Search Results (123)

This study presents a high-performance external strengthening strategy for reinforced concrete (RC) beam–column joints, integrating near-surface mounted (NSM) Carbon Fiber Reinforced Polymer (C-FRP) ropes with externally bonded C-FRP sheets. The X-shaped ropes, anchored diagonally on both principal joint faces and complemented by vertical ropes at column corners, provide enhanced core confinement and shear reinforcement. C-FRP sheets applied to the beam’s plastic hinge region further increase flexural strength and delay localized failure. Three full-scale, shear-deficient RC joints were subjected to cyclic lateral loading. The unstrengthened specimen (JB0V) exhibited rapid stiffness deterioration, premature joint shear cracking, and unstable hysteretic behavior. In contrast, the specimen strengthened solely with X-shaped C-FRP ropes (JB0VF2X2c) displayed a markedly slower rate of stiffness degradation, delayed crack development, and improved energy dissipation stability. The fully retrofitted specimen (JB0VF2X2c + C-FRP) demonstrated the most pronounced gains, with peak load capacity increased by 65%, equivalent viscous damping enhanced by 55%, and joint shear deformations reduced by more than 40%. Even at 4% drift, it retained over 90% of its peak strength, while localizing damage away from the joint core—a performance unattainable by the unstrengthened configuration. These results clearly establish that the combined C-FRP rope–sheet system transforms the seismic response of deficient RC joints, offering a lightweight, non-invasive, and rapidly deployable retrofit solution. By simultaneously boosting shear resistance, ductility, and energy dissipation while controlling damage localization, the technique provides a robust pathway to extend service life and significantly enhance post-earthquake functionality in critical structural connections. Full article

This study investigates the effectiveness of an environmentally friendly coating in mitigating corrosion and preserving the mechanical properties of carbon steel, copper, and aluminium. The coated and uncoated samples were subjected to a 20-day immersion in 5% NaCl solution. Corrosion behaviour was assessed using Linear Sweep Voltammetry (LSV), Open Circuit Potential (OCP), and Electrochemical Impedance Spectroscopy (EIS), while mechanical performance was evaluated through tensile testing. The coating’s thickness, surface roughness, water contact angle, and composition were characterised to understand its protective behaviour. The results show that the coating significantly reduced corrosion rates, with carbon steel exhibiting a 99.99% inhibition efficiency and aluminium showing the lowest corrosion rate due to a synergistic effect between the coating and native oxide layer. Mechanical testing revealed that coated carbon steel retained higher tensile strength and stiffness compared to its uncoated counterpart, while aluminium showed notable recovery in elastic modulus. Copper displayed minimal mechanical changes due to its inherent corrosion resistance. This work highlights the potential of eco-friendly coatings in enhancing both the corrosion resistance and mechanical durability of metallic materials in aggressive environments. Full article

Predicting buckling in large-scale composite structures is hindered by the need for highly detailed Finite Element (FE) models, which are computationally expensive and impractical for early-stage design iterations. This study introduces a macromodelling buckling framework that reduces those models to plate-level size without sacrificing accuracy. An equivalent bending stiffness matrix is derived from strain–energy equivalence, rigorously retaining orthotropic in-plane terms, bending–extensional coupling, and—crucially—the eccentricity of compressive loads about an unsymmetrically stiffened mid-plane, effects overlooked by conventional Parallel-Axis smearing. These stiffness terms contribute to closed-form analytical solutions for homogeneous orthotropic plates, providing millisecond-level evaluations ideal for gradient-based design optimisation. The method is benchmarked against detailed FE simulations of panels with three to ten stringers under longitudinal and transverse compression, showing less than 5% deviation in critical load prediction. Its utility is demonstrated in the sizing optimisation of the upper cover of a scaled Airbus A330 composite wing-box, where the proposed model explores the design space in minutes on a standard workstation, orders of magnitude faster than full FE analyses. By combining analytical plate theory, enhanced smearing, and rapid optimisation capability, the framework provides an accurate, ultra-fast tool for buckling analysis and the preliminary design of large-scale stiffened composite structures. Full article

