Maximum Load Level Research Articles

Effect of Load on Sequential Imperfect Preventive Maintenance and Replacement Schedules of Mechanically Repairable Machines

This paper examines the impact of load on the operational time and maintenance cost of mechanically repairable machines. Three different levels of load with multiplicative impact on the hazard rate of the failure distribution were applied to the working of a cassava grinding machine using a two-parameter Weibull distribution with respective hazard and cumulative hazard functions. Their effect on the preventive maintenance (PM) and replacement schedules revealed that at above maximum load level, the length of the machine’s operational time decreased drastically compared to the decrease at maximum load level and relative decrease at the below maximum load level when compared to the machine’s operational time at the minimum load level. The application of load also results in frequent preventive maintenance actions and an increase in machine downtime for a given cost ratio. This implies that the influence of load on the PM and replacement maintenance schedule of mechanically repairable machines is essential to the design and operation of such machines. The results also provide maintenance engineers with an operational guide for PM and replacement maintenance actions in order to prevent failure maintenance and increase the machine’s availability for enhanced productivity.

Шумовое загрязнение территории многоэтажных жилых застроек города Ставрополя

The article provides measurement results and an assessment of the noise load on the territory of the «Perspektivny» and «Rossiysky» residential complexes in Stavropol. Noise measurements were carried out in the spring-summer and autumn-winter periods of 2022–2023. The measurement results are presented as average noise exposure levels. Based on the data obtained, a mathematical model of the propagation of noise from traffic flow during the deciduous and leafless period was built. To conduct a study and assess the noise load in a multistorey building on the territory of the South-Western district of Stavropol. The measurement of the noise load was carried out in accordance with GOST 23337-2014 “Noise. Methods for measuring noise in residential areas and in residential and public buildings”. To analyze and compare the data obtained with the maximum permissible value, SanPiN 1.2.3685-21 “Hygienic standards and requirements for ensuring the safety and (or) harmlessness of environmental factors for humans” was used. The measurement results revealed excess of maximum permissible noise level on the territory of the residential complex «Perspektivny» and «Rossiysky», and the houses within the residential complex «Perspektivny» suffer most from the proximity of the roadway and the absence or partial landscaping. Noise values were recorded near residential buildings in the range of 70 dBA. On the territory of the residential complex “Rossiysky”, high indicators are found on the sidewalk near the South-Western bypass. No excess of maximum permissible noise load level was noticed directly at the houses. The resulting mathematical model reflects the dependence of the noise level on the presence and absence of foliage and the density of traffic flow. Based on the data obtained, we can conclude that the residential complexes «Perspektivny» and «Rossiysky» are subject to significant noise pollution. This can be attributed to shortcomings in the planning of territory development and the increase in the number of vehicles.

Characterisation of the transverse shear behaviour of binder-stabilised preforms for wind turbine blade manufacturing

Binder-stabilised preforms are being used increasingly in the production of large composite structures, such as wind turbine blades, to increase the throughput. The transverse shear behaviour of the preform is one of the driving factors in the development of wrinkling during manufacturing but has not previously been characterised in the literature. In this paper, the combined intra- and inter-ply deformations during transverse shearing of a binder-stabilised preforms for wind turbine blade manufacturing are characterised by a new test methodology. The results from two experimental campaigns are presented. In the first campaign, preform specimens are subjected to monotonic loading to a nominal transverse shear angle of 18.0° with three different deformation rates. The results show an increase in maximum load levels with greater deformation rates. In the second campaign, preform specimens are subjected to deformation-controlled cyclic loading with two different deformation amplitudes corresponding to a nominal transverse shear angle of 1.5° and 12.2°, respectively. During cyclic loading, permanent deformation is observed in all preform specimens and the maximum load at the 19th cycle is reduced to 48% of the maximum load at the first cycle for the tests with deformation amplitudes of 12.2°. The data generated in this study is freely available at https://doi.org/10.17632/9m78sg3zwn.1.

