Search Results (2,373)

Cross-laminated timber (CLT), an engineered timber product with distinctive features, has significantly broadened the applicability of timber structures. The self-tapping screws (STSs) with excellent anchorage performance have become one of the primary connectors used in CLT structures. However, the long-term withdrawal resistance is susceptible to environmental factors such as temperature and humidity fluctuations, which may lead to reduced CLT density and corrosion-induced degradation of the steel components. These effects represent a critical life-cycle challenge to the structural integrity and safety of timber connections. This study aims to investigate the withdrawal resistance of STSs in CLT under material aging effects. To achieve this, a two-step experimental program was designed. First, the effects of two artificial accelerated aging methods (ASTM D1037 and improved version of ASTM D1037) on the withdrawal resistance of STSs in glued laminated timber (glulam) were compared to validate the feasibility of the improved protocol. This comparison was necessary to ensure that the improved protocol produces a degradation pattern without altering the failure mechanism. Subsequently, a series of CLT specimens with embedded STSs were subjected to 0, 3 and 6 aging cycles to investigate the withdrawal behavior including aging characterization, failure modes, load–displacement curves, withdrawal capacity, and stiffness. The results indicate that the failure mode of CLT joint with STSs under the improved aging scheme was the consistent pull-out of STSs, identical to that observed in the glulam, confirming mechanistic consistency. After three and six aging cycles, the normalized withdrawal capacity retention rates were 104.98% and 95.36%, respectively. The stiffness is more significantly affected by aging. The corresponding normalized stiffness retention rates were 85.60% and 80.94%, respectively. As the number of aging cycles increased, the occurrence of wood fiber tearing became more pronounced and the ratio of the corresponding load to the peak load decreased. Furthermore, ensuring adequate distance from the vertical glue layer was found to lead to greater long-term resilience and withdrawal capacity. Full article

This study investigates pulsed gas metal arc welding (pGMAW) of API 5L X65 pipeline steel for sour service applications where H₂S exposure is anticipated. Mechanized pGMAW in the 5G downhill position was employed to fabricate girth welds using ER70S-6 filler wire with Ar-20%CO₂ shielding. Comprehensive characterization, including optical microscopy, tensile testing, fractography, EBSD, and fracture toughness evaluation via SENT specimens, was conducted on specimens tested in both air and H₂S-precharged sour conditions. Microstructural analysis revealed ferritic–pearlitic base metal, weld metal with acicular ferrite and bainitic constituents, and a transformed HAZ gradient. Tensile testing demonstrated severe hydrogen embrittlement in sour conditions, with elongation dropping from 22% in air to 4% after H₂S exposure, accompanied by a transition from ductile cup–cone fracture to quasi-cleavage morphology. EBSD showed texture sharpening toward ⟨101⟩ fiber post-deformation, with a broader orientation spread under sour conditions, indicating heterogeneous strain localization. Fracture toughness testing revealed approximately a 50% reduction in CTOD values under sour exposure, with the weld centerline exhibiting greater degradation (0.50 mm to 0.27 mm) compared to the HAZ (0.92 mm to 0.47 mm). Fractography confirmed hydrogen-assisted cracking features, including shallow dimples, cleavage facets, and secondary cracking. These findings establish critical baseline data for engineering a critical assessment of pGMAW-welded X65 pipelines in sour service. Full article

The reliable evaluation of the interfacial bonding quality of steel structures strengthened with carbon fiber-reinforced polymer (CFRP) is crucial to ensuring the long-term service safety of the structures. Focusing on the active and passive detection methods based on piezoelectric sensing, this paper takes numerical simulation as the core research method to provide theoretical verification and mechanism explanation for subsequent key experiments, thus supporting the accurate detection of interfacial damage in CFRP–steel plate joints. A 3D piezoelectric–structural coupling finite element model and a 2D ultrasonic guided wave propagation finite element model were established via COMSOL Multiphysics 6.2 to systematically simulate the electromechanical response characteristics of three piezoelectric sensors (PMN-PT, PZT and PVDF). The research focused on analyzing the potential output and voltage–load response of the three sensors, and simultaneously explored the propagation laws and energy evolution mechanisms of ultrasonic waves in the presence of different debonding damages and groove defects in CFRP plates. The simulation results show that the PMN-PT sensor exhibits the optimal detection performance, with its peak potential output reaching 2.66 times that of the PZT sensor and 4.69 times that of the PVDF sensor, with a load sensitivity of 484.3 mV/kN. In the ultrasonic active detection of interfacial debonding damage, the first-wave amplitude has a significant positive correlation with the debonding length, and this characteristic is attributed to the strong reflection effect and energy accumulation caused by the acoustic impedance mismatch at the CFRP–air interface. For the internal groove defects in CFRP plates, the simulation clarifies that the increase in groove length leads to energy trapping in the plate, while the increase in groove depth intensifies ultrasonic wave energy reflection. The numerical simulation results were compared and verified with data from companion experiments conducted by the authors’ team, showing a high degree of consistency, which confirms the accuracy and reliability of the established finite element models. Meanwhile, the physical essence of damage detection is elucidated from the perspective of wave theory, providing a solid numerical analysis foundation and theoretical support for the intelligent monitoring of interfacial damage in CFRP–steel structures. Full article

