Showing papers in "Thin-walled Structures in 2014"

Comparative analysis of energy absorption capacity of simple and multi-cell thin-walled tubes with triangular, square, hexagonal and octagonal sections

Abstract: Energy must dissipate during a collision to prevent damage and injury. To reduce loss from collision, energy absorbers are used that dissipate energy upon deformation and folding to prevent damage to critical parts of a structure. In this paper, simple and multi-cell thin-walled tubes made from aluminum with triangular, square, hexagonal and octagonal sections were subjected to quasi-static loading. The experimental results were then compared with numerical simulations. The results showed that the energy absorption capacity of multi-cell sections is greater than for that of simple sections. Also, hexagonal and octagonal sections in a multi-cell configuration absorbed the greatest amounts of energy per unit of mass.

Geometric imperfections and lower-bound methods used to calculate knock-down factors for axially compressed composite cylindrical shells

Abstract: The important role of geometric imperfections on the decrease of the buckling load for thin-walled cylinders had been recognized already by the first authors investigating the theoretical approaches on this topic. However, there are currently no closed-form solutions to take imperfections into account already during the early design phases, forcing the analysts to use lower-bound methods to calculate the required knock-down factors (KDF). Lower-bound methods such as the empirical NASA SP-8007 guideline are commonly used in the aerospace and space industries, while the approaches based on the Reduced Stiffness Method (RSM) have been used mostly in the civil engineering field. Since 1970s a considerable number of experimental and numerical investigations have been conducted to develop new stochastic and deterministic methods for calculating less conservative KDFs. Among the deterministic approaches, the single perturbation load approach (SPLA), proposed by Huhne, will be further investigated for axially compressed fiber composite cylindrical shells and compared with four other methods commonly used to create geometric imperfections: linear buckling mode-shaped, geometric dimples, axisymmetric imperfections and measured geometric imperfections from test articles. The finite element method using static analysis with artificial damping is used to simulate the displacement controlled compression tests up to the post-buckled range of loading. The implementation of each method is explained in details and the different KDFs obtained are compared. The study is part of the European Union (EU) project DESICOS, whose aim is to combine stochastic and deterministic approaches to develop less conservative guidelines for the design of imperfection sensitive structures.

Axial crushing and optimal design of square tubes with graded thickness

Abstract: Introducing thickness gradient in cross-section is a quite promising approach to increase the energy absorption efficiency and crashworthiness performance of thin-walled structures. This paper addresses the deformation mode and energy absorption of square tubes with graded thickness during axial loading. Experimental study is firstly carried out for square tubes with two types of thickness distributions and numerical analyses are then conducted to simulate the experiment. Both experimental and numerical results show that the introduction of graded thickness in cross-section can lead to up to 30–35% increase in energy absorption efficiency (specific energy absorption) without the increase of the initial peak force. In addition, structural optimization of the cross-section of a square tube with graded thickness is solved by response surface method and the optimization results validate that increasing the material in the corner regions can indeed increase the energy absorption efficiency of a square tube.

Free vibration of quadrilateral laminated plates with carbon nanotube reinforced composite layers

Abstract: The free vibration behavior of quadrilateral laminated thin-to-moderately thick plates with carbon nanotube reinforced composite (CNTRC) layers is studied. The governing equations are based on the first-order shear deformation theory (FSDT). The solution procedure is based on transforming the governing differential equations from an arbitrary straight-sided physical domain to a regular computational one, and discretization of the spatial derivatives by employing the differential quadrature method (DQM) as an efficient and accurate numerical tool. Four different profiles of single walled carbon nanotubes (SWCNTs) distribution through the thickness of layers are considered, which are uniformly distributed (UD) and three others are functionally graded (FG) distributions. The fast rate of convergence of the presented approach is numerically demonstrated and to show its high accuracy, wherever possible comparison studies with the available results in the open literature are performed. Then, the effects of volume fraction of carbon nanotubes (CNTs), geometrical shape parameters, thickness-to-length and aspect ratios, different kinds of CNTs distribution along the layers thickness and different boundary conditions on the natural frequencies of laminated plates are studied.

