Extensive experimental studies reported in the scientific literature suggest to split the flexural response of fibre-reinforced concrete (FRC) beams into three different stages. Considering an initially notched FRC specimen subjected to bending, the structural response starts with an almost linear ascending branch (Stage I), until the onset of the fracturing process. From this point onward, the post-cracking phase of the composite takes place, which depends, among other parameters, on the fibre volume fraction, Vf: a softening or a pseudo-hardening post-cracking response can be observed, suggesting the definition of a minimum (critical) fraction of reinforcing fibres, Vf,min, which is required to achieve a stable post-peak branch (Stage II). Then, the response is finally described by a descending tail (Stage III), up to the complete disconnection of the cracked cross-section. In the present work, it will be shown that the structural response of the composite can be clearly interpreted in the framework of Fracture Mechanics through the Bridged Crack Model, in which a σ-w (stress-crack opening displacement) cohesive softening constitutive law is introduced to take into account the pull-out mechanism of the reinforcing steel fibres in the cementitious matrix. The main advantage of this model relies in the synthetical description of the different post-cracking regimes by means of two dimensionless parameters, NP and Nw, which depend on the structural size-scale, on the fibre volume fraction, Vf, and on the average embedment length of the fibre, wc. As a function of these two parameters, Vf,min can be estimated together with its scale-dependence. In this way, a key-information for the design of FRC structural elements ─still lacking in the structural design codes─ is provided, making a further step towards a safe design framework for FRC structures.
Post-cracking structural behaviour in frc beams: Scale effects and minimum fibre volume fraction / Rubino, A.; Accornero, F.; Carpinteri, A.. - 2021-:(2021), pp. 622-631. (Intervento presentato al convegno 2021 fib Symposium of Concrete Structures: New Trends for Eco-Efficiency and Performance tenutosi a prt nel 2021).
Post-cracking structural behaviour in frc beams: Scale effects and minimum fibre volume fraction
Rubino A.;Accornero F.;Carpinteri A.
2021
Abstract
Extensive experimental studies reported in the scientific literature suggest to split the flexural response of fibre-reinforced concrete (FRC) beams into three different stages. Considering an initially notched FRC specimen subjected to bending, the structural response starts with an almost linear ascending branch (Stage I), until the onset of the fracturing process. From this point onward, the post-cracking phase of the composite takes place, which depends, among other parameters, on the fibre volume fraction, Vf: a softening or a pseudo-hardening post-cracking response can be observed, suggesting the definition of a minimum (critical) fraction of reinforcing fibres, Vf,min, which is required to achieve a stable post-peak branch (Stage II). Then, the response is finally described by a descending tail (Stage III), up to the complete disconnection of the cracked cross-section. In the present work, it will be shown that the structural response of the composite can be clearly interpreted in the framework of Fracture Mechanics through the Bridged Crack Model, in which a σ-w (stress-crack opening displacement) cohesive softening constitutive law is introduced to take into account the pull-out mechanism of the reinforcing steel fibres in the cementitious matrix. The main advantage of this model relies in the synthetical description of the different post-cracking regimes by means of two dimensionless parameters, NP and Nw, which depend on the structural size-scale, on the fibre volume fraction, Vf, and on the average embedment length of the fibre, wc. As a function of these two parameters, Vf,min can be estimated together with its scale-dependence. In this way, a key-information for the design of FRC structural elements ─still lacking in the structural design codes─ is provided, making a further step towards a safe design framework for FRC structures.File | Dimensione | Formato | |
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https://hdl.handle.net/11583/2975503