Point Of Load Application Research Articles

Micromechanical Characterization of Diatom Frustules of Multiple Origin

The siliceous structure that protects diatoms, called frustule, is the main component of diatom sedimentary soils. These particles’ physical and mechanical characteristics are challenging, given their geometric conditions of only a few microns. For this evaluation, specialized tools must be used, such as the Scanning Electron Microscope (SEM), the Atomic Force Microscope (AFM) and X-ray dispersion (XRD), among others. The bibliographic references show significant variability in the “load-deformation” behavior in frustules, diatoms or their organic components. Technical background information usually presents information on a single type of species. This research demonstrated the characterization and micromechanical evaluation of frustules of three morphologically distinguishable species of diatoms (Colombian, Mexican and Peruvian origin). The results showed similarities in the chemical composition of the three samples. The displacement records are variable depending on the species for the same load range. The location of the load application points by AFM on the different types of frustules is presented. The most significant deformation in the Mexican species and the regularity in the results of the Peruvian species stand out. Young’s moduli were also calculated by applying the Hertz Model, which had the highest values in the Colombian sample.

Fatigue cracking prediction of cobblestone interlayer pavement using non-destructive testing and mechanistic-empirical analyses

Several non-destructive testing (NTD) methods have been used to measure surface deflection, which makes to determine the elastic moduli of pavement layers through the back-calculation process and assess the structural capacity of asphalt pavements. In this study was evaluated the back-calculated moduli of the cobblestone interlayer pavements and the load capacity of this type of pavement related to the fatigue cracking criterion based on a mechanistic-empirical analysis. The employed methodology included the performance of on-site trials using non-destructive testing with the Falling Weight Deflectometer (FWD) devices on 84 test points in granular and cobblestone interlayer pavements, determination of deflection basin parameters (DBP), back-calculation layers’ moduli, and estimate of the fatigue cracking performance of the pavements by mechanistic-empirical analyses in MeDiNa software. The pavements with a cobblestone base layer displayed greater deflection measurements on the load application point compared to those measured on pavements with a granular base layer, indicating that conventional pavement displayed more stiffness. Cobblestone interlayer pavement displayed greater amounts of cracked area compared to granular base layer pavements showing lower load capacity based on the fatigue criterion. The DBP-based method by FWD test was able to identify the structural differences between the layers of pavements evaluated and identify the cracking evolution.

Shear Mechanical Behaviours and Size Effect of Band–Bedrock Interface: Discrete Element Method Simulation Insights

The shear band is a prominent feature within the Banbiyan hazardous rock mass located in the Wushan section of the Three Gorges Reservoir area. This band constitutes a latent risk, as the potential for the rock mass to slide along the region threatens the safety of lives and property. Presently, the understanding of the shear mechanisms and the impact of shear band size on the band–bedrock interface is incomplete. In this study, based on band–bedrock shear laboratory tests, DEM simulation is used to investigate the shear-induced coalescence mechanism, stress evolution, and crack-type characteristics of the band–bedrock interface. In addition, the shear mechanical properties of samples considering specimen size, rock step height, and step width are further studied. The results show that the crack initiation and failure crack types observed in the first rock step are predominantly tensile. In contrast, the failure cracks in the remaining rock slabs and steps are primarily characterised by shear mode in addition to other mixed modes. The stress condition experienced by the first step is very near to the position of the applied point load, whereas the stress distribution across the remaining steps shows a more complex state of compressive–tensile stress. The relationship between shear parameters and sample size is best described by a negative exponential function. The representative elementary volume (REV) for shear parameters is suggested to be a sample with a geometric size of 350 mm. Notably, the peak shear strength and shear elastic modulus demonstrate a progressive increase with the rise in rock step height, with the amplifications reaching 91.37% and 115.83%, respectively. However, the residual strength exhibits an initial decline followed by a gradual ascent with increasing rock step height, with the amplitude of reduction and subsequent amplification being 23.73% and 116.94%, respectively. Additionally, a narrower rock step width is found to diminish the shear parameter values, which then tend to stabilise within a certain range as the step width increases.

