Isolation Systems

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31. Study of Seismic Isolation Systems for Computer Floors

This report describes the development and testing of a computer floor seismic isolation systems which uses existing devices developed for the seismic isolation of buildings and shock isolation of military equipment. A computer floor system with raised floor and a generic slender equipment cabinet was constructed. It was isolated by spherically shaped sliding bearings and was highly damped either by utilizing high friction in the bearings or by installing fluid viscous dampers. The spherically shaped bearings provided the simplest means of achieving long period in the isolation system under low gravity load. The isolation system prevented rocking of the cabinet on top of the isolated floor and substantially reduced its acceleration response in comparison to that of a conventional computer floor. An analytical study was also conducted in order to extend the results to a range of parameters which could not be tested.

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30. Experimental and Analytical Study of a System Consisting of Sliding Bearings and Fluid Restoring Force/Damping Devices

This report describes an experimental study of the behavior of a bridge seismic sliding isolation system consisting of flat sliding bearings and fluid restoring force/damping devices. Earthquake simulator tests were performed on a model bridge structure both with isolators and without. The experimental results demonstrate a marked increase of the capacity of the isolated bridge to withstand earthquake forces. Analytical techniques are used to predict the dynamic response of the system and the obtained results are in very good agreement with the experimental results.

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28. Commonly Asked Questions Regarding Seismic Isolation

This paper answers the questions that asked about using viscous dampers in a hospital.

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27. University at Buffalo – Taisei Corporation Research Project on Bridge Seismic Isolation Systems

This paper describes the first part of a project to produce a class of passive sliding seismic isolation systems for bridges. This includes experimental verification of the systems by large scale shake table testing, analytical techniques for interpretation of the experimental results, and design procedures for sliding bridge isolation systems. A quarter length scale bridge model was tested on a shake table. Restoring force was provided by various means. First, spherically shaped sliding bearings (known as FPS bearings) were used to provide restoring and frictional forces within a compact unit. Next, flat sliding bearings were combined with various devices placed between the deck and the pier to provide restoring force and additional energy dissipation capacity. These devices were in the form of: a) arc-shaped rubber elements between a moving central rod and a cylindrical housing, b) wire rope springs, c) fluid spring-damper devices and d) fluid viscous dampers.

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23. Semi-Active Fluid Viscous Dampers for Seismic Response Control

The addition of passive damping to a structure greatly increases its earthquake resistance. It is possible to get further increase through an active or semi-active control system for the dampers. Semi-active damping is preferred due to low external power requirements and fail-safe operation. This paper describes the history of the successful use of semi-active fluidic control devices in military applications and how this technology has been adapted to earthquake hazard mitigation. Testing of a semi-active continuously adjustable damping device through fluid orificing is described. Mathematical models of the behavior of the device are also presented.

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20. Seismic Isolation of Bridges

This unpublished paper by Dr. Michael Constaninou describes the seismic protection of a steel multi-girder highway bridge. Three types of base isolators are included; high damping rubber, lead-rubber and Friction Pendulum. The effect of added viscous damping is also investigated, and is found to greatly enhance the performance of the isolators, even though the dampers required are rather small. This classic paper is hand written by Dr. Constantinou and includes his calculations and his sketches of the bridge, isolation devices and dampers.

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15. Reduction of Shock Response Spectra Using Various Types of Shock Isolation Mounts

This experiment demonstrated how various types of shock absorbers can reduce the overall shock response spectra of a structure subjected to high impact shock. This was accomplished by measuring the acceleration on a weight dropped onto three different shock absorbers from various heights and analyzing the resulting data. A baseline test was performed with a steel hard mount. This was followed by tests with three different soft isolation mounts; a half inch thick neoprene pad, a urethane rubber tube on its side and a hydraulic liquid spring type shock absorber. Results show that both the dominant frequencies and the peak acceleration get lower as the isolation system gets softer. This information can be valuable in the design of isolation systems.

Technical Brief

14. Precise Positioning Shock Isolators

Conventional approaches to the shock isolation of delicate systems often involve the use of low frequency shock mountings. This type of mounting is not usable on systems where precise alignment must be maintained over a long period of time. This paper describes a new type of isolator which combines excellent attenuation with the ability to precisely maintain system alignment in the pre and post shock environment. This new shock absorber acts as a rigid link under normal conditions. Then, when a shock occurs, it strokes in both tension and compression with damping in both directions. After things calm down the shock returns precisely to its original length. Computer simulation and test results are included.

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2. Bridge Design

This paper reports on a non-linear analysis of a bridge supported on sliding bearings with elastomeric restoring spring and viscous dampers. Results were verified with shake table tests.

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1. Application of Energy Dissipating

The design of a structure or mechanism subjected to shock and vibration can be greatly improved by the addition of isolation or damping devices. Improvements Include: Reduced Deflection and Stresses, Reduced Weight, Improved Biodynamics, Longer Fatigue Life, Architectural Enhancement and Reduced Cost.