Search Results (358)

The nominal maximum aggregate size (NMAS) plays a critical role in determining the mechanical performance of cement-stabilized macadam (CSM), yet its meso-mechanical influence mechanism remains insufficiently understood. In this study, three skeleton-dense CSM mixtures with different NMAS values were designed, and a combined experimental–numerical approach was adopted to investigate the macro- and meso-scale mechanical behavior. Uniaxial compression tests and aggregate crushing value tests were conducted to evaluate strength development and load-transfer characteristics, while a three-dimensional discrete element method (DEM) model incorporating realistic aggregate morphology was established to analyze the evolution of contact forces and crack propagation. The results show that increasing NMAS significantly improves the mechanical performance of CSM. Compared with CSM-30, the 7-day compressive strength of CSM-40 and CSM-50 increased by approximately 10.3% and 37.3%, respectively. The stress–strain response indicates that mixtures with larger NMAS exhibit higher stiffness and a higher strain. At the meso-scale, a larger NMAS promotes the formation of a more efficient force-chain network dominated by coarse aggregates. Strong contacts were predominantly carried by aggregates larger than 9.5 mm, and in CSM-50, the proportion of strong contacts in the 37.5–53 mm fraction exceeded 90%, indicating that the largest particles likely form the primary load-bearing skeleton. In addition, increasing NMAS delayed crack initiation, reduced crack propagation rate, and decreased the total number of cracks at failure. These findings demonstrate that macroscopic strength improvement is closely associated with meso-scale optimization of the aggregate skeleton and enhanced load-transfer efficiency. This study provides a mechanistic basis for NMAS selection and gradation optimization in semi-rigid base materials. Full article

In layered systems with porous substrates and a dense solid surface, stiffness and strength are inherently coupled through porosity-dependent relations, influencing their load-bearing behaviour. This work presents a systematic methodology for the assessment and design of such layer-substrate systems based on a criterion of balanced material utilization. A dimensionless parameter is defined to characterize the stress state in both components relative to their admissible limits, from which the optimal layer thickness is determined at equal stress levels in both constituents. Stress distributions are calculated using a numerical half-space model for layered contacts and evaluated through material-dependent equivalent stress criteria. The relationship between material utilization and load-carrying capacity is reduced to a scaling factor that combines the influence of porosity-dependent parameters. The approach establishes a direct link between the governing material parameters and structural design variables. Across the investigated parameter range, the utilization rate scales linearly with optimal layer thickness, whereas the load-carrying capacity follows a cubic relation. For a representative Ashby strength scaling coefficient of 𝐶𝜎 = 0.3, for example, a substrate porosity of 90% leads to a scaling factor of 1.6, corresponding to a possible load amplification of 60% relative to the homogeneous reference. Full article

In goafs formed by underground mineral resource extraction, the remaining pillars are often subjected to uniaxial loading at different loading rates, and their mechanical responses and failure mechanisms directly affect the long-term stability of the goafs. This study uses rock-like materials to conduct uniaxial compression tests at loading rates ranging from 0.001 mm/min to 0.05 mm/min, combined with acoustic emission (AE) monitoring, to systematically investigate the effects of loading rate on the mechanical properties, energy distribution, constitutive model, and AE characteristics of the material. The results show that an increase in loading rate significantly enhances the stiffness and strength of the material, promotes a transition in failure mode from a shear–tension composite to tension-dominated, intensifies brittle characteristics, and simultaneously inhibits full crack development and fragments generation. In terms of energy evolution, an increased loading rate enhances the pre-peak total strain energy and elastic strain energy storage but reduces the efficiency of energy dissipation, leading to an intensified mismatch between energy storage and dissipation capacities at peak stress. A damage variable induced by loading rate was proposed, and a damage constitutive model considering the loading rate was established, with the theoretical curves showing good agreement with the experimental data. AE characteristic analysis further reveals that an increase in loading rate causes the crack type to transition from shear-dominated to tension-dominated, and the fluctuating increase in the b-value reflects a reduction in pre-peak fracture scale and a decrease in the degree of material fragmentation. The research findings are expected to deepen the understanding of the damage and failure mechanisms of rock materials under different loading rates, thereby laying a research foundation for the stability assessment of goaf pillars and disaster warning. Full article

