That pigeons have melted steel.
Richfisher in the comments on Aug.8;

I sand blasted and painted steel bridges and water towers through high school and post secondary summer breaks. I have next to zero hearing left to show for it and two degrees.
The rust created from a pidgeon nest left in the same spot for about 5 years is unbelievable, it can erode a one inch thick steel rivet plate by about half it’s thickness in extreme circumstances.
Box beam bridges like this one are difficult to blast properly, because you can not properly point a stream of sand and air directly at rust spots up inside the beam.
Some inspectors are afraid of heights and will not go out on scaffold rigging to properly inspect crucial junctions for paint thickness or blast quality . I’ve never seen an inspector in a bolsons chair,(window washer) ever.
Now add double crested cormarants roosting on the beams.
My guess is it collapsed because of the rust.

Breitbart (AP), Aug. 22;

Pounded and strained by heavy traffic and weakened by missing bolts and cracking steel, the failed interstate bridge over the Mississippi River also faced a less obvious enemy: Birds, specifically pigeons.
Inspectors began documenting the buildup of pigeon dung on the span near downtown Minneapolis two decades ago.
Experts say the corrosive guano deposited all over the Interstate 35W span’s framework helped the steel beams rust faster.
Although investigators have yet to identify the cause of the bridge’s Aug. 1 collapse, which killed at least 13 people and injured about 100, the pigeon problem is one of many factors that dogged the structure.
“There is a coating of pigeon dung on steel with nest and heavy buildup on the inside hollow box sections,” inspectors wrote in a report.

…about the state of healthcare in Afghanistan, and the Canadian contribution to it.
A snippet:

Nothing is more indicative of the lack of context in Dr. Martin’s piece more than this line, though, as he cites the shortcomings of Afghan medical care:
Afghanistan has an infant mortality rate of 140 per 1,000 births; and the under-five mortality rate of 230 of 1,000 children.
Prior to the fall of the Taliban, Afghanistan had an infant mortality rate of 165 per 1,000 births:
Infant mortality has dropped by 18 percent in Afghanistan since 2001, in one of the first real signs of recovery for the country five years after the ouster of the Taliban regime, health officials said Thursday.
“Despite many challenges, there are clear signs of health sector recovery and progress throughout the country,” said Muhammad Amin Fatimi, the minister of health.
The infant mortality rate – the number of children who die before their first birthday – has dropped to 135 per 1,000 live births in 2006 from 165 per 1,000 in 2001, according to a countrywide survey by Johns Hopkins University, he said. By comparison, the infant mortality rate in France in 2005 was 5 per 1,000, according to Unicef.
That represents a drop of 18 percent and means that 40,000 to 50,000 infants who were dying annually during the Taliban era, are alive today, Fatimi said.

Needless to say, I’m not impressed with his cherry-picking of the facts.