Crashworthiness optimization design for foam-filled multi-cell thin-walled structures

Abstract: Foam-filled thin-walled structure and multi-cell thin-walled structure both have recently gained attentions for their excellent energy absorption capacity. As an integrator of the above two kinds of thin-walled structures, foam-filled multi-cell thin-walled structure (FMTS) may have extremely excellent energy absorption capacity. This paper firstly investigates the energy absorption characteristics of FMTSs by nonlinear finite element analysis through LS-DYNA. Based on the numerical results, it can be found that the FMTS with nine cells has the most excellent crashworthiness characteristics in our considered cases. Thus, the FMTSs with cell number n=9 are then optimized by adopting a multi-objective particle swarm optimization (MOPSO) algorithm to achieve maximum specific energy absorption (SEA) capacity and minimum peak crushing force (PCF). During the process of multi-objective optimization design (MOD), four kinds of commonly used metamodels, namely polynomial response surface (PRS), radial basis function (RBF), Kriging (KRG) and support vector regression (SVR) for SEA and PCF, are established to reduce the computational cost of crash simulations by the finite element method. In order to choose the best metamodel for optimization, the accuracies of these four kinds of metamodels are compared by employing the error evaluation indicators of the relative error (RE) and the root mean square error (RMSE). The optimal design of FMTSs with nine cells is an extremely excellent energy absorber and can be used in the future vehicle body.

Theoretical prediction and crashworthiness optimization of multi-cell triangular tubes

Abstract: The triangular tubes with multi-cell were first studied on the aspects of theoretical prediction and crashworthiness optimization design under the impact loading. The tubes׳ profiles were divided into 2-, 3-, T-shapes, 4-, and 6-panel angle elements. The Simplified Super Folding Element theory was utilized to estimate the energy dissipation of angle elements. Based on the estimation, theoretical expressions of the mean crushing force were developed for three types of tubes under dynamic loading. When taking the inertia effects into account, the dynamic enhancement coefficient was also considered. In the process of multiobjective crashworthiness optimization, Deb and Gupta method was utilized to find out the knee points from the Pareto solutions space. Finally, the theoretical prediction showed an excellent coincidence with the numerical optimal results, and also validated the efficiency of the crashworthiness optimization design method based on surrogate models.

Quasi-static response and multi-objective crashworthiness optimization of oblong tube under lateral loading

Abstract: This paper addresses the energy absorption responses and crashworthiness optimization of thin-walled oblong tubes under quasi-static lateral loading. The oblong tubes were experimentally compressed using three various forms of indenters named as the flat plate, cylindrical and a point load indenter. The oblong tubes were subjected to inclined and vertical constraints to increase the energy absorption capacity of these structures. The variation in responses due to these indenters and external constraints were demonstrated. Various indicators which describe the effectiveness of energy absorbing systems were used as a marker to compare the various systems. It was found that unconstrained oblong tube (FIU) exhibited an almost ideal response when a flat plate indenter was used. The design information for such oblong tubes as energy absorbers can be generated through performing parametric study. To this end, the response surface methodology (RSM) for the design of experiments (DOE) was employed along with finite element modeling (FEM) to explore the effects of geometrical parameters on the responses of oblong tubes and to construct models for the specific energy absorption capacity (SEA) and collapse load ( F ) as functions of geometrical parameters. The FE model of the oblong tube was constructed and experimentally calibrated. In addition, based on the developed models of the SEA and F , multi-objective optimization design (MOD) of the oblong tube system is carried out by adopting a desirability approach to achieve maximum SEA capacity and minimum F . It is found that the optimal design of FIU can be achieved if the tube diameter and tube width are set at their minimum limits and the maximum tube thickness is chosen.

