Search Results (605)

To address the limitations of traditional timber mortise-and-tenon joints, particularly their low pull-out resistance and rapid stiffness degradation under cyclic loading, this study proposes a novel integrated sleeve mortise-and-tenon steel–timber composite beam–column joint. Building upon prior experimental validation and numerical model verification, a comprehensive parametric study was conducted to systematically investigate the influence of key geometric parameters on the seismic performance of the joint. The investigated parameters included beam sleeve thickness (1–10 mm), sleeve length (150–350 mm), bolt diameter (4–16 mm), and the dimensions and thickness of stiffeners. The results indicate that a sleeve thickness of 2–3 mm yields the optimal overall performance: sleeves thinner than 2 mm are prone to yielding, while those thicker than 3 mm induce stress concentration in the timber beam. A sleeve length of approximately 250 mm provides the highest initial stiffness and a ductility coefficient exceeding 4.0, representing the best seismic behavior. Bolt diameters within the range of 8–10 mm produce full and stable hysteresis loops, effectively balancing load-carrying capacity and energy dissipation; smaller diameters lead to pinching failure, whereas larger diameters trigger premature plastic deformation in the timber. Furthermore, stiffeners with a width of 40 mm and a thickness of 2 mm effectively enhance joint stiffness, promote a uniform stress distribution, and mitigate local damage. The optimized joint configuration demonstrates excellent ductility, stable hysteretic behavior, and a high load capacity, providing a robust technical foundation for the design and practical application of advanced steel–timber composite connections. Full article

To evaluate the fire safety performance of the joint region in prefabricated buildings, specifically when the grout in the slurry layer is under an unconstrained state. Total 54 pull-out specimens were designed to investigate the effects of elevated temperatures (20 °C, 200 °C, 300 °C, 400 °C, 500 °C, and 600 °C) and steel bar positions (center, mid-side, and corner) on the bond behavior between the grout and steel rebars. The failure modes, bond strength, ultimate displacement, and load–slip curves of the specimens were recorded. The peak load of the specimens with the temperature increasing first rose and then declined, exhibiting a trend consistent with the variation in compressive strength of the grout with temperature. At 600 °C, the ultimate loads of the center, mid-side, and corner specimens decreased by 53.46%, 52.53%, and 51.28%, respectively, compared with those at ambient temperature. At ambient temperature, the bond strength of the mid-side specimen was 11.24% lower than that of the central specimen, but 19.98% higher than that of the corner specimen. At 500 °C, the bond strength of the mid-side and corner specimens decreased by 15.76% and 39.26%, respectively, compared with that of the center specimen. The failure mode changed from steel-rebar fracture to pull-out failure due to the high temperature exposure and the steel rebar position. Finally, based on the post-heating strength test results of grout specimens, a bond strength calculation formula and a bond–slip constitutive model, considering both steel rebar position and temperature, were developed, achieving a correlation coefficient (R²) close to 1.0. Full article

Background/Objectives: Caffeine is a well-established ergogenic aid in many strength- and endurance-based sports, but its efficacy in sport climbing remains underexplored despite the sport’s unique physical demands on grip strength, power, and muscular endurance. Therefore, this study examined the acute impact of a low caffeine dose (3 mg/kg) on climbing-specific performance, including pull-up and grip tests, in intermediate-advanced climbers. Methods: In a triple-blind, randomized, crossover design, thirteen male climbers (age: 28.2 ± 8.6 years) completed two experimental trials (caffeine vs. placebo). Performance was assessed via a pull-up one-repetition maximum (1RM) and power test at various loads, a pull-up muscular endurance test, and grip tests including maximum dead-hang time, maximum dead-hang strength, and rate of force development (RFD). Results: Caffeine did not significantly enhance performance in any measured variable. While a non-significant increase in peak power was observed at 80% 1RM (+8.0%, 95% CI: −0.232 to 0.304, p > 0.05, g = 0.348), effects at other loads and on pull-up endurance were trivial based on effect size (e.g., repetitions: +3.3%, 95% CI: −3.30 to 4.37, p = 0.292, g = 0.061). For grip metrics, caffeine was associated with a modest reduction in endurance time (+7.4%, p = 0.162, g = 0.171) and a slight increase in maximum strength (+2.4%, p = 0.060, g = 0.120). RFD was unaffected (p > 0.169, g < 0.13). Despite the lack of objective improvement, participants reported significantly greater subjective feelings of strength, energy, and alertness with caffeine (p < 0.05). Conclusions: A 3 mg/kg dose of caffeine, while altering psycho-physiological state, did not elicit statistically or practically meaningful ergogenic effects on pull-up or grip performance in climbers. Higher doses or sport-specific performance tests should be investigated in future research. Full article

