Enhancement of Base-Isolation Based on E-Defense Full-Scale Shake Table Experiments: Dynamic Response of Base-Isolated Building Under Impact Due To Pounding

Abstract eng:
In the recent years, occurrence of large displacement of base-isolation system due to long-duration, long-period ground motions are concerned. Especially, after the 2011 off the Pacific coast of Tohoku Earthquake, a lot of seismologists predicted strong subduction motions in Tokai, Tonankai and Nankai area including strong long period components. The large displacement of base-isolation system may cause rapture of the isolation devices or pounding of the building to the retaining walls at the base. Large impact accelerations due to pounding may strongly affect to the functionality of building. To evaluate impact accelerations due to pounding, full-scale shake table experiments of base-isolated building were conducted. The specimen was four-story RC building with eccentricity supported by two rubber bearings and two sliding bearings. Two types of energy dissipation devises were used; the steel U-shaped dampers and oil dampers. In the experiment, three pounding conditions were assumed; 1) pounding to 150mm-thick rubber blocks attached at the top of retaining walls to mitigate shock with clearance of 400mm, 2) ponding to 150mm-thick rubber blocks with clearance of 300mm and 3) directly pounding to concrete with clearance of 400mm. This paper represents floor response due to pounding and discusses about the accuracy of analysis. Based on the experiment, it was found that floor acceleration larger than 30 m/s2 was observed when superstructure pounded to ridged retaining walls with thickness of 400mm while there was less significant damage to structural members and furniture. It was also found that the 150mm-thick rubber blocks attached at the top of retaining wall can mitigate floor acceleration and displacement pounded retaining walls, however, furniture inside specimen still fell down or slipped.

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