"Decked Out," Feature Article, May 2007

decked out

Corrugated metals may save money
in earthquake country.

by Michael Abrams, Contributing Editor

Thanks to current building codes, houses in the earthquake-prone parts of California are likely to cost a lot more to build than their more stably placed equivalents in the rest of country. But a simple new method of building shear walls has recently passed the shake test—and its low cost may very well revolutionize how buildings are built in the San Francisco Bay area and other regions prone to sudden lateral forces, be they earthquakes or hurricanes.

As of now, there are three ways to construct the walls of a multifamily house near the faults of California: conventional steel frames, concrete block shear walls, and an expensive, patented, proprietary system—essentially, sheet metal bonded to gypsum wallboard—that appeared on the scene a few years ago.

Hoping to fill the need for cheaper quake-resistant walls, Pankow Builders, a building company with a focus on precast concrete, made plans to enter the housing market. It approached Steve Tipping of Tipping Mar and Associates, a structural engineering firm in Berkeley, Calif., with the hopes of developing a less expensive concrete alternative.

"The conclusion was it made no sense in earthquake country," Tipping said. "Concrete buildings are just too heavy." But Tipping encouraged the company to continue research to find a system that would work with load-bearing studs, an alternative to the proprietary method, which, despite its cost, is highly flexible and can be placed anywhere in a structure.

A corrugated wall awaits a manmade earthquake. The sheets of corrugated lined up in the back have already been through the wringer—and they stood up well.

Tipping discovered that off-the-shelf, corrugated metal decking, typically used on a floor, served the purpose. Corrugated doesn't buckle like flat sheet metal, and its strength is only one of its many advantages. "You can't hurt it," he said. "You can kick it. You can whack it with a hammer. It's very light, noncombustive, very stiff, and can be used in lots of combinations. It can get rained on and there are no mold questions. It's sort of the ideal product."

The decking can also be put on any wall, new or already standing, interior or exterior. And in a wood building these corrugated walls would cost about a third as much as the proprietary competitor. If walls are prefabricated in a factory, builders will be able to reap even bigger savings.

As simple as the system sounds—studs, screws, and metal deck—it had to be tested before it could legally be put to use. But when Pankow executives went to their board, directors voted against funding the testing.

Tipping took the idea to the Charles Pankow Foundation, a nonprofit organization established in 2004 by the founder of Pankow Builders. The foundation, which funds research into innovative ideas for building design and construction, issued its first grants last year, and one of those grants covered the study of Tipping's corrugated metal shear walls.

Above: Bozidar Stojadinovic points out where corrugated steel met steel frame. Below: The walls are pushed until they fail. In this case, the bolts have sprung from their holes.

Tipping was able to enlist the research capabilities of Bozidar Stojadinovic, a professor in the Department of Civil and Environmental Engineering at the University of California, Berkeley.

Stojadinovic and Tipping tested a number of combinations using three different gauges of galvanized steel, three different stud gauges, and two screw sizes.

"We put stronger steel around it so it would shear as if it were a building, and the floor would move as if it were in a building," said Stojadinovic. Each configuration was put through a series of push/pull cycles for eight minutes.

A pneumatic actuator applied force at the top of the wall to shove it to and fro—as dictated by Acceptance Code 154. Tipping and Stojadinovic had expected the walls to hold up well to the mock stresses, but they were surprised by just how well they did.

"We were expecting to find that these panels were pretty strong—what you'd normally find with wood panels—but it turned out to be three times as strong," said Stojadinovic. "The one thing I was unsure of was whether the screws would hold. But it was fine."

The strength, affordability, and simplicity of construction are so great that one might wonder why the solution hadn't been dreamed up and adopted long ago.

"People have thought of this before," said Tipping. "If you talk to 10 engineers, at least two of them will say, 'Yeah, I thought about that.' But talk is cheap. We spent two years bringing this to market. First we had to find what material would make it work, then how it's going to be made, and then test it. It's easy to conceptualize; it's a ton of work to make it happen."

The walls aren't quite ready for immediate use, though: They need to be fire tested. Tipping said he is confident that they will pass with ease. Once this is accomplished, most likely in a matter of months, there's already a five-story, 100-unit apartment building in Berkeley waiting to use the new concept. If it does, the owner stands to save about $150,000.

A precondition of the Pankow Foundation's funding was that Tipping's system remain nonproprietary, so neither Tipping nor the Pankow for-profit company are likely to make any riches from the findings. "You might say that what we got out of it is a pat on the back. If it's not proprietary, everyone's interested in using it," Tipping said. "We said, 'Who cares?' Let's have fun with the testing."