Geopolymer gel concrete (GPC) is a kind of environmentally friendly concrete, which has become a potential alternative material to replace ordinary concrete. Traditional mix design of GPC is carried out under experimental conditions, which is time-consuming and labor-intensive. Geopolymer concrete (GPC) is intended for use in hydraulic structures, which are often exposed to water environments. Water flow exerts significant abrasion and erosion on these structures. If the abrasion resistance (AR) of the material is poor, the service life and service quality of hydraulic structures will be substantially reduced under the action of water flow. Therefore, AR is a key performance indicator for GPC in hydraulic engineering applications. This abrasion resistance can be enhanced by using fibers (for example, steel fibers, polyvinyl alcohol (PVA) fibers, and basalt fibers) and nanomaterials. Furthermore, there is a complex nonlinear relationship between the proportions of fibers and nanoparticles added and the properties of GPC. In this study, the circular ring test method and the underwater steel ball test method were conducted to investigate the AR of nano-SiO₂ (NS) and hybrid fiber (NHF) reinforced geopolymer gel concrete (NHF-GPC). A backpropagation (BP) neural network (BPNN) model optimized by the Grey Wolf Optimizer (GWO) (GWO-BPNN) is established to predict the abrasion resistance strength (ARS) and the abrasion rate of NHF-GPC based on the circular ring test method. In addition, the ARS, abrasion rate, and average abrasion depth (AAD) based on the underwater steel ball test method were also predicted. The results indicate that the GWO-BPNN model demonstrates superior performance over the standard BPNN, exhibiting higher prediction accuracy, better fitting performance, and faster convergence speed. Specifically, for the circular ring test method abrasion rate prediction, GWO-BPNN reduced the root mean square error (RMSE) by 30.3% and lowered the mean absolute percentage error (MAPE) to 8.4%. The GWO-BPNN model established in this study can provide efficient and reliable theoretical support for the optimization of the NHF-GPC mix design. Full article

Despite the low thermal conductivity that characterizes the mechanical behavior of cementitious composites like concrete, high temperatures acting for long periods could have devastating effects on the overall integrity and stability of structures. Such damage encompasses not only the structural but also the material level, manifested as a degradation of the strength and stiffness properties together with increasing porosity and the consequent cohesion loss. Adding fibers to the cementitious matrix is a strategy that increases the fire resistance of structures, improving the fracture energy release capacity beyond the peak strength. This fact has been experimentally demonstrated in numerous publications and requires the development of advanced computational constitutive models with the aim of predicting the evolution of both elastic properties and failure behavior in fiber-reinforced concrete. In this work, a temperature-dependent, thermodynamically consistent microplane material model based on the smeared crack approach is developed to simulate the mechanical behavior of preheated steel fiber-reinforced concrete (SFRC) under residual conditions. The influence of high temperatures on the material response is evaluated in terms of stress versus crack opening displacement or crack slip curves, whereas the failure analysis in the form of discontinuous bifurcation is addressed by means of numerical analysis of the acoustic tensor, identifying the critical orientation for varying temperature levels, material properties and boundary conditions. Full article

Coupling beams are critical connecting components in coupled shear wall systems and core tube structures. At the same time, they play an important role when the structure is subjected to an earthquake. Plate-reinforced composite (PRC) coupling beams exhibit superior comprehensive performance in terms of bearing capacity, deformation performance, energy dissipation capacity, and construction efficiency. However, research on PRC coupling beams remains limited both domestically and internationally. To better describe the structural response of steel plate–concrete composite coupling beams, this study collected existing experimental data. The beams had a small span-to-depth ratio. The loading was cyclic. The study normalized the skeleton curves of each specimen. The span-to-depth ratio ranged from 0.9 to 2.5. The plate ratio ranged from 3% to 5%. For these beams, preliminary skeleton curve fitting equations are proposed. The equations are based on existing data. The equations apply to two types of composite coupling beams. One type uses a steel plate and ordinary concrete. The other type uses a steel plate and fiber concrete. These equations are derived using a trilinear model and linear fitting tools. Furthermore, restoring force models for steel plate–conventional concrete and steel plate–fiber concrete composite coupling beams with a small span-to-depth ratio are proposed. Comparative analysis shows that each model captures the hysteretic response of PRC coupling beams with acceptable accuracy in the elastic and decline phases, while the elastic–plastic stage is suitable only for trend prediction. It should be noted that the proposed models are preliminary engineering approximations primarily applicable within the following ranges: a span-to-depth ratio of 0.9~2.5, a plate ratio of 3~5%, concrete strength of C30~C50, a longitudinal reinforcement ratio of 0.86~2.23%, a stirrup ratio of 0.56~0.63%, and a steel plate thickness of 6~10 mm. For configurations significantly outside these ranges, additional experimental validation is required. Full article

