Conference Agenda

This study introduces an analytical model to evaluate the flexural strength of concrete sections with longitudinal reinforcement and steel fibers based on Fracture Mechanics principles. It combines the compressive behavior model from Eurocode 2 with the tensile softening model from Model Code 2010 to accurately simulate the compressive and tensile responses of concrete. The model adopts a parabolic-linear stress-strain relationship for compression and a linear softening law for tension under the flat crack hypothesis. By ensuring compatibility between crack openings and reinforcement elongation, it facilitates precise analyses of stress distribution and fracture depth. The results highlight significant size effects governed by the brittleness number, which accounts for element size, tensile softening, and residual flexural strength. This model provides a practical and reliable tool for predicting the flexural behavior of concrete configurations with low longitudinal reinforcement ratios.

Many researchers have evaluated the structural performance of R/FRC, which refers to fiber-reinforced concrete beams reinforced with rebars. While it is well known that fiber inclusion enhances the shear strength of R/FRC, a unified evaluation method has not yet been developed. This study conducted shear-flexural loading tests on R/FRC beams to understand the effect of tensile softening properties on their shear behavior, by both experiments and simulations. In the experiments, various FRCs with different tensile softening properties were produced by altering fiber types and contents, and the shear failure behavior of the R/FRC beams was observed up to failure. Additionally, the effect of tensile softening properties on shear behavior was investigated using 3D RBSM simulation. The results indicated that the flexural stiffness of R/FRC beams after cracking is influenced by the magnitude of tensile stress in the FRC post-cracking and that the shear strength strongly depends on the tensile softening behavior of the FRC. It was also confirmed that the shear strength could be estimated using the fracture energy of the FRC.

This study investigates the mechanical behaviour of steel-fibre and steel-bar (hybrid) reinforced concrete (HRC) beams including flexural cracking, shear, and flexural crushing failure modes in the framework of Fracture Mechanics by means of the Updated Bridged Crack Model (UBCM). The experiments are carried out via four-point bending tests on 300 beams (3 identical specimens per 100 different cases) with: (1) longitudinal steel-bar percentages of 0.00, 0.06, 0.13, 0.28, and 0.50%; (2) fibre volume fractions of 0.00, 0.10, 0.20, 0.40, and 0.80%; (3) beam depths of 20, 40, 80, and 160 cm; (4) slenderness ratio constant and equal to 6. The UBCM is applied to assess crack propagation and failure mechanisms in hybrid-reinforced concrete beams. The reinforcement brittleness numbers (NP and NP,f) and the pull-out brittleness number (Nw) are thoroughly studied, and the numerical results prove that a softening post-cracking response of the hybrid-reinforced concrete element emerges, and its mechanical performance results to be scale-dependent. The numerical analyses prove the strong interaction between the two design parameters: steel-bar percentage and fibre volume fraction.

The orientation of steel fibers influences the fracture properties of steel fiber reinforced concrete (SFRC) structures. In order to enhance the fracture properties of SFRC structures, the magnetic field method was used to adjust the fiber orientation to maximize the reinforcing efficiency of steel fibers. By this method, the unidirectionally aligned steel fiber reinforced concrete (1D-ASFRC) was manufactured. Furthermore, the two-dimensionally aligned steel fiber reinforced concrete (2D-ASFRC), annularly aligned steel fiber reinforced concrete (AASFRC) and full-field aligned steel fiber reinforced concrete (FASFRC) were prepared based on this fiber orientation adjustment technique, with the aim of promoting the application of ASFRC in various structural forms such as pipe segments, slabs, pavements, bridge decks, and open-hole structures. Subsequently, the advantages of ASFRC in enhancing fracture properties were examined by comparing its performance against that of conventional SFRC specimens. The results indicated that compared to SFRC, both fracture toughness and fracture energy were significantly improved in ASFRC. This implies that using less fibers in ASFRC structures can ensure the fracture properties equivalent to that of SFRC structures. Finally, an investigation into the reinforcement mechanism of ASFRC was conducted from the perspective of fiber distribution characteristics and numerical simulation.

Steel rebar has been an effective and cost-efficient reinforcement for concrete. Corrosion in reinforcements has led to exploring alternate reinforcements such as FRP rebars, hybrid steel core FRP wound GFRP strands rebar and short fiber (steel and polyester, polypropylene, etc) for its effectiveness as a reinforcement to arrest crack initiation and growth and enhancing ductility. The present study reports on the effectiveness of hybrid rebar as a reinforcement in fiber reinforced concrete beams. Thereafter a quasi-brittle phase field-based damage model for short fiber reinforced composites is developed to investigate the effectiveness of fibers in the concrete matrix in providing bridging action needed to enhance the ductility. Steel fiber reinforced concrete (SFRC) is employed as a case study. The model incorporates randomly distributed steel fibers within a macroscale concrete matrix, with fibers represented as two-dimensional truss elements. A traction-separation law governs the fiber-concrete interface, while the concrete matrix is modelled using a quasi-brittle phase field damage approach. The model effectively simulates the classical three-point bending test for SFRC demonstrating good agreement with experimental data. Due to the macroscale representation of the concrete matrix, the model it is possible to extend its application to high-strength steel fiber reinforced concrete (HS-SFRC) by adjusting material properties of concrete. Moreover simulation of complex loading conditions can also be effectively simulated. Results of such simulations carried out will be shown during the presentation.

Textile Reinforced Concrete (TRC) is a thin and light weight cement-fibre composite material. In this study, the mechanical performance of TRC under quasi-static cyclic loading is evaluated through an experimental program. TRC specimen of size 500 x 60 x 10 mm with four layers of AR-glass textile fibers was prepared and tested under uniaxial tensile quasi-static cyclic loading. The load-deflection response and stiffness degradation are evaluated to understand the damage progression in TRC. The result indicates substantial stiffness degradation from 17% to 60% in Zone II due to multiple crack formation indicating an accelerated deterioration process. The combined DIC and AE analysis shows that matrix cracking and crack initiation cause dense and high-frequency AE activity up to the multiple cracking zone (<0.2% strain). As cracks stabilize, widens, and propagates at increasing strain, the density of AE events reduces.