Search Results (7,011)

This study investigates the cyclic behaviour of demountable steel–concrete composite extended end-plate reduced web section (RWS) connections for the first time, aiming to facilitate post-seismic beam replacement. A validated high-fidelity finite element (FE) model was developed to analyse 285 FE models, evaluating response characteristics based on the Ibarra–Medina–Krawinkler model. Key parameters, including the influence of composite action over the web opening, web opening diameter, and end-distance, were considered. Findings indicate that RWS connections with medium to large web openings experience cyclic strength degradation while remaining compliant with American and European seismic standards. Additionally, bolted shear studs yielded a more stable and predictable contribution to the connection’s strength up to 5%, outperforming traditional welded studs in consistency. This research emphasises the importance of aligning web opening size and location with capacity design ratios between connection components for acceptable seismic performance, proposing specific web opening sizes and locations to enhance structural resilience. Full article

In nature, organisms have evolved unique structures that feature low weight, high strength, and damage resistance. The Eurasian eagle-owl serves as a representative example, with specialized feather architectures that enable stable flight in intense and turbulent airflow conditions. Herein, driven by classical design layup guidelines, and inspired by the distinctive fiber architecture of the feather shaft cortex, we propose a regionally tailored layup (RTL) design to enable mass-efficient composite beams with high load-bearing capacity and enhanced damage tolerance. The feather shaft reference lay-up rectangular beam (FSRB) adopts the RTL, and a flange overlap is introduced to preserve the integrity and strength of the flange–web interface; it is then manufactured using inner–outer matched molds in conjunction with vacuum bag molding. Three-point bending shows that the FSRB achieves a flexural strength of 180 MPa and a flexural modulus of 12.1 GPa. Relative to conventional axial (ALRB), Cross-ply (CPRB), single-helix (SLRB), and quasi-isotropic (QLRB) lay-up rectangular beams, the FSRB improves strength by 59.5%, 46.6%, 26.8%, and 21.2%, and increases modulus by 81.7%, 34.7%, 25.1%, and 10.8%, respectively. FEA and SEM observations confirm an RTL architecture in the rectangular beams, characterized by differentiated fiber arrangements in the flange and web. Flanges with an axially dominated layup provide high initial flexural strength and stiffness. The web, formed by a crossed-ply/axial hybrid layup, provides transverse support and redirects crack/delamination growth, thereby promoting progressive failure and enhancing energy dissipation. Overall, this RTL design enables concurrent improvements in load-carrying capacity and damage tolerance. This study offers a design perspective for high-performance load-bearing components. Full article

Delamination is a critical failure mode in composite laminates that degrades the structural performance and load-carrying capacity. This study investigates the improvement of Mode I and Mode II interlaminar fracture toughness of carbon fiber-reinforced polymer (CFRP) laminates through the interleaving of electrospun thermoplastic nanofiber mats. Nanofiber veils were inserted between carbon fiber plies to enhance resistance to delamination under tensile opening (Mode I) and in-plane shear (Mode II) loading. The effects of nanofiber interleaving were evaluated using double cantilever beam (DCB) tests for Mode I and end notch flexure (ENF) tests for Mode II. Both tests were conducted on a symmetric quasi-isotropic laminate [-45/45/90/0₅]_s containing a thick unidirectional 0° ply at the mid-plane. Thermally induced residual stresses resulting from mismatches in ply coefficients of thermal expansion and unsymmetric arm lay-ups were accounted for in the experimental determination of fracture toughness. These stresses, generated during cooling from the cure temperature, influence the effective strain energy release rate and were included in the fracture toughness calculations to ensure accurate toughness evaluation and consistency with numerical predictions. The results demonstrate improved delamination fracture toughness, highlighting the potential of nanofiber interleaving for aerospace and wind energy applications. Full article