Диссипация энергии динамического деформирования в дорожных одеждах автомобильных дорог

Introduction. The network of highways is one of the factors ensuring sustainable development of both plain and mountainous territories. Effective monitoring of road condition using modern non - destructive methods is an integral element of ensuring their normative condition. One of the promising ways to improve nondestructive testing methods is the energy approach based on the indicator of dissipation of deformation energy. Methods. The mathematical model considered in this paper is based on the solution of the system of dynamic Lame equations in displacements. The solution is constructed by applying the properties of the Fourier transform, and methods of discrete harmonic analysis. The output data are the amplitude - time and amplitude - frequency characteristics of the displacements on the pavement surface. The elastic properties of pavement layers are described by the elastic moduli and Poisson’s coefficients of the layer materials, and the viscous properties by the tangents of the loss angles of longitudinal and transverse waves. Results and discussion. A numerical experiment was carried out to investigate the influence of elastic and viscous characteristics of pavement layers on the value of strain energy dissipation. The values of strain energy dissipation were calculated by dynamic hysteresis loops obtained by superimposing the amplitude - temporal characteristic of the shock loading impulse on the amplitude - temporal characteristic of displacements on the pavement surface. It was found that varying the elastic modulus of asphalt concrete has the greatest effect on the amount of energy dissipation in the zone from 0 to approximately 1.8 m from the point of impact load application. The modulus of elasticity of the base layer affects the change in energy dissipation in the entire study area, gradually converging to zero at a distance of 2.1 m from the point of impact loading. The modulus of elasticity of the working layer of the subgrade has a significant effect on the energy dissipation in the whole investigated area. Viscous characteristics have much less influence on the energy dissipation value in some cases leading to qualitative changes in its distribution. Conclusion. The obtained results can serve to improve the existing methods of nondestructive testing of road pavements, in particular, when developing effective procedures for correcting the parameters of the calculated response relative to the experimental one.

Increased force and elastic energy storage are not the mechanisms that improve jump performance with accentuated eccentric loading during a constrained vertical jump.

Accentuated eccentric loading (AEL) involves higher load applied during the eccentric phase of a stretch-shortening cycle movement, followed by a sudden removal of load before the concentric phase. Previous studies suggest that AEL enhances human countermovement jump performance, however the mechanism is not fully understood. Here we explore whether isolating additional load during the countermovement is sufficient to increase ground reaction force, and hence elastic energy stored, at the start of the upward movement and whether this leads to increased jump height or power generation. We conducted a trunk-constrained vertical jump test on a custom-built device to isolate the effect of additional load while controlling for effects of squat depth, arm swing, and coordination. Twelve healthy, recreationally active adults (7 males, 5 females) performed maximal jumps without AEL, followed by randomised AEL conditions prescribed as a percentage of body mass (10%, 20%, and 30%), before repeating jumps without AEL. No significant changes in vertical ground reaction force at the turning point were observed. High load AEL conditions (20% and 30% body weight) led to slight reductions in jump height, primarily due to decreased hip joint and centre of mass work. AEL conditions did not alter peak or integrated activation levels of the knee extensor muscles. The constrained movement task used here, which excluded potential contributions of trunk motion, arm swing, rate of descent, squat depth, and point of load application, allows the conclusion that increased elastic energy return is not the primary mechanism for potentiating effects of AEL on jump performance.

Effect of Veneering Technique on Shear Strength of Porcelain Veneered Zirconia (PVZ): Finite Element Analysis

