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RIGIDITY-PLASTICITY-VISCOSITY: CAN ELECTRORHEOLOGICAL DAMPERS PROTECT BASE-ISOLATED STRUCTURES FROM NEAR-SOURCE GROUND MOTIONS?
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1997
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Seismic protection by lengthening a structure’s fundamental period is achieved with isolation systems, but while flexible bearings shield high‑frequency earthquakes, they can amplify responses to long‑period motions, so a stiff superstructure should be locked to the ground in such cases. This study proposes adding rigidity through a friction‑type (rigid‑plastic) mechanism and controllable fluid dampers to prevent amplification of long‑period ground motions in base‑isolated structures. An analytical investigation of a single‑degree‑of‑freedom base‑isolated system evaluates the feasibility of an electrorheological damper to supply the required friction forces. Friction forces markedly reduce relative displacements and keep accelerations low, yet they cause permanent displacements, while controllable fluid dampers effectively mitigate this issue. © 1997 by John Wiley & Sons, Ltd.
The concept of seismic protection by lengthening the fundamental period of the structure has been implemented through a number of isolation systems. While flexible isolation systems can effectively protect structures from earthquakes containing high frequencies and sharp accelerations, they might amplify the response of the structure when subjected to rapid, long-period motions. In this case of long period excitations the stiff superstructure should be 'locked' to the ground, rather than be supported on flexible bearings. This paper shows through a comprehensive analytical study that a practical solution to this problem is to provide additional rigidity to the structure using a friction-type mechanism (rigid-plastic behaviour). The presence of friction-type forces reduce substantially the relative displacements of a single-degree-of-freedom structure by keeping accelerations at low levels; however, they are responsible for the presence of permanent displacements. Accordingly, the use of controllable fluid dampers is proposed and it is shown that they can be a practical solution to the problem. The response of a single-degree-of-freedom base-isolated structures is investigated, and the feasibility of a proposed electrorheological damper to deliver the required forces is discussed. © 1997 by John Wiley & Sons, Ltd.