Mechanical degradation of ultra-high performance concrete under flexural fatigue loading

This work investigated the behavior of pre-cracked ultra-high performance concrete (UHPC) under flexural fatigue, quantifying its mechanical deterioration during cyclic loading through crack mouth opening displacement (CMOD), stiffness and energy dissipation rate. The flexural fatigue tests were carried at a frequency of 6 Hz on notched pre-cracked prisms in four distinct maximum load levels: 90%, 80%, 70% and 50% of the material residual bending strength at 0.5 mm of CMOD. The results presented expressive gain in fatigue life and performance for UHPC compared to a 50 MPa SFRC. In addition, a linear relationship between the residual bending strength and the initial stiffness was identified. Equations were proposed to predict the fatigue life according to the upper load limit during the cyclic loading. Finally, the post-fatigue behavior of samples that did not fail after 1,000,000 cycles was evaluated under monotonic bending test. No significant damage was observed on samples subjected to load levels below the endurance limit.

Utilization of adaptive swarm intelligent metaheuristic in designing an efficient photovoltaic interfaced Static Synchronous Series Compensator

To cope with the growing load demand of power system due to world’s rapid socio-economic growth, the system compels to run with increased load. Hence, the system must sustain at maximum loading level, termed as the Maximum Loadability Limit (MLL) of the system, without violating its security limits. To increase the system-MLL further the Static Synchronous Series Compensator (SSSC) among existing Flexible AC Transmission Systems (FACTS) devices has been preferred here for its capability of compensating the real and reactive power losses simultaneously. Initially, the SSSC parameters are optimized which are further validated through the dynamic model of the Photovoltaic (PV) interfaced SSSC (PV-SSSC) in MATLAB/SIMULINK. To make the PV-SSSC more efficient, firstly, the maximum feasible power can be acquired from PV system using a robust Maximum Power Point Tracking (MPPT) technique. Secondly, Firing Angle Optimization (FAO) can improve the output power quality of the inverter in SSSC. Thus, this research handles three optimization problems separately i.e., the SSSC parameter optimization, the FAO (minimization), and the MPPT (maximization) problems. For solving such complex, nonlinear, and nonconvex engineering optimization problems, a recently developed swarm-based metaheuristic namely Levy Flight motivated Adaptive Particle Swarm Optimization (APSOLF) technique is employed. Moreover, the superiority of APSOLF is justified over contemporary state-of-the-art techniques using statistical analyses. The APSOLF-based-MPPT can achieve tracking-efficiency above 99.8% and the lowest settling-time. The APSOLF-based-FAO attains 6.7148% THD satisfying the IEEE-519 standard without any filter circuit The MLL point enhancement and bus voltage profile improvement are also the notable observations.

Serviceability behaviour of FRP-reinforced slatted slabs made of high-content recycled aggregate concrete

At service load levels, shear-induced deflections of reinforced concrete (RC) slabs are small and therefore they are usually ignored in deflection calculations. However, shear-induced deflections can be large in RC slabs reinforced with Fibre Reinforced Polymer (FRP) bars, especially after the development of diagonal cracks. This article investigates the serviceability behaviour (deflections and crack widths) of FRP-reinforced slatted slabs cast with recycled aggregate concrete (RAC). Fifteen slabs were tested in flexure, including five slabs cast with normal concrete (NC), five slabs cast with RAC made with 50% recycled concrete aggregate, and five slabs cast with RAC made with 100% recycled concrete aggregate. The test results are compared to crack widths and deflection predictions given by current guidelines and Nonlinear Finite Element Analysis (FEA). The results show that, for the tested slabs with 100% recycled concrete aggregates, the predictions given by ACI 440.1R underestimate the experimental deflections by up to 30% at maximum load levels. Conversely, the sum of the flexural deflections given by Eurocode 2 and of the shear crack-induced deflections (calculated using a model proposed recently by the authors) match better the experimental deflections at both the onset of diagonal shear cracking load, and at the maximum load. The Concrete Damage Plasticity (CDP) model adopted in the FEA was found suitable to predict accurately the deformations of FRP RAC slabs. This study contributes towards the development of new more sustainable structural solutions for FRP RAC elements, as well as towards more accurate models to calculate their deflections.

