Uniform Loading Conditions Research Articles

Numerical study of the asynchronous excitation effect of Boumerdes’ earthquake on a bridge behavior

This paper represents the numerical analysis of asynchronous excitation effects on a bridge response due to the Boumerdes earthquake, using the finite element method in modeling, and the Newmark method for dynamic response analysis. The influence of the time delay of excitation between the supports on the response of structure is investigated and study how these variations can affect structural behaviour during seismic events. The dynamic displacements, normal, and shear forces and bending moments are computed through detailed simulations. The obtained results show that due to the non-uniformity in the earthquake excitation, changes in qualitative and quantitative features of dynamic displacements of the bridges. This will consequently subject the bridges to increased displacements hence compromising their structural safety and integrity. In fact, the analysis also underlines that, due to non-uniform seismic forces, the distribution of normal and shear efforts, along with bending moments, gives important concentrations of stresses that were underestimated under uniform loading conditions. From these observations, one underlines the importance of non-uniform distribution of seismic loading during bridge design or evaluation. It provides useful data to the engineers and designers who will implement the improvement in the seismic resistance of bridge structures in earthquake areas.

Study of Strength under Uniform Loading Conditions of Combined Threaded Joints in Structures of Thermoplastic Parts with Metal Reinforcement

Study of Strength under Uniform Loading Conditions of Combined Threaded Joints in Structures of Thermoplastic Parts with Metal Reinforcement

Structural Analysis of Periodic Trusses and Lattice Materials: States of Self-Stress, Mechanisms, and Mechanical Properties

Abstract In the realm of low relative density, a rigid-jointed lattice material exhibits a mechanical response analogous to that of a pin-jointed periodic truss with an identical micro-architecture. This correspondence simplifies the evaluation of the lattice's structural performance. While established matrix methods in linear algebra are capable of determining the states of self-stress, infinitesimal mechanisms, and mechanical properties of pin-jointed periodic trusses, they lack a systematic approach to deriving closed-form expressions for these properties. This paper presents a straightforward approach to address this gap. Furthermore, we introduce an inventive finite element framework that directly yields self-stress states and infinitesimal mechanisms in periodic trusses subjected to specific uniform macroscopic loading conditions. This framework allows for the determination of mechanical properties for periodic trusses by solving straightforward boundary value problems, such as uniaxial tension/compression or simple shear. The developed finite element framework offers greater simplicity compared to the matrix methods, with its benefits becoming more pronounced for complex micro-architectures. To demonstrate the effectiveness of the two newly developed methods, we conduct structural analyses on five different lattice materials, achieving successful outcomes.

Particle size effect on the thermoelastic behavior of composites—A comparative study between heterogeneous and homogenized beams

The particle size effect on the overall thermoelastic behavior of a composite containing many identical spherical particles reduces with the specimen-particle size ratio (SPR). When SPR is large enough, the effective stiffness converges, and the homogenized properties can represent the composite. This paper addresses two challenging questions: How large of an SPR is enough to reach the convergent results for different loading conditions, and whether is the critical SPR obtained from a uniform loading condition applicable to a nonuniform loading condition? When a uniform load is applied to a composite beam, the elastic moduli and thermal expansion coefficients can be calculated from the material’s response. When the beam is subjected to pure or thermal bending, the deflection can be predicted by the heterogeneous or homogenized beams. The inclusion-based boundary element method (iBEM) is developed for high-fidelity simulation of many-particle systems. Given a volume fraction of particles, particle and beam size, and beam geometry, the local fields and the effective deformation are calculated for uniform and nonuniform loading conditions. The comparative study between a homogenized beam by the micromechanical approach and the numerical simulation of the heterogeneous particle system shows that a much larger SPR is required for thermal bending to reach a convergent result between the heterogeneous and homogenized beam. When the SPR is moderate, a cross-scale modeling method shall replace the micromechanical modeling to achieve accurate results.

Experimental investigation of microchannel heat sink performance under non-uniform heat load conditions with different flow configurations

Cooling methods for multiple hotspots with high heat flux pose a reliability threat to electronic devices. This study investigates the microchannel-based heat sink performance under various non-uniform heat load conditions for different geometry with three different flow configurations (I, U and Z). An in-house designed Heater Array Unit (HAU) facilitates the generation of both uniform and non-uniform heat loads using a heater power supply. Two different microchannel geometries were employed, namely, microchannel-1 (MC-1) with channel and fin widths of 0.6 mm and 0.33 mm, respectively, and MC-2 with dimensions of 0.64 mm and 0.572 mm. Each microchannel incorporates three manifold configurations (I, U, and Z). Each flow configuration is regulated by flow control valves. Various non-uniform heat load patterns were considered, including streamline, non-streamline, and across-streamline conditions. To assess the thermal performance of the heat sinks the parameters used are thermal resistance (Rth), Nusselt number (Nu), and temperature non-uniformity (Ѱ). Experimental findings indicate that the MC-2 design with an I flow configuration is more suitable for uniform heat load conditions. On the contrary, for some non-uniform heat load cases MC-1 also showed up as a suitable design over MC-2.