Structural behavior of concrete filled steel tubular sections (CFT/CFSt) under axial compression

Abstract: In this study, compressive strength, modulus of elasticity and steel tensile coupon tests are performed to determine material properties. Sixteen hollow cold formed steel tubes and 48 concrete filled steel tube specimens are used for axial compression tests. The effects of width/thickness ratio (b/t), the compressive strength of concrete and geometrical shape of cross section parameters on ultimate loads, axial stress, ductility and buckling behavior are investigated. Circular, hexagonal, rectangular and square sections, 18.75, 30.00, 50.00, 100.00 b/t ratio values and 13, 26, 35 MPa concrete compressive strength values are chosen for the experimental procedure. Analytical models of specimens are developed using a finite element program (ABAQUS) and the results are compared. Circular specimens are the most effective samples according to both axial stress and ductility values. The concrete in tubes has experienced considerable amount of deformations which is not expected from such a brittle material in certain cases. The results provide an innovative perspective on using cold formed steel and concrete together as a composite material.

Residual stress distributions in welded stainless steel sections

Abstract: Residual stress magnitudes and distributions in structural stainless steel built-up sections have been comprehensively investigated in this study. A total of 18 test specimens were fabricated from hot-rolled stainless steel plates by means of shielded metal arc welding (SMAW). Two grades of stainless steel were considered, namely the austenitic grade EN 1.4301 and the duplex grade EN 1.4462. Using the sectioning method, the test specimens were divided into strips. The residual stresses were then computed by multiplying the strains relieved during sectioning by the measured Young׳s moduli determined from tensile and compressive coupon tests. Residual stress distributions were obtained for 10 I-sections, four square hollow sections (SHS) and four rectangular hollow sections (RHS). Peak tensile residual stresses reached around 80% and 60% of the material 0.2% proof stress for grades EN 1.4301 and EN 1.4462, respectively. Based upon the test data, simplified predictive models for residual stress distributions in stainless steel built-up I-sections and box sections were developed. Following comparisons with other available residual stress test data, the applicability of the proposed models was also extended to other stainless steel alloys. The proposed residual stress patterns are suitable for inclusion in future analytical models and numerical simulations of stainless steel built-up sections.

The clinching joints strength analysis in the aspects of changes in the forming technology and load conditions

Abstract: This paper presents the strength analysis of joining by clinching for various values of parameter X of the bottom thickness. The maximum joint strength was obtained by performing lap joints, H-shaped samples and T-shaped samples strength test. For the specified value X of the bottom thickness, a test bar of clinching joints was also subjected to complex stress state until destruction. Thus, the impact of joint load direction on the maximum load capacity was determined. The effect of radial clearance between the die and the punch on the forming process, shearing and tearing was also obtained. Moreover, the paper contains an example of new sheet metal joining technology using rivets (ClinchRivet). The complex load tests results of the rivet joints were compared with those obtained for clinching.

Future structural stability design for composite space and airframe structures

Abstract: Space and aircraft industry demands for reduced development and operating costs. Structural weight reduction by exploitation of structural reserves in composite space and aerospace structures contributes to this aim, however, it requires accurate and experimentally validated stability analysis. Currently, the potential of composite light weight structures, which are prone to buckling, is not fully exploited as appropriate guidelines in the field of aerospace and space applications do not exist. This paper deals with the state-of-the-art advances and challenges related to coupled stability analysis of composite structures which show very complex stability behaviour. Two types of thin-walled light weight structures endangered by buckling will be considered; imperfection tolerant and imperfection sensitive structures. For both groups improved design guidelines for composites structures are still under development. This paper gives a short state-of-the-art and presents proposals for future design guidelines.

Nonlinear free vibration analysis of single/doubly curved composite shallow shell panels

Abstract: In this present article, large amplitude free vibration behaviour of doubly curved composite shell panels have been analysed using the nonlinear finite element method. The nonlinear mathematical model is derived using Green Lagrange type geometric nonlinearity in the framework of higher order shear deformation theory. In addition to that all the nonlinear higher order terms are included in the mathematical model to achieve more general case. The nonlinear governing equation of free vibrated curved panel is derived based on Hamilton׳s principle and solved numerically by using the direct iterative method. The developed mathematical model has been validated by comparing the responses with those available numerical results. Finally, some new numerical experimentation (orthotropicity ratio, stacking sequence, thickness ratio, amplitude ratio and support conditions) have been carried out to show the significance and the efficacy of the proposed mathematical model.

