Band 7, Heft 1

Nonlinear flexural analysis of sandwich composite beam with multiwall carbon nanotube (MWCNT) reinforced composite face sheet and bottom sheet under the thermo-mechanically induced loading using finite element method is carried out. Solution of current bending analysis is performed using Newton’s Raphson approach by using higher order shear deformation theory (HSDT) and non-linearity with Von Kármán kinematics. The sandwich laminated composite beam is subjected to uniform, linear and nonlinear varying temperature distribution through thickness of the beam. The sandwich beam with MWCNT reinforced composite facesheet and bottom sheet is subjected to point, uniformly distributed (UDL), hydrostatic and sinusoidal loading. The two phase matrix is utilized with E-Glass fiber to form three phase composite face sheet and bottom sheet by Halpin-Tsai model. The static bending analysis is performed for evaluating the transverse central deflection of three and five layered sandwich composite beam. Transverse central deflection is measured by varying CNT volume fraction, uniformly distributed, linearly and nonlinear varying temperature distribution, thickness ratio, boundary condition, number of walls of carbon nanotube by using interactive MATLAB code.

Transporting mass products from one country to others is essential activities in industrial cycle. Ships are selected as reliable carriers for this objective considering traveling time and operational cost. During its operational, accidental events such as storm, high tide and bad weather may cause the products which are usually packed in freight containers fall into sea, and impacts the ship structure. In this situation, casualties on both involved structures can be detrimental. This work analyzes a series of ship-container collision in maritime territory in order to investigate resulting structural phenomena. The finite element approach is selected to solve the designed collision cases where the discussion is directed to selected crash-worthiness criteria. Impact speed between ship and container structures is chosen as the main parameter in the designed scenario by judging whether this parameter is a good representative of sea state. Overall results indicate that the indication for container rebounding after impact was high. It was followed by a significant increment of the internal energy after higher velocity, which was more than 5 m·s −1 , had been applied to the scenario. Quantification of specific structural performance suggests that approximately more than 80% of the damage occurrs on the contacted area of the container structure.

Background: The success of planning geological and technical measures aimed at intensifying oil production is of high importance. Methodology: To increase the efficiency of operations aimed at oil recovery enhancement, it is necessary to use mathematical models of the rock mass deformation, taking into account the physical and mechanical properties of the rocks. Results: Currently, the application of these models is difficult due to a lack of data. As a result, the use of simpler models is resorted to, which is not always correct in the practical application of these models. This article describes experimental studies aimed at determining the mechanical properties of rock and establishing the correlation between properties and the fluid saturation of the rocks. The study determined the physical-mechanical properties of the rocks (taking into account the stage of field development) and established the dependencies of the change in the oil reservoir rock properties on the saturation and type of load on a sample. Conclusions: The results show that the saturation of the rock with a liquid phase (hydrocarbon or water) decreases the strength of the reservoir rock, which in turn depends on the type of saturating fluid.

The second order statistics of multiple edge crack functionally graded materials (FGMs) under tensile, shear and combined loading assuming uncertain system parameters is presented in this paper. The uncertain parameters used under the present study are the material properties, and crack parameters such as crack length and crack angle. In this present analysis extended finite element method (XFEM) is used. The stochastic analysis is carried out using second order perturbation technique (SOPT) for the evaluation of mean and coefficient of variance (COV) of mixed mode stress intensity factor (MMSIF).

The study solves a system of finite difference equations for flexible shallow concrete shells while taking into account the nonlinear deformations. All stiffness properties of the shell are taken as variables, i.e. , stiffness surface and through-thickness stiffness. Differential equations under consideration were evaluated in the form of algebraic equations with the finite element method. For a reinforced shell, a system of 98 equations on a 8×8 grid was established, which was next solved with the approximation method from the nonlinear plasticity theory. A test case involved computing a 1×1 shallow shell taking into account the nonlinear properties of concrete. With nonlinear equations for the concrete creep taken as constitutive, equations for the quasi-static shell motion under constant load were derived. The resultant equations were written in a differential form and the problem of solving these differential equations was then reduced to the solving of the Cauchy problem. The numerical solution to this problem allows describing the stress-strain state of the shell at each point of the shell grid within a specified time interval.

