This paper presents an experimental investigation on the cyclic behaviour of short steel tubes filled with rubberized concrete (RuC), a composite material that mixes concrete with rubber particles. A brief literature review on the cyclic behaviour of CFST columns, the mechanical properties of RuC and recent research on RuC-filled steel tubes (RuCFSTs) is presented. Then, the tested specimens are characterized, comprising three cross-section shapes (square, rectangular, circular), three steel grades (S235, S275, S355), three concrete mixes (0%, 5%, 15% of rubber particles content) and two axial load levels (10%, 20% of axial plastic load). After that, the loading protocol, test rig and experimental procedure are described in detail. The experimental results are extensively discussed, focusing on the columns’ cyclic strength, failure modes, hysteretic and envelope curves, as well as on the energy-based ductility factors. Finally, conclusions are drawn regarding all these parameters. The most relevant achievement is that a concrete mix with a low content (5%) of rubber particles leads simultaneously to the lowest decrease (5%) in the cyclic strength and the highest increase (52%) in the ductility of RuCFST columns, thus being the most suitable mix to use in seismic areas, where ductility and energy dissipation requirements are mandatory.
No abstract is provided for this article.
No abstract is provided for this article.
Phenine Nanotubes (PhNT) are cylinder-shaped molecules synthetized from 1,3,5-trisubstituted benzene ring building blocks that can form tubular segments of different sizes. Small nanotube segments have been recently synthetized, and efforts are being made to increase the nanotubes' length by adding more "phenine" units. To the authors' best knowledge, a complete characterization of the mechanical properties of these nanotubes has not yet been accomplished. In this work, Reax and AIREBO forcefields were used to model armchair and zigzag PhNTs and Molecular Dynamics simulations were employed to determine their mechanical properties for tensile, compressive, bending and twisting loadings. It was found that PhNTs have a much lower Young's modulus (about 30%) and tensile strengths (about 45%) than carbon nanotubes (CNTs), but can endure longer tensile strains without breaking apart. Although possessing a lower bending and twisting stiffness than CNTs, PhNT have highly flexible sidewalls due to their superior porosity, and therefore can withstand higher angles of twist and angles of bend without breaking bonds. This extra flexibility; extended porosity; possibility for heteroatom doping and reasonable strength, make PhNTs very promising candidates for a wide range of applications, such as sensing, ionic transistors or molecular sieving. Finally, a brief study on the application of elastic continuum shell formulas to predict the critical stress (compression), critical moment (bending) and critical torque (twisting) is also presented.
No abstract is provided for this article.
This paper presents the development and illustrates the application of a beam finite element based on the generalised beam theory (GBT) and intended to analyse the local, distortional and global post-buckling behaviour of thin-walled steel frames. After briefly reviewing the main concepts and procedures required to obtain the GBT system of non-linear equilibrium equations, the paper describes the steps involved in the numerical implementation (incremental-iterative strategy) of a non-linear beam finite element that incorporates the influence of the frame joint behaviour. Next, one uses evidence gathered from shell finite element simulations to establish kinematic constraint conditions ensuring displacement compatibility at frame joints connecting two non-aligned plain/lipped channel members. Finally, the application and capabilities of the proposed GBT-based beam finite element formulation are illustrated by presenting and discussing numerical results concerning the post-buckling behaviour of two “L-shaped” frames and a symmetric portal frame. For validation purposes, most GBT-based results are compared with values yielded by beam and shell finite element analyses carried out in the code Ansys.
The mechanical reinforcement of embedding a carbon nanotube inside metals with different crystal structures (BCC-Fe and HCP-Ti) is investigated using molecular dynamics simulations. Two metallic elements were chosen representing different crystal structures, based on the foreseeable technological benefits of improving the strength of these widely used metals while reducing their weight. Tensile and compressive loadings are applied to CNT-Fe and CNT-Ti nanocomposites which are modeled by inserting a (6,6) CNT into a single-crystal rectangular prism. Two limit boundary conditions are applied to the embedded CNT: (i) loading applied only to the metal matrix and (ii) loading applied to both the metal matrix and the embedded CNT. Curves of energy vs strain and stress vs strain are presented and the mechanical properties are calculated for both situations. Additionally, the mechanical behavior and buckling of the encapsulated carbon nanotube as a result of compression loading applied to the metal nanocomposites is also studied. Lastly, an analysis of the influence of the embedded CNT in the deformation mechanisms of the nanocomposites is presented.