An experimental study on clinched joints realized with different dies

Abstract: An experimental investigation has been conducted on mechanically clinched joints, produced with fixed and extensible dies with different forming forces. Mechanical testing involving single lap shear tests, both with one and two joining points, and peeling tests were conducted under quasi-static conditions to assess the different mechanical behaviors of these joints. The effect of the processing conditions on the main mechanical response of the joints, namely the maximum strength, stiffness and absorbed energy, was investigated. The results showed that the joints produced with the extensible die exhibited a similar strength as compared to those produced with the fixed die in single lap shear tests, while they are characterized by a higher strength (up to 40%) when loaded during the peeling test because of a larger interlock. In addition, the employment of extensible dies allows a drastic reduction of the forming loads as compared to those required by adopting the fixed dies.

Experimental investigation of post-fire mechanical properties of cold-formed steels

Abstract: Cold-formed steel members are widely used in residential, industrial and commercial buildings as primary load-bearing elements. During fire events, they will be exposed to elevated temperatures. If the general appearance of the structure is satisfactory after a fire event then the question that has to be answered is how the load bearing capacity of cold-formed steel members in these buildings has been affected. Hence after such fire events there is a need to evaluate the residual strength of these members. However, the post-fire behaviour of cold-formed steel members has not been investigated in the past. This means conservative decisions are likely to be made in relation to fire exposed cold-formed steel buildings. Therefore an experimental study was undertaken to investigate the post-fire mechanical properties of cold-formed steels. Tensile coupons taken from cold-formed steel sheets of three different steel grades and thicknesses were exposed to different elevated temperatures up to 800 °C, and were then allowed to cool down to ambient temperature before they were tested to failure. Tensile coupon tests were conducted to obtain their post-fire stress–strain curves and associated mechanical properties (yield stress, Young׳s modulus, ultimate strength and ductility). It was found that the post-fire mechanical properties of cold-formed steels are reduced below the original ambient temperature mechanical properties if they had been exposed to temperatures exceeding 300 °C. Hence a new set of equations is proposed to predict the post-fire mechanical properties of cold-formed steels. Such post-fire mechanical property assessments allow structural and fire engineers to make an accurate prediction of the safety of fire exposed cold-formed steel buildings. This paper presents the details of this experimental study and the results of post-fire mechanical properties of cold-formed steels. It also includes the results of a post-fire evaluation of cold-formed steel walls.

Web crippling failure using quasi-static FE models

Abstract: This paper presents an investigation on the use of quasi-static analyses with explicit integration to evaluate the web crippling behaviour of cold-formed steel beams. Web crippling failure occurs due to the application of transverse concentrated loads, which can be applied statically or dynamically. In the majority of the examples found in the literature, the web crippling phenomenon has been investigated by means of purely static shell finite element (SFE) models with implicit integration. In this work, the ABAQUS code was employed to implement SFE models aimed at replicating an experimental test and quasi-static analyses with an explicit integration scheme were adopted. First, a brief literature review on the topic of the numerical investigation of web crippling of cold-formed steel members is presented. Then, the paper addresses the characterisation of the quasi-static analysis concept with particular emphasis on the control of dynamic effects and the SFE model of a lipped channel beam under External Two Flange (ETF) loading is described. Several conventional parameters of standard SFE analysis, such as the SFE type, mesh selection, steel model, hardening effects due to cold-forming, residual stresses, initial imperfections and support conditions are explained, as well as additional specifications pertaining to the adoption of quasi-static analyses, such as the load rate, mass scaling, contact and friction, smoothed amplitude curves and inhibition of inertia (noise) effects. Finally, the results obtained are presented in the context of the ETF case, including load–displacement curves, curves of kinetic-to-internal energy ratio vs. displacement and beam deformed shapes (failure modes). It is concluded that explicit analysis leads to rigorous simulations of experimental test results, in terms of ultimate load, post-collapse load–deflection curve and failure mechanism. The failure mode obtained with the quasi-static analysis provides a better approximation of the one observed experimentally than its non-linear static analysis counterpart. Indeed, the failure mechanism emerges considerably more clearly when the quasi-static analysis is adopted.