Veneering technique is discussed as one of the reasons for chipping of porcelain veneered zirconia (PVZ) restorations, which impacts their longevity and success. This study aims to evaluate the effect of veneering technique; heat-pressed, and hand-layered, on the shear bond strength of PVZ ceramics through finite element analysis. Six cylindrical bilayer material model configurations were analysed; two types of zirconia, IPS e.max® ZirCad (Z) and Luxen Zr (L) and each veneered with three porcelain types, Shofu Vintage ZR (V), IPS e.max® Ceram (C), IPS e.max® Zirpress (P), with dimensions of (10 mm x 1.2 mm) and (5 mm x 3 mm), respectively. The force for threedimensional model configurations were fixed at 5 kN. The results show that heat-pressed groups (ZP and LP) have slightly higher bond strength value 49.12 MPa and 49.03 MPa, compared to hand-layered groups (ZC, LC, ZV, and LV), measuring 48.87 MPa with 0.5% difference at maximum. Bond strength in MPa underwent variance analysis, revealing a significant influence of ceramic material on mean values (p = 0.0017). Thus, the highest stress concentrations occur at the edges of the load application points, gradually decreasing as the distance from the point of load application increases. Results indicate that heat-pressed technique is better than hand-layered veneering technique due to its effectiveness in strong adhering veneer to the zirconia core.

Application of Installations with Uniform-Strength Beams as Working Deformation Standards

A method for obtaining homogeneous deformation along the length of the measuring section of a uniform-strength beam and the possibility of its application as part of a working deformation standard are considered. The results of the analysis of the bending model and the design of a uniform-strength beam are presented. In the focus of attention are the parameters included in the measurement equation and related to methodological factors, as well as influencing the result of relative deformation measurements. The subjects of research are the presence of contact friction forces, heterogeneity of material properties, the special nature of the load application (bending, torsion, the presence of residual stresses in the body, geometrical parameters of the calibration beam, orientation of primary transducers on the beam, application of bending load, measurement of deflection and displacement of the neutral layer). The advantages and disadvantages of using a uniform-strength beam for determining the characteristics of primary strain transducers during testing, calibration, and verification were established. The deviation of signals of primary transducers located outside the axial cross-section when oriented along the beam axis and along the force lines converging at the point of load application was experimentally revealed. The error due to the orientation of the primary transducers on the beam depending on the angle between the lateral faces can range from 0.15 to 0.23 %. The study adds to the theoretical knowledge base on the possibility of using a cantilever uniform-strength beam as a load-bearing element in calibration installations. The conclusions may be useful for testing, calibrating, and verifying primary strain transducers.

Study on the Tensile and Shear Performances of Fully Precast Partially Composite Floor Slab Joints

This study explored the tensile and shear characteristics of fully prefabricated partially composite floor slab joints through the design and testing of two tensile specimens, three steel–concrete specimens, and three concrete–concrete shear specimens. These tests aimed to evaluate how various connection designs influence the joints’ load-bearing capabilities and failure patterns. The findings revealed that the tensile specimens predominantly showed bond failures at the interface of the precast and cast-in-place layers, accompanied by rebar pull-out. Incorporating reinforcing bars or sleeves was found to potentially increase their ultimate load-bearing capacity by about 20%. The shear failures in the steel–concrete specimens were primarily due to interactions between the steel beam and adjacent composite slab, whereas the concrete–concrete specimens mostly underwent local crushing at the load application point and failure at the bonding interface. These observations affirmed the accuracy of the existing methods for calculating tensile and shear strengths, offering vital insights for the architectural design and construction of such floor joints.

Registration and analysis of acoustic emissions in a concrete structure

Improving the efficiency of deformation monitoring systems for engineering structures is an important scientific and technical problem. The objective of the experimental studies presented in this paper is to establish the possibility of using the acoustic emission (AE) method to record inelastic deformation in elements of a large-scale model reinforced concrete structure. The paper presents the results of an experiment in which elastic and inelastic deformation of a large-scale model reinforced concrete structure was performed as a result of local force loading. The experiment was carried out on a special experimental stand that allows studying deformation processes in building and engineering structures with typical linear dimensions of about 10 m. The loading was cyclical - "load - full unloading" with an increase in load at each stage by no more than 10 kN. Registration of AE signals generated in the vicinity of the load application point was carried out by a system of acoustic sensors located at different distances from the AE source. It is shown that the amplitude-frequency composition of the signals changes with increasing distance from the AE source. The high-frequency component of the signal at a distance of more than 2 m from the source practically disappears and only the low-frequency component remains. There is a significant dispersion of the acoustic signal with increasing distance from the source. The possibility of recording and analyzing AE signals at a distance of up to 4 m from the source is shown. The obtained results can be used in the development and creation of automated systems for monitoring deformation processes in large-sized concrete structures using the AE method.