Research on the Support Performance of Internal Feedback Hydrostatic Thrust and Journal Bearing Considering Load Effect

This study aims to analyze the impact of uniform and eccentric load conditions on the performance of internal feedback hydrostatic thrust and journal bearing. Two distinct models are established: a three-degrees-of-freedom uniform load model and a five-degrees-of-freedom eccentric load model. The support stiffness, overturning stiffness, and flow rate for both thrust and journal bearings are calculated. Additionally, numerical analysis is conducted to examine the influence of oil film thickness, inlet pressure, and restrictor size on the operational characteristics of the bearings, revealing the interplay between an eccentric load and journal bearing speed. The validity of the theoretical algorithm is verified through finite element simulation. The research outcomes hold significant guiding implications for the design and application of internal feedback hydrostatic bearings.

Exploiting the flow maldistribution characteristics in parallel microchannel heat sinks of I, U, and Z configurations to tackle the nonuniform heat loads

This study aims to analyze the cooling performance of parallel microchannel heat sinks (PMCHS) under uneven heat flux distributions, taking into account different flow configurations including I, U, and Z. The objective is to demonstrate the potential of utilizing the flow maldistribution inherent in each configuration to effectively manage and mitigate the effects of uneven heat flux distributions. Four different heating arrangements have been considered, namely uniform, non-streamline, streamline, and across-streamline to generate the uneven heat flux distributions. A three-dimensional numerical simulation has been performed to analyze the combined effect of uneven heat flux distributions and flow maldistribution characteristics on the thermal performance of PMCHS. To assess the thermal performances; thermal resistance (Rth), Nusselt number (Nu), temperature nonuniformity (Ψ), and fin efficiency (ηfin) have been employed. The results show that all three flow configurations exhibit similar thermal performances for uniform heat load conditions (0.1 K/W for Rth, 5.5 kW for Nu, 0.3 for Ψ, and 0.98 for ηfin). However, in the case of uneven heat flux distributions, the thermal performance of each configuration is observed to be varying with respect to hotspot positions. This study reveals that each configuration has a huge discrepancy in terms of thermal performance with respect to uneven heat flux distributions. Also, the study concludes that a single flow configuration alone is insufficient to address the cooling challenges that arise due to uneven heat flux distributions. The cooling capability of any configuration to handle uneven heat distributions mainly depends upon the flow maldistribution characteristics of the respective configurations.

Flexural behaviour of GFRP-reinforced concrete pontoon decks under static four-point and uniform loads

Concrete pontoon decks are subject to flexural loading actions under concentrated and uniform loads caused by self-weight, live loads, and wave actions. This study investigated the structural behaviour of concrete pontoon decks reinforced with glass fiber-reinforced polymer (GFRP) bars under static four-point and uniform loading conditions. Five large-scale GFRP-reinforced concrete decks with a length of 2400 mm, width of 1500 mm, and thickness of 125 mm were tested to evaluate their moment capacity, strain behaviour, cracking propagation, and failure mechanism. The effects of the loading configurations, reinforcement arrangement, and cutout simulating the piles' location were evaluated. The edge cut-out initiated flexural-shear cracks, causing the pontoon decks to fail at an effective bending stress 10% lower than the solid decks. Decreasing the span-to-depth ratio from 5.6 to 4.0 increased the induced shear stress of a section and caused the deck to fail by shear compression. Uniform loading resulted in an even load distribution and minimized the stress concentration around the cutout. An increase in the effective depth improved all deck flexural characteristics. The equations in ACI 4401. R-15 and CSA S806–12 provided an accurate prediction for solid decks but overestimated the ultimate flexural strength of the GFRP-reinforced concrete decks with a cutout.

