Why The World Trade Center Collapsed

The University of Sydney's Department of Civil Engineering offers an in-depth engineering discussion of why WTC collapsed.

1 minute read

September 15, 2001, 8:00 AM PDT

By Chris Steins @planetizen


"The structural integrity of the World Trade Center depends on the closely spaced columns around the perimeter. Lightweight steel trusses span between the central elevator core and the perimeter columns on each floor. These trusses support the concrete slab of each floor and tie the perimeter columns to the core, preventing the columns from buckling outwards.After the initial plane impacts, it appeared to most observers that the structure had been severely damaged, but not necessarily fatally.It appears likely that the impact of the plane crash destroyed a significant number of perimeter columns on several floors of the building, severely weakening the entire system. Initially this was not enough to cause collapse."

Thanks to Design Architecture

Friday, September 14, 2001 in Utah Daily Herald

portrait of professional woman

I love the variety of courses, many practical, and all richly illustrated. They have inspired many ideas that I've applied in practice, and in my own teaching. Mary G., Urban Planner

I love the variety of courses, many practical, and all richly illustrated. They have inspired many ideas that I've applied in practice, and in my own teaching.

Mary G., Urban Planner

Cover CM Credits, Earn Certificates, Push Your Career Forward

Aerial view of town of Wailuku in Maui, Hawaii with mountains in background against cloudy sunset sky.

Maui's Vacation Rental Debate Turns Ugly

Verbal attacks, misinformation campaigns and fistfights plague a high-stakes debate to convert thousands of vacation rentals into long-term housing.

July 1, 2025 - Honolulu Civil Beat

Logo for Planetizen Federal Action Tracker with black and white image of U.S. Capitol with water ripple overlay.

Planetizen Federal Action Tracker

A weekly monitor of how Trump’s orders and actions are impacting planners and planning in America.

July 2, 2025 - Diana Ionescu

White and purple sign for Slow Street in San Francisco, California with people crossing crosswalk.

San Francisco Suspends Traffic Calming Amidst Record Deaths

Citing “a challenging fiscal landscape,” the city will cease the program on the heels of 42 traffic deaths, including 24 pedestrians.

July 1, 2025 - KQED

Google street view image of strip mall in suburban Duncanville, Texas.

Adaptive Reuse Will Create Housing in a Suburban Texas Strip Mall

A developer is reimagining a strip mall property as a mixed-use complex with housing and retail.

July 6 - Parking Reform Network

Blue tarps covering tents set up by unhoused people along chain link fence on concrete sidewalk.

Study: Anti-Homelessness Laws Don’t Work

Research shows that punitive measures that criminalized unhoused people don’t help reduce homelessness.

July 6 - Next City

Aerial tram moving along cable in hilly area in Medellin, Colombia.

In U.S., Urban Gondolas Face Uphill Battle

Cities in Latin America and Europe have embraced aerial transitways — AKA gondolas — as sustainable, convenient urban transport, especially in tricky geographies. American cities have yet to catch up.

July 6 - InTransition Magazine