ABSTRACT
In the Great Awaji earthquake of 1995, many cases of bulge buckling of steel bridge piers could be found. It was said by the victims that the vertical movement was severe. Cite of buckling was far away from that of seismometer by the meteorological agency that observed large vertical acceleration of 1.5 G, where G is the gravity acceleration. It was difficult to judge that the vertical acceleration was dominant for the buckling. Since 1995, many seismometers have been installed all over in Japan. Recent vertical acceleration has been reported up to 1 or 2 G. Since there is a concern of epicentral earthquakes in Japan, it is important to investigate the influence of vertical acceleration on the structures such as bridges. Finite element analyses were carried out with the steel pier model of the same configuration as the bulge buckling pier in 1995. Three earthquake waves were chosen for the comparison, ranging the vertical acceleration of 1 to 2G. As the model of superstructure, three patterns were considered. One was beam model of full length of the span. The second was beam model of half-length. The third was concentrated mass. The earthquake acceleration was applied by one vertical direction, two horizontal directions and three directions. Good agreement with the actual case could be seen in case of full length superstructure beam and three directional earthquake acceleration. On the other hand, smaller displacement was obtained by three directional acceleration, comparing with the two directional acceleration.
