Regular Perforations Research Articles

Structural analysis of rack upright frames under a pure compression load by means of a nonlinear Generalized Beam Theory analysis

AbstractRack upright frames of conventional pallet racking systems are obtained by the assembly of uprights and braces or diagonals. Rack uprights are commonly mono‐symmetric open thin‐walled members with regular perforations along their length. These perforations are used to enable the connection with braces and beams by means of bolts or hooks. The structural behaviour of a rack upright frame under a pure compression load, in which the buckling phenomenon has a relevant influence, depends on several geometrical parameters, such as the column cross‐sectional dimensions, perforations characteristics, frame length, distance between braces, etc. Therefore, these particular issues should be considered to perform a proper structural analysis.In this paper, the structural behaviour of a pallet rack frame under a pure compression load is analysed by means of eigenbuckling and geometrically nonlinear Generalized Beam Theory (GBT) analyses. The influence of GBT deformation modes involved in the analysis is discussed. Moreover, different approaches to reproduce the connection between uprights and braces are presented and discussed. Finally, GBT results are compared with beam, shell finite element analysis and experimental values.

Torsional behaviour of thin‐walled members with regular perforation systems

AbstractThin‐walled cold‐formed (TWCF) steel members that are frequently used in steel storage rack systems generally present a monosymmetric cross‐section. The adopted design approaches derive strictly from those developed for the more traditional bisymmetric solid web members, despite i) the presence in rack components of the eccentricity between the shear center and the cross‐section centroid and ii) the regular perforation systems.The paper is addressed to the torsional response of TWCF members used for the vertical elements (uprights) in storage racks, which present regular perforation systems currently neglected in routine design. Attention is focused on the evaluation of the warping constant, which reflects directly in the distribution of the normal stresses associated with the bimoment. The approach considered by the future rack design code is discussed and a refined model based on the theory of elasticity is proposed to account for the sequence of solid and perforated cross‐sections along the longitudinal axis of the member. The proposed numerical applications are related to two different cross‐sections and the discussed research outcomes allow for an appraisal of the errors associated with a warping constant defined by neglecting the presence of regular perforation systems.

The Ritual Use of Animal Scapulae in Central Asia in the Xiongnu-Xianbei-Rouran Period

ABSTRACT The scapula bone is bestowed with a particular prominence among the various traditional Siberian tribes. Besides its rich symbolic importance, the shoulder blade is connected with shamanistic rituals and in particular, fortunetelling. Scapulimancy (telling fortunes from the scapula) is a tradition with its roots in ancient China. Historical chronicles and ethnographic research on scapulimancy in Central Asia had led archaeologists to assign a ritual meaning to scapulae with regular perforations. This paper is to present the problematic matter of distinction of fortunetelling scapulae in the archaeological material. Another aim is to sum up historical and ethnographic data regarding scapulimancy. A comprehensive approach to this topic was also provided by microscopic observations on the materials from the settlement Chultukov Log-9 (Altai, Russian Federation), dated back to the Xiongnu-Xianbei-Rouran period. Excavations were conducted by the authors of this paper in 2012–2016. Experiments were also conducted in order to distinguish shoulder blades of utilitarian character (tools) from those of ritual use. In general, this issue shows the importance of animal symbolism in crucial matters for pastoral, nomadic and semi-nomadic peoples.

Perforated TWCF steel beam-columns: European design alternatives

Steel storage racks are lightweight structures, made of thin-walled cold-formed members, whose behaviour is remarkably influenced by local, distortional and overall buckling phenomena, frequently mutually combined. In addition, the need of an easy and rapid erection and reconfiguration of the skeleton frame usually entails the presence of regular perforations along the length of the vertical elements (uprights). Holes and slots strongly influence their behaviour, whose prediction is however of paramount importance to guarantee an efficient design and a safe use of racks. This paper focuses on the behaviour of isolated uprights subjected to both axial load and bending moments, differing for the cross-section geometry and for the regular perforation systems. According to the European standards for routine design, four alternatives to evaluate the bending moment–axial load resisting domains are shortly discussed and critically compared in terms of member load carrying capacity.

