Overview of Damage to Reinforced Concrete Buildings in Kumamoto

Emrah Tasdemir and Nicole Paul will be co-curators for the Reinforced Concrete Buildings topic on the Kumamoto Japan Earthquake Virtual Clearinghouse.

Emrah Tasdemir is a PhD student at North Carolina State University. 
Nicole Paul works for the Advanced Technology + Research (AT+R) group at Arup in San Francisco as a Structural Analyst.

Overview

Based off of a review of online media and PEER’s Preliminary Reconnaissance Report, the damage most commonly reported for reinforced concrete buildings in the Kumamoto earthquake includes: soft story failures, shear cracking and failure of columns, and damage due to large ground deformations.

In this review, documentation was found on 22 reinforced concrete buildings.  Table 1 shows the statistics for that sample of buildings.

 

Table 1.

Damage Type	Number of Buildings
Soft story failure	8
Shear damage to columns	4
Ground deformation	3
Other moderate to severe damage	4
Other minor to moderate damage	3
Total	22

  

 

The images and reports of damage of the buildings reviewed are collated below, separated by general category of damage.

Soft Story Failure

The most common damage reported in the buildings documented in this set was a soft story failure, most commonly occurring in the first floors above ground.  This is common as the first floors of buildings often are taller than others in order to serve as an entrance or area for parking.

One example of these is a 3-story dental office with penthouse, which collapsed at the first floor.  As can be seen in Figure 1-2 and is documented in the PEER Report, the columns were axially crushed.  This dental office was located in Chuo-ku, Kumamoto city.

 

Figure 1. Photo by Koji Harada/AP.

Figure 2. Source: PEER Report.

Similarly, the 3-story residential building (Figures 3, 4) collapsed at the first floor.  As with the dental office, the first floor was used as an entrance and parking area.

 

Figure 3. Source: Reuters	Figure 4. Source: Asahi

A 7-story residential building exhibited the same type of failure in Kumamoto, Nishi-ku.

 

Figure 5. Source: Mainichi		Figure 6. Source: Earthquake-report
Figure 7. Source: Asahi		Figure 8. Source: Asahi

A 3-story office building in Minami-ku, Kumamoto city also experienced a first story collapse.

 

Figure 9. Source: PEER report.

A mixed-use 5-story building also experienced a first story collapse.

 

Figure 10. Source: PEER report.

Uto City Hall, a 5-story building, experienced a 4th story collapse , with failure of beam-column joints observed at the 3rd and 4th stories.  In addition, flexural failure of columns was observed at the 5th story.

Figure 11. Source: PEER report.

Figure 12. Source: PEER report.

Figure 13. Source: Wall Street Journal.	Figure 14. Source: Kyodo News.
Figure 15. Source: Mainichi.	Figure 16. Source: Asihi.

Total collapse was observed at west wing of a shopping mall.

Figure 17. Source: Wikimedia	Figure 18. Source: Wikimedia

Figure 19. Manufacturing.net

A 6-story residential building with retail area on the first floor experienced collapse of one of the first two floors  in Higashi-ku, Kumamoto City during the main shock on April 16.

 

Figure 20. Source: PEER Report

Shear Damage to Columns

Another common type of damage reported was shear cracking or failure to columns.

Shear failure of a column in a 2-story reinforced concrete frame office building in Minami-ku, Kumamoto City is seen in Figure 21.

 

Figure 21. Source: PEER report

Shear failure of stilt columns, shear failure of beam in outer frame, and shear cracks on wall frames was seen in 4-story apartment building with penthouse.  The shear failure of the columns occurred at the first story, which was used for retail.  The PEER Report noted that the moment frame section was heavily damaged due to a highly eccentric floor plan.

 

Figure 22. Source: PEER Report

Shear cracks on first story columns were also seen in 7-story reinforced concrete apartment building in Nishi-ku, Kumamoto City.  In addition to the shear cracks of the first floor columns, flexural and vertical cracks were seen on the first story beams.

 

Figure 23. Source: PEER Report

Figure 24. Source: PEER Report

One of the two documented Mashiki-machi hospital buildings in the Kamimashiki district experienced shear cracks in short columns and flexural cracks in other columns.

 

Figure 25. Source: PEER Report

Ground Deformation

The Mashiki City Hall was a 3-story building that experienced damage to a connecting corridor due to excessive ground deformation.  This damage included shear cracks to the beams of the outer frame and flexural cracks on the third floor.

 

Figure 26. Source:PEER Report.

The Mashiki School consisted of two 3-story reinforced concrete buildings, connected by two corridors.  Excessive ground deformation resulted in the inclination of part of the school building.  Damage was also observed at the base of columns.  For this building, as well as the next building, movement seems to have occurred at an expansion-joint.

 

Figure 27. Source: PEER Report

One of the other Mashiki-machi hospital buildings also experienced inclination due to excessive ground formation.

 

Figure 28. Source: PEER Report

Other damage – moderate to severe

The Kumamoto City Hospital was reported to be at risk of collapse, with plans of about 300 people to be transferred.  Source.

A 13-story building showed expansion joint damage and partial collapse of parapet walls, as seen below.

 

Figure 29. Source: News	Figure 30. Source: News
Figure 31. Source: News	Figure 32. Source: News

A Mashiki school experienced minor cracking, flexural failure of the first story columns of a connecting corridor, and high residual drifts in a corridor.

 

Figure 33. Source: PEER Report

A 5-story building experienced large residual drifts at top floors, as well as flexural failure at the base of columns and failure at beam column joints.

 

Figure 34. Source: PEER Report

Other damage – minor to moderate

The Kumamoto Central Hospital was reported to have been flooded due to fire sprinklers.  It has been reported to be non-functional.  Source.

The Mashiki town school was reported to have minor cracking and damage to exterior walls.

 

Figure 35. Source: PEER Report

The Mashiki disposal facility also reported damage to exterior wall panels.  In addition, it is reported that ceilings fell.

 

Figure 36. Source: PEER Report