Bobcat punches through ped overpass deck, lands on van 1

[ACtrafficengr]

Apparently it wasn't designed for vehicle loads. I thought it was common practice to design them for H-10 loads for maintenance vehicles and ambulances.

Link

Map view



My glass has a v/c ratio of 0.5

Maybe the tyranny of Murphy is the penalty for hubris. -

http://xkcd.com/319/

 

[BridgeSmith]

Yeah, those concrete barriers provide a significant increase in section modulus...if they don't shear away from the deck.

 

[itsmoked]

But you can't depend on them since a truck thru one would end its support contribution.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[BridgeSmith]

Correct, itsmoked; that's why we don't count on them for structural support of the superstructure. Barriers meeting the prescribed criteria can be included as an 'edge beam' for local support of the deck, but not as part of the girder section.

 

[saikee119]

A Pedestrian bridge is just a footbridge. The International standard for foot traffic is about 5kN/m2 which is half a ton over 3'x3' area. Since soil has a density of around 20kN/m3 so the designed human traffic or live load is 1/4m, about 10", thick of soil on top of the bridge. A common road bridge live load is equivalent to about a full metre of soil or 25kN/m2.

Factor of safety for civil engineering structures like bridges is about 1.4 for self weight and 1.6 for live load, never 8 to 10.

The high safety factor used, say 6 minimum, in structural engineering could be the prestressing wires and cable, pre-drawn to exceed the material's yield point, to give the extraordinary high strength. This can be found in cables hoisting lifts.

A bobcat is a road-going vehicle and should not be allowed onto a pedestrian bridge not designed vehicular traffic.

For maintenance a self-propelled hand-held snow clearing machine will be safe to operate on a footbridge.

 

[TenPenny]

"
A bobcat is a road-going vehicle and should not be allowed onto a pedestrian bridge not designed vehicular traffic.

For maintenance a self-propelled hand-held snow clearing machine will be safe to operate on a footbridge. "

All that is true, however, it makes no sense to anyone living in an area that actually gets snow. Designing and building a bridge that cannot be properly maintained (ie, snow removed) by using any of the rational / usual methods shows that the designer is not thinking practically.

In my opinion.

 

[BrianPetersen]

And to be absolutely clear about that last point (directed at those not familiar with snow) ... A snowblower will throw snow over the side of the bridge ... and land on the roadway, and traffic, below. I'm sure someone got the idea to use a bobcat so that they could push the snow all the way to the other end of the bridge without tossing it over the edge.

 

[BridgeSmith]

BrianPeterson, you're probably right, and it was a good idea. The failure to check whether the bridge could support the loading of the Bobcat is where they obviously went wrong. Just because the bridge will support 75psf over most or all of its length, doesn't mean it can support a 1200 to 1500 lb point load (rear wheel).

 

[CWB1]

Expediency is the name of the game in snow removal. When I was a locally elected official back east every bridge and path in our town had to facilitate either a Bobcat, UTV, or pickup truck with a plow, I believe as a matter of state policy.

Whoever designed this bridge failed epicly.

 

[ACtrafficengr]

Another article says:

Botto says that he has lived near the bridge for 40 years and has never seen anything like what happened Monday. He says that the bridge is typically cleared of snow by hand.

“This is the first time I’ve seen them use a piece of equipment that big on it, rather than someone shoveling,” he says.

It sounds like there's more to the story. Did the operator do it on his own initiative, or was he ordered to?

My glass has a v/c ratio of 0.5

Maybe the tyranny of Murphy is the penalty for hubris. -

http://xkcd.com/319/

 

[LionelHutz]

So, was the driver a new employee or a fill-in due to vacation who didn't know not to do that?

 

[LittleInch]

But who knew that a "bobcat" could weigh so much?

Apparently the weight goes from 2,800 to nearly 10,000 lbs (!!) depending on the model.

Do we know which actual model it was?





Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[SuperSalad]

I could be 100% wrong here, but this smells of Freeholder intervention into Public Works operations to me.

Although with an extensive background in "District Wide Anti-Bullying Coordinator" and "Director of Student Attendance", I can't imagine why Freeholder Best wouldn't be appointed as the Chairman of Public Works for Passaic County.