Transmission towers, as critical infrastructure in power systems, are frequently threatened by multiple hazards such as strong winds and flood scour. Traditional structural health monitoring methods face limitations in data feedback timeliness and mechanical interpretation, making real-time condition awareness and early warning under disaster scenarios challenging. To address these issues, this paper proposes a digital twin framework for transmission tower structures, integrating Building Information Modeling (BIM), Internet of Things (IoT) technology, and the Finite Element Method (FEM) for structural health monitoring and visual warning under wind loads and flood scour effects. The framework achieves cross-platform collaboration through the FEM Open Application Programming Interface (OAPI) and Python scripts. In the physical domain, fluctuating wind loads are simulated based on the Davenport spectrum, flood scour depth is modeled using the HEC-18 formulation, and foundation constraint degradation is represented through nonlinear spring stiffness reduction. In the FEM domain, dynamic time-history analyses are conducted to obtain structural responses. In the BIM domain, a three-level warning mechanism based on stress change rate (ΔR) is established to achieve intuitive rendering and dynamic feedback of structural damage. A 44.4 m high latticed angle steel tower is employed as the case study for validation. Results demonstrate that the simulated wind spectrum closely matches the theoretical target spectrum, confirming the validity of the load input. A critical scour evolution threshold of 40% is identified, beyond which the first two natural frequencies exhibit nonlinear decay with a maximum reduction of 80.9%. Non-uniform scour induces significant load transfer, with axial forces at leeside nodes increasing from 27 kN to 54 kN. During the 0–60 s wind loading process, BIM visualization accurately captures the full stress evolution from the tower base to the upper structure, showing excellent agreement with FEM results. The proposed framework establishes a closed-loop interaction mechanism of “physical sensing–digital simulation–visual warning”, effectively enhancing the timeliness and interpretability of structural health monitoring for transmission towers under multiple hazards, providing an innovative approach for intelligent disaster prevention in power infrastructure. Full article

Reinforced concrete (RC) structures in marine environments face severe durability challenges due to chloride-induced corrosion. This study investigates the corrosion mechanism and degradation of axial compressive performance in RC columns under the combined effects of sustained loading and corrosion, taking the permanent–temporary integrated RC columns of the Pinglu Canal project as an example. The experimental variables included different sustained load levels and degrees of corrosion. Twelve rectangular RC columns were designed and tested. A specialized setup was developed to simultaneously apply sustained load and induce corrosion to the columns, while monitoring their creep deformation. The columns were subjected to accelerated electrochemical corrosion in a 5% NaCl solution, concurrently under sustained loads of 0, 0.3, and 0.6 times their designed axial compressive capacity, with exposure durations of 0, 30, 60, and 120 days, respectively. The study examined the effects of sustained load level and corrosion degree on the failure mode, concrete creep deformation, and load–displacement curves of the corroded RC columns. The results indicated that sustained loading shortened the duration of concrete expansion deformation and reduced its peak value. Furthermore, the expansion deformation of concrete delayed the creep of corroded columns by 25 to 35 days; after the expansion recovery, the creep rate increased significantly. For corroded columns without sustained loading, the ultimate bearing capacity decreased by 32.0% to 47.8%, with degradations in both stiffness and ductility. The application of sustained loading alleviated the degradation in the ultimate bearing capacity and stiffness of the corroded columns but exacerbated the degradation of their ductility. Finally, considering the effects of concrete expansion deformation and steel corrosion, a predictive model for the creep of RC columns under the coupled action of sustained loading and corrosion was proposed, aiming to provide a theoretical basis for the durability design and maintenance of RC structures in the Pinglu Canal project. Full article

Sandwich structures are increasingly employed in high-performance applications due to their excellent strength-to-weight ratio. However, their mechanical reliability often depends on the structural core, which remains susceptible to failure under shear and flexural loads. Additive manufacturing (AM) enables the design and fabrication of complex, bio-inspired core architectures, such as those derived from Voronoi tessellations, which can potentially enhance energy absorption and mechanical performance. This study investigates the mechanical behavior of PLA-based cellular cores, produced via Fused Filament Fabrication (FFF), under quasi-static and intermediate strain rates (up to 33 s⁻¹). Two infill geometries were compared: a standard cubic pattern and an open Voronoi-based structure inspired by biological morphologies. The results demonstrate strain-rate sensitivity in both configurations, characterized by increased stiffness and peak stress at higher loading rates. While the Voronoi structure exhibited lower maximum strength compared to the cubic pattern, it demonstrated a more gradual post-peak softening, indicating potentially superior energy dissipation capabilities. These findings support the potential of bio-inspired, additively manufactured structures in energy-absorbing applications. Full article

