Is Your Home Earthquake Resistant?
By Awake! correspondent in Japan
“HELP me! Help me!” In the early morning darkness of January 17, 1994, a man cried out from the first floor of an apartment house into which the top two stories had collapsed and lay like a stack of pancakes. An earthquake measuring 6.6 on the Richter scale had struck Los Angeles, California, U.S.A., taking the lives of 16 people in that building. The death toll in the area was over 50.
On September 30, 1993, an earthquake of slightly lower magnitude hit the state of Maharashtra in western India. It killed as many as 30,000 people. “If it had happened someplace else where . . . the houses were well-built, there would not have been so great a tragedy,” said Sri Krishna Singh, a seismologist. Most of the houses in the affected area were made of mud bricks.
On the other hand, a quake of about the same magnitude as that in India struck Tokyo, Japan, in 1985. It was the strongest to hit the area in 56 years. Yet, there were no deaths, no fires, no large-scale destruction of property. What made the difference?
One answer lies in the construction methods used for the buildings. Many countries in earthquake-prone areas require structural engineers to adhere to strict building codes to make structures earthquake resistant. As an example, let us see how earthquake-resistant structures are built in Japan.
Traditional Japanese buildings had earthquake-resistant features unwittingly built into them. Since most houses were constructed of wood, a variety of joints were used. This allowed the house to give and flex under the shock of a temblor and yet not collapse. Pagodas and castles using these principles have survived from medieval times. Studies of these structures reveal that the secret lies in their being flexible rather than rigid. This idea is being put to use in modern buildings.
In high-rise buildings, the effective use of steel determines whether a building will resist earthquakes or not. Not only may steel girders and beams be used but steel reinforcing rods are laced through concrete pillars, floors, and walls to form a strong but flexible structure. Steel supplies the flexibility that helps hold the building together when an earthquake strikes.
New research has also made it possible to learn how an earthquake moves a building. This has led to a very important consideration in designing an earthquake-resistant building: its rate of vibration. A small building or a rigid structure has a higher, thus more destructive, rate of vibration than a taller or more flexible building. In addition, it is important that the building be designed to vibrate at a rate different from that of the ground on which it stands. This will reduce the effect of resonance, which amplifies the force of the shock.
Another consideration is the foundation. A company has successfully tested a structure built on rubber pads that use viscous dampers. These act as shock absorbers and actually decrease the seismic effects by some 60 percent in the upper part of the structure. In some cases, pilings have to be driven down to the more firm subsoil layer. Even a basement may supply enough stability to keep a building from tilting.
Putting Up an Earthquake-Resistant Building
The Watch Tower Society’s Japan branch built a new addition to its printing plant in 1989. The building is 220 feet [67 m] long, 150 feet [45 m] wide, and six stories high, with a full basement. To make the building earthquake resistant, 465 concrete pilings were drilled into the ground.
At the site a noiseless, nonvibrating method was used to drive piles into the ground. The pilings, measuring 30 inches [80 cm] in diameter and 40 feet [12 m] in length, were tubes. After an auger with drill bits at its tip was inserted into the piling, it was hoisted to a vertical position over the spot into which it was to be driven. As the auger was turned, it removed earth through the center of the piling, and the piling was gradually forced into the tight-fitting hole. For greater depth, another section of piling could be welded onto the piece already driven.
Once at the desired depth, the drill bits at the tip of the auger were spread out, and a larger hole was excavated at the bottom of the piling. After the auger was removed, concrete was forced down the piling and into this cavity, and the piling was secured in place when the concrete solidified.
After all the pilings were thus set in the foundation, they were tied together with beams on which the floor and walls of the basement would rest. With such a foundation, the building should be able to withstand a reasonable amount of shock.
Is your home safe in an earthquake? No design strategies or other precautions can guarantee that a building will remain unscathed in a temblor. An earthquake might be of such magnitude that even the best-designed buildings would not withstand its devastation, as the severe earthquake in Kobe, Japan, in January demonstrated. Still, by choosing to live in a building that was conscientiously built, you can feel safer when an earthquake hits your area.