Attenuator Truck Ballast

[rhythmsection26]

An attenuator truck used for traffic control like the one shown in the link below doesn't meet the weight requirement set forth by the NJDOT. In order to meet the weight requirement of 10 tons, a ballast was placed in the bed of the truck. A drawing of the ballast is attached.
In order to prove that this truck is safe, the ballast must be proven to be capable of withstanding 90kips. The ballast is mounted by welded connections as shown in the attached drawing.

Will this be controlled by shear at the welded connections, rupture of the HSS wall in tension, or crippling of the compression wall? Tension or compression at the weld assumes the strength of the member so it shouldn't fail.

HSS Members - 50ksi steel
E70XX Electrodes
4800 lbs concrete encased

Any help would be greatly appreciated, thanks everyone!

http://www.energyabsorption.com/products/products_safestop_trailer.asp

 

[Ron]

You have not provided enough information to provide guidance.

Have you done an analysis? If so, that should tell you which will control...it could be either tension or shear, depending on the location/installation of the device in the truck bed, and the potential interaction between the concrete and the frame. For example, the concrete might provide enough global rigidity to cause the frame to act a certain way, potentially forcing an overturning condition or a mostly shear condition...can't tell which without addnl info.

I assume the frame is welded to the bed. Is the frame robust enough to engage and contain the concrete block? Where is the frame mounted relative to the shock absorbers at the rear of the truck? If it is mounted much higher, the truck will try to shear from under it and overturning will be reversed.

Give a bit more info. Show the truck.

 

[rhythmsection26]

The Frame is welded to the bed. I did an analysis which was controlled by shear at the interface of the weld. Since the concrete sits firmly against the frame I assumed that there would be no impact force on the frame due to independent movement. The frame is robust enough to handle the weight of the concrete.

Since the frame is mounted higher than the shock absorbers and the center of gravity of the frame is quite a bit higher than that, I assumed the truck would try to shear out from the frame.

I attached pictures.

 

[rhythmsection26]

Picture 2

 

[Ron]

I wouldn't want to be the driver sitting in there when the truck gets hit! That mass of concrete will smash the cab of the truck.

Your frame will hold the concrete under static load, but what about dynamic? I would want a secondary knee brace to keep that mass intact.

You have to check both shear and tension in concert for a unity check. I would be surprised if it complies with a unity check.

 

[PEinc]

For the attenuator trucks I worked on in NJ, I kept my added concrete weight low on the truck bed. The concrete slab covers and is attached to the truck bed. The trucks are dedicated to attenuation duty so there is no need to remove the ballast. Conecting a low, concrete slab is easier than connecting a tall, concrete block.

http://www.PeirceEngineering.com