The paper extends recently developed idea of stable evaluation of the Gaussian kernel. Owing to this, the Gaussian radial basis function that is sensitive to the shape parameter can be stably evaluated and applied to interpolation problems as well as to solve differential equations, giving highly accurate results. But it can be done only with grids being the Cartesian product of sets of points, what limits the use of this idea to rectangular domains. In the present paper, by the association of an appropriate transformation with the mentioned method, the latter is applied to solve biharmonic problems on quadrilateral irregular domains. As an example, in the present work this approach is applied to solve bending as well as free vibration problem of thin plates. In the paper some strategies for the implementation of the boundary conditions are also presented and examined due to the accuracy. The numerical tests show high accuracy and usefulness of the method.

The golden number has been one of the most important measures of beauty from ancient Greece till now. Although the reason still unclear, it is certain that the golden ratio has a direct correlation with beauty. This nice feeling can come from listening to a musical piece or watching a visual art, which is based on this wondrous number. Although the golden number is more suitable from beauty or harmony’s perspective, for some researches it is a requirement to develop Architectural designs. Therefore, in this article a masterpiece (Shah-mosque Isfahan) was investigated to find its golden relations. This mosque was chosen because of the precise and harmonious proportions. In this research: plan, sections, facade and decorations of ceiling tiles in main dome, were analyzed by Phi-matrix software in which, existence of the golden ratio has been proven undoubtedly.

In this paper, non-linear transverse deflection, stress and stress concentration factors (SCF) of isotropic and laminated composite sandwich plate (LCSP) with and without elliptical cutouts subjected to various trans-verse loadings in hygrothermal environment are studied. The basic formulation is based on secant function-based shear deformation theory (SFSDT) with von-Karman nonlinearity. The governing equation of non-linear deflection is derived using C 0 finite element method (FEM) through minimum potential energy approach. Normalized trans-verse maximum deflections (NTMD) along with stress concentration factor is determined by using Newton’s Raphson method through Gauss point stress extrapolation. Influence of fiber orientations, load parameters, fiber volume fractions, plate span to thickness ratios, aspect ratios, thickness of core and face, position of core, boundary conditions, environmental conditions and types of transverse loading in MATLAB R2015a environment are examined. The numerical results using present solution methodology are verified with the results available in the literatures.

Due to their high numerical efficiency, homogenization models are often employed in the analysis of corrugated laminates. They are usually derived assuming periodic behavior in the corrugated direction and generalized plane strain in the out-of-plane direction, which corresponds to the assumption of infinite dimensions of the structure. As a consequence, any influences of edge effects are not mapped, although they can have a significant impact on the mechanical behavior of a given structure. The objective of this manuscript is to investigate the influence of boundary conditions - a combination of free-edges and clamping - on the structural stiffness of corrugated laminates. A total of six load cases are investigated which correspond to the line loads considered in the classical theory of laminated plates. The results of this parameter study allow the identification of several critical loading situations, where free edges can significantly alter structural stiffness. The given investigations hence contribute to the investigation of the validity range of homogenization models.

The present paper aims at studying the nonlinear ultrasonic waves in a magneto-thermo-elastic armchair single-walled (SW) carbon nanotube (CNT) with mass sensors resting on a polymer substrate. The analytical formulation accounts for small scale effects based on the Eringen’s nonlocal elasticity theory. The mathematical model and its differential equations are solved theoretically in terms of dimensionless frequencies while assuming a nonlinear Winkler-Pasternak-type foundation. The solution is obtained by means of ultrasonic wave dispersion relations. A parametric work is carried out to check for the effect of the nonlocal scaling parameter, together with the magneto-mechanical loadings, the foundation parameters, the attached mass, boundary conditions and geometries, on the dimensionless frequency of nanotubes. The sensitivity of the mechanical response of nanotubes investigated herein, could be of great interest for design purposes in nano-engineering systems and devices.

