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After Mexico City quake, big structural risk remains

Rong-Gong Lin II and Cecilia Sanchez, Los Angeles Times on

Published in News & Features

But Mexico City hasn't had that level of discourse, and there is an expectation that owners would also oppose mandatory retrofits. Alcocer, who is a member of a mayoral commission established to make recommendations for the city's long-term seismic resiliency efforts, said he imagined offering owners economic incentives such as waiving property taxes or easing the financial burden with city loans or bonds.

In California, retrofits of smaller apartment buildings typically cost tens of thousands of dollars, while strengthening taller buildings can exceed $1 million.

Alcocer estimated that the cost of retrofits in many cases would be 15 percent to 20 percent of the cost of replacing a building.

A total of 42 buildings collapsed and as many as 1,000 more were damaged in the Sept. 19 earthquake that was centered about 80 miles southeast of Mexico City.

Many of the buildings that fell were made of brittle concrete, including a seven-story office building on Avenida Alvaro Obregon in Mexico City, where 49 people died -- the largest death toll at any one site.

That building was a "flat slab" structure, a design that lacks horizontal beams that are far more durable in an earthquake. Flat slab construction was very popular in Mexico City in the 1960s and '70s, Alcocer said.

"This system is not a proper system for a high seismic area," he said.

Retrofitted buildings survived just fine in the earthquake.

"We have the prescription," said Saif Hussain, a Los Angeles-based structural engineer who visited Mexico City in October with the Applied Technology Council, which develops nationally recognized retrofit standards. "It's just a matter of people being aware of it, and implementing it -- and the political will."

Alcocer said he recently met with Mexico City's mayor, Miguel Angel Mancera, and suggested the city make a plan to review and eventually strengthen certain classes of buildings known to be hazardous, as well as evaluate all schools, hospitals and markets. "He's very open to it," Alcocer said.

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