Abstract
Conventional seismic design approaches rely on the ability of structures to dissipate the input earthquake energy through inelastic deformations in the designed regions of steel frames, implying substantial structural damage and potential residual drifts after a major earthquake event. Peak response quantities, such as peak story drifts and peak floor accelerations, are typically considered to evaluate the performance of different structural systems under seismic loads. However, several studies have shown that residual drifts, which occur due to the nonlinear behavior of yielding components of a structural system, may hold an important role in defining the performance of a structure after a seismic event and in the evaluation of potential damage. To enhance the seismic performance of structural systems, systems that can provide stable energy dissipation with full self-centering capabilities are desirable. These systems, known as self-centering or re-centering, exhibit a flag-shaped hysteric response with the ability to return to small or zero deformation after each cycle. Such a self-centering system controls structural damage while minimizing residual drifts.
This dissertation proposes a hybrid passive control device and investigates its performance in improving the response of steel frame structures subjected to multi-level seismic hazards. The proposed superelastic viscous damper (SVD) relies on shape memory alloy (SMA) cables for re-centering capability and employs a viscoelastic damper, which consists of two layers of a high damped blended butyl elastomer compound, to augment its energy dissipation capacity. First, the design and behavior of the proposed device are introduced. Then, the influences of various design parameters on the mechanical response of the device are investigated. Numerical models for the SVDs and steel moment frame buildings are developed in a finite element analysis program to determine the dynamic response of the structure to various levels of seismic hazards. The performance of steel structures retrofitted or newly designed with the installed SVDs is explored through nonlinear response history analyses. In addition, the seismic collapse resistance of steel frame buildings with SVDs is comparatively evaluated. The aftershock performance of steel frame buildings, with and without installed SVDs, is also investigated. Next, the effect of the ambient temperature on the performance of the proposed device is assessed. Finally, the seismic loss assessment of steel buildings with and without SVDs is conducted. It shows that steel buildings designed with SVDs have improved seismic performance and post-earthquake functionality.
