Showing papers in "Thin-walled Structures in 2016"
TL;DR: In this article, the nonlinear free vibration behavior of shear deformable sandwich porous beam is investigated within the context of Timoshenko beam theory, where two non-uniform functionally graded distributions are considered based on the equivalent beam mass associated with a uniform distribution for purpose of comparison.
Abstract: The nonlinear free vibration behavior of shear deformable sandwich porous beam is investigated in this paper within the context of Timoshenko beam theory. The proposed beam is composed of two face layers and a functionally graded porous core which contains internal pores following different porosity distributions. Two non-uniform functionally graded distributions are considered in this paper based on the equivalent beam mass, associated with a uniform distribution for purpose of comparison. The elastic moduli and mass density are assumed to vary along the thickness direction in terms of the coefficients of porosity and mass density, whose relationship is determined by employing the typical mechanical characteristic of an open-cell metal foam. The Ritz method and von Karman type nonlinear strain-displacement relationships are applied to derive the equation system, which governs the nonlinear vibration behavior of sandwich porous beams under hinged or clamped end supports. A direct iterative algorithm is then used to solve the governing equation system to predict the linear and nonlinear frequencies which are presented by a detailed numerical study to discuss the effects of porosity coefficient, slenderness ratio, thickness ratio and to compare the varying porosity distributions and boundary conditions, providing a feasible way to improve the vibration behavior of sandwich porous beams.
273 citations
TL;DR: In this article, the authors present an experimental investigation on mechanical and associated properties of seawater and sea sand concrete (SWSSC) filled glass fibre reinforced polymer (GFRP) and stainless steel (SS) circular tubes.
Abstract: This paper presents an experimental investigation on mechanical and associated properties of seawater and sea sand concrete (SWSSC) filled glass fibre reinforced polymer (GFRP) and stainless steel (SS) circular tubes. A proper SWSSC mix was developed to achieve the target strength and desirable workability. A total of 24 stub columns, including hollow sections and SWSSC fully filled tubes or double-skin tubes, were tested under axial compression with the load applied to concrete and tubes simultaneously. The stress-strain curves of the core concrete indicate that concrete strength and ductility is enhanced due to the confinement effect. Discussion focuses on the influence of tube diameter-to-thickness ratio, outer tube types and inner tube types on concrete confinement. Capacity formulae are proposed to estimate the load carrying capacity of SWSSC fully filled SS or GFRP tubes, and that of double skin tubes with four combinations of inner and outer tubes, i.e. SS and SS, SS and GFRP, GFRP and GFRP and GFRP and SS.
166 citations
TL;DR: In this article, the authors combine the isogeometric analysis, the level set and a simple first-order shear deformation theory (S-FSDT) to form a new effective and accurate approach for simulating free vibration and buckling problems of laminated composite plates with cutouts.
Abstract: We combine the isogeometric analysis, the level set and a simple first-order shear deformation theory (S-FSDT) to form a new effective and accurate approach for simulating free vibration and buckling problems of laminated composite plates with cutouts. The problem domain is discretized using non-uniform rational B-spline (NURBS) basis functions, which are utilized for geometry and field variables approximation. In S-FSDT, the shear locking effect is no longer valid and more interestingly, low computational cost is saved because of having fewer unknowns. The trimmed NURBS surface often used in existing approaches, which has some disadvantages in describing the geometrical structure with internal cutouts due to the tensor product of the NURBS basis functions, is no longer required in the present formulation, and the level set method (LSM) is employed to describe the cutouts instead. More interestingly, the numerical integration in the developed method is performed only inside the physical domain. All those features make the method effective in modeling cutouts with complicated shapes. Numerical examples are presented to show the performance of the method. The results obtained are validated against reference solutions showing a good agreement and performance.
154 citations
TL;DR: In this paper, the buckling analysis of radially loaded solid circular plate made of porous material is presented, where the boundary conditions of the plate are assumed to be clamped and the plate is assumed to have geometrically perfect.
