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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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17. San Bernardino County Medical Center replacement Project Technical Specifications

This specification covers the set of 186 fluid viscous dampers used on the five buildings of the new San Bernardino County Medical Center located in Colton, California. Three major faults are close to this location. The dampers operate in parallel with elastomeric base isolators, and reduce the required isolator stroke from +/- 48 inches to +/- 22 inches. This specification is very detailed and includes testing requirements.

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18. Seismic Control of Structures with Damped Resonant Appendages

This paper shows how Tuned Mass Dampers can provide seismic protection for structures. These dampers consist of a relatively small mass, a spring, and a dashpot attached to a point of maximum vibration and in resonance with the structure to which they are attached. They are widely used to control the response of buildings, bridges, towers, chimneys and other structures to wind forces, machine vibrations and occupant activity. For the most part however, these dampers have been considered ineffective to reduce the seismic response of structures. This paper demonstrates that such devices can be used effectively to control the seismic response of structures. The paper presents a basic mechanism that explains under what conditions such dampers may work effectively under earthquake loads. It also provides recommendations for the selection of the mass, stiffness and damping factors. It includes the results of a series of numerical and experimental tests which verify that properly designed Tuned Mass Dampers effectively and consistently reduce the response of many types of structural systems to various types of earthquake excitations.

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19. Seismic Damage Control with Passive Energy Devices: A Case Study

This paper presents a theoretical case study of the effectiveness of supplemental passive damping to reduce structural response to seismic excitation. A six story special moment resistant reinforced concrete frame is studied with and without the aid of supplemental dampers. Response predictions are presented for each case. Fluid dampers proved to be a very cost effective way to significantly reduce the seismic response of the building investigated. Preliminary cost estimates indicate that positive damage control can be economically achieved.

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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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