Retrofit of suspension bridges in the Central and Eastern United States using distributed supplemental damping.

The purpose of this investigation is to evaluate the use of distributed supplemental damping in the retrofit of suspension bridges in the central and eastern portions of the United States to decrease the seismic vulnerability of these bridges. Supplemental damping, a type of passive control, can be used to augment a structure's natural level of damping. This is achieved by installing devices such as fluid viscous dampers into the structure. Distributed damping refers to the placement of these devices at many points throughout a structure, rather than at a small number of discrete points. Three types of damping devices are considered: friction, hysteretic, and fluid viscous. The study consists of two distinct phases. In phase I, a set of ground motion records is assembled. The set consists of both simulated and real recorded motions. The simulated ground motions used are based on previously developed synthetic motions characteristic of the Central and Eastern United States. The recorded ground motions consist of recordings of El Centro, Campano-Lucano, and San Fernando events. These motions were included due to their comparative value, high long-period motion content, and as a comparison to the long-period rich motions of the other records, respectively. In the second phase, analytical methods are employed to evaluate the efficacy of the proposed retrofit. Finite element models of a realistic suspension bridge configuration are subjected to earthquake ground motions. Using these models, various types of damping devices are inserted throughout the suspension structure. Responses are calculated using nonlinear time history analyses of the finite element models. The results of the investigation clearly indicate that the unretrofitted bridge is found to be vulnerable to seismic ground motions, even at very large epicentral distances. However, the use of distributed damping devices is effective in reducing response. A retrofit configuration is developed which substantially reduces the seismic demands on the superstructure and substructures. Of the three devices considered, friction and hysteretic damping devices are found to be the most effective, while fluid viscous devices prove difficult to implement.Ph.D.Applied SciencesCivil engineeringSocial SciencesTransportationUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/132649/2/9977228.pd