To promote the industrial development of reinforced concrete engineering and enhance the construction quality of prefabricated buildings, an innovative partial prefabricated construction method is proposed in this paper, namely the prefabricated reinforced cage–cast in situ concrete (PRC-CISC) structure with an innovative steel bar connection technology. The connection techniques, including direct thread rolling of steel bars and hot-forged sleeves, are adopted. With the design axial compression ratio and the layout of couplers in the reinforcement cage as the main parameters, quasi-static tests are carried out to investigate the failure mode, seismic behavior, and mechanical mechanism of couplers of PRC-CISC columns. The results indicate that all specimens present typical compression–bending failure with plump hysteretic curves, gradual stiffness degradation, good ductility, and energy dissipation capacity. The new couplers can effectively satisfy the seismic performance requirements of PRC-CISC columns. With the increase in axial compression ratio, the bearing capacity rises while ductility decreases, and the stress of longitudinal bars increases. The layout of couplers exerts a controllable influence on the mechanical and deformation performance of specimens. The steel stress in the core stress region of PRC-CISC columns shows a bilinear distribution with stress concentration at both ends of the sleeves, which is related to the material difference in couplers. Finally, two “non-equal” calculation methods (plastic hinge model and fiber model) are established based on experimental results and finite element analysis, forming a systematic calculation theory for the new material–new technology–new structure system. The research provides important references for the engineering application of such structures. Full article

Glass fiber–reinforced polymer (GFRP) reinforcement provides an effective alternative to conventional steel in concrete structures due to its corrosion resistance. Nevertheless, the lower elastic modulus of GFRP necessitates careful consideration of serviceability behavior in GFRP-reinforced concrete members. This study presents a numerical sectional analysis model for predicting the flexural response and ultimate capacity of hybrid reinforced concrete beams incorporating embedded GFRP profiles in combination with either mild steel or GFRP reinforcement bars under monotonic static loading. The proposed model employs realistic nonlinear stress–strain relationships for concrete and steel, together with secant moduli of elasticity evaluated at different loading stages. Particular emphasis is placed on detailed stress distribution in flexural sections, including the contribution of tension stiffening in the post-cracking regime. The formulation integrates nonlinear constitutive material behavior with theoretical sectional equilibrium to evaluate the effective flexural secant stiffness. For practical serviceability assessment and to reduce dependence on complex analytical procedures, strain vectors and stiffness matrix components are derived using elasticity coefficients that reflect modulus degradation obtained from numerical analysis. The accuracy of the model is verified through comparison with experimental results, including ultimate flexural capacity and moment–deflection responses. Many crucial parameters were studied, such as the longitudinal reinforcement ratio, type of reinforcement, concrete compressive strength, position of the I-GFRP profile, and rotation of the I-GFRP profile. The results of this study demonstrated that both the longitudinal reinforcement ratio and the rotation of the I-GFRP profile have a significant influence on the ultimate load capacity and deflection behavior. The close agreement between numerical predictions and experimental observations demonstrates the reliability and applicability of the proposed model for structural engineering analysis and design. Full article