Background: Tendons adapt to mechanical loading by increasing cross-sectional area (CSA), stiffness, and matrix organization, with structural remodeling critical for both rehabilitation and performance. Collagen supplementation has been proposed to enhance this process by supplying key amino acids for collagen synthesis; however, inconsistent results across trials have limited its clinical and athletic application. Methods: A systematic review of randomized controlled trials evaluating collagen supplementation in humans was conducted. PubMed, EMBASE, CINAHL, and Web of Science were searched from database inception through May 2025. Risk of bias was assessed using the PEDro scale (≥6/10 classified as good-to-excellent quality). Due to substantial heterogeneity in supplementation protocols, training modalities, and outcome measures, results were synthesized narratively without meta-analysis. Data extraction included collagen type, dose, training modality, intervention duration, and outcome measures. Results: Of 887 unique citations, eight RCTs (n = 257; ages 18–52; 246 M:11 F) met the inclusion criteria. All studies incorporated resistance or plyometric training (3–15 weeks). Three of four studies reported significantly greater increases in tendon CSA in collagen groups versus placebo. Four studies investigated tendon stiffness and Young’s modulus; the two using higher doses (15–30 g/day) demonstrated significant between-group improvements favoring collagen, while lower-dose studies (~5 g) showed only within-group effects. Muscle strength improved with training in all trials, but no additive effects of collagen were observed. One study reported improvements in eccentric rate of force development and deceleration impulse with collagen, though gross explosive metrics (e.g., jump height) were unaffected. Conclusions: Collagen supplementation (15–30 g) with vitamin C (≥50 mg) may enhance tendon remodeling when combined with high-intensity resistance training (≥70% 1 RM). The current literature suggests strong evidence (GRADE A) for increases in tendon CSA and stiffness, strong evidence (GRADE A) against an effect on muscle strength, and conflicting evidence (GRADE C) for muscle cross-sectional area and physical performance. Limitations include small sample sizes, heterogeneous protocols, and short intervention durations. Full article

To address the prominent problem of early rutting distress in asphalt pavements under heavy-load traffic in China, this study proposes a composite modifier consisting of direct coal liquefaction residue (DCLR), styrene–butadiene–styrene block copolymer (SBS), and styrene–butadiene rubber (SBR). The preparation process and formula were optimized through single-factor experiments and orthogonal tests. Systematic investigations were conducted on its conventional performance, water damage resistance, aging resistance, fatigue performance, rheological properties, and microscopic mechanism, with comparisons made against base asphalt, single DCLR-modified asphalt, SBS-modified asphalt, and SBS/SBR-modified asphalt. The results indicate that the optimal preparation process for the novel composite high-modulus modified asphalt is as follows: DCLR particle size of 0.3 mm, addition in molten state, shear temperature of 170 °C, shear rate of 5000 r·min⁻¹, shear time of 50 min. The optimal formula is 10% DCLR + 3% SBS + 2% SBR + 3% compatibilizer, with the addition sequence of “DCLR → SBS + compatibilizer → SBR”. This asphalt exhibits a softening point of 77.8 ± 2.1 °C, a Brookfield viscosity at 135 °C of 1.928 ± 0.105 Pa·s, and a grading of 5 for adhesion to aggregates; the rutting factor at 64 °C reaches 10.8 ± 0.9 kPa (6.43 times that of the base asphalt), the creep stiffness at −12 °C is 136 ± 12.5 MPa, and the low-temperature limit temperature is −17 °C; the freeze–thaw splitting strength ratio (TSR) is 94.6 ± 1.8%, and both aging resistance and water damage resistance are significantly superior to those of the control group asphalts (p < 0.05). The novel composite high-modulus modified asphalt showed improved overall laboratory performance and may be suitable for heavy-load traffic and complex climatic conditions, however, field validation is needed. Full article

