Dimensions Of Structural Elements Research Articles

Robust safety assessment of functionally graded structures with interval uncertainties

This paper investigates the problem of non-deterministic static analysis of functionally graded structures involving interval uncertainties through both Euler-Bernoulli and Timoshenko beam theories. Within the generalized analysis framework of the Finite Element Method (FEM), a novel computational scheme is developed to effectively tackle such intricate, yet frequently encountered, engineering problems. The proposed method establishes a unified non-stochastic uncertainty analysis framework, which can incorporate the interval uncertainties of material properties of the functionally graded structural members, the dimensions of structural elements, as well as the externally applied thermal and mechanical loads. By introducing an alternative FEM formulation, the governing equation for the interval uncertain static analysis of functionally graded structures can be meticulously transformed into two standard nonlinear programming (NLP) problems, so the extreme bounds of any concerned structural behaviours can be effectively determined. In addition, the proposed method is able to provide the critical information regarding the uncertain parameters that are actually causing such extreme structural behaviours at zero computational cost. Consequently, such by-products of the analysis can certainly be beneficial for subsequent structural design, and also the physical feasibility of the original problem can be rigorously maintained.

Energy of coronal mass ejections and large-scale structure of solar magnetic fields

The relationship between variations of the energy and linear velocity of coronal mass ejections (CME) and the typical dimensions of structural elements of the large-scale solar magnetic field structure (LSMFS) is investigated for the period of 1996–2014. It is shown that the maximum linear velocity and maximum energy of CME correspond to the values of the effective solar multipole index n ~ 4.0–4.4. These values determine the maximum size of the complexes of active regions, which, together with the observed maximum values of magnetic field intensity in the complexes, limit the possible maximum CME energy.

Numerical modelling of reinforced‐concrete structures under seismic loading based on the finite element method with discrete inter‐element cracks

SummaryThe behaviour of the earthquake excitated reinforced concrete (RC) structures up to the collapse, previously designed according to the prescriptions of Eurocode 8 cannot be fully predetermined because of the diversity of the nature of the earthquake. Thus, one needs to make a judicious choice between the two ductility classes balancing between the desired response of the structure, dimension of structural elements, costs and complexity of the design and construction. Powerful numerical models stand as significant tools to obtain more insight into the peculiarity of each structure. This paper presents a numerical model for dynamic analysis and prediction of the collapse of RC structures under the seismic loading based on finite discrete element method. The model includes several numerical algorithms which are essential for realistic description of highly non‐linear effects of these structures: cyclic crack opening‐closing mechanism based on discrete cracks, interaction between the reinforcement and concrete taken by steel strain‐slip relation, the influence of adjacent cracks to the slip of reinforcing bar, local slip of reinforcing bar because of a high plastic deformation under reversed cyclic loading, the influence of the curvature of reinforcing bar to yield stress reduction of the steel and cyclic behaviour of concrete and steel. Performance of the model was demonstrated through incremental dynamic analysis of RC wall, previously designed according to the Eurocode 8 for medium and high ductility classes. The presented results demonstrated the ability of the model for simulation of the crack patterns and collapse of these structures. Copyright © 2016 John Wiley & Sons, Ltd.

THE FINITE ELEMENT MODELLING OF GLULAM TROPICAL TIMBER BEAM IN BENDING

A full scale bending testing of glued laminated (glulam) timber beam can be costly and time consuming. Therefore, computer modeling is an economical and an efficient tool to achieve the result within the acceptable accuracy. Among other modeling techniques, the finite element modeling (FEM) is widely used for its reliability to simulate and to verify the behaviour of structural elements exactly in the same way the elements perform in the experimental test. Further results of different structural element dimensions or materials can be predicted by modifying the input parameters that are of interest to the study. This study presents the verification of FEM with experimental bending test results on simply supported glulam timber beams made of Keruing and Resak species. The two dimensional (2D) FEM with LUSAS 14.3 software was used. The verification showed an acceptable agreement between the FEM and the experimental results.

Analysis of structural changes when processing aluminum alloy roll billets produced by ingotless rolling

The paper reviews structural changes after processing the roll billet manufactured of lightweight Al–Mn–Fe–Si aluminum alloys by ingotless rolling. It was also proposed to identify the texture by the generalized pole density index and to set the structural element dimensions depending on the field of coherent X -rays scattering. Correlating the findings with the phases of the material, as well as evaluating the matching of hardening with the cold rolling plastic deformation, the place of annealing between the passes was defined by selection and due to convergence of the generalized pole density value after its determination by X -ray patterns of the roll billet samples and the strip after each pass.

