External Load Research Articles

Study on the bond-slip behavior between steel bar and rammed earth

The steel bars significantly enhance the mechanical properties of rammed earth, as they together withstand external loads. In order to investigate the bond performance between steel bars and rammed earth, the pull-out tests were conducted on 60 specimens. This study investigated the distribution of bond stress along the anchorage length of steel bars by embedding strain gauges inside the bars. The effects of four types of anchorage length, three types of cover thickness, three types of steel bar diameter and three types of compressive strength of rammed earth on the bond-slip behavior were investigated. Through experimental research and theoretical analysis, the distribution law of the bond stress along the anchorage length was obtained. The transfer mechanism of the bond stress and the failure mode of the specimens were analyzed. An improved bond-slip constitutive model was proposed to reflect the influence of the position function of bond stress distribution. Furthermore, a theoretical formula for the bond strength was proposed based on the analytical approach of elastic solid mechanics and the failure modes of the specimens, and its accuracy was validated by experimental results.

On a lack of stability of parametrized BV solutions to rate‐independent systems with nonconvex energies and discontinuous loads

AbstractWe consider a rate‐independent system with nonconvex energy under discontinuous external loading. The underlying space is finite‐dimensional and the loads are functions in . We investigate the stability of various solution concepts w.r.t. a sequence of loads converging weakly* in with a particular emphasis on the so‐called normalized, ‐parametrized balanced viscosity solutions. By means of three counterexamples, it is shown that common solution concepts are not stable w.r.t. weak* and even intermediate (or strict) convergence of loads in the sense that a limit of a sequence of solutions associated with these loads need not be a solution corresponding to the load in the limit. We moreover introduce a new solution concept, which is stable in this sense, but our examples show that this concept necessarily allows “solutions” that are physically meaningless.

Flexible piezoresistive pressure sensor based on a graphene-carbon nanotube-polydimethylsiloxane composite

Flexible sensors are used widely in wearable devices, specifically flexible piezoresistive sensors, which are common and easy to manipulate. However, fabricating such sensors is expensive and complex, so proposed here is a simple fabrication approach involving a sensor containing microstructures replicated from a sandpaper template onto which polydimethylsiloxane containing a mixture of graphene and carbon nanotubes is spin coated. The surface morphologies of three versions of the sensor made using different grades of sandpaper are observed, and the corresponding pressure sensitivities and linearity and hysteresis characteristics are assessed and analyzed. The results show that the sensor made using 80-mesh sandpaper has the best sensing performance. Its sensitivity is 0.341 kPa−1 in the loading range of 0–1.6 kPa, it responds to small external loading of 100 Pa with a resistance change of 10%, its loading and unloading response times are 0.126 and 0.2 s, respectively, and its hysteresis characteristic is ∼7%, indicating that the sensor has high sensitivity, fast response, and good stability. Thus, the presented piezoresistive sensor is promising for practical applications in flexible wearable electronics.

Anisotropic Liesegang pattern for the nonlinear elastic biomineral-hydrogel complex.

The Liesegang pattern is a beautiful natural anisotropic patterning phenomenon observed in rocks and sandstones. This study reveals that the Liesegang pattern can induce nonlinear elasticity. Here, a Liesegang-patterned complex with biomineral-hydrogel repetitive layers is prepared. This Liesegang-patterned complex is obtained only when the biomineralization is performed under the supersaturated conditions. The Liesegang-patterned complex features a nonlinear elastic response, whereas a complex with a single biomineral shell shows a linear behavior, thus demonstrating that the Liesegang pattern is essential in achieving nonlinear elasticity. The stiff biomineral layers have buffered the concentrated energy on behalf of soft hydrogels, thereby exposing the hydrogel components to reduced stress and, in turn, enabling them to perform the elasticity continuously. Moreover, the nonlinear elastic Liesegang-patterned complex exhibits excellent stress relaxation to the external loading, which is the biomechanical characteristic of cartilage. This stress relaxation allows the bundle of fiber-type Liesegang-patterned complex to endure greater deformation.

