Shear failure in conventional reinforced concrete (R/C) beams is characterized by pronounced brittleness, limited energy dissipation capacity, and a high propensity for catastrophic collapse due to the absence of discernible warning signs. This study investigates the use of high-ductility fiber-reinforced cementitious composites (Engineered Cementitious Composites, ECC) to enhance the shear performance of concrete beams. An experimental program was conducted on both R/C and reinforced ECC (R/ECC) beams subjected to shear, complemented by a novel numerical approach to quantify the contributions of arch action (V_a[jls-end-space/]) and beam action (V_b[jls-end-space/]) to shear resistance. The findings reveal a strong positive correlation between the efficiency of arch action and overall shear performance, including shear carrying capacity, deformation capacity, and ductility. Building on these insights, an optimized design strategy incorporating partial ECC replacement and pre-defined voids is proposed, illustrating the potential of a mechanism-driven approach to achieve superior shear behavior in structural elements.

Engineered cementitious composite (ECC) has been effectively applied in shear-critical structures due to its high ductility under tension and fiber bridging effect to resist crack opening and sliding. This study employed a novel monitoring system incorporating distributed strain gauges to investigate the shear resistance mechanism in reinforced ECC beams. The system enabled the measurement of full-length strain distribution along the stirrups and longitudinal reinforcement. By capturing stirrup strains precisely along the critical shear cracking path, the shear contributions from transverse reinforcement (V_s) and ECC matrix (V_c) could be accurately quantified. A total of 20 reinforced ECC beams were tested under shear, and the role of governing parameters (e.g., shear span-to-depth ratio, stirrup and longitudinal reinforcement ratio) was analysed. Based on the observed shear failure mechanism, a modified truss-strut model and a simplified equation for predicting shear strength are proposed for the shear design of reinforced ECC beams.

Understanding the bond behavior between reinforcement and concrete under varying confinement conditions is essential for the design and performance assessment of reinforced concrete structures. This study employs a discrete lattice model to investigate the reinforcement-concrete bond mechanism, focusing on crack propagation, fracture processes, and stress distribution. Experimental data involving lap-spliced reinforcement bond test under different confinement conditions serve as benchmarks. In the model, concrete, reinforcement, and their interface are discretized into beam elements, while the interface properties remain constant and independent of confinement conditions. A key finding is that generating the lattice mesh through the Delaunay triangulation scheme enables the model to reproduce realistic strut-cracking patterns and conical stress transfer phenomena, thereby capturing stirrup-induced passive confinement effects without modifying interface properties. The results clarify the role of stirrup confinement in restricting concrete dilatancy and bond splitting, while bond failure is shown to depend on concrete fracture under weak confinement and on interface failure only under strong confinement. Overall, this study not only validates the discrete lattice approach for reinforced concrete bond modeling but also provides deeper insights into lap-splice failure mechanisms, offering a robust framework for structural assessment and design.

The fiber's bridging effect across the shear cracks is considered to play an important role of resisting shear in engineered cementitious composite (ECC), and fiber reinforced material in general. To quantify the shear crack kinematics (i.e., shear crack opening and sliding displacements) in reinforced ECC (R/ECC) beams, a crack measuring algorithm based on the full-field displacement spectrum is developed by using the Digital Image Correlation (DIC) technology. In addition, a novel distributed strain-measuring methodology was used to detect the strain distribution along the transverse and longitudinal reinforcement. Reinforced beams made of traditional concrete (R/C) and mortar (R/M) were used as reference. Through aforementioned monitoring schemes, the role of matrix (V_c) and stirrups (V_s) in shear resistance mechanism could be independently understood and evaluated. The R/ECC beams exhibited much higher V_c than the reference reinforced concrete (R/C) beams (by 68%∼104%). Nevertheless, the shear crack measuring results revealed that the higher shear strength in R/ECC did not always result from the fiber's bridging effect across the critical shear crack (CSC) but of high shear-resisting contribution from ECC in shear-compression zone. For a better understanding of the shear failure mechanisms, phenomenological models of shear crack kinematics in R/C and R/ECC beams are proposed.

