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Damage-avoidance self-centring steel rocking frames

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Title: Damage-avoidance self-centring steel rocking frames
Authors: Kibriya, Leena
Item Type: Thesis or dissertation
Abstract: This thesis investigates the dynamic behaviour of rocking steel frames that employ gap-opening mechanisms at the column-foundation and beam-column connections to avoid inelastic deformations under lateral loads. Current realizations of these structures incorporate supplementary energy-dissipation elements aimed at providing control against large demands. Therefore, they rely largely on yielding components that accumulate damage during strong dynamic action. Although the provision of yielding devices in rocking frames can improve their seismic performance in certain conditions, it obscures the understanding of their complex and unconventional nonlinear dynamics. Besides, sacrificial yielding components often result in systems with permanent post-earthquake deformations that require non-negligible labor in terms of replacement, re-centring and repair. To address these shortcomings, this thesis starts by investigating the complex non-linear dynamics of pure rocking frames and proposes a Finite Element modelling framework that accurately represents their behaviour over a wide range of excitation frequencies and amplitudes. The methodology, applied to multi-storey steel frames, captures the presence of sub-harmonic resonances and higher-modes. Additional demands due to the asymmetric member boundary conditions are identified in the rocking columns. The knowledge gained is then applied to develop a novel damage-avoidance solution that utilizes the controlled plastic buckling of tape-spring elements with curved cross-sections, often used as components of deployable spacecraft structures. Glass-Fibre Reinforced Polymer is selected as the material due to its high strength-to-weight ratio, elastic buckling properties, and geometric design flexibility. A numerical simulation protocol for the bracing members is developed and a comprehensive parametric study is presented. It is demonstrated that the system performs successfully under static and discrete sine-sweep loads for single-bay one and three-storey rocking frames. These concepts are extended to realistic multi-storey multi-bay rocking buildings. The performances of the proposed systems are compared to conventional steel moment frames. The buildings are subjected to a series of static load cycles, discrete sine-sweep ground motions, and earthquake records (using Incremental Dynamic Analysis). It is thereby demonstrated that Buckling-enabled Bracing enhances the static, non-linear dynamic, and seismic performance of rocking buildings by significantly reducing the member forces and response quantities. The fragility curves demonstrate that rocking frames equipped with BECB (or BEB) exhibit lower probabilities of exceedance for storey drifts and accelerations, than conventional moment frames. Subsequently, these findings are summarized and future research areas are discussed.
Content Version: Open Access
Issue Date: Dec-2020
Date Awarded: Apr-2021
URI: http://hdl.handle.net/10044/1/97616
DOI: https://doi.org/10.25560/97616
Copyright Statement: Creative Commons Attribution NonCommercial Licence
Supervisor: Málaga-Chuquitaype, Christian
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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