Acute Response to Training after Returning from the Off-Season in Elite Rugby League Athletes.

The purposes of this study were to quantify the physiological response to the initial two-week preseason period in elite male rugby league (RL) athletes, and to determine if a repeated bout effect (RBE) occurs. Eighteen RL players were monitored for the initial two-week preseason period. Blood samples were collected on days (D)1, D2, D4, D5, D8, D9, D11 and D12 to measure creatine kinase (CK). Neuromuscular power was assessed on D1, D5, D8 and D12. During field-based sessions, the external training load was quantified using global positioning system technology, whilst the internal load was quantified using the training impulse and the session rating of perceived exertion. Resistance-based gym session volume was quantified by total repetitions x weight lifted. Perceived measures of fatigue and muscle soreness were assessed on all training days. Two-way (day x week) repeated measures analysis of variance and Bonferroni's corrected post-hoc tests identified significant changes. There were no significant changes in CK activity (649.2 ± 255.0 vs. 673.8 ± 299.1 µL; p = 0.63) or internal training load measures from week 1 to week 2. External training load measures including total distance (4138.1 ± 198.4 vs. 4525.0 ± 169.2 m; p < 0.001) and repeated high-intensity efforts (12.6 ± 1.8 vs. 17.5 ± 1.8 au; p < 0.001) significantly increased in week 2 compared to week 1. Internal training loads and CK activity did not change in response to an increase in external training loads during the initial preseason. The current results provide support for a 'real world' perspective of the RBE phenomenon that may be more applicable for team sport practitioners.

The Effect of Different Motocross Circuit Typologies on Internal Load and External Load Responses in Riders

Background: Several physical and physiological changes occur during a motocross race, mainly due to the type of circuits, and therefore the impact of different types of circuits on training load responses continues to need to be fully clarified. Objective: The main aim of the present study was to compare the internal load and external load responses of motocross riders from different classes and on circuits of different types. Method: A quasi experimental design research was used in the study.The sample consisted of 10 motocross riders (28.10 ± 7.53 years; 74.60 ± 9.70 kg; 176.50 ± 7.18 cm; 23.88 ± 2.18 BMI), male., distributed by the Mx Elite and Mx Hobby categories. The pilots were evaluated before and after the race in relation to indicators of external load (accelerations and decelerations, maximum speed and average speed and impacts) and internal load (Heart rate, blood lactate and rating of perceived exertion) on two circuits of different types. Results: There was a trend towards higher internal load responses in the Mx Hobby class compared to the Mx Elite class (p ≤ 0.05), regardless of the circuit. Regarding external load responses, the Mx Hobby class has a tendency towards higher maximum and average speeds, while the Mx Elite class presents the same tendency for accelerations and decelerations. Conclusions: Different circuit types appear to influence pilots’ internal load and external load responses.

Fatigue Life and Crack Initiation of K and N Type Jacket Structure Using 3D Fatigue FE Analysis

Jacket structures are widely used as foundation structures for offshore wind energy. The jacket structure as a truss shape structure is not deformed easily and has the advantage of keeping the structure stable under wind load. The offshore jacket structures are subjected to unstable repetitive loads such as wind, and wave loads in the deep sea. These harsh environments lead to the deterioration of material performance and fatigue failure with cracks in the structure. It is crucial to locate fatigue cracks since they might compromise a structure's overall stability.In this study, fatigue life and crack initiation for different braced jacket structures were investigated. First, 3D non-steady heat conduction analysis and thermal elastic-plastic analysis were performed to reproduce the initial state of the weld joint in the jacket structure. The heat history obtained from the 3D non-steady heat conduction analysis was enforced as an input in thermal elastic-plastic analysis to calculate welding deformation and residual stress. Next, the fatigue FE analysis of the jacket welding structure was carried out using the residual stress and welding deformation as initial values along with the external cyclic loadings. The 3D fatigue FE analysis employed cyclic hysteresis constitutive equations and fatigue damage theory to calculate the fatigue life and crack initiation. The 3D fatigue FE results were compared with the S-N curve by European code 3 and the hot spot stress (HSS) method. The results show that the 3D fatigue FE method effectively calculates the fatigue life and finds crack initiation.