Sensitivity analysis for buckling characterisation using the vibration correlation technique

The Vibration Correlation Technique (VCT) is a non-destructive method to predict buckling loads for imperfection-sensitive structures. While successfully used to validate numerical models and predict experimental buckling loads, recommendations for defining the VCT experiment are scarce. Here, its sensitivity towards the number of load steps and the maximum load level measured is studied, and an uncertainty quantification of the measured frequency affecting the VCT prediction is performed First, a series of finite element (FE) models representing nominally identical cylinders, and validated by buckling experiments, are used to perform a sensitivity study. When no frequency deviations are introduced in the FE results, a positive correlation between the VCT predictions and the maximum load used for measurements is found, the number of load steps used being only relevant in reducing the errors. Introducing frequency deviations deterred the predictions correlation with the maximum load, while using more load steps reduced this influence. Second, a sensitivity study based on experimental data confirmed most of the trends previously observed using the FE results, the exception being a poor prediction sensitivity as a function of the maximum load, owing to several cylinders for which the VCT method gave predictions that progressively decreased with increasing the load.

Shear fatigue behavior of reinforced concrete beams produced with manufactured sand as alternatives for natural sand

Compared to natural sand, manufactured sand (M-Sand) has significant differences in terms of stone powder content, particle size distribution, and particle shape. The fatigue performance of M-Sand concrete structures is a crucial problem for the application of M-Sand in significant engineering structures. In this study, four different types of fine aggregates were selected to investigate the shear fatigue behavior of reinforced concrete (RC) beams by considering the influence of the maximum load level. Next, the performance indexes of the fatigue life of M-Sand concrete beams were evaluated. The results showed that the fatigue failure processes of concrete beams produced with different sand types were similar. The fatigue life of concrete beams was found to be related to the stress or load range. At the same maximum load level, the methylene blue (MB) value is a critical index that influenced the fatigue life of concrete beams containing M-Sand. Moreover, the fatigue life showed a linear logarithmic relationship with the average permanent deflection of Stage II. The total dissipation energies of the concrete beams in Stage II were different for the various fine aggregates. Generally, the higher the total dissipation energy, the longer the fatigue life of the concrete beam. The average dissipation energy in Stage II can be used as a characteristic index for evaluating the fatigue performance of concrete beams produced with different types of fine aggregates. • Shear fatigue behaviors of sixteen reinforced concrete beams containing manufactured sand were innovative analyzed. • Three different types of manufactured as well as natural sand were used in experimentally program. • The fatigue life of manufactured sand concrete beams was found to be related to the stress or load range. • The magnitude of the dissipation energy together with permanent deflection could indicate the fatigue life of concrete beams.

Mechanical behaviour of medium-grained sandstones exposed to differential cyclic loading with distinct loading and unloading rates

This work aims to investigate the mechanical behaviour of medium-grained sandstones under cyclic loading with different loading/unloading rates. This type of cyclic loading is called differential cyclic loading (DCL) and is considered for testing rock behaviour. In the experiments, constant amplitude and multi-level cyclic loadings were performed. Three loading modes were designed to consider different relationships between loading and unloading rates. Axial strain evolution and energy dissipation were analysed for different loading/unloading rates and maximum cyclic load level. The correlations between P-wave velocities and strengths of rocks deduced from this research are compared with existing published data. The relationships between final strength and axial strain at failure under different loading patterns were also discussed and a rough assessment of the remaining fatigue life is introduced using the predicted value by fitting the axial peak strain.

Damage evolution detection in a pipeline segment under bending by means of acoustic emission

A steel pipeline segment of 2.5 m length was subjected to quasi-static four-point bending load in three steps for studying the initial cracking and damage accumulation based on the Acoustic Emission (AE) technique and by the direct current potential drop (DCPD) technique. For the latter, a new post-test analysis method was established. AE is found more sensitive to crack initiation than DCPD. Formation of mesoscopic and macroscopic cracks as well as their closure and the resulting friction generate weighted peak frequencies below 400 kHz, whereas microscopic cracking produces AE with broad band spectra identifiable by weighted peak frequencies above 400 kHz. Critical states alike the maximum load level and the leak opening were accompanied by peak amplitudes above 85 dBAE. This rather fundamental study provides a data base for possibly developing advanced strategies of detection and alarm systems based on acoustic monitoring of pipelines, or at least, steel structures.

