That Mexican school that collapsed? It was a brittle concrete building — a type known to be vulnerable in quakes
By Rong-Gong Lin II
U.S. Department of Veterans Affairs
To structural engineers, it’s no mystery why the earthquake in Mexico this week turned a school into a death trap: The building was made of brittle concrete.
Such buildings don’t have enough steel reinforcing bars, known as rebar, which are encased in the concrete and act as a cage, allowing columns to crack and bend without crumbling.
Unlike steel or wood, concrete is non-ductile — it breaks before it bends. In an earthquake, concrete not sufficiently caged in steel can fall out, first piece by piece, then in catastrophic bursts that can bring down a building.
A concrete column without adequate reinforcement can snap like a piece of chalk.
In the case of Mexico’s City private Enrique Rebsamen school, where the bodies of 21 children and four adults have been recovered, a photograph published by the Los Angeles Times shows a concrete column leaning at a severe angle.
[...]