Structural response of hybrid timber ‐ cold formed steel floors

AbstractThe paper examines the composite performance of hybrid steel‐timber lightweight floor assemblies incorporating cold‐formed steel (CFS) profiles and plywood (PW) flooring panels with varying degrees of shear connection achieved by means of self‐drilling screws. Material, push‐out, and three‐point short‐span floor tests with or without web openings were carried out. The results and observations from the tests provide a detailed insight into the inelastic properties and ultimate response of such floor systems. Push‐out tests indicate that denser connector arrangements increase connection stiffness, while push‐out and short beam tests suggest an optimum connector spacing equal to the beam depth for a balance between structural performance and constructability. The experimental observations indicate that the ultimate condition of the short composite beams was characterized by CFS web crippling under the load application point, followed by a pull‐through of the self‐drilling screws. Web openings reduced the strength of the floor elements compared to the members with full webs. Complementary numerical studies are undertaken using nonlinear finite element procedures which were validated against the beam tests, offering a detailed insight into the stress levels in the timber, steel, and connectors. Codified procedures for determining the capacity of composite CFS sections are compared with the test results, and guidance for the practical design and construction of such systems is given.

INVERSE PROBLEM FOR A TIMOSHENKO BEAM WITH AN ADDITIONAL VISCOELASTIC SUPPORT UNDER NONSTATIONARY DEFORMATION

The non-stationary loading of a mechanical system consisting of a beam hinged at the edges and an additional support installed in the span of the beam is considered. The deformation of the beam is modeled on the basis of Timoshenko's hypotheses, taking into account the influence of rotatory inertia and shear. The deformation of the beam is described by a system of partial differential equations, which is solved analytically by means of expansion of the unknown functions into the relevant Fourier series and further use of the Laplace integral transformation. It is assumed that the additional support has linear-elastic and linear-viscous components, and the displacements coincide at the point where the additional support is connected to the beam. The reaction between the beam and the additional support is replaced by an external unknown concentrated force applied to the beam, which varies in time. The law of time variation of this unknown reaction is determined by solving the Volterra integral equation. The inverse problem of deformable solid mechanics is solved, that is, it is assumed that the deflection at a point of the beam with the additional support is known, whereas the law of time variation of the external impulse load causing the deflection is unknown. The application point of the external load and the point of the additional support connection are considered to be known and do not change in the process of deformation (when obtaining the solution of the problem it was supposed that these could be any points of the beam except for its ends). The described inverse problem is reduced to a system of two Volterra integral equations of the first kind with regard to the unknowns of the external disturbing load and reaction between the plate and the additional support, which is solved by analytical and numerical method. Analytical relations and calculation results for specific numerical parameters are given. The results obtained in this work can be used for indirect measurement of impulse and shock loads acting on beams with additional supports, for which not only elastic but also linear-viscous characteristics are taken into account.

Buckling in columns. Solution of the indeterminations of Euler's theory and derivation of an equation for inelastic buckling

Buckling in columns under central load has always been a complex problem and until now remains unclear. This work consists of two parts. In the first, a theory is presented to solve the indeterminations of Euler's theory, such as: Moment, slope, deflection, moment and shear reactions. In this sense, the column is analyzed as if it were a prismatic member under pure bending, due to the application of a bending moment and consequently the elastic curve of the column is calculated by the traditional method. Using a second hypothesis, it is established that elastic buckling occurs when the compressive and bending energies become equal; and solving it the Euler's Formula for the critical load is obtained exactly. In the second part, and with the indeterminations already resolved, the maximum-strain-energy failure criterion is raised, in the critic section, where the maximum moment occurs, due to the compressive load and subsequent bending. This allows us to obtain an extraordinary equation for inelastic flexural buckling that predicts highly accurate results consistent with laboratory tests. In the stress diagram versus slenderness, we can see the flat zone of the short columns, and the critical slenderness ratio, that in the case of ASTM-A36 structural steel, points directly to one hundred and twenty (120). And, of course, we can calculate the critical stress according to the type of cross-section and buckling axis and direction. An ideal column is considered, i.e., without initial deflection, with the application point of load on the centroid, and without residual stresses. A lineal stress-strain diagram is used until the yield point.

