An update on building damage from the Tohoku earthquake

Just after the March 11 Tohoku earthquake it was announced that zero buildings had collapsed, which everyone naturally assumed was a testament to the strict building codes in Japan.

However, it has now been acknowledged that 100 apartment buildings in Sendai city have been completely destroyed.

The understanding of the extent of damage to buildings in Sendai, and across eastern Japan, went through three stages:

— (Stage 1) Apartment buildings were strong —

A survey by the Condominium Management Companies Association of 1642 apartment buildings in Tohoku’s six prefectures found that none collapsed, none were seriously damaged, 26 were half damaged, 283 were slightly damaged, 1024 had very little damage and 309 reported no damage.

Given that there were no reports of buildings collapsing or even suffering major damage, there was a general feeling that apartments were very well-built and could withstand such large earthquakes.

— (Stage 2) The “killer pulse” was weak —

After things began to settle down following the initial chaos from the disaster,  Professor Takashi Furumura from the University of Tokyo’s Earthquake Research Institute and Yuki Sakai from the University of Tsukuba  began to analyze the mechanisms of the earthquake and the ‘killer pulse’ that it produced.

A killer pulse occurs when an earthquake’s wave cycle is 1 ~ 2 seconds. This is the pulse that is most destructive to buildings.

According to the two professors, the Tohoku earthquake produced a killer pulse that was only 20 ~ 50% of the pulse produced during the 1995 Hanshin earthquake. Because the pulse was less, the magnitude 9 earthquake did not have the same destructive power.

Their research was published in the May 17, 2011, edition of the Jutaku Shimpo newspaper under the title “The misunderstanding that apartments were strong against earthquakes.” The article explained that the limited damage caused by the Tohoku earthquake was not because buildings had high earthquake-resistance, but because the killer pulse generated by the quake was not strong enough to cause serious damage. This article helped to increase awareness of the mechanism of the earthquake and the affect on buildings.

A very good English explanation of the damage from the March 11 earthquake along with a guide to “killer pulses” can be downloaded here:

— (Stage 3) Apartment buildings themselves were weak against earthquakes —

In response to the theory presented by the professors, NHK Television ran a segment during their “Morning Closeup” program on September 13, 2011, announcing that over 100 apartment buildings in Sendai City were deemed to be completely destroyed. This was also published in countless local and national newspapers. The figure was calculated by the number of “Disaster Certificates” that were issued to buildings in Sendai City.

On October 28, 2011, the Japan Institute for Condominium Living featured this data in their published journal. Serious concerns and fears were raised over the potential weakness of apartments.

— Architectural Institute Standards vs. Cabinet Office Standards —

The criteria used by the Architectural Institute when designating building damage includes:

– Collapse
– Serious damage
– Half damage
– Slight damage
– Very little damage
– No damage

Meanwhile, the government evaluates the damage under just three different criteria:

– Completely destroyed: No longer inhabitable and damage cannot be repaired.
– Partial destruction: Part of the structure is uninhabitable, but damage can be repaired.
– No damage, or only damage to one part

— Why the difference? —

The Architectural Institute’s criteria closely follows the building standards act which says that even if a building sustains major damage in a large earthquake, those inside the building can escape without injury.

The government’s standards are based on the livelihood of the building’s residents, e.g. whether the inhabitants can continue to live in the building or whether it needs reconstruction following the disaster.

One example to show the difference in assigning the level of damage is the damage to the front door of an apartment. If the door becomes jammed following an earthquake and cannot be opened, the Institute will deem this as little to slight damage. However, since the door cannot be opened, the apartment cannot be used by the occupants and is uninhabitable until repaired. Because the apartment is uninhabitable until the door is repaired, the government will classify the building as being ‘partially destroyed’.

— The 1995 Great Kobe earthquake —

The following is data on building damage from the Kobe earthquake.