Abstract: This study presents the buckling analysis of radially loaded solid circular plate made of porous material. Properties of the porous plate, where pores are assumed to be saturated with fluid, vary across its thickness. The boundary condition of the plate is assumed to be clamped and the plate is assumed to be geometrically perfect. The higher order shear deformation plate theory (HSDT) is employed to derive the governing equations. The equilibrium and stability equations, derived through the variational formulation and based on the Sanders non-linear strain–displacement relation, are used to determine the prebuckling forces and critical buckling loads. The results are compared with the buckling loads of circular plates made of porous material and reported in the literature based on the classical plate theory (CPT) and the first order shear deformation plate theory (FSDT).
131 citations
TL;DR: In this paper, the structure of bamboo was introduced to increase the axial and lateral energy absorption of thin-walled tubes by using bionic design method, and the results showed that the energy absorption was excellent due to the gradient distribution of vascular bundles, nodes and density.
Abstract: In natural environment, many biological structures are tubular and exhibit excellent mechanical properties that can reduce self-weight effectively and transport more water and nutrients, such as bamboo. In this paper, the structure of bamboo was introduced to increase the axial and lateral energy absorption of thin-walled tubes by using bionic design method. Energy absorption ability of bamboo was tested by drop-weight experiments. The results showed that the energy absorption was excellent due to the gradient distribution of vascular bundles, nodes and density. These advantages of the bamboo make it possible to design of bionic structure which composed of 1 bionic node and 3 bionic inner tubes with 18, 9 and 4 bionic elements in each inner tube. Numerical examples of bionic structures under axial/lateral impacts were solved with nonlinear finite element method (FEM). The results indicated that the bionic design enhances the specific energy absorption (SEA) of tubes. Thus, the bionic structure is exactly excellent energy absorption under lateral/axial impact and can be used in the future.
126 citations
TL;DR: In this paper, two different origami patterns were introduced to circular tubes and the influence of the patterns on the energy absorption capacity and deformation mechanism of tubes under uniaxial loading were investigated both numerically and experimentally.
Abstract: Thin-walled tubes are widely used as energy absorption components. In this study, two different origami patterns were introduced to circular tubes. The influence of the origami patterns on the energy absorption capacity and the deformation mechanism of tubes under uniaxial loading were investigated both numerically and experimentally. The results showed that the initial peak force of origami tubes would be significantly reduced, while the energy absorption capacity could be improved or maintained. Brass tubes with and without origami patterns were fabricated using 3D printing and were tested to validate the finite element models.
122 citations
TL;DR: In this paper, a novel foam-filled ellipse tube (FET) is proposed and compared with other hollow and foamfilled tubes with different cross-sections under multiple loading angles, which include square, circle and rectangle.
Abstract: In this paper, a novel foam-filled ellipse tube (FET) is proposed and compared with other hollow and foam-filled tubes with different cross-sections under multiple loading angles, which include square, circle and rectangle. First, finite element analyses of these tubes reveal that the FET tube has the best crashworthiness under multiple loading angles. Second, design of experiments (DOE) was used to analyze the parameters that radial rate f, thickness of wall t and foam density ρ f . Third, the Non-dominated Sorting Genetic Algorithm (NSGA-II) is used to optimize the FET tube, in which the optimal parameter variation is sought for maximizing specific energy absorption (SEA) and minimizing peak crush force (PCF) under multiple loading angles. The optimized FET tube exhibits better crashworthiness than the origin FET tube and other tubes with different cross-section, indicating that the FET tube can be a potential energy absorber especially under oblique impact loading.
119 citations
TL;DR: In this paper, the authors present an experimental study on concrete-filled circular tubes that consisted of seawater and sea sand concrete (SWSSC), stainless steel (SS) tube, carbon fiber reinforced polymer (CFRP) tube and basalt fibre reinforced polymer tube.
Abstract: This paper presents an experimental study on concrete-filled circular tubes that consisted of seawater and sea sand concrete (SWSSC), stainless steel (SS) tube, carbon fibre reinforced polymer (CFRP) tube, and basalt fibre reinforced polymer (BFRP) tube. A total of 38 stub columns, which included 12 hollow section tubes, 12 fully SWSSC-filled tubes and 14 SWSSC-filled double-skin tubes, with four combinations of inner and outer tubes, were tested under axial compression. Tensile coupon tests and “disk-split” tests were conducted to obtain the material properties of SS, CFRP and BFRP. Ultimate strain of SWSSC-filled tubes and stress-strain curves of the confined concrete were characterised in the study. The effects of some key parameters (e.g., tube diameter-to-thickness ratio, cross-section types, outer tube types, and inner tube types) on the confinement effects were also discussed. Comparisons were made among CFRP, BFRP and glass fibre reinforced polymer (GFRP) in terms of confinement to SWSSC. The capacity prediction formulae previously proposed by the authors for SWSSC filled GFRP tubes were found to be reasonable for estimating the load carrying capacity of SWSSC filled CFRP and BFRP tubes.