Active support systems are being increasingly applied in the control of large deformation in soft rock tunnels, and exploring the bearing characteristics of prestressed anchor bolts is of great engineering value for improving the long-term stability of tunnel structures. To address the problems of insufficient quantitative characterization of the bearing performance of prestressed anchor bolt support in soft rock tunnels and the difficulty of small-scale model tests in revealing the synergistic bearing law of support and surrounding rock, this study took a 350 km/h double-line high-speed railway tunnel as the prototype and established a large-scale tunnel structure model test system to conduct comparative tests under three working conditions: unsupported, ordinary bolt support, and prestressed anchor bolt support. By monitoring the tunnel failure process and mechanical response of the support structure throughout the test, the failure modes, bearing capacity, deformation characteristics, and axial force distribution of anchor bolts of tunnels under different support forms were systematically analyzed to quantitatively reveal the active support mechanism and bearing strengthening effect of prestressed anchor bolts. The results show that the design bearing capacity of the tunnel model with prestressed anchor bolt support is increased by 127.3% and 31.6% compared with that of the unsupported and ordinary bolt support models, and the ultimate bearing capacity is increased by 120.0% and 43.5%, respectively. Its secant stiffness in the initial loading stage reaches 80.0 kPa/mm, which is five times that of the ordinary bolt support and can effectively restrain the early plastic deformation of the surrounding rock. When the design bearing capacity is reached, the tensile stress of prestressed anchor bolts accounts for 40.2~69.8% of the ultimate tensile strength, with a more uniform axial force distribution and a much higher utilization rate of material mechanical properties than ordinary anchor bolts, which can fully mobilize the bearing potential of deep rock mass and realize the synergistic bearing of support and surrounding rock. This study accurately quantifies the bearing strengthening law of prestressed anchor bolts on tunnel support systems and clarifies the core mechanism of their active support. The research results provide important experimental basis and theoretical reference for the optimal design and engineering application of prestressed anchor bolts in soft rock tunnel engineering. Full article

Wheeled multifunctional motorized crossing frames represent a new type of crossing equipment for high-voltage transmission line construction. The initial design is too conservative, having a large safety margin and high material redundancy. Therefore, it is necessary to study a lightweight design version. However, as the structure constitutes an assembly consisting of multiple components, it also exhibits relatively high complexity. In a lightweight design, optimizing multi-component and multi-size parameters can lead to structural interference and separation, seriously affecting the smooth progress of design optimization. Therefore, an optimization design method of a multi-parameter complex assembly structure is proposed to solve this problem. Firstly, the typical stress conditions of the wheeled multifunctional motorized crossing frame were analyzed using its structural model. Then, a finite element model of the beam was established in ANSYS 2021 R1 Workbench, and the mechanical characteristics were analyzed. The results show that the arm support is the key load-bearing component and has significant optimization potential. Subsequently, functional mapping relationships were established among the 14 dimension parameters of the arm support, reducing the number of design variables to six and successfully avoiding component separation or interference during optimization. Through global sensitivity analysis, the height, thickness, and length of the arm body were screened out as the core optimization parameters from six initial design variables. Then, 29 groups of sample points were generated via central composite design (CCD), and a response surface model reflecting the relationships among the arm body’s dimensional parameters, total mass, maximum stress, and maximum deformation was established using the Kriging method. Leave-one-out cross-validation (LOOCV) was performed, and the coefficients of determination (R²) for model fitting were all higher than 0.995, indicating extremely high prediction accuracy. Taking mass and deformation minimization as the optimization objectives, the MOGA algorithm was adopted to perform multi-objective optimization and determine the optimal engineering parameters. Simulation verification was conducted on the optimized arm support, and an eigenvalue buckling analysis was performed simultaneously to verify structural stability. Finally, the proposed optimization method was experimentally verified through mechanical performance tests of the full-scale prototype under symmetric and eccentric loads. The results show that the mass of the optimized arm support is reduced from 217.73 kg to 189.8 kg, with a weight reduction rate of 12.8%. Under an eccentric load of 70,000 N, the maximum deformation of the arm support is 8.9763 mm, the maximum equivalent stress is 314.86 MPa, and the buckling load factor is 6.08, all of which meet the requirements for structural stiffness, strength, and buckling stability. The maximum error between the experimental and finite element results is only 4.64%, verifying the accuracy and reliability of the proposed method. The proposed optimization methodology, validated on a wheeled multifunctional motorized crossing frame, serves as a transferable paradigm for the lightweight design of complex assemblies with coupled dimensional constraints, thereby offering a general reference for the structural optimization of multi-component transmission line equipment, construction machinery, and other multi-component engineering systems. Full article

