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99. APPLICATION OF ENERGY DISSIPATION TECHNOLOGY FOR RETROFITTING STEEL STRUCTURES WITH VULNERABLE PRE-NORTHRIDGE CONNECTIONS

Prior to the 1994 Northridge earthquake, modern welded moment resisting steel frame structures were regarded as highly resistant to earthquake induced damage and few engineers regarded earthquake induced collapse of such structures as credible. This paradigm changed following the 1994 Northridge, California and 1995 Kobe, Japan earthquakes, creating a new class of potentially hazardous structures. In response to this new information, the Federal Emergency Management Agency retained a consortium of the Structural Engineers Association of California, the Applied Technology Council and the California Universities for Research in Earthquake Engineering, known as the SAC Joint Venture, to research the cause of the unexpected poor performance of these buildings and develop recommended design criteria. The resulting FEAM-351 publication provides performance based design criteria for the evaluation and upgrade of these structures. This paper presents the application of the FEMA-351 criteria to the design of structural upgrades employing energy dissipation technology to an existing 10-story steel structure. The East Bay Municipal Utility District (EBMUD) administration building is nine stories tall, with three below grade basement levels and a rooftop, mechanical penthouse. It was completed in 1991, employing the standard vulnerable moment connections. Alternative upgrade strategies were investigated, including modification of individual connections and application of energy dissipation criteria. The latter approach, using viscous dampers, was selected.

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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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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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32. Application of Fluid Viscous Dampers to Earthquake Design

This article summarizes the extensive viscous dampers investigation performed by NCEER at State University of New York, Buffalo Campus. This included computer modeling of both the dampers and complete isolated systems, along with shake table testing and correlation of results. The article also describes a very large damper projects; dampers + base isolation for a set of five hospital buildings near San Bernardino, CA.

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34. Fear of Trembling

This article describes the effects of both Kobe earthquake and the Northridge earthquake in detail, including technical and economic details. It also discusses building codes and practices and what is being done around the world to decrease the risk of severe seismic damage.

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