118 citations
TL;DR: In this article, the analytical formulas of mean crashing force for four different hexagonal tubes with multiple cells were first derived based on the Simplified Super Folding Element (SSFE) theory through several typical constituent elements: corner element, three-panel angular element I and three panel angular element II.
Abstract: In this paper, the analytical formulas of mean crashing force for four different hexagonal tubes with multiple cells were first derived based on the Simplified Super Folding Element (SSFE) theory through several typical constituent elements: corner element, three-panel angular element I and three-panel angular element II. The numerical simulations of hexagonal multi-cell configurations were then correlated with the derived analytical solutions. Finally, both analytical formulas and finite element analysis (FEA) based surrogate models were employed to optimize the cross-sectional dimensions of the hexagonal tubes. From the optimization results, web-to-web (W2W) is the most efficient configuration in improving the crashing behavior, while corner-to-corner (C2C) is the worst of these four configurations. Importantly, the Pareto fronts obtained from the analytical formulas agree well with those from the FEA based surrogate models. As a result, analytical formulas could be recommended in crashworthiness optimization for the sake of computational efficiency.
114 citations
TL;DR: In this paper, the performance of prediction methods on short, medium and long circular Concrete Filled Steel Tube (CFST) columns was examined. But, they focused on a narrow region of configurations.
Abstract: This paper presents 18 tests conducted on short, medium and long circular Concrete Filled Steel Tube (CFST) columns. To explore the impact of column parameters and confinement effect three L/D ratios, two D/t ratios, two steel qualities and three concrete classes were employed. Some specimens have properties within application limits of EC4 and AISC 360-10 whereas others have properties beyond the application limits. Since new, large and efficient structures require adoption of high strength materials, it is compulsory to push the limits of design specifications. It is shown that 56 MPa and 66 MPa concretes provide very smooth and ductile load-shortening curves which imply high deformation capacity of such concrete classes. Brittle nature of 107 MPa concrete is shown by very sharp transitions from pre-peak to post-peak region and sudden discharge of loading in load-shortening curves. Additionally, 239 experimental data were collected from literature to assess EC4 and AISC 360-10 predictions within application limits and beyond application limits. Instead of focusing on a narrow region of configurations, this paper examines the performance of prediction methods on short, medium and long CFST columns. EC4 predictions indicate much better agreement with the test results. However AISC 360-10 predictions are conservative for all combinations of parameters. The application limits of EC4 can be widened to cover solutions of columns with broader properties. Confinement effect should be handled elaborately in AISC 360-10 formulations. L/D and relative slenderness are key parameters and have direct impact on column behaviour. However D/t does not have direct impact on column behaviour.
113 citations
TL;DR: In this paper, three configurations of nested tube systems were experimentally analyzed under various loading conditions, and the effects of geometrical and loading parameters on the responses of the best nested tube system were explored via performing parametric analysis.
Abstract: This paper presents the responses of nested tube systems under quasi-static and dynamic lateral loading. Nested systems in the form of short internally stacked tubes were proposed as energy absorbing structures for applications that have limited crush zones. Three configurations of nested tube systems were experimentally analysed in this paper. The crush behaviour and energy absorbing responses of these systems under various loading conditions were presented and discussed. It was found that the quasi-static and dynamic responses of the nested systems were comparable under an experimental velocity of v=4.5 m/sec. This is due to insignificant strain rate and inertia effects of the nested systems under the applied velocity. The performance indicators, which describe the effectiveness of energy absorbing systems, were calculated to compare the various nested systems and the best system was identified. Furthermore, the effects of geometrical and loading parameters on the responses of the best nested tube system were explored via performing parametric analysis. The parametric study was performed using validated finite element models. The outcome of this parametric study was full detailed design guidelines for such nested tube energy absorbing structures.
