Photo from Matt Hardigree / jalopnik.com  Brought to my attention by Max Eternity.

This section of an Atlanta parking garage collapsed Monday.  Although the support frame in this garage is concrete, while the support frame at Univesity Square is steel, the double T beams in Atlanta are similar to those used in the University Square Parking Garage, in University Heights, Ohio.  Below is a image from an Atlanta TV station (whose site ads locked up my computer so I won't give them credit) showing a concrete horizontal support which popped out of the side of the garage. 

Did this horizontal failure start the collapse, or was it a knocked out by planks dropping?

The Domino Effect:  if any beam slips off its seat on an upper deck, it will take out all the floors below.

That's what happened in Atlanta.

Since the recent temperature in Atlanta has been 100F, the concrete floor beams have been expanding in length.  Then at night they cool and shrink in length.  The only connection between the supporting ends of the concrete planks and their horizontal supports is friction - ie gravity.   If the beam length becomes shorter than the distance (span) between the supporting frame, the floor plank will fall.   There is no mechanical connection between the supporting frame and the floor beams.  

The 100F heat could have caused the floor planks to jack out the perimeter supporting frame.   Creep, Creep. 

Or a floor plank could have failed on its own and snapped.

Same at University Square.   The image 6.9.09  below shows a column which is being jacked horizontally away - notice the torn caulking - from the top floor (hot sun)slabs at University Square. 

Who's minding the store?