Combined Loading Research Articles

Mechanical behaviour and instability mechanism of sandstones with impact tendency under different loading paths

ABSTRACT To reveal the instability and failure mechanism of pillars with impact tendency, the Brazilian test, uniaxial compressive test, cyclic loading and unloading (CLU) tests were performed on sandstones which had impact tendency. The stress drop phenomenon was obvious in the fracture stage during the Brazilian test. The main tensile crack with penetration type appeared. Under the CLU condition, the CLU had a significant effect in enhancing the mechanical character of rocks. Under the combined loading, the character stress of rocks tested with the CLU was greater than the uniaxial loading. Moreover, the greater the first cyclic threshold, the greater the character stress of rocks. Under the uniaxial loading, the failed samples showed tensile fractures. The damage location of the samples was closely related to the Poisson effect and the ending face effect. With the electron microscope which had the same magnification, the crack deterioration degree of samples under the uniaxial loading was greater than the CLU condition. Moreover, with the first cycle threshold increasing, the surface roughness of rocks gradually decreased. The quantity of secondary micro cracks gradually decreased. The propagation and penetration phenomenon gradually disappeared. The micro structure and loading properties of rocks were affected by the bonding force and structural characters between the internal structure and matrix. Based on the micro-seismic signal of the damaging threshold, the seismic source damage location can be located. Moreover, the pillar-typed burst area can be forewarned. This research benefits predicting the pillar-typed burst disaster.

Bearing capacity of large-diameter pile foundation under combined VHM loadings in soft clay

ABSTRACT The large-diameter pile foundation is with an intermediate depth, widely used in engineering fields such as ports, breakwaters and rapid construction of artificial islands as a supporting structure to resist lateral loads. However, there is limited research on the bearing performance of such large-diameter, intermediate-depth pile foundations. In this paper, the finite element method is used to investigate the bearing capacity of the large-diameter pile foundation with different embedment ratios in homogeneous soil and normally consolidated soil and the prediction formulas for uniaxial and combined bearing capacity are developed. This study also sets up three different skirt wall–soil interface properties to discuss their influence on the bearing performance of the large-diameter pile foundation. The research is systematic, and relevant analysis can provide practical suggestions for engineering design.

Deformation and fracture behaviors of Ti6Al4V alloy fabricated by laser powder bed fusion under combined tension and shear loading

The present work aims to study the deformation and failure behavior of laser powder bed fusion (LPBF) manufactured Ti6Al4V alloy. Uniaxial tension, pure shear, combined tension and shear specimens in horizontally, inclined and vertically (0°, 45° and 90°) building directions have been tested and observed by digital image correlation (DIC) technique. Significant anisotropy in ultimate strength, strain hardening and maximum elongation were observed. The failure mechanisms of 0°, 45° and 90° built LPBF Ti6Al4V alloy under different stress states are revealed by fractographical analyses. As the stress triaxiality increases from 0 to 0.33, distortion and shearing of micro voids induce the failure of shear specimen whilst void nucleation, growth and coalescence is the dominant failure mechanism of LPBF Ti6Al4V alloy under tension. The inherent defects significantly affect shear and tensile performance, large interlaminar shear deformation appears in horizontally built shear specimen, the tensile loading is prone to open the defects of vertically built uniaxial tensile sample due to the building direction. It can help to better understand the failure mechanism and improve the quality of LPBF Ti6Al4V in practical applications.

The relationship between back handspring step out performance and take-off technique in female gymnasts

ABSTRACT Although the back handspring step out (BHS) is a foundational skill in balance beam routines, it can be performed using different take-off techniques. Back injuries are highly prevalent in the BHS due to the combination of high spine extension and joint loading. However, it is unclear which technique minimises injury risk or leads to better BHS performance. The purpose of the study was to identify techniques used for the BHS take-off and analyse the resulting BHS performance. Gymnasts were found to use either: Simultaneous Flexion—trunk and knees flex at the same time; Sequential Flexion—trunk reaches its maximum flexion followed by knee flexion; or Double-Bounce—knees and trunk both flex and then the knees extend and flex again. To assess performance, point deductions were calculated, and dynamic balance, ground reaction forces (GRFs) and relevant joint angles were analysed. The techniques had no differences in point deductions or dynamic balance, but there were differences in GRFs, spine extension and knee flexion. The Sequential Flexion technique had the lowest spine extension, which potentially reduces back injuries and the lowest knee flexion, which is a BHS requirement. These results support the use of Sequential Flexion technique when performing the BHS.