Structural displacement monitoring is an essential component of structural health monitoring of bridges, providing valuable information for performance evaluation, numerical model validation, and damage detection. While conventional contact-based sensors provide high accuracy, their installation is often complex, costly, and disruptive to traffic. Recent developments in unmanned aerial vehicle (UAV) platforms and vision-based measurement techniques offer a flexible, non-contact alternative; however, platform motion remains a major source of uncertainty. This study evaluates the accuracy and operational feasibility of UAV-based homography for static and dynamic displacement monitoring. The proposed approach is validated through three complementary experimental campaigns: a controlled calibration field test, a beam static load test, and bridge monitoring under traffic loading, with direct comparison to LVDT and RTS measurements. Under controlled conditions, sub-millimetre vertical precision was achieved, with RMSE values below 0.3 mm. In full-scale bridge applications, the method captured traffic-induced displacement trends with errors generally within 1–2 mm compared to LVDT data and with RMSE values below 1.4 mm. The results demonstrate that, when appropriate reference point configuration and imaging geometry are ensured, UAV-based homography provides a practical and sufficiently accurate solution for bridge displacement monitoring which is especially important in applications where sensor installation is difficult or unsafe. Full article

The effective bending stiffness formula for cross-sections of timber–concrete composite (TCC) beams was derived under semi-sinusoidal loading condition in Eurocode 5; however, this formula does not account for the non-uniform distribution of bending stiffness along the span. This limitation prevents it from characterizing the mechanical behavior under real loading conditions, which could potentially compromise the safety and serviceability of the structural design. To investigate the distribution pattern of bending stiffness, differential segment analysis was conducted, incorporating interfacial slip effects. A governing differential equation for curvature was established, and the resulting curvature distribution was used to compute deflections by means of the conjugate beam method. The results demonstrate that the bending stiffness distribution depends critically on shear connector arrangement and loading conditions. Under third-point loading, the bending stiffness monotonically decreases from the mid-span to the load application points and increases toward the supports. Under uniform loads, bending stiffness peaks at the mid-span and declines gradually toward the supports. Reducing shear connector spacing enhances composite action while amplifying bending stiffness non-uniformity. Experimental validation confirms that both the conjugate beam method (using analytical curvature solutions) and the simplified approach in Eurocode 5 achieve 99% average accuracy in predicting the mid-span deflection of TCC beams. In addition, careful attention must be paid to the deflection values at loading points, particularly when the loading position is close to the supports. Full article

Multichannel vortex beams serve as an essential physical source for enabling multi-spot laser processing and high-dimensional spatial multiplexing communications. We demonstrate a compact, flexibly tunable multichannel vortex beam generator using spatially structured bidirectional two-color pump vortex four-wave mixing in a single ¹³³Cs vapor cell. To enhance spatial multiplexing, both sides of the cell are utilized. By engineering the propagation directions and frequencies of five input beams, we establish a nonlinear interaction region that supports 16 concurrent phase-matching conditions, thereby enabling the parallel generation of up to eight vortex channels. The orbital angular momentum of the output beams follows deterministic algebraic rules, allowing for programmable control via tailored input orbital angular momentum combinations. Moreover, the channel count can be linearly tuned by selectively deactivating pumps—each switched-off pump reduces the number of output channels by two. This flexible control over orbital angular momentum states, together with channel count and spatial arrangement, establishes a highly integrated platform for on-demand vortex generation. This work highlights the potential of spatially bidirectional structured pumping in atomic vapor to expand optical dimensionality and enhance multiplexing capacity, paving the way toward multidimensional communications, quantum networks, and integrated photonics. Full article