TL;DR: In this article, the Particle Swarm Optimization (PSO) method was used to determine the flexural strength of CFS beam sections with the Eurocode 3 (EC3) geometrical requirements and with manufacturing and practical constraints.
Abstract: Cold-formed steel (CFS) cross-sections can be optimised to increase their load carrying capacity, leading to more efficient and economical structural systems. This paper aims to provide a methodology that would enable the development of optimised CFS beam sections with maximum flexural strength for practical applications. The optimised sections are designed to comply with the Eurocode 3 (EC3) geometrical requirements as well as with a number of manufacturing and practical constraints. The flexural strengths of the sections are determined based on the effective width method adopted in EC3, while the optimisation process is performed using the Particle Swarm Optimisation (PSO) method. To allow for the development of a new ‘folded-flange’ cross-section, the effective width method in EC3 is extended to deal with the possible occurrence of multiple distortional buckling modes. In total, ten different CFS channel cross-section prototypes are considered in the optimisation process. The flexural strengths of the optimised sections are verified using detailed nonlinear finite element (FE) analysis. The results indicate that the optimised folded-flange section provides a bending capacity which is up to 57% higher than standard optimised shapes with the same amount of material.
TL;DR: In this paper, a thin-walled tube design with a pre-folded kite-shape rigid origami pattern as an energy absorption device was presented, and a numerical simulation of the quasi-static axial crushing of the new device showed that a smooth and high reaction force curve can be achieved in comparison with those of conventional square tubes.
Abstract: This paper presents a novel thin-walled tube design with a pre-folded kite-shape rigid origami pattern as an energy absorption device. Numerical simulation of the quasi-static axial crushing of the new device shows that a smooth and high reaction force curve can be achieved in comparison with those of conventional square tubes, with an increase of 29.2% in specific energy absorption and a reduction of 56.5% in initial peak force being obtained in the optimum case. A theoretical study of the energy absorption of the new device has also been conducted, which matches reasonably well with the numerical results.
TL;DR: In this article, the authors evaluate the through-the-thickness profiles of strain, stress and displacement components of several doubly-curved panels reinforced by curvilinear fibers.
Abstract: The main aim of this paper is the evaluation of the through-the-thickness profiles of strain, stress and displacement components of several doubly-curved panels reinforced by curvilinear fibers. The placement of the reinforcing phase along curved paths allows to obtain mechanical properties which change point by point and affects the static behavior of shell structures. Some numerical applications based on both higher-order Equivalent Single Layer (ESL) and Layer-Wise (LW) theories are shown in order to underline the curvilinear fiber influence on the static analysis. The structural model, which is based on the so-called Carrera Unified Formulation (CUF), is completely general and can deal easily with variable stiffness shells. An appropriate recovery procedure based on the three-dimensional elasticity equations in principal curvilinear coordinates is presented to compute strains and stresses. The equation system which governs the static problem under consideration is solved numerically through the Generalized Differential Quadrature (GDQ) method. The same numerical technique is employed to evaluate the geometrical parameters needed for the characterization of the shell reference surface, according to the differential geometry.
TL;DR: In this article, a review on the structural behavior and buckling of vertical, aboveground tanks employed to store oil and fuels is presented, focusing on buckling problems of such tanks under static or quasi-static loads, including uniform pressure, wind, settlement of foundation, and fire.
Abstract: Research on the structural behavior and buckling of vertical, aboveground tanks employed to store oil and fuels have significantly increased during the past two decades. Interest in this shell form is related not just to the cost of the infrastructure, but also because failures in cases of accidents or natural disasters may cause huge economic, environmental and social losses. This review concentrates on buckling problems of such tanks under static or quasi-static loads, including uniform pressure, wind, settlement of foundation, and fire. In all cases, buckling is considered as a static process. Attention is given to the load definition in each case, followed by buckling studies under previously defined pressures or temperatures. The structural configuration of tanks is first described in order to understand what is specific about this structural form. Next, the theoretical framework for stability and buckling is briefly described to place each contribution in a wider context. Each loading case is first explained, experiments or case-studies are briefly described, and computational analytical modeling is reviewed; finally, efforts towards improving design are mentioned. Most papers published in the literature have been motivated by wind effects on tanks, but the review shows that other areas, such as thermal buckling under an adjacent fire, are currently receiving increasing attention.
