Load Ratio Research Articles

Comparison and regional suitability evaluation of different backfill source heat pumps using TRNSYS

As global energy demand and carbon emissions continues to rise year by year, the use of renewable energy for heating becomes increasingly urgent. This study employs solar and geothermal energy to supply heat to mining facilities. Initially, three distinct heating systems for mining areas were modeled in TRNSYS: the Backfill Source Heat Pump (BSHP), the Solar Assisted Backfill Source Heat Pump (SABSHP), and the Solar Assisted Backfill Source Heat Pump with Seasonal Heat Storage (SABSHP-SHS). Following a decade of simulation, the optimal system was identified through a comparative analysis that encompassed backfill temperature equilibrium, the inlet and outlet water temperatures for buried pipes, Coefficient of Performance (COP), Partial Load Ratio (PLR), and economic factors. Over the 10-year simulation period, the COP and PLR of the SABSHP-SHS system outperformed both the BSHP and SABSHP systems, showing higher energy efficiency and better heat pump performance. To further assess the regional adaptability of the SABSHP-SHS system, simulations were conducted across four regions with diverse climatic profiles: Shijiazhuang, Yan’an, Xining, and Hegang. The analysis focused on heat collection, efficiency, backfill temperature variation, system energy consumption, and the energy efficiency ratio. The findings indicate that Hegang exhibits the highest solar heat collection efficiency at 89.9% during the non-heating season, while Xining achieves a significantly higher heat collection efficiency of 54.1% during the heating season. These results suggest that the SABSHP-SHS system is particularly effective in regions with pronounced seasonal variations, characterized by extended cold winters and brief, intense summers.

Tribofilm distribution and tribological analysis of piston ring-cylinder liner interfaces under realistic engine conditions

The study investigates tribofilm distribution and tribology performance on piston ring-cylinder liner surfaces under realistic internal combustion (IC) engine conditions. By examining the effects of load, temperature, and oil film thickness ratio, the research reveals that the tribofilm is significantly greater on the cylinder liner surface compared to the piston ring surface. The findings highlight that a specific excitation pressure is necessary for tribofilm formation. An oil film thickness ratio of 1.8041 is evaluated as an accurate boundary for tribofilm distribution on the cylinder liner surface. These insights provide valuable data for designing piston ring-cylinder liner interfaces and improving IC engine performance.

Effect of Impact Energy on the Interface Microstructure of Explosively Clad Mild Steel and Titanium

Effect of load ratio (R) on the interface microstructure and phase stability was investigated in mild steel/Grade-2 Ti explosive clads using experimental and JMatPro® computations. At low-impact-energy conditions (i.e., R = 1.07), the interface exhibited a symmetrical wavy morphology with molten metal entrapped in isolated regions within the vortices of the waves, while at high-impact loading conditions (R = 3) the interface had complex weld solidification structure consisting of planar interface, columnar and equiaxed dendrites. Based on the study, it was concluded that under high-impact loading conditions, the interface microstructure of the explosive clads will resemble fusion welded joints, but with relatively lower thickness of the interaction zones.

Influence of reinforcement reductions on the response of reinforced concrete half-joints

Reinforced concrete half-joints are susceptible to deterioration mechanisms primarily due to the leakage of surface water, often contaminated with chlorides from de-icing salts, through the expansion joint. Due to the joint geometric form, favourable conditions can be created inside the joint for the corrosion of steel reinforcement. To this end, seven reinforced concrete half-joints were tested to failure under three-point bending to investigate the effect of reinforcement reductions that simulate common deterioration scenarios arising from the corrosion of reinforcement. The results were then compared to the predictions of nonlinear finite element analyses and the strut-and-tie method. The results demonstrated that a reduction in the amount of reinforcement close to the re-entrant corner has major influence on the load-deflection response of reinforced concrete half-joints. The largest reductions in load-carrying capacity were obtained from the half-joints with a full removal of diagonal bars and a combined removal of diagonal and U-bars, both showing reductions in load capacity of more than 50 %. The failure mode in each case of simulated deterioration scenarios involved a shear failure at the nib, except one case which displayed a shear failure in the full depth section due to the reduced anchorage of the bottom reinforcement. Furthermore, it was shown that nonlinear finite element analyses provide accurate predictions of the load-deflection response and failure crack patterns. The strut-and-tie method was found to result in overly conservative predictions, with an average observed-to-predicted load ratio of 1.48 and a coefficient of variation (COV) of 10.2 %. This is considerably higher than an average load ratio of 1.05 and a COV of only 3.1 % obtained from the nonlinear finite element analyses.

