Publications
198 results found
Wadee MA, Gardner L, 2012, Cellular buckling from mode interaction in thin-walled I-section beams, 6th International conference on coupled instabilities in metal structures, Pages: 223-230
Wadee MA, Bai L, 2012, Cellular buckling from mode interaction in thin-walled I-section columns, 6th International conference on coupled instabilities in metal structures, Pages: 327-334
McCann F, Wadee MA, Gardner L, 2012, Lateral stability of discretely-braced steel beams, 6th International conference on coupled instabilities in metal structures, Pages: 247-254
Yiatros S, Wadee MA, 2012, Investigating mode interaction and localization in sandwich beam-columns, 6th International conference on coupled instabilities in metal structures, Pages: 619-626
Sato M, Wadee MA, Iiboshi K, et al., 2012, Buckling patterns of complete spherical shells filled with an elastic medium under external pressure, International Journal of Mechanical Sciences, Vol: 59, Pages: 22-30, ISSN: 0020-7403
The critical buckling characteristics of hydrostatically pressurized complete spherical shells filled with an elastic medium are demonstrated. A model based on small deflection thin shell theory, the equations of which are solved in conjunction with variational principles, is presented. In the exactformulation, axisymmetric and inextensional assumptions are not used initially and the elastic medium is modelled as a Winkler foundation, i.e., using uncoupled radial springs with a constant foundation modulus that is independent of wave numbers of shell buckling modes. Simplified approximations based on a Rayleigh-Ritz approach are also introduced for critical buckling pressure and mode number with a considerable degree of accuracy. Characteristic modal shapes are demonstrated for a wide range of material and geometric parameters. A phase diagram is established to obtain the requisite thickness to radius, andstiffness ratios for a desired mode profile. The present exact formulation can be readily extended to apply to more general cases of non-axisymmetric buckling problems.
Wadee MA, Völlmecke C, Haley JF, et al., 2012, Geometric modelling of kink banding in laminated structures, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 370, Pages: 1827-1849, ISSN: 1364-503X
An analytical model founded on geometric and potential energy principles forkink band deformation in laminated composite struts is presented. It is adaptedfrom an earlier successful study for confined layered structures which wasformulated to model kink band formation in the folding of geological layers.The principal aim is to explore the underlying mechanisms governing the kinkingresponse of flat, laminated components comprising unidirectional compositelaminae. A pilot parametric study suggests that the key features of themechanical response are captured well and that quantitative comparisons withexperiments presented in the literature are highly encouraging.
Wadee MA, Gardner L, 2012, Cellular buckling from mode interaction in I-beams under uniform bending, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 468, Pages: 245-268, ISSN: 1364-5021
Beams made from thin-walled elements, whilst very efficient in terms of the structural strength and stiffness to weight ratios, can be susceptible to highly complex instability phenomena. A nonlinear analytical formulation based on variational principles for the ubiquitous I-beam with thin flanges under uniform bending is presented. The resulting system of differential and integral equations are solved using numerical continuation techniques such that the response far into the post-buckling range can be portrayed. The interaction between global lateral-torsional buckling of the beam and local buckling of the flange plate is found to oblige the buckling deformation to localize initially at the beam midspan with subsequent cellular buckling (snaking) being predicted theoretically for the first time. Solutions from the model compare very favourably with a series of classic experiments and some newly conducted tests which also exhibit the predicted sequence of localized followed by cellular buckling.
Wadee MA, Bai L, 2012, Interactive buckling of thin-walled I-section columns, Dubrovnik, Croatia, CST 2012: 11th International Conference on Computational Structures Technology, Publisher: Civil-Comp Press, ISSN: 1759-3433
Wadee MA, Hunt TA, Gardner L, 2012, Analytical modelling of mode jumping in the buckling of prestressed stayed columns, London, UK, ISTS-14: 14th International Symposium on Tubular Structures, Pages: 663-670
Wadee MA, Yiatros S, 2011, Discussion: "On interactive buckling in a sandwich structure" by C. D. Coman, Z ANGEW MATH PHYS, Vol: 62, Pages: 183-188, ISSN: 0044-2275
A recent article by Coman (Z Angew Math Phys 2009) on the response of compression sandwich struts made some claims on the quality of the simplified version of the interactive buckling model presented in Hunt and Wadee (Proc R Soc A 454(1972):1197–1216, 1998). Some of these claims are examined in detail herein; it is concluded that great care must be exercised when performing parametric studies with equations that have been derived from simplifying a mechanical model. This is because the resulting system of equations does not necessarily describe the original mechanical system in full, since the key assumptions necessarily change.