TL;DR: In this paper, a new design of multi-cell devices was proposed, and evaluated in terms of crashworthiness capability under quasi-static axial and oblique (9°, 18° and 27°) loading.
Abstract: A new design of multi-cell devices was proposed in this paper, and evaluated in terms of crashworthiness capability under quasi-static axial and oblique (9°, 18° and 27°) loading. The structures studied in the present paper were single and multi-cell members made up of two straight columns with the same shape of cross-section connected together by several ribs. They included several sectional configurations such as triangle, square, hexagon and circle with different scales (i.e. 0, 0.25, 0.5, 0.75 and 1). Finite element code LS-DYNA was used to simulate the crashworthiness behavior of the proposed members under quasi-static loads. Several crashworthiness indicators including SEA, F max and CFE were obtained at different crushing angles for all the columns, and a powerful decision making method known as COPRAS was then implemented to choose the best energy absorber with the criteria of having higher specific energy absorption and lower initial peak force. From the COPRAS calculations, the multi-cell members with inner tube and scale number of 0.5 were selected as the better energy absorbers, and the column with circular cross-section was also found to be the best energy absorbing device.
TL;DR: In this paper, a comprehensive experimental and numerical investigation into the structural performance of stainless steel circular hollow sections (CHS) under combined compression and bending moment has been performed and is fully reported in the present paper and its companion paper.
Abstract: A comprehensive experimental and numerical investigation into the structural performance of stainless steel circular hollow sections (CHS) under combined compression and bending moment has been performed and is fully reported in the present paper and its companion paper. The experimental programme employed four CHS sizes made of austenitic stainless steel, and included material tensile coupon tests, four stub column tests and twenty combined loading tests. The initial loading eccentricities for the combined loading tests were varied to provide a wide range of bending moment-to-axial load ratios. In conjunction with the testing programme, a numerical modelling programme was performed to simulate the experiments. The developed FE models were shown to be capable of replicating the key test results, full experimental curves including the post-ultimate range and deformed failure modes. Upon validation of the FE models, a series of parametric studies were conducted in the companion paper, aiming at extending the current test data pool over a range of cross-section sizes and combinations of loading. The experimental data, together with the generated parametric study results, were analysed and employed to evaluate the applicability of the codified provisions given in the European code, American specification and Australia/New Zealand standard for design of CHS under combined loading. Improved design rules were also sought through extension of the deformation-based continuous strength method (CSM) to the case of stainless steel CHS under combined loading.
TL;DR: Wang et al. as discussed by the authors proposed a sinusoidal corrugation tube (SCT) to control the collapse mode, and minimize the initial peak crushing force (IPCF) and fluctuations.
Abstract: Thin-walled structures are widely used as energy absorbing devices for their proven advantages on lightweight and crashworthiness. However, conventional thin-walled structures often exhibit unstable collapse modes and excessive initial peak crushing force (IPCF) followed by undesirable fluctuation in force-displacement curves under impact loading. This paper introduces a novel tubal configuration, namely sinusoidal corrugation tube (SCT), to control the collapse mode, and minimize the IPCF and fluctuations. Through validating the finite element (FE) models established, the effects of wavelength, amplitude, thickness and diameter of SCTs on collapse mode and energy absorption were investigated. The results showed that SCTs can make the deformation mode more controllable and predictable, which can be transformed from a mixed mode to a ring mode by simply changing the wavelength and amplitude. Compared with the traditional straight circular tube, the IPCF is reduced appreciably. Furthermore, SCTs have lower fluctuation in the force–displacement curves than traditional straight circular tubes. Finally, a multiobjective optimization is conducted to obtain the optimized SCT configuration for maximizing specific energy absorption (SEA), minimizing IPCF under the constraint of fluctuation criterion. The optimal SCTs are of even more superior crashworthiness and great potential as an energy absorber.
TL;DR: In this paper, the free vibration and instability characteristics of nanoshells made of functionally graded materials (FGMs) with internal fluid flow in thermal environment are studied based upon the first-order shear deformation shell theory.