Ultra-high performance fiber reinforced concrete (UHPFRC) is an advanced cementitious composite with high compressive strength and low permeability. Due to its excellent mechanical properties and superior durability, UHPFRC is considered promising for strengthening of the existing concrete bridges. In order to examine its strengthening efficiency for shear capacity, an experimental study is carried out on shear-deficient beams without stirrups. Strengthening method comprising precast UHPFRC laminates being glued with epoxy resin on two lateral sides of the reinforced concrete beams, is examined. To investigate the robustness of the system under severe exposure conditions, some beams are subjected to freeze-thaw (FT) cycles. Beams are tested to failure under three-point bending configuration. Test results show that for epoxy resin bonding, UHPFRC shear strengthening is a promising method to increase the load and deformational capacity, and to limit the crack openings. The load capacity is doubled, and the deformational capacity is increased by around 60%. After exposure to 30 FT cycles, the strengthening efficiency and fracture behaviour of UHPFRC composite beams seem not to be affected. It seems that the interfacial bond strength is sufficient to prevent premature debonding between UHPFRC and NC, which under combined action of environmental exposure (e.g. FT) and mechanical loading might become a challenge. Finally, a finite element model is developed to predict and understand the shear behaviour of the reference and strengthened beams. In general numerical results show good agreement with the experimental results in terms of failure pattern and peak load prediction once the perfect bond model is used for the interface between UHPFRC and NC. In order to better understand the role of governing parameters on the shear capacity of the composite member, parametric studies are conducted focusing on the role of varying UHPFRC softening behaviour and UHPFRC-concrete interface properties.

Aimed at realizing the effective strengthening and durable repair of concrete structures, particularly in emergencies like traffic interruption triggered by broken roads and damaged bridges, nine groups of specimens were designed and tested in this paper to develop the high-early-strength Engineered Cementitious Composites (HES-ECC) featured as both high early-strength and superior long-term-deformability. The high-early-strength effect of sulphoaluminate cement, silica fume, and Portland cement on HES-ECC was compared, as well as their influence on the deformation ability of HES-ECC. Moreover, the interfacial behaviors between HES-ECC and existing concrete structure were clarified, considering the effects of interfacial agents, interfacial treatment methods, and interfacial roughness. The results indicate that HES-ECC with 6% silica fume mixed could obtain both the high early-strength and superior long-term-deformability. The flexural strength at 3 h could reach 66.67% of that at 28d. The compressive strength could reach up to 28.7 MPa at 3 h, and the ultimate tensile strain could remain 4.21% at 28d. Cement paste interfacial agent could enhance the chemical adhesive bonding between HES-ECC and existing concrete while polymer modified interfacial agent was incompatible. The increased roughness of chiseled interface was beneficial to both the bearing capacity and the deformation ability. Interfacial shear performance of the grooved interface was scarcely deteriorated even if the roughness decreased by 54.18% compared with the chiseled interface. The recommended interfacial treatment is chiseled interface combined with grooved interface, as well as a thickness of 1–2 mm cement paste interfacial agent. This study provides valuable and credible experimental data for promoting the application of HES-ECC in repairing existing concrete structures in practice.

The bond between concrete and reinforcement is one of the critical parameters influencing the structural behavior of reinforced concrete (RC). This research proposes a mathematical methodology to scale the reinforcement-concrete bond-slip relationship in a beam lattice modeling framework. A simplified, generalized approach based on stochastic analysis is proposed to model the interaction between the reinforcing bar and surrounding concrete at the macroscale. The approach considers the randomness of the lattice mesh and the mesh size and adopts an analytical model for the interface assuming the pull-out failure of reinforcement as input, thereby including also the mesoscale geometric effect of ribs. By using the geometric configuration of Delaunay triangulation in the random lattice mesh, the interface elements can reproduce the basic conical stress transfer mechanism in concrete. Consequently, depending on boundary conditions, and without changing the interface properties, a splitting failure and bond-slip relation for splitting failure can be predicted. The model is systematically validated in different types of pull-out tests, through flexural and finally shear tests. With limited input (properties of the concrete and analytical equation for pull-out failure), having a (strong) physical background, the model was shown to capture the fundamental fracture mechanisms in RC under different loading and confinement conditions.

Application of fiber-reinforced polymer (FRP) reinforcement in concrete beams may cause large deflection and crack width, as well as low shear capacity and ductility due to relatively small stiffness of FRP materials. To avoid these unfavorable factors and evaluate the shear behavior of FRP-reinforced structural members, a high-performance strain-hardening cementitious composite (SHCC) is introduced to substitute conventional concrete in reinforced beams, and four-point bending test is conducted in this study. Six FRP-reinforced SHCC beams with different transverse reinforcement ratios and shear spans, as well as one concrete reference beam, were tested. According to the test results, the FRP-reinforced SHCC beam showed enhanced shear carrying capacity and superior ductility compared with the concrete beams. The shear span to effective depth ratio as well as the stirrup ratio has a great influence on the shear behavior of FRP-reinforced SHCC beams, including the failure mode, load-carrying capacity, crack propagation, and ductility. Finally, a simplified truss-strut model for predicting shear carrying capacity of steel or FRP-reinforced SHCC beams is proposed, and a good agreement is achieved with the experimental results.