Experimental Investigation on Bending Behavior of Innovative Poplar LVL Floor Diaphragms

Poplar laminated veneer lumber (poplar LVL) is made of fast-growing poplar veneer and structural adhesive, which owns the advantages of sustainability and stable quality. Here an innovative poplar LVL floor diaphragm is presented, mainly made up of orthogonal rib beams fitted together using L-shape steel connectors. The paper mainly deals with an experimental study on the bending behavior of the floor under transverse uniform load. Full-scale testing on eight 3.6 m × 4.8 m specimens shows that the damage phenomena of the floor mainly exhibited as the separation between the rib beams and pulling out from the rib beam for the tapping screw. Though some local damage phenomena appeared before the preset maximum loading level, the load-deflection curves basically kept linear for most of the specimens. Under the service load level of 2.5 kN/m2, the distribution of deflection and strain for the full-length rib beam substantially exhibited the characteristic of a two-way slab. In contrast, for the segmented rib beam, the situation was much more complex. Due to the parametric design of the specimens, testing results illustrated that the rib beam height played the most important role in floor stiffness. Next was the sheathing panel, while the role of segmented rib beam spacing was relatively unremarkable. At last, a revised pseudo-plate method was proposed to evaluate the maximum deflection of the novel floor, which considered the composite action by rigidity factors.

Predictive capabilities of Vibration-Correlation Technique applied to axially compressed CFRP truncated cones

The paper deals with the application of the non-destructive Vibration-Correlation Technique (VCT) to estimate the buckling load of thin-walled, unstiffened CFRP truncated cones. After validating the structural response, detailed attention was devoted to assessing the predictive capabilities of the VCT for two conical structures at different load levels. In addition, parametric studies were carried out considering changes in the nominal bottom radius, the semi-vertex angle and the length of the cone. Two FE models were defined in the numerical analyses that accurately and roughly model the boundary conditions during compression. The measured initial mid-surface and thickness imperfections were taken into account in the numerical models. The results of the conducted study showed a slightly higher sensitivity of the VCT to ply topology design and to the scheme of initial imperfections it generates than it can be seen only on the basis of the structural response. Parametric studies revealed considerable conservativeness of the predictions provided by the use of VCT (99.93% of considered cases). The influence of thickness imperfection was found to be insignificant. In general, an increase in the maximum load level under consideration correlated with an increase in the predictive capabilities of the VCT and a decrease in divergence from the nonlinear buckling load.

The Impacts of Distinct Flexibility Enhancements on the Value and Dynamics of Natural Gas Power Plant Operations

The rapid increase of renewable generation and its anticipated continued growth requires greater operational flexibility in modern power systems. Previous studies explored the addition of more flexible resources to improve system flexibility, but this may also be achieved at lower cost by enhancing existing power plants via flexibility retrofits. Potential flexibility upgrades to existing thermal plants include modifications that enable faster ramp rates, increase maximum load levels, decrease minimum load levels, and provide faster and lower cost startup operations. In this paper, we focus on improvements to existing natural gas combined cycle generators, and apply a unit commitment model to analyze the impact that each specific upgrade has on their operational dynamics and profitability from both the system perspective and from the asset owner perspective. We show that the value of each type of flexibility improvement varies depending on the capacity factor and usage pattern of the generator before the upgrade, and that the relative benefit of each type of flexibility varies. We demonstrate diminishing returns to increased flexibility when upgrading multiple generators simultaneously. Sensitivity tests for several shares of renewable generation, different generation mixes and different net load realizations confirm the generality of the results shown.

