Publications
70 results found
Rotter JM, Sadowski AJ, 2017, Development of circular tube slenderness classifications under axial and bending actions, Eurosteel 2017
Wang J, Sadowski AJ, 2017, Buckling of elastic cylindrical shells under symmetric but nonuniform bending moment distributions, Eurosteel 2017
Sadowski AJ, Rotter JM, Ummenhofer T, 2017, On recent characterisations of the post-yield properties of structural carbon steels, Eurosteel 2017
Fajuyitan OK, Sadowski AJ, Wadee MA, 2017, Buckling of very short elastic cylinders with weld imperfections under uniformbending, Steel Construction, Vol: 10, Pages: 216-221, ISSN: 1867-0539
The length-dependent behaviour domains of thin elastic cylindrical shells under uniform bending have recently received significant research attention. Ovalization is known to affect very long cylinders that undergo significant cross-sectional flattening before failing by local buckling. This effect is restrained by the end boundary conditions in shorter cylinders, which instead fail by local buckling at moments close to the classical analytical prediction. In very short cylinders, however, even this local buckling is restrained by the end boundary, and failure occurs instead through the development of a destabilizing meridional fold on the compressed side. Although this is a limit point instability under bending, ovalization does not play any role at all. This ‘very short’ length domain has only recently been explored for the first time with the aid of finite element modelling.A brief overview of the non-linear buckling behaviour of very short elastic cylinders under uniform bending is presented in this paper. Two types of edge rotational restraint are used to illustrate the influence of a varying support condition on the stability in this short length range. It is shown that short cylinders under bending do not suffer at all from local short-wave buckling. Additionally, when the meridional dimension of such cylinders becomes particularly short, the resulting numerical models may predict indefinite stiffening without a limit point, even when the shell is modelled using more complete 3D solid continuum finite elements. Idealized weld depressions, which are realistic representations of a systemic manufacturing defect, are used to demonstrate only a very mild sensitivity to geometric imperfections at such short lengths owing to a pre-buckling stress state dominated by local compatibility bending. The topic should be of interest to researchers studying shell problems dominated by local bending with computational tools and designers of multi-segment shells wi
Sadowski AJ, Fajuyitan OK, Wang J, 2017, A computational strategy to establish algebraic parameters for the Reference Resistance Design of metal shell structures, Advances in Engineering Software, Vol: 109, Pages: 15-30, ISSN: 0965-9978
The new Reference Resistance Design (RRD) method, recently developed by Rotter [1], for the manual dimensioning of metal shell structures effectively permits an analyst working with only a calculator or spreadsheet to take full advantage of the realism and accuracy of an advanced nonlinear finite element (FE) calculation. The method achieves this by reformulating the outcomes of a vast programme of parametric FE calculations in terms of six algebraic parameters and two resistances, each representing a physical aspect of the shell's behaviour.The formidable challenge now is to establish these parameters and resistances for the most important shell geometries and load cases. The systems that have received by far the most research attention for RRD are that of a cylindrical shell under uniform axial compression and uniform bending. Their partial algebraic characterisations required thousands of finite element calculations to be performed across a four-dimensional parameter hyperspace (i.e. length, radius to thickness ratio, imperfection amplitude, linear strain hardening modulus).Handling so many nonlinear finite element models is time-consuming and the quantities of data generated can be overwhelming. This paper illustrates a computational strategy to deal with both issues that may help researchers establish sets of RRD parameters for other important shell systems with greater confidence and accuracy. The methodology involves full automation of model generation, submission, termination and processing with object-oriented scripting, illustrated using code and pseudocode fragments.