The article presents a comparative analysis of mechanical properties of M8 threaded joints produced using three different methods, in rectangular nylon (PA 12) specimens manufactured in SLS technology. Threaded holes in specimens were made by direct thread printing (specimens marked PT), thread reinforcement with Helicoil inserts (HT), and the use of heat-set inserts (IT). The specimens were subjected to a tensile testing at a constant displacement rate of 2 mm/min. The maximum force and the displacement at failure were recorded. The results indicated that the lowest load-bearing capacity F_MF was observed in the printed thread specimens, with an average value of 3.41 kN. The use of heat-set inserts increased F_MF to 3.83 kN, representing a 12% improvement. The highest load-bearing capacity was achieved in specimens reinforced with Helicoil inserts, which enhanced joint strength by 40% compared to printed thread specimens, reaching an average F_MF of 4.78 kN. In all cases, failure occurred due to the thread or insert pull-out from the specimen material. Studies have shown that the use of metal inserts significantly enhances the strength of threaded joints in SLS-printed PA12 components. Helicoil inserts provide the highest F_MF load capacity, while heat-set inserts offer better technological advantages. Although printed threads are easier to manufacture, their applicability is limited to larger thread sizes and lower mechanical loads. Full article

The embedded through-section (ETS) technique is a promising method for fiber-reinforced polymer (FRP)-strengthening reinforced concrete (RC) structures, offering higher bond resistance and reduced surface preparation compared to externally bonded or near-surface mounted FRP systems. A common failure in ETS applications is debonding at the FRP bar-to-concrete interface. However, current design standards often assume uniform bond stress and lack predictive models that account for debonding propagation and its effect on load capacity. Furthermore, a detailed analysis of interfacial stress development, including debonding initiation and progression along varying bond lengths, remains limited. To address these gaps, this study introduces an analytical model that describes the complete debonding process in ETS FRP bar-to-concrete joints, incorporating both long and short bond lengths and frictional effects. Based on a trilinear cohesive material law (CML), closed-form expressions are deduced for the load–slip response, maximum load, interfacial shear stress and strain distribution along the FRP bar. The proposed model is validated experimentally through pull-out tests on glass FRP (GFRP) bars adhesively bonded to concrete with different strength grades. The results show that the analytical predictions agree well with both the self-conducted experimental data for short joints and existing test results for long joints given in the literature. Therefore, the developed design-oriented solution enables accurate evaluation of the actual contribution of ETS FRP reinforcement to RC members by explicitly modeling debonding behavior. This provides a rigorous and mechanics-based tool for performance-based design of ETS FRP-to-concrete joints, addressing a critical gap in the future refinement of current design standards. Full article