Improving the end-of-life performance of polylactic acid (PLA) for food packaging requires strategies that enhance biodegradability, solubility, and dispersibility without compromising essential material properties. PLA-based films were produced by melt extrusion using polyvinylpyrrolidone (PVP) as a hydrophilic modifier, aiming to enhance the water uptake and affinity of PLA, which may potentially lead to faster environmental degradation. Two PVPs with distinct molar masses at varying concentrations were used to investigate their effects on the structural, thermal, mechanical, optical, and barrier behavior of the films. Thermal analysis revealed a slight depression in glass transition temperature, more evident in blends with low-molecular-weight PVP10, indicating increased chain mobility and partial miscibility. A two-step degradation process with extended thermal decomposition profiles was observed upon the inclusion of PVP. SEM and ATR-FTIR analyses confirmed enhanced dispersion and non-covalent interactions in PVP10-based blends, in contrast to the pronounced phase separation and micro-voids observed in PVP40-based systems. Mechanically, films containing 5 and 10 wt.% of PVP10 retained tensile strength and stiffness, whereas PVP40 led to embrittlement. Optical properties were modified by increasing the PVP content, resulting in greater opacity and color differences, which potentially offer benefits for light-sensitive packaging. Altogether, PLA films containing 5 and 10 wt.% of PVP10 demonstrated the most favorable balance between water affinity-oriented design and packaging-relevant performance. Full article

Slab-replacement operations are crucial for restoring deteriorated CRTS I slab ballastless tracks to operational standards. This study investigates the structural implications of the operation by evaluating the strength characteristics and material properties of track components both prior to and following replacement. Apparent strength was measured using rebound hammer tests on three categories of slabs: retained, deteriorated, and newly installed track slabs. In addition, samples of old and new filling resins were collected and tested to determine their elastic moduli. These empirical data were subsequently used to develop a refined finite-element model that captures both pre- and post-replacement conditions. Under varying temperature loads, disparities in component performance were found to significantly affect stress distribution. Specifically, before replacement, deteriorated track slabs exhibited 10.74% lower strength compared to adjacent retained slabs, whereas, after replacement, new slabs showed a 25.26% increase in strength over retained ones. The elastic modulus of old filling resin was measured at 5.19 kN/mm, 35.13% below the minimum design requirement, while the new resin reached 10.48 kN/mm, exceeding the minimum by 31.00%. Although the slab-replacement operation enhances safety by addressing structural deficiencies, it may also create new weak points in adjacent areas, where insufficient stiffness results in stress concentrations and potential damage. This study offers critical insights for optimizing maintenance strategies and improving the long-term performance of ballastless track systems. Full article

The aerospace industry is increasingly turning to composite materials due to their exceptional strength, stiffness, and beneficial physical properties. However, increased reliance on carbon fibre composites has substantial environmental implications, particularly concerning waste management. Recycling these materials is a potential solution to these sustainability issues, provided the recycled fibres retain adequate mechanical strength and durability. This study evaluates the mechanical capabilities of recycled carbon fibres in a scaled-down aircraft spar model (AMT-600 GURI), contrasting them with the capabilities of conventional spars. The primary objective is to ascertain whether recycled composites can fulfil the stringent structural requirements of aerospace applications, employing both simulation and experimental validation methods. The recycled carbon fibre composites were manufactured using hand lay-up and vacuum bagging techniques, and their properties were validated through rigorous tensile and compressive strength testing. These validated results were then used to inform a finite element model developed in HyperWorks software. Simulations revealed that the recycled spar achieved maximum stress values of 3.87 MPa under lift forces, a slight increase of +8.95% compared to the original spar, and 55.05 MPa under drag forces, a significant improvement of +36%. Aerodynamic evaluations further confirmed the structural resilience of the recycled spar, with displacement measurements of 141.4 mm for lift and 504.8 mm for drag, closely aligning with the original spar’s performance. In summary, this study demonstrates that recycled carbon fibre composites can serve as effective substitutes for traditional aerospace materials, thereby supporting sustainability initiatives without compromising performance. The outlined approach provides a reliable framework for incorporating recycled materials. Full article