Analysis of circular concrete-filled double skin tubular slender columns with external stainless steel tubes

Abstract: This paper investigates the strength and behaviour of concrete-filled double skin steel tubular (CFDST) slender columns under axial compression. The lean duplex stainless steel material (EN 1.4162) which has recently gained significant attention is considered herein as the external jacket of such columns. Finite element (FE) analyses of several CFDST columns are conducted. Careful consideration is taken in the modelling for the concrete behaviour, for which both of the compressive and the tensile behaviours and the non-linear behaviour due to cracking are fully considered. The accuracy of the current FE models is ensured through the comparison with the existing columns in literature. A parametric study is then conducted to investigate the behaviour of such columns under different affecting factors; the slenderness ratio, the concrete confinement effect, the hollow ratio, the concrete compressive strength and the thickness ratio. The behavioural differences between intermediate length and very long CFDST columns are carefully addressed. Analytically obtained ultimate strengths are compared with design strengths calculated by European and American specifications. European design strength is found to give better predictions compared to the American specifications. However, it is shown that both strengths cannot be used in design because they overestimate the ultimate strengths and thereby do not satisfy the safety requirements. Therefore, a modification is suggested to the European design model which is shown to be able to estimate the compressive resistance of the CFDST columns more accurately than other methods.

Buckling and vibration of shear deformable functionally graded orthotropic cylindrical shells under external pressures

Abstract: In this study, the vibration and buckling of functionally graded (FG) orthotropic cylindrical shells under external pressures is investigated using the shear deformation shell theory (SDST). The basic equations of shear deformable FG orthotropic cylindrical shells are derived using Donnell shell theory and solved using the Galerkin method. Parametric studies are made to investigate effects of shear deformation, orthotropy, compositional profiles and shell characteristics on the dimensionless frequency parameter and critical external pressures. Some comparisons among various theories have been performed in order to show the differences between the parabolic shear deformation theory (PSDT) and several higher-order shear deformation theories (HSDTs).

Hybrid optimization of hierarchical stiffened shells based on smeared stiffener method and finite element method

Abstract: In this study, Smeared Stiffener Method (SSM) of hierarchical stiffened shells is derived to release the prediction burden of buckling loads. Then, a minimum-weight optimization formulation for hierarchical stiffened shells is developed based on SSM, attempting to demonstrate the higher lightweight potential of hierarchical stiffened shells compared to the traditional ones. Further, the main aim of this paper is to present a hybrid optimization framework of hierarchical stiffened shells including imperfection sensitivity, combining the efficiency of SSM with the accuracy of FEM, since there are currently no closed-form solutions to take imperfections into account accurately. The illustrative example demonstrates that the proposed framework has a higher optimization efficiency and global optimization capability compared to the conventional methods.

Multiobjective crashworthiness optimization of hollow and conical tubes for multiple load cases

Abstract: Much attention of current design analysis and optimization of crashworthy structures have been largely paid to the scenarios with single load case in literature. Nevertheless the designed structures may often have to be operated in other load conditions, thus raising a critical issue of optimality. This paper aims to understand and optimize the dynamic responses and energy absorption of foam-filled conical thin-walled tubes under oblique impact loading conditions by using multiobjective optimization method. The crashworthiness criteria, namely specific energy absorption (SEA) and crushing force efficiency (CFE), are related to loading parameters and design variables by using D-optimal design of experiments (DoE) and Kriging model. To obtain the optimal Pareto solutions of hollow and foam-filled conical tubes, design optimization is first performed under different loading case (DLC) using multiobjective particle swarm optimization (MOPSO) algorithm separately. The optimal designs indicate that hollow tube has better crashing performance than the foam-filled tube under relatively high impacting velocity and great loading angle. To combine multiple load cases (MLC) for multiobjective optimization, a double weight factor technique is then adopted. It is found that the optimal foam-filled tube has better crashing performance than empty conical tube under any of overall oblique loading cases concerned. The study gains insights in deriving multiobjective optimization for multiple load cases, providing a guideline for design of energy absorber under multiple oblique loading.