Experimental Research on the Anti-Reflection Crack Performance of Basalt Fiber Modified Rubber Asphalt Stress-Absorbing Layer.

Reflection cracks are one of the most common problems in semi-rigid base pavement. Setting a stress absorption layer can effectively delay the occurrence of reflection cracks, but further improvement is still needed in its interlayer bonding performance and anti-reflection crack performance. Considering the excellent crack resistance of basalt fibers and the good elastic recovery ability of rubber asphalt, it is considered worthwhile to incorporate them into traditional stress absorption layers to improve performance. To simulate the actual pavement layer effect, composite specimens consisting of a cement-stabilized macadam base + basalt fiber rubber asphalt stress-absorbing layer + AC-20 asphalt mixture surface layer were prepared to evaluate their performance through interlayer direct shear tests, interlayer tensile tests, three-point bending tests, and overlay tests (OTs). To determine the optimal fiber blending combination, four fiber lengths (3 cm, 6 cm, 9 cm, 12 cm) and four fiber proportions (120 g/m2, 140 g/m2, 160 g/m2, 180 g/m2) were selected respectively. The specific effects of basalt fibers with different lengths and dosages were analyzed. The results show that compared with the absence of fibers, the improvement of interlayer bonding performance of rubber asphalt with basalt fibers is not significant, and it has certain limitations; however, the improvement of anti-reflective crack performance is significant, with an increase of up to 305.5%. This indicates that the network structure formed by basalt fibers and rubber asphalt stress absorption layer can effectively absorb and disperse external loads, causing an excellent crack resistance effect. Meanwhile, the results indicate that the main factor affecting its interlayer bonding strength and anti-reflective crack performance is the fiber content. Based on the comprehensive analysis of the performance and economy of the stress absorption layer of basalt fiber rubber asphalt, the optimal fiber parameter combination recommended is as fiber length 9 cm and fiber content 160 g/m2. These results can provide a reference for the design and performance evaluation of basalt fiber rubber asphalt stress absorption layer, and have certain application value.

Research on cable dynamic response of a catenary anchor leg mooring system based on ANCF

This paper presents a dynamic analysis model for a catenary anchor leg mooring (CALM) system based on the absolute nodal coordinate formulation (ANCF) method, combined with continuum mechanics and finite element theory. This model uses absolute slope coordinates instead of traditional angle coordinates to better describe the large deformation and large displacement of the cables. The paper derives the element mass matrix, generalized stiffness matrix, and the element external load matrix, including the Morison force transformed into the ANCF framework, based on the virtual work principle. The accuracy and reliability of the ANCF program are validated using static and dynamic beam models, as well as submerged tether models. Furthermore, a comparative analysis of the ANCF mooring cable model with OpenFAST and MoorDyn accentuates the program's practical value in real engineering applications. Finally, we systematically analyzed the dynamic characteristics of a CALM single-point mooring system, revealing that the mooring forces in the cables significantly influence the high-frequency motion of the buoy. Additionally, the reduction in the length of the mooring cables, to an appropriate extent, enhances the stability of the system, which further attests to the effectiveness and practicality of the ANCF model that has been developed.