Punching shear failure in reinforced concrete RC slabs is one of the most significant and detrimental failure modes due to its sudden nature and its dependence on a complex interaction between concrete strength, the reinforcement, and the loading conditions. In recent years, there has been increasing interest in utilizing sustainable cementitious materials and steel fibers as a way of enhancing structural performance and improving the durability of concrete. The study aims to assess the structural behavior of RC slabs utilizing a partial cement substitution with limestone powder (LP) and granulated blast-furnace slag (GBFS), with the addition of steel fibers. Twelve RC slabs were examined under uniform concentric loading to analyze cracking behavior, load–deflection relationship, stiffness variation, and ultimate punching shear strength. The results demonstrated that using limestone powder (LP) had a significant impact on the crack distribution pattern and resulted in a slight reduction in initial stiffness, with the load-bearing capacity decreasing to approximately 55.8% of the control mixture at high replacement ratios. Due to a slower hydraulic reaction than with other mixtures, increasing additional granulated blast-furnace slag resulted in a decrease in crack resistance and relative deformation. With a load-bearing capacity of approximately 92.9% of the control mixture, a tertiary mixture of limestone powder and granulated blast-furnace slag (GBFS) demonstrated a better balance in structural behavior, leading to improved crack control while maintaining a sufficient level of load-bearing capacity. The steel fibers also significantly contributed to enhanced post-cracking behavior by decreasing crack width and improving the stress redistribution mechanism within the RC slab. This led to increased punching shear resistance and enhanced energy absorption, with the ultimate load increased to 119 kN compared to the control mixture. Overall, the findings show that combining sustainable cementitious materials with steel fibers can effectively improve punching shear performance and enhance the efficiency and durability of reinforced concrete. Full article

Ultra-high-performance concrete incorporating coarse aggregates (UHPC-CA) exhibits pronounced multi-scale heterogeneity and staged damage evolution. However, existing single-scale reinforcement strategies often fail to address the complete micro-to-macro fracture process, leaving a critical research gap in achieving full-stage crack control. To address this, this study introduces a novel cross-scale toughening strategy using hybrid steel fibers (SF) and calcium carbonate whiskers (CCW), and decouples the coupled influences of water-to-binder (W/B) ratio, coarse aggregate (CA), and multi-scale fibers via an orthogonal design. Mechanical properties, fiber dispersion, and pore structure are jointly characterized to establish structure–property relationships. An optimal composition (W/B = 0.32, CA = 18%, SF = 2%, CCW = 1%) is identified, achieving a balanced enhancement of strength and ductility. Results indicate that matrix densification is primarily controlled by W/B via pore refinement, while mechanical performance is governed by the interplay between fiber spatial uniformity and interfacial integrity; the roles of CA and CCW are clearly stress-state dependent. Furthermore, a novel cross-scale synergistic mechanism is revealed, in which micro-scale CCW regulates microcrack initiation and stabilizes the pre-peak response, whereas macro-scale SF dominates post-peak behavior through crack bridging and pull-out energy dissipation. This sequential activation enables a full-stage enhancement of tensile performance, shifting failure from brittle localization to pseudo-ductile multiple cracking. The findings provide a correlative framework for tailoring UHPC-CA through multi-scale hybrid reinforcement. Full article

High friction composite brake shoes containing reinforced steel fibers are now widely used in freight train tread braking systems. With the demand for higher transportation efficiency on railway lines with long steep slopes, it is necessary to explore the braking capabilities of existing general freight train high friction composite brake shoes under continuous braking conditions. In this paper, continuous braking tests at different speed levels were conducted using a friction and wear test rig. Through material characterization and interface damage analysis, it was found that reinforced steel fibers can exist as a contact platform at the brake shoe friction interface. Due to the strip-like morphology and high strength features of steel fibers, even after the steel fiber layer is fragmented, it can still promote the formation of a continuous contact platform with complex material composition on the surface, maintaining the progress of the braking process. For existing general freight train high friction composite brake shoes, at speeds up to 80 km/h, although the friction coefficient decreases to some extent, the wear rate maintains a relatively low range. When the speed increases to 100 km/h, the friction coefficient of the braking interface deteriorates severely, and the wear rate of the brake shoe increases sharply, seriously endangering braking safety. The research results reveal the evolution of wear behavior of high friction composite brake shoes containing reinforced steel fibers at different speed levels, providing theoretical support for exploring the braking capabilities and design optimization of brake shoes. Full article

Iron-based shape memory alloy (Fe–SMA) rebars can generate internal prestress in cement-based members after restrained thermal activation; however, the temperature actually reached by embedded rebars in cracked UHPFRC is difficult to infer from exposed bar segments. This study investigates electrical resistance activation of 4% prestrained Fe–SMA rebars embedded in pre-cracked UHPFRC beams and clarifies the activation-control problem by combining thermocouple measurements with a calibrated two-dimensional electro-thermal simulator. Twelve beams (150 × 150 × 600 mm) containing either Dramix 3D or Dramix 4D hooked steel fibers were first loaded in three-point bending to a mid-span displacement of 4 mm. The 4D series reached a 9.47% higher average pre-cracking load, confirming that fiber geometry modified the cracked state before heating. During activation, the exposed rebar segment reached 200 °C after approximately 77 s, whereas the embedded working segment reached the same target only after approximately 213 s; at that moment, the exposed segment was already close to 350 °C. The calibrated simulator reproduced the target activation time with an error of approximately 3 s and visualized the localized heat transfer from Fe–SMA to UHPFRC. The results demonstrate that activation control based only on exposed-bar temperature may cause under-activation of the embedded reinforcement, and that direct internal temperature monitoring is required for reliable Fe–SMA activation in cracked UHPFRC members. Full article