Xu Z, Gardner L, Sadowski AJ, 2017, Nonlinear stability of elastic elliptical cylindrical shells under uniform bending, International Journal of Mechanical Sciences, Vol: 128-129, Pages: 593-606, ISSN: 0020-7403
Cylindrical metal shells with elliptical cross-sections are gaining increasing popularity as hollow sections due to their unique aesthetic appearance and different geometric properties about their two principal axes, with one axis exhibiting properties that are significantly more favourable than the other under flexure. However, in comparison with other hollow geometries, elliptical cross-sections have only recently begun receiving significant research attention. This is partly because even simple analytical treatments inevitably encounter cumbersome elliptical integrals that have no closed-form solutions, a problem now attenuated by powerful modern computing capabilities.A recent computational study investigated the nonlinear buckling resistance of perfect elastic circular cylindrical shells under uniform bending, establishing four distinct length-dependent domains of behaviour and characterising these in compact form using specially chosen dimensionless parameters. The present study extends this work to cylinders with elliptical cross-sections under bending about both principal axes. The same qualitative domains of length-dependent nonlinear elastic behaviour are found as for circular cylinders, but requiring a different algebraic characterisation that takes account of the varying elliptical radii. On the basis of computational results, a reference equation for the moment governing the ‘Brazier’ ovalisation cross-sectional failure mode for long elliptical thin-walled cylinders is deduced and presented for publication for the first time.
Sadowski AJ, Rotter JM, Stafford PJ, et al., 2016, On the gradient of the yield plateau in structural carbon steels, Journal of Constructional Steel Research, Vol: 130, Pages: 120-130, ISSN: 0143-974X
New design methodologies are being developed to allow stocky steel members to attain and exceed the full plastic condition. For theoretical validation, such methods require a characterisation of the uniaxial stress-strain behaviour of structural steel beyond an idealised elastic-plastic representation. However, the strain hardening properties of carbon steels are not currently guaranteed by the standards or by any steel manufacturer. Assumptions must thus be made on what values of these properties are appropriate, often based on limited information in the form of individual stress-strain curves. There is very little consistency in the choices made.This paper first illustrates, using an example elastic-plastic finite element calculation, that a stocky tubular structure can attain the full plastic condition at slendernesses comparable with those defined in current standards and supported by experiment when using only a very modest level of strain hardening, initiated at first yield. It is then hypothesised that the yield plateau in the stress-strain curve for structural carbon steels, classically treated as flat and with zero tangent modulus, actually has a small but statistically significant positive finite gradient. Finally, a robust set of linear regression analyses of yield plateau gradients extracted from 225 tensile tests appears to support this hypothesis, finding that the plateau gradient is of the order of 0.3% of the initial elastic modulus, consistent with what the finite element example suggests is sufficient to reproduce the full plastic condition at experimentally-supported slendernesses.
Rotter JM, Sadowski AJ, 2016, Full plastic resistance of tubes under bending and axial force: exact treatment and approximations, Structures, Vol: 10, Pages: 30-38, ISSN: 2352-0124
The full plastic resistance under a combination of bending and axial force of tubes of all possible wall thicknesses, from thin cylinders to circular solid sections, does not ever seem to have been thoroughly studied, despite the fact that this is a relatively simple analysis. The first part of this paper presents a formal analysis of the state of full plasticity under longitudinal stresses in a right circular tube of any thickness free of cross-section distortions. The derivation leads to relatively complicated algebraic expressions which are unsuitable for design guides and standards, so the chief purpose of this paper is to devise suitably accurate but simple empirical descriptions that give quite precise values for the state of full plasticity whilst avoiding the complexity of a formal exact analysis. The accuracy of each approximation is demonstrated. The two limiting cases of a thin tube (cylindrical shell) and circular solid section are shown to be simple special cases. The approximate expressions are particularly useful for the definition of the full plastic condition in tension members subject to small bending actions, but also applicable to all structural members and steel building structures standards, as well as to standards on thin shells where they provide the full plastic reference resistance. These expressions are also useful because they give simple definitions of the orientation of the plastic strain vector, which can assist in the development of analyses of the plastic collapse of arches and axially restrained members under bending.
