A study of the damage of subway structures during the 1995 Hanshin-Awaji earthquake

Abstract

During the 1995 Hanshin-Awaji earthquake, underground subway structures suffered significant damage, including middle column shear failure which has never been experienced in the past. The present paper describes analytical studies for damage verification and for failure mechanism investigation. Focusing on box culvert structure with middle columns at Kamisawa station, Kobe city municipal subway, the following three series of analytical studies have been conducted. In the first study, soil deposit dependent ground response are investigated using equivalent linear response analysis computer program based on multi-reflection theory. The increase of the deposit layer thickness provides less acceleration, but more displacement responses, which causes more in the way of damage in the present underground structure. In the second study, structure and ground responses are investigated with using two-dimensional soil-structure interaction computer program. As a result, the horizontal motion dependent flexural shear section force has more of an effect, but the vertical motion dependent axial force has less of an effect on the middle column damage. That section force is more affected by displacement amplification of ground dependent on deposit layer. In the third study, three-dimensional FE static nonlinear analysis is conducted to investigate failure mechanism of the damaged structure subjected to earth pressure load, which is obtained in the second study. Analytical results predict shear failure of the top story middle column prior to the flexural yielding of the slabs and walls.