With the accelerated development of urban underground spaces, prefabricated tunnel linings have become a research focus due to their advantages in construction efficiency and cost effectiveness. However, issues such as stress concentration at joints and insufficient overall stability hinder their broader application. This study investigates a cut-and-cover prefabricated tunnel project in the Chongqing High-Tech Zone through scale model tests and numerical simulations to systematically compare the mechanical behaviors of cast-in situ linings and three-segment prefabricated linings under surrounding rock loads. The experimental results show that the ultimate bearing capacity of the prefabricated lining is 15.3% lower than that of the cast-in situ lining, with asymmetric failure modes and cracks concentrated near joint regions. Numerical simulations further reveal the influence of joint stiffness on structural performance: when the joint stiffness is 30 MN·m/rad, the bending moment of the segmented lining decreases by 37.7% compared to the cast-in situ lining, while displacement increments remain controllable. By optimising joint pre-tightening forces and stiffness parameters, prefabricated linings can achieve stability comparable to cast-in situ structures while retaining construction efficiency. This research provides theoretical and technical references for the design and construction of open-cut prefabricated tunnel linings. Full article

This study investigates the effects of repeated mechanical recycling on the structural, thermal, mechanical, and aesthetic properties of poly(butylene succinate) (PBS), a commercially available bio-based and biodegradable aliphatic polyester. PBS production scraps were subjected to five consecutive recycling cycles through semi-industrial extrusion compounding followed by injection molding to simulate realistic mechanical reprocessing conditions. Melt mass-flow rate (MFR) analysis revealed a progressive increase in melt fluidity. Initially, the trend of viscosity followed the melt flow rate; however, increasing the reprocessing number (up to 5) resulted in a partial recovery of viscosity, which was caused by chain branching mechanisms. The phenomenon was also confirmed by data of molecular weight evaluation. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) confirmed the thermal stability of the polymer, with minimal shifts in glass transition, crystallization, and degradation temperatures during the reprocessing cycles. Tensile tests revealed a slight reduction in strength and stiffness, but an increase in elongation at break, indicating improved ductility. Impact resistance declined moderately from 8.7 to 7.3 kJ/m² upon reprocessing; however, it exhibited a pronounced reduction to 1.8 kJ/m² at −50 °C, reflecting brittle behavior under sub-ambient conditions. Despite these variations, PBS maintained excellent color stability (ΔE < 1), ensuring aesthetic consistency while retaining good mechanical and thermal properties. Full article

In advanced structural applications—aerospace and automotive—fiber-laminated composite (FRP) materials are increasingly used for their superior strength-to-weight ratios, making the reliability of their mechanical joints a critical concern. Mechanically fastened joints play a major role in ensuring the structural stability of FRP Composite structures; however, accurately predicting their failure behavior remains a major challenge due to the anisotropic and heterogeneous nature of composite materials. This paper presents a progressive damage modeling approach to investigate the failure modes and joint strength of mechanically fastened carbon fiber-laminated (CFRP) composite joints. A 3D constitutive model based on continuum damage mechanics was developed and implemented within a three-dimensional finite element framework. The joint model comprises a composite plate, a steel plate, a steel washer, and steel bolts, capturing realistic assembly behavior. Both single- and double-lap joint configurations, featuring single and double bolts, were analyzed under tensile loading. The influence of clamping force on joint strength was also investigated. Model predictions were validated against existing experimental results, showing a good correlation. It was observed that double-lap joints exhibit nearly twice the strength of single-lap joints and can retain up to 85% of the strength of a plate with a hole. Furthermore, double-lap configurations support higher clamping forces, enhancing frictional resistance at the interface and load transfer efficiency. However, the clamping force must be optimized, as excessive values can induce premature damage in the composite before external loading. The stiffness of double-bolt double-lap (3DD) joints was found to be approximately three times that of single-bolt single-lap (3DS) joints, primarily due to reduced rotational flexibility. These findings provide useful insights into the design and optimization of composite bolted joints under tensile loading. Full article