Shen J, Wadee MA, Sadowski AJ, 2016, Interactive buckling in long thin-walled rectangular hollow section struts, International Journal of Non-Linear Mechanics, Vol: 89, Pages: 43-58, ISSN: 0020-7462
An analytical model describing the nonlinear interaction between global and local buckling modes in long thin-walled rectangular hollow section struts under pure compression founded on variational principles is presented. A system of nonlinear differential and integral equations subject to boundary conditions is formulated and solved using numerical continuation techniques. For the first time, the equilibrium behaviour of such struts with different cross-section joint rigidities is highlighted with characteristically unstable interactive buckling paths and a progressive change in the local buckling wavelength. With increasing joint rigidity within the cross-section, the severity of the unstable post-buckling behaviour is shown to be mollified. The results from the analytical model are validated using a nonlinear finite element model developed within the commercial package Abaqus and show excellent comparisons. A simplified method to calculate the local buckling load of the more compressed web undergoing global buckling and the corresponding global mode amplitude at the secondary bifurcation is also developed. Parametric studies on the effect of varying the length and cross-section aspect ratio are also presented that demonstrate the effectiveness of the currently developed models.
Boyez A, Sadowski AJ, Izzuddin BA, 2016, A novel 'boundary layer' finite element for the efficient analysis of thin cylindrical shells, Computers and Structures, Vol: 182, Pages: 573-587, ISSN: 0045-7949
Classical shell finite elements usually employ low-order polynomial shape functions to interpolate between nodal displacement and rotational degrees of freedom. Consequently, carefully-designed fine meshes are often required to accurately capture regions of high local curvature, such as at the ‘boundary layer’ of bending that occurs in cylindrical shells near a boundary or discontinuity. This significantly increases the computational cost of any analysis.This paper is a ‘proof of concept’ illustration of a novel cylindrical axisymmetric shell element that is enriched with rigorously-derived transcendental shape functions to exactly capture the bending boundary layer. When complemented with simple polynomials to express the membrane displacements, a single boundary layer shell element is able to support very complex displacement and stress fields that are exact for distributed element loads of up to second order. A single element is usually sufficient per shell segment in a multi-strake shell.The predictions of the novel element are compared against analytical solutions, a classical axisymmetric shell element with polynomial shape functions and the ABAQUS S4R shell element in three problems of increasing complexity and practical relevance. The element displays excellent numerical results with only a fraction of the total degrees of freedom and involves virtually no mesh design. The shell theory employed at present is kept deliberately simple for illustration purposes, though the formulation will be extended in future work.
Shen J, Wadee MA, Sadowski AJ, 2016, Local-global mode interaction in box-section struts under axial compression, Coupled Instabilities in Metal Structures, Publisher: CIMS
An analytical model describing the interactive buckling of a thin-walled box-section strut under axial compression, where global buckling is critical, is formulated based on variational principles. A system of nonlinear differential and integral equations subject to boundary conditions are derived and solved using numerical continuation. The results show that when the local buckling load is close to the global buckling load, unstable interactive buckling dominates. Equilibrium behaviour, characterized by the equilibrium paths and the progressive change in local buckling wavelength, is highlighted. The results from the analytical model have been validated using the finite element method in conjunction with the static Riks method and show excellent comparisons.
