Engineers Design Self-righting Buildings That Survive Earthquake Test İn Style

A new earthquake-resistant structural system for buildings, just successfully tested in Japan, will not only help a multi-story building hold itself together during a violent earthquake, but also return it to standing up straight on its foundation afterward, true and plumb, with damage confined to a few easily replaceable parts.

The team that designed the system was led by researchers at Stanford University and the University of Illinois. During testing on a massive shake table, the system survived simulated earthquakes in excess of magnitude 7, bigger than either the 1994 Northridge earthquake or the 1989 Loma Prieta earthquake in California.

"This new structural system has the potential to make buildings far more damage resistant and easier to repair, so people could reoccupy buildings a lot faster after a major earthquake than they can now," said Greg Deierlein, professor of civil and environmental engineering at Stanford, who led the team that designed the new system.

The system dissipates energy through the movement of steel frames that are situated around the building's core or along exterior walls. The frames can be part of a building's initial design or could be incorporated into an existing building undergoing seismic retrofitting. They are economically feasible to build, as all the materials employed are commonly used in construction today and all the parts can be made using existing fabrication methods.

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

The rocking frames are steel braced-frames, the columns of which are free to rock up and down within steel "shoes" secured at their base. To control the rocking and return the frame to vertical when the shaking stops, steel tendons run down the center of the frame from top to bottom. These tendons are made of high-strength steel cable strands twisted together and designed to remain elastic during shaking. When shaking is over, they rebound to their normal length, pulling the building back into proper alignment.

At the bottom of the frame sit steel "fuses" designed keep the rest of the building from sustaining damage.

"The idea of this structural system is that we concentrate the damage in replaceable fuses," Deierlein said. The fuses are built to flex and dissipate the shaking energy induced by the earthquake, thereby confining the damage. Like electrical fuses, the steel fuses are easily replaced when they "blow out."

Deierlein and his colleagues conducted shake testing of the new system in the last few weeks at the Hyogo Earthquake Engineering Research Center in Miki City, Japan. Using different types of fuses and various shaking parameters, they conducted four major tests, the last on Aug. 24. They had previously developed and tested the individual components of the system and performed computational analyses to simulate the system's performance at laboratories at Stanford and the University of Illinois.