Calculating impact load on bridge railing of a Cat 797 mining truck 2

[foreng]

In the conceptual stages of designing a bridge for 797 cat haul trucks (700 ton GVW), looking to calculate an order of magnitude estimate of the force of a 797 truck travelling at 50 km/hr on a concrete barrier. In order to calculate the impact force I need to know the vehicle crush and barrier deflection which is not easy to come by, especially the crush or crumple zone of the truck. One suggestion was to take load for AASHTO TL 6 barrier load of 780 KN compare energy of 36,000 kg tractor trailer, at 80 km/hr, at 15 degree angle to 797 truck at 50 km/hr at same angle. Rough calc. is about 10 times energy or about 8000 KN force.

Any suggestions, does this approach seem reasonable or is it way off base. Again order of magnitude to understand the relationship between this loading an standard barrier design.

 

[graybeach]

The standard bridge barrier design is based on testing. I don't think your approach to use calculations to scale up for a truck over 15 times heavier is reasonable. By inspection, I think the barrier will be toast.

 

[MikeHalloran]

It's probably cheaper to just make the bridge wider, put a couple rows of consumable/replaceable delineators on the bridge itself, and maybe some small rock mountains on either side of the approaches to try and get the trucks properly lined up before they attack the bridge.




Mike Halloran
Pembroke Pines, FL, USA

 

[Lomarandil]

Or to slow them down.

 

[cvg]

slowing down cuts production and costs $$, cheaper to widen the bridge and add a six foot high berm and let them stay in high gear

 

[PEinc]

I don't think you want an off-road truck speeding across your temporary bridge.

www.PeirceEngineering.com

 

[foreng]

The bridge we are building is considered permanent, main haul bridge for next 20 years, probably a truck on it every 2 min.
Our current design has standard mine haul road earth berms 2m high on approaches to the bridge, the railing was to be a continuation across the structure. The bridge has a 40m wide running surface to accommodate loaded and empty trucks passing (standard width for mine roads or 3 X truck widths).
The barrier discussion came up during a risk assessment to determine the consequences if a truck were to malfunction. The bridge has a 4% downgrade for about 500m and is 135 m long so there is the potential for something to occur although a low probability (trucks going off the road are rare). Bridge is also 18m above the river so certainly a fatality if a truck were to go over.

As full scale testing is unlikely (not going to crash a $4M dollar truck)sounds like our only option is to engage some experts and create a model.

Thanks

 

[dhengr]

Foreng:
The bridge may be (3)(truck width) wide 40m, and have your 2m high berms on either side, at each end, but then I would add a splitting berm in the middle at each end of the bridge, fairly long, and funnel shaped, for good alignment. I would make the bridge with 2 lanes (1.1)(truck width) wide. Thus, you would have 4 massive side barriers, alignment guide ways, retaining walls, if you wish, 10' high (.6 - .7)(wheel dia. high) and 2' thick concrete. The trucks would literally be self steering through this guide way, or rub the tire sides. And, the walls would be high enough and strong enough so the truck wheels could not climb them. Furthermore, if the truck passed btwn. the berms at the ends, it could not develop an angle of attach of more than 1 or 2̊ on the walls. With a 40m wide bridge the middle lane could be for picnics or for normal traffic. If you can develop an angle of attack across a 40m wide bridge, there probably isn’t a wall strong enough.

 

[capliard]

Main risk is driver falling asleep.

Have it really wide. And with really good lighting. I would agree on 4 to 5 truck width for a two way, 3 truck width for a one way bridge.

You cannot stop such a truck at full speed. I strongly advise to have them slow down to manageable speeds. Rapidly, like 60 Km/h.

Also, if you have a system like Wenco or Minestar, GPS tracking, you could send warnings to operators entering the bridge / on bridge.

You could also program a no-go zone or some sort of signal that downshifts the trucks.

I strongly disagree with Dheng concerning rubbing the truck tires. Those things are worth a lot of money on 400 ton trucks and your customer is going to reject that option for sure.

Finally, ask your customer if they considered installing a crusher / conveyor system to eliminate risk. 20 years seems like a long time hauling on that route. And conveyor are usually cost efficient over trucking for runs over 1 km.

Ingenieur Minier. QuTbec, Canada.