Fire Resistance Performance of Constrained H-Shaped Steel Columns with Uneven Vertical Temperature Distributions

Steel columns, which are widely used in building frameworks and spatial structures, are susceptible to capacity degradation during fires, potentially leading to the overall collapse of buildings. Existing research on the fire resistance of steel columns assumes that the temperature loads encountered by steel columns are evenly distributed vertically. However, real-world fire scenarios often feature significant vertical temperature differences. Therefore, this study comprehensively investigated these variations to derive a temperature curve that accurately represents real fire conditions. Subsequently, the fire resistance limits of steel columns were studied using this temperature curve, leading to a revised calculation formula for the critical fire resistance temperatures of steel columns. The following conclusions were drawn: (1) Nonuniform longitudinal temperature distributions are influenced by parameters such as the fire source distance, the heights of ventilation openings, and the distance between a vent and the temperature measurement point. Among them, the fire source distance has the greatest impact, with the maximum longitudinal temperature difference reaching over 500 °C. (2) Variations in the load ratio and longitudinal temperature differences alter the failure positions of steel columns, reducing their critical temperatures by up to 200 °C. (3) The revised critical fire resistance temperature formula is more accurate and safer compared with that outlined in the “Technical Code for Fire Protection of Steel Structures” (GB51249-2017). These findings offer valuable insights for the fire designs of steel columns.

Motor function is related to the lower phase angle than to muscle mass of the lower limbs in older females with hip osteoarthritis: a cross-sectional observational study

BackgroundMuscle mass and phase angle (PhA) can be measured using multi-frequency bioelectrical impedance analysis (BIA). Osteoarthritis of the hip (OAhip) causes decreased muscle mass and PhA in the deformed lower limb. However, previous studies have not accounted for the influence of sex, and thus, the relationship between muscle mass, PhA, and motor function remains unclear. This study aimed to elucidate the relationship between PhA, an index of muscle mass and quality measured using BIA, and motor function during gait and standing in female patients with OAhip.MethodsMuscle mass and PhA of patients with OAhip were measured using BIA. Motor function was evaluated using the Timed Up and Go test, ground reaction/weight, rate of force development/weight, and load ratio between the osteoarthritic (OA) and contralateral sides when standing up. The difference between the OA side and the contralateral lower limb was tested to clarify the characteristics of the deformed lower limb. The relationship between each motor function was determined using a partial correlation coefficient with age as a control variable and multiple regression analysis with each motor function as the dependent variable and age, OA-side muscle mass/body weight ratio, and PhA as independent variables.ResultsThis study involved 60 patients with OAhip (age 65.6 ± 7.6 years, height 154.2 ± 6.0 cm, weight 56.8 ± 10.5 kg) scheduled for unilateral total hip arthroplasty. Muscle mass, PhA, and lower limb load ratio were significantly decreased in the lower limbs on the OA side. Furthermore, using a partial correlation coefficient with age as a control variable, PhA showed significant correlations with motor functions related to standing up and walking, and multiple regression analysis revealed that PhA was independently related to each motor function. ConclusionsEvaluation and interventions that consider muscle quality rather than muscle mass are important.