A method for calculation of lateral displacements of buildings under distributed loads

Lateral displacement is a vary important parameter that we need to calculate when structures are subjected to lateral loads like earthquake and wind loads. In this study, a method is proposed for lateral displacement calculation of structures with different structural systems in different planes. This method is based on the continuum system calculation model. The method suggested in the literature for only top displacement in the case of uniform loading, is developed in this study for the calculation of displacements at each storey level and also in both uniform and triangular loading conditions. At the end of the study, twenty-eight storey building with shear wall-frame bearing system, which was taken from the literature, was solved with the presented method and Finite Element Method. The shear walls were modelled with three different element types for the analysis with the Finite Element Method with structural engineering program used. The results, obtained from the Continuum Method and Finite Element Method were presented in tables and by figures. Thus, the compatibility of the proposed method with the classical Finite Element Method was investigated. From the compared results of the method and the literature or finite element models it was seen that the method used for the case of uniform or triangular distributed loading gives very close results.

A generalized finite difference method for 2D dynamic crack analysis

This paper presents a new framework for efficient and accurate analysis of transient elastodynamic cracks by using the generalized finite difference method (GFDM). The method first discretizes the solution domain into a set of overlapping small subdomains, and then in each of the subdomains, the unknown functions and their derivatives are approximated by using the local Taylor series expansions and moving-least square approximation. The degree of the Taylor series used in the local subdomain is increased automatically in the regions near the crack-tips, in order to appropriately describe the local asymptotic behavior of near-tip displacement and stress fields. The path-independent J-integral and sub-domain technique are adopted to compute the dynamic stress intensity factors (SIFs) of the cracked bodies. Preliminary numerical experiments for dynamic SIFs with both uniform and variable loading conditions are given to show the efficient and accuracy of the present method for transient elastodynamic crack analysis.

Exploring new frontiers in gridshell design: The FreeGrid benchmark

Gridshell structures require an intricate design activity that shall comply with several design goals of diverse nature. This design phase can be approached with different methods and strategies and usually requires multiple competencies from different scientific fields. In this context, a common benchmark, called FreeGrid, is proposed to the scientific and practitioners’ communities in order to test and compare different approaches to the design and optimization of steel gridshells on the bases of ad-hoc defined performance metrics. FreeGrid sets three design baseline problems: a barrel vault, a parabolic dome, and a hyperbolic paraboloid, having their spring line partially not constrained (free-edge) and subjected to uniform and piecewise uniform load conditions. Participants are called to modify the baseline gridshell(s), observing a limited number of design constraints (related to geometry, external constraints and material), in order to improve their structural, buildability, and sustainability performances through the maximization of a bulk quantitative performance metric. Specifically, the structural performance metric accounts for both ultimate and serviceability behavior, through the calculation of the critical Load Factor and maximum vertical displacement; the buildability performance metric includes the evaluation of face planarity, uniformity of structural joints and members; the sustainability performance metric is based on the structure embodied carbon. This paper describes the baseline gridshells setups, the proposed performance metrics and the recommended method for performance assessment. The complete data of the baseline structures are made available according to an Open Data policy, together with postprocessing utilities intended to align the procedure to obtain the performance metrics.

Nonlocal stress gradient integral model with discontinuous and symmetrical conditions for size-dependent fracture of centrally-cracked nanobeams

We study the fracture of nanobeams containing central cracks using nonlocal stress gradient integral model (NSGIM) with discontinuous and symmetrical conditions. Compared with the traditional NSGIM, the present model includes some definite integral terms in the constitutive boundary constraints and the newly introduced constitutive continuity conditions. Subsequently, the Mode I and Mode II fracture problems are studied under given uniform loading (or concentrated force) conditions in opposite and same directions. In the numerical simulations, the effects of nonlocal and gradient length scale parameters on normalized energy release rates and works by external loads are investigated in detail.

Finite deformation analysis of the elastic circular plates under pressure loading

As one of the most commonly used engineering components, thin plates usually undergo large deflections when subjected to intense pressure loadings. In addition to the material nonlinearity, such as plastic yielding, the geometric nonlinearity caused by this finite deformation also has a great influence over its total response. In this study, a finite deformation approximation solution is given theoretically for the elastic circular plate, based on the von Kármán equations and the uniform membrane strain assumption. Through comparisons with the corresponding finite element simulations and the existing theoretical solution, the present solution is confirmed to be both accurate and efficient, for thin plate under uniform pressure loading, in both static and dynamic loading conditions. Thereafter, the competing effects and the respective dominant ranges of bending and stretching are investigated.Besides, based on the accurate stress prediction provided by the proposed high-order deformation model, the limit state of the elastic stage is analyzed, including the location that first reached the elastic limit and the corresponding instant. Thus, the present approximate solution will be valuable in future studies of failure criteria and subsequent inelastic behavior.