This paper presents and illustrates the application of an elastic-plastic Generalised Beam Theory (GBT) formulation, based on J2-flow plasticity theory, that makes it possible to perform physically and geometrically non-linear (post-buckling) analyses of prismatic thin-walled members (i) with arbitrary cross-section shapes, (ii) exhibiting any type of deformation pattern (global, local, distortional, warping, shear), (iii) made from nonlinear materials with isotropic strain-hardening and (iv) containing initial imperfections, namely residual stresses and/or geometric imperfections, having generic distributions.After providing a brief overview of the main GBT assumptions, kinematical relations and equilibrium equations, the development of a novel non-linear beam finite element (FE) is addressed in some detail.Moreover, its application is illustrated through the presentation and discussion of numerical results concerning the post-buckling behaviour of a fixed-ended I-section steel column exhibiting local initial geometrical imperfections, namely (i) non-linear equilibrium paths, (ii) displacement profiles, (iii) stress diagrams/distributions and (iv) deformed configurations.For validation purposes, the GBT results are also compared with values yielded by ABAQUS rigorous shell FE analyses.
This paper presents and illustrates the application of an elastic-plastic Generalised Beam Theory (GBT) formulation, based on J2-flow plasticity theory, that makes it possible to perform physically and geometrically non-linear (post-buckling) analyses of prismatic thin-walled members (i) with arbitrary cross-section shapes, (ii) exhibiting any type of deformation pattern (global, local, distortional, warping, shear), (iii) made from non-linear materials with isotropic strain-hardening and (iv) containing initial imperfections, namely residual stresses and/or geometric imperfections, having generic distributions. After providing a brief overview of the main GBT assumptions, kinematical relations and equilibrium equations, the development of a novel non-linear beam finite element (FE) is addressed in some detail. Moreover, its application is illustrated through the presentation and discussion of numerical results concerning the post-buckling behaviour of a fixed-ended I-section steel column exhibiting local initial geometrical imperfections, namely (i) non-linear equilibrium paths, (ii) displacement profiles, (iii) stress diagrams/distributions and (iv) deformed configurations. For validation purposes, the GBT results are also compared with values yielded by ABAQUS rigorous shell FE analyses.
The structural behaviour of hybrid fibre reinforced polymer (FRP) pultruded members under concentric compression is studied in this paper (Part 2) through the use of numerical models – the experimental characterisation was presented in preceding paper (Part 1, Nunes et al., 2015). The hybridization of glass-FRP (GFRP) profiles is made through the partial replacement of the glass reinforcement with (stiffer) carbon fibres. First, a brief literature review shows the absence of available finite element (FE) models that take into account all the nonlinearities (material and geometrical) that influence the FRP column behaviour, and indicates the need to develop reliable and consistent models. Then, the FE model developed in this paper is described in detail. The elastic buckling behaviour of the columns tested in Part 1, with similar I-section shape but different configurations of carbon fibre reinforcement and different lengths, is evaluated. Three failure criteria for composite materials (Maximum Stress, Tsai–Hill and Hashin) are presented, implemented and their differences discussed. Using the Hashin criterion associated with a material damage model, progressive failure analyses were performed to simulate the nonlinear behaviour and failure of the hybrid columns. The numerical results comprise load–displacement curves, ultimate loads, stress–strain curves and failure modes, which are validated by comparison with the experimental results. Finally, the available design procedures for FRP columns are critically reviewed and applied to evaluate the columns’ ultimate loads. In this regard, it is shown that buckling prevails over material strength and that existing standards do not predict accurately the ultimate load of short columns or laterally braced columns.
In this chapter, the atomistic simulation of carbon nanotubes (CNTs) is presented and their behavior (stiffness, strength, and toughness) under local deformation is investigated by taking into account the contributions of the authors to the current state of the art. First, the atomistic modeling of CNTs is described and the three most adopted methods are briefly addressed. One of these, molecular dynamics (MD), is then explained in more detail (the selection of potentials and time integration scheme). After that, three main topics are addressed: (1) the suitability of continuum shell models to simulate the nanotube behavior (in comparison with MD), (2) the influence of combined shortening–twisting on the local buckling behavior of nanotubes, and (3) the chirality and anisotropic effects in nanotubes. Several illustrative examples are shown and attention is focused on the MD results, namely, the nanotube stiffness, strength, and toughness. Then, some final remarks and future developments are drawn.
This paper presents the formulation of a Generalised Beam Theory (GBT) developed to analyse the vibration behaviour of composite thin-walled members made of laminated plates and displaying arbitrary orthotropy. Initially, the equilibrium equations and corresponding boundary conditions are derived and their terms are physically interpreted, i.e., related to the member mechanical properties. Then, the derived equations are used to study the local and global vibration behaviour of lipped channel members displaying cross-ply orthotropy. The GBT results are validated through a comparison with numerical values obtained from finite element analyses, which employ thin-shell elements to discretise the member. Finally, a brief investigation is carried out in order to assess the variation of the fundamental frequency value and vibration mode nature with the member length.