Design of improved multi-cell L-shaped CFST columns under compression and bending

In recent years, there has been a notable surge in proposals for various forms of special-shaped concrete-filled steel tubular (CFST) columns. Despite various methods developed by researchers for determining the bearing capacity of multi-cell special-shaped CFST columns under different loading conditions, these methods remain lack unified. In this study, FE models were developed to simulate performances of improved multi-cell L-shaped CFST (ML-CFST) column under compression and bending. Parametric analyses have been performed to evaluate impact of various factors, including steel yield strength fy, compressive strength of concrete fcu, steel thickness t, loading direction θ, web height c, and axial load ratio n, on performances of ML-CFST columns. The findings of study indicate that the unidirectional flexural capacity of ML-CFST member exhibits a nearly linear relationship with the variables of t, fy, and c, with a minimal impact observed from fcu on flexural capacity. The width of extended section b, fcu, fy, and t have a certain effect on flexural capacity at any angle, particularly fy, t, and b. While fcu, fy, and t exert some influence on N/Nu-M/Mu correlation curves, their influences are marginal compared to the loading direction, which is the predominant influencing factor. Additionally, Mx0/Mπ/4-My0/M3π/4 curves gradually protrude outward with the increase in n. The effects of t, fy, and fcu on the shape of Mx0/Mπ/4-My0/M3π/4 curve were relatively insignificant. Simplified unidirectional flexural capacity calculation models were proposed based on stress analysis of cross-section under ultimate states. Given that flexural capacities estimated by simplified calculation model are slightly conservative, it is recommended to increase the flexural capacities by 10 %. Furthermore, an elliptical equation was formulated to predict the flexural capacity at any angle, with the predictions being slightly conservative. Based on ultimate equilibrium theory, a simplified calculation method was presented to predict unidirectional eccentric bearing capacities of ML-CFST columns. Through regression analysis, a simplified calculation method expressed as polar coordinate form for biaxial eccentric bearing capacity was established, with calculated values aligning well with FE results.

Urban Sharing Logistics Strategies against Epidemic Outbreaks: Its Feasibility and Sustainability

Epidemic (e.g., COVID-19) outbreaks can seriously disrupt logistics, and the coordination of intercity logistics and urban distribution plays an important role in goods distribution. In previous studies, some scholars analyzed different sharing logistics mechanisms for cost reduction and efficiency improvement, while others analyzed the disruption problems in both logistics and supply chain management. In this study, we combine these two operational management philosophies and first develop a two-echelon logistics benchmark model (BM), with two intercity logistics companies and two urban distribution companies, taking into consideration the load ratio and the disruption factor. This is the first time that the load ratio is considered in research on logistics, and it will make the supply and demand as well as the cost structure of logistics services much more practical. We then develop three urban sharing logistics models with two intercity logistics companies and one urban sharing logistics distribution company, with the sharing mechanisms SM1 (only sharing logistics), SM2 (sharing logistics with revenue sharing), and SM3 (sharing logistics with equity investment). We compare the pros and cons of the three sharing mechanisms and identify the optimal and suboptimal Pareto improvements for the BM. We identify different sharing decisions with respect to different load ratios and the disruption ratio. Finally, we analyze the sustainability of the three sharing mechanisms from the load ratio, low-carbon, and low-disruption dimensions. The managerial implications drawn from the model and case study provide a practice framework for sharing logistics operations: vertical integration, the standardization of logistics technology and equipment, and coordination and sharing.

Dynamic response characteristics of variable hyperbolic circular-arc-tooth-trace cylindrical gear transmission system considering wear effect

To illustrate the impact of tooth surface wear on the dynamic response of the cylindrical gear transmission system with variable hyperboloid circular-arc-tooth-trace (VH-CATT), a nonlinear dynamic model of VH-CATT cylindrical gear that considers wear effect was developed in this article. Firstly, according to the analysis conducted through the finite element method, the time-varying meshing stiffness of VH-CATT cylindrical gear is calculated, and the time-varying meshing stiffness considering wear is characterized by introducing wear fault characteristics. Then, the load ratio is introduced to represent the relationship between the error amplitude and the excitation load. By using the error amplitude as the bifurcation parameter, this parameter describes how the excitation load affects the dynamic characteristics of the VH-CATT cylindrical gear. Finally, the bifurcation diagram and maximum Lyapunov exponent of the VH-CATT cylindrical gear transmission system under various wear depths are computed using the fourth-order Runge-Kutta method. At the same time, the response state of the VH-CATT cylindrical gear is verified by phase diagram, Poincaré mapping and time history diagram. The findings indicate that the vibration amplitude of the VH-CATT cylindrical gear system increases as the error amplitude increases. The vibration phenomenon of VH-CATT cylindrical gear transmission system with wear fault is more obvious, and the system enters the bifurcation and chaos effect state in advance. Therefore, the wear of the tooth surface will lead to the decrease of the gear meshing stiffness, which will lead to the increase of the vibration amplitude of the system, resulting in the phenomenon that the dynamic response state of the system is advanced. The research results will provide a theoretical basis for high-quality VH-CATT cylindrical gear transmission and gear nonlinear dynamics research.

