UC Irvine

During the 20th century, over 1200 major earthquakes occurred, causing damage estimated to be upwards to $1 trillion worldwide. On average, 10,000 people have died annually from 1900 to 1999. Several studies have shown that nearly three-quarters of earthquake fatalities occurred due to building collapse. Consequently, an earthquake-resistant design philosophy was adopted by the earthquake engineering community. Two common strategies to reduce the displacement and acceleration response of the structure include base isolation, which separates the structure from the ground, and incorporating vibration suppression devices within the structure. For this dissertation, several different types of devices such as tuned mass dampers, inerters, and semi-active devices have been used in a variety of settings to provide further reduction of the response of civil structures. A tuned mass damper (TMD) is an auxiliary mass attached to the structure using spring and damper in parallel. The stiffness and damping are selected such that the first mode vibrations of the structure are reduced. Several studies have shown that TMDs are effective in reducing the response of a structure yet require a large mass and footprint to house the TMD. Inerters are devices that provide a force proportional to the relative acceleration of the two ends. They provide an apparent mass that is several times larger than the physical mass of the device. Both TMDs and inerters are broadly classified as passive devices since they require no power to operate. On the other hand, semi-active devices are those that require a small power source usually provided by an on-site battery. These devices can alter the stiffness or damping properties of the structure. For this dissertation, a semi-active resettable spring (SRS) was used. This device provides continuous stiffness, while also dissipating energy by resetting its unstretched length. Both inerters and SRSs have been incorporated individually in tuned mass damper systems. Yet, a hybrid system incorporating both devices has not been studied before. One objective of this dissertation was to determine the effectiveness of incorporating a SRS and inerter within a tuned mass damper system, known as a semi-active tuned mass damper inerter (SATMDI). Single and multi-story structures were considered, and the results showed that the SATMDI can provide additional reductions to the displacement and acceleration responses, while also significantly reducing the required footprint to house the control system. The selection of the stiffness and damping of a TMD is what is known as the tuning strategy. Several different tuning strategies for TMDs have been proposed that assume harmonic or white noise base excitations. Other strategies use the modal properties of the structure within the tuning strategy. Researchers have studied systems where an inerter is incorporated within a TMD, known as a tuned mass damper inerter (TMDI). The tuning strategies for TMDIs are based on those used for TMDs. In this dissertation, an alternative tuning strategy for a tuned mass damper inerter (TMDI) is proposed. This tuning strategy is also based on that of a TMD, yet instead uses the modal properties of the structure to tune the TMDI. The results of this alternative tuning strategy show that significant improvements in reducing the displacement and acceleration responses can be achieved for a significantly smaller TMD mass and inerter. Moreover, the footprint required to house the TMDI is much smaller as compared with other tuning strategies. Base-isolation has been shown to be effective in reducing the response of a structure by separating the structure from the ground. The isolators provide lateral flexibility, reducing the amount of energy transferred to the structure. While these devices provide adequate protection, there is some evidence to suggest otherwise. To remedy this, researchers have proposed hybrid systems, where TMDs are attached to the base. In particular, a non-traditional TMD (NT-TMD), which attaches the spring, mass, and damper in series has been proposed. It has been shown that the NT-TMD can provide reductions in the displacement, while also reducing the footprint to house the NT-TMD. In this dissertation, a novel NT-TMD is introduced, known as a non-traditional semi-active TMD (NT-SATMD). The results of this work show that the NT-SATMD can provide the same level of performance as a NT-TMD for a significantly smaller mass. Moreover, the footprint required to house the NT-SATMD is comparable to that of a NT-TMD.

The single and multi-story structures considered assume only lateral motion, which occurs if the distribution of the mass and/or stiffness of the structure is uniform. In cases where this is not possible, an eccentricity is developed between the center of resistance and center of mass, coupling the lateral and rotational motion. Buildings that have this property are called asymmetric. In this dissertation, the SRS has been used to reduce the lateral and rotational response of an asymmetric structure. A parametric study over a wide range of structure periods was considered in addition to studying rotational stiff, flexible, and strongly coupled structures. Two strategies for determining the optimal placement for the devices were proposed, both leading to roughly the same performance. It was found that distributing the semi-active devices such that it produces an eccentricity equal in magnitude, but opposite in sign to the structure’s eccentricity lead to the greatest reductions in the flexible and stiff edges. Guidelines and limitations on the selection of the device distribution were also provided for design purposes.