Sato M, Wadee MA, Sekizawa T, et al., 2011, Hydrostatically pressurized buckling of complete spherical shells filled with an elastic medium, J JSCE Ser. A2 (Appl Mech (AM)), Vol: 67, Pages: I_15-I_22, ISSN: 1345-9139
The critical buckling characteristics of hydrostatically pressurized complete spherical shells filled with an elastic medium are presented. A model based on small deflection thin shell theory, the equations of which are solved using exact methods in conjunction with variational principles, is presented. In the current formulation, axisymmetric and inextensional assumptions are not used initially and the elastic medium is modelled as a Winkler foundation, i.e.using uncoupled radial springs with a constant foundation modulus that is independent of wave numbers of shell buckling modes. Critical buckling pressures and characteristic modal shapes are demonstrated for a wide range of material and geometric parameters. A phase diagram is established to obtain the requisite thickness to radius, and stiffness ratios for a desired mode profile. The present formulation can be readily extended to apply to more general cases of non-axisymmetric buckling problems.
Wadee MA, Gardner L, Hunt TA, 2011, Mode jumping in prestressed stayed columns: A spring and link model approach, Rome, Italy, ENOC 2011: 7th European Nonlinear Dynamics Conference, Publisher: European Mechanics Society
A simplified model comprising discrete rigid-links and springs is presented that aims to mimic the post-buckling response of a prestressed stayed column. A recent finite element study showed that interactive buckling was only a significant issue when higher modes become critical, although the model parameters driving this behaviour were not obvious. The results of the current pilot study reveal a similar behaviour 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.
Wadee MA, Gardner L, 2011, Localization and cellular buckling in I-beams under uniform bending, Rome, Italy, ENOC 2011: 7th European Nonlinear Dynamics Conference, Publisher: European Mechanics Society
Beams comprising thin-walled elements, while highly structurally efficient, are susceptible to complex instability phenomena. The interaction between global lateral-torsional buckling and local buckling of a flange plate suggests that failure will localize towards midspan. A variational formulation, leading to a pair of nonlinear differential equations subject to integral constraints, describes the post-buckling response. These are solved by numerical continuation techniques, such that the response far into the unstable postbuckling range can be portrayed and cellular buckling is theoretically predicted. Solutions from the model compare very favourably with some newly conducted tests which also exhibit the theoretically predicted sequence of localization followed by cellular buckling.
Wadee MA, Völlmecke C, 2011, Semi-analytical modelling of buckling driven delamination in uniaxially compressed damaged plates, IMA J APPL MATH, Vol: 76, Pages: 120-145, ISSN: 0272-4960
A geometrically nonlinear model is developed to investigate the buckling behaviour of plates with a pre-existing delamination under uniaxial compression. The Rayleigh-Ritz procedure, based on trigonometric out-of-plane displacement functions, is used in conjunction with potential energy principles to describe the buckling and postbuckling response. The formulation is enhanced with the introduction of a discrete cohesive zone model to allow the delamination to grow under further loading. Different cases are investigated with residual capacities of the plates being evaluated in the neighbourhood of a transitional depth of delamination, where the postbuckling behaviour changes from thin- film to mixed mode to global buckling. The model isvalidated with the commercial finite element code Abaqus and criteria are proposed such that the component may be exploited beyond the critical loads.
Völlmecke C, Yiatros S, Wadee MA, 2011, Modelling the nonlinear elastic instability phenomena of laminated composite panels and sandwich structures, Boston, USA, EMI2011: ASCE/EMI Conference
Yiatros S, Wadee MA, 2011, Interactive buckling in sandwich beam-columns, IMA J APPL MATH, Vol: 76, Pages: 146-168, ISSN: 0272-4960
Recent work on localized buckling with different core bending theories in sandwich struts is adapted for a sandwich beam-column that combines the effects of bending and compression. The two distinct bifurcations present in the pure compression case are replaced by a single pitchfork bifurcation point that combines local and global buckling behaviour. Several models with a various number of degrees of freedom (DOFs) are developed to account for the explicit effect of end moments. All models are formulated using total potential energy and variational principles, which are used to derive the governing equations that are solved using the numerical continuation package Auto97. Results are validated with a finite element model formulated in the commercial package Abaqus. Comparisons with the interactive buckling profiles and the mechanical response in the nonlinear range are very favourable and the models with more DOFs are determined to be superior.
Saito D, Wadee MA, 2010, Optimal prestressing and configuration of stayed columns, P I CIVIL ENG-STRUCT BUILD, Vol: 163, Pages: 343-355, ISSN: 0965-0911
A steel column that is reinforced by prestressed stays generally has an increased strength in axial compression. In the past, greater emphasis was placed on obtaining its higher critical buckling load. However, detailed knowledge of the post-buckling behaviour is important to ensure the safety and the efficiency of the structure. Although previous work revealed that the optimal design should be determined with the post-buckling response, the actual values of the optimal prestress had not been previously evaluated. The present work examines the issue of the true optimal prestress for stayed columns through proposed structural optimisation indicators involving both instability and material quantity measures. Nonlinear finite element analysis was performed to investigate the nonlinear buckling behaviour, which gives values for these indicators. Through a comparison of these values, suggestions for the configurations for improving the structural efficiency are presented.