Finite Element Analysis of Shear Performance for Reinforced Concrete T-Beams by Polymer Bars Strengthened with Carbon Fiber Using Embedded Through Section Technique

The purpose of this research presents the research results obtained from a numerical simulation using the ABAQUS/CAE version 2019 finite element software. This study tested the shear behavior of T-beams made of reinforced concrete (RC). The structure is reinforced with a carbon fiber reinforced polymer (CFRP) bar embedded through a section (ETS). The numerical validation approach implicated using numerical analysis on the experimental data collected from twelve reinforced concrete (RC) T-beams divide into two groups each group include reference beam, the field of numerical analysis was expanded to encompass the examination of many aspects, such as the impact of the diameter of CFRP bars. The main objective of this project is to create a computational model that accurately transcribes the complex nonlinear properties inherent in beams. This work conducts a comparative investigation of computational and experimental models, with a specific focus on their load-deflection features and cracking patterns. The study found that the average ratio of ultimate load to deflections in numerical model simulations for beams was 1.011, whereas in experimental testing it was 0.928. The research findings establish a clear correlation between the diameter of CFRP bars and the stiffness of a beam, assuming a constant angle of inclination and spacing.

Fire resistance of square double-skin concrete-filled steel tubular columns and concrete-filled double steel tubular columns

Square double-skin concrete-filled steel tubular (DSCFST) columns and concrete-filled double steel (CFDST) columns possess excellent load-carrying capacity and ductility. However, there has been limited research on the responses of DSCFST and square CFDST columns exposed to fire. This paper presents a series of tests on such columns loaded concentrically to determine the effects of the steel tube thickness, the strength of materials, load ratio, and boundary conditions on their fire resistance. Additionally, finite element (FE) models are established using ABAQUS, in which the concrete’s transient creep strain is considered through the development of the user-subroutine UEXPAN. A parametric study is undertaken by simulating 156 FE models to further study the behavior of DSCFST and CFDST columns under fire exposure. The fire test and numerical results suggest that both the load ratio and strengths of the internal tube and concrete core play significant roles in determining the fire resistance of DSCFST and CFDST columns. The developed FE models are demonstrated to capture well the fire behavior of loaded DSCFST and CFDST columns. The proposed design model predicts the ultimate loads of DSCFST columns with good accuracy; therefore, it can be employed in the practical design of DSCFST columns.

Flexural performance of narrow RC beams hybrid strengthened by TRECC plate

This paper proposes a novel hybrid strengthening method for narrow reinforced concrete (RC) beams that combines fiber-reinforced polymer (FRP) textile-reinforced engineered-cementitious composites (TRECC) plates along with a self-locking anchorage system. To evaluate the effectiveness of the proposed system, a series of four-point bending tests were conducted. These tests were designed to understand the effects of different strengthening methods, number of FRP grid layers, and TRECC bond lengths. The results showed that the hybrid strengthening system could effectively prevent the end debonding failure and impede the development of the intermediate debonding in the TRECC plate. Consequently, the TRECC plate can continue to carry the force, leading to a significant increase in strengthening efficiency, quantified as the increased ratio of the peak load of the strengthened beams to that of the reference beam. Furthermore, increasing the number of FRP grid layers can also improve the strengthening efficiency. However, longer TRECC bond length in hybrid strengthened beams will reduce the strengthening efficiency since the intermediate debonding will be more susceptible to occur; the design for appropriate bond length is necessary. Finally, an analytical model to predict the flexural capacity was derived and verified against the experimental results.

