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PFRC size effect prediction
Size effect on plain concrete is well known and is the reason why fracture develops at lower values of the nominal strength when the size of a concrete specimen increases while keeping the same proportions. When fracture in plain concrete is numerically reproduced, the size effect can be correctly captured by means of a cohesive zone formulation that uses a well-characterised softening diagram.
The size effect on plain concrete specimens is well known and can be correctly captured when performing numerical simulations by using a well characterised softening function. Nevertheless, in the case of polyolefin-fibre-reinforced concrete (PFRC), this is not directly applicable, since using the same softening diagram cannot capture the material behaviour on elements with different sizes because it does not take into account the changes of the orientation factor of the fibres with the size of the specimen. In previous works, the use of a trilinear softening diagram proved to be highly convenient for reproducing fracture of PFRC elements, but only if it is previously adapted for each specimen size. In this work, a predictive methodology is used to reproduce fracture of PFRC specimens of various sizes under three-point bending tests. Fracture is reproduced by means of a well-known embedded cohesive model, with a trilinear softening function that is defined specifically for each specimen size. The fundamental point of these softening functions is that they are defined a priori by using empirical expressions proposed in past works, based on an extensive experimental background. Therefore, the numerical results are obtained in a predictive manner and then compared with a previous experimental campaign in which PFRC notched specimens of different sizes were tested with a three-point bending test setup, showing that this approach properly captures the size effect, although some values of the fundamental points in the trilinear diagram could be defined more accurately.
2. Fibres as Reinforcement in Concrete
The softening diagrams are not equal for all specimen sizes and should be adjusted for each of them. This is mainly due to a different orientation factor that varies with the size of the specimen.
The maximum residual loads obtained for each size present a linear trend on the load–displacement diagram, which does not agree completely with the experimental observations, although the load–displacement and load–CMOD curves properly agree with the experimental envelopes for the three studied sizes.
Modifying rwr and wf wf affects the maximum residual load on the load–displacement diagram and modifies the last part of this diagram but cannot capture the nonlinear trend of the residual load among specimen sizes.
The entry is from 10.3390/ma14143795
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