Publications
198 results found
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.
Liu EL, Wadee MA, 2016, Geometric factors affecting I-section struts experiencing local and strong-axis global buckling mode interaction, Coupled Instabilities in Metal Structures, Publisher: CIMS
A recent analytical model describing the post-buckling behaviour of an I-section strut experiencing strong axis global–local buckling interaction is extended to investigate the effects of modifying the strut geometry. Using a combination of analytical and finite element (FE) methods, the global slenderness is varied parametrically to determine the regions of interactive behaviour. The effects of stress relieved initial global imperfections are also investigated. It is observed that the strut can exhibit one of five distinctive post-buckling behaviours, the geometries for which are identified. The strut can exhibit local buckling only, global buckling only, global–local buckling interaction with either the global or the local buckling mode being triggered first, or the critical case where both global and local buckling modes are triggered simultaneously. The strut is found to be highly sensitive to initial imperfections in the interactive region, and the implications that this has on the design and the practical use of such components are discussed.
Wadee MA, Yu J, 2016, Mode jumping and snaking in prestressed stayed columns, Metz, France, 2016 EMI International Conference, Publisher: University Press of Universite de Lorraine, Metz, France, Pages: 308-308
Bai L, Wadee MA, 2016, Slenderness effects in thin-walled I-section struts susceptible to local-global mode interaction, Engineering Structures, Vol: 124, Pages: 128-141, ISSN: 0141-0296
A variational model that describes the nonlinear interaction between the global and local buckling of a thin-walled I-section strut under pure compression is presented and subsequently exploited. A parametric study is conducted for two limiting cases, where the flange–web joint is assumed to be pinned or rigid. For a chosen set of geometries, the most undesirable parametric spaces are identified for both global and local slendernesses, in terms of the strut length and the flange width respectively, where highly unstable behaviour is observed in the post-buckling range. Practical implications are discussed in terms of the idealized design strength relationship.
Yu J, Wadee MA, 2016, Nonlinear mechanics of prestressed stayed columns with multiple bays, Boca Raton, USA, 6th International Conference on Structural Engineering, Mechanics and Computation, Publisher: CRC Press, Pages: 257-263
Liu EL, Wadee MA, 2016, Imperfection sensitivity of I-section struts experiencing local and strong-axis global buckling mode interaction, Boca Raton, USA, 6th International Conference on Structural Engineering, Mechanics and Computation, Publisher: CRC Press, Pages: 732-737
Wadee MA, Madrazo-Aguirre F, Li P, et al., 2016, Analytical modelling of structural components and systems vulnerable to interactive buckling: Recent developments, Boca Raton, USA, 6th International Conference on Structural Engineering, Mechanics and Computation, Publisher: CRC Press, Pages: 220-226
Shen J, Wadee MA, Sadowski AJ, 2016, Local–global mode interaction in thin-walled rectangular hollow section struts, EMI/PMC 2016
McCann F, Wadee MA, Gardner L, 2016, Harmonic analysis of elliptical hollow section tubes in bending, EMI/PMC 2016
Liu EL, Wadee MA, 2016, Mode interaction in perfect and imperfect thin-walled I-section struts susceptible to global buckling about the strong axis, Thin-Walled Structures, Vol: 106, Pages: 228-243, ISSN: 0263-8231
A recently developed analytical model for a perfect I-section strut experiencing a nonlinear interaction between local buckling and global buckling about the strong axis is enhanced and subsequently extended. The initial enhancement is achieved by devising a simplified and calibrated model that provides an improved prediction of the local buckling load. A purely numerical model is then constructed within the commercial finite element (FE) software Abaqus for validation purposes and excellent comparisons are observed, demonstrating that the analytical model is considerably improved on previous work. The model for interactive buckling is then developed subsequently to include the effects of global and local geometric imperfections, which are introduced individually and in combination. The strut is found to be sensitive to all considered shapes of imperfection and the combined imperfection case correlates excellently with an equivalent FE model, particularly in the neighbourhood of the secondary instability that leads to mode interaction. This demonstrates that the enhanced analytical model predicts the actual load carrying capacity and the structural mechanics accurately.
