they must be bonded to a hard uncracked concrete surface, which need may not be met in many cases. This paper assesses the usage of a temporary compressive force that was applied parallel to the beam depth in the cracking-shear zone in order to close all the existing shear cracks prior to the application of the CFRP-strengthening sheets. This force was kept constant till full curing of the CFRP epoxy adhesive, and after the epoxy had cured, it was completely removed. The advantages that result from the shear strengthening of RC beams using the new proposed technique are that closing of all existing cracks and removing the temporary compressive force generates tension force in the CFRP-strengthening strips, which in turn delays the formation and propagation of the shear cracks and develops a compressive force in the internal stirrups, which in turn increases their efficiency. These advantages were verified by testing of seven RC beams designed to fail in shear. Two beams were strengthened using the proposed technique, two beams were repaired by epoxy injection before being strengthened using CFRP, one beam was strengthened using CFRP applied directly over the cracked concrete surface, one beam was strengthened without preloading, and one beam was tested without strengthening and served as a control. Finally, the authors present and comment upon a comparison between the present experimental results and the predictions using the available formulations recommended by some international guidelines.
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TL;DR: In this article, a review of the characteristics and behaviors of FRP-strengthened reinforced concrete (RC) beam members under various loading conditions is presented, and a straightforward perspective of strengthening and retrofitting techniques for RC beams using FRP composites is provided.
Abstract: Fiber-reinforced polymer (FRP) composites are extensively used in advanced concrete technology given their superiority over traditional steel reinforcements. These materials possess high strength capacity and corrosion resistance and can be employed as the main reinforcements in combination with adhesives and anchorages to strengthen reinforced concrete (RC) beam members. RC beams are designed to provide resistance against flexure , shear, torsion, fatigue, impact, and blast loading. The strength and ductility of RC beams can be improved via FRP strengthening techniques with a combination of fibers. The overall strength of FRP composites in RC beams is controlled by fiber type , configuration, and materials and strengthening technique. This review focuses on the characteristics and behaviors of FRP-strengthened RC beams under various loading conditions. It also presents the typical FRP composites with the properties, features, and applications. This review demonstrates that FRP composites can be used to recover the strength of damaged and corroded beams and exhibit good durability and insulation performance. It also provides a straightforward perspective of strengthening and retrofitting techniques for RC beams using FRP composites.
206 citations
TL;DR: The gaps in the present state of knowledge and the potential research directions for FRP-strengthened structures that lead to better understanding and establishment of design guidelines are identified.
112 citations
TL;DR: In this article, an experimental and analytical study examining the blast load performance of steel reinforced (RC) concrete columns retrofitted with externally bonded carbon fiber reinforced polymer (CFRP) sheets is presented.
36 citations
TL;DR: In this article, a repairing technique of the AFRP sheets that effectively strengthens reinforced concrete beams, controls both the failure modes and the stress distribution around the beam chords and enhances the serviceability of pre-cracked reinforced concrete (RC) beams with openings is presented.
Abstract: Strengthening reinforced concrete (RC) beams with openings by using aramid fiber reinforcement polymers (AFRP) on the beams’ surfaces offers a useful solution for upgrading concrete structures to carry heavy loads. This paper presents a repairing technique of the AFRP sheets that effectively strengthens RC beams, controls both the failure modes and the stress distribution around the beam chords and enhances the serviceability (deflection produced under working loads be sufficiently small and cracking be controlled) of pre-cracked RC beams with openings. To investigate the possible damage that was caused by the service load and to simulate the structure behavior in the site, a comprehensive experimental study was performed. Two un-strengthened control beams, four beams that were pre-cracked before the application of the AFRP sheets and one beam that was strengthened without pre-cracking were tested. Cracking was first induced, followed by repair using various orientations of AFRP sheets, and then the beams were tested to failure. This load was kept constant during the strengthening process. The results show that both the preexisting damage level and the FRP orientation have a significant effect on strengthening effectiveness and failure mode. All of the strengthened specimens exhibited higher capacities with capacity enhancements ranging from 21.8 to 66.4%, and the crack width reduced by 25.6–82.7% at failure load compared to the control beam. Finally, the authors present a comparison between the experimental results and the predictions using the ACI 440.2R-08 guidelines.
28 citations
TL;DR: In this paper, a field test was conducted on three actual-size precast pretensioned double-tee (DT) girders having different levels of damage and retrofitted using CFFP sheets.
Abstract: Precast prestressed double-tee (DT) girders are considered a crucial element of modern infrastructure used to accelerate building construction worldwide. These girders can be deficient because of local damages and develop cracks as a result of improper transportation and handling. Therefore, it is very important to develop an efficient retrofitting technique in order to restore the lost capacity and/or even outperform it. The objective of this paper is to develop retrofit strategy of the deficient girders using the externally bonded carbon-fiber-reinforced polymer (EB-CFRP) technique and verify it using field data. A field test was conducted on three actual-size precast pretensioned DT girders having different levels of damage and retrofitted using CFFP sheets. The girder stems for two of them were strengthened in flexure using unidirectional U-shaped CFRP sheets, while all girders were shear-strengthened at their dapped ends. Each girder was loaded incrementally up to collapse while the deflection of the girder and normal strains developed on both concrete surface and the CFRP sheets were recorded at each load increment. Test results assured the adequacy of the adopted strengthening technique with respect to both ultimate capacity and ductility. In addition, the experimental flexural and shear resistances of the retrofitted girders are far greater than those obtained from equations available in design codes by at least 60%.
