Carbyne chains are the thinnest structures found in nature. The synthesis of long and stable inside carbon nanotubes has recently drawn renewed attention to this linear one-dimensional carbon allotrope. Carbyne’s mechanical properties have been predicted to exceed that of carbon nanotubes and graphene, making it a very suitable structural component for many nanoscale applications. While carbyne’s mechanical behavior under tensile loading is superlative, this linear chain of bonded carbon atoms readily buckles due to thermal fluctuations, showing minimal strength under compressive loading. Here we present a detailed study on the enhancement of carbyne’s mechanical properties under compression by confinement in small diameter carbon nanotubes. First, we develop a new classical empirical forcefield based on ab-initio calculations. Molecular dynamics (MD) simulations are then carried, using this forcefield, to determine the mechanical properties of carbyne under tensile loading, namely to assess their dependence on chain length and temperature. The bending rigidity of carbyne and its persistence length are also calculated. After the validation of the new forcefield, MD simulations are employed to study the mechanical behavior of carbyne under compressive loading, when confined inside (5,5), (6,6) (7,7) and (8,8) CNTs. It is found that the mechanical behavior of confined carbyne chains depends on the confinement radius and the chain length, and can be described in three stages. For “tight” confinements, carbyne chains assume a rigid rod behavior, allowing the calculation of compressive mechanical properties and attesting an effective “bracing” effect. For “looser” confinements, a spring like behavior arises which can be modeled by Hooke’s law. In the third stage confined carbyne chains tend to buckle into a large local bend, losing the elastic flexibility that characterizes the previous stage.
This issue of Structures and Buildings presents five papers on different scientific topics, ranging from steel structures to reinforced-concrete structures.They shed light on technical problems usually dealt with in current engineering practice.
This paper presents the formulation of a shear deformable Generalised Beam Theory (GBT) developed to perform accurate analyses of the buckling behaviour of laminated plate composite thin-walled members displaying arbitrary orthotropy. Besides including the "conventional" (non-shear) deformation modes, this GBT formulation also incorporates a set of (new) shear deformation modes. Following the derivation of the equilibrium equations and corresponding boundary conditions, their terms are physically interpreted, i.e., related to the member mechanical properties. Then, the derived shear-deformable orthotropic GBT is used to investigate the influence of shear deformation on the local and global buckling behaviour of lipped channel columns displaying cross-ply orthotropy. The GBT results are validated through a comparison with numerical values yielded by thin-shell FEM analyses.
The international conference series on Advances in Steel Structures was initiated in 1996, under the auspices of the Hong Kong Polytechnic University, which remained very active in fostering its continuation - joined, a few years later, by the Hong Kong Institute of Steel Construction. The eighth conference of the series, ICASS’2015, took place in Lisbon, Portugal on July 21-24, 2015 - the venue was Instituto Superior Técnico from the University of Lisbon. It was the first conference of the series to take place outside of Asia. Indeed, the first, second, third and sixth conferences were held in Hong Kong, the fourth in Shanghai, the fifth in Singapore and the seventh in Nanjing. As its predecessors, ICASS’2015 aimed at providing a forum for the discussion and dissemination, by both researchers and designers, of the most recent theoretical, numerical and experimental advances in the analysis, behaviour, design and construction of steel, aluminium and composite steel-concrete structures.
This paper gives the formulation and illustrates the application of a generalized beam theory (GBT) developed to analyze the structural behavior of thin-walled members displaying arbitrary orthotropy. First- and second-order GBT equations are derived and physically interpreted, and the GBT equations are then used to investigate the local and global buckling behavior of FRP-lipped channel columns displaying general orthotropy.