Evaluation of the early-age-shrinkage of Fiber Reinforced Concrete (FRC) using image analysis methods

Cracking of concrete due to early-age shrinkage is a common problem that generally leads to several problems experienced by concrete structures, mainly influencing and reducing durability and lifetime. This is of particular relevance in the case of slabs type structures such as pavements, industrial floors, bridge decks, tunnel lining and precast elements, that show much larger surface areas compared with other kinds of structural components, such as beams and columns. In addition, the cracks allow water and other chemical agents to penetrate into concrete and get in touch with steel reinforcements, leading to reinforcement corrosion, even to breakage. Consequently, curing is the unique traditional method to avoid such problems. However, in certain applications, due to the severe environmental conditions and/or due to the actual dimensions of structural elements, curing does not fit the purpose in the prevention of cracks. For the above said, fibers have been incorporated in concrete to reduce and/or prevent the propagation of the early-age-shrinkage cracking. In fact, the utilization of fibers has increased progressively over the past years in structural applications. The present paper focuses on early-age shrinkage cracking with a special attention given to new concretes aiming at reduced shrinkage phenomena through the addition of different types of macro fibers within the cement matrix. In order to estimate the effectiveness in preventing the growth of the cracks, an easy methodology, based on image analysis (IA), has been developed. The results show different considerations regarding distinct materials: in terms of the effectiveness of fibers, the addition of polypropylene and polyethylene macro fibers exhibits the best performance and leads to a certain delay and a wide decreasing in cracking formation. The use of fibers has been found to be very effective in the width reduction of the cracks and, even if not so significantly, in the length reduction.

Research on the one-way magnetic attraction force of the armature in a solenoid electromagnet

The one-way magnetic attraction force of the armature is studied for a given range of extreme deviations of the dimensions of structural elements in a solenoid electromagnet. This force is caused by magnetic flux irregularity in areas occupied by nonworking gaps. This is especially important for low-frequency machines and vibratory impact devices with an electromagnetic drive. The armature travel frequency of such devices reaches 50 s–1 under high friction losses. The one-way magnetic attraction forces of the armature, when the solenoid electromagnet construction symmetry is impaired, are numerically determined with the finite-element magnetic field simulation in the Finite Element Method Magnetics (FEMM) software. It is shown that the one-way magnetic attraction force of the armature and its components are comparable with the driving force in the specific gap under a given range of extreme deviations of the real armature gaps and drifts. To improve dynamic design accuracy, it is necessary to take into account irregularity of the magnetic field and the appearance of an armature magnetic attraction force component in the areas occupied by an inductor.

Development of parameter-orientedmodels of bladed disks for static strength analysis

In today's competitive production is important shortening time-processing products, which can be achieved using modern digital technology. Work is devoted in creating parametric finite element models of the compressor and the low-pressure turbine rotor wheels and a free turbine of modernized gas compressor unit NK-36ST using the package ANSYS Mechanical. The developed models of blades and disks allow to control grid of finite elements and the geometrical parameters of the structure in a wide range: the geometry of the blade, shapes and sizes for radius transition, shank geometry, dimensions of structural elements of the disc. The geometry of the airfoil blades is read from the file received as a result of gas-dynamic calculations. Models rotor wheels consider contacting a locking connection. Approach to the creation of the finite element mesh is to use structured and hybrid scheme that reduces the amount of grids and as a consequence, reduces the calculation time. The use of such models for the calculation of static strength under changing the geometric parameters of the gas-dynamic optimization when allowed to make them as soon as possible. With the help of the developed models in the future produced calibration calculations and confirmed reserves of strength.

Seismic hazards assessment of Kumaun Himalaya and adjacent region

The ongoing continent–continent collision between Indian and Eurasian plates houses a seismic gap in the geologically complex and tectonically active central Himalaya. The seismic gap is characterized by unevenly distributed seismicity. The highly complex geology with equally intricate structural elements of Himalaya offers an almost insurmountable challenge to estimating seismogenic hazard using conventional methods of Physics. Here, we apply integrated unconventional hazard mapping approach of the fractal analysis for the past earthquakes and the box counting fractal dimension of structural elements in order to understand the seismogenesis of the region properly. The study area extends from latitude 28°N–33°N and longitude 76°E–81°E has been divided into twenty-five blocks, and the capacity fractal dimension (D 0) of each block has been calculated using the fractal box counting technique. The study of entire blocks reveal that four blocks are having very low value of D 0 (0.536, 0.550, 0.619 and 0.678). Among these four blocks two are characterized by intense clustering of earthquakes indicated by low value of correlation fractal dimension (D c ) (0.245, 0.836 and 0.946). Further, these two blocks are categorized as highly stressed zones and the remaining two are characterized by intense clustering of structural elements in the study area. Based on the above observations, integrated analysis of the D c of earthquakes and D 0 of structural elements has led to the identification of diagnostic seismic hazard pattern for the four blocks.

