23.06.14 KB. Ok to add accepted version to spiral, Elsevier says ok while mandate not enforced

Existing cross-section and member buckling test data on CHS were collected;  Numerical simulation was conducted to generate further data on CHS;  New design rules were developed to capture the elasto-plastic behaviour of semi-compact CHS;  Accuracy of the current Eurocode 3 and proposed methods were assessed and compared;  Reliability of the proposed design rules was confirmed through statistical analyses.

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.

This paper explores the use of solid continuum finite elements and shell finite elements in the modelling of the nonlinear plastic buckling behaviour of cylindrical metal tubes and shells under global bending. The assumptions of shell analysis become increasingly uncertain as the ratio of the radius of curvature to the thickness becomes smaller, but the classical literature does not draw a clear line to define when a shell treatment is inappropriate and a continuum model becomes essential. This is a particularly important question for the bending of tubular members, pipelines, chimneys, piles, towers and similar structures. This study is therefore concerned solely with the uniform bending of thin tubes or thick shells which fail by plastic buckling well into the strain-hardening range. The analyses employ finite element formulations available in the commercial software ABAQUS because this is the most widely used tool for parametric research studies in this domain with an extensive and diverse element library. The results are of general validity and are applicable to other finite element implementations. This paper thus seeks to determine the adequacy of a thin or thick shell approximation, taking into account geometric nonlinearity, complex equilibrium paths, limit points and bifurcation buckling, extensive material ductility and linear strain hardening. It aims to establish when it is viable to employ shell elements and when this decision will lead to outcomes that lack sufficient precision for engineering design purposes. Sciences, 74, 143-153. DOI: http://dx.doi.org/10.1016/j.ijmecsci.2013 continuum elements to model tubes in bending is found to become increasingly uneconomical as the R/t ratio rises above 25 with reduced advantages over shell elements, both in terms of the accuracy of the solution and the computation time.

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

analysis of a tall metal wind turbine support tower with realistic geometric imperfections. Earthquake Engineering and Structural Dynamics, 46(2), pp. 201-219. doi: 10.1002/eqe.2785 This is the accepted version of the paper.This version of the publication may differ from the final published version. Permanent AbstractThe global growth in wind energy suggests that wind farms will increasingly be deployed in seismically active regions, with large arrays of similarly-designed structures potentially at risk of simultaneous failure under a major earthquake. Wind turbine support towers are often constructed as thin-walled metal shell structures, wellknown for their imperfection sensitivity, and are susceptible to sudden buckling failure under compressive axial loading.This study presents a comprehensive analysis of the seismic response of a 1.5 MW wind turbine steel support tower modelled as a near-cylindrical shell structure with realistic axisymmetric weld depression imperfections. A selection of twenty representative earthquake ground motion records, ten 'near-fault' and ten 'far-field', was applied and the aggregate seismic response explored using lateral drifts and total plastic energy dissipation during the earthquake as structural demand parameters.The tower was found to exhibit high stiffness, though global collapse may occur soon after the elastic limit is exceeded through the development of a highly unstable plastic hinge under seismic excitations. Realistic imperfections were found to have a significant effect on the intensities of ground accelerations at which damage initiates and on the failure location, but only a small effect on the vibration properties and the response prior to damage. Including vertical accelerations similarly had a limited effect on the elastic response, but potentially shifts the location of the plastic hinge to a more slender and therefore weaker part of the tower. The aggregate response was found to be significantly more damaging under near-fault earthquakes with pulse-like effects and large vertical accelerations than far-field earthquakes without these aspects. KeywordsThin metal shell structure, imperfection sensitivity, seismic response, multiple stripe analysis, near-fault ground motions, vertical ground acceleration.

Modern design procedures for steel structures increasingly employ more realistic representations of the stress-strain behaviour of steel rather than a simple ideal elasticplastic. In particular, for buckling failure modes in the plastic range, stresses in excess of the yield stress are always involved, together with a finite post-yield stiffness.Moreover, the 'plastic plateau' in buckling curves for stocky structural members cannot be predicted computationally without a significant strain hardening representation. If a good match is to be sought between experiments and computational predictions in the elastic-plastic zone, strain hardening must be included. Most studies have either used individual laboratory measured stress-strain curves or educated guesswork to achieve such a match, but it is not at all clear that such calculations can reliably be used for safe design since the same hardening properties may not exist in the next constructed structure, or even within a different batch of the same steel grade.A statistical exploration is presented here to assess the reliable magnitudes of postyield properties in common structural grade steels. For simplicity, only two critically important parameters are sought: the length of the yield plateau and the initial strain hardening tangent modulus. These two are selected because they both affect the elastic-plastic buckling of stockier structural elements. The statistical analyses exploit proprietary data acquired over many years of third-party auditing at the Karlsruhe Institute of Technology to explore possible regressed relationships between the postyield properties. Safe lower bounds for the selected properties are determined.

Metal silos used to store granular solids often take the form of a cylindrical shell with an aspect ratio in the range 2 < H/D < 6. It has long been recognised that the most serious load case for all silos is probably the condition of eccentric discharge of its stored solid, but in circular metal silos this is especially true. More failures have occurred under this condition than any other. This high failure rate is chiefly due to the complexity of the pressures exerted by an eccentrically discharging granular material, and the difficulty in understanding the pattern of stresses that develops in a shell wall under such unsymmetrical pressure regimes. The nonsymmetric behaviour of a shell structure under unsymmetrical pressures is not at all well described in the voluminous shell structures literature, and only a few studies have explored the mechanics leading to high local stresses which in turn lead to buckling failure under eccentric discharge.This study follows an earlier initial exploration [26], in which buckling in a moderately slender perfect silo was explored. Here, the work is taken further to explore a very slender structure, and to investigate the imperfection sensitivity of this failure mode. The pressures caused by eccentric discharge are characterised using the new rules of the European Standard EN 1991-4 [5] that defines the Actions in Silos and Tanks. Using this new improved description of unsymmetrical eccentric discharge pressures, it is now possible to perform relatively realistic calculations relating to this common but complicated shell buckling condition. The calculations described here are part of a wider study believed to be the first of its kind and are