Background and Objective: Streetlifting is a developing strength sport derived from calisthenics and based on maximal external load performance in weighted pull-ups, dips, muscle-ups, and squat variations. Its rapid global expansion has raised interest in identifying sport-specific nutritional and recovery strategies that can support performance and health. However, scientific evidence directly focused on streetlifting remains limited. This narrative review aims to summarize current knowledge regarding body composition, nutrition, supplementation, and sleep in streetlifting athletes by integrating findings from related strength sports. Methods: A narrative review design was adopted due to the scarcity of empirical studies on streetlifting. Searches were performed using the terms “streetlifting AND nutrition,” “streetlifting AND body composition,” and “streetlifting AND sleep quality.” Peer-reviewed studies involving comparable strength disciplines were included when directly applicable to performance or recovery determinants. Results: Performance in streetlifting appears strongly driven by strength-to-bodyweight ratio, supported by low-to-moderate fat mass and adequate lean mass. Evidence from resistance training literature suggests that meeting energy requirements, consuming 1.2–1.5 g/kg/day of protein, and using nutrient timing around training may enhance muscle protein synthesis and glycogen replenishment. Creatine supplementation shows consistent benefits for maximal strength and ATP turnover, whereas other supplements lack robust evidence. Sleep duration and quality contribute to neuromuscular recovery, endocrine balance, and cognitive readiness, though sport-specific findings are insufficient. Conclusions: Streetlifting athletes may benefit from integrated nutritional planning, evidence-based supplementation, and sleep optimization. Further sport-specific interventional and longitudinal studies are required to develop validated performance and health guidelines. Full article

In agricultural workplaces, upper-body strain arises not only from lifting and carrying harvest crates but also from pushing, pulling, twisting, and squatting motions. Drawing inspiration from the momentary shoulder contraction and whole-body coordination characteristic of traditional Japanese martial arts, this study proposes a method for “moving efficiently with minimal exertion” across multiple task actions, specifically, lateral pushing, fore-aft pulling, and trunk rotation. Each action is modeled as a control system, and mechanical-engineering simulations are employed to derive optimal muscle-output patterns. Simulation results indicate that peak muscular force can be lowered compared with conventional techniques. A simple physical test rig confirms the load-reduction effect, showing decreases in both perceived exertion and electromyographic activity. These findings offer practical knowledge that can be immediately applied not only to agriculture but also to logistics, nursing care, and other settings involving repetitive handling of heavy objects or machine operations. Full article

The mechanical performance of rail fasteners plays a crucial role in the track–structure interaction of high-speed railways. A reasonable lateral stiffness of the fastener system can enhance the stability and safety of train operation and prevent derailment accidents. Under seismic action, adjacent bridge spans undergo reciprocating displacement, causing the rail-fastener system near the beam ends to be subjected to lateral cyclic forces. To investigate the mechanical and deformation behavior of the WJ-8B fastener system under lateral loading, low-cycle reciprocating loading tests were conducted on the rail-fastener system considering different bolt torques. The load–displacement curves and torque–rotation curves of the fastener system were obtained, and formulas for calculating the characteristic values of the mechanical properties of the WJ-8B fastener system were fitted, which show good agreement with the experimental results. The results indicate that the lateral mechanical behavior of the WJ-8B fastener exhibits significant nonlinear characteristics, marked by three distinct inflection points in the load–displacement curve that delineate five stages: initial stage, rail shearing stage, rail sliding stage, rail contact stage, and three-point contact. The bolt torque is positively correlated with the lateral stiffness of the fastener system. Increasing the torque from 115 N·m to 190 N·m enhances the lateral bearing capacity by 29.06% in the push direction and by 38.74% in the pull direction. Meanwhile, the system torque decreases by 21.45% in the push direction and increases by 21.14% in the pull direction. Full article