An experimental investigation on solid and perforated steel storage racks uprights

Thin-walled cold-formed (TWCF) profiles are extensively used in adjustable selective pallet racks that represent the most common typology between the logistic solutions. In these structures, vertical members (uprights) are usually channels, often provided with intermediate stiffeners, rear flanges and additional lips. Furthermore, in order to allow for a rapid connection with beams and bracing components, usually uprights present regular perforation systems along their length. Nowadays, theoretical approaches available to design TWCF members are based on equations valid only for few unperforated (solid) cross-section geometries. As a consequence, rack manufacturing engineers frequently adopt the well-known design-assisted-by-testing approach to overcome this limitation and to assess accurately member performance. This approach, time consuming and cost demanding, stresses the need of further improvements required to cover aspects currently not considered in design codes.The paper summarizes the results of a study focused on the response of a commercial upright profile. In particular, 48 compression and 24 bending tests on perforated and unperforated profiles have been carried out. A summary of the experimental program is proposed together with the re-elaboration of test data. Furthermore, the influence of perforation is discussed as well as key design geometric parameters. Finally, owing to the lack of information in major rack standard codes, three different proposals to evaluate the effective second moments of area have been developed, discussed and applied, hoping to contribute to standard improvements.

Data‐Driven Decision‐Making in the Design Optimization of Thin‐Walled Steel Perforated Sections: A Case Study

The rack columns have so distinctive characteristics in their design, which have regular perforations to facilitate installation of the rack system that it is more difficult to be analyzed with traditional cold‐formed steel structures design theory or standards. The emergence of industrial “big‐data” has created better innovative thinking for those working in various fields including science, engineering, and business. The main contribution of this paper lies in that, with engineering data from finite element simulation and physical test, a novel data‐driven model (DDM) using artificial neural network technology is proposed for optimization design of thin‐walled steel specific perforated members. The data‐driven model based on machine learning is able to provide a more effective help for decision‐making of innovative design in steel members. The results of the case study indicate that compared with the traditional finite element simulation and physical test, the DDM for the solving the hard problem of complicated steel perforated column design seems to be very promising.

Experimental investigations of wearable antenna on flexible perforated plastic substrate

ABSTRACTIn this article, the performance of a rectangular patch antenna on inexpensive perforated flexible plastic substrate is investigated experimentally. The antenna is designed for wearable application operating at Wi‐Fi and HiperLAN frequency bands. The regular perforations in the substrate material help in reducing the dielectric losses which is common with other textile materials thus improving the antenna performance. The prototype model of the proposed antenna is developed and measured. Various parameters such as return loss, VSWR, radiation pattern and gain are presented to validate the suitability for wearable applications. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:265–270, 2017

Simple estimation of effective elastic constants for thin plates with regular perforations and an application to the vibration of distillation column trays

The horizontal perforated sheet metal plates are commonly used in the process industries as trays in distillation columns, important internal parts for fractionating the input liquid mixture. Normally, the operating performance of such trays is satisfactory. However, cases have been reported of abnormally high levels of tray vibration during operation at particular conditions. The trays then experienced fatigue cracking accompanied by the loosening of bolts and fixings, which led to expensive failures. The excitation of structural resonance was suspected as a component in flow-induced vibration. Using linear stress superposition, a simple but robust analytical method is developed to provide high-quality predictions for the stress and strain distributions for in-plane loaded thin perforated plates with periodic hole arrangements. This approach is built on the classical solution for the elastic stress field around a single circular hole in a large plate. The perforated plates with square penetration patterns are investigated in this article, although the same approach is applicable to any regular penetration pattern. Stress concentration factors as well as the effective elastic constants, which can be used to describe the bending properties of the perforated plates, are then verified against both the established theoretical solutions and the results from finite element simulations. Excellent agreement to both previously published physical experiments and complex modelling is observed in all cases, with small-to-medium (up to 40%) hole-area fraction. The proposed analytical method is much simpler and computationally efficient than finite element analysis. The computed effective elastic constants are used in a finite element modal analysis to estimate the free vibration frequencies of a stiffened distillation column tray example; the first 30 vibration modes are found to be almost uniformly distributed between 25 and 70 Hz, which matches the vibration frequency range reported from plant operations.

