Tire Impact Loading On Post
Tire Impact Loading On Post
(OP)
I have been designing the barrier system for V8 a race in Australia.
For the concrete barriers the calculations were pretty straight forward. We assumed that 4 - 3 barriers would act together through catenary action to resist the load. I assumed an inelastic collision between the car and the wall and determined system velocity. From there i used the weight of 4-3 walls and calculated the stopping distance of the wall due to the friction. I did the calculations for several situations and confirmed my results with the FIA standards which uses the same logic.
The problem occurred when designing the debris fences.
To calculate the load of the tire on the mesh I calculated an equivalent spring constant of the mesh, treating it as simply supported between the posts. From there I calculated how far the fence would need to deflect to take out the kinetic energy of the tire in an Inelastic Collision - (this combines the fences weight and the tires and gives a systems velocity which is resisted by its elasticity) . It came to be about 8 KN which is close to the FIA standards.
For the post I realized there is no way I can assume an inelastic collision and it would be much closer to perfectly elastic.
The question is how can I calculate my impulse loads on the posts?
Using conventional mechanics will give a ridiculous force because the deflection of such a stiff post is so small.
Say for a tire weighing 9 Kg with a velocity of 27 m/s.
Fence post will be CHS 114.3 * 3 spaced at 4 m.
Does anyone no of any standards or have experience in this area?
I have only been out of uni for 12 weeks so tread lightly lol.
For the concrete barriers the calculations were pretty straight forward. We assumed that 4 - 3 barriers would act together through catenary action to resist the load. I assumed an inelastic collision between the car and the wall and determined system velocity. From there i used the weight of 4-3 walls and calculated the stopping distance of the wall due to the friction. I did the calculations for several situations and confirmed my results with the FIA standards which uses the same logic.
The problem occurred when designing the debris fences.
To calculate the load of the tire on the mesh I calculated an equivalent spring constant of the mesh, treating it as simply supported between the posts. From there I calculated how far the fence would need to deflect to take out the kinetic energy of the tire in an Inelastic Collision - (this combines the fences weight and the tires and gives a systems velocity which is resisted by its elasticity) . It came to be about 8 KN which is close to the FIA standards.
For the post I realized there is no way I can assume an inelastic collision and it would be much closer to perfectly elastic.
The question is how can I calculate my impulse loads on the posts?
Using conventional mechanics will give a ridiculous force because the deflection of such a stiff post is so small.
Say for a tire weighing 9 Kg with a velocity of 27 m/s.
Fence post will be CHS 114.3 * 3 spaced at 4 m.
Does anyone no of any standards or have experience in this area?
I have only been out of uni for 12 weeks so tread lightly lol.






RE: Tire Impact Loading On Post
If a wheel and tire assembly hit the catch fence over my head I am NOT going to complain if the posts bend permanently.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Tire Impact Loading On Post
I have sort of come to a mental road block.
Ive been reading some complex impulse theory and the math is beyond my ability to follow and probally most engineers and is not practical out side of the lab.
RE: Tire Impact Loading On Post
RE: Tire Impact Loading On Post
RE: Tire Impact Loading On Post
Have you contacted CAMS?
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Tire Impact Loading On Post
Based on this work I did, I believe that you will have to approach the problem by allowing the posts to contribute to the point where a plastic hinge develops. There were some specialists in the field who ran sophisticated software that could "marry" the changing load diagram with the energy absorbed by plastic deformation. I don't have the name any more, so you'd have to trawl the 'net.
RE: Tire Impact Loading On Post
I have been reading into plastic hinges in seems the way to go for this type of analysis.
But i think the direction were heading is the post will fail for all intesive purposes in the worst case scenario. We will have to design the debris fences to act as system which will give the required deflection to be on the safe side.
RE: Tire Impact Loading On Post
RE: Tire Impact Loading On Post