Wadee MA, Yiatros S, Theofanous M, 2010, Comparative studies of localized buckling in sandwich struts with different core bending models, INT J NONLIN MECH, Vol: 45, Pages: 111-120, ISSN: 0020-7462
Analytical models with geometric non-linearities accounting for interactions between local and global instability modes leading to localized buckling in sandwich struts are formulated. For the core material response, two increasingly sophisticated bending models are compared against each other: Timoshenko beam theory (TBT) and Reddy–Bickford beam theory (RBT). Numerical solutions of the analytical models are validated with the commercial finite element code ABAQUS. It is found that there is a small but significant difference in the critical load between the two models and that the previously obtained solution slightly underestimates the linear buckling strength. More importantly, it is found that the RBT model predicts the onset of interactive buckling before the TBT model and, according to the results from the finite element study, matches the actual behaviour of a strut in both its initial and advanced post-buckling states with excellent correlation.
Völlmecke C, Wadee MA, 2010, Residual capacities of uniaxially compressed composite panels under buckling driven delamination, London, SEMC 2010: 4th International Conference on Structural Engineering, Mechanics and Computation, Publisher: CRC Press, Pages: 537-540
Yiatros S, Wadee MA, 2010, Localized buckling in sandwich beam-columns, London, SEMC 2010: 4th International Conference on Structural Engineering, Mechanics and Computation, Publisher: CRC Press, Pages: 523-527
Wadee MA, Saito D, 2009, Interactive buckling in prestressed stayed columns, Singapore, ASCCS 2009: 9th International Conference on Steel, Concrete, Composite and Hybrid Structures, Publisher: Research Publishing Services, Pages: 690-696
Völlmecke C, Wadee MA, 2009, Buckling driven delamination in uniaxially compressed composite panels, International conference on computational and experimental engineering and sciences
Wadee MA, 2009, Nonlinear instabilities in sandwich construction and composite materials, Reflections in nonlinear mechanics, Publisher: Bath Institute for Complex Systems
Wadee MA, Völlmecke C, 2009, Analytical modelling of buckling driven delamination in composite plates, Blacksburg, USA, The joint ASCE-ASME-SES conference on mechanics and materials, Pages: 113-114
Wadee MA, Yiatros S, Theofanous M, 2009, Effects of core models in the interactive buckling of sandwich struts, Blacksburg, USA, The joint ASCE-ASME-SES conference on mechanics and materials, Pages: 123-124
Saito D, Wadee MA, 2009, Buckling behaviour of prestressed steel stayed columns with imperfections and stress limitation, ENG STRUCT, Vol: 31, Pages: 1-15, ISSN: 0141-0296
A steel column that is reinforced by prestressed stays, generally has an increased strength in axial compression. In the past, greater emphasis was placed on obtaining a higher critical buckling load. However, detailed knowledge of the post-buckling behaviour is important to ensure the safety and efficiency of the structure. The current work examines the buckling behaviour of a stayed column with geometrical imperfections, and stress limitation relating to possible material failure. A geometrically nonlinear model accounting for imperfect buckling behaviour of a stayed column was formulated using the Rayleigh–Ritz method, and then validated, using the finite element method. It is shown from these studies that the system tends to be most sensitive to imperfections at a prestress level that yields the highest critical load, and that the real maximum load capacity seems to increase as the prestress increases with a given configuration. The findings suggest that the optimal prestress should be greater than that found from using the previous convention that was based on linear analysis.
Saito D, Wadee MA, 2009, Numerical studies of interactive buckling in prestressed steel stayed columns, ENG STRUCT, Vol: 31, Pages: 432-443, ISSN: 0141-0296
A steel column that is reinforced by prestressed stays generally has an increased strength in axial compression. In the past, greater emphasis was placed on obtaining its higher critical buckling load. However, detailed knowledge of the post-buckling behaviour is important to ensure the safety and the efficiency of the structure. Although a few studies into the post-buckling behaviour exist, interactive buckling behaviour has never been investigated. As interactive buckling can lead to more dangerous instabilities, the current work examines this for the most popular stayed column configuration using nonlinear finite element analysis. It is shown that interactive buckling becomes the worst case, with a commensurate decrease in the maximum load capacity, where a higher mode governs the critical buckling response.
Gardner L, Chan TM, Wadee MA, 2008, Shear response of elliptical hollow sections, Proceedings of the Institution of Civil Engineers: Structures and Buildings., Vol: 161, Pages: 301-309, ISSN: 0965-0911
Following the introduction of hot-finished elliptical hollow sections to the construction industry, recent research has been performed to develop supporting structural design guidance. This paper focuses on shear resistance. Twenty-four shear tests were performed on hot-finished steel elliptical hollow section members. The shear tests were arranged in a three-point bending configuration with span-to-depth ratios ranging from 1 to 8. This enabled the study of cross-section resistance in shear and the interaction between shear and bending. Measurements were taken of cross-section geometry, local initial geometric imperfections and material properties in tension. Test results, including moment-rotation histories, are presented. Additional results were generated numerically. These results have been used to verify proposed design expressions for shear resistance and resistance to combined shear and bending. Further investigations into design criteria for shear buckling are currently under way.
Völlmecke C, Wadee MA, 2008, Nonlinear buckling of uniaxially compressed delaminated composite panels, 2nd international conference on buckling and postbuckling behaviour of composite laminated shell structures with COCOMAT workshop, Publisher: COCOMAT
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