Identification of Elastic Response of Asphalt Pavements Layers Using Deflectometric Tests With Different Load Levels

It is a unusual practice in national new pavement designs and rehabilitations to consider the nonlinear elastic behavior of the materials that constitute or will constitute the pavement layers. However, the linear elastic response is a simplification of the actual pavement layers behavior, since the materials used in the structure have stiffness dependent on the stress state (granular layers and subgrade) or on the temperature and time of load application (asphalt concrete). In view of this, this paper aims to study the elastic behavior of the pavement structures of two monitored sites in the city of Santa Maria/RS, through tests with FWD equipment, applying four different levels of loading on the full extension of these two sites. In these structures, the pavements showed a tendency to stiffening with increasing load acting at initial measuring distances (near the FWD load application point), which represent the elastic compression of all layers that make up the pavement. The measuring distances farther from the load application point, referring to the elastic compression of the subgrade, indicated, in most cases, a tendency to linear behavior of the load-deflection relationship in both sites. The backcalculated resilience modulus confirmed the impressions drawn from the load-deflection relationships, indicating the nonlinear elastic behavior of the granular layers (base and sub-base) of the analyzed sites, with resilience modulus directly proportional to the increase of the confining stress. The subgrade of the experimental sites exhibited varied behavior, and could be simplified by linear elasticity, without considerable loss. The same fact happened for the asphalt concrete material used in the pavement of site 1. For site 2, the backcalculated modulus indicated asphalt concrete stiffness dependent on the vertical surface stress increment at the center of the load plate.

Failure modes of shaft steelwork in the state of advanced corrosion

This paper presents a novel analysis of the failure modes of shaft steelworks. Shaft steelwork structures uphold the rectilinear movement of hoist conveyances in thousands of mine shafts worldwide. Major problems in underground shaft steelwork design and maintenance include high corrosion loss, diverse loads, and demanding safety requirements. To accurately assess the load-carrying capacity of the shaft steelwork in these conditions, correctly identifying the possible failure modes is necessary. In this study, a numerical model for a typical shaft steelwork construction in a deep coal mine in Upper Silesia (Poland) was developed and validated based on field tests. An advanced numerical analysis of the steelwork structure and structure weakened by a joint break was performed. The analysis reflected different load application points, directions, and corrosion loss, indicating the failure modes for various degrees of corrosion-loss levels of members. Nine modes of structural failure, mostly omitted by the current design procedures, were revealed. The presented analysis and results can be used to determine a failure mode for a given corrosive deterioration and steelwork characteristics. This, in turn, can enable rational, safe, and cost-effective planning of steelwork repairs and upgrades, as well as improve the operational safety of shaft hoist systems.

ОПРЕДЕЛЕНИЕ ВЯЗКОУПРУГИХ ХАРАКТЕРИСТИК ЭЛЕМЕНТОВ МНОГОСЛОЙНЫХ КОНСТРУКЦИЙ НА ОСНОВЕ АНАЛИЗА ДИССИПАЦИИ ЭНЕРГИИ

The deteriorating operating conditions of roads is one of the most important problems facing specialists in the road industry. It is mainly associated with a reduction in the rigidity of road pavements made as extended multi-layer structures. To identify the causes of rigidity reduction, non-destructive testing is used, which is based on solving the inverse coefficient problem of restoring the elastic constants based on the response on the surface. Purpose of the study: We aimed to provide a rationale for a new pavement condition indicator that would take into account the history of deformation and loading from a source on the surface, based on which it would be possible to solve the inverse problem of restoring the elastic and viscous characteristics of pavement layers. Methods: To do that, we performed mathematical modeling of the stress-strain state of a multi-layer medium based on the solution of a system of dynamic Lame equations. Viscosity is taken into account by introducing tangents of the angles of wave energy losses in the materials of layers. Results: The results obtained in modeling for the first time made it possible to establish the relationship between changes in the modulus of elasticity as well as tangents of the angles of energy losses in pavement layers and the amount of energy dissipation in the structure. Discussion: It should be noted that it is possible to switch from the bowl of maximum dynamic deflections as the main pavement condition indicator to the analysis of hysteresis loops on the road structure surface, recorded at different distances from the point of load application and being an analogue of the full bowl of dynamic deflections showing the history of the test object loading.