Unravelling the Relationship between External Load and the Incidence of Hamstring Injuries in Professional Soccer Players

Objectives. The study aimed to analyze external load indicators with the incidence of non-contact hamstring injuries. Material and methods. A non-experimental correlative, retrospective cohort study was carried out. The data were collected from 31 professional male soccer players over the course of one season. The following load indicators were examined: duration (D), total distance travelled (TDT), distance travelled at high intensity (DTHI) &gt; 20km/h, number of efforts between 20-25 km/h (NE 20-25km/h), distance travelled at more than 25km/h (DR+25km/h), number of sprints greater than 25km/h (NE &gt; 25km/h), number of accelerations greater than 1m/s² (Acc), and number of minor decelerations at -1m/s² (Dcc). Only non-contact hamstring injuries were included in the analysis. For the multivariate analysis, we applied a logistic regression model, where a value of P &lt; 0.05 was established both for the statistical significance of the model (X²) and for each of the regressor variables (X²), the confidence interval level was 95%. Results. Two injuries were recorded and diagnosed: injury grade 2 and muscle fatigue. The load indicators analyzed did not show a significant correlation with hamstring injury. Therefore, no association was found between external load and hamstring injury in professional soccer players. Conclusions. The logistic regression model (p &gt; 0.05) did not present statistical significance. Consequently, none of the external load variables monitored explain the rate of non-contact hamstring injuries in this population.

Stress-strain state of steel corrugated I-beams prestressed by flange drawing

The material distribution in structures is an urgent scientific and technical problem. Corrugated and prestressed steel structures are efficient and reliable.Purpose: The aim of this paper is to study the operation of steel I-beam with a thin corrugated wall, prestressed by flange drawing.Methodology/approach: Finite element modeling of beams with corrugated and flat walls (models with flat wall, transversely corrugated wall, downward corrugation at an angle of inclination 20 degrees, ascending corrugation at an angle of inclination 20 degrees). The proposed method is used for prestressing the lower beam flange using negative temperature effects. Numerical experiments in LIRA-SAPR software allow to obtain the stress distribution isofields and deformation patterns. A comparative analysis of the stress-strain state.Research findings: The normal stress distribution over flanges of corrugated beams with and without prestress under the external load has low difference. Prestress produces significant deflections of structures and the greatest deflection of the beam with ascending corrugations.

Mixed-Method Heat Acclimation Induces Heat Adaptations in International Triathletes Without Training Modification

Abstract Purpose Heat acclimation (HA) kinetics often necessitates that the intervention is conducted in the weeks immediately preceding athletic competitions, potentially interfering with a training taper. Therefore, we investigated the efficacy of a mixed-method HA protocol, superimposed over planned external training loads, during the 3-weeks prior to the 2022 U23 World Triathlon Championships. Methods Six international triathletes completed 8 pre-competition HA sessions (5 active: running/cycling, 3 passive: hot water immersion [HWI]), across 2-weeks. Outdoor high-intensity training sessions were followed by 30–60 min HWI, whilst low-intensity cycling/running sessions were completed in a hot, humid environmental chamber. To assess heat adaptations, participants completed three 25 min heat stress tests (HST) involving iso-speed treadmill running (session 1 = HST1, session 5 = HST2, and session 8 = HST3). Physiological, haematological and wellbeing monitoring were conducted throughout HA. Results Reduced heart rate (~ − 6 beats/min) was observed within HST3 (P = 0.01, ηp2 = 0.64), versus HST1 and HST2. No changes in core temperature were observed across HSTs (P = 0.055,ηp2 = 0.44). Sweat sodium concentration was lower by HST2 at the arm (− 23 ± 16 mmol/L, P = 0.02) and back (− 27 ± 17 mmol/L, P = 0.01). White blood cell count reduced from baseline to the end of HA (P = 0.02, ηp2 = 0.27), but no changes were found in any other haematological markers (all P &gt; 0.05). Perceptual wellbeing measures did not change across HA (all P &gt; 0.05). Conclusion By HST3, seven prior mixed-method HA sessions improved markers of heat adaptation (exercising HR and sweat concentration) within international triathletes. Mixed-method HA may be implemented without modifying training load, with no apparent detrimental effects on athlete health or training stress markers.

