Title

Numerical study of a hybrid re-centering viscous fluid energy dissipative device for seismic protection

Date of Award

December 2014

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

Advisor(s)

Eric M. Lui

Keywords

frame re-centering, nonlinear time history analysis, performance-based seismic design, shape memory alloys, Steel moment resisting frames, viscous fluid damper

Subject Categories

Engineering

Abstract

A hybrid re-centering viscous fluid (RCVF) energy dissipative device is proposed and numerically evaluated in this thesis. Based on the results of a series of nonlinear analyses, performance characteristics of a series of multi-story frames are discussed, and design guidelines for implementing the device in moment resisting frames (MRF) are provided.

In performance-based seismic design, peak and residual displacements are important performance indices that engineers can use to evaluate the performance and damage level of a structure. Steel MRF are commonly used for buildings, but they tend to develop large peak and residual displacements in severe earthquakes. Many performance enhancing devices such as viscous fluid damper, metallic yield damper, and buckling restrained braces have been studied and proposed over the years to enhance the performance of MRF. Although these devices can reduce the peak response of MRF, they are not capable of re-centering MRF that have experienced inelastic deformations. The proposed hybrid RCVF device has both energy dissipation and re-centering capabilities to improve the overall performance of MRF.

The hybrid RCVF device comprises two parts: shape memory alloy (SMA) wires and a viscous fluid (VF) damper. Due to their superelasticity effect, the SMA wires are able to provide the necessary re-centering capability even when the structure has deformed into the inelastic range. On the other hand, the viscous fluid damper can absorb seismic energy transmitted to the structure, thus increasing its equivalent damping ratio which in turn helps to reduce its peak deformation. The hybrid RCVF device can be mounted on top of supporting braces in the form of inverted Chevron brace or connected directly to the core wall as part of a link beam.

Nonlinear static and time history analyses are conducted on a series of shear frames and MRF to demonstrate the effectiveness of the proposed hybrid RCVF device in structural re-centering and seismic energy dissipation. The frames are modeled using finite element method incorporating beam-column elements with geometric and material nonlinearities. The SMA wires are modeled with an established constitutive model, and the viscous fluid damper is modeled using a linear Maxwell model. The performance of the proposed hybrid RCVF device is compared with other energy dissipative devices in the numerical analyses. The results suggest that the hybrid RCVF can be very effective in reducing peak and residual deformations of MRF.

Design guidelines are proposed to facilitate the implementation of the hybrid RCVF device in MRF. A design example is provided, and the design is verified using nonlinear static and time history analyses.

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