This paper summarises an investigation carried out to predict the structural behaviour of CFRP-strengthened cold-formed steel lipped channel columns−more specifically, it addresses the applicability of the provisions of Eurocode 3 (EC3) and the AISI Specification (AISI-DSM, direct strength method), both developed for cold-formed steel members, to estimate their load-carrying capacity. It is worth noting that EC3 and AISI-DSM adopt different approaches to perform this task: while the former is based on the “effective width” concept, the latter may adopt the “Direct Strength Method”. First, the most relevant aspects related to the experimental and numerical investigations carried out to obtain “exact” column collapse loads are briefly presented. Then, an extensive numerical study is performed, which is intended to evaluate the benefits of CFRP-strengthening for different CFRP ply configurations, number of CFRP plies and steel yield stresses. After proposing different methodologies to extend the application of the EC3 and AISI-DSM design provisions to CFRP-strengthened cold-formed steel columns, the estimates provided by them are compared with the experimental values. On the basis of these comparisons, some concluding remarks are drawn concerning the merits and shortcomings of extending the domain of application of the current EC3 and AISI-DSM design approaches, so that they may cover also CFRP-strengthened lipped channel columns.
This paper presents a formulation of Generalised Beam Theory (GBT) intended to perform thorough first-order elastic-plastic analyses of thin-walled members subjected to arbitrary deformations and made of an isotropic non-linear material. The J2-flow theory is used to model plasticity in conjunction with the Euler-Backward return-mapping algorithm. After presenting the formulation, its application is illustrated by means of the first order analysis of a simply supported Z-section beam made of an elastic-perfectly plastic material (e.g., carbon steel) and acted by a load uniformly distributed along the flanges. The set of GBT-based results comprises the load-deflection curves (equilibrium paths), displacement profiles, stress distributions (diagrams and 3D contours), and deformed shapes (modal amplitude functions and 3D configurations). These results are compared with the ones obtained from shell finite element analyses (SFEA) using ABAQUS. It is seen that the GBT results display a very good agreement with the SFEA values.
Numerical analysis of the local buckling behaviour and ultimate cross-sectional strength of tubular elliptical profiles in compression has been performed. After validating the model against previous experimental results, a parametric study comprising a total of 270 elliptical sections was conducted in order to examine the influence of cross-section aspect ratio, geometric imperfections and local slendernesses. The obtained ultimate capacities, load–deformation responses and failure modes are discussed. It was found that for lower cross-section aspect ratios the behaviour of The Elliptical Hollow Sections (EHS) was similar to that of cylindrical shells across a number of metrics; as the aspect ratio increased, more plate-like stable postbuckling behaviour was observed. A design method has been proposed for Class 4 EHS members that reflects the reduction in capacity due to local buckling with increasing slenderness, but also recognises the improved postbuckling stability with increasing aspect ratio.
No abstract is provided for this article.
This paper presents a study on the transverse fracture behaviour of pultruded glass fibre reinforced polymer (GFRP) materials in compression, namely the assessment of transverse compressive fracture toughness (G2 −) and transverse compressive residual strength (σr). These properties were assessed through experimental Compact Compression (CC) tests of six different GFRP materials, which were coupled with a data reduction method to determine experimental predictions of G2 − and numerically calibrated as a function of the experimental load vs. displacement curves. Through this process, the expected experimental overestimation of G2 −, attributed to contact stresses behind the notch tip, was evaluated and accurate numerical estimates of G2 − were determined. The numerical calibration considered both G2 − and σr, by considering a bi-linear cohesive law. Through the numerical calibration, the G2 − results ranged between 36 and 67 N/mm and σr values varied from 9% to 16% of transverse compressive strength (7.6 and 16.9 MPa, in absolute values). Finally, the G2 − results were analysed as a function of transverse fibre reinforcement percentage and compared to transverse tensile fracture toughness results (G2 +) determined in a previous work. This study showed that G2 − is generally higher than G2 + and that the compressive-to-tensile ratio is inversely proportional to the transverse reinforcement percentage.
This paper presents a numerical investigation on the ductility and strength of short steel tubes filled with Rubberized Concrete (RuC), which is a composite material that mixes concrete with rubber particles. This research concerns the enhancement of both ductility and energy absorption of CFST by considering a core of RuC instead of normal concrete (NC). First, a brief literature review on the topic is presented. Then, based on an experimental programme conducted by the authors, numerical models of CFST and RuCFST columns are developed. The results of non-linear analyses (ultimate strengths, load-shortening curves and failure modes) are validated using experimental data, and good agreement is shown. Finally, a numerical study on the properties of confined NC and RuC is conducted. It is concluded that the concrete damaged plasticity model can be used to simulate RuC. The dilation angle plays a key role in RuC and its lower value (compared to that of NC) influences the concrete confinement. Taking into account the RuC dilation angle, steel yield stress and tube local slenderness, a new formula is proposed to predict the concrete core confinement of the studied CFST and RuCFST columns with circular sections.
In this work, an in-depth numerical study is conducted on the influence of the stringer cross-section geometry on the mechanical behavior of curved stiffened carbon-fiber reinforced polymer panels under compression, used as fuselages of commercial aircrafts. The numerical model of a reference panel is described and the numerical results are firstly validated, by comparison with experimental results available in the literature, and then analyzed in detail. A study of the influence of different cross-section geometries of stringers (T-, I-, C-, J-, and Ω-shaped) on the behavior of the panel is then conducted. Finally some conclusions are drawn.