European alternatives to design perforated thin-walled cold-formed beam–columns for steel storage systems

Summary Rack systems to store goods and products are one of the most important applications for thin-walled cold-formed steel members. Adjustable pallet racks are used widely worldwide and are characterized by regular systems of perforations along the uprights (i.e. vertical members) to connect easily pallet beams and diagonal members forming the skeleton frame. Design rules are based on the well-established approaches for the more traditional solid members, suitably extended to account for the presence of regular perforations via component tests accurately described in rack specifications. This paper focuses on the performance of isolated uprights under axial load and gradient moment. In particular, three European alternatives to design beam–column rack members have been discussed and applied: the first and the second are traditionally used for thin-walled cold-formed steel members while the latter, the so-called general method of Eurocode 3 part 1-1, allows to take directly into account the key features associated with upright response. The geometry of the cross-sections and of their perforation system, the member slenderness and the load condition has been assumed as parameters of this study. Research outcomes demonstrate that the predicted performances can result significantly different, reflecting directly on the weight and the cost of the whole storage system. Furthermore, numerical analyses and design calculations show that standard codes need urgent revisions, leading in few cases to design beam–columns from the unsafe side.

Electronic and transport properties in geometrically disordered graphene antidot lattices

A graphene antidot lattice, created by a regular perforation of a graphene sheet, can exhibit a considerable band gap required by many electronics devices. However, deviations from perfect periodicity are always present in real experimental setups and can destroy the band gap. Our numerical simulations, using an efficient linear-scaling quantum transport simulation method implemented on graphics processing units, show that disorder that destroys the band gap can give rise to a transport gap caused by Anderson localization. The size of the defect induced transport gap is found to be proportional to the radius of the antidots and inversely proportional to the square of the lattice periodicity. Furthermore, randomness in the positions of the antidots is found to be more detrimental than randomness in the antidot radius. The charge carrier mobilities are found to be very small compared to values found in pristine graphene, in accordance with recent experiments.

Column demands in steel plate shear walls with regular perforations using performance-based design methods

The design force demands on the columns of steel plate shear walls tend to be very large. Several methods have been proposed to reduce the moments and axial forces on the columns, while still achieving good system performance. One such method is to reduce the strength of the infill plate by perforating it using a regular pattern of circular holes. The diameter of the holes selected and their center-to-center spacing control the decrease in lateral shear strength of the system. An appropriate performance-based design method is proposed and used to study the suitability of the perforated system. The results of a variety of finite element models showed that although introducing the perforations into the infill plates reduces the lateral strength of the system, the net demand on the columns can in some cases actually increase. The perforated system behavior is also sensitive to the pattern of holes selected; a small change in the arrangement of the holes can have a significant effect on the moment demand on the columns. Also, the flexibility of the beam-to-column connections influences the sensitivity of the column design forces to the pattern of holes selected and affects the column demands considerably.

Density functional study of graphene antidot lattices: Roles of geometrical relaxation and spin

Graphene sheets with regular perforations, dubbed as antidot lattices, have theoretically been predicted to have a number of interesting properties. Their recent experimental realization with lattice constants below 100 nanometers stresses the urgency of a thorough understanding of their electronic properties. In this work we perform calculations of the band structure for various hydrogen-passivated hole geometries using both spin-polarized density functional theory (DFT) and DFT based tight-binding (DFTB) and address the importance of relaxation of the structures using either method or a combination thereof. We find from DFT that all structures investigated have band gaps ranging from 0.2 eV to 1.5 eV. Band gap sizes and general trends are well captured by DFTB with band gaps agreeing within about 0.2 eV even for very small structures. A combination of the two methods is found to offer a good trade-off between computational cost and accuracy. Both methods predict non-degenerate midgap states for certain antidot hole symmetries. The inclusion of spin results in a spin-splitting of these states as well as magnetic moments obeying the Lieb theorem. The local spin texture of both magnetic and non-magnetic symmetries is addressed.

