The University of Sydney's Department of Civil Engineering offers an in-depth engineering discussion of why WTC collapsed.
"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
FULL STORY: World Trade Centre - New York - Some Engineering Aspects

Maui's Vacation Rental Debate Turns Ugly
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Planetizen Federal Action Tracker
A weekly monitor of how Trump’s orders and actions are impacting planners and planning in America.

San Francisco Suspends Traffic Calming Amidst Record Deaths
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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.

Study: Anti-Homelessness Laws Don’t Work
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In U.S., Urban Gondolas Face Uphill Battle
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