Abstract: The free vibration and instability characteristics of nanoshells made of functionally graded materials (FGMs) with internal fluid flow in thermal environment are studied in this paper based upon the first-order shear deformation shell theory. In order to capture the size effects, Mindlin's strain gradient theory (SGT) is utilized. The mechanical and thermal properties of FG nanoshell are determined by the power-law relation of volume fractions. The Knudsen number is considered to analyze the slip boundary conditions between the flow and wall of nanoshell, and the average velocity correction parameter is used to obtain the modified flow velocity of nano-flow. The governing partial differential equations of motion and associated boundary conditions are derived by Hamilton's principle. An analytical solution method is also employed to solve the governing equations under the simply-supported end conditions. Then, some numerical examples are presented to investigate the effects of fluid velocity, longitudinal and circumferential mode numbers, length scale parameters, material properties, temperature difference and compressive axial loads on the natural frequencies, critical flow velocities and instability of system.
TL;DR: In this paper, the structural behavior of SCS sandwich composite wall based on a series of combined compression and uniaxial bending tests on short SCS composite wall with interlocking J-hook connectors is investigated.
Abstract: Steel–concrete–steel (SCS) sandwich wall infilled with ultra-lightweight cement composite has been developed and proposed for applications in offshore and building constructions. A new form of J-hook connector is introduced to connect the external plates to improve the composite action between the steel face plates and cement composite core to form an integrated unit which is capable of resisting extreme loads. This research experimentally investigates the structural behaviour of SCS sandwich composite wall based on a series of combined compression and uniaxial bending tests on short SCS sandwich composite wall with interlocking J-hook connectors. From the tests, it is found that the SCS sandwich wall exhibits good ductility behaviour with a bending failure mode. Nonlinear finite element (FE) model is also developed to simulate the mechanical behaviour of sandwich wall in terms of ultimate strength and load-deflection curves. Analytical studies show that the N–M interaction model based on Eurocode 4 may over-predict the combined resistance of the SCS sandwich walls subjected to eccentric compression. Therefore, a new approach is proposed to evaluate the resistance of sandwich wall. The axial force versus moment capacity interaction diagrams of sandwich wall are calculated. The validation against the test and FE results shows a reasonable and conservative estimation on the combined resistance of SCS sandwich wall.
TL;DR: In this paper, the potential and benefit of tube shrinking to improve crashworthiness performance of conical tubes are analyzed, and the authors show that both thickness increase and material hardening during tube shrinking lead to up to 120% increase in energy absorption.
Abstract: Crashworthiness performance of conical tubes with various thickness distributions are investigated in the present work. Specimens are fabricated by tube shrinking process and axial crushing tests are carried out to study their energy absorption characteristics. The potential and benefit of tube shrinking to improve crashworthiness performance of tubes are analyzed. Both thickness increase and material hardening during tube shrinking lead to up to 120% increase in energy absorption with even less structural mass. Although the peak force of tubes is increased after shrinking, the load uniformity is still improved due to larger increase in mean crushing force. Numerical simulations are also conducted for tubes with quadratic thickness distributions. The material hardening during fabrication is included and the numerical results compare well with experiment. In addition, crashworthiness optimization of conical tubes with nonlinear thickness distribution is performed by surrogate method. Influences of relevant thickness parameters on performance of the structure are analyzed.
TL;DR: In this article, the flexural behavior of circular concrete filled steel tubes (CFST) under sustained load and chloride corrosion was studied, and a finite element analysis (FEA) model was developed to study the full range behavior of CFST under corrosion.
Abstract: This paper studies the flexural behavior of circular concrete filled steel tubes (CFST) under sustained load and chloride corrosion. 7 CFST specimens were tested under a four-point bending load. It was found that corrosion causes noticeable deterioration to the flexural strength, while the ductility of CFST keeps well. A finite element analysis (FEA) model was developed to study the full-range behavior of CFST under corrosion. A parametric study was conducted to find the main parameters that influence the residual flexural strength, based on which a simplified model was proposed to calculate the residual flexural strength of circular CFST under long-term load and corrosion.
TL;DR: In this article, the imperfection sensitivity of a 4.5m-diam isogrid stiffened shell under axial compression is investigated, and the measured imperfection, NASA SP-8007 and several types of assumed imperfections, including eigenmode-shape imperfection and dimple shape imperfections are introduced into the FE model to predict the knockdown factors (KDFs), respectively.