While steel sheets are an effective strengthening technique for existing structures, experimental evidence on galvanised steel sheets is limited, necessitating their evaluation as a durable and cost-effective solution for the flexural strengthening of reinforced concrete (RC) beams. This study analyses the influence of external reinforcement using galvanised steel sheets applied to RC beams. The structural behaviour of the specimens was assessed through flexural tests, with monotonic loading applied at one-third and two-thirds of the effective span, in accordance with ASTM C78 guidelines. In addition, an analytical model was formulated to capture the non-linear behaviour of concrete, reinforcing steel, and galvanised steel sheets. The results indicate that beams strengthened with external reinforcement exhibit an increase in load-bearing capacity of up to 69% in the elastic range, together with significant improvements in ductility of up to 22%. Moreover, the use of vertical U-wrap sheets and anchor bolts enhances the bond between the sheets and the concrete, thereby reducing the risk of premature debonding. Overall, the findings confirm that the use of galvanised steel sheets is an effective and practical strengthening technique for improving the flexural performance of RC beams. Full article

We propose a unmanned aerial vehicle (UAV)-assisted integrated sensing, communication, and jamming (U-ISJC) framework, in which a multifunctional UAV first detects the sensing target to obtain sensing information, and subsequently transmits the information to communication users via a unified beam in the presence of multiple eavesdroppers. To avoid functional conflicts, a time slot frame structure is designed for the UAV’s multifunctional capabilities, enabling communication, sensing, and jamming tasks within each timeslot. The time slot allocation factor dynamically adjusts based on the UAV’s flight trajectory for efficient UAV resource utilization. Additionally, to prevent security rate leakage caused by eavesdroppers, a jamming beam is added to serve both jamming and sensing functions. Our objective is to maximize the the worst-case total secure data transmission rate by jointly optimizing sub-time slot allocation, beamforming, and UAV trajectory. To address this problem, we propose a joint optimization algorithm that adopts the concave–convex procedure (CCCP) technique and semi-definite relaxation (SDR), under the block coordinate descent (BCD) framework. The simulation results show that compared with the baseline scheme, the proposed algorithm substantially improves the communication security rate while ensuring the quality of communication and sensing. Full article

In recent decades, the reliability and safety of large engineering structures have become a critical issue due to failures caused by undetected micro-level deformations. Fiber-optic strain sensors, especially Fiber Bragg Grating (FBG) and interferometric systems, are widely used in structural health monitoring (SHM); however, their standard sensitivity is often insufficient for early detection of nano-strain level damage. This paper presents a comparative analysis and system-level optimization of the main sensitivity enhancement methods, including mechanical amplification, functional coatings and composite embedding, interferometric schemes, and advanced spectral signal processing. Analytical modeling and numerical simulations were performed. It is shown that flexure-beam amplifiers provide a stable sensitivity gain of 2.1–4.8, whereas lever-type mechanisms achieve higher amplification (5.6–9.3) at the cost of dynamic degradation. Functional coatings increase the strain transfer coefficient from 0.62 to 0.68 to 0.91–0.97, but introduce temperature-induced errors up to 1.5–2.0 µε. Interferometric systems can detect strains at the 10⁻⁸ level but exhibit high temperature cross-sensitivity. Advanced spectral processing reduces the Bragg wavelength estimation error by 8–15 times, improving the equivalent strain resolution to (2–5) × 10⁻⁸. Based on these results, an optimized integrated approach combining moderate mechanical amplification (2.5–3.5), improved strain transfer (η ≈ 0.85–0.92), and efficient spectral processing is proposed. This improves the equivalent strain resolution from 1 × 10⁻⁶ to (1.5–3.0) × 10⁻⁸ while keeping temperature-induced errors within 15–25% and limiting the computational load increase to 2–3 times. The proposed solution is suitable for long-term monitoring of large engineering structures. Full article

