Sun. That was my first thought.
It's 110° today where I live. Was my first thought as well. Also, the quote from one of the engineers "Today's bridge test exceeded our expectations." was somewhat disquieting. I would think they'd have dialed in their expectations pretty close to reality, as we have a pretty good handle these days on material sciences for the most part.
The careful text books measure
(Let all who build beware!)
The load, the shock, the pressure
Material can bear.
So when the buckled girder
Lets down the grinding span,
The blame of loss or murder,
Is laid upon the man!
Not on the stuff-the man!
-The Hymn of the Breaking Strain by Rudyard Kipling