This paper presents and illustrates a GBT formulation to analyse the elastic localized web buckling of thin-walled steel beams under concentrated loads. The theme of localised web buckling is first introduced by describing the parameters that most influence the buckling behaviour of slender plates subjected to edge loads. After that, a GBT formulation to analyse the elastic localized web buckling of thin-walled steel beams under concentrated loads is presented: the GBT equations are derived and the determination of deformation modes is briefly addressed. Then, two illustrative examples are shown and validated by comparison with shell finite element results: (i) cold-formed steel plain channel beams with web crippling configurations and (ii) welded steel I-section beams with patch loading configurations. It is found that both pre-buckling longitudinal normal ( σ x x 0 ) and shear ( τ x s 0 ) stresses have to be included in the buckling analyses of cold-formed steel beams with External One Flange (EOF) and Internal One Flange (IOF) configurations as well as welded steel beams with Patch Loading Test (PLT) configuration. Furthermore, the pre-buckling transverse normal ( σ s s 0 ) stresses have to be included in the buckling analysis of cold-formed steel beams with External Two Flange (ETF) and Internal Two Flange (ITF) configurations as well as welded steel beams with Opposite Patch Loading Test (OPLT) configuration. In beams with EOF, IOF, PLT configurations, the GBT pre-buckling analysis should consider global and shear modes while the GBT buckling analysis may only consider local modes. In beams with ETF, ITF, OPLT configurations, the GBT pre-buckling analysis should consider transverse extension modes while the GBT buckling analysis may only consider local modes.
No abstract is provided for this article.
This paper presents the main steps and procedures involved in the development of a Generalised Beam Theory (GBT) formulation to perform dynamic analyses of thin-walled members subjected to initial perturbations or acting loads. It combines (i) the GBT modal discretisation of the cross-section deformation with (ii) the commonly adopted vibration mode superposition approach – this combination leads to an original “doubly modal” representation of the displacement field, which (i) provides deep insight into the mechanics involved in the dynamic response under consideration and, moreover, (ii) makes it possible to obtain accurate results with surprisingly low degree of freedom numbers. The application and potential of the formulation is illustrated by presenting and discussing numerical results concerning the dynamic responses of cold-formed steel lipped channel beam in several situations, namely (i) the damped oscillations following the release from a deformed configuration, (ii) the action of uniformly distributed loads with periodic (sinusoidal and square-wave) and impulsive (rectangular) time variations, and (iii) the effect of a point load moving along the span with constant speed. For validation purposes, the GBT-based results are compared with values yielded by Ansys shell finite element analyses – the total number of degrees of freedom involved in the GBT analyses was significantly lower.
The behavior of lean duplex stainless steel plate girders (LDIPGs) with slender unstiffened webs is studied in this paper. Firstly, shell finite element models are validated using experimental test results available in the literature. Secondly, these models are used to investigate the behavior of LDIPGs subjected to uniform bending. Parametric studies for the LDIPGs are carefully designed based on three parameters: the radius of gyration of the compression flange (rT ), the section modulus (Sx ), and the unbraced length (Lb ). The results showed that LDIPGs with higher rT but similar Sx values can attain higher flexural strengths compared to their yield strengths because of the higher torsional rigidity of the flanges and stockier webs. On the other hand, by increasing the Sx value of the girder but keeping fixed the rT values, the moment carried by the girder is found relatively to decrease with the simultaneous increase in the amount of steel. Finally, the numerical results are compared with predictions given by design standards. It is found that the EC3 provides conservative bending predictions. Accordingly, the imperfection factor associated to buckling curve (c) is recommended to be used in the scope of the design method provided by EN 1993-1-4.
This paper presents an experimental study on the web-crippling behavior of pultruded glass fiber reinforced polymer (GFRP) I-section profiles under localized one-flange loading. The study had two objectives: (i) to gain insight into the behavior of profiles under localized one-flange loading, which has not yet been sufficiently investigated, and (ii) to provide comprehensive experimental data for the future development of design methods. A total of 61 specimens were tested, 31 under end-one-flange (EOF) loading and 30 under interior-one-flange (IOF) loading. The test parameters included three bearing lengths (15/40/70 mm) and four profiles. The results showed that the shape and material properties of the profiles had negligible effects on the failure modes and transverse compressive strain distributions. Conversely, the bearing length had a significant impact on the ultimate loads. The IOF ultimate loads were higher than the EOF ones with the shortest bearing length (15 mm), whereas the opposite occurred for the longest bearing length (70 mm); possible reasons for this are discussed.