Inorganic materials and coatings produced by EBPVD

The present paper describes the process of high speed electron beam evaporation of inorganic substances under vacuum and process parameters controlling the deposition, structure and properties of thick condensates (films). Considered are examples of single phase and multiphase metal, metal–ceramic, cermet and ceramic condensates of the thickness from several micrometres to several millimetres with dispersed, multilayer, porous and graded structures in a broad range of structural element dimensions. Dimensional effects in the structure and mechanical properties of thick condensates are noted. Areas of practical application of inorganic materials deposited from the vapour phase are described.

Size effects in the analysis of reinforced concrete structures

The mechanical properties of engineering materials are routinely determined by testing. In practice, the dimensions of structural elements are often much larger than those of the samples that, for technical or economic reasons, can be subjected to laboratory testing. Consequently, testing is usually conducted on reduced scale models or material samples. At the same time, available theories of material behavior that predict size or strain rate effects are receiving increasing attention in the technical literature. However, finite element models or similar representations, used for engineering predictions of the strength or loading capacity of large structures, rarely consider the influence of scale. The so-called discrete element method (DEM), in which a solid is replaced by a three-dimensional lattice of one-dimensional elements linking lumped nodal masses, has been extensively used to determine the dynamic response of concrete structures subjected to loads that produce fracture and fragmentation. In this paper, it is shown how the two major causes of size effects, namely the non-homogeneous character of the materials and the occurrence of fracture, can be incorporated in the analysis, in order to improve the prediction capability of the method. The latter is validated by numerically analyzing geometrically similar reinforced concrete beams, tested to rupture by Leonhart and Walter (1965). Those tests were later reproduced by Ramallo et al. (1993). Both the non-homogeneous character of concrete and steel were taken into account in the DEM, by assuming that the initial modulus and specific fracture energy are random fields in three-dimensional space. The constitutive criteria for the lattice elements, employed earlier by the authors to account for the energy dissipated by fracture, is adopted in the paper, with improvements in the consideration of the cross-correlation between relevant variables. As additional evidence of the reliability of the approach, the discrete numerical model was also used to numerically simulate experimental results due to Vliet et al. (2000), aimed at quantifying the influence of sample size on the tensile strength of concrete.

Role of nonequilibrium nonlocality and memory effects in structure formation of dynamically deformable media. I. Nonlocal hydrodynamic theory

A new theoretical approach to the description of structure formation processes in a solid under dynamic stress, which are initiated by this stress, is developed in the present paper. This approach is based on the similarity between the behavior of a dynamically deformable solid and hydrodynamics of fast processes and differs from classical hydrodynamics by several essential aspects. First, the new approach is based on the nonlocal system description, that is, it retains the integral information on the system as a whole while describing its local properties and also takes into account the long-range influence of the environment. Second, this approach considers the influence of boundary conditions of the problem on the structure formation process in a self-consistent way, by introducing a feedback into the system. The model of the medium suggested here describes the intermediate situation between a perfectly rigid body (the nonlocality parameter increases infinitely) and a viscous liquid (the nonlocality parameter is close to 0). As a result of branching of solutions to the general nonlinear problem of dynamic deformation of a medium for the nonlocal model, the dimensions of structural elements and the types of kinematic deformation mechanisms are simultaneously determined for different scale levels. The results obtained are confirmed by a number of experimentally observed regularities.

Automating constructibility reasoning with a geometrical and topological project model

Due to fragmentation in the construction industry, structural engineers do not generally use explicit constructibility knowledge when making decisions about the layout and dimensions of structural elements. By interfacing with a geometrical and topological model of a design, an on-line construction expert automates the input of construction expertise to these decisions and allows use of more efficient construction methods on a project. Developing such an expert system poses three main challenges: formalizing and representing constructibility knowledge; developing a product model schema to represent project data; and integrating the project model with the knowledge. This paper summarizes the first and third tasks and describes the project model in detail.

Identifying the linear cracking resistance characteristics for normal detachment in a composite

A method has been devised for determining the structural characteristics of the cracking resistance for an orthotropic composite on a rectangular specimen having a central notch, which includes calculations on the state of strain in the notched specimen and determination of the structural-element dimensions, as well as choosing specimens for tests and determining the failure loads, followed by statistical processing.