Topological optimization has established itself as an efficient tool for the design of highly complex structures and the rational use of materials, especially in problems involving multiple constraints and conflicting objectives. This work presents a new multi-material topological optimization approach based on the ESO smoothing method (SESO), formulated as a multi-objective optimization problem in a MATLAB R2021a environment. The multi-objective formulation simultaneously considers the minimization of the maximum von Mises equivalent stress (or minimum principal stress) and the maximum displacement, which are fundamental criteria for structural engineering design. The proposed methodology also incorporates a reliability analysis using the First-Order Reliability Method (FORM), modeling uncertainties associated with the applied force, volume fraction, and modulus of elasticity through normal and lognormal probability distributions, with a target reliability index of ${\beta }_{target}=3.0$. The consistency of the reliability analysis was evaluated using Monte Carlo simulations, validating the reliability indices obtained via FORM. The approach was applied to two classical three-dimensional numerical examples: a cantilever beam under base and center loads and an MBB beam, considering two widely used engineering materials, steel and concrete. The results indicate improved multi-material distribution in the design domain and greater structural robustness against unfavorable loading planes, variations in the modulus of elasticity, and volume constraints imposed by FORM. Furthermore, the minimum yield stress of steel (${\sigma }_y^{min}$) and the compressive strength of concrete ($f_{ck}^{min}$) were calibrated, representing the minimum material strengths required to resist the maximum von Mises stress in steel and the minimum principal stress (${\sigma }_3$) in concrete, ensuring the target reliability index is achieved. This method, thus, highlights the integration of SESO with multi-material, multi-objective, and reliability-based optimization as a consistent, robust, and practically relevant strategy with potential for future applications in structural engineering projects. Full article

Prediction of fatigue failure in concrete structures remains a major challenge due to progressive material degradation. Reliable prediction, therefore, requires modeling the 3D heterogeneous microstructure of concrete to explain the underlying mechanisms governing fatigue failure. While such mesoscale models can reliably predict the fatigue-induced fracture mechanisms, the identification of the associated material parameters remains a significant challenge due to the high-dimensional parameter space introduced by the model. The key challenge addressed in this study is to capture microcrack initiation and coalescence under fatigue loading, using a model capable of representing fracture process: crack initiation, crack propagation, and final failure. Firstly, concrete domain is discretized into Voronoi cells, enabling explicit representation of aggregates and mortar by randomly assigning cohesive links connecting Voronoi cells as aggregates and mortar. After this, mortar links are modeled as coupled damage–plasticity 3D Timoshenko beam elements with nonlinear kinematic hardening and isotropic softening introduced using embedded discontinuity formulation, enabling fracture Modes I–III, whereas aggregate links are modeled as elastic 3D Timoshenko beam elements. The model efficiency is additionally reinforced by using surrogate model approach, with corresponding material parameter identification carried out by multi-objective Bayesian optimization framework to reproduce experimental results. The performance of the proposed model is illustrated by reproducing experimental results obtained from concrete cube compression test and three-point bending test under low-cycle fatigue loading, where the errors between experimental and numerical results are reduced by 82% (stress) and 88% (energy) for the cube test and by 86% (force) and 93% (energy) for the bending test, relative to the initial dataset error. Full article

The strengthening of reinforced concrete (RC) beams requires repair systems that can enhance strength, stiffness, and energy dissipation without significantly increasing self-weight or compromising durability. This study explores the structural response of RC beams strengthened using an integrated shear–flexure system combining near-surface-mounted carbon fiber-reinforced polymer (NSM-CFRP) ropes and steel-reinforced geopolymer overlays in the compression zone. Monotonic three-point bending tests were performed on two RC beam specimens, one unstrengthened control and one strengthened beam, to obtain preliminary observations of load–deflection behavior, stiffness, ductility, and energy absorption. The strengthened specimen exhibited increases in ultimate load (28.6%), stiffness (13.6%), and energy absorption (7.65%) relative to the control beam, suggesting the potential for effective composite action between the CFRP ropes and geopolymer material. A three-dimensional nonlinear finite element model was developed using ATENA to support interpretation of the experimental response, incorporating detailed constitutive models for concrete, steel reinforcement, and CFRP ropes. The numerical predictions showed reasonable agreement with the experimental results. Within the limitations of the test matrix, the results indicate that the proposed dual strengthening system may offer a viable and sustainable approach for enhancing the shear–flexural performance of RC beams. Full article

