| dc.description.abstract | Structures, artwork, and expensive equipment are often susceptible to significant damage from vertical dynamic motion such as that generated by earthquakes. Several systems exist which seek to mitigate damage caused from motion, but the study of vertical dynamic motion isolators lags behind that of horizontal motion isolators. This thesis explores the design of a vertical isolation system utilizing two laterally loaded arches, acting as beams, to generate negative stiffness. This negative stiffness is counteracted by a positive, linear stiffness from a parallel spring to create a quasi-zero stiffness. The quasi-zero stiffness shifts the natural frequency of the system to almost zero, causing frequency ratios experienced by the system to approach infinity. As a result, the system experiences low transmissibility from the base of the system to the point of interest, which in the case of this research is at the connection joining the beams to which the isolated mass is attached. Essentially, it allows for this connection to be effectively isolated from the effects of vertical accelerations at the base of the system.
Both an experimental prototype and two different theoretical models are examined in this thesis, which allows for a physical system to be compared to theories in order to determine the efficacy of the system and to help validate the theories. The experimental prototype is produced with a focus on using lightweight materials and allowing for a low profile. In order to achieve this goal, 3D printed parts are used. This allows for high levels of control when designing for different system variables such as the length of the beams, the stiffness of the beams, and the initial rise of the beams. Static testing is performed on the prototype to characterize properties of the beam and spring and to optimize the system. This is done simultaneously alongside the development of the two theoretical models, which aimed to aid in and simplify the design process, as beam properties could be roughly determined before being 3D printed. MATLAB is used in combination with OpenSees in order to test the different theoretical models before they are fabricated on the 3D printer. As static testing is performed, changes to the system are made in order to both improve system performance and calibrate it for future dynamic testing. Following the completion of the static testing and the implementation of small modifications into the system, dynamic testing is performed using a vertical shake table to evaluate the isolation performance of the system.
The motions the system is subjected to are a variety of harmonic excitations at different frequencies and amplitudes and white noise. The accelerations of the isolated mass are measured. This then allows for the isolation performance of the system to be determined by comparing the accelerations experienced by the mass to the accelerations at the base of the system. A comparison of the experimentally determined results and the theorized results is performed and will be used for the development of future research, including the development of systems similar to the one discussed in this research. | en_US |
