Tuesday, October 10, 2017

Stanford Engineering: Lives Lost in Mexico Quake Could Have Been Saved

From ABC (US) News:
Warm lighting would enhance the wood floors' natural glow, the developer promised, so when all the custom lightbulbs burnt out, Anahi Abadia and her husband grudgingly drove to Home Depot to replenish supplies for their chic new flat in southern Mexico City.

They had just reached the register when the earthquake hit, shaking the store so fiercely the structure screeched. Minutes later, a text came in from their neighbor: The elegant apartment they had purchased only six months earlier had collapsed, rendering their new home a pile of crushed concrete.
They were among the fortunate: Two women working in their building and dozens more perished on Sept. 19 in structure failures that several prominent engineers now say could have been prevented. 

Nearly two-thirds of the 44 buildings that fell in Mexico City were designed with a construction method called flat slab — in which floors are supported only by concrete columns — now forbidden in parts of the United States, Chile and New Zealand according to data compiled by a team of structural engineers at Stanford University and obtained by The Associated Press.

Mexico City officials were widely lauded for tightening their building codes after thousands died in the 1985 earthquake. But they left out one crucial reform: a prohibition on the building technique that caused 61 percent of the building collapses in last month's magnitude 7.1 quake, which killed 369 people and blanketed tree-lined avenues in rubble.

"I keep thinking about what would have happened if I had still been in bed that afternoon." said Abadia, 26, who was in her bedroom that morning recovering from thyroid cancer, dreaming of furnishing the home she and her husband moved into in March. "That was where we used to feel safe."

The concrete slabs used to build floors and ceilings can be cast to include some rebar for reinforcement, and give builders greater flexibility in room layout and allow for higher ceilings.
But in an earthquake, without reinforced concrete walls or lateral bracing to resist forces pushing structures sideways, buildings with that design can move too much. The columns, and connections between the slabs and columns, can easily break, prompting collapse, as was the case at a school where 26 people died, most of them children.

"We have known for 30 years that this system killed lots of people, so why are we still using it?" asked Eduardo Miranda, a professor of civil and environmental engineering at Stanford and global expert on earthquake-resistant design who compiled the data. "The right decision after '85 would have been to completely ban this kind of construction. We could have saved lives."...MUCH MORE