Publications
198 results found
Wadee MA, Farsi M, 2014, Local-global mode interaction in stringer-stiffened plates, Thin-Walled Structures, Vol: 85, Pages: 419-430, ISSN: 0263-8231
A recently developed nonlinear analytical model for axially loaded thin-walled stringer-stiffened plates based on variational principles is extended to include local buckling of the main plate. Interaction between the weakly stable global buckling mode and the strongly stable local buckling mode is highlighted. Highly unstable post-buckling behaviour and a progressively changing wavelength in the local buckling mode profile is observed under increasing compressive deformation. The analytical model is compared against both physical experiments from the literature and finite element analysis conducted in the commercial code Abaqus; excellent agreement is found both in terms of the mechanical response and the predicted deflections.
Simão PD, Girão Coelho AM, Wadee MA, 2014, Buckling of a column with random initial geometrical imperfections, The seventh European conference on steel and composite structures (Eurosteel 2014)
Wadee MA, Farsi M, 2014, Cellular buckling in stiffened plates, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 470, ISSN: 1364-5021
An analytical model based on variational principles for a thin-walled stiffened plate subjected to axial compression is presented. A system of nonlinear differential and integral equations is derived and solved using numerical continuation. The results show that the system is susceptible to highly unstable local–global mode interaction after an initial instability is triggered. Moreover, snap-backs in the response showing sequential destabilization and restabilization, known as cellular buckling or snaking, arise. The analytical model is compared to static finite element models for joint conditions between the stiffener and the main plate that have significant rotational restraint. However, it is known from previous studies that the behaviour, where the same joint is insignificantly restrained rotationally, is captured better by an analytical approach than by standard finite element methods; the latter being unable to capture cellular buckling behaviour even though the phenomenon is clearly observed in laboratory experiments.
Wadee MA, Bai L, 2014, Cellular buckling in I-section struts, Thin Walled Structures, Vol: 81, Pages: 89-100, ISSN: 0263-8231
An analytical model that describes the interactive buckling of a thin-walled I-section strut under pure compression based on variational principles is presented. A formulation combining the Rayleigh-Ritz method and continuous displacement functions is used to derive a system of differential and integral equilibrium equations for the structural component. Numerical continuation reveals progressive cellular buckling (or snaking) arising from the nonlinear interaction between the weakly stable global buckling mode and the strongly stable local buckling mode. The resulting behaviour is highly unstable and when the model is extended to include geometric imperfections it compares excellently with some recently published experiments.
Wadee MA, 2014, Sir James Lighthill: A life in waves, 50 visions of mathematics, Editors: Parc, Oxford, Publisher: Oxford University Press, Pages: 160-162, ISBN: 9780198701811
Parc S, 2014, 50 visions of mathematics, Oxford, Publisher: Oxford University Press, ISBN: 9780198701811
Wadee MA, Champneys AR, 2014, Fail safe or fail dangerous?, 50 visions of mathematics, Editors: Parc, Oxford, Publisher: Oxford University Press, Pages: 163-167, ISBN: 9780198701811
Madrazo-Aguirre F, Ruiz-Teran AM, Wadee MA, 2014, Dynamic behaviour of under-deck cable-stayed bridges under the action of moving loads, Pages: 1528-1535
Under-deck cable-stayed bridges are innovative bridge configurations in which stays are located underneath the deck. This bridge typology can lead to highly efficient and slender decks, resulting in a large reduction of the amount of materials employed. Nevertheless, if very slender decks are designed, vibration problems can arise potentially compromising the comfort of bridge users. The dynamic response of an under-deck cable-stayed bridge with a steel-concrete composite deck under the action of moving loads is studied. After an initial modal analysis, the contribution of each mode is identified. Loads applied eccentrically on the cross-section of the deck are found to increase accelerations substantially. Amplification and cancellation speeds are observed to govern the maximum accelerations registered on the deck. A parametric analysis reveals the maximum slendernesses that can be achieved to satisfy different comfort criteria.
