January 1, 2007 To develop designs that can survive extreme seismic events, and to devise retrofit solutions for older homes, civil engineers who specialize in structural design test realistic models of homes in earthquake simulators. They place the homes on two adjacent shake tables designed to move in three directions, creating realistic earthquake motions. Cameras and accelerometers measure the rate of movement.
BUFFALO, N.Y. -- Homes are made to withstand the test of time. But the ultimate test is one that can survive a large-scale earthquake. And simulating an earthquake in a lab helps improve homes in real quake zones.
Most people don't ever want to experience an earthquake.
"I experienced a very strong earthquake in 1997 in Athens," Ioannis Christovasilis, an Earthquake Structures Graduate Student at University at Buffalo in N.Y., tells DBIS. "I was a little bit frightened, yes."
University at Buffalo Structural Engineer Andre Filiatrault says, "We had an aftershock, maybe a magnitude five ... That was pretty dicey. You felt the shaking work up."
But today, Filiatrault is eager to watch an earthquake simulator shake this house to a magnitude 6.7 quake. The full-scale, fully furnished home is built like many in earthquake zones, but prone to damage. The test shows how much shaking a wood home can endure.
Filiatrault says, "We shook this building past its so-called design level. We shook it to an extreme event." The house sits on two adjacent shake tables designed to move in three directions, creating realistic earthquake motions. Cameras and sensors called accelerometers measure the rate of movement.
The test reproduced California's 1994 Northridge Quake that killed 51 people and caused $44 billion in damage. The structure fared better than researchers thought, but they warn it's still unsafe.
"If I was a homeowner, right now, and this was my home, it'd be borderline for me to go back in," Filiatrault says.
Results from the test will help builders design homes ready to survive earthquakes and retrofit solutions for older homes. Filiatrault says, "All this data is important to improve the way we do things in the future" ... future improvements to help homeowners prepare for future earthquakes.
Next, a six-story, wood-frame structure will be built and shipped to Japan to be tested on the world's largest shake table in 2009.
BACKGROUND: Engineers at the University of Buffalo are launching a series of unprecedented seismic tests on a full-scale wood frame townhouse (see video on the University of Buffalo's Web site). The 73,000-pound, 1,800-square-foot structure will be the largest wooden structure to undergo seismic testing on a shake table in the United States. The townhouse is equipped with 250 sensors that will provide detailed information about how each nook and cranny behaves during five simulated earthquakes of escalating severity. A dozen video cameras will record the damage as it occurs. The tests will help engineers give people tips on keeping their homes protected during an earthquake, and will lead to larger, taller wooden structures being safely built in seismic regions nearby.
WHAT CAUSES QUAKES: An earthquake is a vibration that travels through the earth's crust. It can be caused by any number of things, including meteor impacts, underground explosions (from a nuclear test, for example) or collapsing structures, such as a mine. But most naturally-occurring earthquakes are caused by the movement of the earth's tectonic plates. The earth's surface is made up of large plates that slide over the underlying layer. At the plate boundaries, plates can move apart, push together, or slide against each other.
WHOSE FAULT IS IT ANYWAY: Wherever plates meet, there will be faults at the boundaries: breaks in the earth's crust where the blocks of rock on each side are moving in different directions. There are many different kinds of faults, but in all of them, the various blocks of rock push together tightly and produce friction. With enough friction the plates can become locked, increasing the pressure until the plates suddenly give way and snap forward suddenly, sending out a series of seismic waves. These fault lines are the main source of earthquakes.
WHAT IS ELASTICITY? Different materials can withstand different amounts of deformation, a property known as elasticity. Most materials are elastic to some degree: When they are deformed or bent by an infusion of incoming energy, they will bounce back to their original shape. But elastic materials all have their limits. Metal springs and rubber bands are very elastic. Plaster and glass are not very elastic; instead, they are brittle and snap with even a small deformation.
The American Society of Civil Engineers and the Incorporated Research Institutions for Seismology, Inc. contributed to the information contained in the TV portion of this report.