This study focuses on the characterization of the fracture properties of the concrete-epoxy interface (CEI) under FRP sheets and FRP Uwraps. In particular, the Mode I and Mode II fracture energies are obtained with and without the effect of the FRP Uwrap anchor. Results indicate that fracture energy of the CEI increases due to the confining effect of Uwrap. These material properties, along with a proposed bond-slip model, are used in numerical simulations of concrete elements strengthened with externally bonded FRP sheets and anchored with FRP Uwraps. Results show that the characterization of the fracture properties of the CEI is needed to accurately predict the complex behavior of the CEI under the FRP Uwrap.

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.

This CD-ROM contains 10 papers sponsored by ACI committees 440 & 446. The papers provide information on recent developments on the use of the framework of fracture mechanics to evaluate the performance of reinforced concrete (RC) structures strengthened with FRP composites. The information provided is useful to researcher and practicing engineer by presenting experimental and analytical tools based on a fracture approach that can assess the shear and flexural capacity of strengthened RC members. 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-286

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.

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.