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Journal articleZaharie DZ, Phillips ATM, 2018, , Journal of Biomechanical Engineering, Vol: 140, Pages: 1-11, ISSN: 0148-0731
The pelvic construct is an important part of the body as it facilitates the transfer of upper body weight to the lower limbs and protects a number of organs and vessels in the lower abdomen. In addition, the importance of the pelvis is highlighted by the high mortality rates associated with pelvic trauma. This study presents a mesoscale structural model of the pelvic construct and the joints and ligaments associated with it. Shell elements were used to model cortical bone, while truss elements were used to model trabecular bone and the ligaments and joints. The finite element (FE) model was subjected to an iterative optimization process based on a strain-driven bone adaptation algorithm. The bone model was adapted to a number of common daily living activities (walking, stair ascent, stair descent, sit-to-stand, and stand-to-sit) by applying onto it joint and muscle loads derived using a musculoskeletal modeling framework. The cortical thickness distribution and the trabecular architecture of the adapted model were compared qualitatively with computed tomography (CT) scans and models developed in previous studies, showing good agreement. The sensitivity of the model to changes in material properties of the ligaments and joint cartilage and changes in parameters related to the adaptation algorithm was assessed. Changes to the target strain had the largest effect on predicted total bone volumes. The model showed low sensitivity to changes in all other parameters. The minimum and maximum principal strains predicted by the structural model compared to a continuum CT-derived model in response to a common test loading scenario showed good agreement with correlation coefficients of 0.813 and 0.809, respectively. The developed structural model enables a number of applications such as fracture modeling, design, and additive manufacturing of frangible surrogates.
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Journal articleBai L, Wang F, Wadee MA, et al., 2017, , Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 473, Pages: 1-22, ISSN: 1364-5021
A variational model that describes the interactive buckling of a thin-walled equal-leg angle strut under pure axial compression 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. Solving the equations using numerical continuation reveals progressive cellular buckling (or snaking) arising from the nonlinearinteraction between the weak-axis flexural buckling mode and the strong-axis flexural-torsional buckling mode for the first time - the resulting behaviour being highly unstable. Physical experiments conducted on 10 cold-formed steel specimens are presented andthe results show good agreement with the variational model.
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Journal articleLapira L, Wadee MA, Gardner L, 2017, , Structures, Vol: 12, Pages: 227-241, ISSN: 2352-0124
Prestressed stayed columns have an enhanced resistance to buckling through the effective use of crossarms and pretensioned stays when compared to conventional columns. An analytical derivation of the minimum, linear optimum and maximum initial pretension forces for configurations of prestressed stayed columns with multiple crossarms and additional stays is presented for the first time. The findings are validated through comparisons with finite element models developed in the commercial package ABAQUS. The influence of the initial pretension on the load-carrying capacity of the configurations considered is also analysed, providing insight into the actual optimum initial pretension force for the configurations accounting for the significance of geometric nonlinearities.
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Journal articleYu J, Wadee MA, 2017, , International Journal of Non-Linear Mechanics, Vol: 88, Pages: 47-66, ISSN: 1878-5638
Prestressed stayed columns are an innovative type of structural system where the compressive load-carrying capacity can be enhanced through prestressed external cable stays. A nonlinear analytical model for prestressed stayed columns with multiple crossarm systems along the column length, based on the Rayleigh Ritz method, is presented that capture modal interactions for perfect geometries explicitly for the first time. It is demonstratedcthat the theoretical compressive strength enhancements under certain configurations canconly be obtained at the expense of triggering a sequence of destabilizing bifurcations. This can give rise to dangerously unstable interactive post-buckling behaviour inluding so-called "mode jumping" and "snaking" phenomena. Parametric spaces where the system is most susceptible to the modal interactions are identified and it is for those configurations that the system is likely to be highly sensitive to initial imperfections. The model is validated using a nonlinear nite element model formulated within the commercial code ABAQUS and excellent comparisons are obtained.
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Conference paperLakin MR, Phillips A, 2017, , 23rd International Conference on DNA Computing and Molecular Programming (DNA), Publisher: SPRINGER INTERNATIONAL PUBLISHING AG, Pages: 1-16, ISSN: 0302-9743
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Journal articleLi P, Wadee MA, Yu J, et al., 2016, , Journal of Constructional Steel 91桃色, 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.
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