REAL-TIME MANAGEMENT OF CRITICAL IT-SYSTEMS BASED ON NEURAL NETWORK TECHNOLOGIES

The paper investigates a relevant applied problem associated with building decision support systems for critical information services. An original approach is proposed, based on neural network forecasting, within which a method of dynamic local approximation using neural network models has been developed. The principles of constructing and implementing the operational algorithm (under conditions of uncertainty of the external load profile) of a combined proactive system for managing computational resources are outlined. Experiments have been conducted that confirm the effectiveness of the method and the approach as a whole.

Analysis of external load and internal load in AirBadminton

The aim of this study was to compare internal load and external load between AirBadminton and traditional indoor badminton. The research was conducted with 8 badminton players from the Alicante Technification Centre, including both men and women. The study was carried out based on the recommendations and guidelines of the International Badminton Federation. The procedure included competitions in both 1vs1 and 2vs2 formats, first on sand and then on hard court. Various variables related to players' internal and external load were analysed, using devices such as WIMU PRO for external load and Polar H7 transmitters for internal load. Data analysis was performed using statistical tests such as T-Student and Wilcoxon. Results showed significant differences between indoor badminton and AirBadminton in terms of internal and external load. In the 1vs1 format, indoor badminton was found to be more demanding, with higher intensity efforts, greater distance covered, and higher heart rate compared to AirBadminton. Similar results were observed in the 2vs2 format, confirming that indoor badminton involves greater effort. AirBadminton may be a healthier and more accessible alternative, suitable for different age groups, as it is less explosive and lighter in terms of internal and external load. Future research should focus on technical, tactical, and full-match duration aspects of this new modality.

Super-Toughness Carbon Nanotube Yarns by Bio-Inspired Nano-Coiling Engineering.

Lightweight structural materials are commonly used as effective fillers for advanced composites with high toughness. This study focused on enhancing the toughness of direct-spun carbon nanotube yarns (CNTYs) by controlling the micro-textural structure using a water-gap-based direct spinning. Drawing inspiration from the structural features of natural spider silk fibroin, characterized by an α-helix in the amorphous region and β-sheet in the crystalline region, multiscale bundles within CNTYs are reorganized into a unique nano-coil-like structure. This nano-coiled structure facilitated the efficient dissipation of external mechanical loads through densification with the rearrangement of multiscale bundles, improving specific strength and strain. The resulting CNTYs exhibited exceptional mechanical properties with toughness reaching 250Jg-1, making them promising alternatives to commercially available fibers in lightweight, high-toughness applications. These findings highlight the significance of nano-coiling engineering for emulating bio-inspired micro-textural structures, achieving remarkable enhancement in the toughness of CNTYs.

Beam modeling in a floating frame of reference for torsion dynamics of helicopter rotor blades

AbstractIn the ongoing development of DLR’s Versatile Aeromechanics Simulation Tool, an elastic-beam model is integrated into the multibody system based on the floating frame-of-reference formulation. Although the application of this formulation for one-dimensional beam models has already been addressed in the literature, the challenge remains to properly model the torsion dynamics of rotor blades – especially under high centrifugal loads. To this aim, this work suggests the consideration of rotational shape functions in the inertia shape integrals and in the application of gravitational, inertial, and external loads. This modified approach is validated based on the structural analysis of a rotor blade with complex geometrical properties.

Calculating Load and Intensity Using Muscle Oxygen Saturation Data.

