Abstract The paper presents an investigation of the mechanical behavior of fiber‐reinforced concrete utilizing waste tire and industrially manufactured fibers. The first part of the paper concentrates on material research, indicating that the incorporation of fibers enhances concrete performance, particularly in terms of prismatic compressive strength, which averaged 45.7 MPa, with a notable 14.6% increase observed in specimens 2C. Specimens with a dose of fibers demonstrated a significantly enhanced f R3 , depending on the geometry and end shape of the fibers. The second part examines the shear resistance in reinforced concrete elements without shear reinforcement. Fibers markedly improved shear performance across all mix designs, with specimen 2B realizing a 26.7% increase in shear resistance. Normalized results substantiate the advantageous effects of all tested fiber types. The study concludes that the standard MC 2020 for predicting shear resistance with fibers provides a safe and cost‐effective structural design.

Abstract This investigation addresses the synergistic effects of nanosilica (NS) and used foundry sand (UFS) on the strength and microstructural performance of concrete. In response to the environmental concerns posed by excessive extraction of natural fine aggregates and cement production, investigations have sought to create a sustainable concrete blend incorporating industrial waste and nanomaterials. UFS was used to partially replace natural sand at 10%–40%, while NS was added at 1%–5% of the binder content. Mechanical tests, including compressive, split tensile, and flexural strength evaluations, were conducted at 7 and 28 days. Response surface methodology was used for statistical modeling and optimization of mix proportions. Microstructural characterization was performed via various techniques. The results revealed that the optimized blend, comprising 3.34% NS and 25.79% UFS, exhibited substantial improvements in mechanical strength and matrix densification. Scanning electron microscopy and x‐ray diffraction analyses revealed a more compact pore structure, enhanced generation of calcium silicate hydrate, and a significant decrease in portlandite content in the optimized mixture. These findings indicate that the synergistic use of NS and treated foundry sand constitutes a viable approach for producing eco‐friendly concrete that promotes sustainable construction and circular economic efforts.

Abstract In cold regions, concrete channels are subjected to the combined effects of freeze–thaw cycles (FTC) and abrasion, leading to severe deterioration of the channel structures. However, the performance of desert sand concrete (DSC) under common environmental conditions such as freeze–thaw and abrasion remains unclear. In this study, desert sand (DS) was used to partially replace river sand (RS) to prepare. The performance variations of river sand concrete (RSC) and DSC under FTC, abrasion, and freeze–thaw–abrasion coupling action were investigated. Microstructural analysis of the concrete was conducted using scanning electron microscopy (SEM) to explore the damage mechanisms of DSC under the freeze–thaw–abrasion coupling action. The results indicate that incorporation of DS enhances the FTC resistance and abrasion resistance of the concrete. Under the sole action of abrasion, the abrasion resistance of DSC was 59.7% higher than that of RSC. Under the same number of FTC, the compressive strength of DSC consistently remained higher than that of RSC. Under the freeze–thaw–abrasion coupling action, the abrasion resistance of RSC and DSC decreased by 64.5% and 63.39%, respectively. Microstructural analysis revealed that the coupled damage from freeze–thaw and abrasion is far from a simple superposition of individual effects, exhibiting a significant synergistic interaction: FTC causes structural loosening of the concrete, exacerbating abrasion damage, while surface damage from abrasion accelerates water ingress, thereby intensifying freeze–thaw damage. This study provides theoretical insights for the practical application of DSC in engineering projects in desert and cold regions.