The interface of a cholesteric liquid crystal with an isotropic fluid can display a range of unusual properties, such as a layer of topological defects close to an undulated interface. These properties have been know for a long time and have been explored for technological applications as a tunable substrate for colloidal self-assembly. However, from a fundamental point of view, this interface remains poorly understood and even basic properties, such as the dependence of the surface tension on the attributes of the liquid crystal, remain unknown. Here, we present a systematic calculation of the structure and surface tension of the cholesteric-isotropic interface and how these vary with the properties of the liquid crystal. We also suggest the intriguing possibility of wetting of this interface by a blue phase.
No abstract is provided for this article.
This paper presents an experimental and computational study on the behaviour of pre-tensioned thin solar sails. Firstly, a set of experimental tests of thin rectangular sheets made of Kapton® subjected to uniaxial tension were conducted to characterize the mechanical properties of the membrane. Then, tri-dimensional digital image correlation technique was used to capture the evolution of the wrinkling (shape and amplitude) in pre-tensioned specimens, a phenomenon that often affects the serviceability of solar sails. The influence of membrane thickness and specimen dimensions on the wrinkling behaviour were also studied. Next, nonlinear finite element models were used to simulate the membranes and to study the onset and growth of wrinkles in solar sails. First, by pre-tensioning the membrane with truss cables and using combinations of the eigenmodes extracted from buckling analysis as the membrane initial geometrical imperfections, nonlinear analyses were performed. The computational methodology was verified by comparing the experimental results of membrane specimens with those obtained from finite element analysis. Because the number of truss cables that pre-tension the solar sail plays a key role in their behaviour, two distinct configurations were considered: (i) five points connected sail and (ii) multiple points connected sail. Sensitivity studies were performed, including the influence of (i) membrane size and (ii) pre-tensioning magnitude on the solar sail wrinkling. Larger sails exhibit higher wrinkle dispersion and amplitude. Higher pre-tensioning induces more wrinkles, higher amplitudes and lower wavelengths. The solar sail configuration with multiple connected points connected presents less wrinkles with lower amplitude, and it is preferable to the configuration with five connected points. Finally, it was revealed that the wrinkling maximum amplitude varied approximately in a power law with the pre-tensioning level.
An experimental investigation on the strength and ductility of short steel tubes filled with rubberised concrete (RuC), sourced from recycled scrap tyres, is presented in this paper. Firstly, a brief literature review on (i) concrete-filled steel tubes (CFST) and (ii) mechanical characterisation of rubberised concrete is presented. Then, the experimental investigation is described and test results are shown and discussed, namely, the assessment of (i) RuC and steel mechanical properties and (ii) RuCFST column structural properties. The influence of various parameters, such as the cross-section shape (square, rectangular, circular), steel grade, and concrete mix (standard concrete versus RuC), on the short column strength and ductility is analysed and discussed. Eurocode 4 is considered (i) to determine the strength of the tested columns and, in particular, (ii) to assess its applicability to RuCFST columns based on a comparison with the experimental results. The main conclusion of this research is that RuCFST short columns present higher ductility than those made of standard concrete, even though they also show lower strength. This improved ductility is noticeable in columns with circular sections, rather than in square and rectangular sections. From a practical viewpoint, this could be a major benefit for structures in seismic areas where energy dissipation is needed.
No abstract is provided for this article.
No abstract is provided for this article.
This paper presents the development and illustrates the application of a beam finite element based on Generalised Beam Theory (GBT) and intended to analyse the elastic post-buckling behaviour of thin-walled steel members exhibiting arbitrary open cross-section and with non-standard support conditions (e.g., in-span bracing systems). 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 non-standard support conditions. Finally, the application and capabilities of the proposed GBT-based beam finite element are illustrated by means of the presentation and discussion of numerical results concerning the post-buckling behaviour of lipped I-section columns and lipped channel columns and beams with and without localised displacement restraints. For validation purposes, most GBT-based results are compared with values yielded by shell finite element analyses carried out in the commercial code Ansys.
<p>This paper presents and illustrates the application of an elastic-plastic Generalised Beam Theory (GBT) formulation, based on J<sub>2</sub>-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.</p>
<p>This paper presents and illustrates the application of an elastic-plastic Generalised Beam Theory (GBT) formulation, based on J<sub>2</sub>-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.</p>
This paper presents the derivation and illustrates the application of a Generalised Beam Theory (GBT) developed to analyse the buckling behaviour of a class of thin-walled steel members displaying (open) "branched" cross-sections. Following a very brief review of the conventional GBT, the modifications that must be incorporated into its cross-section analysis procedure, in order to handle the "branching" points, are described and discussed in detail. Particular attention is paid to the choice and characterisation of the appropriate warping and flexural "elementary functions". The derived equations are then used to study the local and global buckling behaviour of simply supported columns and beams with a singly symmetric I-section. The GBT results are validated through a comparison with numerical values obtained from finite strip and finite element analyses (the latter employ shell elements to discretise the members).