Enhancing Pullout Load Capacity of Helical Anchor in Clay with Adjusted Load Application Point under Inclined Loading Condition

Enhancing Pullout Load Capacity of Helical Anchor in Clay with Adjusted Load Application Point under Inclined Loading Condition

Numerical evaluation of reinforced concrete slabs with fixed support under impact load

Reinforced concrete (RC) structural members may be subjected to impact load besides quasi-static load or other dynamic loads like earthquake and wind loads in their service periods. Many research emphasized that although impact load acts on structural members for a short time, it caused considerable damage to these members or even collapses the whole structure. Thus, it becomes crucial to consider and accurately evaluate the impact load effect in the design process. The present study intends to introduce a finite element model (FEM) verified with the test data for the accurate evaluation of load-deflection behavior and damage patterns of the fixed supported RC slabs exposed to impact load. First, a nonlinear FEM including strain-rate effect for both concrete and steel reinforcement, and crack visualization algorithm has been established by using LS-DYNA software. Then, the dynamic responses obtained by the present FEM have been compared with the experimental data presented in a previous study existing in the literature and it is found that the present FEM yields accurate results for the RC slab subjected to impact load and it can be safely used in the design process. In the second part of the study, using the verified FEM, the effects of applied input impact energy, the application point of impact load, and hammer geometry on the dynamic responses and failure characteristics of the RC slabs exposed to the impact loading were investigated and interpreted in detail.

A technique for measuring the clinical retentive forces of mandibular implant-supported overdentures

A novel device for measuring the clinical retentive forces of mandibular implant overdentures is described. The device addresses several drawbacks of the conventionally used methods regarding the application of pure vertical dislodging forces perpendicular to the occlusal plane and the elimination of nonaxial dislodging forces and tipping or rotation of overdentures during the measurements. Moreover, the technique allows for the standardization of the occlusal plane and points of load application.

Cylindrical shear waves in soil around underground pipelines

A method of numerical solution of one-dimensional problem of cylindrical shear wave propagation in an elastic and elastic-plastic soil is developed in the article using the finite difference method. The numerical results obtained are presented in the form of graphs. From the results obtained, the attenuation of the parameters (shear stress, shear strain, and angular velocity) of cylindrical wave propagation with distance in an elastic and elastic-plastic soil was determined. The attenuation of waves with distance is justified by the dissipation of strain energy on the expanding cylindrical soil layer. In the case of load exceeding the elastic limit, plastic strains occur in soil near the point of load application. The boundaries of elastic-plastic strain of soil are determined.

2D Green’s functions for an elastic layer on a rigid support loaded by an internal point force

The problem of a homogeneous isotropic elastic layer resting on a rigid base and loaded by an internal point force is analytically investigated under plane strain conditions. The displacement field is sought as the superposition of a fundamental solution (doublet state) and a homogeneous solution which allows satisfying the boundary conditions at the upper and lower boundaries of the layer. The displacement field is represented through convergent Fourier integral transforms. Once the closed form solution in the transformed domain is found, the displacement and stress fields are assessed by numerical inversion of transforms. Results concerning both the displacements and stresses for different positions of the load application point are reported and compared to FEM solution, finding very good agreement. The solutions obtained for horizontal and vertical point forces define the Green’s functions for the layer, which can be used to describe the mechanical interaction between the layer and an embedded body. As a striking application, the interaction between an elastic layer and an embedded laterally loaded wall or diaphragm is finally addressed, finding the contact pressure and, in turn, the internal forces in the diaphragm.