Reinforcement corrosion is one of the primary deterioration mechanisms affecting the long-term seismic performance of reinforced concrete (RC) structures. Although the effects of corrosion on individual RC members have been widely investigated, its influence on the cyclic behavior of RC frame systems has received limited attention. This study numerically investigates the seismic response of a single-bay reinforced concrete frame subjected to cyclic lateral loading under various corrosion scenarios. A three-dimensional nonlinear finite element model was developed in ABAQUS, incorporating corrosion-induced effects such as reinforcement cross-sectional loss, degradation of mechanical properties, bond strength deterioration, and concrete softening. The corrosion propagation rate and exposure duration were considered as key parameters, and different corrosion scenarios were comparatively evaluated. The numerical model was validated using an experimentally tested non-corroded reinforced concrete frame subjected to cyclic loading. The results demonstrate that reinforcement corrosion leads to significant degradation in the seismic performance of RC frames. Depending on corrosion severity, reductions of up to approximately 25% in lateral load capacity and up to 27% in both initial stiffness and energy dissipation capacity were observed. The findings further indicate that stiffness- and energy-based performance indicators are more sensitive to corrosion damage than strength-based indicators. The study highlights the importance of explicitly accounting for corrosion effects in the seismic performance assessment of reinforced concrete frame systems and provides a practical numerical framework for evaluating corrosion-induced performance degradation. Full article

Traditional virtual synchronous generator (VSG) control in photovoltaic–storage systems struggles with severe dynamic deterioration under high-impedance weak grid conditions. Through small-signal modeling, this paper analytically reveals that increased grid inductance forces the system’s dominant poles to migrate significantly toward the real axis, inducing a critical “overdamped hysteresis” that degrades transient tracking speed and oscillation attenuation. To break these physical constraints, an improved exponential synergistic adaptive control strategy is proposed. By establishing a synergistic optimization mechanism between the virtual inertia and damping coefficients via a square-root coupled exponential function, the proposed method achieves precise multi-parameter coordination. During the initial phase of disturbances, it triggers an explosive parameter surge to provide “stiff” transient support, strictly limiting frequency deviations and the rate of change of frequency (RoCoF). During the recovery phase, it drives a precipitous parameter decay to actively neutralize the overdamped coupling effect, forcibly pulling the migrated poles back to the ideal underdamped region. Rigorous switching-model simulations demonstrate that, compared to conventional fixed-parameter and power function-based adaptive methods, the proposed synergistic strategy significantly improves transient performance. Quantitatively, during load steps, it restricts the frequency nadir to 49.85 Hz (compared to 49.73 Hz for fixed parameters). During extreme grid stiffness transitions (SCR drops), it completely eliminates active power tracking hysteresis by reducing the settling time to just 0.26 s and aggressively clamps AC overcurrent peaks from 38 A down to 31 A. Supported by coordinated PV–storage energy management, the proposed method offers a highly robust grid-forming framework for renewable-dominated weak power grids. Supported by coordinated PV–storage energy management, the proposed method offers a highly robust grid-forming framework for renewable-dominated weak power grids. Full article