Exercise-induced muscle damage (EIMD) is characterized by structural muscle tissue damage and elevated biochemical markers following high-intensity or unaccustomed exercise. This study evaluated the utility of a small animal grip strength measurement device as a model for EIMD. Thirty-four male mice were divided into four groups: one control and three experimental groups, and sacrificed at 2, 4, and 7 days post-exercise. The exercise protocol involved 50 tail-pull contractions at 60 Hz using a forelimb grip strength device. Biochemical biomarkers, inflammatory gene expression, and oxidative stress markers from blood and muscle tissue were assessed at each sacrificial time point. Muscle damage marker, plasma aldolase activity, showed significant elevation at 4 days post-exercise (p < 0.01). Inflammatory gene expression in triceps brachii showed no significant changes. Oxidative stress analysis revealed significantly decreased biological antioxidant potential (BAP) at 7 days and a trend toward a significant increase in Diacron-reactive oxygen metabolites (d-ROMs) at 4 days. NF-kB expression showed a trend toward significance increase. The grip strength exercise model induced modest biochemical alterations suggesting possible involvement of oxidative stress. The early release of aldolase and subsequent oxidative stress suggest that this model replicates EIMD and may serve as a valuable tool for quantitative loading on muscles, studying EIMD mechanisms and facilitating EIMD-based interventions. Full article

This study presents an energy-efficient, room-temperature synthesis and characterization of methacrylated pullulan (Pull-MA) hydrogel developed for controlled nutrient delivery in agricultural applications. Fourier Transform Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC) analyses confirmed the successful functionalization of pullulan with methacrylate groups, accompanied by a decrease in thermal transition temperatures, indicative of increased polymer chain mobility. The synthesized Pull-MA hydrogel exhibited a high swelling capacity, reaching an equilibrium swelling ratio of 1068% within 5 h, demonstrating its suitability as a carrier matrix. The room-temperature synthesis approach enabled the in situ incorporation of microbial inoculant into the hydrogel network, preserving microbial viability and activity. SEM analysis performed under the different magnifications (1000, 2500, 5000, 10,000, 25,000×) has confirmed brittle nature of xerogels and increasing in structural irregularities with increasing in cultivation broth content.The biological performance of the fertilizer-loaded hydrogels was evaluated through seed germination assays using maize and pepper as model crops. The optimized formulation, T2 (Pull-MA: cultivation broth 1:5 w/w), significantly improved germination efficiency, as evidenced by increased relative seed germination (RSG), root growth rate (RRG), and germination index (GI) compared to both the control and the low-fertilizer formulation (T1, 1:2.5 w/w). These findings highlight the potential of Pull-MA hydrogels as bioactive seed-coating materials that enhance early seedling development through controlled nutrient release. The results lay a solid foundation for further optimization and future application of this system under real field conditions. Full article

Energy-dissipating braces are novel structural components as they not only accommodate the seismic energy demand but also enhance both the flexibility and overall earthquake resistance of the structure, preventing brittle or non-ductile behavior. The novel brace proposed in this study was developed to achieve two primary objectives: first, to restrict relative displacements at its ends by dissipating energy through U-shaped flexural plates (UFPs), and second, to provide a self-centering mechanism through the use of post-tension (PT) to ensure structural re-centering after cyclic loading. The novelty of this research lies in the experimental findings showing that post-tensioned (PT) braces exhibit a flag-shaped self-centering hysteretic response, improved initial stiffness, and reduced residual displacements by 72%, while non-PT braces behave as conventional metallic dissipators with larger residual displacements. Increasing UFP thickness from 6 to 8 mm enhances strength by 22%. Stainless steel UFPs offer superior plastic recovery, whereas regular steel UFPs dissipate ~%10 more energy through greater plasticity. Energy dissipation of the brace increases with increasing PT forces and displacement due to the PT force pulling the force–displacement curve towards high force levels. This study highlights the importance of PT force and UFP parameters in a brace configuration with self-centering and metallic dissipators such as U-shaped flexural plates. Full article

