A team of researchers from the University of California, San Diego and Johns Hopkins University tested a 10-story, cold-framed steel building for seismic safety on Monday morning.
The 10-story building’s skeleton is made from cold-formed sheets of construction-grade steel that are then shaped at room temperature to make individual structural components — studs and floor joists, for example. These are then fastened together to form walls and floors. Cold-formed steel is easy to manufacture, strong, light and made from recycled steel. The material has become more popular as a substitute for timber in the past four decades, partially because it can be shaped into components similar to those used in timber construction, such as two-by-fours. It also doesn’t burn when exposed to fire.
The UC San Diego shake table, located on an industrial lot off Pomerado Road, is the only outdoor facility of its kind in the world and the only simulator capable of testing a building of that height.
The researchers ran multiple earthquake motions, including the 1989 6.9 magnitude Loma Prieta earthquake that hit northern California
“We imparted a peak input acceleration of .3 G’s — that’s 30% of gravity in one axis — and almost .5 G’s in the other axis, so real earthquake motions,” said Tara Hutchinson, who is a professor of structural engineering at UC San Diego.
During the earthquake simulation, the building moved very little, just some gentle swaying during the most intense parts of the test. According to the researchers on hand, visually, the building passed the test.
“It’s good that the building didn’t move that much,” Hutchinson said.
“I think we’re building it right,’ added Nicole Winfield, who works with the Onyx Building Group. “When you don’t see hardly any movement and you know it’s a large earthquake — well, we’re doing something right.”
In the coming days, weeks and months, UC San Diego researchers will dig deeper into the data. Hundreds of wires were attached to more than 800 sensors throughout the structure.
“They measure all sorts of quantities, displacement, acceleration, strain, forces and so on,” said Joel Conte, who is also a professor of structural engineering at UC San Diego. “One aspect of seismic resilient structures is not only that they don’t collapse and save lives, but that they can be re-used very soon after the earthquakes and repaired easily.”
Current building codes in the United States only allow for six-story buildings when cold-formed steel is the chosen structural system. The results of this test will help to determine if that height limit can safely be increased.
“We’re able to test new ideas and push the boundaries of what we’re doing in structural design and construction,” Hutchinson said. “Cold-formed steel is a great example of a promising, lightweight, sustainable and highly durable material, ideal for use in regions of high seismic hazard and for construction of tall buildings.”
“It’s taller than we’ve gone before, bigger than we’ve gone before, and it’s pretty well controlled,” said Ben Schafer, professor of civil and systems engineering at Johns Hopkins. “We saw a response that makes sense to us that’s similar to our models, so as engineers, we’re pretty excited that we are on the right path with this kind of innovation. We’re looking at an innovative building system that we can use in the U.S.A. and other earthquake countries that can be constructed quickly, with sustainable materials, all the things we need to build more housing and more commercial buildings in the U.S.”