Karbandies’ masonry ribs construction technology is influenced by form and size, on one hand, and traditional architects’ creativity, on the other hand. Some of the exclusive characteristics of construction techniques of Kar-bandies’ ribs are revealed, after investigating and identifying of some of traditional construction ways of them, investigating contemporary studies conducted in the field and comparing the methods. The masonry ribs have been built in different forms over time and such different forms result in formation of different construction technologies. The masonry ribs’ form and size and the bricks’ arrangement way have direct effect on their construction process. The aim of the present paper is to determine construction technology of the masonry ribs used in different Karbandies. Hence, in line with achieving this goal, it also tries to investigate geometric arrangement of bricks in masonry ribs. The present study, for the first time, presents a comparative structure to study different implementation ways of Kar-bandies’ masonry ribs and reasons for similarities and differences among different samples. Moreover, the present study tries to draw implementation way of different types of ribs with the aid of 2D and 3D software and by doing library studies, field understandings and interviewing the related masters and then the collected data were studied, comparatively. Data-gathering of this research included library studies which included written, listening and visual methods of books, articles and dissertations. Interviewing traditional masters, who are expertise in the field, were used in the samples analysis. Then according to the master builders’ advice, structural form of karbandi ribs was modelled using three-dimensional software type. In this study karbandie’s masonry ribs were divided into three categories of radial brick vault, pitched brick vault and a combination of them based on their brick arrangement way. Investigation of the results indicated that the bricks due to their geometrical form and variety in shape can result in various combinations. Different factors including materials, centering, dimensions, bay size and other factors are influential in bricks arrangement of the ribs. ter builders’ advice, structural form of karbandi ribs was modelled using three-dimensional software type. In this study karbandie’s masonry ribs were divided into three categories of radial brick vault, pitched brick vault and a combination of them based on their brick arrangement way. Investigation of the results indicated that the bricks due to their geometrical form and variety in shape can result in various combinations. Different factors including materials, centering, dimensions, bay size and other factors are influential in bricks arrangement of the ribs.

This study aims to investigate the damping behavior of the fundamental mode of a foam-filled carbon fibre reinforced polymer composite (CFRP) tube when subjected to base excitations. In particular, expanded polystyrene (EPS) foam balls (with negligible mass) of different sizes are used as fillers in the tube and the enhancement in damping ratio of the fundamental mode w.r.t the empty condition is evaluated for different intensity of base excitation. Shake table tests are performed on cantilever CFRP composite square hollow tube subjected to base excitation with varying amplitudes. The tube is filled with foam balls (of two different sizes) for varying depths of filling (no filling, one-third, two-third, and full). Accelerometers are mounted at different positions along the tube length and at the table to record the accelerations data for evaluation of damping ratio. From the recorded responses, frequency, mode shape and damping ratio of the fundamental mode are evaluated using a well-known approach. The damping ratio is noted to be around 1.41x (times) higher for the completely foam ball (bigger size) filled case under r.m.s base acceleration of 0.3 g when compared with the values corresponding to the empty case. The results suggest that the bigger foam balls enhance the damping ratio significantly without altering the natural frequency owing to additional energy dissipation in friction and impact generated through the sliding and collision of the balls while the tube is in motion.

In this study, a numerical investigation tensile test using ANSYS on three different carbon and alloy sheets of steel: AISI 1030 medium carbon steel, AISI 1080 high carbon steel and high-strength low-alloy (HSLA) A606 steel, has been carried out. The influences of three different specimen geometries on the stress–strain curve were also investigated. Understanding the properties of these materials, such as stress–strain obtained from a tensile test, is important. Materials are subjected to forces or loads when in use, for example, steel in a ship’s hull experiences significant stresses and strains. In such situations, it is necessary to understand the characteristics of the material because grounding or collisions can occur, which deform the materials. The differences in stress and strain obtained from three specimens with different geometries and mesh sizes of 2.5, 5, 7.5, and 10 mm for all proposed steels, were observed. The results showed that the ultimate tensile strength was always lower in specimen 2 compared to the other specimens. Furthermore, the highest von Mises stress and strain contour was located in the midsection of specimens 1 and 3 in all of the proposed materials.

We present a simple methodology to design curved shell finite elements based on Nzengwa-Tagne’s shell equations. The element has three degrees of freedom at each node. The displacements field of the element satisfies the exact requirement of rigid body modes in a ‘ shifted-Lagrange ’ polynomial basis. The element is based on independent strain assumption insofar as it is allowed by the compatibility equations. The element developed herein is first validated on analysis of benchmark problems involving a standard shell with simply supported edges. Examples illustrating the accuracy improvement are included in the analysis. It showed that reasonably accurate results were obtained even when using fewer elements compared to other shell elements. The element is then used to analyse spherical roof structures. The distribution of the various components of deflection is obtained. Furthermore, the effect of introducing concentrated load on a cylindrical clamped ends structure is investigated. It is found that the CSFE3-sh element considered is a very good candidate for the analysis of general shell structures in engineering practice in which the ratio h/R ranges between 1/1000 and 2/5.