To address the engineering challenges of frequent flexural deformation and instability of composite roadway roofs and the difficulty in accurately controlling the support strength range during deep coal mining, this study takes the soft–hard interbedded composite roof of the working face in the West No. 1 Mining Area of Shuangyang Coal Mine in Shuangyashan as the engineering background. Typical fine sandstone (hard rock) and tuff (soft rock) from the on-site roof were selected to prepare layered composite specimens, and indoor four-point bending tests were conducted. Combined with theoretical calculations, strain monitoring, and acoustic emission (AE) real-time localization technology, the regulatory mechanisms of three key factors—lithological combination, loading rate, and span—on the flexural mechanical properties, deformation and failure modes, and fracture evolution laws of layered composite rock masses were systematically investigated. The research results show the following: (1) The flexural performance of layered composite rock masses is dominated by the interlayer interface effect. Their flexural strength is 46.7% and 41.1% lower than that of single hard rock and soft rock specimens, respectively, and the competitive mechanism between interface slip and delamination fracture is the core inducement of strength deterioration. (2) The strength and deformation characteristics of layered composite rock masses exhibit a significant loading rate effect. When the loading rate increases from 0.002 mm/s to 0.02 mm/s, the flexural strength decreases by 51.8% and the mid-span deformation deflection reduces by 50.1%. High loading rates will exacerbate the deformation mismatch between soft and hard rock layers, trigger premature failure of interface bonding, and inhibit the full development of structural plastic deformation. (3) Increasing the span significantly optimizes the flexural bearing performance of layered composite rock masses. When the span increases from 170 mm to 190 mm, the flexural strength increases by 65.7% and the mid-span deformation deflection synchronously increases by 65.7%. A large span can extend the flexural deformation path, promote the coordinated deformation of rock layers, and suppress local stress concentration. (4) The flexural failure of layered composite rock masses is dominated by Mode II shear cracks, while single-lithology specimens are mainly dominated by Mode I tensile cracks. Loading rate and span significantly change the crack propagation mode and energy release law. This study establishes a calculation method for the equivalent flexural stiffness of layered composite rock masses and reveals the mesoscopic mechanism of flexural failure of heterogeneous layered rock masses. The research results can provide a theoretical basis and experimental support for the optimization of support schemes and the prevention and control of roof collapse hazards for composite roofs of deep coal mine roadways. Full article

Tire-Derived Aggregate (TDA) is a recycled fill material made by cutting scrap tires into small pieces that satisfy the gradation requirements in ASTM D 6270. Since its introduction to civil engineering applications, TDA fill and TDA backfill have been successfully implemented in many projects. However, the dynamic behavior of the TDA backfill under significant earthquakes has not been substantially addressed. The present study used nonlinear time-history Finite Element Analysis (FEA) to analyze the dynamic behavior of a retaining wall with TDA backfill captured from the full-scale shake table test. Unlike typical soil failure observed in a similar retaining wall with conventional soil backfill, significant wall sliding occurred because lightweight TDA contributed to reducing the friction resistance of the wall footing. Therefore, the analysis required modeling capability of rigid body motion and impact loading from the separation between the wall stem and the backfill. With adequate friction models and softened contact models, the FEA generated the dynamic motion of the retaining wall that matched well with the measured responses, including the wall sliding. The friction model between the wall footing and soil was most critical in accurately reproducing wall sliding motion. It was determined to use different friction coefficients for the two different earthquakes used in the study in order to simplify the rate dependence of the coefficient. Also, the softened contact model generated more reasonable impact force by allowing overclosure and finite stiffness during impact. The FEA model and modeling technique in the present study can be used for the seismic design of various field-scale retaining walls with TDA backfill. Full article

With the active modernization of power facilities and the increasing deployment of maneuverable combined-cycle gas turbines (CCGTs), the selection of rational start-up strategies becomes increasingly important from the perspective of power quality. Excessive acceleration of power ramp-up may lead to undesirable voltage deviations, particularly in transmission networks with limited grid stiffness. This study investigates the impact of CCGT start-up ramp rate on voltage dynamics and power quality indicators at a 110/220 kV grid node. A detailed model of the Almaty power hub was developed in MATLAB/Simulink, taking into account the network structure, generating units, transformers, and aggregated loads. Three start-up scenarios were analyzed: an existing combined heat and power plant, a 504 MW combined-cycle gas turbine unit, and a 560 MW combined-cycle gas turbine unit with fuel afterburning. Voltage dynamics were evaluated using RMS-based indicators and a stabilization criterion incorporating a 5 s sliding time window and an 80% admissibility threshold. The simulation results reveal a nonlinear relationship between the start-up ramp rate and voltage quality. Increasing the ramp rate reduces the voltage stabilization time; however, beyond approximately 0.05 MW/s, further acceleration does not lead to additional improvement in power quality. The results indicate the existence of an optimal range of start-up ramp rates that provides a compromise between start-up speed and voltage quality requirements. The proposed approach can be used in the development of start-up algorithms for modern combined-cycle power plants connected to 110/220 kV transmission networks. Full article