Continuum and Discrete Approaches for Failure Analysis of Fiber-Reinforced Concrete

Abstract

As extensively accepted, fiber inclusions lead to significant improvements of post-cracking behavior of mortar composites by bridging cracks and providing resistance to crack opening processes. Typically localized failure modes of plain concrete or other mortar composites may turn quasi-ductile through the addition of steel fibers in cement mortar. In this case, the development of multiple crack patterns lead to strain-hardening/softening processes characterized by relatively large energy absorption prior to fracture localization. From the structural standpoint, fiber reinforced concrete structures (FRCS) exhibit superior ductility not only when subjected to compressive but also to tensile loading.
In this work fiber reinforced concrete is analyzed and modeled with two different approaches. On the one hand, a macroscopic continuum (smeared-crack) evaluation based on non-linear microplane theory is presented. Following approaches recently proposed inPietruszczak and Winnicki(2003) and others, the microplane model is formulated on the basis of the mixture theory, byTruesdell and Toupin (1960), to describe the coupled action between concrete and fiber reinforcements. On the other hand, a constitutive theory is presented to model the non-linear response of fiber reinforced mortar-mortar interfaces in the framework of discrete approach for failure analysis. Final aim of this strategy is the mesoscopic observation of FRC failure behavior based on FE discretizations accounting for the three main concrete constituents: aggregates, mortar and mortar-aggregate interfaces. Non linear behavior of fiber reinforced mortar is modeled by inelastic mortar-mortar interfaces where fibers are considered to be located. The interface model considers the quadratic hyperbola in terms of contact stresses proposed byCarol et al.(1997) as mortar/concrete maximum strength criterion. While the microplane model is founded on a linear function for shear and normal strengths. Their softening laws for post-peak behavior are formulated in terms of the fracture energies release under mode I, II and/or mixed failure modes. Similarly to the macroscopic smeared-crack based model, the mixture theory is taken into account to model the composites mortar-mortar interfaces reinforced with steel fibers. Also the fiber-concrete and fiber-mortar interactions in the form of fiber debonding and dowel effects are similarly treated in both macroscopic and interface models.
After describing both constitutive models the paper focuses on numerical analysis of FRC failure behavior. The main objective of these analyses is to evaluate the capabilities of the proposed models and numerical tools to capture the transition from brittle to ductile behavior of fiber-reinforced concrete when different levels of fiber contents are considered as well as different fiber directions.