Strength of fabricated enclosed roadway support structure for TBM-excavated coal mine roadways: Experimental and numerical study

An increasing number of tunnel boring machines (TBMs) had been successfully applied in underground coal mines in China in recent years. While The tunnelling speed of TBM-excavated roadways has been difficult to exceed 600 m/month in deep-buried underground coal mines, which is still slow compared with the TBM tunneling speed in traffic and water conservancy tunnels. The lesson learnt from the engineering applications suggests that the rockbolting is the main factor that delays the TBM tunnelling operations. This paper proposed a fabricated enclosed roadway support structure (FERSS) for TBM-excavated roadways. The full-scale model tests under uniform and non-uniform loading conditions were conducted. The strain distribution and deformation behaviors of models were studied by using both conventional monitoring technologies and new emerged photogrammetric deformation monitoring system. The deformations of the models are negligible throughout almost the whole tests. Near the end of the tests, the displacement of models increased dramatically and then the failure of models occurred immediately. The bearing capacity of models dropped significantly from 6454.09 kN to 3481.21 kN when the lateral coefficient increased from 1 to 2. Moreover, the numerical models of FERSS were established by ABAQUS software and numerical tests were implemented under various conditions thereby obtaining further data which cannot be acquired from experimental tests. The results of numerical tests are in good agreement with those of the experimental tests and the influence factors of FERSS bearing capacity were analyzed.

Effect of Dimension Variables on the Behaviour of Slopes Stabilised by an Integrated Method Combining Gabion-Faced Geogrid-Reinforced Retaining Wall with Embedded Piles

Severe slope instability exists in the area of South Gippsland in Victoria state located in south-east Australia. An integrated slope-stabilisation method, which includes a pile-retaining structure installed at toe of the gabion-faced geogrid-reinforced retaining wall, has widely been used in this district. A continuous steel rail wall embedded in the concrete pile then provides lateral support to the retaining wall. The effectiveness of the integrated method is first illustrated by comparing the slope stability evaluated by strength reduction method and behaviours of the slope obtained by elastoplastic analysis. A series of parametric studies are then performed to investigate effects of facing inclinations, embedded geogrid length, and vertical spacing of geogrid layers on the stability and behaviour of the slope and the behaviour of the pile under various uniform surcharge load conditions. The numerical results indicate that additional contribution from piles can increase the stability of the slope up to 42.9%. The dimensional variables of gabion-faced geogrid-reinforced retaining wall also impose significant impact on the behaviour of slopes and piles, and the effect of each variable has also been quantitatively evaluated and qualitatively described. The effect of the geogrid amount on behaviours of slopes and piles has also been investigated through the comparison between two slope configurations with maximum and minimum geogrid amount. The results from the parametric studies can then be used as a design reference for the future applications of this integrated slope-stabilisation method.

Mechanical testing and biomechanical CT analysis to assess vertebral flexion strength of Chinese cadavers.

Biomechanical CT (BCT), i.e., quantitative computed tomography-based finite element analysis (QCT-FEA), promises an improved technique over bone mineral density (BMD) in predicting bone strength and the risk of osteoporotic vertebral fractures. However, most of the BCT models only consider a uniform compressive loading condition and they have not been validated for Chinese subjects. This study examined the ability of BCT to predict wedge fracture-related vertebral flexion strength in a cohort of Chinese cadaveric vertebrae. Twelve human vertebrae were scanned with dual energy X-ray absorptiometry (DXA) and QCT to measure areal and volumetric BMD, respectively. To produce wedge fractures, the cadaveric vertebrae were experimentally loaded until failure under a 15^° flexion. Vertebral flexion stiffness and strength were measured from the force-displacement curve. Voxel-based heterogeneous FE models of the vertebrae were created and virtually tested in uniform compression and 15^° flexion to compute compressive and flexion strength (and stiffness), respectively. The predictions of vertebral flexion strength with BMD or BCT measures were evaluated with linear regression analyses. Results showed weak correlations between experimentally-measured flexion strength vs. DXA-aBMD (R²=0.26) or QCT-vBMD (R²=0.39). However, there were strong correlations between experimentally-measured flexion strength vs. BCT-computed vertebral strength under either flexion (R²=0.71) or compression (R²=0.70) loading conditions, although flexion reduced the BCT-computed vertebral strength by 9.2%. These results suggest that, regardless of whether a uniform compression or a flexion loading is simulated, BCT can predict in vitro vertebral flexion strength better than BMD.