Li P, Wadee MA, Yu J, et al., 2016, Stability of prestressed stayed steel columns with a three branch crossarm system, Journal of Constructional Steel Research, Vol: 122, Pages: 274-291, ISSN: 1873-5983
Analytical and numerical investigations of the stability of prestressed stayed columns with three crossarms branching laterally and symmetrically are presented. It is shown that modal symmetry is broken automatically if the critical mode is antisymmetric, which distinguishes it from the stayed columns studied hitherto. The governing imperfection distribution that should be adopted within finite element analysis to capture the actual load-carrying capacity is also obtained. The findings suggest that when the critical buckling mode is symmetric, the governing imperfection distribution should also be symmetric. Conversely, if the critical buckling mode is antisymmetric, a symmetric imperfection distribution or an asymmetric imperfection distribution may be adopted as the most severe imperfection distribution depending on the system characteristics. This would enable designers to determine an accurate prediction of the actual strength through nonlinear finite element analysis.
Gosaye J, Gardner L, Wadee MA, et al., 2016, Compressive behaviour and design of prestressed steel elements, Structures, Vol: 5, Pages: 76-87, ISSN: 2352-0124
Zschernack C, Wadee MA, Völlmecke C, 2016, Nonlinear buckling of fibre-reinforced unit cells of lattice materials, Composite Structures, Vol: 136, Pages: 217-228, ISSN: 1879-1085
Truss-based lattice materials are cellular materials with an outstanding potential for multi-functional use. This is owing to properties of high compressive strength to density ratios combined with a periodic and open structure. However, such structures at low relative densities are particularly vulnerable to elastic buckling failure. Fibre-reinforcement that increases the buckling strength of lattice materials is proposed and the behaviour of unit cells that are tessellated within the lattice is investigated. A two-dimensional square orientated unit cell and a three-dimensional tetrahedron-shaped unit cell are both modelled discretely using energy principles with the nonlinear interactive buckling behaviour being analysed. The analytical approach, based on a perturbation method, exhibits excellent agreement for the mechanical response when compared to results from numerical continuation for moderately large displacements. A fundamental understanding of the mechanical behaviour of a unit cell can be upscaled in future work. It is postulated that this will enable the determination of the constitutive behaviour of such lattice materials.
Bai L, Wadee MA, 2015, Imperfection sensitivity of thin-walled I-section struts susceptible to cellular buckling, International Journal of Mechanical Sciences, Vol: 104, Pages: 162-173, ISSN: 0020-7403
A variational model that describes the nonlinear interaction between global and local buckling of an imperfect thin-walled I-section strut under pure compression is developed. An initial out-of-straightness of the entire strut and an initial local out-of-plane displacement in the flanges are introduced as a global and a local type of imperfection respectively. A system of differential and integral equilibrium equations is derived for the structural component from variational principles, an approach that was previously validated. Imperfection sensitivity studies focus on cases where the global and local critical loads are similar. Numerical results reveal that the strut exhibiting cellular buckling (or ‘snaking’) is highly sensitive to both types of imperfections. The worst forms of local imperfection are identified in terms of the initial wavelength, amplitude and degree of localization and these change with the generic imperfection size and highlight the potential dangers of unsafe predictions of actual load-carrying capacity.
