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The people of a country that experiences frequent earthquakes must be vigilant. Researchers across Japan are conducting cutting-edge experiments that, they hope, will make the nation and its inhabitants safer and more prepared for the next earthquake, whether it's a small tremor or “the big one.”
Partial Float
This is the Wind Tunnel Testing Laboratory at the Institute of Technology. The building weighs in at 2,900 tons (6,393,000 lbs.); about half of this weight floats on 1,500 tons (3,307,000 lbs.) of water in a 3.5m (11.5 ft.) -deep basement. The rest of the weight is supported by an isolation system composed of laminated rubber isolators.
(Photo & Illustration: Courtesy of Shimizu Corporation)
Dr. Takumi Ohyama, general manager of the Center for Advanced Computational Engineering at the Institute of Technology, Shimizu Corporation, is a captain of sorts: He's at the helm of a floating building at the Institute's Wind Tunnel Testing Laboratory in Tokyo.
The structure is situated in what's essentially a gigantic in-ground swimming pool. The “Shimizu Partial Float” is the latest in seismic isolation systems, which are designed to minimize seismic shaking by literally floating a building.
“We designed it for buildings up to eight stories high,” Ohyama explains. “The water buoyancy extends a structure's characteristic period to 4 to 5 seconds, which significantly lessens seismic impact. The system also incorporates a specially designed damping device that reduces the waves' magnitude by taking advantage of water's viscosity.” What's more, Ohyama adds, the water is a practical means of life support. “If people are ever trapped in a building that employs this dampening system, they can pump water out of the foundation without seriously affecting the functioning of the seismic isolation.”
Types of Anti-Earthquake Design
Earthquake Resistance
Earthquake-resistant buildings are constructed following a particular architectural design and utilizing specialized materials.
Earthquake Control
Dampers placed on a building's frame absorb seismic waves, helping enhance safety, functionality and living comfort in earthquake-prone regions.
Seismic Isolation
Anti-earthquake design also features isolation devices such as rollers or damper rubbers between the ground and the building. It's just as if the structure was perched atop soft springs that lengthen its unique seismic period, increasing the difference between the building's and the quakes' periods. This helps reduce the swaying a high-rise undergoes during an earthquake.
E-Defense
The illustration above shows the basic design of the gigantic Shaking Table and its mechanism. Measuring 20m (65.6 ft.) x 15m (49.2 ft.) and 5.5m (18 ft.) thick, it can handle loads up to 1,200 tons (2,646,000 lbs.). Moving in three dimensions, 24 actuators are controlled from a hydraulic operation room to simulate different types of earthquakes. In less than a second, the system can create a rapid 1m (3.3 ft.) back-and-forth (2m or 6.6 ft. total) movement in any direction.
(Illustration: Courtesy of Hyogo Earthquake Engineering Research Center)
After examining the heaps of debris caused by the Great Hanshin Earthquake in 1995, some researchers argued that they needed a real test subject, rather than scale models and computer simulations, so they could formulate plans to more effectively mitigate seismic damage. Thus was born a plan to build a 3-D Full-Scale Earthquake Testing Facility to simulate quake effects at the Hyogo Earthquake Engineering Research Center, National Research Institute for Earth Science and Disaster Prevention (NIED). Using this Shaking Table, located north of Kobe in the city of Miki, researchers have been experimenting with actual-size buildings to obtain detailed information about their movement, damage and collapse.
“At 20m (65.6 ft.) by 15m (49.2 ft.), the Shaking Table is the largest of its kind in the world; it can hold a real six- or seven-story building and shake it until it collapses,” says Dr. Takahito Inoue, head of the Planning Section at the center, which has been nicknamed E-Defense. “Actual iron bars used for reinforcement have small bumps on their surface, helping them bond more tightly with concrete — tighter than the smooth bars that are used in miniature experiments, the results of which are not accurate enough to be fully applicable to real-world settings.”
Shaking Table
(Photo: Courtesy of Hyogo Earthquake Engineering Research Center)
Two real two-story houses belonging to families living in a nearby city for more than 30 years were transported in for experiments.
(Photo: Courtesy of Hyogo Earthquake Engineering Research Center)
NIED researcher Dr. Takuya Nagae conducted an experiment in March 2008 in which a mockup of a 20-story (approx. 80m or 262.5 ft.) building with specifications dating prior to 1980 took its place on the Shaking Table. “It represented a typical skyscraper of the period, reflecting real conditions,” he said. Due to structural limitations of the E-Defense facilities, however, only the first four floors of the test building were built to actual specifications. The remaining 16 floors were constructed of 200-ton (440,900 lbs.) three-layer structures that would accurately simulate the swaying upper floors experience during an earthquake. “We gauged the deformation at the lower floors and the degrees of sway on the upper levels,” Dr. Nagae told us, adding that the experiment's primary purpose was to confirm that the lower fifth of a tall building bears the brunt of an earthquake's destructive force.
The experiments Dr. Nagae and his group conducted were part of a five-year Special Project for Earthquake Disaster Mitigation in the Tokyo metropolitan area being sponsored by the Ministry of Education, Culture, Sports, Science and Technology. Starting in 2007, experiments were conducted in anticipation of long-period quakes that could devastate Japan's crowded cities. Data from the tests will be applied to make super-tall skyscrapers more robust against the earthquakes that will, inevitably, shake them.
Nature often reminds us that we are not the masters of the world. Earthquakes are one of the most jolting examples of this simple truth. Humans do, however, have the capacity to create solutions that meet the challenges of living on a very active, sometimes hostile, planet. In the case of earthquakes, Japan is leading the way. Out of necessity and out of respect for the tremendous forces at work beneath their feet, we will continue to make buildings more durable, more adaptable and safer.
The unique design of Nikon's mirror balancer immediately stops the main mirror from vibrating.
The innovative design of Skyhook virtually eliminates external vibrations before they can reach the projection lens.
It's very important for precision equipment to have safeguards against vibration, which can adversely affect performance. The technology in our cameras and i-line scan field steppers is a good example of how Nikon combats “the shakes.”
The main mirror in an SLR camera swings up for shooting then immediately returns to its starting position. It's vital for the mirror to stop in precisely the correct location, otherwise autofocus operation and the image's clearness in the finder will be inferior. For example, if the mirror is jostled even slightly, the light sent to the autofocus module via the main and sub mirrors, and the viewfinder, will not be stable.
Imagine how little time is available for accurate autofocus operation during nine-frames-per-second continuous shooting. Enabling precise, instantaneous, full-stop action on the mirror may give the camera an extra millisecond of stable light. That may not seem like much, but it's an eternity in high-speed continuous shooting.
To address such problems, Nikon developed a new mirror balancer. We designed it to function as a vibration-control device. A unique balancer support rod stops the mirror in its tracks, absorbing its energy and instantly stabilizing it. Then, the kinetic energy of the mirror is negated by a friction brake mechanism before the balancer is quietly returned to its starting position.
For our world-class steppers, we've developed Skyhook Technology, an anti-vibration mechanism consisting of a projection lens suspended from three wires. This suspension system replaces the rigid frame typically used in steppers, which easily transfers vibrations from the wafer stage movement and the floor to the projection lens. With Skyhook, vibrations are transferred only through wires. If shaking occurs, the vibrations are detected by an acceleration sensor and immediately canceled. Nikon demands super-high precision; we will not tolerate vibration, no matter how miniscule. Skyhook Technology is just the latest example of a Nikon breakthrough in LSI miniaturization.
