“Earthquake and Buildings in Japan”
May 31, 2006
Mr. Masanori Izumi,
Advisor,
Institute of Technology of Shimizu Corp.,
Professor Emeritus at Tohoku University
When an owner wishes to design and construct a building, he or she will firstly consult with a designer based on its planned size and budget. A designer will then ask an authorized architect to work out a structural design. Such authorized architect is supposed to design a building not only in compliance with applicable laws, but also by taking additional measures coping with potential hazardous factors.
Under present circumstances, however, an authorized architect uses software prepared by a programmer, because it will end up being cheaper. Such software is prepared subject only to the laws, but with no further consideration, and only minimum necessary quantities of materials are taken into consideration in budget calculation. Lately, falsified data were found to have been used for structural designs. There are certain problems in the inspection institutions as well. In both public and private institutions, decreasing is the number of personnel who can intuitively judge whether a structure can resist certain power that cross-sectionally works. Excessive reliance on calculation by a computer could also produce some unforeseen results.
Reduction of reinforcing steel or concrete would help cut only a slight cost, considering whole expenses. One-third of the total costs of building construction are composed of prices for equipment, such as cooling and heating devices. Another one-third is for the costs of finishing or interior works. The remaining one-third or one-fourth of total costs will be spent for the building structure. It is best to construct a building of which the core part is safe and use it for a long time.
Let’s talk about earthquakes in Japan. The island of Japan is surrounded by the Pacific Plate, the Philippine Sea Plate, and the North American Plate on which the Eurasian Plate lies. It means that Japan is a nest of earthquakes.
Is it possible to foresee an outbreak of earthquakes? There had been only one successful example in the world. That was for the Sea Castle earthquake in China of 1975 (M=7.2), at which time a disaster warning was issued because well-water levels changed drastically in Liaoyang.
In Japan, an attempt is being made to predict earthquakes using a substantial number of seismometers and tiltmeters installed from Suruga Bay through the Sea of Enshu. There is no question that an earthquake will break out some day in the future. But it will cause great trouble if the prediction fails. If an earthquake is predicted, it will cost \200~300 million for emergency measures. Persons in charge are placed in a serious circumstance where they can neither “overlook” even a symptom for an earthquake, nor “announce” a prediction that will not turn into reality.
There are various methods to predict earthquakes. But I hope a GPS (global positioning system) method will work successfully. Using GPS, the movement of ground surface will be indicated on a map after an earthquake broke out, and the process of such movement can be analyzed to find spots where unusual movement can be seen, which will become useful to predict earthquakes.
Until 1995, we believed that the Japanese quake-resistant technology was the best in the world. But we suffered a disaster, which disproved such belief on the occasion of the Kobe earthquake. There were three buildings with the same structure when an earthquake broke out in Mexico in 1985. A building in the front collapsed with its top floor bent, reaching the land surface. A building in the middle fell down twisting to the ground. The third building was broken up, but not collapsed. Residents of the first and second buildings were all killed, but no resident of the third building was dead. Even experts could not have been able to predict this difference before the earthquake. We can never say that quake-resistance diagnoses made rather by experts is perfect. There is only a thin line between the safety and the danger.
There are five principles required for quake-resistant buildings, and they are:
・To be built on solid ground
・To be built with a light structure (especially the roof should be lighter)
・To be built by a strong and tenacious construction method
・To make the structure not resonate with earthquake. To implement quake-absorbing measures using steel plates and rubber.
・To implement quake-lowering measures to absorb energy for skyscrapers.
Security is not given by others, but is to be seized by ourselves. We should not have a house built on weak or soft ground. An old wooden building should always be reinforced. We should buy an RC high-rise condominium constructed by trustworthy developers. Fixation of large furniture should be taken care of by individual persons. If we unfortunately suffer an earthquake in a large city, we may encounter nothing but scary matters. We may have no choice but to conduct ourselves considering how to protect ourselves, always bearing in mind where safe streets and an evacuation center are in our neighborhood.