This paper describes the widespread destruction caused by the Loma Prieta earthquake in the San Francisco Bay Area. It deals extensively with some of the worst damage, which was the destruction of huge circuit breakers. The article discusses how the repetitive nature of the seismic input excited resonance in many structures.
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.
This paper presents a review of supplemental damping devices used for the control of the seismic response of structures. The mechanical properties of these devices are discussed and considerations in the design of energy absorbing systems are presented. Conventional structures passively resist earthquakes through a combination of strength, deformability and energy absorption. They have very little damping, so elastic energy absorption is small. Strong earthquakes deform these structures well beyond their elastic limit through localized plastic hinging, which results in increased flexibility and energy dissipation. Most of the earthquake energy is absorbed by the structure through localized damage of the lateral force resisting system. This is somewhat of a paradox in that the effects of earthquakes (i.e. structural damage) are counteracted by allowing structural damage. Structural performance can be greatly improved if a large portion of the input energy can be absorbed, not by the structure itself, but by some type of supplemental device. This paper describes a number of ways to do this, including friction devices, yielding metal systems, elastomeric viscoelastic dampers and fluid viscous dampers.
This unpublished paper by Dr.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.
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.
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.
This specification covers the set of ten linear fluid viscous dampers along with their mounting brackets and pins for the Rockwell Building located at Jamboree Road and Birch in Newport Beach, California. These dampers provide an output force in either tension of compression that is directly proportional to the relative velocity between the two ends of the dampers. The damper output force varies only with velocity and does not change with damper stroke position or orientation angle. The function of the dampers is to absorb earthquake energy, thereby reducing the amount the building moves when an earthquake occurs.
This paper describes a large variety of passive energy dissipating devices which can be used within a structural system to absorb seismic energy. These devices can produce significant reductions of inter-story drifts in moment- resisting frames. Furthermore, these devices may under elastic conditions, reduce the design forces.
Experimental study of both a moment frame building and a single span bridge, both with and without viscous dampers, are described here. Additions of viscous dampers significantly reduced both drift and shear forces.
This paper is a condensed version of Technical Paper.