Seismic isolation systems are an effective passive protection strategy that decouples structures from ground motion. Their performance depends heavily on the elastomeric materials used, which must retain mechanical integrity under environmental stressors. In recent years, low-cost isolators made from natural and recycled rubber have gained attention as an affordable solution for protecting low-rise buildings in seismic-prone developing regions, particularly due to their environmental benefits and ease of installation. However, their long-term performance under real environmental conditions remains insufficiently explored. This study evaluates the durability of two types of low-cost seismic isolators: those made with natural rubber matrices (UN-FREIs) and those that use recycled rubber matrices (UR-FREIs). Mechanical tests were carried out before and after exposing the specimens to accelerated aging and low-temperature conditions, simulating environmental degradation. Changes in stiffness, damping, and energy dissipation were analyzed for both the rubber matrix and the scaled isolator prototypes. The findings indicate that both materials degrade over time, with recycled rubber exhibiting greater susceptibility to stiffness loss at low temperatures. Nevertheless, both isolator types maintained functional performance after aging, supporting their applicability in regions with moderate thermal variations. These results provide evidence for the feasibility of adopting low-cost isolators in low-rise buildings exposed to variable climates, while also emphasizing the need for standardized durability protocols during the design stage. Full article

The development of biocompatible, conductive hydrogels via direct ink writing (DIW) has gained increasing attention for strain sensor applications. In this work, a hydrogel matrix composed of polyvinyl alcohol (PVA) and κ-carrageenan (KC) was formulated and enhanced with polyvinylidene fluoride (PVDF) and silver nanoparticles (AgNPs) to impart piezoelectric properties. The ink formulation was optimized to achieve shear-thinning and thixotropic recovery behavior, ensuring printability through extrusion-based 3D printing. The resulting hydrogels exhibited high water uptake (~280–300%) and retained mechanical integrity. Rheological assessments showed that increasing PVDF content improved stiffness without compromising printability. Electrical characterization demonstrated that AgNPs were essential for generating piezoelectric signals under mechanical stress, as PVDF alone was insufficient. While AgNPs did not significantly alter the crystalline phase distribution of PVDF, they enhanced conductivity and signal responsiveness. XRD and SEM-EDX analyses confirmed the presence and uneven distribution of AgNPs within the hydrogel. The optimized ink formulation (5% PVA, 0.94% KC, 6% PVDF) enabled the successful fabrication of functional sensors, highlighting the material’s strong potential for use in wearable or biomedical strain-sensing applications. Full article

In structural health monitoring, visual inspection remains vital for detecting damage, especially in concealed elements such as columns and beams. To improve damage localization, many studies have investigated and implemented deep learning into damage detection frameworks. However, the practicality of such models is often limited by their computational demands, and the relative accuracy may suffer if input features lack sensitivity to localized damage. This study introduces an efficient method for estimating damage locations and severity in buildings using a neural network array. A synthetic dataset is first generated from a simplified building model that includes floor flexural behavior and reflects the target dynamics of the structures. A dense, single-layer neural network array is initially trained with full floor accelerations, then pruned iteratively via the Lottery Ticket Hypothesis to retain only the most effective sub-networks. Subsequently, critical event measurements are input into the pruned array to estimate story-wise stiffness reductions. The approach is validated through numerical simulation of a six-story model and further verified via shake table tests on a scaled twin-tower steel-frame building. Results show that the pruned neural network array based on the Lottery Ticket Hypothesis achieves high accuracy in identifying stiffness reductions while significantly reducing computational load and outperforming full-input models in both efficiency and precision. Full article