Assessment of Ductility Demand-Based Blast Damage to Reinforced Concrete Columns under Blast Loads

This study was conducted to evaluate the influence of various structural variables on the blast damage to reinforced concrete columns. The selected primary variables were the longitudinal reinforcement ratio, transverse reinforcement ratio, and axial load ratio, with the analysis based on the ductility demand to assess the blast damage. A parametric study based on finite element analysis was performed to analyze the effects of these variables. The results revealed that an increase in the longitudinal and shear reinforcement ratios significantly decreased the level of damage sustained by the columns under blast exposure, whereas an increase in the axial load ratio resulted in a comparatively lower reduction in damage. Columns with higher transverse reinforcement ratios experienced more severe damage owing to compression-induced brittle failure as the axial load ratio increased. This study provides guidelines for the appropriate selection of design variables to mitigate blast damage in columns.

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.

A Model to Account for the Effects of Load Ratio and Hydrogen Pressure on the Fatigue Crack Growth Behavior of Pressure Vessel Steels.

A phenomenological model for estimating the effects of load ratio R and hydrogen pressure PH2 on the hydrogen-assisted fatigue crack growth rate (HA-FCGR) behavior in the transient and steady-state regimes of pressure vessel steels is described. The "transient regime" is identified with crack growth within a severely embrittled zone of intense plasticity at the crack tip. The "steady-state" behavior is associated with the crack growing into a region of comparatively lower hydrogen concentration located further away from the crack tip. The model treats the effects of R and PH2 as being functionally separable. In the transient regime, the effects of the hydrogen pressure on the HA-FCGR behavior were negligible but were significant in the steady-state regime. The hydrogen concentration in the steady-state region is modeled as being dependent on the kinetics of lattice diffusion, which is sensitive to pressure. Experimental HA-FCGR data from the literature were used to validate the model. The new model was shown to be valid over a wide range of conditions that ranged between -1≤R≤0.8 and 0.02≤PH2≤103 MPa for pressure vessel steels.

Energy performance analysis of multi-chiller cooling systems for data centers concerning progressive loading throughout the lifecycle under typical climates

AbstractThe increasing demand for cooling energy in data centers has become a global concern. Existing studies lack a comprehensive analysis of the energy performance of widely used multi-chiller cooling systems in air-cooled data centers throughout their lifecycle, especially concerning progressive loading. To bridge this gap, this study conducts a thorough assessment of the energy performance of multi-chiller cooling systems throughout the entire lifecycle. Additionally, the impact of climate conditions on the energy efficiency of the cooling systems is analyzed, considering design variations for typical climates. Multi-chiller cooling system models are developed using the test data of cooling equipment and typical control algorithms. The energy performance of the cooling system is thoroughly analyzed under full-range cooling loads and climate conditions. Results show that free cooling time could differ up to 1442 hours at different part load ratios in the same location. Furthermore, the cooling system’s coefficient of performance (COP) varies significantly, by up to 6, at different part load ratios, corresponding to a difference in power usage effectiveness (PUE) up to 0.14. Notably, the average cooling system COP throughout the lifecycle loading is found to be only 11.7, 2.9 lower than the design system COP.

Practical solutions for global buckling analysis in tall buildings: classic sandwich continuous model

Static stability analysis of global buckling and critical load ratio calculation are among the fundamental and most important parameters for structural analysis and design in numerous engineering applications across various fields. Particularly in the field of structural engineering, the critical load ratio is a parameter that determines the overall performance of tall buildings; however, due to the complexity of coupled differential equations with variable coefficients associated with different classical continuous models, its analysis has not been widespread, and only specific cases have been solved. This article utilizes the classic sandwich beam, widely studied in the literature, to propose an analytical solution and a generalized numerical solution to address the elastic buckling problem with applications in tall building stability analysis. The analytical solutions are applicable to uniform structures and consider point, uniform, and variable compression loads along their length that can be expressed through polynomial functions. The generalized numerical solution addresses the general case of structures with uniform or variable properties. Numerical applications and parametric analyses show excellent agreement between the results of the proposed methods and those of one-dimensional finite element methods. The influences of key parameters on the behavior of the eigenvalue associated with global buckling analysis are analyzed, and graphs and tables are proposed for direct practical application by engineers. Due to their mathematical formulation and excellent precision in results, the proposed methods can be safely used in the preliminary and final analysis of tall buildings and can be easily adapted to other engineering fields.