Magnetic-flux periodic response of nanoperforated ultrathin superconducting films

We have patterned a hexagonal array of nano-scale holes into a series of ultrathin, superconducting Bi/Sb films with transition temperatures 2.65 K $<T_{co} < $5 K. These regular perforations give the films a phase-sensitive periodic response to an applied magnetic field. By measuring this response in their resistive transitions, $R(T)$, we are able to distinguish regimes in which fluctuations of the amplitude, both the amplitude and phase, and the phase of the superconducting order parameter dominate the transport. The portion of $R(T)$ dominated by amplitude fluctuations is larger in lower $T_{co}$ films and thus, grows with proximity to the superconductor to insulator transition.

Perforated monodomain YBa 2Cu 3O 7− x bulk superconductors prepared by infiltration-growth process

For various applications such as FCL, motor flyweel or bearing, … the core of bulk superconductors need to be fully oxygenated and some defects like cracks, pores and voids suppressed, in order that the material can carry high current densities. In order to study and minimise the above defects, we have developed a new elaboration technique. YBa 2Cu 3O y (Y123) bulks have been prepared by combining liquid infiltration and top seed growth (ITSG) process. This process involves negligible shrinkage and an uniform distribution of Y211 inclusions. In addition, we prepare a regular perforation of the Y123 sample in view to magnify the specific surface and by then increase oxygen diffusion into the core of the material. Neutron texture analysis demonstrates the non-perturbative effect of the holes in the bulk from the orientation point of view. The advantages of the ITSG-process and of the novel perforated Y123 bulk are discussed.

ENDOBACTERIA IN THE DIATOM PINNULARIA (BACILLARIOPHYCEAE). I. “SCATTERED ct‐NUCLEOIDS” EXPLAINED: DAPI–DNA COMPLEXES STEM FROM EXOPLASTIDIAL BACTERIA BORING INTO THE CHLOROPLASTS1,2

A local strain of the pennate diatom Pinnularia cf. “nobilis” was investigated using cytochemistry and fluorescence and EM techniques. The regular perforation of the chloroplasts of P. “nobilis” and the lack of a typical diatom pyrenoid were confirmed at the ultrastructural level. Cavities and channels in the complex secondary plastid were found to harbor symbiotic bacteria, and their DNA elicited DAPI fluorescence. Wheat germ agglutinin, labeling bacteria walls, elicited a similar fluorescence pattern. Previous speculation that the apochlorotic DNA‐positive dots in the plastids of several Pinnularia species are “scattered ct‐nucleoids” is thus refuted. Bacteria were rod shaped and gram negative. They resided in the lumen of the endoplasmic reticulum (ER) during host interphase confined to the specialized ER compartment housing the secondary plastid, that is, to the space between the third and the fourth membrane profile, encircling the chloroplast. TEM images of chemically and cryofixed cells revealed that cavities resulted from the interaction of bacteria with the plastid according to the following sequence, alignment, attachment, deformation, and disintegration. This occurred without visible injury to the primary chloroplast envelope or the relict cell membrane of the reduced ancestral red alga that surrounds the chloroplast. The patterned arrangement of bacteria suggests recognition sites on the vestigial cell membrane, thought to interact with surface groups on the bacteria. The intimate association between bacteria and secondary plastid inside the common specialized ER cisterna suggests they form a functional unit. Comparison of thylakoid profiles, disrupted by bacteria in Pinnularia, with those disrupted by the pyrenoid in other pennate diatoms (e.g. Trachyneis) revealed a significant ultrastructural resemblance. No aposymbiotic Pinnularia cells were found at the sampling site.