Abstract This study evaluates the thermal properties and effects of elevated temperatures on the residual properties of concretes containing lithium slag (LS) at cement replacement levels of 20%, 40%, and 60%. The results indicate that LS reduced the thermal conductivity of concrete by 1.08%, 4.47%, and 14.31% for using 20%, 40%, and 60% LS, respectively, while decreasing thermal diffusivity with the addition of LS. Conversely, volumetric heat capacity increased from 1.85 MJ/m 3 ·K (control) to 1.87, 1.92, and 2.06 MJ/m 3 ·K, indicating enhanced heat‐retention capability with the increase of LS content. In the elevated temperature tests, the 20%–40% LS concretes showed finer cracks compared to those in the control and 60LS concretes. No spalling was observed up to 800°C. Mass loss increased with the increase of temperature, reaching 7.2% at 600°C for the 60LS mix, whereas the 20%–40% LS concretes showed slightly lower mass losses than the control. Residual compressive strength also decreased with the increase of temperature, with the 20%–40% replacement retaining higher strength up to 600°C, while the 60% LS concrete experienced the highest strength loss. Ultrasonic pulse velocity results indicated progressive internal degradation, with a notable drop at 800°C. TGA confirmed enhanced thermal stability in the 20%–40% LS concretes through reduced Ca(OH) 2 decomposition and increased formation of stable hydration products. The SEM analysis showed denser microstructures in the 40LS mix compared to higher porosity in the control and 60LS concretes. Overall, the 20%–40% LS concretes demonstrated superior thermal resistance and high‐temperature performance.

Abstract This study develops a sophisticated finite element model (FEM) to investigate the flexural behavior of reinforced concrete (RC) beams strengthened with combined steel plate and ultra‐high‐performance concrete (SP‐UHPC) in terms of flexure. The simulation covers the full strengthening process, including four‐point bending pre‐damage, unloading, SP‐UHPC application, and reloading to failure with four‐point bending. The FEM of the SP‐UHPC beam successfully reproduces both the interface debonding and key bending moments. To study flexural behavior, ideal bonding is assumed for parametric analysis. Results show that each 20 mm increase in UHPC thickness improves bearing capacity by 7.3%, stiffness by 16.2%, and cracking moment by 53.2%. Additionally, increasing steel plate thickness by 1 mm enhances the flexural performance parameters by 12.0%, 14.7%, and 18.0%, respectively. The optimal UHPC‐to‐RC depth ratio for strengthening efficiency is 1:10. Additionally, the analytical results become gradually larger than the numerical ones as the UHPC layer thickness increases and a correction factor is proposed for the analytical model. Based on a surrogate model with reasonable assumptions, the heights of RC beams corresponding with the UHPC layer and steel plate thicknesses are optimized to have low weight and cost, but high cracking moment, stiffness, and flexural capacity for the strengthened beams.

Abstract This paper presents an experimental campaign of five reinforced concrete members subjected to cyclic axial loading alternating between tension and compression. Fiber optical sensors and digital image correlation , in combination with automated crack detection and measurement , were used to investigate, among other aspects, the development of crack opening and crack closure, tension stiffening and bond behavior. Bond shear stresses were derived by equilibrium from the steel stress gradient along the reinforcement, requiring accurate knowledge of the cyclic stress–strain relationship of the reinforcement in order to obtain reliable steel stresses from the measured steel strains. To this end, novel customized reversed cyclic material tests were carried out on reinforcing bars short enough to avoid premature buckling. The experimental results show that rather than occurring at a specific load level, crack closure occurs over a loading range in which the cracks close sequentially. Furthermore, the results indicate pronounced tension stiffening when the reinforcement exhibits plastic deformation, and bond shear stress reversal was observed during unloading from tension and reloading in compression. The findings, combined with the open‐access experimental data, are a valuable source for developing and validating mechanical models for reinforced concrete subjected to reversed cyclic loading.