Numerical study on restrained thermal elongation of cold-formed steel Column subjected to non-uniform thermal loading under transient state

Cold-formed steel (CFS) is extensively used as non-load bearing and load-bearing structural members because of its less weight to strength ratio, transportation economy, and handling ease. Since CFS members are treated as slender sections, they are highly susceptible to buckling under the compression loads at ambient and elevated temperatures. The codes IS801, EN1993–1.3, AS/NZS4600, and BS5950 are used to design the cold-formed steel compression members at ambient temperature, and the code EN1993–1.2 is used to design the CFS member by treating it as a slender member with a limiting temperature of 350 °C. Many researchers have attempted to study the behaviour of CFS members at elevated temperatures, both numerically and experimentally, under uniform thermal loading conditions at steady-state. However, studies on non-uniform thermal loading under transient states are minimal. The present study focuses on the numerical modelling of buckling behaviour of CFS members with restrained thermal elongation under non-uniform temperature conditions. The numerical modelling of the CFS column subjected to non-uniform temperature under a transient state is validated with the past results. The parametric study is carried out by varying the initial load, the member's slenderness ratio, the stiffness of the supporting structure, the width-thickness ratio(w/t), and the temperature difference between flanges.

Collective elastic properties of mechanical metamaterials

Recent studies of the unusual frequency–wavenumber dependences and the related phenomena of the negative effective mass and stiffness in phononic metamaterials unveiled many futuristic opportunities for the acoustical and heat transfer engineering [1], [2], [3], [4], [5]. They also facilitated investigations of quasistatic responses of architected material systems in a quest for negative elastic moduli [6], [7], [8], [9], [10] and other unusual basic properties [11], [12], [13], [14], [15] expected at uniform loading conditions. In this letter, we show that materials with discrete internal structure may also demonstrate strong dependences of their effective (continuum equivalent) mechanical properties on the wavenumber/spatial frequency of static sinusoidal pressure waves. The Fourier mode stiffness, a ratio of the periodic load amplitude and a response amplitude is a quadratic function of the load’s wavenumber in continuum materials. However, in discrete periodic lattices, we show it to be a squared sine function of the wavenumber, which flattens down when the wavelength becomes comparable with a unit cell size. As a result, comparing similarly loaded continuum and lattice materials leads to a varying dependence of the effective longitudinal and shear moduli on the wavenumber. Practically, this means that both material design and static load patterning can influence an effective elastic modulus of a mechanical metamaterial, and it can be seen from collective responses of a large group of unit cells.

Mechanisms of shear strain accumulation in laboratory experiments on sands exhibiting cyclic mobility behavior

The factors and mechanisms controlling the accumulation of shear strains of clean uniform sands exhibiting cyclic mobility behavior under level-ground conditions are examined. This phenomenon is investigated through a series of constant-volume cyclic direct simple shear (DSS) tests subjected to uniform and irregular loading conditions, and undrained cyclic element tests collected from the literature. Experimental data show that the rate of shear strain accumulation per loading cycle depends on the relative density, cyclic stress amplitude, and effective overburden stress. Mechanisms of shear strain accumulation are investigated by decoupling the shear strain developed in each loading cycle in two components: γ0, developed at near-zero effective stress, and γd, developed during dilation. Results show that γ0 mostly depends on the shear strain history, while γd depends on the cyclic stress amplitude and relative density. These dependencies of γd and γ0 are used to provide an explanation for the gradual decrease of the rate of shear strain accumulation that is observed while increasing the number of post-triggering loading cycles in tests performed on dense specimens.

Модель стенда для дослідження конструкцій з листового скла

The use of sheet glass as a structural material capable of bearing significant loads is complicated by the lack of regulatory documents for calculating the stress-strain state. This is primarily due to the variability of the strength characteristics of sheet glass. In practice, these necessary indicators are obtained by conducting full-scale research. A large number of factors that affect the strength of glass makes the test results statically heterogeneous, which leads to a high cost of research. The use of the capabilities of modern 3D modeling software systems can significantly reduce the cost of testing by virtually simulating the impact on the model of the structural element. The glass plate model is free of production defects, so its study allows for determining the general direction of the influence of structural factors on the structure's performance and its optimization. This paper presents a stand model developed in the SOLIDWORKS environment for the study of sheet glass structures under the action of uniformly distributed pressure. Analyzing the model in the SOLIDWORKS Simulation module according to the proposed settings allows to study of the stress state of flat glass depending on the parameters of the rubber gasket and to justify the design of the support unit. The model allows to estimate of the stress-strain state of structural elements based on the Mohr-Coulomb failure criterion (for a glass plate), and stresses (according to Mise, and others) for support elements. The above settings of the program ensure its conflict-free operation with low machine resource consumption. There is a possibility of variations in the design of the support unit, including taking into account the conditions of fixing (friction) elements. The localization of critical stresses in the glass plate coincides with the data from field experiments, which indicates the adequacy of the model. The developed model of the stand allows for the investigation of the stressed state of sheet glass under uniform load conditions, depending on the parameters of the rubber gasket.