Sadowski AJ, Camara A, Malaga Chuquitaype C, et al., 2016, Seismic analysis of a tall metal wind turbine support tower with realistic geometric imperfections, Earthquake Engineering & Structural Dynamics, Vol: 46, Pages: 201-219, ISSN: 1096-9845
The global growth in wind energy suggests that wind farms will increasingly bedeployed in seismically active regions, with large arrays of similarly-designedstructures potentially at risk of simultaneous failure under a major earthquake. Windturbine support towers are often constructed as thin-walled metal shell structures, wellknownfor their imperfection sensitivity, and are susceptible to sudden buckling failureunder compressive axial loading.This study presents a comprehensive analysis of the seismic response of a 1.5 MWwind turbine steel support tower modelled as a near-cylindrical shell structure withrealistic axisymmetric weld depression imperfections. A selection of twentyrepresentative earthquake ground motion records, ten ‘near-fault’ and ten ‘far-field’,was applied and the aggregate seismic response explored using lateral drifts and totalplastic energy dissipation during the earthquake as structural demand parameters.The tower was found to exhibit high stiffness, though global collapse may occur soonafter the elastic limit is exceeded through the development of a highly unstable plastichinge under seismic excitations. Realistic imperfections were found to have asignificant effect on the intensities of ground accelerations at which damage initiatesand on the failure location, but only a small effect on the vibration properties and theresponse prior to damage. Including vertical accelerations similarly had a limited effecton the elastic response, but potentially shifts the location of the plastic hinge to a moreslender and therefore weaker part of the tower. The aggregate response was found to besignificantly more damaging under near-fault earthquakes with pulse-like effects andlarge vertical accelerations than far-field earthquakes without these aspects.
Shen J, Wadee MA, Sadowski AJ, 2016, Local–global mode interaction in thin-walled rectangular hollow section struts, EMI/PMC 2016
Shen J, Wadee MA, Sadowski AJ, 2015, Numerical study of interactive buckling in thin-walled section box columns under pure compression, ICASS 2015
Sadowski AJ, Fajuyitan OK, Rotter JM, 2015, A Study of Imperfect Cylindrical Steel Tubes under Global Bending and Varying Support Conditions, 8th International Conference on Advances in Steel Structures (ICASS 2015)
Sadowski AJ, Van Es SHJ, Reinke T, et al., 2015, Harmonic analysis of measured initial geometric imperfections in large spiral welded carbon steel tubes, ENGINEERING STRUCTURES, Vol: 85, Pages: 234-248, ISSN: 0141-0296
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- Citations: 26
Sadowski AJ, Rotter JM, Reinke T, et al., 2015, Analysis of variance of tensile tests from spiral welded carbon steel tubes, CONSTRUCTION AND BUILDING MATERIALS, Vol: 75, Pages: 208-212, ISSN: 0950-0618
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- Citations: 13
Sadowski AJ, Rotter JM, Reinke T, et al., 2015, Statistical analysis of the material properties of selected structural carbon steels, STRUCTURAL SAFETY, Vol: 53, Pages: 26-35, ISSN: 0167-4730
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- Citations: 60
Rotter JM, Sadowski AJ, 2014, Thin Tubular Members Design for Bending: Uniform Bending with Small Axial Loads, Eurosteel 2014
The behaviour of large tubular members under bending and axial load is complex due to the interaction of several nonlinear phenomena, including plasticity, buckling, ovalisation and the influence of geometric imperfections. Such members are currently either designed as a thin tube according to EN 1993-1-1 [1] or as a thick shell according to EN 1993-1-6 [2], depending on the diameter or radius to thickness ratio. But there is currently a very large discrepancy between the predicted design strength from these two standards at the boundary between their two scope limits. There should instead be a smooth transition. The RFCS-funded Combitube research project [3], involving a partnership of several European universities and companies, aims to correct this problem through an extensive programme of experimental and numerical studies.
Reinke T, Sadowski AJ, Ummenhofer T, et al., 2014, Large Scale Bending Tests of Spiral Welded Steel Tubes, Eurosteel 2014
Combined constructions of steel tubes and sheet metal are used as retaining walls where high differences in ground levels have to be secured [1]. Such 'Combiwalls' consist of vertically positioned steel tubes (usually spiral welded) with diameter to thickness ratios in the range d/t = 70 - 100 (d = 800 – 1200 mm) that provide the necessary bending stiffness, together with infill sheeting composed of standard sheet pile profiles (Fig. 1). The experimental and numerical investigation of these thick-walled steel tubes in bending is the main objective of the RFCS-funded Combitube research project, which aims to improve the existing design rules for buckling. The project is a partnership between the Universities of Delft (Netherlands), Thessaly (Greece), Karlsruhe (Germany) and Edinburgh (Scotland) together with the industry partners ArcelorMittal (Luxemburg) and BAM Infraconsult (Netherlands). This paper focuses on large scale bending tests of a set of spiral welded steel tubes that were conducted at the Karlsruhe Institute of Technology (KIT) which aimed to investigate the bearing behaviour of these tubes under a bending moment and axial force. The effect of the geometric imperfections caused by the spiral welding process is investigated and compared with the test results.