Damage to apartment buildings:
(1) Collapse / Serious damage – 83 buildings (10 of these buildings were constructed to the latest shin-taishin earthquake codes)
(2) Half damage – 108 buildings (41 were shin-taishin)
(3) Slight damage – 353 buildings (173 were shin-taishin)
(4) Very little damage – 1988 buildings (1 was shin-taishin)
(5) No damage – 2729 buildings

Apartments that were rebuilt following the earthquake
(1) Collapse / Serious damage – 64 of the 83 buildings (5 were shin-taishin)
(2) Half damage – 31 of the 108 buildings (6 were shin-taishin)
(3) Slight damage – 14 of the 353 buildings (2 were shin-taishin)
(4) Very little damage – 6 of the 1988 buildings (1 was shin-taishin)

While it makes sense that many of the seriously damaged buildings were rebuilt, it is important to note that several of the less damaged buildings also had to be rebuilt. Although these buildings were not considered seriously damaged under the Institute’s guidelines, they were no longer able to provide a suitable living environment for the residents.

— As many as 200 buildings completely destroyed, 1000 partially destroyed in East Japan —

When the Condominium Management Companies Association announced that no buildings had collapsed, everyone breathed a sigh of relief and the general consensus was that apartments were very strong against earthquakes. However, opinion quickly changed once it was announced that 100 buildings had been completely destroyed.

In April 2011, the Condominium Association published data on the condition of apartment buildings in Tohoku’s six prefectures. In September, they added data from the Kanto region, which included Tokyo city and six other prefectures.

Although it has not been officially announced, there were over apartment 400 buildings in Sendai city that were deemed to have been completely or partially destroyed. With 100 apartment buildings completely destroyed and 300 partially destroyed in the one city, estimates for the entire Tohoku and Kanto region suggest that as many as 200 buildings may have been completely destroyed and 1000 may have been partially destroyed.

Of particular note is the high percentage of shin-taishin buildings that suffered slight to half damage. From the Condominium Association’s data, 34 of the 44 buildings (77%) that were half damaged were shin-taishin buildings, and 941 of the 1184 buildings (79%) with slight damage were shin-taishin. In other words, many shin-taishin buildings may also be deemed to be completely or partially destroyed by the government under their disaster certification criteria.

There is also a chance that some apartment buildings may not be included in the data above as the management companies have not applied for the disaster certificates. The application center for disaster certification in Sendai city closed on December 28, 2011. Also, receiving a disaster certificate can significantly lower the resale value of the apartments.

— Disaster situation report —

The Condominium Association published their disaster situation report on September 21, 2011. The main points of the report were:

(1) 11 buildings and houses were temporarily unusable following the earthquake
(2) 27 assembly halls, multistory carparks and machine carparking structures suffered damage from leaning which made them temporarily unusable
(3) 87 tower carpark and machine carparking facilities suffered damage to their machinery which made them unusable
(4) 797 buildings suffered damage to their lifelines due to land subsidence and required repair work to restore the utilities
(5) 33 buildings had damage to their water tanks. Of those buildings, 5 were unable to repair the damage. In many cases, it took more than one month before services were restored (data from a sample of 106 buildings in and around Sendai city)
(6) The elevators in 102 buildings had stopped operating. Only 3 buildings had the elevators operating again on the same day. The majority had them operating within 2 ~ 3 days. In one building, the elevator ropes had to be replaced which took one week (data from a sample of 106 buildings in and around Sendai city).

The president of the Miyagi Prefecture Mansion Managers Association, Kouji Akihabara, said that the damage from the earthquake exceeded cracks and fissures. A great number of properties reported shear failure to outer walls, including collapse. He mentioned that a construction professional was quoted in the May 2011 issue of the Condominium Management Center’s magazine saying that even though the non-supporting walls and expansion joints had broken, it was not a problem. Mr. Akihabara said he was concerned whether this statement was true or not.

“Along with shear failure to outer walls causing cause broken concrete to fall down, the apartment openings (windows and doors) may also become jammed and block escape routes. Under this scenario, the building would no longer serve its function as a residence and the occupants would be forced to move out. Repairing the building could take time and residents might not be able to return to their apartments for as long as one year.

— Building repair costs of 2 million Yen per owner —

A 2 year old building with 50 units in Izumi-ku, Sendai, that was damaged in the earthquake received a total repair bill of 100 million Yen (1.3 million USD), not including further repairs to the apartment interiors. The financial burden for each apartment owner is 2 million Yen (26,000 USD). To be eligible for compensation from the government, the building will have to apply for a “disaster certificate”. However, once a building receives a disaster certificate, the apartment values drop significantly.

Source: Nikkei Business Publications, January 10, 2012.