Abstract: Stiffened shells in launch vehicles are very sensitive to various forms of imperfections. In this study, the imperfection sensitivity of a 4.5 m diam isogrid stiffened shell under axial compression is investigated. The measured imperfection, NASA SP-8007 and several types of assumed imperfections, including eigenmode-shape imperfection and dimple-shape imperfections (produced by the single perturbation load approach (SPLA) and worst multiple perturbation load approach (WMPLA)), are introduced into FE model to predict the knockdown factors (KDFs), respectively. Then, the buckling test of this full-scale stiffened shell under axial compression is carried out to validate the above numerical approaches. It can be found that the KDF predicted by the WMPLA is very close to the test results, while the ones predicted by eigenmode-shape imperfection and NASA SP-8007 are extremely conservative. Besides, the measured imperfection and other assumed imperfections are proven to be risky, because these methods overestimate the actual load-carrying capacity. Finally, it can be concluded that the WMPLA is a potential and efficient approach to predict KDFs in the design stages for future launch vehicles.
TL;DR: In this paper, a practical design equation of the ultimate bearing capacity of hexagonal CFT stub columns was proposed based on the superposition principle, with an average ratio of predicted to measured capacity of 1.08 and a standard deviation of 0.05.
Abstract: Four groups of axial compression tests on hexagonal CFT stub columns have been carried out aiming to investigate the effects of the concrete strength and steel ratio on the behaviour of hexagonal CFT stub columns. Studies on parametric analysis and composite action between core concrete and steel tube have been carried out using FE modelling which had been benchmarked using the test data. Based on the essential data obtained in this paper, the ratio of axial stress-yield strength of steel tube was determined at the ultimate state. The stress contour of core concrete was simplified to an unconfined area without constraint and a confined area with uniform constraint imposed by hexagonal steel tube. Eventually, a practical design equation of the ultimate bearing capacity of hexagonal CFT stub columns was proposed based on the superposition principle. An excellent agreement between the proposed equation and the experimental results was observed, with an average ratio of predicted to measured capacity of 1.08 and a standard deviation of 0.05.
TL;DR: In this article, the mechanical properties of heat-treated high tensile strength low alloy structural steel RQT 701 with proof strength of 740 MPa at elevated temperatures were investigated experimentally.
Abstract: This paper investigates experimentally the mechanical properties of heat-treated high tensile strength low alloy structural steel RQT 701 with proof strength of 740 MPa at elevated temperatures. Standard axial tensile tests at elevated temperatures were carried out by using both steady-state and transient-state methods. The test results were compared with those from mild steels of grades up to S460. The comparisons indicate that the RQT 701 steel has smaller relative thermal elongation, and higher reductions of effective yield strength and elastic modulus at elevated temperatures. The test results on proportional limit, effective yield strength and elastic modulus were fitted into Eurocode stress–strain models for numerical analysis and fire resistant design.
TL;DR: In this article, a combination of tests and non-linear finite element analyses is used to investigate the effect of such holes on web crippling under end-one-flange (EOF) loading condition.
Abstract: Web openings could be used in cold-formed steel beam members, such as wall studs or floor joints, to facilitate ease of services in buildings. In this paper and its companion paper, a combination of tests and non-linear finite element analyses is used to investigate the effect of such holes on web crippling under end-one-flange (EOF) loading condition. The present paper includes a testing programme on web crippling of channel section and material tensile coupons, followed by a numerical study, where the models are firstly validated against the performed experiments. The results of 74 web crippling tests are presented, with 22 tests conducted on channel sections without web openings and 52 tests conducted on channel sections with web openings. In the case of the tests with web openings, the hole was either located centred above the bearing plates or having a horizontal clear distance to the near edge of the bearing plates. A non-linear finite element model is described, and the results compared against the laboratory test results; a good agreement between the tests and finite element analyses was obtained in term of both strength and failure modes.
TL;DR: In this article, the effects of the temperature dependence of the material properties and the initial thermal stresses together with the material graded index and the geometrical parameters on the free vibration of the functionally graded (FG) truncated conical panels are investigated.
