A 10-story building looms above UC San Diego’s earthquake shake table near Scripps Ranch. Next week, the device will simulate an earthquake to see whether a structure made from a lightweight, recycled steel material can withstand it.
The building’s load-bearing system, its walls, floors and roofing are all made from cold-formed steel. In the real world,d building codes would only allow a building like this to be six stories high in a seismic zone like California.
“So a big aspect we’re testing here is can we push the envelope and see robust seismic performance beyond six stories. So you see, we’ve got a ten story building, so we’re all really excited! We’ve already broken code limitations with this structure,” said Tara Hutchinson, a professor of structural engineering at UCSD.
Cold-formed steel (CFS) got its name because its final step of production and shaping is done at room temperature. It’s supplied to builders in coils of thin steel.
“The raw material is sheet steel. The same steel that goes into the automotive industry to make fenders and bumpers and hoods,” said Don Allen, executive director of the Steel Framing Industry Association.
Allen said cold-formed steel is recycled steel. The material comes from old cars, fridges, ovens, just to name a few. The used steel is melted down and pressed into sheets that are less than a tenth of an inch thick. But Allen said CFS is surprisingly strong.
“The thing is once you melt it down and get it back down to its iron molecules, then you can make steel out of it that’s stronger than the original steel,” he said. “So if you’re making a fridge, the side of that refrigerator doesn’t have to be very strong at all. But you can melt that down and make this stuff that can carry these 10, 15 story structures.”
The advantages of cold-formed steel include its small carbon footprint, thanks to recycling. It’s non-combustible, very strong but very lightweight.
UCSD shake-tested a 10-story wood-framed building made of mass timber a couple years ago. It also was environmentally friendly, made from a renewable resource. But Hutchinson said it was twice as heavy as the CFS building on the shake table now.
“Now if you’re in a seismic realm, an earthquake realm, lightweight materials are fantastic because the forces that we generate are proportional to the mass that we put into the structural system. So if we can lighten up the structural system, we can reduce those seismically induced forces,” Hutchinson said.
The cold-formed steel building will be tested on the earthquake shake table on Monday. If the test is successful, Hutchinson hopes to see a change in building codes to allow greater use of the material in the near future.