Andrew H.

http://www.mototribology.com

 

[JG2828]

Do we know which actual model it was?

The video in the original post appears to show S100.
I couldn't find it on the US site but the EU site says it is either 1,860kg or 2,149kg depending on HD or Solid tires (tyres).
So between 4,100 lbs and 4,739 lbs.

https://www.bobcat.com/eu/loaders/skid-steer-loaders/models/s100/specs-options

 

[saikee119]

In the article posted by ACtrafficengr it can be seen this pedestrian footbridge remain structurally sound as its main members are substantial steel girders spanning over the highway below. The failed portion is a lightly reinforced concrete slab, possibly spanning between the main steel girders, visually showed to be between 2.5" to 3". Since the Bobcat fell somewhere near the mid span I wonder how many of us would walk to the hole to inspect the damage and ignore the fact part of the deck is likely has been overloaded by the previous Bobcat and could collapse at any time.

There is a year (1959) stamped on the bridge abutment which has some corrosion problem exposing some of its vertical reinforcing steel. If the stamped year is correct, which to me looks about right by the design and the extent of the concrete corrosion of the bridge, the structure is 60 years old!

The bridge deck is of reinforced concrete construction. In Civil engineering installations reinforced concrete typically has a design life 30 to 50 years. One needs to go to a nuclear power station to find concrete designed to 80 to 100 years life. After the design life lapses the concrete is expected to be well carbonated, unable to protect the embedded reinforcement which would corrode away. Once the reinforcement has been compromised the structural integrity of the bridge is gone. Anybody driving a Bobcat over it is asking for trouble.

At the end of the day it is the public to decide what bridge they want. A road bridge will have to carry 400% to 500% more load and must be designed to the national standard so that a fully laden lorry can cross it too. So the cost will be at least 15 to 20 times the pedestrian version because a road bridge needs to be a lot wider too. No doubt some may argue why not 4 instead of 2 lanes etc.... The residents have to justify the installation of a road bridge and this will have to be supported by the nearby traffic data logged over a long period of time.

 

[BridgeSmith]

In order for this bridge to have been adequate for the Bobcat, likely the only change needed would have been more substantial reinforcement and possibly a slightly thicker deck. If it required a thicker deck, it might have needed slightly larger girders (heavier or deeper) as well. While it would represent a modest increase in cost, it presumably would be going beyond the design requirements for a bridge too narrow to fit a road vehicle on. If the 1959 date saikee119 posted represents the timeframe in which it was built (very likely), equipment like the Bobcat didn't exist, so it would have not been an anticipated loading. This was not a design failure. "What we've got here is failure to communicate." That, or a failure to heed the limitations that were communicated.

What should have happened when equipment like the Bobcat were starting to be used for snow removal by the city, is the bridge should have been evaluated. When it was found inadequate for wheeled vehicles, bollards should have been installed at the ends of the bridge, so that the Bobcat could not get on it.

 

[Comcokid]

If saikee199 is correct with the 1959 construction date then that explains why no one would have anticipated a Bobcat or similar small vehicle on the bridge and designed and/or limited access accordingly. A quick internet check finds that the Bobcat originated as a farm implement in 1958.

https://www.bobcat.com/company-info/history/story

In the late 1950's, the only four wheel vehicles that might have access to a pedestrian bridge like that would have been a Cushman, and a quick check shows they weighed around 350 lbs max plus occupant(s), and would have had a sight more spread-out wheelbase than the pictured Bobcat.

 

[msquared48]

I thought Bobcats were not more than 100 pounds...

Mike McCann, PE, SE (WA)

 

[WinelandV]

m^2,

It feels like more than 100 pounds when they jump on you from a tree. F = ma after all.

 

[ACtrafficengr]

Actually, Lynx rufus tops out at 40 lbs, but considering what an 8 lb housecat did to my forearms when I had to take her to the vet, I wouldn't want to tangle with one.

My glass has a v/c ratio of 0.5

Maybe the tyranny of Murphy is the penalty for hubris. -

http://xkcd.com/319/

 

[msquared48]

If the operator did a neutral steer, for whatever reason, then the stresses would be locally increased for a short time with torsional as well as gravity shear forces.

Mike McCann, PE, SE (WA)