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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Showing 1-5 of 11 Abstracts search results
May 1, 2012
Chris J. Burgoyne, Mithila Achintha, and Garfield X. Guan
A major research program was carried out to analyze the mechanism of FRP debonding from concrete beams using global-energy-balance approach (GEBA). The key findings are that the fracture process zone is small so there is no R-curve to consider, failure is dominated by Mode I behavior, and the theory agrees well with tests. The analyses developed in the study provide an essential tool that will enable fracture mechanics to be used to determine the load at which FRP plates will debond from concrete beams. This obviates the need for finite element (FE) analyses in situations where reliable details of the interface geometry and crack-tip stress fields are not attainable for an accurate analysis. This paper presents an overview of the GEBA analyses that is described in detail elsewhere, and explains the slightly unconventional assumptions made in the analyses, such as the revised moment-curvature model, the location of an effective centroid, the separate consideration of the FRP and the RC beam for the purposes of the analysis, the use of Mode I fracture energies and the absence of an R-curve in the fracture mechanics analysis.
In this paper, the problem of debonding in flexural members strengthened with FRP layers bonded on their tensed and compressed faces is investigated using the fracture mechanics theory. This problem is particularly relevant to double sided FRP applications for the strengthening of masonry or reinforced concrete walls to resist cyclic or dynamic loading. The paper adopts an analytical methodology and compares between two fracture mechanics based approaches for the assessment of the initiation, evolution, and stability of the debonding process. The first approach uses the nonlinear fracture concept of the cohesive interface. The second approach adopts the classical fracture mechanics concept of the energy release rate. In both models, the effect of geometrical nonlinearity and buckling of the compressed layer and its role as the driving force for the debonding process are considered. The two approaches are compared and emphasis is placed on the stability of the debonding process and the post-debonding behavior. These aspects are illustrated through a numerical study that focuses on a masonry specimen strengthened with double-sided FRP systems and subjected to flexure. Conclusions on the behavior of the unique structural system, its stability, and its handling using the fracture mechanics approaches close the paper.
F. da Porto, E. Stievanin, E. Gabin, and M.R. Valluzzi
The paper deals with the application of composite materials named Steel Reinforced Grout (SRG) for strengthening reinforced concrete (RC) elements. They differ from the well-known Fiber Reinforced Polymer (FRP) for the use of small unidirectional steel cords, combined to create a metallic fabric drowned in a matrix of cement mortar. In particular, this work develops an experimental program composed by two consequential phases. The first phase is aimed to find cement mortar matrixes with the best bond properties through pull-off tests in the case of cementitious substrate. The second part deals with flexural tests on RC beams strengthened with two SRG composites. On the basis of pull-off results two inorganic matrixes were selected according to their bonding and impregnation properties. The two SRGs were applied at the bottom of RC beams which were preliminary repaired with polymer-modified mortars in order to simulate a real on-site application of a strengthening layer on degraded RC elements. Flexural test results underline the high potentiality of the SRG strengthening technique also in the case of a double interface, concrete/ repair layer and repair layer/SRG. This technique needs a low level of specialization of workers and it is less expensive than FRP.
Fabio Matta, Paolo Mazzoleni, Emanuele Zappa, Michael A. Sutton, Mohamed ElBatanouny, Aaron K. Larosche, and Paul H. Ziehl
The size effect in shear in reinforced concrete (RC) one-way members without shear reinforcement becomes more of concern when using glass fiber reinforced polymer (GFRP) reinforcement. In fact, the lower axial stiffness of GFRP reinforcement typically results in wider flexural cracks with respect to steel RC counterparts. This issue is especially relevant for the case of flexural members without stirrups, such as retaining walls and slab bridge superstructures. Little evidence has documented the extent of such effect. Cognizant of this knowledge gap, ACI Committee 440 (FRP Reinforcement) introduced the current nominal shear strength algorithm, which was calibrated in a conservative fashion based on test results from small beams. This algorithm assumes that the shear strength at the critical section is resisted predominantly through the uncracked concrete above the tip of the shear crack. Based on the same fundamental assumption, a fracture mechanics algorithm for steel RC beams was recently proposed by ACI Committee 446 (Fracture Mechanics of Concrete). In this paper, the ACI 440 and 446 algorithms are verified and discussed based on experimental evidence from tests on scaled GFRP RC beams without stirrups. The latter algorithm is modified to account for the smaller elastic modulus of GFRP, under the hypothesis that its relevant parameters and the shear failure mechanism are similar irrespective of the reinforcement material.
Tommaso D’Antino, Carlo Pellegrino, Valentina Salomoni, and Gianluca Mazzucco
Structural behavior of Reinforced Concrete (RC) beams strengthened in shear by means of Fiber Reinforced Polymer (FRP) sheets is a very complex subject actually under discussion. A number of experimental programs have shown the importance of the FRP debonding/peeling failure and the mutual interaction between the existing steel web reinforcement and the external FRP sheets/laminates for the evaluation of the whole shear capacity of the structural element.
In this work a three dimensional numerical Finite Element procedure, accounting for Mazars’ damage law, included in a contact algorithm, to model the mechanisms at the FRP-concrete interface, was implemented to catch the global failure mechanisms that characterize the ultimate shear capacity of RC members with transverse steel reinforcement and FRP strengthening.
The study is based on the experimental tests, described in Pellegrino and Modena (2002), carried out on RC beams with transverse steel reinforcement with and without FRP shear strengthening. It has been shown that the numerical approach is able to describe the experimental behavior of the structural member taking into account the interaction between concrete, steel and FRP contributions to shear capacity and, in particular, how the presence of external FRP sheets can modify steel contribution to the ultimate shear strength of the beams when FRP debonding/peeling failure occurs.
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