Ultimate load-carrying capacity of cold-formed thin-walled columns with built-up box and I section under axial compression

Abstract: The use of cold-formed thin-walled steel structures has increased in recent years, and some built-up section members are motivated and also widely used for their excellent structural behaviors. In this paper, a series of axially-compressed tests on built-up box section members composed of two C-section by self-drilling screws at flanges are conducted. The differences of global, local and distortional buckling behaviors between members with built-up and single sections are investigated at first. Then the effects of installation error and fastener spacing on ultimate load-carrying capacity of built-up members are analyzed. A strength estimation method for built-up members under axial compression is proposed based on the experimental investigation in this paper, as well as some existing experiments, and corresponding numerical analysis studies. Finally, the predicted capacity obtained by using the proposed strength estimation method is compared with experimental results and the nominal axial strength determined according to the AISI provisions, by which the suitability and accuracy of the proposed strength estimation method have been established.

Worst Multiple Perturbation Load Approach of stiffened shells with and without cutouts for improved knockdown factors

Abstract: An optimization framework of determining the worst realistic imperfection was proposed by the present authors to study the reduction of the load-carrying capacity of unstiffened cylindrical shells. However, with regard to stiffened shells, especially when cutouts are included, the dimple combination pattern should be judged in a more rational manner. In this study, node coordinates are utilized to describe the position of each dimple-shape imperfection for Worst Multiple Perturbation Load Approach (WMPLA), which is an improvement of the MPLA using an optimization algorithm to find the application positions that will reduce the buckling load. Further, a novel method to determine the density of possible positions of dimple-shape imperfections is proposed based on eigenmode shape for stiffened shells without cutout. In addition, the effects of cutouts on the proposed method are investigated in detail. The effectiveness of the proposed method is demonstrated by comparison of several conventional methods to obtain improved knockdown factors (KDFs).

Ferritic stainless steels in structural applications

Abstract: Ferritic stainless steels are low cost, price-stable, corrosion-resistant materials. Although widely used in the automotive and domestic appliance sectors, structural applications are scarce owing to a dearth of performance data and design guidance. The characteristics of ferritics make them appropriate for structures requiring strong and moderately durable structural elements with attractive metallic surface finishes. The present paper provides an overview of the structural behaviour of ferritic stainless steels, including a summary of the findings of a recent European project (SAFSS) on ferritics. Laboratory experiments have been completed including material tests as well as structural member tests, both at ambient and elevated temperatures. The experimental data is supplemented by numerical analysis in order to study a wide range of parameters. The findings of this work have enabled design guidance to be proposed, as discussed herein.

Flexural behavior of FRP-HSC-steel composite beams

Abstract: This paper reports on an experimental study on the flexural behavior of fiber reinforced polymer (FRP)-high-strength concrete (HSC)-steel composite beams. Seven double-skin tubular beam (DSTBs) and a concrete-filled FRP tube (CFFT) with an internal steel I-beam were tested as simply supported beams in four-point bending. The main parameters of the experimental study included the cross-sectional shapes of inner steel reinforcement and external FRP tube, concrete strength, presence (or absence) of concrete filling inside the steel tube, and effects of the use of mechanical connectors on the inner steel tube. The results indicate that DSTBs are capable of developing very high inelastic flexural deformations. However, the results also indicate that slip between the concrete and the steel tube of the DSTB can be relatively large, unless the bond between concrete and steel tube is enhanced through the use of mechanical connectors. The results of the beam tests illustrate that the flexural behavior of DSTBs is influenced significantly by the diameter and thickness of the inner steel tube. Concrete-filling the inner steel tube and increasing the concrete strength increase the flexural capacity of DSTBs without affecting their overall ductility. Furthermore, the shape of the inner steel tube influences both the flexural capacity of DSTBs and the occurrence of slippage between the concrete and the inner steel tube. It is shown that the bond slip between the concrete and inner steel tube can be prevented through the use of mechanical connectors. These results are presented together with a discussion on the influence of the main parameters on the flexural behavior of DSTBs.

