A Lesson from Japan’s Latest Destructive Earthquake on How to Strengthen Older Schools (and Buildings)
by Peter Yanev
Yanev Associates and Kuramoto Earthquake Investigation Team Technical Leader
Once again, I find myself in Japan immediately after a big earthquake. I left California the day after a Magnitude (M) 7.0 earthquake hit Japan’s Kyushu Island to join several colleagues in investigating the effects of the earthquake. Critically, I also came to Japan to learn from the successes of Japanese engineers. Older school strengthening programs are one of the great successes of Japan. Our earthquake investigation team did not review the overall performance of schools in the affected area of the earthquake, but we were able to observe the performance of several schools in the area of the strongest shaking, including the Mashiki area.
The Town of Mashiki straddles the Futagawa Fault, where the some of the largest fault displacements in the earthquake were found – nearly 2m (6 ft.) of horizontal displacement and about 0.7m (2+ ft.) of vertical displacement. The town and its region lie along a river, and its buildings, mostly houses are built on river alluvium and along the hills on both sides. The houses in the Mashiki area experienced the worst damage that I have ever observed to wood-frame buildings – that includes about 120 earthquakes around the world.
We observed that, generally, there was no visible structural damage to the schools in the area. In the first day of investigations, we looked briefly at two schools and investigated one in detail, the Mashiki Tsumori Elementary School which is very, very close to the fault that ruptured the ground and caused the earthquake. The school is located in the middle of some of the worst damage caused by the earthquake. The area experienced some of the strongest, if not the strongest, shaking in this major earthquake. The performance of the school in the earthquake is a great lesson in good engineering and good social risk management.
We visited the school on April 19, 2015, five days after the earthquake. We noted that there was no tag on the building(s) indicating that the school had been officially inspected for safety and restart of operation. We poked around a few minutes and while taking some exterior photographs, we were greeted by some of the teaching and maintenance staff. They were curious why we were there and what were we doing. When we explained, and within a few minutes, we were conducting an unofficial damage and safety assessment of the school with the school principal and several of the teaching staff. It was remarkable that the school had not been officially inspected, especially given the results of our impromptu and much appreciated investigation.
The investigation took perhaps 30 minutes. We visited all of the several relatively small buildings, many of the classrooms and other rooms of the school, and its sport auditorium.
Of course, the reason we stopped by in the first place was that it was obvious to me that the school was older and had been strengthened (retrofitted) for earthquakes sometime after it was originally constructed. Such strengthening of schools started sometime after the 1978 Magnitude 7.4 Sendai (Miyagi-Ken-oki), Northern Japan earthquake. That was my first earthquake investigation in Japan, as well as my first visit to Japan and I saw firsthand a number of collapsed school buildings. The earthquake damaged extensively many schools and university buildings in the Senday area; a few buildings collapsed. Since then, I have investigated many earthquakes in Japan and have visited Japan 40 to 50 times. I also opened an office in Tokyo, Japan for my former company, EQE International shortly after the 1975 Kobe earthquakes and worked on many earthquake-engineering projects throughout the country, including projects on some of Japan’s nuclear power plants following the Magnitude 8.8 earthquake and tsunami of 2011.
Figure 4 above, shows one of the most common details that are used for the strengthening of schools throughout the world. It involves inserting new, solid and well reinforced concrete walls (called shear-walls) between existing columns in order to strengthen the buildings. These walls can be added to the exterior, as in this school, or to the interior (which tends to be less architecturally disruptive but also more expensive). Working with the World Bank, for example, we have managed the strengthening of over 1,000 such buildings (mostly schools and health-care buildings) in the Istanbul, Turkey area since 2005, using this technique.
With the principal and some of his staff we walked throughout the school looking for damage. Some of this damage, and the lack of it, and some of the interiors and exteriors of the buildings are shown in the pictures below. The Principal showed me some of the damage that was of concern to him. It turned out to be superficial damage that has no effect on the strength of the post-earthquake buildings and the safety of the students and staff. The damage included minor cracking, especially around some of the so-called seismic joints that separate adjacent buildings and are expected to be lightly damaged (he, of course, did not know that), fallen pictures and books and other minor furnishings, a bit of ground settlement in the yards around the school, a few fallen ceiling tiles (in the gym) and other light fixtures (yes, they can injure people), the fallen temple monuments surrounding a small shrine on the school grounds (which could have hurt badly someone standing next to them), etc.
It was remarkable, once again, how little was damaged, given the size and the strength of the earthquake. The damage, or really the lack of it, shows how well we understand the effects of earthquakes on school buildings and how well we can protect our kids and their teachers. It also shows that the strengthening of our older schools (those designed to outdated codes, written before the lessons of so many recent earthquakes) reduces dramatically the risk to their occupants. This has now proven to be the case in all recent major earthquakes in Japan, as well as in California and Chile, for example, where society has provided the needed funding to do the engineering and construction work. I saw similar performance in many old but strengthened schools in Chile in their M9.0 2010 earthquake and in Japan in the M8.8 2011 earthquake that caused the major tsunami and the destruction of some of the Fukushima Nuclear Plants (which was actually caused by the flooding as a result of the lack of adequately high tsunami walls). In fact, one of the most memorable sights of that earthquake was an old school near Nishinomaki that had been strengthened for earthquakes. The structure of the school was barely damaged, even after it was shaken by a Magnitude 9 earthquake for several minutes and was then hit by the great tsunami plus a localized fire, likely caused by leaking gas. So, the performance of the Mashiki Elementary School was not surprising to me. I expect that of those schools in Japan, and elsewhere, that have been strengthened. I just hope that we continue fixing schools, and other public and private buildings and infrastructure, before their respective and expected earthquakes occur.