Huang X, Hanley KJ, O'Sullivan C, et al., 2014, DEM analysis of the influence of the intermediate stress ratio on the critical-state behaviour of granular materials, Granular Matter, Vol: 16, Pages: 641-655, ISSN: 1434-5021
Bai L, Wadee MA, 2014, Implications of interactive buckling in thin-walled I-section struts, EMI 2014: Engineering Mechanics Institute Conference, McMaster University, Hamilton, Ontario, Canada
Wadee MA, Liu EL, 2014, Analytical modelling of interactive buckling in thin-walled lipped I-section struts, EMI 2014: Engineering Mechanics Institute Conference, McMaster University, Hamilton, Ontario, Canada
McCann F, Wadee MA, Gardner L, 2013, Lateral stability of imperfect discretely braced steel beams, Journal of Engineering Mechanics, Vol: 139, Pages: 1341-1349, ISSN: 0733-9399
The lateral stability of imperfect discretely braced steel beams is analyzed using Rayleigh-Ritz approximations for the lateral deflection and the angle of twist. Initially, it is assumed that these degrees of freedom can be represented by functions comprising only single harmonics; this is then compared with the more accurate representation of the displacement functions by full Fourier series. It is confirmed by linear eigenvalue analysis that the beam can realistically buckle into two separate classes of modes: a finite number of node-displacing modes, equal to the number of restraints provided, and an infinite number of single harmonic buckling modes, where the restraint nodes remain undeflected. Closed-form analytical relations are derived for the elastic critical moment of the beam, the forces induced in the restraints, and the minimum stiffness required to enforce the first internodal buckling mode. The position of the restraint above or below the shear center is shown to influence the overall buckling behavior of the beam. The analytical results for the critical moment of the beam are validated by the finite-element program LTBeam, whereas the results for the deflected shape of the beam are validated by the numerical continuation software AUTO-07p, with very close agreement between the analytical and the numerical results.
Girão Coelho AM, Simão PD, Wadee MA, 2013, Imperfection sensitivity of column instability revisited, Journal of Constructional Steel Research, Vol: 90, Pages: 265-282, ISSN: 0143-974X
The buckling of columns is the classic problem in structural stability. It has been studied by many researchers over a large number of years, and it is well known that the severity of the buckling response can be greatly amplified by initial geometric imperfections in the column shape. The current paper presents and discusses the effects of imperfection shape, orientation and magnitude on the buckling behaviour of columns. Analyses are conducted for elastic columns with overall initial imperfections in the form of out-of-straightness and sway displacements, as well as local imperfections that, for instance, model constructional and material defects. Traditionally, the initial imperfections are modelled with the first buckling mode with a size selected according to fabrication tolerances. This approach will not necessarily provide a lower limit to the column prebuckling stiffness and strength. These assertions are supported by numerical results for imperfection-sensitive columns. The influence of end restraint on column strength is also studied since columns in actual frameworks are connected to other structural members such that their ends are restrained.
, 2013, Design by inelastic analysis – 2010 AISC specification, Research and Applications in Structural Engineering, Mechanics and Computation, Publisher: CRC Press, Pages: 475-476
Osofero AI, Wadee MA, Gardner L, 2013, Numerical studies on the buckling resistance of prestressed stayed columns, Advances in Structural Engineering, Vol: 16, Pages: 487-498, ISSN: 1369-4332
The structural behaviour of prestressed stayed columns is investigated through nonlinear finite element modelling. The models were developed using the commercial software ABAQUS and validated against a series of recently conducted experiments. The sensitivity of the load-carrying capacity to the geometry of the stayed column, the initially applied prestress level within the stays and the initial global imperfection is investigated through parametric studies. It is found that there is a substantial increase in load-carrying capacity with increasing cross-arm length, provided the critical buckling mode remains symmetric. Once the critical buckling mode becomes antisymmetric, mode interaction becomes significant and the load-carrying capacity reaches a plateau and the component generally becomes more sensitive to imperfections. It is also found that the relative level of initial prestress required to maximize the load-carrying capacity of a given stayed column tends to reduce with increasing cross-arm length.
Wadee MA, Gardner L, Osofero AI, 2013, Design of prestressed stayed columns, Journal of Constructional Steel Research, Vol: 80, Pages: 287-298, ISSN: 0143-974X
General design procedures for prestressed stayed columns with a single cross-arm system are presented. The accuracy of the proposed design expressions is confirmed by comparison with the results of physical experiments and validated finite element simulations. Reliability is assessed by following the approach set out in Annex D of EN 1990. The presented resistance expressions for prestressed stayed columns are a function of the system geometry, the level of initial prestress in the cables and the global imperfection level. Worked examples are also presented to illustrate the application of the developed design approach.
