Role of the Matrix Layers in the Stress-Transfer Mechanism of FRCM Composites Bonded to a Concrete Substrate

Abstract

in place of the thermosetting organic matrix (usually epoxy) employed for FRP strengthening overcomes some important issues such as the degradation attributable to ultraviolet (UV) and high-temperature exposure and the lack of permeability relative to the concrete substrate.The literature regarding FRCM composites is still very limited, and a comprehensive study of the stress-transfer mechanism in FRCM-concrete joints is not available. The limited number of studies published report that FRCM-concrete joints fail because of debonding of the fibers within the embedding matrix (Carloni et al. 2013;D'Ambrisi et al. 2012D'Ambrisi et al. , 2013a. The debonding process is complicated by the so-called telescopic behavior, a mechanism that leads to a differential slip of the fiber filaments within the fiber bundle principally because of the different matrix impregnation of the outer filaments with respect to the core filaments (Banholzer 2004).The study of the stress-transfer mechanism between the composite and the concrete substrate is of fundamental importance to determine the load-carrying capacity of FRCM-concrete joints. The stress-transfer mechanism between the fibers and the surrounding matrix has been recently studied using a fracture mechanics approach assuming that the shear stresses transferred from the embedded fibers to the two matrix-fiber interfaces are equal (D'Ambrisi et al. 2012;D'Antino et al. 2014). This paper examines this as-sumption and the role of each matrix layer in the stress transfer.

An Investigation of PBO FRCM-Concrete Joint Behavior using a Three-Dimensional Numerical Approach

“…It should be noted that the idealized load response depicted in Figure 2 is valid when the bonded length is longer than the effective bond length eff l , i.e. the minimum length needed to fully develop the stress-transfer mechanism [21,22]. After a linear branch, up to point A in Figure 2, the applied load -global slip behavior is characterized by a non-linear response.…”

“…Specimen DS_330_43_S_5 had a bonded length and bonded width of 330 mm and 43 mm, respectively, and included 5 longitudinal fiber bundles. It should be noted that at the peak load P * , the applied load was not evenly distributed among the different bundles in specimen DS_330_43_S_5 [22]. However, since the applied load was evenly distributed among the fiber bundles up to the onset of debonding, the specimen was considered for the numerical analysis and good results were obtained, as discussed below.…”

“…The experimental program and results are presented in detail in [20][21][22] and are summarized in this section for comparison with the numerical simulation presented in the next section.…”

“…The transversal fiber bundles were not included in the numerical model since the fracture mechanics approach used to define the model parameters was determined without taking into account the presence of the transversal fiber bundles [22]. Each of the two matrix layers had a length, thickness, and width of 330 mm, 4 mm, and 10 mm, respectively, and was implemented in the numerical model as a continuum body with the fiber bundle placed in a through-length hole at the center of the body cross-section.…”

“…The numerical approach adopted was calibrated and validated by the experimental results previously obtained by the authors on FRCM-concrete joints tested with a single-lap direct-shear set-up [20][21][22]. The numerical model of one of the specimens tested is shown in this paper.…”