Diagnostic imaging is essential in veterinary practice, and cone-beam computed tomography (CBCT) has emerged as a promising tool to complement radiography. This study aimed to optimize the image quality of a novel multimodality veterinary X-ray prototype integrating direct digital radiography, fluoroscopy and CBCT, and to assess its potential clinical applications, focusing on the CBCT component. The study was conducted in three phases: optimization of CBCT image quality using postmortem samples, comparison of CBCT and 16-slice multidetector CT (MDCT) images of four cadavers (two dogs and two cats), and potential clinical applications in 24 live patients. Comparative evaluation in postmortem scans revealed that CBCT achieved equal quality in 65% of bone compared to MDCT and a slightly inferior quality in 90% of soft-tissue structures using the bone reconstruction protocol, with beam hardening as the main limiting factor. Clinical validation showed that CBCT was particularly useful for identifying small fractures and mineralized structures, providing diagnostic information not clearly visible on radiographs. Integration of radiography, fluoroscopy, and CBCT in a single device facilitated workflow and allowed a more precise diagnosis in most of the patients examined with the prototype, which demonstrated promising diagnostic performance in small-animal and exotic veterinary practice. Full article

This study used finite element simulation and theoretical analysis to predict the crack distribution patterns that may occur during the shrinkage cracking process of rectangular timber beams. Based on the predictions, experimental specimens with six typical crack distribution patterns (I–VI) were designed. Subsequently, a four-point bending test method was employed to conduct large-sample size fracture tests on a total of 1200small-sized Pinus sylvestris var. mongolica specimens, quantifying the effects of the crack depth, location, and distribution patterns on the specimens’ load-bearing capacity. The results indicate that when multiple cracks exist in a timber beam, their collective effect is not a simple superposition of individual cracks but a spatial distribution coupling effect. Both the depth and location of the cracks play crucial roles in their interaction. This study introduces three coefficients for evaluating the influence of cracks on timber beams, namely the load-bearing capacity coefficient (R), the decline ratio of load-bearing capacity (D), and the comprehensive crack-influence coefficient (β), which can effectively quantitatively evaluate crack damage effects. The framework established in this study, which links shrinkage crack characteristics with the load-bearing capacity of timber beams, along with the experimental data provided, can serve as a reference for the safety evaluation and scientific maintenance of historical timber components and modern timber structures with shrinkage cracks. Full article

Prediction of the ultimate moment capacity (Mu) of BFRP-reinforced concrete beams is complicated by nonlinear parameter interactions and the linear-elastic response of BFRP, reducing the accuracy of conventional design models. This study develops an optimized machine learning (ML) framework incorporating random forest, extra trees, gradient boosting, adaboost, bagging, support vector regression, histogram-based gradient boosting, and ensemble voting and stacking strategies for reliable prediction of the Mu of BFRP-reinforced concrete beams. A comprehensive database of material, geometric, reinforcement, and BFRP mechanical parameters was analyzed, and model performance was evaluated using an 80/20 train–test split and 10-fold cross-validation based on R², RMSE, MAE, and MAPE. The stacking regressor demonstrated superior predictive performance, achieving an R² of 0.999 (RMSE = 0.590) in training and an R² of 0.988 (RMSE = 2.487) in testing, indicating excellent robustness and strong generalization capability in predicting Mu. Furthermore, interpretability analyses based on SHAP, PDP, ALE, and ICE demonstrate that span length (L) and beam depth (h) constitute the governing parameters in the prediction of Mu. Unlike prior studies focused mainly on predictive accuracy, this work proposes an optimized and interpretable stacking ensemble framework that integrates explainable AI with classical flexural mechanics for physically consistent and reliable prediction of the ultimate moment capacity of BFRP-reinforced concrete beams. Full article