12 citations
References
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01 Jan 2002
TL;DR: The Emerging Technology Series as mentioned in this paper is a series of information and recommendations based on available test data, technical reports, limited experience with field applications, and the opinions of committee members, with a focus on the development and appropriate use of new and emerging technologies.
Abstract: *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.
2,963 citations
TL;DR: In this paper, a simple, accurate, and rational design proposal for the shear capacity of FRP-strengthened reinforced concrete beams which fail by FRP rupture is presented.
Abstract: A recent innovation in shear strengthening of reinforced concrete beams is to externally bond fiber-reinforced polymer (FRP) composites. Many studies have been undertaken on this strengthening technique. These studies have established clearly that such strengthened beams fail in shear mainly in one of the two modes: FRP rupture and FRP debonding, and have led to preliminary design proposals. This paper is concerned with the development of a simple, accurate, and rational design proposal for the shear capacity of FRP-strengthened beams which fail by FRP rupture. To this end, existing design proposals are reviewed, and their efficiencies highlighted. A new strength model is then developed, which recognizes the fundamental characteristics of FRP. The model is validated against experimental data collected from the existing literature. Finally, a new design proposal is presented.
236 citations
TL;DR: In this paper, an extensive experimental investigation on reinforced concrete T-beams retrofitted in shear with externally bonded carbon fiber-reinforced polymer (CFRP) is presented.
Abstract: The results of an extensive experimental investigation on reinforced concrete T-beams retrofitted in shear with externally bonded carbon fiber-reinforced polymer (CFRP) are presented. The authors researched the CFRP ratio, the internal shear steel reinforcement ratio and the shear length to the beam's depth ratio. By studying the aforementioned parameters, the behavior of reinforced concrete T-beams strengthened in shear with externally applied CFRP was analyzed. It appears that the contribution of CFRP to shear resistance depends on if a strengthened beam is reinforced in shear with internal transverse steel reinforcement, and not on the CFRP stiffness provided. It seems that the American Concrete Institute and the Canadian Standards Association guidelines fail to incorporate the presence of the transverse resistance and overestimates the shear resistance for high fiber reinforced polymer thickness.
153 citations
TL;DR: In this paper, the shear resistance mechanisms involved in reinforced concrete reinforced concrete (RC) beams strengthened in shear with externally bonded fiber-reinforced polymer (FRP) composites are investigated.
Abstract: In recent years, numerous investigations have addressed the shear strengthening of reinforced concrete (RC) beams with externally bonded fiber-reinforced polymer (FRP) composites. Despite this research effort, the mechanisms of shear resistance that are developed in such a strengthening system have not yet been fully documented and explained. This clearly inhibits the development of rational and reliable code specifications. This paper aims to contribute to the understanding of the shear resistance mechanisms involved in RC beams strengthened in shear with externally bonded FRP. It is based on results obtained from an experimental program, involving 17 tests, performed on full size T beams, and using a comprehensive and carefully optimized measuring device. The resistance mechanisms are studied by observing the evolution of the behavior of the strengthened beams as the applied loads are increased. The local behavior of the FRP and the transverse steel, in particular in the failure zones, are thoroughly examined. The operative resistance mechanisms are also studied through the load sharing among the concrete, the FRP, and the transverse steel, at increasing levels of applied load.
143 citations
TL;DR: In this paper, a simple model is proposed to predict the contribution of FRP to the shear capacity of the beam at the complete debonding of the critical FRP strip.
Abstract: Substantial research has been conducted on the shear strengthening of reinforced concrete (RC) beams with bonded fiber reinforced polymer (FRP) strips. The beams may be strengthened in various ways: complete FRP wraps covering the whole cross section (i.e., complete wrapping), FRP U jackets covering the two sides and the tension face (i.e., U jacketing), and FRP strips bonded to the sides only (i.e., side bonding). Shear failure of such strengthened beams is generally in one of two modes: FRP rupture and debonding. The former mode governs in almost all beams with complete FRP wraps and some beams with U jackets, while the latter mode governs in all beams with side strips and U jackets. In RC beams strengthened with complete wraps, referred to as FRP wrapped beams, the shear failure process usually starts with the debonding of FRP from the sides of the beam near the critical shear crack, but ultimate failure is by rupture of the FRP. Most previous research has been concerned with the ultimate failure of FRP wrapped beams when FRP ruptures. However, debonding of FRP from the sides is at least a serviceability limit state and may also be taken as the ultimate limit state. This paper presents an experimental study on this debonding failure state in which a total of 18 beams were tested. The paper focuses on the distribution of strains in the FRP strips intersected by the critical shear crack, and the shear capacity at debonding. A simple model is proposed to predict the contribution of FRP to the shear capacity of the beam at the complete debonding of the critical FRP strip.
140 citations