Design and assessment of seismic protective systems for near-field ground motions

The objective of this research is to assess the effectiveness of existing seismic protective devices and design novel controllers for the protection of civil infrastructure systems against near-field ground motions.; The characteristics of near-field ground motions and their effects on linear and nonlinear structural systems are investigated to gain an understanding of the effect of the excitation properties on structural responses. The results indicate that the responses of these structures subjected to recorded near-field ground motions are controlled by the pulse components of these records represented by the frequency, shape, damping and amplitude. Near-field ground motions cause distinct strength and ductility demands, and energy dissipation requirements on structures. The response modification factor versus ductility ( R-mu) relationships for pulse excitations are found to match the lower bound of the recorded ground motion results for low Tn /Tp (ratio of structure-excitation period) values and match the Newmark-Hall's relationship otherwise.; The performance of existing passive energy dissipation systems in protecting linear and nonlinear structures against near-field excitations is investigated. It is found that the effectiveness of these systems is related to the ratio of structure-excitation period, Tn/Tp, and the frequency contents of near-field excitations. Passive viscous damping is most effective in reducing structural responses near resonance caused by dominant pulse effects; otherwise, it is only effective in reducing the responses caused by broadband frequency components. Yielding dampers are only effective in reducing responses caused by excitations having Tn> Tp and they may amplify the structural responses otherwise.; In this study, optimal active and semi-active controllers are designed by incorporating a frequency-domain pulse filter into modern control algorithms. The results indicate that these controllers developed for the augmented structural systems have distinct advantages over many other existing methods and yield more significant base and superstructure response reductions with the same amount of control force. Systematic parametric studies demonstrate that these controllers are robust with respect to the variation of the characteristic filter parameters in a substantial range.; A hybrid controller utilizing the advantages of viscous damping and variable stiffness mechanisms is proposed for the control of flexible structures against long-period excitations. Analysis results indicate that this controller is capable of significantly reducing displacements caused by long-period pulse-type and near-field excitations for flexible structures through instantly adjusting damper parameters.; Both base-isolated building and bridge benchmark models are employed to investigate the effectiveness of the proposed control systems. Numerical analyses using the benchmark models demonstrate that the proposed control systems are very effective in reducing the responses caused by near-field ground motions and have much better overall performance than the sample controllers provided in the benchmark packages.