McCann F, Gardner L, Wadee MA, 2013, Design of steel beams with discrete lateral restraints, Journal of Constructional Steel Research, Vol: 80, Pages: 82-90, ISSN: 0143-974X
Discrete lateral restraints offer an effective means of stabilising beams against lateral-torsional buckling. Design expressions for simply-supported beams braced regularly along their span with elastic restraints, based on analytically-derived formulae, are presented herein. These include the minimum restraint stiffness required to force the beam to buckle in between the restraint nodes and the forces induced in the restraints, along with a brief treatment of the critical moment of the beam. It is demonstrated that there is close agreement between the values obtained from the design formulae and their original analytical counterparts. These are also compared with the results from design formulae based on analogous column behaviour, an approach commonly used in design codes. It is found that the column rules used by design codes return values that, when compared with the results of the current analysis, are overly conservative for cases where the restraints are positioned at the compression flange of the beam but unsafe for restraints positioned at the shear centre.
Wadee MA, Bai L, Camotim D, et al., 2013, Behaviour of I-section columns experiencing local-global mode interaction: Analytical and finite element modelling, 5th International Conference on Structural Engineering, Mechanics and Computation, Pages: 1249-1254
An extension of recent work on the local-global buckling mode interaction in thin-walled I-section columns is presented. The results obtained from an analytical model based on variational principles, which describes the column nonlinear buckling behaviour, are compared with those yielded by finite element analyses from the commercial software ANSYS. The comparisons are good and this provides encouragement to advance the understanding of the complex instability phenomena associated with nonlinear modal interactions.
O'Sullivan C, Wadee MA, Hanley KJ, et al., 2013, Use of DEM and elastic stability analysis to explain the influence of the intermediate principal stress on shear strength, Geotechnique, Vol: 63, Pages: 1298-1309, ISSN: 0016-8505
One interesting aspect of soil response is the sensitivity of the mechanical behaviour to the intermediate principal stress. In this study, a fundamental mechanism that explains the influence of the intermediate stress ratio (b) on soil shear strength is proposed. Prior experimental, numerical and analytical studies have indicated that soil failure occurs when the strong force chains that transmit stress through the material buckle. These strong force chains are networks of contacting particles that are relatively highly stressed and aligned in the direction of the major principal stress. The buckling resistance is thought to be determined by “weaker” lateral networks of less-stressed contacting particles that are orthogonal to the strong force chain orientation. Discrete Element Method (DEM) simulations of true triaxial tests show that as b is varied, so too is the relative support provided by the force chains orientated in the directions of the intermediate and minor principal stresses. At a macro-scale, the effective axial stiffnesses along these directions vary. The DEM dataset is complex and so a conceptually simple model is used to assess the influence of lateral support on the buckling resistance of a single column of connected nodes, analogous to a single force chain. The lateral support is modelled using linear springs. When the stiffnesses of these springs are selected to reflect the variation in axial stiffness with b observed in the DEM simulations, the reduction in axial buckling load with b is found to be similar to the reduction in major principal stress with b. When combined, the DEM data and simple analytical model support a hypothesis that failure under three-dimensional stress conditions is determined by buckling of the strong force chains. It is the variation in lateral support provided by the force network aligned along the minor and intermediate stress directions that determines, in part at least, the relation between soil shear str
Yiatros S, Wadee MA, Völlmecke C, 2013, Modelling of interactive buckling in sandwich struts with functionally graded cores, ASCE Journal of Engineering Mechanics, Vol: 139, Pages: 952-960, ISSN: 0733-9399
An analytical pilot model for interactive buckling in sandwich struts with cores made from a functionally graded material based on total potential energy principles is presented. Using a Timoshenko beam approach, a system of nonlinear differential and integral equations is derived that predicts critical and secondary instabilities. These are validated against numerical simulations performed within the commercial finite-element package Abaqus. Good agreement is found, and this offers encouragement for more elaborate models to be devised that can account for face-core delamination—a feature where functionally graded materials are known to offer distinct advantages.