A physical‒data-driven combined strategy for load identification of tire type rail transit vehicle

Tire load is one of the basic input parameters required for vehicle design and safety evaluation. Identifying the tire load with high accuracy is of great significance. However, the direct measurement of tire load is often high-cost and complex. Meanwhile, load identification solely based on physical measurement or data has great limitations of low accuracy and low robustness. This paper proposes a physical‒data-driven combined load identification strategy that includes an extended Kalman filter (EKF) and a data-driven correction model. These two models are configured in series. Derived from a physical state-space model of the vehicle dynamics, the EKF is used for the preliminary identification of the load. The data-driven model extracts the spatial and temporal characteristics of signals through the convolutional neural network and bidirectional gated recurrent unit, and then predicts the errors of the extended Kalman filter and corrects the identified results. The presented strategy is applied to an APM300 rubber wheel vehicle for load identification. The results have shown that the physical‒data-driven combined strategy can reduce the influence of parameter perturbation and improve the identification accuracy (6.4%). Thanks to organically combining the physical- and data-driven methods and integrating the rules and experience of the entire system, the strategy has strong generalization performance. Compared with traditional algorithms, the presented strategy could effectively reduce the error of load identification, improve adaptability under different operating conditions, and handle the measurement error of different noise levels, which are of practical application value in the engineering field.

Development of Approaches for Strengthening and Retrofitting of Concrete Beams Using Structural Steel

In structural analysis, the term 'frame' typically refers to a robust structure comprising various elements such as slabs, beams, columns, and footings. These components are cast together to create a monolithic construction, effectively functioning as a single integral unit. The frame is subject to various forces, which are transferred through its different components. Additionally, changes in facility usage or the introduction of additional live loads can exert further stresses on the structure. Consequently, it is imperative that the elements of the frame possess sufficient strength to withstand these loads. In this study, we focus on the development of approaches for strengthening and retrofitting concrete beams using structural steel elements. Specifically, our investigation involves the analysis of beams under different load combinations to enhance their integrity performance. To achieve this, angles and steel plates are utilized for reinforcement. We conduct numerical analysis through finite element modeling using ANSYS Workbench. Multiple beam models are created within the ANSYS platform, allowing us to study and compare various outcomes, including total deformation. This comprehensive approach aims to contribute to the advancement of methods for enhancing the structural resilience of concrete beams in real-world applications.

Energy absorption of braided composite tubes under quasi-static combined shear-compression loading

In this paper, the energy absorption performance of braided composite tubes under combined shear-compression loading is investigated. ABAQUS/Explicit is employed to analyze the energy absorption of braided composite tubes, and quasi-static compression tests are carried out. Braided composite materials absorb energy through the damage accumulation in laminate. Thus, to maximize energy absorption performance, a progressive crushing mode should be induced. While extensive research has been conducted on cases of axial loading, understanding of the energy absorption performance of braided composite tubes under combined shear-compression loading remains limited. Experimental results reveal that under both axial and combined shear-compression loading at 30 degrees, the braided composite tube exhibits a progressive crushing mode. The test results are utilized to validate the finite element model. Through finite element analysis, it is confirmed that the damage accumulation in laminate is maximized due to the induction of a progressive crushing mode. It means that the energy absorption principles of braided composites apply similarly to combined shear-compression loading, allowing for the maintenance of superior energy absorption performance of braided composites under various load angles.

Evaluation of the mechanical properties of stiffened composite panels under consideration of water load

Abstract To meet the strength evaluation requirements of a typical stiffened composite panel of the lower fuselage of a new generation amphibious aircraft underwater load, the experimental testing technique and finite element analysis method were investigated. Firstly, according to the loading and support requirements of the typical stiffened composite lower fuselage panel, a testing device for combined axial and pneumatic loading was designed and developed. Then, a finite element model of the stiffened composite plate and the combined load testing device were created. Based on the experiments and finite element analysis, the static strength of the stiffened composite plate was verified to meet the load-bearing capacity requirements, and the strain behavior during loading was determined. Compared with the experimental results, the maximum strain error at the skin is 6.16%, and the maximum strain error at the stiffener is -11.6%. This confirms the effectiveness of the finite element model and also confirms that the test technique and equipment can accurately simulate in-plane axial loading and out-of-plane water loading. Finally, based on the validated finite element model, the load-bearing capacity of the stiffened composite panel under combined loads was predicted.

