[bobduke]

From the article, the posted weight limit was 26 tons. A quick google search ("bus weight") shows that buses can easily exceed that limit and the bus on the bridge was a "double" bus.

Maybe the bus wasn't supposed to cross that bridge?

[michaelrpeskin]

I seem to remember that bridge weight limits aren’t as clear as just a number like that. I’d have to look at the DOT site, and I’m on my phone and too lazy right now. But I’d be willing to bet that a limit is per axle with other factors multiplied in for how close tandem axles are. It’s more about weight distribution than total weight. The posted signs are meant to be read by truckers who know the formulae.

[intrasight]

A couple days before the collapse, there was a heavy snowfall. Deep heavy snow. I calculate that the weight of the snow was about 200 tons.

[Johnny555]

How did you calculate that? I don't know how much snow there was, but 10 inches of snow has around 1 inch (2.5cm) of water.

The bridge was 136m long, by about 13m wide and assuming 2.5cm of water content:

136m * 13m * .025m = 44 m^3 of water, or 44,000 kg, roughly 50 US tons.

A newspaper report said there was a light snow with 1 or 2 inches accumulated since 2am the morning of the collapse. Photos of the scene showed grass and small rocks on the ground visible through the snow, so it doesn't seem like there was a lot of snow on the ground. Even if there was heavy snow a couple days before the collapse, most of it would have been plowed off, I don't see big berms of snow on pictures of the collapse.

So if there was just a couple inches of snow, then it was probably closer to 10 tons worth of snow.

https://www.cnn.com/2022/01/28/us/pittsburgh-bridge-collapse...

[intrasight]

We had almost 8 inches of heavy snow. But Still my math must have been off (did in my head). Doing again I get

10 lb/ft * 450ft * 45ft / 2000 = ~100 tons

[beerandt]

This is a failure mode already accounted for in determining the posted weight limits.

[alksjdalkj]

Looks like the bus named in the NTSB report is 39000-45500 lb, so under the bridge's weight limit: https://en.wikipedia.org/wiki/New_Flyer_Xcelsior

[mosseater]

But what if it was at that top range, 22.75 tons. The math would add up, with 5 other cars on the bridge weighing an average of 1.4 tons each, we would have 29.75 tons or so on the bridge. Before the 10 or so tons of snow is added.

[jachee]

Bridge weight ratings are per vehicle.