Delamination remains a critical failure mode in carbon fiber-reinforced polymer (CFRP) composites, particularly under cyclic loading in aerospace and automotive applications. This study explores whether nanoscale reinforcement with graphene-based materials can enhance delamination resistance and identifies the most effective nanofiller type. Two distinct graphene nanospecies—reduced graphene oxide (rGO) and carboxyl-functionalized graphene nanoplatelets (HDPlas)—were incorporated at 0.5 wt% into CFRP laminates and tested under static and fatigue mode I loading using double cantilever beam (DCB) tests. Both nanofillers enhanced interlaminar fracture toughness compared to the neat composite: rGO improved the energy release rate by 36%, while HDPlas achieved a remarkable 67% enhancement. Fatigue testing showed even stronger effects, with the fatigue threshold energy release rate rising by 24% for rGO and 67% for HDPlas, leading to a fivefold increase in fatigue life for HDPlas-modified laminates. A compliance calibration method enabled continuous monitoring of crack growth over one million cycles. Fractography analysis using scanning electron microscopy revealed that both nanofillers activated crack bifurcation, enhancing energy dissipation. However, the HDPlas system further exhibited extensive nanoparticle pull-out, creating a more tortuous crack path and superior resistance to crack initiation and growth under cyclic loading. Full article

Integrating Wire Arc Additive Manufacturing (WAAM) into the Selective Paste Intrusion (SPI) process represents a groundbreaking approach for fabricating reinforced concrete structures with complex geometries. This study investigates the bond strength between concrete and WAAM reinforcement under varying temperature conditions to understand the behavior of heated reinforcement bars within fresh concrete and its effect on the related bond strength. By conducting pull-out tests according to RILEM RC6, WAAM reinforcement bars were heated to predefined temperatures of 20 °C (ambient), 60 °C, 80 °C, and 200 °C for 18 min. The results show that while moderate thermal exposure (60 °C and 80 °C) led to a slight reduction in the maximum bond strength, a notable degradation occurred at 200 °C, indicated by a marked decrease in both maximum bond stress and early bond development. These findings provide initial insights into the thermal limitations of WAAM integration within SPI processes. The goal is to address the challenges associated with integrating WAAM into SPI, particularly the adverse effects of high temperatures generated during the welding process on the rheological properties of the cement paste, the penetration behavior of the paste in the particle bed, and ultimately, the mechanical properties of the hardened concrete. This technique allows for producing nearly free-formed reinforcements, thus complementing the advantage of SPI in producing free-formed structures of almost any geometry. Full article

This paper investigates the use of recycled carbon fibre (rCF) from wind turbine blades in fibre-reinforced concrete (FRC). The research demonstrates the combined effects of fibre length (25 mm, 35 mm, and 45 mm) and fibre content (0.29%, 0.58%, and 0.87% by volume). The experimental programme included the investigation of compressive and tensile splitting strengths, as well as the determination of the Brittleness Index and fracture energy. The transfer of tensile forces through fibres was assessed based on the surface area of split samples. Tensile strength was determined for two loading directions: parallel and perpendicular to the direction of concreting. It was found that the maximum fibre addition reduced the compressive strength by up to 9% and that the tensile strength was significantly dependent on the fibre orientation, which was determined by the direction of concreting. The tensile strength perpendicular to the direction of concreting increased by a maximum of 11.8% and parallel to the direction of concreting by a maximum of 66% compared to plain concrete, depending on the fibre content and length. The research also demonstrated the synergy of pull-out and rupture of fibres in transmitting tensile forces. These studies provide important insights into the applicability of rCF as a dispersed reinforcement in concrete and have important implications for sustainability in the construction sector. Full article

In this article, two wideband high-efficiency Class-J power amplifiers operating in X and Ku bands, respectively, are designed based on continuous mode. The optimal impedance regions of the transistors are determined using harmonic load-pull techniques. An on-chip output matching network with second harmonic control functionality is designed to achieve Class-J operation. To verify the feasibility of designed circuits, both power amplifiers are designed and fabricated using a 0.25 mm GaAs pseudomorphic high electron mobility transistor (pHEMT) process. The power amplifiers are both biased at 6 V/−1 V. The measured results show the X-band and Ku-band power amplifiers achieve peak saturated output powers of 31.2 dBm and 30.8 dBm, respectively. The power-added efficiencies (PAEs) of the two amplifiers within their operating bands reach up to 48% and 45.3%, respectively. Compact size and high efficiency make them suitable for integration into phased array transmit/receiver (T/R) modules. Full article