Compressive strength of circular concrete-filled double skin tubular short columns

Abstract: This paper focuses on the compressive strength of the concrete-filled double skin steel tubular (CFDST) short columns. Columns with external and internal circular carbon steel tubes are merely considered. First, this paper summarises previously developed formulas for predicting the compressive strength of the CFDST columns, along with the formula recently suggested by Yu et al. (2013) for solid and hollow circular concrete-filled tubular (CFST) columns. The various formulas for predicting compressive strength are then compared with test results. Test results are then organised and evaluated according to the relevant test specimen parameter; the diameter-to-thickness ratio ( D / t e ). It is found that the available tests do not cover the full range of the D / t e ratio. Hence, numerical nonlinear simulations, based on the finite element (FE) method using the software package ABAQUS/Standard, are constructed to compensate for the shortage in the available results. Through comparison with test and FE results, a new design formula is suggested. Such formula is shown to be more accurate than available formulas for estimating the compressive strength of the CFDST short columns. This recommended design model requires relatively less calculation efforts, and provides less scattered predictions than those using the current design rules. At the end, an illustrative example for the calculation of the compressive strength of the CFDST columns using the currently proposed formula is provided.

Numerical and experimental study of crashworthiness parameters of honeycomb structures

Abstract: Crashworthiness parameters of aluminum hexagonal honeycomb structures under impact loads are investigated by using finite element methods and conducting experiments. To validate the finite element models, numerical results are compared with experimental measurements and theoretical results reported in literature. In numerical simulations of honeycomb structures, out-of-plane loads are considered while the aluminum foil thickness, cell side size, cell expanding angle, impact velocity and mass are varying, and dynamic behavior and crashworthiness parameters are examined. It is observed that there are good agreements between numerical, experimental and theoretical results. Numerical simulations predict that crashworthiness parameters depend on cell specification and foil thickness of the honeycomb structure and are independent of impact mass and velocity.

Natural FRP tube confined fibre reinforced concrete under pure axial compression: A comparison with glass/carbon FRP

Abstract: Flax fibre has the potential to replace glass fibre in fibre reinforced polymer (FRP) composite and coir fibre can be used as reinforcement in concrete due to its highest toughness amongst natural fibres. To design a concrete structure with high performance-to-cost ratio, a new flax FRP (FFRP) tube confined coir fibre reinforced concrete (CFRC) cylinder is proposed. The compressive behaviour of FFRP tube confined plain concrete (PC) and confined CFRC is experimentally investigated. Results show that both the proposed cylinders offer high compressive strength and ductility (measured by fracture energy). Coir fibre inclusion with an optimum mass content can further increase the fracture energy of the confined CFRC, compared to the confined PC specimens. Experimental result is compared with the existing glass/carbon FRP (G/CFRP) confined concrete regarding to confinement effectiveness. It shows that the confinement effectiveness of the proposed cylinders is close to or comparable to the G/CFRP confined concrete. This is true despite the tensile strength of FFRP composite, as obtained from flat coupon tensile testing, being significant lower than that of G/CFRP.

