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Abstract

Considerable damages to structural and non-structural components in building structures are persistently observed in the aftermath of several recent major seismic events, incurring downtime and disproportionally high economic losses in well-populated areas. These earthquake consequences highlight the need for widening the use of passive seismic protective devices, such as viscous fluid dampers (FVDs) and dynamic vibration absorbers (DVAs), in newbuilt and in existing structures to enhance seismic building performance beyond the one achieved by ductility-based earthquake resistant design approaches adopted by current seismic codes of practice. To this end, in recent years, the concept of the inerter, a lightweight device resisting relative acceleration through the inertance property, has been heavily considered in the scientific literature to improve the seismic building response mitigation capacity of FVDs and DVAs, giving rise to new promising classes of inerter-based seismic protective devices, such as the linear tuned mass damper inerter (TMDI). This thesis makes significant contributions to this body of research through novel analytical and numerical work by proposing innovative practically advantageous TMDI-based device configurations, leveraging nonlinear device/component behavior for enhanced seismic response mitigation in buildings and underpinned by simplified, yet theoretically rigorous, optimal device tuning approaches accounting for nonlinear device behavior.

First, the potential for seismic protection of buildings of a nonlinear TMDI (NTMDI) featuring a FVD with nonlinear power law force-velocity relationship, commonly encountered in commercial FVDs, is compared vis-à-vis the conventional linear TMDI. This is facilitated by a practicable and computationally efficient optimal NTMDI tuning approach which accounts for any NTMDI connectivity to the building structure, modelled as a linear single-mode dynamical system, and employs statistical linearization to treat the nonlinear damping term assuming stationary random ground acceleration excitation. Response history analysis results for a benchmark 9-storey steel building with optimally tuned NTMDI demonstrate that reduced NTMDI stroke and inerter force are achieved with negligible change in peak storey drifts and floor acceleration responses under recorded ground motions by lowering the FVD exponent, leading to practically advantageous NTMDI deployments.

Next, an innovative top-floor (N)TMDI configuration in conjunction with top-storey seismic isolation, implemented by standard nonlinear elastomeric bearings, is introduced termed nonlinear isolated roof-top TMDI (IR-TMDI). The IR-TMDI leverages the localized top floor softening, enabled by the isolation layer, to potentially enhance the seismic vibrations mitigation capacity of the TMDI throughout the elevation of multi-storey buildings, applicable to new and existing building structures. A simplified statistical linearization-based approach is devised for optimal IR-TMDI tuning under stationary random colored seismic excitations compatible with a given design/response spectrum, accounting for the nonlinearity of the isolation layer, modelled through a Bouc-Wen force-deformation hysteretic law, and of the FVD. Different IR-TMDI tuning criteria are considered, and it is shown that maximization of energy dissipation by the FVD yields a well-balanced and practically advantageous performance vis-a-vis minimization of structural displacement and acceleration response criteria in terms of TMDI and isolation layer force and deformation demands. Comprehensive response history analysis results pertaining to a 3-storey and a 9-storey steel benchmark structures with optimally tuned IR-TMDIs of various nonlinear isolation layer and FVD properties, exposed to well-populated sets of far-field, near-fault non-pulse, and near-fault pulse-like recorded earthquakes are examined to assess the seismic response mitigation potential of the IR-TMDI. It is found that reduced storey drifts and floor acceleration demands along the buildings’ height are achieved by increasing the flexibility of the roof-top isolation layer (i.e. post-yielding period). Further, by lowering the nonlinear FVD exponent, reduced IR-TMDI displacement demands (i.e. TMDI stroke and isolators’ deflection) and improved robustness of seismic storey drifts and floor acceleration demands to record-to-record variability is achieved.

Overall, the herein reported numerical data demonstrate a remarkable effectiveness of the herein conceived NTMDI and IR-TMDI configurations in controlling RMS and peak response along the full building height, even for the flexible 9-storey benchmark building under near-fault pulse-like excitations. This is despite the low fidelity modeling of the earthquake excitation description (i.e. stationary random excitation) of the structural behavior (i.e. single-mode and linear) and of the seismic performance quantification (i.e. second-order stationary response statistics) adopted in the optimal tuning of the absorbers, purposely assumed to promote practicable easy-to-use design tools, attractive to both practitioners and researchers. This consideration suggests that even more favorable seismic response mitigation performance of the proposed nonlinear inerter-based vibration absorbers may be anticipated by adopting more refined models in the optimal tuning of the absorbers as well as by extending both the optimization-driven design to include the properties of the isolation layer and the assessment to account for severe excitations leading to nonlinear structural behavior.

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

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