Delivering holistic energy-saving operation for heterogeneous all-parallel chiller plant systems through two-stage optimization assisted by input convex neural networks

With the rapid growth of building cooling demand and energy consumption, the potential for energy-saving operations gave rise to the popularity of implementing heterogeneous all-parallel chiller plant systems in large-scale public buildings. Meanwhile, heterogeneity, multi-dimensionality, and tight coupling interactions considerably complicate the holistically optimal operation of the system. Although artificial neural networks (ANN) have achieved great success in complex system identification, the endogenous non-convexity of classical feedforward neural networks (FNN), which are widely applied in model-based optimization for chiller plant operation, makes conventional optimizers prone to falling into local optima, forcing previous methodologies to sacrifice model precision for computational tractability. In this study, a special type of ANN named input convex neural network (ICNN) was leveraged to identify five individual convex models for energy-consuming units in the chiller plant system, providing convex input-output mappings while preserving high-resolution representations. Then, a two-stage optimizer with a sequential integration of a global searcher and a local optimizer was developed to effectively solve the holistic energy-saving problem by optimizing ten decision variables including chilled water supply temperature, partial load ratio of chillers, speed ratios of pumps and cooling tower fans, cooling water flow rate of cooling towers, and on/off states of devices. Finally, the methodology was deployed to a case study using on-site operation data and was compared with conventional candidates. Average holistic energy-saving ratios of 13.37% and 9.14% were achieved with average runtimes of 1.12 s and 1.07 s by the proposed optimizer in the high-load and light-load scenarios, respectively, showcasing more advantageous in resolving the operation optimization of complicated chiller plant systems.

The Evolution of Surfaces on Medium-Carbon Steel for Fatigue Life Estimations

Early in fatigue life, fatigue cracks are often initiated at persistent slip bands (PSBs), which play the main role in surface evolution when the components are subjected to cyclic loading. Therefore, this paper aims to study the behavior of the surface development of medium-carbon steel, specifically 42CrMo4 (SAE 4140). Tests were conducted using tension–compression fatigue testing with stress amplitudes set at 30%, 40%, and 50% of the ultimate tensile strength (UTS); a load ratio of R = −1; and a frequency of f = 10 Hz. The ultimate number of test cycles was 2 × 105. The fatigue test specimens with as-machined surface quality (Ra < 100 nm) were tested on a servo-hydraulic push–pull testing machine, and the tests were interrupted a few times to bring the specimens out for surface measuring with a confocal microscope. The linear roughness values of the arithmetic mean deviation (Ra), maximum height (Rz), maximum profile peak height (Rp), and maximum profile valley depth (Rv) were investigated and further used to determine the roughness evolution during cyclic loading (REC) by analyzing the inclinations of the fitting curves of roughness and number-of-cycles diagrams. REC could then be used to estimate and classify the fatigue lifetime.

Effect of Connection Detailing on Reverse Cyclic Behaviour of Precast Beam to Column Grouted Cementitious Billet Connections

In reinforced concrete framed structures exposed to high lateral loads, the performance of the beam to column joints has been acknowledged to have a significant impact on the overall behaviour of the structures. The present study conducted an experimental investigation on four 1/3rd scale Precast Concrete (PC) beam-to-column grouted cementitious billet connections subjected to reverse cyclic loading. Their performance was compared with a reference monolithic connection. The various precast connections studied are Billet with Dowel (BD) connection, Billet with Dowel-cleat Angle (BD-CL) connection, and Extended Billet with Dowel-cleat Angle (EBD-CL) connection. The ultimate load-carrying capacity, ductility factor, hysteretic behaviour, load ratio, energy dissipation, and stiffness degradation of the monolithic (MO) and precast (PC) specimens were studied, and a comparison of their performances was made. The results show that the EBD-CL connection has comparable ductility and strength.