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Nonlinear stability of prestressed stayed beam-columns

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Title: Nonlinear stability of prestressed stayed beam-columns
Authors: Wu, Kaidong
Item Type: Thesis or dissertation
Abstract: Slender struts supported with prestressed cable-stays in conjunction with periodically-spaced crossarms distributed longitudinally, offer an attractive, innovative and pragmatic solution to reducing structural self-weight while maintaining buckling strength. The use of the crossarm--stay system generally results in a higher load-carrying capacity. Previous research has been primarily conducted for vertical stayed members, but there is a potential demand for very long struts to be used in the horizontal plane. Hence, the current thesis investigates the buckling and post-buckling behaviour of stayed beam-columns where the axial load and the self-weight act orthogonally to each other. Mechanical modelling is employed to determine the zones of behaviour in the stayed beam-column. Two of the existing three zones for vertical stayed columns are each sub-divided into two further sub-zones owing to self-weight. It is found that there is considerable post-buckling reserve especially at relatively higher prestressing levels, and the arrangement where the upper crossarm is shorter than the lower crossarm has a beneficial effect in some cases. A nonlinear analytical model for prestressed stayed beam-columns with doubly-symmetric and mono-symmetric configurations, based on the Rayleigh--Ritz method, is subsequently presented. It captures modal interactions for perfect geometries explicitly. It is also found that the varying prestressing levels and crossarm length ratios can lead to different buckling modes. From the obtained insight, finite element models are then employed to investigate the post-buckling behaviour including pre-cambering, imperfection and prestressing sensitivities. The actual optimum prestressing force is determined considering ultimate behaviour and efficiency indicators. It is found that mono-symmetric cases are more sensitive to the level of pre-cambering than doubly-symmetric cases, and for cases with upward pre-cambering, mono-symmetric arrangements perform better than their doubly-symmetric counterparts. Moreover, recommended upper and lower limits on prestressing levels are presented. Finally, a set of design equations is proposed based on the findings, such that stayed beam-columns may be used safely in practice.
Content Version: Open Access
Issue Date: Jun-2020
Date Awarded: Nov-2020
URI: http://hdl.handle.net/10044/1/89788
DOI: https://doi.org/10.25560/89788
Copyright Statement: Creative Commons Attribution NonCommercial NoDerivatives Licence
Supervisor: Wadee, Mohammad Ahmer
Gardner, Leroy
Sponsor/Funder: China Scholarship Council
Department: Civil and Environmental Engineering
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Civil and Environmental Engineering PhD theses



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