The Risks Of Non-Ductile Concrete Buildings
Drive through urban areas and there’s a good chance you’ll pass any number of concrete buildings. It was 1904 when the first concrete high-rise went up in Cincinnati. These structures were popular across the country as early as the turn of the 20th century. Concrete buildings remained prevalent throughout the United States into the 1980s, though the West Coast began phasing out concrete construction decades earlier because their lack of flexibility makes them susceptible to damage in seismic activity. Non-ductile concrete buildings might look sturdy, but that appearance can be deceiving.
“We know from past earthquakes, non-ductile reinforced concrete buildings don’t perform well in earthquakes, all around the world,” Reginald DesRoches, chair and professor in the School of Civil and Environmental Engineering at Georgia Tech said in a Live Science article. “They collapse.”
Most of these concrete buildings are referred to as “non-ductile” or “non-ductile reinforced concrete.” Ductile is a synonym for flexible or elastic, so as the term would infer, non-ductile concrete buildings lack flexibility. The concrete used in them – the reinforced portion of the term – is embedded with steel mesh and/or steel rebar.
Non-ductile concrete buildings may have met the building codes and standards in the era they were built, but experience has shown those codes didn’t account for weaknesses in an earthquake. Studies suggest older non-ductile buildings would sustain significant damage in a strong earthquake, if not collapse completely.
The primary issue with older concrete buildings is they lack enough steel reinforcement in load-bearing columns to hold them in place. These columns fail during the sideways movement of a major seismic event, leaving the building vulnerable to destruction. Newer concrete buildings, especially those erected after improved building codes, feature more advanced columns, using more of and strategically spacing steel ties or spiral reinforcements.
FEMA Calls Non-Retrofitted Buildings “Single Biggest Contributor to Seismic Risk”
There’s a frightful saying among seismic engineers that “earthquakes don’t kill people, buildings do.” In fact, the U.S. Federal Emergency Management Agency (FEMA) calls non-retrofitted buildings “the single biggest contributor to seismic risk in the United States today.” Indeed, these older buildings, including non-ductile concrete buildings, represent a threat during major seismic activity. As a result, they need retrofitting to make them more ductile or flexible.
A group known as the Concrete Coalition estimates there are as many as 17,000 of these older concrete buildings in the state of California, with more than 1,000 in Los Angeles alone. These includes some schools and government buildings. Research studies suggest that, according to even “conservative estimates,” up to 50 of these buildings would totally collapse during a major earthquake in Los Angeles. Engineers also warn that many business owners make an erroneous assumption that because their building survived a previous earthquake it will do so again.
Damage or collapse isn’t the only concern for concrete building owners. Some municipalities are starting to move toward regulations mandating seismic retrofits. Los Angeles began requirements for retrofitting in 2015. Santa Monica, West Hollywood and Pasadena have followed suit. Other cities currently have voluntary retrofitting policies in place.
Because the cost has been a major deterrent to retrofit, there are some assistance programs that exist – such as PACE in Los Angeles – and many local governments are allowing some of the costs to be shared with building tenants, removing the totality of the burden from building owners.
Retrofitting needs will vary for different buildings, but real estate owners have options – and they’re options that should be considered a priority.
“I think many people think there’s nothing you can do about an earthquake other than hope it doesn’t happen while you’re in the building or while you’re living in that area,” DesRoches said. “I think our test and other tests have shown that, in fact, there are fairly straightforward ways that you can retrofit a structure to significantly improve this behavior, so that either it doesn’t collapse or even is fully operational after an earthquake.”