Bridge Weight Limits

[pabusnut]

A NON-Busnut coworker sent me this link.

https://www.carscoops.com/2018/10/35-ton-bus-ignores-weight-limit-bending-old-suspension-bridge/


It shows one, but it looks like one on the other side already made it.

I think these are "professionals" as opposed to us amateurs!

Steve

[chessie4905]

Maybe coach was empty. Maybe the weight limit was reduced to limit commercial vehicles from using that route. Maybe that is the route that he was directed to take. Maybe other drivers from same company told him to go that way because they use it all the time with no issues..Or...maybe the driver is an idiot.😳

[lostagain]

The tour escort/director said: "my other drivers go across all the time".

JC

[chessie4905]

There you go! 2👏

[neoneddy]

That just does not seem safe.

While in the back roads of Wisconsin recently I had to be vigilant of bridges weight ratings.  I came up to one without any markings, yet all I saw was wood planks.   I actually stopped and looked under the bridge, sure enough it was probably the best built one I crossed that day, it was full concrete and steel supports and beams with just wood top planking.

What about those smaller bridges that say 20T limit, but are short enough tow here I'd never be on them with all axels?  I'm around 30T with a 30/70-ish split front to back.  I'm figuring it's safe to cross so much as the load on the span is never over 20T right?

[Geoff]

Looks to me like the bridge passed the excess weight test. It straightened out just perfect after the bus passed.  That just proves sound engineering.

[TomC]

I agree with Geoff-it was doing what a "suspension" bridge is supposed to do-suspend. It got compressed then sprang back to original shape. Sounds like good suspension to me! Good Luck, TomC

[Iceni John]

That bus supposedly weighed 35 tons (70,000 lbs)   Really?

Some years ago when bicycling to and around Scotland we rode over the Forth Road Bridge north of Edinburgh  -  it's a long suspension bridge, only slightly shorter than the Golden Gate Bridge.   When we stopped for a rest in the middle of it, we were being gently bounced up and down every time a truck passed us, and you could see a slight rolling wave in the bridge ahead and behind every heavy truck.   Fun!   Suspension bridges are designed to flex, just like most engineering structures.   I wish I could ride over the Humber Bridge and see if it also has bouncy waves (it's so long that the two towers are a few inches out of parallel due to the Earth's curvature!).

John

[bevans6]

That just does not seem safe.

While in the back roads of Wisconsin recently I had to be vigilant of bridges weight ratings.  I came up to one without any markings, yet all I saw was wood planks.   I actually stopped and looked under the bridge, sure enough it was probably the best built one I crossed that day, it was full concrete and steel supports and beams with just wood top planking.

What about those smaller bridges that say 20T limit, but are short enough tow here I'd never be on them with all axels?  I'm around 30T with a 30/70-ish split front to back.  I'm figuring it's safe to cross so much as the load on the span is never over 20T right?

How did you get 60,000 lbs in a MC-9?  Seems quite a lot.   I've read the GVWR on a MC-9 is officially 36,500 lbs, which is 18 1/4 tons.  Anyway, that looks like an MCI with a max GVWR of 54,000 lbs, or 27 tons.  Still way over a 10 ton bridge weight limit...

[Ed Hackenbruch]

Ever seen the video of "Galloping Gerty" at Tacoma Wa.  flexing before it finally came apart?   The weight limit signs are usually less than what the bridge will actually hold, but from what i have read, 1/4 of all bridges are in need of repair or replacement.  My 5A was under 15 tons but i tried to stay off bridges that were rated for less than 20 tons. 

[Jeremy]

The famous collapse of the Tacoma Narrows bridge was caused by wind rather than it being overloaded, but oddly enough I watched a documentary on Youtube only last week about the collapse of another first-generation suspension bridge in the US which was caused by too-heavy vehicles driving over it.

In that documentary they interviewed various local townspeople about the circumstance leading-up to the bridge collapse and they all said "Yes you could feel it flexing every time you drove over it, but none of us were worried because we thought it was supposed to do that". The reality was that every time the bridge flexed it caused wear and fatigue in the joints of the main suspension cables, one of which eventually failed when two lanes of stationary traffic were sitting on the bridge due to a traffic jam

In that case the suspension 'cables' weren't cables as such but actually chains made-up of iron castings linked together, and it was one of the joints between those links that failed - but there are plenty of older style suspension bridges still in use that use that system

Jeremy

[uncle ned]

Love to cross the 2 bridges . One over the Ohio and than a few miles the other crosses the Mississippie.

If you meet a tractor trailer you both come to a idle and just crawl by each other.

Mama went to the back of the coach when that happens.

Can go to 4 states in a few hours there.

Got this from the great BK.

uncle ned

[Jim Blackwood]

Jeremy, I think you are referring to the Silver Bridge Collapse which occurred on the Ohio river at Point Pleasant between Ohio and W.Va. a few miles from where I grew up, that would have been in the late 60's. They immediately closed down the sister bridge at South Point, Ohio. The fault was found to be a stress fracture in one of the suspension link bars.

Doesn't take much to cause a bridge to fail, so they try to build in multiple redundancies. That was found to be a less reliable design. Bridges are also built with a larger than usual safety factor but overstressing the structure even once is very likely to reduce it's design life. Repeated overstressing is a sure formula for disaster. As good as the inspectors are, they can't hope to find everything that can go wrong.

The New River Gorge Bridge is an underslung steel arch design with very massive quadruple arches built from box sections big enough to walk through that have walls that average about 1-1/2" thick. You might not even realize you are on this 1.3 mile long span. There is a catwalk underneath the deck, and once a year they have Bridge Day and allow bungie jumpers and parachutists. Out in the center span you can feel the deck lift and lower as vehicles go across. It is simply impossible to build a totally rigid structure, especially one that large.

Jim

[Jeremy]

Yes that was it exactly, the collapse of the Silver Bridge. The video I mention is below if you're interested - oddly enough I see it's actually an Open University film, the Open University being a long-established organisation here in the UK that runs distance-leaning degree courses. I expect this film was part of an engineering course of some sort

https://www.youtube.com/watch?v=8w5Fjouvma8

Jeremy

[Jim Blackwood]

Thanks Jeremy. It's a pretty good documentary. I was 13 at the time and I suppose like many in the area I was permanently affected and have never completely trusted bridges and other large man made structures since. Of course even natural structures are also prone to collapse from time to time. Despite that I've done things like night time explorations of the arch structure and under deck of the NRG bridge. Gives me a bad feeling though to see things like that bus.

Jim