New Flexible Building Survives Powerful Test Earthquake

A new method of construction that uses steel tendons and replaceable "fuses" to help a building survive strong earthquakes was successfully tested recently.

On a giant shake table, the system survived simulated earthquakes in excess of magnitude 7, more powerful than both the Northridge earthquake in 1994, which rocked the Los Angeles region, and the Loma Prieta earthquake in 1989 that devastated parts of the San Francisco Bay Area.

The massive force of earthquakes often leave behind damaged buildings that are either beyond repair or very costly to fix.

"Most buildings that we design today for large earthquakes are designed such that when there is a large earthquake, the building, in a sense, sacrifices itself to save the occupants," said Greg Deierlein, a professor of civil and environmental engineering at Stanford University who led the research team.

To reduce structural damage, the new system relies on steel braced-frames, built into a building’s exterior walls, which are designed to rock up and down whenever an earthquake strikes. Running down the middle of the frames are steel tendons that are elastic enough to control the rocking. The tendons also help lift the building back to its proper alignment once the shaking stops.

"What is unique about these frames is that, unlike conventional systems, they actually rock off their foundation under large earthquakes," Deierlein said.

Steel "fuses" that sit at the bottom of the frame also keep the rest of the building from sustaining damage. The fuses are built to flex and dissipate the seismic energy, which confine the damage to certain areas. Like electrical fuses, the steel fuses are easily replaced when they "blow out."

"The idea of this structural system is that we concentrate the damage in replaceable fuses," Deierlein said.

While various researchers have been working for 10 or 15 years on some of the ideas and techniques incorporated in the new system, this is the first time anyone has put them all together and demonstrated their performance, Deierlein said.

The system can be installed as part of a building's initial design or retrofitted into an existing building. It is also economically feasible to implement since it can be built from materials commonly used in construction, researchers say.

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