Polymeric fibers can be used in concrete elements to improve the properties in the fresh or hardened state. In the latter case, structural macrofibers can be added to increase the residual load-bearing capacity after matrix cracking, and as such, can partially or entirely replace traditional reinforcement. Polymeric fiber reinforced concrete (PFRC) can be designed according to the Model Code 2010, but no design guidelines are given to take creep behavior into account, limiting the usage of FRC in structural applications. The tensile creep behavior of cracked PFRC is dependent on the creep deformation of individual fibers and on the creep behavior of the interface between fiber and matrix. Because of the different factors involved, a fundamental understanding of FRC creep can only be obtained by taking both mechanisms into account. Therefore, a numerical model with discrete treatment of individual fibers is set up. The results of the finite element analysis (FEA) is compared against experimental tests. In the experiments, the concrete cores are precracked to localize crack formation and growth and the time-dependent crack widening is measured over the crack. To calibrate the material models used in the FEA, the creep behavior of individual fibers as well as the pull-out behavior (short-term and creep) of the fiber is determined for a range of different embedded lengths and angles. In the finite element model, polypropylene fibers are randomly generated in an FRC beam. In a next step, a core is taken from the beam, and subsequently notched during which the effect of fiber cutting is simulated. The location of the crack in the numerical model is known (i.e. in the notched section) and fibers crossing this crack contribute to the load-bearing capacity of the element. An algorithm is implemented in MATLAB that calculates the embedded length of each crack-crossing fiber at both its ends. The material model governing pull-out behavior is then assigned to every load-bearing fiber based on its embedded length and angle, as determined by the multi-scale testing. The fibers are assigned a creep behavior model based on the experimental tests. Because of the low stresses involved, a linear elastic material model for concrete is adopted. The load, expressed as a percentage of the residual capacity, is imposed for 180 days on both the physical test specimen and on the numerical model and the crack widening is compared. Good agreement can be obtained and the model is able to capture crack growth of PFRC. Furthermore, the use of finite element modelling allows to determine the fiber stress in a cracked section of FRC, and based on the results presented here, an average fiber stress was obtained of 10% and 15% of the fibers ultimate strength for the two considered load ratios.

A two-phased and multi-scale finite element analysis of the tensile creep behavior of polypropylene fiber reinforced concrete

di Prisco, M.
2018-01-01

Abstract

Polymeric fibers can be used in concrete elements to improve the properties in the fresh or hardened state. In the latter case, structural macrofibers can be added to increase the residual load-bearing capacity after matrix cracking, and as such, can partially or entirely replace traditional reinforcement. Polymeric fiber reinforced concrete (PFRC) can be designed according to the Model Code 2010, but no design guidelines are given to take creep behavior into account, limiting the usage of FRC in structural applications. The tensile creep behavior of cracked PFRC is dependent on the creep deformation of individual fibers and on the creep behavior of the interface between fiber and matrix. Because of the different factors involved, a fundamental understanding of FRC creep can only be obtained by taking both mechanisms into account. Therefore, a numerical model with discrete treatment of individual fibers is set up. The results of the finite element analysis (FEA) is compared against experimental tests. In the experiments, the concrete cores are precracked to localize crack formation and growth and the time-dependent crack widening is measured over the crack. To calibrate the material models used in the FEA, the creep behavior of individual fibers as well as the pull-out behavior (short-term and creep) of the fiber is determined for a range of different embedded lengths and angles. In the finite element model, polypropylene fibers are randomly generated in an FRC beam. In a next step, a core is taken from the beam, and subsequently notched during which the effect of fiber cutting is simulated. The location of the crack in the numerical model is known (i.e. in the notched section) and fibers crossing this crack contribute to the load-bearing capacity of the element. An algorithm is implemented in MATLAB that calculates the embedded length of each crack-crossing fiber at both its ends. The material model governing pull-out behavior is then assigned to every load-bearing fiber based on its embedded length and angle, as determined by the multi-scale testing. The fibers are assigned a creep behavior model based on the experimental tests. Because of the low stresses involved, a linear elastic material model for concrete is adopted. The load, expressed as a percentage of the residual capacity, is imposed for 180 days on both the physical test specimen and on the numerical model and the crack widening is compared. Good agreement can be obtained and the model is able to capture crack growth of PFRC. Furthermore, the use of finite element modelling allows to determine the fiber stress in a cracked section of FRC, and based on the results presented here, an average fiber stress was obtained of 10% and 15% of the fibers ultimate strength for the two considered load ratios.
2018
Computational Modelling of Concrete Structures - Proceedings of the conference on Computational Modelling of Concrete and Concrete Structures, EURO-C 2018
9781138741171
polypropylene fibres, Fibre reinforced concrete, creep
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11311/1085249
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