Iraq’s extreme summer temperatures pose critical challenges to pavement durability, as conventional asphalt mixtures often fail under prolonged thermal stress. This paper provides a comparative evaluation of the high-temperature performance of unmodified (40/50 penetration grade) and polymer-modified (PG 76-10) asphalt mixtures for the asphalt course layer. Marshall stability, flow, and stiffness were measured at elevated temperatures of 60 °C, 65 °C, 70 °C, and 75 °C after short-term (30 min) and extended (24 h) conditioning. Results show that while both mixtures experienced performance degradation as the temperature increased, the polymer-modified mixture consistently exhibited superior thermal resistance, retaining approximately 9% higher stability and 28% higher stiffness, and displaying 18% lower flow deformation at 75 °C compared to the unmodified mixture. Stability degradation rate (SDR), stiffness degradation rate (SiDR), and flow increase rate (FIR) analyses further confirmed the enhanced resilience of PG 76-10, showing nearly 39% lower FIR under thermal stress. Importantly, PG 76-10 maintained performance within specification thresholds under all tested conditions, unlike the conventional 40/50 mixture. These findings emphasize the necessity of adapting mix design standards to regional climatic realities and support the broader adoption of polymer-modified asphalt binders to enhance pavement service life in hot-climate regions like Iraq. Full article

Shear lag stresses increase significantly in cracked concrete box girders; however, most existing models assume intact sections and are, therefore, unsuitable for rapid field diagnosis. This study integrates a stepped stiffness model with deflection influence lines to accurately capture the mechanical response of damaged, simply supported box girders. Regions containing flexural cracks are assigned a reduced bending stiffness ${EI}^{\prime }$, whereas intact zones retain the original stiffness $EI$. A closed-form stiffness-reduction coefficient $\phi ={EI}^{\prime }/EI$ is obtained from crack geometry and, independently, from the second derivative of the deflection influence line. Embedding $\phi$ in a variational shear lag formulation yields explicit expressions for flange displacement and normal stress without numerical iteration. This approach is validated by finite element simulations of a plexiglass scale model with four preset damage levels and by a load test on a 30 m prestressed concrete box girder bridge. Field measurements show that midspan stiffness decreased to 81% of the as-built value; the proposed method reproduces this value with a deviation of 3%. Predicted upper-flange stresses differ from measured values by 5.7–13.6% and from finite element results by less than 10% for damage ratios up to 40%. The second derivative of the influence line difference exhibits a distinct peak at the cracked region, accurately localizing the damage. Compared with classical formulas, the proposed model (i) is fully closed-form, (ii) links global deflection data to local shear lag stresses, and (iii) delivers conservative estimates suitable for routine bridge assessment. Full article

Hamstring strain injuries (HSIs) are the most common time loss injury sustained in male Australian Football League (AFL) athletes, causing significant financial cost, time cost, and impaired team and individual performance. In a squad of 42 players, HSIs accounted for 4.86 new injuries sustained by players per club per AFL season in 2020. This is consistent with injury reporting over the last decade in AFL, despite best efforts to reduce the rate. This scoping review sought to firstly identify the reported hamstring injury prevention risk factors in elite AFL, discern the impact of these factors, and map the gaps in the current literature using a biopsychosocial understanding of injury prevention. The scoping review process was based on the Askey and O’Malley framework. Five relevant online databases (MEDLINE, Proquest, CINAHL, SPORTdiscuss, and EMBASE) were systematically searched using a series of Boolean and operator terms following the PRISMA-ScR protocol using the criteria: (1) assessing male professional/elite athletes in AFL; (2) written in English and peer-reviewed; (3) full text available; and (4) published after 2006. Only manuscripts that fit the search terms and inclusion criteria were retained in the scoping review. Following an initial search, 246 potential studies were identified, with 12 studies meeting the inclusion criteria after full-text screening. The risk factors examined were subclassified into modifiable and non-modifiable categories. Modifiable factors include high-speed running exposure, gluteus medius activation, eccentric hamstring strength, shorter bicep femoris fascicle length, use of interchange, and hamstring stiffness. Non-modifiable factors include previous history of HSI and limb injury, age, and size of injury on MRI. This scoping review highlights the need for continued monitoring of high-speed running volumes as rapid increases in completed distances present as a substantial risk factor. The modifiable mechanistic risk factors of eccentric hamstring strength and hamstring stiffness were identified as important components of player screening to reduce the risk of future HSI. Risk factors identified throughout will help develop comprehensive injury profiling for athletes. Further research is warranted to develop a holistic approach to injury profiling. Full article