Abstract: The influences of thermal environment on the free vibration characteristics of functionally graded (FG) truncated conical panels are investigated based on the first-order shear deformation theory (FSDT). By taking into account both the temperature dependence of material properties, which are assumed to be graded in the thickness direction, and the initial thermal stresses, the equations of motion and the related boundary conditions are derived using Hamilton's principle. The differential quadrature method (DQM) is employed to discretize the equations of motion subjected to any types of classical boundary conditions. After studying the convergence of the method, its accuracy is demonstrated by solving different examples in the limit cases. Then, the effects of the temperature dependence of the material properties and the initial thermal stresses together with the material graded index and the geometrical parameters on the free vibration of the FG truncated conical panels are investigated. It is shown that in addition to the temperature dependence of material properties, the initial thermal stresses have significant effects on the vibrational characteristics of the FG conical shell panels and cannot be ignored.
TL;DR: In this article, the authors conducted experimental tests to investigate the crashworthiness of three different types of tailor welded blanks (TWB) hat-shaped structures and established finite element (FE) models corresponding to each of the samples to perform crashworthiness analysis.
Abstract: Tailor welded blanks (TWB) have been widely applied in automobile industry. This paper firstly conducts experimental tests to investigate the crashworthiness of three different types of TWB hat-shaped structures. Their combinations provide three representative TWB configurations: namely the same material grade with different wall thicknesses; different grades with the same thickness, different material grades with different thicknesses, respectively. Secondly, the finite element (FE) models corresponding to each of the samples are established to perform crashworthiness analysis. It is exhibited that the FE simulations are in good agreement with the experimental tests. Thirdly, the surrogate models are constructed to approximate the crashworthiness responses of these TWB structures. Fourthly, a sensitivity analysis is conducted to explore the effects of the weld line location, wall thickness and material properties for each segment of TWB structures subject to crashing load. The results showed that the wall thickness is most sensitive to the crashworthiness of TWB structures. Finally, reliability based design optimization is carried out by taking into account the uncertainties in the TWB configuration. The results demonstrate that the optimized TWB tubes are capable to improve energy absorption as well as enhance the reliability, potentially being an ideal structure for crashworthiness.
TL;DR: In this article, a double functionally graded (DFG) structure was introduced, which comprises of a functionally graded honeycomb filler in a functional graded thickness (FGT) tube, and the comparison of deformation modes and critical crushing angles clearly indicated that the DFG structure is of better and more stable crashing characteristics, being a crashworthy structure.
Abstract: Circular tube filled with cellular materials becomes a fairly attractive structural option in energy absorbing devices, such as crash box and front rail in vehicle. This paper introduces a novel configuration, namely double functionally graded (DFG) structure, which comprises of a functionally graded honeycomb filler in a functionally graded thickness (FGT) tube. Based on the validated finite element (FE) models, a comparative study on the DFG tube, single functionally graded (SFG) tube, and traditional uniform honeycomb filled uniform thickness (H-UT) tube were carried out to explore the crashing behaviors of different structures under multiple load cases. It is found that as crushing displacement increases, DFG structure exhibits superior capacity of energy absorption over other configurations and this trend is positively related to the impact angles. In addition, the comparisons of deformation modes and critical crushing angles clearly indicate that the DFG structure is of better and more stable crashing characteristics, being a crashworthy structure. Following the configurational comparison, further parametric studies on the DFG structures were conducted to explore the effects of tubal thickness range and honeycomb thickness range on the crashworthiness. It is found that the tube thickness range is more important to crashworthiness, which provides a basis for structural optimization.
TL;DR: In this paper, an innovative application for high and ultra-high strength steel material is proposed which enhances the overall behavior of structural elements, and the effect of heat on the material properties of the hybrid section has also been considered.
Abstract: With the increasing application of high strength steel material in industries, there is a high potentiality for taking advantage of the exceptional load-bearing capacities of this material in construction practice. In the present study, an innovative application for high and ultra-high strength steel material is proposed which enhances the overall behavior of structural elements. The high strength and ultra-high strength steel with nominal tensile strengths of 750 MPa and 1250 MPa, respectively, are proposed to be utilized as tube elements welded to corners of mild steel plates shaping an innovative hybrid section. This section takes advantage of the combined material properties of the two constituting elements in terms of strength, local buckling behavior and ductility. Large-scale tests and numerical analysis have been conducted to compare the behavior of the proposed sections against conventional welded sections. The effect of heat on the material properties of the hybrid section has also been considered. These effects are included in the finite element modeling of innovative columns where numerical outputs have been verified accordingly.