Mesoscale Model for FRP-Confined Concrete

The role of material fabric in confined concrete

“…In the corresponding DEM specimens, the confinement due to the CFRP wraps is modeled using radial springs. 15 The elastic spring constants are chosen to replicate the properties of the CFRP (Section 3.3.2). The springs give rise to radial forces in response to lateral strains in the concrete (Figure 5B).…”

“…In order to study the behavior of concrete under external confinement, Xiao and Wu 3 tested cylinders wrapped with carbon fiber reinforced polymer (CFRP) wraps, with wrap thickness varying between one layer (0.381 mm), two layers (0.762 mm), and three layers (1.143 mm) of CFRP. In the corresponding DEM specimens, the confinement due to the CFRP wraps is modeled using radial springs 15 . The elastic spring constants are chosen to replicate the properties of the CFRP (Section 3.3.2).…”

“…The hoop strain will give rise to elastic hoop stresses in the CFRP, which in turn will give rise to a confining pressure on the concrete core. The equivalent elastic springs are assigned spring stiffness $${k}_r$$, computed as 15 : $$\begin{equation}{k}_r = 2{t}_f{E}_f/D\ \end{equation}$$where D is the diameter of the specimen, $${t}_f$$ is the thickness of the confinement wraps and $${E}_f$$ is its elastic modulus. The confining pressure on the i th ring is then computed as: $$\begin{equation}{f}_{r,i} = {k}_r\ \varepsilon _{\theta \theta ,i}^n\end{equation}$$…”

“…14 Hence it is likely that the hardening behavior of confined concrete would be influenced by some of these factors as well. Previous work 15 by the authors has highlighted the role of mortar damage in determining the slope of the hardening curve. Mortar damage appears to provide an important distinction between the meso-structural processes driving failure in confined and unconfined concrete, since failure in unconfined concrete largely occurs through crack growth along the aggregate mortar interface.…”

“…The above hypothesis is verified using simulation results obtained using a recently developed DEM code. 15,31 It is used to investigate the influence of fabric in concrete specimens generated by packing discrete rigid polyhedral particles under gravity. This enables the code to account for the wide variation of particle size and shape in concrete; in particular, the influence of shape on surface area 23 and on the interface area between interacting aggregates is readily accounted for.…”