Yiatros S, Marangos O, Wadee MA, et al., 2015, Localized buckling in sandwich struts with inhomogeneous deformation in both face plates, Composite Structures, Vol: 133, Pages: 630-641, ISSN: 1879-1085
A nonlinear analytical model for investigating localized interactive buckling in simply supported thin-face plate sandwich struts with weak cores is extended to account for local deformations in both face plates, which have been observed in experiments and finite element simulations. The original model is based on potential energy principles with large displacement assumptions. It assumes Timoshenko shear deformable theory for the core and approximates the overall mode as a half-sine wave along the length of the strut while the local face plate displacements are initially unknown and are found as solutions of the governing equations. The extended model is able to capture measurable local face plate displacements in the less compressed face plate, beyond the secondary bifurcation which leads to localized interactive buckling, for the case where overall buckling is critical. Moreover, the allowance of local displacements in both face plates allows the extended model to predict the post-buckling behavior better in cases where local buckling is critical. The results from this model compare very well with nonlinear finite element simulations with respect to both the equilibrium paths and panel deformations.
Madrazo Aguirre F, Wadee MA, Ruiz-Teran AM, 2015, Non-linear stability of under-deck cable-stayed bridge decks, International Journal of Non-Linear Mechanics, Vol: 77, Pages: 28-40, ISSN: 1878-5638
The stability of comparatively more slender decks of under-deck cable-stayed bridges is studied, by considering both the critical loads and the post-buckling behaviour. A potential energy approach is applied to a simplified discrete link and spring model that allows for an exact nonlinear formulation of the equilibrium equations. The physical response is found to be dependent on the ratio of the axial stiffness of the cable-staying system to the flexural stiffness of the deck. The influence of several parameters is analysed and unstable mode interaction is observed to occur under certain geometric conditions. The presented analytical model is compared with a nonlinear finite element model that shows good correlation. Finally, some design criteria and recommendations are suggested, which are relevant for designers of this innovative typology of cable-stayed bridges.
Madrazo-Aguirre F, Ruiz-Teran AM, Wadee MA, 2015, Dynamic behaviour of steel-concrete composite under-deck cable-stayed bridges under the action of moving loads, Engineering Structures, Vol: 103, Pages: 260-274, ISSN: 0141-0296
The dynamic response of under-deck cable-stayed bridges with steel–concrete composite decks under moving loads is presented, and different parameters are considered. The vibrational modes with a strong contribution in the response, the key parameters that control the modal frequencies, and those that reduce the maximum accelerations registered on the deck in a cost-effective manner, are identified. It is found that relatively high accelerations occur and that these can be increased by large load eccentricities. It is also found that maximum accelerations are conditioned by the amplification and cancellation speeds of the loads. Increasing the depth of the deck is determined to be the most effective way to reduce the maximum accelerations. Decks formed by I-beams seem to be quite appropriate from the perspective of dynamic behaviour, while box sections tend to increase the overall cost of the bridge. The findings provide effective strategies to define the most efficient configurations that satisfy the limit state of vibrations, which is critical for this type of bridge.
Liu EL, Wadee MA, 2015, Interactively induced localization in thin-walled I-section struts buckling about the strong axis, Structures, Vol: 4, Pages: 13-26, ISSN: 2352-0124
A variational model describing the behaviour of a thin-walled I-section strut suffering from local–global buckling mode interaction is presented where global (Euler) buckling about the strong axis is the critical mode. A system of differential and integral equations is derived that describe the equilibrium states from variational principles and are solved numerically using the continuation and bifurcation software Auto-07p for the perfect case. Initially stress relieved out-of-straightness imperfections are subsequently introduced and the nonlinear response is modelled. The modelled interaction is between the critical global buckling mode about the strong axis and local buckling in the flange and web simultaneously, where the flange–web joint is assumed to be free to rotate as a rigid body. The initial eigenmode is shown to be destabilized at a secondary bifurcation where interactive buckling is triggered. A progressive change in the buckling mode is then observed, initially with local buckling localizing at the mid-span of the compression flange, which also triggers sympathetic local buckling in the web. The results from the analytical model have been validated using the commercial finite element (FE) software Abaqus with good comparisons presented for the initial post-buckling behaviour. The strut also exhibits sensitivity to initial out-of-straightness imperfections, with a notable decrease in the ultimate load as the imperfection size increases. The ultimate loads for a range of imperfection amplitudes are found using both analytical models and FE analysis, with very good correlation observed.
