Date of Award
Doctor of Philosophy (PhD)
Civil and Environmental Engineering
Lui, Eric E. M. L.
energy dissipation, nonlinear time history analysis, OpenSees, snap-through, steel frames, variable stiffness
Civil and Environmental Engineering | Civil Engineering | Engineering
Structures without energy dissipation devices rely primarily on plastic or inelastic deformations to dissipate energy from earthquakes. As a result, the amount of inelastic deformations and damage level will increase as the earthquake severity increases. However, structures equipped with energy dissipation devices are expected to experience less inelastic deformations and so their safety and integrity can be better preserved.In this research, a new device called the variable stiffness energy dissipation device is conceptualized and numerically studied. Using nonlinear time history analysis, results are obtained to illustrate the effectiveness of the proposed device in enhancing the seismic performance of shear and moment resisting frames. Additionally, design guidelines on how to apply the proposed device to moment resisting frames are provided. Over the years, various types of energy dissipation devices have been developed and used to dissipate energy imparted to a structure. However, the use of snap-through instability to dissipate energy and control vibration is rather new. The proposed energy dissipation device is a passive device that can exhibit snap-through and snap-back behaviors; and in the process of doing so, is able to dissipate energy from earthquakes. Since the load-deflection behavior of the device is nonlinear, its stiffness (and hence its natural frequency) varies continuously; thus reducing the possibility of resonance under the applied earthquake excitations. The device also possesses large stiffness that can help control lateral displacement of the structure under frequent earthquakes. Composed of a series of helical springs with a specific initial inclination angle placed between an inner and an outer tube, snap-through and snap-back occur in the springs when they are pushed by stationary bushings mounted on a rigid bar as the bar slides inside the inner tube as a result of inter-story displacement. Because the device is placed between the top of an inverted Chevron bracing and the beam above, it is activated when the apex of the Chevron brace moves relative to the connecting beam. Due to the complexity of constructing a structural model for a series of helical springs arranged in the afore-mentioned patterns, the device is modeled as an axially loaded member made from a material that can exhibit snap-through and snap-back characteristics. The behavior of this device was programmed using C++ and built into the framework of an open-source software OpenSees. The device can be invoked by issuing specific codes in the Tool Command Language (TCL) file of OpenSees to an axially loaded member to simulate the snap-through and snap-back behaviors. To demonstrate the effectiveness of the proposed device in dissipating energy and reducing structural vibration, nonlinear time history analysis is performed on several shear and moment resisting frames equipped with this device. The results show that the proposed energy dissipation device is very effective in reducing peak and residual displacements of these frames. A parametric study is then conducted to investigate how varying the snap-through force and snap-to distance can influence the performance of moment resisting frames when they are subjected to three levels of seismic excitations. Analysis is also performed on two groups of four-story mixed frames for which the device is only installed on selected floors of the frames. The first group uses a moment resisting frame as the base frame and the second group uses a Chevron braced frame as the base frame. Even though the device is not installed on all four stories of these frames, the results show that the device is still capable of reducing peak and residual top story and inter-story displacements for the moment resisting frame, as well as reducing bracing member force for the Chevron braced frame. Based on these numerical results, design guidelines are proposed and a six-step procedure to guide the design of the proposed device for use in moment resisting frames is recommended. A design example is then given to illustrate how to apply the proposed design guidelines. The completed design is verified using ten ground motion records and the results are shown to be satisfactory.
Zheng, Tie, "A Variable Stiffness Energy Dissipation Device for Vibration Control of Steel Frames" (2021). Dissertations - ALL. 1460.
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