Glass fiber-reinforced polymer (GFRP) composites offer a compelling solution to the durability degradation of reinforced concrete (RC) structures in harsh marine and de-icing environments. Hybridizing fiber-reinforced polymer (FRP) with conventional steel reinforcement synergizes the superior corrosion resistance of FRP with the high ductility of steel. However, the synergistic mechanisms of GFRP–steel hybrid reinforced columns confined by either GFRP or steel spiral stirrups under axial compression remain insufficiently quantified. This study systematically investigates the axial compressive performance of such structures through material testing, static axial compression tests on seven short column specimens, and advanced finite element (FE) modeling. The investigation focuses on the effects of the steel-to-GFRP area ratio and the spiral stirrup type. Experimental results reveal that spirally confined hybrid columns exhibit failure modes remarkably similar to conventional RC columns. The incorporation of GFRP bars significantly enhanced the ultimate load-bearing capacity, while the steel bars ensured the requisite ductility. Notably, a higher ultimate capacity was achieved at a steel-to-GFRP area ratio of 1:1 under steel spiral confinement, retaining a ductility index equivalent to 83.6% of a pure RC column. Furthermore, an ABAQUS-based FE model was developed and rigorously validated against experimental data, successfully capturing the failure progression and ultimate capacities across diverse parameters. Ultimately, based on the superposition principle, by quantifying the independent load-bearing contributions and synergistic interactions of the spalled concrete cover, confined core, and hybrid bars, this study derives a theoretical formula. The proposed model accurately predicts the axial compressive capacity of spirally confined hybrid columns, providing an analytical tool for resilient structural design. Full article

Designing ultra-high-performance concrete (UHPC) mixtures requires balancing multiple, often conflicting, performance criteria, particularly mechanical strength and rheological behavior. However, the limited availability of publicly accessible datasets containing synchronized multi-property measurements, together with cross-source heterogeneity, poses a major challenge for robust data-driven modeling under small-sample conditions. To address this issue, this study proposes an integrated framework combining cross-source data harmonization, Variational Autoencoder (VAE)-based latent-space augmentation, multi-output deep learning, interpretability analysis, and Genetic Algorithm (GA)-driven inverse design. A dataset comprising 139 valid UHPC records was curated from 22 peer-reviewed studies and expanded to 2780 samples through VAE-based augmentation. Using the augmented dataset, a multi-output deep neural network was developed to jointly predict compressive strength, flexural strength, yield stress, and plastic viscosity. On the independent test set, the model achieved R² values of 0.8601, 0.9212, 0.8464, and 0.6603, respectively. Comparative benchmarks and augmentation ablation analyses further showed that VAE-based augmentation consistently improved predictive performance and generalization, especially under small-sample conditions. SHAP and partial dependence analyses identified curing age, steel fiber content, water-to-binder ratio, and superplasticizer dosage as the dominant factors governing UHPC performance. Finally, the trained surrogate model was coupled with a GA for multi-objective inverse optimization, and experimental validation of three candidate mixtures confirmed good agreement between predicted and measured values. This study provides a transparent and engineering-oriented methodology for the integrated prediction, interpretation, and optimization of UHPC mixtures. Full article

In recent years, Ultra High-Performance Fiber-Reinforced Concretes (UHPFRCs) have gained significant attention for their applications in structural components, particularly for improving impact resistance and post-cracking behavior. This study explores the behavior of thin Ultra High-Performance Concrete (UHPC) panels reinforced with synthetic fibers, focusing on the potential use of these materials for building façades. Three different synthetic fiber-reinforced mixes were developed, utilizing polyvinyl alcohol (PVA) microfibers, polypropylene (PP) macrofibers, and a hybrid combination of both. These thin, unreinforced panels were subjected to impact testing using a free-falling steel ball to evaluate their mechanical response. The results were analyzed in terms of crack patterns, crack openings, and overall impact resistance. Additionally, numerical analysis was implemented by using the ABAQUS^TM finite element code, in order to predict the panels’ performance under impact, providing a comparison between experimental results and numerical simulations. This investigation highlights the significant contribution of synthetic fibers in enhancing the toughness and impact resistance of UHPC panels, demonstrating their viability for structural applications requiring enhanced durability. Full article