Abstract
The problem of the pullout of a viscoelastic synthetic fibre embedded in a cementitious matrix and subjected to an external time-dependent axial load is considered in the present work. A 1D phenomenological model able to simulate the contribution of viscoelastic relaxation as well as the hardening behavior due to abrasion phenomena during slippage is developed. The cement matrix compliance is neglected with respect to the fibre elongation. The interfacial shear stress between the fibre and the surrounding matrix is assumed to depend on the slippage distance through a second degree polynomial law, thus involving three constitutive parameters. Two distinct phases are recognized: An earlier debonding stage followed by the effective fibre pullout process. Two different creep functions have been assumed for modelling the viscous response of polymeric fibres: A function based on the fraction-exponential Rabotnov operator and a classical exponential model. Identification of the governing constitutive parameters allows obtaining the relation between the external strain and the axial displacement, which has been compared with experimental results provided by pullout tests both on plain and treated fibres, finding a good agreement. It is shown that the proposed approach can predict the whole pullout process of discrete synthetic macrofibres.
Highlights
Concrete is widely used in civil engineering because its versatility and cheapness as compared with other building materials like steel and masonry
The constitutive parameters τ0, a, b of the interface frictional model introduced in eqn (1) have been calibrated by fitting the pullout curves provided by the experimental tests performed by Di Maida et al [17] (Fig. 3) with the theoretical strain-displacement curve obtained from eqns (7), (9) and (11) for the debonding and pullout phases, respectively, and they are listed in Tab. 2
It is worth noting that both creep functions considered in the present investigation allows reproducing closely the experimental results in terms of axial strain εL (t) of the outer part of the fibre vs its axial displacement u/L
Summary
Concrete is widely used in civil engineering because its versatility and cheapness as compared with other building materials like steel and masonry. Preprint submitted to Elsevier lightweight concrete, ultra-high-performance concrete (UHPC), self-compacting concrete and foamed concrete (e.g. Scerrato et al [1]) Despite these advantageous properties, concrete is a brittle material undergoing various damaging phenomena like crack initiation and growth, especially under the action of tensile stresses and impact loads (aging effects in concrete structures have been discussed in [2], [3]). The constitutive parameters characterizing the frictional interface behavior as well as the rheological response of the fibre have been determined by comparing the relations between the pull-out load and the displacement of the actuated fibre cross section provided by theoretical simulations with those obtained from the test performed by Di Maida et al.
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