DESIGN FOR DISASTER Photos show what engineers say were big flaws in construction of Xinjian Primary School. Photo: (Du Bin for The New York Times)

Hollow, pre-fab concrete floor panels hang, hiding blackboards. Engineers said such flooring was a problem in China’s 1976 Tangshan quake.

Hollow, pre-fab concrete floor panels hang, hiding blackboards. Engineers said such flooring was a problem in China’s 1976 Tangshan quake.

Columns buckled, probably due to inadequate re-bar reinforcement and transverse binding (small wires).

Details matter: Engineers said ends of wire-like rods binding re-bar must be bent back, hook style, to hold if a column starts to fail. Here, they end in a 90-degree bend, which allows the re-bar to splay.

Details matter: Engineers said ends of wire-like rods binding re-bar must be bent back, hook style, to hold if a column starts to fail. Here, they end in a 90-degree bend, which allows the re-bar to splay.

Experts said the concrete appeared to have too much “aggregate” (gravel mixed with cement), of wrong size.

Nine fourth graders survived out of a class of 48. otographed in June. (Photo: China Photo Press)

(Photo: China Photo Press)

Tens of thousands of schools worldwide, from Portland, Ore., to Tehran, face the same risk and are not reinforced. For more on earthquakes and schools, explore earthquake posts and links at The New York Times Dot Earth blog: dotearth.blogs.nytimes.com Also….

Geohazards International : geohaz.org Earthquake Engineering Research Inst .: eeri.org OECD School Safety : oecd.org/edu/schoolsafety Coalition for Global School Safety : interragate.info/cogss Asian Disaster Reduction Center : adrc.or.jp International Strategy for Disaster Reduction : unisdr.org

Geohazards International : geohaz.org

Earthquake Engineering Research Inst .: eeri.org

OECD School Safety : oecd.org/edu/schoolsafety

Coalition for Global School Safety : interragate.info/cogss

Asian Disaster Reduction Center : adrc.or.jp

International Strategy for Disaster Reduction : unisdr.org