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Too soon to tell how Mexico City buildings held up in quake, UB engineers say

Volunteers and rescuers working at a collapsed building at Colonia Roma, Mexico City, after the Sept. 19 earthquake. UB earthquake engineers say that while there are instances in which buildings have performed poorly, they do not yet have a clear picture of how structures in the city fared as a whole. Photo: ProtoplasmaKid / Wikimedia Commons / CC-BY-SA 4.0

By CHARLOTTE HSU

Published September 22, 2017

The images emerging from Mexico City in the wake of Tuesday’s 7.1 magnitude earthquake are devastating: Collapsed buildings. Rescue workers digging through piles of rubble, sometimes with bare hands. A frantic search for survivors at a school where many children died.

But these early pictures do not mean that engineering across this region of 20 million people failed, say UB earthquake engineers.

“In the earlier stages of an earthquake, you see the collapsed buildings, and it is dramatic and it is horrible. But the reality is that in a city of 20 million like the greater Mexico City area, the deaths are not yet enormous at this point,” Michel Bruneau, a professor of civil, structural and environmental engineering in the School of Engineering and Applied Sciences, said on Thursday morning.

“You see a number of isolated cases where the buildings have performed poorly, but we do not yet have a clear picture of how the city as a whole fared,” he said. “That is not to minimize the suffering that has been experienced — but just to say that we need more time before we can understand the scope of what happened.”

A city with earthquake engineering expertise

Tuesday’s earthquake took place on the anniversary of an 8.0 magnitude temblor that killed thousands of people in the Greater Mexico City area in 1985.

Since that 1985 event, Mexico has upgraded its building codes significantly, and the region’s universities produce engineering graduates who are very knowledgeable in earthquake engineering, said Michael Constantinou, SUNY Distinguished Professor of Civil, Structural and Environmental Engineering.

Constantinou is familiar with seismic engineering in the region, having worked on the award-winning structural design of the Torre Mayor, a 738-foot-tall skyscraper that was the tallest building in Mexico at the time of its completion in 2003. The tower was outfitted with a system of seismic dampers, similar to shock absorbers in cars, that were made by Taylor Devices in Western New York, he said.

“In the Mexico City area, the building codes are quite advanced,” Constantinou said. “They have many modern buildings there that are in very good condition to sustain strong earthquakes — not any earthquakes, but strong earthquakes.”

Older buildings still a problem

One major challenge, Constantinou and Bruneau say, lies with older buildings, which are found in any city in any part of the world.

Bruneau traveled to Mexico City after the 1985 quake to assess the damage there, and says many of the photos he has seen of collapsed buildings from Tuesday’s temblor are eerily familiar. On Tuesday, as in 1985, masonry structures toppled and concrete buildings pancaked, with one floor piled on top of the next after supporting pillars failed.

“You have to realize that in a city of 20 million people, not every building has been built the same year, so you have buildings of different vintages that have been built to different codes,” he said. “You may have the best code today, but still have hundreds of thousands of buildings that were built before that code was in place.”

“Every city will be like that,” Bruneau added.

Lessons for the future

For earthquake engineers, the buildings that did not collapse in Mexico City will be just as interesting as those that did.

Due to better seismic design, modern structures weakened by earthquakes usually do not collapse, Bruneau said. Instead, they sustain more subtle damage. While these problems get little media attention, earthquake engineers will be watching with interest.

“There can be a lot of new lessons to learn from the damage to these well-conceived buildings,” Bruneau said. “This is going to be a test to see if they did what they were expected to do, and in some cases there are surprises that pop out. It can be a matter of days or weeks before damage is noticed because some of these defects will be hidden by architectural features, so they’re not easy to spot.”