Wadee MA, Farsi M, 2013, Analytical modelling of cellular buckling in stiffened plates, Northwestern University, Evanston, Illinois, USA, EMI 2013: Engineering Mechanics Institute Conference
Wadee MA, Gardner L, 2012, Cellular buckling from interactive buckling in thin-walled I-section beams, Sixth International Conference on Coupled Instabilities in Metal Structures – CIMS 2012. 3rd-5th December, 2012, 223-230.
McCann F, Wadee MA, Gardner L, 2012, Lateral stability of steel beams with discrete restraints, Sixth International Conference on Coupled Instabilities in Metal Structures – CIMS 2012. 3rd-5th December, 2012, 247-254.
Wadee MA, Hunt TA, Gardner L, 2012, Analytical modelling of mode jumping in the buckling of prestressed stayed columns, Tubular Structures XIV, Pages: 663-670, ISBN: 9780415621373
Prestressed stayed columns, typically comprising tubular cross-sections, offer an innovative solution where designs demand long and slender elements under compression. The cross-arms and pretensioned cables provide additional and significant lateral support to the columns that results in a marked increase of the buckling capacity. Recent finite element analysis has indicated that these structural components are likely to exhibit interactive buckling phenomena, particularly if the critical buckling mode is antisymmetric, leading to highly unstable responses. A simplified model, comprising discrete rigid-links and springs, is presented that is designed to mimic the post-buckling response of a prestressed stayed column. The results from the present model reveal similar behaviour to that observed in the earlier finite element study when certain combinations of spring stiffnesses are used. A sequence of bifurcations are found that switch the post-buckling response from one mode to another via a path of mixed modes and the effects of the sudden slackening of the cable stays is discussed.
Ellen ME, Gosaye J, Gardner L, et al., 2012, Design and construction of long-span post-tensioned tubular steel structures, Tubular Structures XIV, Pages: 687-693, ISBN: 9780415621373
The design of long-span post-tensioned tubular steel structures in which steel cables are housed within the hollow profiles is outlined from fundamental principles. Treatment of the structural form as a planar catenary is discussed and then extended to three dimensional shell structures. The effect of post-tensioning on the behaviour of individual members is examined through numerical and analytical modelling. The influence of the bonding material between the post-tensioned cable and tubular casing is discussed, since this is crucial to the performance of these structures. The construction methodology is outlined and examples of implemented structures spanning up to 120 m are presented.
Ellen ME, Gosaye J, Gardner L, et al., 2012, Design and construction of long span post-tensioned tubular steel structures, London, UK, ISTS-14: 14th International Symposium on Tubular Structures (ISTS-14), Pages: 687-693
Wadee MA, Yiatros S, Haley JF, et al., 2012, Geometric modelling of kink banding instabilities in composite laminates, University of Notre Dame, Notre Dame, Indiana, USA, EMI/PMC 2012: Joint Conference of the Engineering Mechanics Institute
Wadee MA, 2012, Interactive buckling in structural components: Analytical modelling, Graz, Austria, ESMC 2012: 8th European Solid Mechanics Conference
Yiatros S, Völlmecke C, Wadee MA, 2012, Advances in the mechanical modelling of interactive buckling in sandwich structures, University of Notre Dame, South Bend, USA, EMI/PMC 2012: Joint Conference of the Engineering Mechanics Institute
Osofero AI, Wadee MA, Gardner L, 2012, Experimental study of critical and post-buckling behaviour of prestressed stayed columns, Journal of Constructional Steel Research, Vol: 79, Pages: 226-241, ISSN: 0143-974X
A full scale experimental investigation into the strength and behaviour of prestressed steel stayed columns in compression has been conducted. Results, including full load versus end-shortening curves, for a total of 18 test specimens are presented. Two critical modes of buckling — symmetric and antisymmetric — with interactive post-buckling are demonstrated experimentally and the imperfection sensitivity of the stayed columns is investigated. Interactive buckling is observed primarily when the individual buckling loads of the antisymmetric and symmetric modes are close or when the antisymmetric mode is critical. Analysis of the results reveals that increased prestress leads to an increased load-carrying capacity when instability occurs in the symmetric mode, but the reverse trend is found when the antisymmetric mode is critical.
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