Rotter JM, Sadowski AJ, Chen L, 2014, Nonlinear stability of thin elastic cylinders of different length under global bending, International Journal of Solids and Structures, Vol: 51, Pages: 2826-2839, ISSN: 0020-7683
Many thin-walled cylindrical shells are used in structural applications in which the dominant loading condition is global bending. Key examples include chimneys, wind turbine support towers, pipelines, horizontal tanks, tubular piles and silos. The buckling behaviour of these structures in bending is complex due to the coupling between cross-section ovalisation and local bifurcation buckling. Analytical treatments of this problem have a history going back almost a century and still constitute an active and challenging research area.This paper investigates in detail the effect of cylinder length on the nonlinear elastic buckling behaviour of clamped cylindrical tubes under global bending, covering a very wide range of lengths. It is found that the behaviour may be classified into four distinct length-dependent domains with clearly-defined boundaries which have here been assigned the names ‘short’, ‘medium’, ‘transitional’ and ‘long’. Algebraic characterisations of the computed nonlinear moment–length relationships are proposed for design purposes.
Sadowski AJ, Rotter JM, 2014, Modelling and behaviour of cylindrical shell structures with helical features, COMPUTERS & STRUCTURES, Vol: 133, Pages: 90-102, ISSN: 0045-7949
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- Citations: 19
Sadowski AJ, Rotter JM, 2013, Buckling in Eccentrically Discharged Silos and the Assumed Pressure Distribution, JOURNAL OF ENGINEERING MECHANICS, Vol: 139, Pages: 858-867, ISSN: 0733-9399
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- Citations: 5
Sadowski AJ, Rotter JM, 2013, Solid or shell finite elements to model thick cylindrical tubes and shells under global bending, International Journal of Mechanical Sciences
Sadowski AJ, Rotter JM, 2013, On the relationship between mesh and stress field orientations in linear stability analyses of thin plates and shells, Finite Elements in Analysis and Design
Sadowski AJ, Rotter JM, 2013, Exploration of novel geometric imperfection forms in buckling failures of thin-walled metal silos under eccentric discharge, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, Vol: 50, Pages: 781-794, ISSN: 0020-7683
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- Citations: 9
Sadowski AJ, Rotter JM, 2012, Slender thin cylindrical shells under unsymmetrical strip loads, THIN-WALLED STRUCTURES, Vol: 61, Pages: 169-179, ISSN: 0263-8231
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- Citations: 5
Rotter JM, Sadowski AJ, 2012, Cylindrical shell bending theory for orthotropic shells under general axisymmetric pressure distributions, ENGINEERING STRUCTURES, Vol: 42, Pages: 258-265, ISSN: 0141-0296
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- Citations: 17
Sadowski AJ, Rotter JM, 2012, Structural Behavior of Thin-Walled Metal Silos Subject to Different Flow Channel Sizes under Eccentric Discharge Pressures, JOURNAL OF STRUCTURAL ENGINEERING-ASCE, Vol: 138, Pages: 922-931, ISSN: 0733-9445
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- Citations: 9
Sadowski AJ, Rotter JM, 2011, Steel silos with different aspect ratios: I - Behaviour under concentric discharge, JOURNAL OF CONSTRUCTIONAL STEEL RESEARCH, Vol: 67, Pages: 1537-1544, ISSN: 0143-974X
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- Citations: 30
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