“SCATTERED CP‐NUCLEOIDS” IN DIATOMS EXPLAINED: BACTERIA ‐ INSIDE THE ENDOPLASMIC RETICULUM ‐ PIERCE THE PLASTIDS OF PINNULARIA

Geitler's (1937) observation on the regular perforation of the chloroplasts of Pinnularia nobilis and the lack of a typical pyrenoid is supported using cytochemistry, and fluorescence &amp; electron microscopy. Chloroplast cavities and channels harbour bacteria, their DNA elicit DAPI‐fluorescence. Previous speculations on the DNA‐positive, achromatic dots in the plastids of several Pinnularia species being “scattered chloroplast nucleoids,” and the consequent separation of diatom plastids in “primitive” and “advanced” types, are thus refuted. Bacteria are rod‐shaped and as suggested by their TEM‐profiles gram‐negative proteobacteria. They occur inside the endoplasmic reticulum throughout the cell, in interphase prevailingly in the space between the periplastidial membrane (PPM) and the CER membrane. Clusters of bacteria inside ER‐cisternae near the nucleus in preprophase, and near the new plasmalemma after cleavage, indicates a cell‐cycle dependent translocation within the diatom. Cavities in the plastids seem to be created by a combination of mechanical and chemical forces, in the sequence: alignment, attachment, deformation and lysis, initially without an obvious disruption of the PPM and the chloroplast‐envelope. Our future goal is to identify the bacteria and their metabolic function in the hereditary association with the plastids in Pinnularia. Their intracellular, but extraplasmatic, location may reflect an ancestral constellation, and the apparent worldwide distribution may substantiate this view.

Use of FEM in performance assessment of perforated plates subject to general loading conditions

Perforated plates, also called tube plates, are widely used in power generating plants and chemical processing refineries as components in heat exchangers and steam generators (particularly in nuclear power stations). The integrity of these plates under general (from hydrostatic pressure differentials) and other loading conditions (such as those generated by tubes flexing or the influence of constraints) is vital to the safety of plant. In this paper a general methodology is developed which is applicable to any regular perforation (or penetration) pattern. The solution procedure isolates a unit module from which, by successive reflections and translations, the whole plate can be constructed. The unit perforation module, composed of isotropic material, is replaced by a unit solid brick-shaped module of an equivalent anisotropic plate with identical overall dimensions. Then, by comparing the responses of the isotropic perforated and the anisotropic solid models, the equivalent “effective” elasticity constants E ∗, v ∗ and G ∗ are calculated for the equivalent plate, which enable a nominal stress field, for any loading state, to be evaluated. A series of curves, referred to as stress multiplier factors, are also compiled which, together with the nominal stresses, allow the behaviour of the plate on the periphery of the perforation, the most severely stressed zone, to be estimated. The finite element method (FEM) involves the calculation of the elasticity matrix [ K] (from {σ ∗} = [K]{ε ∗} ) and then the evaluation of the anisotropic engineering constants-by the inversion of [ K] into [φ]. Two particular penetration patterns (square and triangular) are examined but the method employed is general and can be readily extended to deal with other perforation patterns of different ligament efficiencies.

Societies and Academies

LONDON. Royal Anthropological Institute, December 9.—H. Balfour: The origin of the art of stencilling in the Fiji Islands. The use of stencils in the Fiji Islands, for decorating bark-cloth, does not appear to have been introduced into the group from the outside, and it was suggested that the stencil designs, which are cut in leaves almost invariably, may very probably have been suggested by leaves which have been tunnelled by insect larva? while still in the tightly rolled up state of the budding leaf. The leaves, when they unroll in the course of their development, exhibit transverse alignments of regular perforations, which bear a striking resemblance to some of the simpler Fijian stencil designs.