247.10: The combination of TTV viral load and BKV-neutralizing antibody titers aids in stratifying the risk of BKV viremia.

247.10: The combination of TTV viral load and BKV-neutralizing antibody titers aids in stratifying the risk of BKV viremia.

Analytical and FE modeling of a bi-directional functionally graded Timoshenko beam under thermomechanical loading

Functionally graded materials (FGMs) have variable volume fractions in different directions, making structural analysis challenging due to shear deformation. This study investigates the behavior of a two-directional functionally graded material (TDFGM) Timoshenko beam under thermomechanical loads. Varied material properties in both axial and transverse directions are analyzed using a mathematical approach and a finite element model. The mathematical approach involves transforming the system of two ordinary differential equations to a single fourth-order differential equation to determine deflection and rotation. Additionally, a bilinear quadrilateral element is used to validate the mathematical solution. The results show that increasing grading parameters reduced transverse deflection, with a maximum reduction of 38.97% for CF beams and 39.26% for SS beams when the gradation index az increased from 0 to 1 under mechanical loading. Under combined mechanical and thermal loading, higher temperatures on the beam’s hot side lead to increased deflection, with notable increases at higher gradation indices. Moreover, increased maximum deflection by 6.29% for CF beams and 4.05% for SS beams when considering temperature-dependent properties. It was observed that when TDFGM Timoshenko beams were heated for thermal loading, the SS beam deflected in the opposite direction of the applied mechanical load. The results agree with previous research and indicate alignment between mathematical and finite element solutions. The impact of boundary conditions on the deflection of Timoshenko beams made of TDFGM is discussed. The introduced methodology enhances TDFGM beam bending analysis, allowing control over behavior through grading parameters and boundary conditions selection.

Analysis and Design of Box Culvert for Durability against Varying Thickness of Cushion

Abstract: This study presents the structural analysis of a reinforced concrete (RCC) box culvert with dimensions 1m x 2m x 1.5m, subjected to varying cushion loadings of 0.770m, 1.010m, and 1.200m, using STAAD.Pro software. The analysis focuses on both Ultimate Limit State (ULS) and Serviceability Limit State (SLS) criteria to ensure the structural integrity and durability of the culvert. For ULS, load combinations include dead load, live load, earth pressure, and cushion load, assessing the culvert's capacity to withstand maximum expected loads without failure. The study evaluates bending moments, shear forces, and ensures that the flexural and shear strengths of the culvert are within permissible limits. Results indicate that even under the highest cushion loading, the culvert design remains robust with appropriate reinforcement. For SLS, the analysis incorporates quasipermanent load combinations to evaluate deflections and crack widths, ensuring the structure's functionality and aesthetic durability under normal service conditions. Deflections and crack widths for all cushion depths were found to be within acceptable limits, demonstrating the culvert's ability to maintain serviceability and resist long-term degradation. Overall, the analysis confirms that the RCC box culvert, when designed according to the principles of ULS and SLS, achieves a balance between safety, functionality, and durability, ensuring reliable performance over its service life.

Dynamic Adaptative Surveillance Training in a Virtual Environment Using Real-Time Cognitive Load and Performance

Dynamic difficulty adjustment of serious games is a field of research seeking to assist participants attain an ideal learning state. To achieve this, the difficulty of a game is adjusted in real-time to approach the capabilities of the player. Many dynamic difficulty adjustment systems only measure a few variables, often solely player performance, and adjust a limited number of in-game aspects. Little research has sought to ascertain if measuring a combination of cognitive load with measures of performance in real-time leads to a more effective dynamic difficulty adjustment system. Building on research which defined ‘mental efficiency’, we conducted a novel experiment to address this gap. This is achieved by comparing two versions of a surveillance training serious game; one a linear approach and the other with our unique cognitive load and performance-based dynamic difficulty adjustment system. Our experiment included n=52 participants (26 per treatment group). The experiment demonstrates that our approach achieved similar performance outcomes with lower cognitive load, in less time than the linear difficulty approach. These results indicate that our system enhances learning capacity and may prove beneficial for future serious games.