DETERMINATION OF THE FAILURE MODE AND BEARING CAPACITY OF CONCRETE COLUMNS WITH MESH REINFORCEMENT

Paper deals with the results of experimental test of reinforced concrete columns withmesh reinforcement. Experimental investigations of columns were performed using hydraulic presswith a maximum load level of 480 tones. On the basis of previous theoretical research three series ofexperimental samples which are represented with simply concrete columns (BS-0), concrete columnsin mesh holder (BS-P) and concrete columns in mesh holder with additional reinforcement rings (BSPS)were produced. The height of all samples is 1000mm and the diameter is 450mm. There threeschemes of experimental tests were considered: static loading using press’ plates (I), monocycle (II)and static (III) loading using additional round steel plates. The results of tests were obtained in theform of failure mode and breaking forces for three series of samples. According to the results of testsover the first scheme, it is obtained that the destruction of columns with mesh reinforcement goesmore slowly than concrete columns. The appearance of cracks started at the level of loading equalto 100 tones for BS-0 samples and 200-250 tones – for BS- and BS-PS samples. The level of breakingforces for BS-P samples and for BS-PS samples is 18-26 % and 21-28 % higher than for BS-0 samplesrespectively. After monocycle loading it is obtained that breaking forces for BS-P and BS-PS samplesare 5 % and 23 % higher than BS-0 samples. It is noted that cracking processes for all samplesstarted near the moment of total destruction, so the failure of samples was brittle and sharp.According to the third scheme of loading the difference between breaking forces for BS-0 and BS-Psamples is about 5 %, BS-0 and BS-PS is 7 %. Failure mode for third scheme is similar to secondscheme, but it is also mentioned multistage destruction of columns when after achieving the level ofbreaking force level of loading falls and increases several times. It is recommended to apply loadover whole cross section of column in real structures, because it plays a significant role in increasingof bearing capacity. The results of experimental tests were compared with results of numericalanalysis, which showed qualitative and quantitative coincidence.

MEDICAL EFFECT OF SPORTS ON IMPROVING THE MAXIMUM OXYGEN

ABSTRACT Introduction: Maximum oxygen uptake is an effective indicator of the level of human cardiopulmonary function and aerobic work capacity. Observing the effects of aerobic training and formulating scientific training plans are of considerable value. Objective: To observe the effect of physical exercise on the human body's maximum oxygen uptake and arterial blood ketone body ratio. Methods: Before and after 4 weeks of physical exercise, the maximum oxygen uptake, blood lactic acid and heart rate changes, and ketone body content in the incremental load exercise experiment was measured in the human body. Results: The subjects’ maximum oxygen uptake, maximum exercise load, heart rate, and blood lactic acid levels increased significantly after physical exercise. Conclusion: The human body's maximum oxygen uptake is enhanced under sports. Level of evidence II; Therapeutic studies - investigation of treatment results.

Investigation of earthquake behavior of unreinforced masonry buildings having different opening sizes: Experimental studies and numerical simulation

In this study, three calcium silicate unreinforced masonry buildings were investigated via experimental studies and numerical simulation in order to determine their earthquake behavior. For building behavior, full-scale (1:1) masonry buildings, having different opening sizes, were subjected to cyclic loading. In each cycle, load and displacement values were recorded by computer setup and the occurred damage was marked on the building. It was observed that behavior of the building was linear until approximately 77% of maximum load and that there was no damage except for a few hairline cracks. Subsequent to this load level, change in the displacement value moved away from being linear and nonlinear behavior was observed at about 88% of the maximum load level. Hereafter, characteristic damage formation began and crack sizes increased. Torsional effect was also observed because of the stiffness difference due to the opening size in the walls. After maximum load level, it was determined that the building dissipated energy with opened-closed cracks and reached the collapsing limit at nearly a 1% story drift ratio. In the scope of numerical simulation, first masonry building was modeled with macro modeling using ANSYS software and the system was simulated by a similar load effect as the experimental study. The damage that occurred during the experimental studies was evaluated in terms of masonry building behavior and the numerical results were compared with the experimental results. The numerical simulation results were consistent with the experimental results until the maximum load level, but after this load level, the simulation results were not consistent with the experimental results.

