Laterial Load Distribution for Tracked Vehicles

[structeng24]

Hello,
I am performing a load rating for a bridge and the rating vehicle is a tracked rig. The lateral track spacing and contact area of the tracks is similar to but not the same as an H20 truck. I was going to use the distribution factors in the aashto standard specs, but then I decided to calculate the distribution as if the deck was simply supported between beams. If I calculate the distribution factors as if the deck is simply supported between beams it results in a greater load than if I use the aashto dist. factor. If I calculate the distribution factors as if the deck is simply supported between beams, will this in any way give me a non-conservative distribution factor? Does anyone have experience with distributing this type of live load?
Thanks,

 

[bridgebuster]

Out of curiosity - what sort of traffic does the bridge carry if a tracked rig is the rating vehicle?

Distribution factors are intended to account for the support provided by adjacent members.

You can use the distribution factors in AASHTO. They're not limited to an H20 truck. You could also calculate a factor assuming a continuous beam or plate supported on two edges.

 

[ACtrafficengr]

You could check the Army Corps of Engineers' Field Manual 3-34, Military Nonstandard Fixed Bridging. It includes a method for load-rating bridges for tracked vehicles. It's probably online somewhere.

By the way, in Army-speak, a nonstandard bridge is anything that is not a Bailey, MGB (medium girder bridge), or other standard military prefab structure.

 

[wiktor]

You can use assumption that the deck is simply supported, as this will give you the most conservative results. You may also use the distribution factors from AASHTO, as in your case these will be conservative too, as long as your vehicle track spacing will be more than AASHTO wheel spacing.
On the other hand, why not use the grillage analogy and create a simple computer model which will give you exact distribution?

 

[MiketheEngineer]

And if a "non-tracked" truck were to ever venture over the bridge??

 

[structeng24]

Thanks for all the responses. I think I will continue as if the deck were simply supported, which may be a little conservative. This is a typical vehicular bridge, although it's being rated for this special, tracked vehicle to pass over it.

 

[a7x1984]

Is this track vehicle over legal loads? In MD non-legal track vehicles, that wish to cross bridges >= 20', must be on a trailer.

"Structural engineering is the art of modelling materials we do not wholly understand into shapes we cannot..."...ah...screw it, we don't know what the heck we are doing.