Wadee MA, 2015, Review of "Vibration analysis and structural dynamics for civil engineers" by Alphose Zingoni
Wadee MA, Farsi M, 2015, Imperfection sensitivity and geometric effects in stiffened plates susceptible to cellular buckling, Structures, Vol: 3, Pages: 172-186, ISSN: 2352-0124
An analytical model for axially loaded thin-walled stringer stiffened plates based on variational principles is exploited to study the sensitivity to initial geometric imperfections and the effects of altering geometric properties. Studies on different forms of global and local imperfections indicate that the post-buckling response governs the worst case imperfections. The investigation also focuses on the effect of changing the global and the local slendernesses on the post-buckling behaviour. The parametric space in which the stiffened plates are imperfection sensitive and susceptible to highly unstable cellular buckling is identified.
Yu J, Wadee MA, 2015, Numerical and analytical studies of prestressed stayed columns with multiple cross-arms, ICASS 2015
Liu EL, Wadee MA, 2015, Mode interaction of global and local buckling in thin-walled I-section struts with rigid flange-web joints, Eighth International Conference on Advances in Steel Structures (ICASS) 2015
A variational model describing the behaviour of a thin-walled I-section compression membersuffering from local–global buckling mode interaction is presented. Using the Rayleigh–Ritz methodcombined with displacement functions, a system of differential and integral equations is derived to describethe equilibrium states of the strut. In the present work, the interaction is between the criticalglobal (Euler) buckling mode about the weak axis and local buckling in the flange and web simultaneously,where the flange to web connection is assumed to be free to rotate as a rigid body. The initialeigenmode is shown to be destabilized at a secondary bifurcation where interactive buckling is triggered.A progressive change in the buckling mode is then observed, initially with local buckling in the compressionflange. Owing to the nature of the flange to web connection, this also triggers local buckling inthe web, which displaces in sympathy with the flange. The results from the analytical model have beenvalidated using the commercial finite element software ABAQUS, with good comparisons presented forthe post-buckling behaviour.
Shen J, Wadee MA, Sadowski AJ, 2015, Numerical study of interactive buckling in thin-walled section box columns under pure compression, ICASS 2015
Yu J, Wadee MA, 2015, Analytical studies of prestressed stayed columns with multiple cross-arms, EMI 2015
Wadee MA, Gardner L, Hunt TA, 2015, Buckling mode interaction in prestressed stayed columns, Proceedings of the Institution of Civil Engineers - Structures and Buildings, Vol: 166, Pages: 403-412, ISSN: 0965-0911
Prestressed stayed columns offer an innovative and aesthetically attractive solution where designs demand long and slender elements under compression. The addition of cross-arms and pretensioned cables to the columns provide significant lateral and rotational support that can result in a marked increase of the buckling capacity. The current work presents a simplified model, comprising discrete rigid-links and springs with a mathematically exact formulation including the destabilizing effect of cable slackening, which mimics the response of stayed columns and reveals the governing physical parameters that drive the behaviour. A recent finite element study had 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. However, by its very nature, that study could not reveal the bifurcational structure of the equilibrium response. The results from the present model reveal similar behaviour to that observed in the earlier finite element study. A sequence of bifurcations is found that switch the post-buckling response from one mode to another via a path of interactive buckling.
Madrazo-Aguirre F, Ruiz-Teran AM, Wadee MA, 2015, Design criteria of under-deck cable-stayed bridges for short and medium spans, Structural Engineering International, Vol: 25, Pages: 125-133, ISSN: 1016-8664
Under-deck cable-stayed bridges are innovative bridge schemes that can lead to lightweight and highly efficient construction. However, the design of slender bridges may be governed by the vibrations under traffic live loads. After a historical review of bridges with under-deck cable-staying systems and the consequent research, the dynamic response of medium- and short-span bridges is analysed. Eccentric traffic loads are shown to increase accelerations considerably, and the second vertical mode is found to be the main contributor to the response. A parametric study shows the strong influence of resonance effects in the maximum accelerations registered on the deck. In addition, under-deck cable-staying systems are found to be more appropriate for medium-span than for short-span bridges from the dynamic viewpoint. Moreover, for medium spans, much more slender decks can be achieved compared with conventional bridges without cable-staying systems. Finally, some design criteria are provided that may be useful for structural designers.