The study aimed to calculate training intensity and load using muscle oxygen saturation (SmO2) during two differentiated physical tasks. 29 university athletes participated in a 40-m Maximal Shuttle Run Test (MST, 10 × 40-m with 30 s recovery between sprints) and a 3000-m time trial run. Distance and time were used to calculate external load (EL). Internal load indicators were calculated based on percentage of maximum heart rate (%HRMAX) and SmO2 variables: muscle oxygen extraction (∇%SmO2) and the cardio-muscle oxygen index (CMOI) was also provided by relating ∇%SmO2 ÷ %HRMAX, and the training load were calculated as the product of speed (m/min × IL) and the efficiency index [Effindex (m/min ÷ IL)]. A student t test was applied based on Bayesian factor analysis. As expected, EL differed in the 40-m MST (331 ± 22.8) vs. 3000-m trials (222 ± 56.8) [BF10 = 6.25e+6; p = <0.001]. Likewise, IL showed higher values in 40-m MST (39.20 ± 15.44) vs. 3000-m (30.51 ± 8.67) in CMOI: [BF10 = 1.70; p = 0.039]. Training load was greater in 40-m MST (85.77 ± 27.40) vs. 3000-m (15.55 ± 6.77) [(m/min × ∇%SmO2): BF10 = 12.5; p = 0.003] and 40-m MST (129.27 ± 49.44) vs. 3000-m (70.63 ± 32.98) [(m/min × CMOI): BF10 = 169.6; p = <0.001]. Also, the Effindex was higher in 40-m MST (10.19 ± 4.17) vs. 3000-m (6.06 ± 2.21) [(m/min × ∇%SmO2): BF10 = 137.03; p = <0.001] and 40-m MST (9.69 ± 4.11) vs. 3000-m (7.55 ± 1.87) [(m/min × CMOI): BF10 = 1.86; p = 0.035]. This study demonstrates calculations of training intensity and load based on SmO2 as an internal load indicator along with speed as an external load indicator during two differentiated exercises.

Parallel FEM for structural analysis of reinforced systems

Calculations in software systems based on the finite element method (FEM), performed with account for genetic nonlinearity, i.e., assembling, are not feasible for a number of construction problems. In particular, in buildings made of factory-made and cast-in-place concrete, the latter is gradually involved in deformation and external load processes. In reconstructed buildings, during the increase in the element cross-section (e.g., reinforced concrete or metal casing), the reinforcing and reinforced materials are also involved in deformation and external load processes at different time. As a result, there are initial stresses and strains in the "old" part of the element by the time its "new" part installation and strength gain. At the same time, in the reinforcing material or cast-in-place element, the stress-strain state is zero until the additional load is applied.Thus, during the structural analysis, a change in the finite element stiffness is required. But FEM software systems have no finite element capable of changing (increasing) the stiffness. This determines the relevance of the developed algorithm for the structural analysis of factory-made and cast-in-place concrete buildings using the parallel FEM.Purpose: The aim of this work is to improve the parallel FEM and develop a calculation algorithm based on it.Research findings: Based on the parallel FEM, the calculation algorithm is proposed for factory-made and cast-in-place concrete buildings. The proposed algorithm accounts for the structural properties of such buildings, including the gradual involvement of different-aged materials in the deformation process. Using the proposed algorithm, the structural analysis is conducted for the reconstructed system, in which the finite element is replaced by the parallel element, and the hinge coupling of elements is simultaneously replaced by a rigid one.

Association between External Load and Injury Incidence in Professional and Elite-Youth Football Players

Association between External Load and Injury Incidence in Professional and Elite-Youth Football Players

Accelerated construction of projection-based reduced-order models via incremental approaches

We present an accelerated greedy strategy for training of projection-based reduced-order models for parametric steady and unsteady partial differential equations. Our approach exploits hierarchical approximate proper orthogonal decomposition to speed up the construction of the empirical test space for least-square Petrov–Galerkin formulations, a progressive construction of the empirical quadrature rule based on a warm start of the non-negative least-square algorithm, and a two-fidelity sampling strategy to reduce the number of expensive greedy iterations. We illustrate the performance of our method for two test cases: a two-dimensional compressible inviscid flow past a LS89 blade at moderate Mach number, and a three-dimensional nonlinear mechanics problem to predict the long-time structural response of the standard section of a nuclear containment building under external loading.