Linear and Nonlinear Ultrasonic Techniques for Monitoring Stress-Induced Damages in Concrete

Abstract When stress in concrete exceeds certain threshold value, microcracks are nucleated, these microcracks can propagate and coalesce forming macrocracks, resulting in the gradual decay of the mechanical properties of concrete and eventual failure of the concrete structures. For safety concerns, one needs to develop suitable nondestructive testing methods capable of detecting past overloads of concrete structures during its service life. In this work, the stress-induced damage in concrete is monitored using ultrasonic techniques, exploiting the coupling between the stress level experienced by concrete and its wave propagation parameters. Cyclic compression tests with increasing maximum load level have been performed on specimens made of concrete with coarse-grained (CG) aggregates. Experimental results have been analyzed by two different ultrasonic methods—the linear and the nonlinear ultrasonic techniques. In linear ultrasonic technique, the stress level experienced by the specimens is related to the variations in signal amplitude and velocity of ultrasonic waves. In nonlinear ultrasonic method, the sideband peak count (SPC) technique is used for revealing the stress-induced damage corresponding to each load step. In comparison to linear ultrasonic parameters, the nonlinear ultrasonic parameter SPC-I appears to be more sensitive to the variations of the internal material structures during both loading and unloading phases. Moreover, the SPC technique has shown to be capable of identifying both the initial damage due to the evolution and nucleation of microcracks at the microscopic scale, and the subsequent damages induced by high overload, resulting in an irreversible degradation of the mechanical properties.

Stress-strain properties of aponeurotic suture in anterior abdominal wall after a midline laparotomy

Objective: method development for preventing postoperative ventral hernias based on experimental assessment of the stress-strain properties of aponeurosis in various types of a midline laparotomy. Materials and methods. We evaluated 42 fascia muscular aponeurotic complexes of the anterior abdominal wall. Based on the technique for dissecting the aponeurosis and its suturing, the complexes were divided into two groups (each containing 21 samples): Group 1 with a bypass of the umbilical ring on the left, and Group 2 with umbilical ring dissection. Results. Fascia aponeurotic complexes dissected and sutured through the umbilical ring (Group 2) had, on the average, higher values of mechanical characteristics. E.g., mean values of tensile stress (S), tensile stress at a maximum load (Smax), Young’s modulus (E), aponeurotic tensile strain (D), aponeurotic tensile strain at a maximum load (Dmax), and maximum load level (Load) were higher in Group 2 by 35.4; 39.8; 14.9; 34.6; 30.2 and 40.2 (%), respectively. Conclusion. We conducted the development, experimental application and evaluation of a novel method for preventing postoperative ventral hernias after a midline laparotomy based on the assessment of the stress-strain properties of aponeurosis.

Plastic Limit Analysis Using the Simplified Theory of Plastic Zones

Abstract The simplified theory of plastic zones (STPZ) was mainly developed to determine strain ranges and accumulated strains in the state of shakedown at cyclic loading between prescribed levels of loading. Kinematic hardening is an indispensable feature of the STPZ. The plastic limit load, however, is defined for monotonic loading and elastic–plastic material behavior without hardening. Simply assigning a zero value or a numerically very low value of the tangent modulus when applying the STPZ is generally not possible due to arising numerical instabilities. It is, therefore, not immediately obvious how the STPZ can be used to determine the maximum load level that can be applied to a structure without developing a kinematic mechanism. This paper describes the theory and the analysis steps required and provides some illustrative examples. Typically, between one and three linear elastic analyses and some local calculations are required to provide either the exact value or at least a reasonable estimate of a range of the plastic limit load, as well as of the associated stress and strain fields and displacements that are not provided by classical limit analysis.

Effect of indentation loading type on the mechanical properties of advanced high strength steel grade DP 800

The goal of this study was to acquire mechanical properties of a dual-phase grade advanced high strength steel (AHSS) by means of different microindentation loading conditions. Conventional, cyclic, and multi-step indentations were performed on DP 800 sample; and Young’s modulus, hardness values were obtained by the depth-sensing indentation technique. Effects of different load levels (50–300 mN) and type of indentation on the results were also analyzed through ANOVA. The load levels experimented yielded overall material response rather than its constituents (e.g., martensite and ferrite). Both hardness and Young’s modulus tend to decrease with increasing maximum indentation load level, especially from 50 to 100 mN, which is regarded as indentation size effect.