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PhD Candidate, University of Maryland at college park

PINBOARD SUMMARY

This research proposes the use of rate-independent linear damping for the protection of inter-story isolated structures. Inter-story isolated structures have an isolation layer installed at an intermediate story, a unique contrast to more traditional base-isolated structures. The major benefit of inter-story isolation is the creation of nominally independent structural systems above and below the isolation layer. The accelerations of the floors above the isolation layer are reduced when compared to a conventional structural system at the expense of large isolation layer displacements. In retrofit applications where extra stories added using inter-story isolation, the installation is simple and disruption-free (assuming there is adequate gravity load capacity in the existing columns). Additionally, the base shear demand on the total structure is not significantly increased. As with traditional base isolation, large displacements can lead to undesired behavior and damage in the isolation layer. Supplemental control methods are needed to restrict large displacements without increasing the accelerations above the isolation layer. Rate-independent linear damping provides direct control over displacement, a desirable feature for low-frequency structures. When low-frequency structures are subjected to high-frequency ground motions, rate-independent linear damping produces similar response displacements and velocities in comparison to other damping types; however, the damping forces and resulting floor accelerations are substantially smaller. These features are desirable for the isolation layer; however, in rate-independent linear damping, the restoring force is proportional to displacement and in phase with velocity, a non-causality that has limited its practical applications. A filter-based approach is proposed to determine a causal approximation of rate-independent linear damping which can then be tracked by a semi-active damper in the isolation layer. The approach is demonstrated through the shake table real-time hybrid simulation of a 14-story inter-story isolated structure. The isolation layer, supplemental MR damper control device, and upper stories are experimentally represented while the lower stories are numerically modeled. The results compare well to noncausal numerical simulations in both damping forces and structural responses, achieving the desired displacement suppression without amplifying accelerations.

10 ITEMS PINNED

Shake table real-time hybrid simulation techniques for the performance evaluation of buildings with inter-story isolation

Abstract: Interstory isolation systems have recently gained popularity as an alternative for seismic protection, especially in densely populated areas. In inter-story isolation, the isolation system is incorporated between stories instead of the base of the structure. Installing inter-story isolation is simple, inexpensive, and disruption free in retrofit applications. Benefits include nominally independent structural systems where the accelerations of the added floors are reduced when compared to a conventional structural system. Furthermore, the base shear demand on the total structure is not significantly increased. Practical applications of inter-story isolation have appeared in the United States, Japan, and China, and likewise new design validation techniques are needed to parallel growing interest. Real-time hybrid simulation (RTHS) offers an alternative to investigate the performance of buildings with inter-story isolation. Shake tables, standard equipment in many laboratories, are capable of providing the interface boundary conditions necessary for this application of RTHS. The substructure below the isolation layer can be simulated numerically while the superstructure above the isolation layer can be tested experimentally. This configuration provides a high-fidelity representation of the nonlinearities in the isolation layer, including any supplemental damping devices. This research investigates the seismic performance of a 14-story building with inter-story isolation. A model-based acceleration-tracking approach is adopted to control the shake table, exhibiting good offline and online acceleration tracking performance. The proposed methods demonstrate that RTHS is an accurate and reliable means to investigate buildings with inter-story isolation, including new configurations and supplemental control approaches.

Pub.: 21 Dec '16, Pinned: 30 Jun '17