Diagrids represent one of the emerging structural systems employed worldwide for the construction of high-rise buildings. Their potential relies on the peculiar architectural effect and their great lateral stiffness. Because of the modular nature of the diagrid triangular element, optimization processes are usually carried out to assess the best arrangement of the external diagonals in order to enhance the structural performance while using the lowest amount of structural material. In this contribution, we make use for the first time of the desirability function approach to investigate the optimal geometry of the dia-grid system. A 168-meter tall building, with four different floor shapes, is analyzed, and the inclination of the external diagonals is varied between 35° and 84°. The desirability function approach is applied to find the most desirable geometry to limit both the lateral and torsional deformability, the amount of employed material as well as the construction complexity of the building. A sensitivity analysis is also carried out to investigate the influence of the individual desirability weight on the obtained optimal geometry. The effect of the building height is finally evaluated, through the investigation of sets of 124-, 210- and 252-meter tall diagrid structures.

Architects and engineers have been always attracted by concrete shell structures due to their high efficiency and plastic shapes. In this paper the possibility to use concrete shells to support footbridges is explored. Starting from Musmeci’s fundamental research and work in shell bridge design, the use of numerical form-finding methods is analysed. The form-finding of a shell-supported footbridge shaped following Musmeci’s work is first introduced. Coupling Musmeci’s and Nervi’s experiences, an easy construction method using a stay-in-place ferrocement formwork is proposed. Moreover, the advantage of inserting holes in the shell through topology optimization to remove less exploited concrete has been considered. Curved shell-supported footbridges have been also studied, and the possibility of supporting the deck with the shell top edge, that is along a single curve only, has been investigated. The form-finding of curved shell-supported footbridges has been performed using a Particle-Spring System and Thrust Network Analysis. Finally, the form-finding of curved shell-supported footbridges subjected to both vertical and horizontal forces ( i.e. earthquake action) has been implemented.

Venus and the Ocean Worlds are emerging areas of interest for space exploration, as they can potentially host, or have hosted, conditions compatible with life. Landers and probes for in-situ exploration, however, must deal with very high external pressure, due to the environmental conditions, often resulting in thick and heavy structures. Robust, reinforced shell structures can provide a lightweight solution for the primary structure. In this frame, the isogrid layout is already a standard in aerospace, especially for flat panels or cylindrical shells. In this paper, isogrid-stiffened hemispherical shells, or “geodesic domes”, are described, focusing on the case of a concept of a Venus lander. Early design methods for both plain and geodesic domes subjected to external pressure are presented, providing design equations. Additive Manufacturing is identified as the key technology for fabricating metallic geodesic domes, due to the complexity of the internal features. Moreover, it allows to fabricate ports and integrated thermostructural systems in the same process, potentially resulting in improved performance or cost and schedule savings.

This paper presents a study on Singular Value Decomposition (SVD) of pressure coefficients hyperbolic parabolic roofs. The main goal of this study is to obtain pressure coefficient maps taking into account spatial non-uniform distribution and time-depending fluctuations of the pressure field. To this aim, pressure fields are described through pressure modes estimated by using the SVD technique. Wind tunnel experimental results on eight different geometries of buildings with hyperbolic paraboloid roofs are used to derive these pressure modes. The truncated SVD approach was applied to select a sufficient number of pressure modes necessary to reconstruct the measured signal given an acceptable difference. The truncated pressure modes are fitted through a polynomial surface to obtain a parametric form expressed as a function of the hyperbolic paraboloid roof geometry. The superpositions of pressure (envelopes) for all eight geometry were provided and used to modify mean pressure coefficients, to define design load combinations. Both symmetrical and asymmetrical pressure coefficient modes are used to estimate the wind action and to calculate the vertical displacements of a cable net by FEM analyses. Results clearly indicate that these load combinations allow for capturing large downward and upward displacements not properly predicted using mean experimental pressure coefficients.

Structural analysis is an intricate subject when nonlinearities occur. They make the structural behavior complex and may have important consequences in the design choice as well. Especially for lattice domes, as snap-through phenomena and local Eulerian instabilities generally affect the structural response, linear analysis is not enough. In this paper, a semi-analytical formulation is used in order to study the geometrically nonlinear behavior of lattice domes subject to vertical loads. The formulation is derived from the equilibrium equations written in the deformed configuration, considering large displacements and taking also into account local buckling conditions. The resulted system of equations, being strongly nonlinear, has been solved by means of a numerical procedure, based on a mixed load-displacement control scheme, leading to the evaluation of the complete equilibrium path. The influence of geometrical parameters on the critical load multiplier and shape of the load-displacement curve is also discussed. In particular, a complex equilibrium path for a sixteen-member five-node lattice structure is analyzed, which is characterized by several branches which can generate ‘snapping’ conditions.