Experimental study of web crippling behaviour of hollow flange channel beams under two flange load cases

Abstract: This paper presents the details of an experimental study of a cold-formed steel hollow flange channel beam known as LiteSteel beam (LSB) subject to web crippling under End Two Flange (ETF) and Interior Two Flange (ITF) load cases. The LSB sections with two rectangular hollow flanges are made using a simultaneous cold-forming and electric resistance welding process. Due to the geometry of the LSB, and its unique residual stress characteristics and initial geometric imperfections, much of the existing research for common cold-formed steel sections is not directly applicable to LSB. Experimental and numerical studies have been carried out to evaluate the behaviour and design of LSBs subject to pure bending, predominant shear and combined actions. To date, however, no investigation has been conducted on the web crippling behaviour and strength of LSB sections. Hence an experimental study was conducted to investigate the web crippling behaviour and capacities of LSBs. Twenty-eight web crippling tests were conducted under ETF and ITF load cases, and the ultimate web crippling capacities were compared with the predictions from the design equations in AS/NZS 4600 and AISI S100. This comparison showed that AS/NZS 4600 and AISI S100 web crippling design equations are unconservative for LSB sections under ETF and ITF load cases. Hence new equations were proposed to determine the web crippling capacities of LSBs based on experimental results. Suitable design rules were also developed under the direct strength method (DSM) format.

Mechanical properties of Miura-based folded cores under quasi-static loads

Abstract: Sandwich structures with folded cores are regarded as a promising alternative to conventional honeycomb sandwich structures in the aerospace industry. This paper presents a parametric study on the mechanical properties of a variety of Miura-based folded core models virtually tested in quasi-static compression, shear and bending using the finite element method. It is found that the folded core models with curved fold lines exhibit the best mechanical performances in compression and shear while the multiple layered models outperform the other folded core models in bending. Furthermore, the folded core models are compared to a honeycomb core model with the same density and height. In this case, it is shown that the honeycomb core has the best performance in compression while the folded cores have comparable or even better performances in the shear and bending cases. The virtual test results reported in this paper can provide researchers with a general guideline to design the most suitable folded core structure for certain applications.

Discussion on the use of stainless steel in constructions in view of sustainability

Abstract: Recent years have seen an increase in the use of stainless steel in buildings, mainly owing to its corrosion properties and therefore long service life. Among stainless steels, ferritic and lean duplex grades are characterized by low nickel content resulting in a more cost-stable and economic material compared to austenitic stainless steels. These grades have comparable (or even higher) strength than carbon steel and good corrosion resistance at lower cost. That is why, lately, they have been more often used in structural components. In this paper, attention is first paid to the advantages associated with the use of stainless steel in recent construction projects in view of sustainability. Second, life cycle analysis and the background of the new European standard EN 15804 are introduced, including module D, which allows credits to be taken now for the eventual reuse or recycling of material in the future, at the end-of-life stage. Life cycle inventories of stainless steel products (cold-rolled coils and quarto plate) are presented. Depending on the fraction of material recovered at the end of the lifespan, two potential impacts (Primary Energy Demand and Global Warming Potential) are presented for four grades: 1.4301 (AISI 304) and 1.4401 (AISI 316) austenitic grades, 1.4016 (AISI 430) ferritic grade and 1.4462 (AISI 2205) duplex grade. The influence of module D is underlined.

On the shear deformation modes in the framework of Generalized Beam Theory

Abstract: This paper extends previous work concerning the determination of cross-section deformation modes in thin-walled members with arbitrary polygonal cross-section, in the framework of Generalized Beam Theory (Goncalves et al., 2010 [1] ). In particular, the paper addresses the so-called “natural shear deformation modes” (i.e. the deformation modes that involve non-null membrane shear strains and are independent of the cross-section discretization employed), which are relevant for capturing the behaviour of thin-walled members with complex multi-cell cross-sections undergoing torsion and/or distortion. The contributions of the paper are (i) the derivation of fundamental properties of the shear modes, (ii) the proposal of an efficient mode extraction procedure and (iii) the development of analytical results for several particular cases. In order to illustrate the application of the proposed mode extraction procedure and demonstrate the validity of the derived properties, several cross-sections are analyzed, including complex multi-cell tubes.