Analysis on slope stability by anchorage based on soil creep with flood effect

In order to analyze the adverse effect of flood affection on slope stability, the analytical expressions of buoyancy force and capillary force, hydrodynamic pressure and impact force, and scour erosion were proposed based on the aging characteristics of soil shear strength and limit equilibrium theory. According to the load combination and flood action, shear failure occurs preferentially at the foot of slope. Then, the plastic zone continues to extend upward to produce traction landslide disaster mode. Furthermore, the power function relation between shear strength index and time was established. The nonlinear accelerated creep model was also obtained. At the same time, the safety factor formula for flood loading effect slope aging stability, the time-varying characteristic value of anchor force and the compensation value of anchor force were also obtained and used to research sliding mechanism. In addition, the numerical calculation example shows that the slope safety factor decreases by more than 20 % considering the effect of flood ascending scour and impact, and the compensation value of anchorage force increases obviously with time increasing. Simultaneously, the change rate of compensation value of anchorage force increases nonlinearly with the increase of design safety factor.

Stress relaxation assessment of high-temperature bolts under combined biaxial loads: Theory and simulation

Estimating bolt stress within high-temperature bolted connection systems is crucial for determining bolt preload and assessing bolt assembly integrity. This work proposes a theoretical model for estimating high-temperature bolt load under combined tension, bending, torque, and shear loads, considering the characteristics of bolt stress distribution and relaxation. To assess the model's accuracy, finite element analysis was employed to examine the impact of various creep parameters and load combinations on bolt stress relaxation. The results indicate that the introduction of bending moments, torque, and shear loads accelerates axial stress relaxation in bolts. Under a high-temperature load for 300,000 h, the stress relaxation predicted by the theoretical model aligns well with the results from finite element analysis.

Experimental investigation and probabilistic analysis of the buckling load of isotropic cylinders under multiaxial loading

This paper presents a multitude of experimental results for cylindrical shells under combined loading. The loading is a combination of axial compression and bending moment. These are accompanied with numerical simulations. The load ratio itself is subject to scatter, a direct comparison and application of results for the sizing of shells is not straight forward. Therefore, a new approach is presented, which transfers the results to normalized load factors.

Experimental behavior and fracture prediction of a novel high-strength and high-toughness steel subjected to tension and shear loading tests

In this study, laboratory testing and numerical simulation methods are used to investigate the mechanical behavior and perform fracture prediction of a novel high-strength and high-toughness steel with a negative Poisson's ratio (NPR) effect under combined tensile-shear loading conditions. A test device capable of meeting different tensile-shear combination test angles is designed and manufactured, wherein the mechanical experiments on the NPR (Negative Poisson's Ratio) steel specimens are carried out at various testing angles. Q235 steel and MG400 steel are used as experimental control groups. The results show that the mechanical deformation of NPR steel is significantly better than that of Q235 steel and MG400 steel. Its tensile-shear test curve has no yield plateau and it has quasi-ideal elastic-plastic mechanical properties. The loading direction gradually changes from tension-dominated to shear-dominated as the tension-shear angle increases, and the strength and deformation of the specimens show a decreasing trend. Based on the laboratory test results, a finite element numerical model of NPR steel is established. A series of numerical simulations are carried out under the conditions of different tension and shear angles and the average stress triaxiality and fracture strain data are obtained. The fracture data of NPR steel are fitted using the Johnson-Cook fracture criterion, and the Johnson-Cook fracture parameters under the tensile-shear test conditions of NPR steel are thus obtained. The numerical simulation verifies that the fracture model can accurately predict the tensile-shear fracture behavior of NPR steel.

On thermo-mechanical buckling of porous bi-directional functionally graded plates using isogeometric analysis

The combined thermal and mechanical loads usually lead to buckling failure of key structures in various engineering fields. It is found that porous functionally graded structures can be used to reduce and evenly prevent potential impact on the stability of structures from extremely high temperature loads. In this paper, we employ the isogeometric analysis (IGA) method to investigate the thermo-mechanical coupling buckling behaviors of porous bi-directional functionally graded (PB-FGM) plates with porosity. The material properties such as Young's modulus, Poisson's ratio, and thermal expansion coefficient are assumed to be linearly dependent on the x-axial and z-axial coordinates. Such a gradient property can be easily realized by changing the porosity distribution. Based on the first-order shear deformation theory (FSDT), the thermo-mechanical buckling behaviors of PB-FGM rectangular and circular plates under combined thermal and mechanical loads are numerically studied. This paper elucidates the mechanical mechanism through which gradient indexes, aspect ratios, loading types, and boundary conditions influence the critical thermo-mechanical coupling-induced buckling temperature.

