Overview of the Damage of Bridges in Aso area

The 2016 Kumamoto earthquakes includes the main shock earthquake with M_w=7.0 on April 16 and a foreshock earthquake with M_w=6.2 on April 14. Such earthquakes caused strong response and significant damage to bridges. In this article, three damaged bridges in Aso area are reviewed. This area is characterized by active volcanos and soft ground composed of volcanic cohesive soil. Landslides of the soft ground caused by the series of earthquakes were the main cause of the severe damage to bridges such as Aso Bridge, Minami-Aso Bridge, Choyo Bridge and Toshita Bridge.

 

 Figure 1. Location of damaged bridges in Also Area.

 

Aso Bridge(阿蘇大橋)

Aso bridge is a 200-meter-long arch bridge. The Aso-ohashi bridge opened in 1971. It was situated at the western tip of the caldera of Mount Aso. The Kurokawa river runs 80 meters below. The Aso Campus of Tokai University and the Aso Volcanological Laboratory of Kyoto University are also located near the site of the collapsed bridge.(source: https://theextinctionprotocol.wordpress.com/2016/04/16/large-road-bridge-collapses-as-new-quake-hits-kumamoto/) The bridge collapsed after the main shock earthquake due to landslide.

 

Figure 1. Photo by Akiyama.	Figure 2. Photo by Akiyama.

Minami Aso Bridge(南阿蘇大橋)

The dampers at the south end of Minami Aso Bridge was separated from the abutment after the mainshock. Though detailed investigation has not been conducted, this damage was considered to be caused by high axial force applied to the girder of the bridge by ground deformation (Source).

 

Figure 3. Photo by Akiyama.	Figure 4. Photo by Akiyama.

Choyo Bridge(長陽大橋)

The failure due to a landslide was observed at the abutment. The road to the bridge was also damaged.

 

Figure 5. Photo by Akiyama	Figure 6. Photo by Akiyama

Toshita bridge (戸下大橋)

Toshita bridge  is a reinforced concrete bridge, a damaged RC column was falling down due to a landslide. No significant damage was observed at the remaining RC columns.

 

Figure 7. Photo by Akiyama.	Figure 8. Photo by Akiyama.