Due to their excellent properties, graphene-like 2D structures have been widely used to reinforce aluminium nanocomposites. However, the interfacial behaviour presented by different types of holey graphenes and their reinforcing effect on the mechanical properties of the nanocomposites are still not completely clear. In this work, Molecular Dynamics simulations are used to investigate the interfacial behaviour between five different graphenes and an aluminium matrix (Al-graphene, Al-Phagraphene, Al-haeckelite, Al-N-holey-graphene (hG) and Al-B-hG). Using pull-out loading test, the influence of the 2D nanofillers porosity on the mechanical properties of the nanocomposites is assessed. Additionally, and regarding the aluminium matrix, two different cases were studied: (i) the aluminium matrix was not recrystallized and (ii) the aluminium matrix was melted and then recrystallized. It was found that the introduction of porous graphene improves the interfacial adhesion in the nanocomposites while the pull-out force and interfacial shear strength of the nanocomposites are significantly higher when the aluminium matrix is previously melted and then recrystallized.
No abstract is provided for this article.
The objective of this work is to describe the main steps involved in the derivation of a GBT (Generalised Beam Theory) formulation to analyse the vibration behaviour of loaded cold-formed steel members and also to illustrate the application and capabilities of this formulation. In particular, the paper presents and discusses the results of a detailed investigation about the local and global free vibration behaviour of lipped channel simply supported columns. After reporting some relevant earlier GBT-based results dealing with the buckling and vibration behaviours of columns and load-free members, the paper addresses mostly issues concerning the variation of the column fundamental frequency and vibration mode nature/shape with its length and axial compression level. For validation purposes, some GBT-based results are also compared with values obtained by means of 4-node shell finite element analyses performed in the code ABAQUS.
This paper presents an investigation on the out-of-plane behaviour of graphene when cyclically loaded in-plane. Using an atomistic finite element approach, previous developed and validated by the authors, the stress-strain behaviour of graphene is evaluated under different cyclic loading tests (uniaxial, biaxial, shear). To simulate the bonds between carbon-carbon (C–C) atoms, beam elements are used, with their stiffness being described by the Morse potential associated to an elastoplastic law. Monotonic and hysteretic tests are performed and a comparison with the in-plane behaviour results, recently obtained, is accomplished. The instabilities of graphene, that occur in compression, are discussed and the buckling stresses are compared with those calculated from simple analytical formulae. The graphene failure modes obtained are also analysed. Finally, some concluding remarks are drawn about the main differences between the monotonic and hysteretic behaviour, as well as the in-plane and out-of-plane ones.
In this paper, the mechanical behaviour of short rubberized concrete-filled steel tubular (RuCFST) columns with square cross-section under combined cyclic bending and (monotonic) compression is studied numerically. For this purpose, dynamic explicit analyses with kinetic energy control (for the quasi-static behavior to be obtained) using the commercial finite element modelling package ABAQUS were performed. Firstly, a brief introduction and literature review on the topic is made. Then, the numerical models are described in detail with emphasis on the modelling of the materials (natural aggregate concrete (NAC), rubberized concrete (RuC) and steel) under cyclic loading. An in-depth presentation of the numerical results is made afterwards. It includes firstly a verification of the models by comparison of the numerical results with their experimental counterparts, the latter previously obtained by the authors. Secondly, a numerical study on the effectiveness of RuC on the energy dissipation capacity of CFST columns under lateral cyclic loading is performed. It is concluded that the models yield similar results regarding stiffness, maximum loads, load–displacement curves and failure modes as those obtained experimentally, with RuC leading to a moderate reduction (of up to 2%) of the strength of the columns. Regarding the energy dissipation capacity of the columns, it is concluded that RuC generally leads to a reduction of this property (of circa 2.5% per each 5% of rubber aggregates replacement). The lower strength and stiffness of the RuC mixes designed for this study compared to NAC are found to generally offset the benefit of their lower brittleness in increasing the energy dissipation capacity of the columns.