Dietary Interventions for Cancer Prevention: An Update to ACS International Guidelines.

Cancer, the second leading cause of death worldwide, demands the identification of modifiable risk factors to optimize its prevention. Diet has emerged as a pivotal focus in current research efforts. This literature review aims to enhance the ACS guidelines on diet and cancer by integrating the latest findings and addressing unresolved questions. The methodology involved an advanced PubMed search with specific filters relevant to the research topic. Topics covered include time-restricted diet, diet quality, acid load, counseling, exercise and diet combination, Mediterranean diet, vegetarian and pescetarian diets, weight loss, dairy consumption, coffee and tea, iron, carbohydrates, meat, fruits and vegetables, heavy metals, micronutrients, and phytoestrogens. The review highlights the benefits of the Mediterranean diet in reducing cancer risk. Adherence to overnight fasting or carbohydrate consumption may contribute to cancer prevention, but excessive fasting may harm patients' quality of life. A vegetarian/pescetarian diet is associated with lower risks of general and colorectal cancer compared to a carnivorous diet. High heme and total iron intake are linked to increased lung cancer risk, while phytoestrogen intake is associated with reduced risk. Coffee and tea have a neutral impact on cancer risk. Finally, the roles of several preventive micronutrients and carcinogenic heavy metals are discussed.

An improved similarity method for stiffened plates subjected to combined loads of longitudinal compression and lateral pressure

Structures’ ultimate strength has been increasingly valued in the past few decades. The model test is an important and reliable way to estimate the ultimate strength. For large and complex structures, like ship hull structures, the test subject is usually scale models due to the limitation of loading capacity and space of laboratories. Therefore, the similarity method and the design of scale models are of great importance. The stiffened plate is the minimum unit that makes up thin-walled structures. The similarity method of the ultimate strength of stiffened plates is the base of the similarity method of large and complex structures. This paper is a further study of an existing similarity method proposed in our previous work. A stiffened plate from a real ship is taken as the subject. 22 combinations of scale ratios are used to design scale models. The 23 models (including the original model) are subjected to a combined load of longitudinal compression and lateral pressure. The non-linear finite element method is used to analyze these models. The results revealed that the previous method is only suitable for scale models with small degrees of geometrical distortion. It didn't consider the effect of geometrical distortions. An improved similarity method and scale model design method are proposed to solve these problems. The improved methods consider the geometrical distortion of scale models and are applicable to more geometrically distorted scale models. More numerical examples are performed to verify the correctness and advantage of the improved methods.

Flexural behavior of corroded RC beams repaired with high performance cementitious mortar under cyclic loading

AbstractThe understanding of the cyclic performance of reinforced concrete (RC) elements is of vital importance in relation to the extent of the service life of buildings and infrastructures. Steel rebar corrosion plays a major role in this regard because it significantly affects the overall structural integrity, especially under cyclic loads, leading to reduced stiffness and load‐bearing capacity of structural elements. Cyclic condition has the potential to accelerate the corrosion‐induced cracking and spalling, the effectiveness of the bond strength between rebar and concrete, and also the ductility and energy dissipation characteristics of the structure. The primary objective of this study is to investigate the effectiveness of a high‐performance thixotropic repairing cementitious mortar in improving the fatigue behavior of RC elements through a multiscale experimental approach. First, at the material scale of concrete specimens, two different concrete classes together with the repairing one‐component, pre‐blended, thixotropic cementitious mortar, were tested under incremental cyclic condition. Based on the results obtained from material scale, four reinforced concrete beams were exposed to different levels of accelerated corrosion by means of the impressed current technique and, subsequently, repaired by bonding a layer of the thixotropic high‐performance mortar onto the tension side. Finally, beams were tested under incremental cyclic four‐point bending test to investigate the fatigue behavior in terms of crack onset, propagation and energy dissipation. The resulting cyclic properties and cracking behavior of the structural elements were related to the level of corrosion achieved through the accelerated test and the effectiveness of the structural repair mortar was proven. In terms of code compliance, the repairing mortar was able to fulfill the requirements of frequent and quasi‐permanent combination of loads, remaining below all the threshold values provided by the Italian NTC2018 and Eurocode.