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Figure 2.26: Damage due to Liquefaction at Rio Banano Bridge
2.3.5 1995 Hyogo-Ken-Nanbu (Kobe) Earthquake
The M W 6.9 Kobe earthquake was the most damaging earthquake to strike Japan since the Kanto
Earthquake of 1923. Peak accelerations ranged from 0.50 g to 0.80 g near the rupture zone, and
0.20 g to 0.50 g approximately 20 km away. The duration of the strong motions was roughly 10
to 15 seconds. Widespread ground failure was observed throughout the strongly shaken region
along the margin of Osaka Bay (Hamada et. al. 1995; Shibata et al. 1996). On Rokko Island and
Port Island, which are reclaimed lands in Osaka Bay, liquefaction caused subsidence in inland
areas of roughly 0.5 to 1.2 m. Major bridge damage resulted from the earthquake.
One of the hardest hit was the Harbor Highway located along the margins of Osaka Bay. Every
bridge along this route from Nishinomiya to Rokko Island suffered damage. The entire area
along the coast was subject to severe liquefaction and large soil movements. Consequently,
bridge foundations that had little resistance from the weak foundation soils rocked and displaced
during the earthquake. Bridge superstructures fell off their bearings, and in some cases off their
substructure. There was damage at almost every expansion joint along the highway. The Rokko
Island Bridge was damaged by excessive substructure movements. A bearing failure on one side
of the bridge racked the arch leading to buckling the cross-framing. Other damage along the
highway included the settlement of approach fills and the shattering of piers.
Bridge damage as a result of ground deformation was also experienced on the Hanshin
Expressway Route 5. The Shukugawa Bridge, a three-span continuous box girder, is supported
on concrete multi-column bents and pile footings (Shinosuka 1995). During the earthquake,
liquefaction was widespread in the general area of the bridge and lateral spreading was evident at
many locations. Both banks of the Shukugawa were subject to large soil deformations and
moved towards the center of the river. Piers at either end of the bridge displaced (0.5 m to 1.0 m)
with the soil and dislodged the bearings under the main girders as well as the approach spans.
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