Chile's concrete code for buildings called into question

Published 2 April 2010

Since 1985, some 10,000 buildings three stories or higher were built in Chile — constructed in compliance with a strict building code introduced after a power earthquake which rocked the country; only 1 percent will have to be demolished as a consequence of the magnitude-8.8 earthquake that struck on 27 February; still, engineers who inspected the damage in many of the bearing-wall concrete frames of 12- to 26-story buildings say the damage calls into question the effectiveness of Chile’s building code, which does not require confinement reinforcing steel for concrete members

The good news for Chileans is that less than 1 percent of the 10,000 buildings three stories or taller, constructed since Chile’s 1985 earthquake, will have to be demolished as a consequence of the magnitude-8.8 Maule earthquake that struck on 27 February. The bad news is that the type of structural damage observed in many of the bearing-wall concrete frames of 12- to 26-story buildings is calling into question the effectiveness of Chile’s building code, which does not require confinement reinforcing steel for concrete members (see “Engineering Earthquake-resistant Buildings,” 8 March 2010 HSNW). A code change in the future is likely, say engineers who inspected the damaged areas.

ENR’s Nadine M. Post writes that of the 10,000 buildings three stories or taller built since 1985 in the area affected by the Maule quake, there were 2,000 buildings nine stories or taller.

The total number of collapsed buildings is roughly five, says Rene Lagos, owner of the Santiago-based structural firm that bears his name. There are another estimated 50 buildings that will have to be demolished, he adds.

“In the U.S., in a maximum-considered earthquake, we talk about 10 percent of buildings being damaged beyond repair, not 1 percent,” says Jack Moehle, professor of structural engineering at the University of California, Berkeley, and the leader of the Earthquake Engineering Research Institute’s 30-member team that toured affected areas in Chile. “The buildings did really well,” he adds.

The trip, from 10 to 20 March, was sponsored by the National Science Foundation (NSF). The multidisciplinary teams of four or five studied seismic performance of all types of engineered structures, building components and interior finishes, hospitals and the impact of the tsunami.

Most high-rise apartment buildings in Chile have bearing-wall concrete frames, rather than shear wall frames more common in the U.S. Still, many lessons can be learned from the Maule quake, says Moehle.

The Earthquake Engineering Research Institute now is waiting for drawings of a selection of Chile’s buildings and recordings of ground motions during the quake. The buildings then will be computer-modeled using the American Concrete Institute’s “ACI 318” code. The goal is to determine whether U.S. codes are too conservative or need to be ramped up. “This is a good testing ground for our building code,” says Moehle.

Post writes that in Chile, the “Seismic Design Code NCh 433-1996,” which provides minimum requirements for life safety, is a translation of “ACI 318-95.” There are some exceptions