Quakes Rattle Building Codes
Jun. 10, 2016
Two new challenges have come to light from NHK World's coverage on building-reinforcement efforts, and through interviews with specialists on quake-resistance.
Officials from the central and local governments have been applying lessons they learned from the Great Hanshin Earthquake in and around Kobe in 1995.
They've been urging that structures built according to a quake-resistance standard introduced in 1981 be reinforced.
Despite this effort, a series of powerful earthquakes in April destroyed or severely damaged at least 7,000 homes in Kumamoto Prefecture.
A public office in the City of Kobe is in charge of retrofitting homes to improve their earthquake-resistance.
"Requests for structural inspections are pouring in," says one worker there.
The quakes in Kumamoto triggered a flood of inspection applications. The office got as many as 180 a month, 5 times more than usual. Now the inspectors are fully booked through July.
"The quakes in Kumamoto pushed up the number of requests. Applicants say they're worried and want to have their homes checked," says architect Tominori Marutani.
He has checked the quake-safeness of roughly 7,000 housing units over the past 20 years. An NHK crew accompanied him during one of his inspections.
One of the buildings he inspected was a 2-story wooden house in the city of Akashi, near Kobe, that was built in 1979.
Marutani first focused on the front of the house. The first floor lacks supporting walls because of the garage. He says this makes the structure susceptible to lateral shakes.
"Since there's a garage, the floor doesn't have many walls. Without enough walls to withstand the jolts, there's a good chance the structure will collapse," Marutani says.
Up in the attic, another problem is spotted. Big cracks were found in a beam -- a reminder of how powerful the 1995 quake was. Housing units throughout Hyogo and Osaka prefectures still show traces of similar damage.
The quake that struck the region measured a maximum 7 on the Japanese intensity scale. About 250,000 housing units were destroyed or badly damaged.
The house in Akashi was relatively close to the epicenter, but escaped heavy damage. However, Muratani says the quake dislodged a beam, causing cracks.
A gap between a beam and the wall in the attic "indicates that the jolts probably loosened the nuts" that fastened the bolts, he says.
The joints in the pillars and beams play a key role in quake-resistance. Many of them cracked or loosened, but they were left as they were.
"A structure already deformed by one big jolt will sustain greater damage when another strikes. In Kumamoto, some buildings that managed to survive the first quake ended up coming down when another jolt struck 2 days later. We're very worried about what may happen when another big one hits," Marutani says.
He explained the problems to the house's occupant.
"The 1995 quake's impact was evident in many areas. Cracks were found, which is a concern," Marutani said.
"From the outside, the house looks fine, so I was indeed shocked by the inspection results," the owner of the house says.
Another expert points to a further problem. Professor Yasuhiro Hayashi of Kyoto University studies quake-resistant structures.
He studied buildings in Mashiki in Kumamoto Prefecture. The town was hit by 2 quakes at the top of the Japanese intensity scale.
On a map, he shows where housing structures came down in the first quake. They're marked in red. But they're far outnumbered by the blue marks. Those show houses that were flattened by the second jolt -- the main one.
Many of them were up to the building codes introduced in 1981.
"When the 1995 quake struck, experts concluded that the structures built in 1981 or later were safe. But the new findings showing that such buildings sustained major damage, or even collapsed, sent a shock wave through the people involved," Hayashi says.
What can be done to keep houses from falling down? One house was built to the standards in place in 1987, and was retrofitted to help it withstand bigger jolts.
"This room and these walls were reinforced," Marutani says.
Six walls are now 5 times more resistant. Workers also used metal fittings to reinforce 200 beam and pillar joints.
Marutani says he thinks such buttressing is vital even for housing built to current standards.
"We never know when a quake will strike. But to prevent casualties, I want people to have their homes checked and reinforced if necessary as soon as possible," Marutani says.
NHK World's Shu Morino joined anchor Kyoko Tashiro in the Osaka studio.
Tashiro: Mr. Morino, how much damage is remaining from the 1995 quake?
Morino: The 1995 Great Hanshin Earthquake measured a maximum 7 on the Japanese intensity scale in southern Hyogo prefecture. Over 100,000 houses and buildings collapsed, mainly those built to the old standards. Mr. Marutani, the architect, says there are many cases in and around Kobe where houses that showed strong jolts are now showing traces of the damage.
Tashiro: With the Kumamoto earthquake, even the homes that met the new building code, updated after the 1995 quake, collapsed. Why?
Morino: Construction experts who investigated the site estimate one reason is that 2 intensity-7 jolts hits these homes. Even for Japanese standards, 2 consecutive serious jolts was unexpected. Some surveys show there may have been issues in design and construction when the houses were built. I went along to one of the inspections. There were cases where the parts that reinforce pillars and beams were not attached appropriately, and where the walls on the first and second floors were not vertically aligned. Last month, the national government set up a committee to investigate why such houses collapsed. They're aiming to reach a conclusion by July at the earliest.
Tashiro: Meanwhile, what about quake-resistance standards for hotels?
Morino: Yes, that is a concern. In the Kumamoto earthquake, there have been no reports of hotels collapsing. The national government is moving on quake resistance for buildings used by many people such as hotels and shopping centers. Three years ago, quake resistance inspections became a legal obligation, especially for buildings built to the old standards which are now dangerous. People are required to reinforce the buildings if it's found that they're not quake resistant. The hotel that was used at the G7 Ise-Shima summit last month had just conducted such work prior to the summit. However, because such work is costly, many hotels have still not completed the work. We're now seeing a huge increase in visitors to Japan from overseas. To give them peace of mind during their time here, steady progress needs to be made on the quake-resistance work.