SALT LAKE CITY — A University of Utah professor has found three ways concrete and steel columns fail, and the first is a likely culprit in the Surfside, Florida condo collapse.
"The first is corrosion,” said Professor Chris Pantelides, with U of U Civil and Environmental Engineering.
High-rise construction columns have rebar inside, giving vertical strength and flexibility. On the outside: reinforcing spirals, most often steel. Those spirals can get exposed, wet and rusty...and that damage spreads.
“And if you see a little bit of corrosion, it doesn't mean it's there where you see it. It's actually a little bit to the left and to the right,” said Pantalides.
Pantalides’ research, published in the Journal of Composites for Construction, tested steel, composite and hybrid columns under corrosive conditions, finding steel spirals prone to corrosion, which compromises the cement and can lead to corrosion of internal rebar.
In areas prone to such conditions, his paper, coauthored by Michael Gibbons and Lawrence Reaveley, showed hybrid columns suffered less corrosion.
Talking about the environment in Utah, Pantalides said some areas have more damage from corrosion than one would expect in a dry climate, because of road surface treatments in the winter.
“We use salt water, the icing salt on the bridges, and so you'll be surprised that some parking garages in Utah actually have corrosion problems in the basement,” he said.
The second way columns can fail: stability issues related to load shifting.
In Surfside, one researcher found evidence of ground settlement at the location of the tower, and a nearby construction project created shaking in the Champlain South Tower that disturbed residents.
“If the load moves a little bit to the right or to the left of the center of the column, then the capacity of the column starts to reduce almost proportionately,” said Pantalides.
The third factor that can lead to column damage is lateral, or seismic, motion. Pantalides did not see this as a likely factor in the Florida disaster.
Pantalides had two messages for residents and managers of high rises:
- Maintenance is crucial.
- Buildings have lifespans and sometimes need to be replaced.
In a previous version of this article, Dr. Pantalides mentioned concerns about post-tensioning steel. He has since learned his information was incomplete.