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PhD Dissertation Defense

Event Date/Time
Event Location
3546D EB
Speaker
Mansour Turki M Alturki
Event Description
PhD Defense

ABSTRACT

ENERGY DISSIPATION FROM ELASTIC INSTABILITIES OF COSINE-CURVED DOMES

FOR SEISMIC PROTECTION IN REINFORCED CONCRETE STRUCTURES

By

Mansour Turki M Alturki

Advisor – Prof. Rigoberto Burgueño

December 12, 2019

Time: 2:00 pm – 4:00 pm

Room 3546D, Engineering Building

            Conventional seismic design is based on designing structures to resist the imposed seismic loads within their inelastic range of response. This requires the structures to undergo large permanent deformations. Although this design strategy usually satisfies safety requirements, the economic aspects are not usually met due to extensive irreparable damage to the structures in case of strong ground motion. Therefore, research trends are now focused on satisfying safety requirements as well as making structures operational immediately after an earthquake. This has led to the development of new and innovative systems of seismic structural protection that aim to minimize seismic energy input and to localize demands in replaceable or elastic elements. Several supplemental passive energy dissipation devices have been developed to achieve this goal. However, they possess some performance shortcomings such as the requirement of repair or replacement and the significant increase in the initial stiffness of the host structural system.

            In this research, a new self-centering energy dissipation system that relies on elastic instabilities is proposed as a damping mechanism in structures resisting seismic actions. The system is composed of serially connected multistable cosine-curved domes (CCD) featuring snap-through instability. The system exhibits a hysteretic response via the generation of multiple consecutive snap-through buckling events. Numerical studies and experimental tests were conducted on the geometric and material properties of individual CCD units and on a system of units proposed to examine the force-displacement and energy dissipation characteristics. Finite element analyses (FEA) were performed to: (1) study the controlling geometric and material properties of the CCD to characterize the snap-through response, and (2) simulate the hysteretic response of the system to develop a multilinear analytical model, which was used to study the energy dissipation characteristics of the system. Experimental tests were conducted on 3D printed CCD units and system specimens to: (1) validate the FEA model of the units, and (2) to analyze the system and validate the analytical model. Good agreement was observed using the developed relations for the CCD response and the analytical model with the results from FEA and experimental tests. Results show that the energy dissipation of the system mainly depends on the number and the apex height-to-thickness ratio of the CCD units.

            The damping characteristics of the proposed system were investigated to facilitate the direct displacement-based seismic design of structures incorporating such systems as the main damping mechanism to dissipate seismic energy. Time-history analyses of linear and nonlinear single degree of freedom systems were performed to compare spectral displacements and the equivalent viscous damping (EVD) ratios of the hysteretic response of the system to their substitute linear systems in terms of maximum displacements. A set of 62 ground motion records were considered for the analysis. A statistical study was conducted on the resulting displacements and the EVD ratios to develop expressions for EVD ratios of the hysteretic response. Results show that using proposed EVD ratios for the substitute linear systems yield good approximation for the peak spectral displacements compared to the original nonlinear systems. Finally, the seismic performance of typical reinforced concrete structures incorporating the proposed system in various configurations was evaluated. Direct displacement-based design and nonlinear time-history analyses of example structures subjected to two historic ground motion records were conducted. The modified structures using the proposed system showed an enhanced seismic response compared to the original structures by increasing damping and eliminating damage.