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The Kobe Earthquake and Recent Research on Earthquake Resistant Performance of Highway Bridge Piers in Japan

by J. Stoyle

On April 4, 1996, Mr. Masahiro Terada presented a seminar at the University at Buffalo entitled "The Kobe Earthquake and Recent Research on Earthquake Resistant Performance of Highway Bridge Piers in Japan." Mr. Terada is a researcher in the Steel Structure Development Center, Steel Research Laboratories, Nippon Steel Corporation.

Mr. Terada provided a brief overview of the seismological aspects of the Kobe earthquake. He presented many slides showing earthquake damage to rail lines and stations, reinforced concrete and steel bridge piers, and buildings.

He described two research projects currently underway at Nippon Steel to examine the seismic performance of steel bridge piers. Both projects are part of a larger research effort in Japan sponsored by the Public Works Research Institute (PWRI) of the Ministry of Construction, Metro Expressway Public Corp., Hanshin Expressway Public Corp., Association of Bridge Fabricators, Nippon Steel Corp. and other major Japanese steel makers. Its purpose is to determine how to improve the performance of existing highway piers and to recommend changes to design codes following the Kobe earthquake.

The first project conducted at Nippon is entitled "Experimental Study on Improvement of Seismic Performance of Existing Steel Bridge Piers," sponsored by PWRI, Yokogawa Bridge Corp. and Nippon Steel Corp. The purpose of this research is to test the effectiveness of various retrofitting schemes to improve the performance of steel bridge piers. Eight specimens, half rectangular and half circular, were subjected to quasi-static testing. Preliminary conclusions indicate that for rectangular columns, reinforcement of the corners is the most effective. For the circular specimens, the proposed retrofit consists of installing a circular ring of steel outside the existing column in the expected buckling region. A critical parameter that affects performance is the size of the clearance gap between the outside of the column and the inside of the added ring.

The second research project is entitled "Pseudo Dynamic Testing of Steel Bridge Piers," sponsored by PWRI, Yokogawa Bridge Corp. and Nippon Steel Corp. In this project, researchers are simulating the response of steel bridge piers under earthquake conditions through both experimental testing and numerical analysis. This research is currently in progress, however, preliminary conclusions indicate that steel bridge piers designed according to current codes were not seriously damaged and that the Usami model can be used to obtain the response of steel bridge piers under strong earthquake ground motions.

An interesting discussion followed Mr. Terada's presentation. The debate centered around the merits of dual level design and the use of steel vs. concrete in bridge piers. Over 25 people attended the seminar.

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