ABSTRACT
Concrete is one of the most commonly utilized building materials and has a significant environmental footprint due to its production process. Over the past decades, considerable progress has been made in developing high-performance and ultra-high-performance concretes (HPC/UHPC) and incorporating fiber reinforcement in structural concrete, resulting in improved strength and durability and opening the possibility of creating slenderer structures, leading to significant material savings. However, adequate models and design approaches must accompany these material improvements to fully realize the potential benefits. This work focuses on the material behavior aspect of high- and ultra-high-performance fiber-reinforced concrete (HPFRC/UHPFRC), investigating damage processes and mechanisms occurring at small scales, which are not readily observable during loading tests. To this end, it presents a framework based on image-derived mesoscale models generated from X-ray computed tomography (CT) scans of laboratory-scale specimens. These models incorporate realistic pore and steel fiber distributions, enabling detailed simulations of crack initiation and propagation processes that are not directly accessible in experiments. A finite element model utilizing zero-thickness cohesive interface elements is applied to simulate the cracking of fiber-reinforced concrete specimens. The zero-thickness interface elements are equipped with a cohesive-frictional traction-separation law. The steel fibers are considered explicitly and modeled as elastoplastic Timoshenko beam elements. The embedment of fibers into the cement matrix is facilitated via a penalty-based coupling algorithm that enables flexible placement of fibers without needing to conform with the background mesh. The bond between the cement matrix and fibers is modeled via an elastoplastic bond-slip law, whose parameters are calibrated based on single-fiber pullout experiments. The capabilities of the proposed framework are demonstrated by the reanalysis of an experimental scenario involving UHPFRC beam subjected to 3-point bending and comparison of the results with the available experimental data.
