Applying a pure tensile load from a strap or rope sling

[avantibngrant]

I am analysing a seat belt pulling on a seat. Is there a way to apply a load as a closed loop seat belt would apply it with no compression or bending being applied?
This would be very useful.
The remote load direct transfer seems as close as I can get to simulate it, but from the example given in the cosmosworks designer course book, it seems to be able to impart a moment and deliver a compressive force.
A general question on remote loads - if I pick 2 surfaces to apply the load on, does it apply the full force to each or 1/2 of the force to each?
I am using sw 2006 5.1. I can also use 2007 5.0 or 2008 0.0 if that would help to simulate this.
Thanks

Neil Grant
P.S. I have asked this on the SW forum also as I am trying to get the best solution for my client hopefully today.

 

[texag]

Your question is inclear. What are you trying to apply a load to? It sounds like you are trying to analyze the resultant forces on the belt mountings caused by the occupant being restrained.

A FBD would help if you could sketch and attach, you may even answer your own question by doing so.

texag

 

[avantibngrant]

Texag, you have identified what I am trying to do. Looking at the lap belt only for simplification, there is a FMVSS 210 test which requires a seatbelt anchorage system to be pulled with a pelvic block at a force forward with a 10 deg slope upwards. Straight on it is easy to calculate the resultants from the belts. Our seat is not straight with respect to the vehicle, hence the pelvic block is pulled 75 deg from straight forward. Hence the resultants on the bolts (magitude and direction) are much dependent on the final geometry of the belt. The belt material is tensile only, not able to take a moment or to take compression. I am trying to simulate it now as a very fine wire (.06" dia)made from a material with a high E value to reduce deflection. I am thinking the small diameter will bend easy
and not impede flexibility much.
The force applied to this wire will load the seat similar to what the actual test will. As the seatbelt is attached to the seat, I plan to predict the performance of the seat when it is tested.
I cannot share the seat info, but it seems obvious what the problem is - modeling a tensile only part attached to the seatbelt mnts which can be wrapped around a block similar to the human pelvis and pulled on at 75 degrees from forward and 10 deg up from horizontal. Any ideas on a better method are appreciated.
Regards

Neil Grant

 

[cbrn]

Hi,
the curve described by the wire/rope/belt would be a tensioned catenary, if the belt was not "constrained" to go all around the body.
However, with the help of the CAD you can find out the directions by which the belt "leaves" the seat on one side and "comes back" on the other side: it will match the body shape, and where it "leaves" the body you can consider it straight.
Once you have the angles, you can trivially apply "directional" forces with amplitude corresponding to the belt tension.
In order to calculate belt tension once the direct loads acting on it are known, there are plenty of formulas in the books, simply calculate the belt as if it was a "rope" (you will have to know some properties of the belt's section, however).

Regards