Seismic Engineer Eases Tower's Rebar Congestion

Cary Kopczynski pioneers the use of high-strength rebar with high-strength concrete in tall buildings in earthquake-prone areas

Reinforcing steel congestion has long been the bane of builders of tall, high-strength reinforced concrete buildings in seismic zones. “The challenge we continually face is providing seismic confinement and seismic detailing that is buildable,” says structural engineer Cary Kopczynski, of the Bellevue, Wash., firm that bears his name.

Cary Kopczynski & Company At Seattle project, workers are having an easier time building columns.

For Escala, a 31-story residential building in Seattle, Kopczynski saw a chance to do something to ease the pain. He decided to specify 100-ksi rebar instead of 60-ksi rebar for use as seismic confinement in columns that use 14,000 psi concrete. The high-strength rebar reduces the amount of rebar and the congestion. That makes the beam-column connection faster to construct.

The decision was bold. Currently 100-ksi rebar is not in building codes for use as seismic confinement. But Kopczynski, as a member of the American Concrete Institute’s building code committee, knew that was likely to change. A prosposal was in the works that would add 100-ksi rebar to the code.

Armed with the research that formed the basis for the code change, Kopczynski took his idea to the city of Seattle for approval. To be prudent, the engineer had designed Escala conventionally in case the city shot down his scheme.

The city “put us through our paces, turning us down a couple of times,” says Kopczynski.

Multimedia  View Award of Excellence Luncheon and Acceptance Speech of Cary Kopczynski  April 3, 2008

But approval ultimately came. The building is currently under construction, scheduled to open in June 2009. Kopczynski is the first structural engineer in North America, and likely the world, to use 100-ksi rebar for column confinement. “I really believe this has so much potential to enable the industry to build large concrete structures in seismic zones in a better way,” says the engineer.

The potential may be realized soon. The new code provision was approved as part of ACI 318-2008.  “It will be on the streets soon,” says Jack Moehle, a professor of structural engineering at the University of California, Berkeley, and the chair of the ACI 318 seismic subcommittee. Moehle expects the provision to be adopted as part of the 2009 International Building Code. Jurisdictions will then have the opportunity to adopt it.

Other seismic engineers agree that 100-ksi rebar is promising. But they are concerned about adequate material supply and price escalation because the only producer to date is MMFX Technologies Corp., Irvine, Calif.

That may change. At least one potential producer is checking out the market.   “We are...working on developing products that keep up with where the market is going, and to meet the needs being created by visionaries such as Mr. Cary Kopczynski,” says Jim Petersen, sales manager for Nucor Steel Seattle Inc. “We do appreciate the work being pioneered by Mr. Kopczynski and particularly for the fact that it enables new possibilities of poured-in-place concrete construction methods.”

Kopczynski now is considering using 100-ksi steel at three other projects. For these, he is applying lessons learned at Escala. “The biggest challenge we face is to work out the cost model so you gain more buildability but also save money,” says Kopczynski. “At Escala, we haven’t saved what we hoped for.”

This was mostly because the rebar placer’s price was set before the city gave its approval to use the 100-ksi product. Therefore, the price did not reflect the efficiencies of placement that the material offers.

“We need to sit with the general contractor and placer in advance and make sure they appreciate they can do this more quickly and that we can expect a cost reduction,” says Kopczynski.

The material’s cost has also crept up.  But Kopczynski isn’t defeated. He looks forward to more price competition on the supply end and lower prices on the installer’s end. “Then we’ll have a workable system,” he says.