Simulating crack initiation and failure in a multilayer composite: Effective-strength distribution in a unidirectional reinforced composite

A unidirectionally reinforced composite is considered, whose components are homogeneous in elastic properties but stochastically inhomogeneous in strength parameters. The material is represented as a continuous set of structural elements composed of fiber segments, matrix, and adhesive layers. A combined theoretical and experimental approach has been used to determine the microstrength distribution parameters for rectangular specimens having thin notches, which includes an analytical calculation on the state of strain and the determination of structural element dimensions, as well as experimental determination of the failure load and statistical processing.

Stress state of turbine blade elements containing holes for shrouding

In the process of designing powerful steam turbines, problems often arise in the selection of optimum shapes and dimensions of structural elements distinguished by high stress levels. Among these are in the first place long, naturally twisted blades. The active part of such a blade, subjected to the effect of a system of (tensile, flexural, and torsional) forces, is in a state of complex stress. The range of problems solved in the course of designing such blades is very wide. It includes problems of the state of overall stress, and also investigations of the effects of a local nature connected with the abrupt change of shape of the conjugate structural elements.

Phenylvinylsylsesquioxane polymers

The structure of polyphenylsylsesquioxanes containing 1·5 to 7·5 mole% vinylsilyl groups was studied using dynamic flow birefringence and it was shown that the addition of these groups disrupts the ladder structure of macromolecules thus altering flexibility, increasing the homogeneity of the supermolecular structure, reducing the dimensions of structural elements, increasing adhesion and internal stress. A study was made of thermal oxidizing breakdown of phenylvinylsylsesquioxanes in pigmented and non-pigmented films and it was shown that initial cracking of polymer films is preceded by increased internal stress.

Crosslinking and structural changes of cellulose fibers

AbstractThe supermolecular structure of various cellulose fibers modified with crosslinking reagents has been investigated by electron microscopy methods. The density, degree of crystallinity (DC), and length changes in alkaline solutions were measured for the modified celluloses. The samples treated with monofunctional analogs of the crosslinking reagents as well as the fiber preparations containing linear and network polymer were also investigated. Three main problems are suggested for the discussion: (1) the general regularities of the structural changes in cellulose in the process of crosslinking; (2) the specific features of the structural changes, as observed in different cellulose samples; (3) the relation between the degree of modification, the type of modifying reagent, and the structure of the crosslinked cellulose. The characteristic structural changes, i.e., the increase in the thickness of fragments, the specific cogged edges, the increase in the lateral dimensions of structural elements all seem to be most representative in native cellulose fibers and are perfectly well distinguished. Similar changes are found in viscose fibers but are less clearly defined. Crosslinking proceeds rather uniformly through the whole of the fiber cross section. It appeared to be most evident when the cross sections are treated with solvents, or when etched in gaseous discharge. Only in cases when the modification is performed in nonaqueous solutions does the reaction proceed mainly in the peripherial regions of the fiber. In fibers subjected to strong swelling, crosslinking results in a real increase in the lateral dimensions of the microfibrils, with the layer thicknesses remaining the same. As a rule, the modification does not imply significant changes in the fiber surface. The crystallite size decreases in the process of crosslinking. This appears to be peculiar to viscose fibers, especially to those subjected to crosslinking in the swollen state. The degree of crystallinity and density of the fibers decrease sharply, which seems to be especially evident in epichlorohydrin‐modified samples. Cellulose structure remains unchanged when linear or network polymer forms in the fiber or when the samples are treated with monofunctional reagents. Changes in properties and structure of cellulose caused by crosslinking are most apparent if elongation of the fibers in alkaline solution before and after the modification is compared.

Structural investigations of crosslinked cellulose derivatives

AbstractElectron microscopy methods are used for investigation of the structure of cellulose fibers modified by some bifunctional reagents (dimethylolurea, formaldehyde, acrolein, epichlorohydrin, and propylene oxide). For sample preparation, mechanical and ultrasonic dispersion, ultrathin sectioning, and treatment by some reagents were used. Some data were obtained indicating extensive changes of the fiber supermolecular structure as a result of crosslinking between the structural elements. These changes are expressed in redistribution of the effective dimensions of structural elements toward their increasing (increase in layer thickness and diameters of fibrillar bundles) and even in the alteration of mutual arrangement of structural elements under very high degrees of substitution, as compared with the untreated fibers. Modification may proceed not only in the most accessible regions of the fiber, between the microfibrils as well as between the secondary wall layers, but also inside the microfibrils themselves, and in some cases affects the most dense fiber regions—crystallites. All these changes of the supermolecular structure after modification leads to essential alterations in the mechanical properties of the fibers.