City Research Online

Abstract

Whilst sufficient to achieve life safety performance by meeting the no-collapse requirements, the conventional ductility-based design approach for earthquake-resistant building structures may incur disproportionally high downtime and economic loss in well-populated areas in the event of major seismic events. Thus, there is scope to develop practicable passive seismic energy dissipation device setups to mitigate the risk of earthquake-induced structural damage in new-built and existing buildings. In recent years, inerter devices, resisting relative acceleration through the inertance property, have been considered in the scientific literature to develop promising setups of passive lightweight seismic protective devices, such as the tuned mass damper inerter (TMDI), for earthquake response mitigation of buildings. This thesis, makes novel contributions to this line of research by proposing novel practicable TMDI setups from a structural and architectural viewpoint, leveraging local structural soft-storey design to enhance the TMDI seismic motion mitigation capability, while maintaining linear structural behaviour. Comprehensive analytical and numerical work is undertaken to demonstrate the improved level of seismic building protection vis-à-vis conventional TMD(I) setups using simplified structural models to support parametric studies, as well as detailed finite element (FE) models of case-study real-life structures.

First, a comprehensive review of previous TMD(I) setups, highlighting their performance
limitations and setting the stage for exploring novel advantageous inerter (TMDI)-based
seismic protective setups. Then, a novel linear soft-top-floor TMDI setup is proposed, which circumvents the practical drawbacks of previous TMDI configurations, including requirements for spanning several floors or for utilising nonlinear partial seismic isolation. Using a simplified single-mode structural model that explicitly considers the stiffness of the top-floor, an optimal soft-top-floor TMDI tuning problem is formulated assuming design response spectrum compatible stochastic seismic excitation and numerically solved in state-space. A parametric numerical study is undertaken demonstrating that a soft top story significantly improves structural single-mode performance by reducing peak and RMS structural displacements and accelerations.

Further parametric studies are undertaken adopting multi-modal structural models pertaining to multi-storey shear frame buildings, allowing for comparisons of the herein proposed optimally tuned soft-top-floor TMDI setup vis-à-vis TMDI configurations installed across more than one floor. Moreover, the performance of the soft-top-floor TMDI setup is numerically assessed using response history analysis results for spectrum compatible ground motions for a real-life 11-story modern residential building in Kathmandu, Nepal. This is based on a high-fidelity FE model of the structure, provided by the structural design office. The results indicate substantial improvements in seismic performance, confirming the effectiveness of the proposed TMDI setup for a range of easy-to-accommodate local structural modifications for top-floor flexibility.

Additionally, the potential of soft-ground-floor TMDI setup is explored, for the seismic
protection of a landmark 200m tall reinforced concrete residential tower designed for a high-seismicity area according to the current Eurocode 8. The effectiveness of the proposed TMDI setup is compared to the case of a conventional top-floor TMD. It is found that the proposed inerter-based device setup yields base shear reductions of about 15%, without requirements for a large top-floor suspended mass posed by the conventional TMD. It is thus concluded that ground-floor TMDI provides a viable solution for improving the seismic vulnerability of high-rise buildings designed to have a soft ground story.

Overall, the provided numerical data demonstrate the effectiveness of the herein conceived linear TMDI setups to mitigate the seismic demands and the design seismic loads in multi-storey buildings with a purposely designed soft-story. Further, the explored setups prioritise practical feasibility and cost-effectiveness while promoting enhanced seismic safety and structural resilience to seismic hazard. Although the study is primarily analytical, the proposed TMDI reduces the required attached mass significantly compared to traditional TMDs. This can directly translate to lower construction costs and the low attached mass stroke makes the solution more practicable for high-rise buildings. It is thus envisioned that this thesis paves the way of bringing inerter-based vibration absorbers one step closer to practical implementation.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > T Technology (General) T Technology > TA Engineering (General). Civil engineering (General) T Technology > TH Building construction
Departments:	School of Science & Technology > Department of Engineering School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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