Hanley KJ, O'Sullivan C, Wadee MA, et al., 2015, Use of elastic stability analysis to explain the stress-dependent nature of soil strength, Royal Society Open Science, Vol: 2, ISSN: 2054-5703
The peak and critical state strengths of sands are linearly related to the stress level, just as the frictional resistance to sliding along an interface is related to the normal force. The analogy with frictional sliding has led to the use of a ‘friction angle’ to describe the relationship between strength and stress for soils. The term ‘friction angle’ implies that the underlying mechanism is frictional resistance at the particle contacts. However, experiments and discrete element simulations indicate that the material friction angle is not simply related to the friction angle at the particle contacts. Experiments and particle-scale simulations of model sands have also revealed the presence of strong force chains, aligned with the major principal stress. Buckling of these strong force chains has been proposed as an alternative to the frictional-sliding failure mechanism. Here, using an idealized abstraction of a strong force chain, the resistance is shown to be linearly proportional to the magnitude of the lateral forces supporting the force chain. Considering a triaxial stress state, and drawing an analogy between the lateral forces and the confining pressure in a triaxial test, a linear relationship between stress level and strength is seen to emerge from the failure-by-buckling hypothesis.
Bai L, Wadee MA, 2015, Mode interaction in thin-walled I-section struts with semi-rigid flange-web joints, International Journal of Non-Linear Mechanics, Vol: 69, Pages: 71-83, ISSN: 0020-7462
A recently developed variational model that describes the nonlinear interaction between the global and local buckling of a thin-walled I-section strut under pure compression is extended to include semi-rigid flange--web connections. 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. Cellular buckling, observed in the case where the web is assumed to provide no more than a simple support to the flanges, is found to be rapidly eroded by increasing the connection rigidity, although the local buckling wavelength still reduces as the post-buckling deformation is increased. The model is validated using finite element analysis; the results compare very well particularly when a high rigidity between the section web and flanges is simulated.
Madrazo-Aguirre F, Ruiz-Teran AM, Wadee MA, 2015, Nonlinear behaviour of under-deck cable-stayed bridges with steel-concrete composite decks, Pages: 542-549
The effect of geometric nonlinearities in the response of under-deck cable-stayed bridges with steel-concrete composite decks is studied. Influence lines for deflections and bending moments at different sections of the deck are obtained, and these are found to be different to those for conventional bridges. Nonlinearities affect principally the response of lateral subspans, in which both deflections and bending moments are amplified. The permanent state should be studied by taking nonlinearities into account. Deflections under further loads can be obtained with linear models. Geometric nonlinear effects increase design bending moments under ultimate loads by 12% when compared with linear models. Some additional design criteria for designers aiming to design under-deck cable-stayed bridges are hence provided.
Gosaye J, Gardner L, Wadee MA, et al., 2014, Tensile performance of prestressed steel elements, Engineering Structures, Vol: 79, Pages: 234-243, ISSN: 0141-0296
Prestressed steel trusses can offer efficient structural solutions for long span applications such as aircraft hangars, stadia and warehouses. In the current study, the tensile behaviour of prestressed steel elements, which comprise tubular steel members with internal prestressing cables, is investigated. The stability of the elements under prestress and the load–deformation response of the prestressed elements to the subsequent application of tensile loading are examined analytically, numerically and experimentally, with good correlation achieved between the three approaches. The benefits of prestressing, in terms of increased member strength and stiffness, are demonstrated, and optimal prestress levels are investigated.
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