Abstract This study presents nonlinear finite element analyses to investigate the punching shear behavior of unbonded post‐tensioned concrete flat slabs at slab‐edge column connections. A parametric analysis was conducted to evaluate the influence of four critical parameters on the punching shear resistance: the distribution of prestressing tendons, the presence of unbalanced moments parallel to the free edge, the flexural reinforcement ratio, and the concrete compressive strength. The numerical models were calibrated and validated against experimental data, demonstrating satisfactory accuracy in reproducing load–displacement behavior and failure mechanisms. The analysis revealed that the distribution of prestressing tendons significantly affects punching shear capacity. Configurations with tendons concentrated perpendicular to the free edge exhibited a notable increase in ultimate load and a transition from punching shear to a flexural‐punching failure mode characterized by ductile behavior. The presence of unbalanced moments parallel to the free edge resulted in a reduction of approximately 20% in punching shear resistance, accompanied by non‐symmetric slab rotation, stress concentrations, and increased cracking on one side of the slab. Parametric studies further showed that increasing the reinforcement ratio enhances punching shear capacity by about 30%, while higher concrete compressive strength contributes an increase of approximately 15%. The reinforcement ratio was found to exert a greater influence on punching resistance than concrete strength. Comparative analysis with design codes—NBR 6118:2023, fib Model Code 2020, ACI 318‐19, and the final draft of Eurocode 2—indicated that most codes provide conservative estimates, particularly under unbalanced moment conditions. This conservatism stems from tendon force increments due to slab deflection and the empirical safety factors used to penalize the effects of unbalanced moments. Overall, the study highlights the importance of accurately modeling prestressing tendon distribution and unbalanced moments to predict punching shear behavior, emphasizing the need for improved design provisions to reduce conservative biases in code‐based predictions.

Abstract Modular integrated construction (MIC) is an innovative prefabricated building system that involves connecting precast concrete modular units with cast‐in‐place concrete. In this system, MIC composite shear walls and infill walls serve as the primary vertical components. However, due to the fundamental differences in the coordinated deformation mechanisms between infill walls and the main structure, as opposed to those in traditional cast‐in‐place structures, the influence of infill walls on MIC composite shear walls remains unclear. To address this issue, three composite shear wall specimens with varying structural configurations were designed for this study. Quasi‐static loading tests were conducted to analyze the complete mechanical response, failure mechanisms, hysteretic behavior, strength degradation, stiffness degradation, and energy dissipation capacity of the specimens. The test results indicated that all three specimens experienced flexure‐shear failure. Their hysteresis loops were well developed, stiffness gradually degraded, and energy dissipation capacities were favorable. The infill wall significantly influenced the failure mode of the MIC composite shear wall. Compared to the bare specimen DZ‐1, specimen DZ‐2 with infill walls exhibited a 40.8% enhancement in ultimate load‐bearing capacity and a 26% increase in cumulative energy dissipation capacity. However, this configuration also induced accelerated strength degradation and a reduction in structural ductility. By incorporating a flexible isolation panel connection, specimen DZ‐3 demonstrated a 7.7% reduction in ultimate load‐bearing capacity and a 9% decrease in cumulative energy dissipation compared to DZ‐2. Nonetheless, this design effectively enhanced structural ductility and mitigated stiffness degradation. Based on experimental findings, a refined finite element model of the wall was developed using ABAQUS software to further investigate the collaborative load‐bearing mechanisms between MIC composite shear walls and infill walls of varying dimensions and material types. Corresponding design recommendations were subsequently proposed. This study clarifies the coordination mechanism of infill walls and their previously underexplored seismic performance, thereby establishing a theoretical foundation for MIC composite shear walls. Based on these findings, corresponding design recommendations are proposed to advance the development of prefabricated modular construction.

Abstract The previous seismic events indicated the vulnerability of old reinforced concrete (RC) structures against earthquakes due to the absence of seismic detailing and capacity design specifications in such buildings. In this context, beam‐column joints (BCJ) of the existing RC structures built before the 1970s have exhibited poor structural performance under earthquake scenarios. Among the governing factors contributing to such brittle failures in BCJs, the bond‐slippage phenomenon occurring between longitudinal steel bars and concrete is one of the major contributing factors to such failures and requires further investigation since limited research has been conducted on the topic. In the present study, the results of several pull‐out tests are presented, and a numerical validation of different bond‐slip models is established. Moreover, the corresponding bond‐slip models have been employed in the numerical model of a beam‐column joint constructed with plain rebar, and the results obtained from each of the bond‐slip models are illustrated and compared with the previous experimental results of the plain rebar BCJ specimen for both monotonic and cyclic loading scenarios. Among the employed models for the BCJ, except for FIB‐CEB and Melo model cyclic results, all the other models satisfied the maximum capacity level recorded by the experimental testing for the same BCJ. The reliability of the proposed bond‐slip models is then discussed to provide further insight into the application of these models for better understanding the bond‐slip between concrete and plain reinforcement in existing RC structures.