How do treads distribute wheels loads 3

[mikeh]

We are looking at placing some equipment below grade that needs to remain accessible in an area used for military manuevers. In order to do this, we plan to place a removable structure (similar to grating) above a shored excavation. This structure (about 3m by 5m in plan) may be run over by military tanks. My question is that since only about 3 or 4 of the 12 tanks wheels will be over the structure, how will the tank treads serve to distribute the weight of the tank to the surrounding soil and the structure as the tank travels over the excavation.

 

[Ginger]

We tend to distribute each tyre over a contact area of 300mm x 300mm. Then use a method such as influence lines ( or in simple cases, engineering judgement ) to assess where this set of wheels will have to be on the structure to create the worst loading conditions.<br>
<br>
Regards<br>
<br>
Ginger <p>Andy Machon<br><a href=mailto:Andy@machona.freeserve.co.uk>Andy@machona.freeserve.co.uk</a><br><a href= > </a><br>

 

[RiBeneke]

Presumably you are referring to tanks that have 'caterpillar-type' tracks. Various types of suspension systems are used with caterpillar tracks, with varying degrees of load distribution between the wheels.<br>
The most rigid types have the wheels mounted in a frame, and when riding over uneven ground, the wheels on the highest points will carry most of the load, while the other wheels will hang in the air. Thus it is also possible for the front and back wheels on a track to carry all the load while the track bridges over a hollow or over soft ground.<br>
Some types of suspension have pairs of wheels mounted on short bogies to equalise wheel loads within a pair of wheels.<br>
Other more sophisticated suspensions may allow more vertical wheel movement and equalise the wheel loads even better.<br>
Another point to remember is that tracked vehicles tend to lurch (pitch) whel travelling over uneven ground. Even if your structure is shorter than the track length (wheelbase), the full load of one track may come onto the front wheel of the track if the vehicle has just crossed over a high spot on the ground. <br>

 

[Imagineer]

You might try looking at the Army Corps of Engineer’s Tech. Manuals. I’m positive they have this info. In general they are available at <A HREF="

http://www.usace.army.mil/inet/usace-docs/"

TARGET="_new">

http://www.usace.army.mil/inet/usace-docs/</A>.

See my earlier post “Magnificent Source of Technical Information”.<br>
<br>
In specific, you might try the following Tech Manuals: <br>
TM 5-822-2/AFM 88-7, Chap. 5 GENERAL PROVISIONS AND GEOMETRIC DESIGN FOR ROADS,<br>
TM 5-809-6/AFM 88-3, Chap. 6 STRUCTURAL DESIGN CRITERIA FOR STRUCTURES OTHER THAN BUILDINGS<br>
<br>
From Ref. 2 above:<br>
“a. Highway. Design of highway bridges will be in accordance with the AASHTO Standard specifications for Highway Bridges and American Institute of Steel Construction (AISC) Highway Structures Design Handbook. Loading for military vehicles will be in accordance with TM<br>
5-312 and FM 5-36.”<br>
<br>
TM5-312 and FM 5-36 is not available on their website but if you are doing something involving Tanks you should be able to get info from your army POC.<br>
<p> Imagineer<br><a href=mailto: > </a><br><a href= > </a><br>

 

[ishvaaag]

Codes as spanish IAP cover for tank effect...as long the bridge is of traditional construction. An d in fact the load in Spain is called not &quot;The Truck&quot;, but &quot;The Tank&quot;.

Distribution of the load will depend on how th structure is itself. Some heavy grating may should still analyzable as some grill, which most FEM packages are able to analyze. If you plan allowing for repeated inelastic deformations, maybe you can go a bit further with the same material, but grills are not as good as mats or orthotropic plates in redistribution. Furthermore at your size of grill the big tanks of today must place significant lateral loads forcing the grill arrangement in keying against is boundaries, and introducing compression.

If possible I would try to cover the thing with earth except if the application does not allow it. The tank soles will eat and locally damage bars every time it threads upon.