pipe bollards 1

[tko61]

I have been asked to design a single pipe bollard to stop a 36 kip bus traveling at 4 miles and hour. My experience with pipe bollards has been for protection of dock doors and equipment. Usually 6" to 8" pipe embedded 3' to 6' in the ground encased in concrete creating a deadman, not really designed. I talked to a bridge engineer who said highway bridge rails are designed for a 10 kip load applied 2'-9" above the pavement and can be distributed over 5' of rail. I've looked back at old physics and dynamics books for equations. I know I will have a completely inelastic or plastic impact. I know that in the gravitation system the 36 kip bus must be converted to slugs. All of the conservation of momentum formulas and examples, that I've found, deal with movement after impact regardless of whether one was stationary before impact. Looking for reference material, guide lines, or applicable physics formula.

 

[Bagman2524]

F = Ma. You have to figure out the time for the bus to go from 4 mph to 0 mph. Then you can figure out your acceleration = v/Delta t, from which you can figure out your force.

 

[theonlynamenottaken]

Or treat it as an energy problem. The kinetic energy of the bus is easy. The "energy capacity" of the pipe bollard can be determined by computing the area under the Load/Deflection curve - though you need to consider post-yield response.

If you need reference material, look and see if you can find anything on "pipe whip". Members at nuclear plants are designed to withstand a certain speed and weight of pipe that whipped loose.

Then the only question is whether "small deflection" mechanics apply.

 

[msquared48]

Pack the pipe with C4...

- that'l stop the bus...


Mike McCann
McCann Engineering

 

[JAE]

Well, pipe bollards technically aren't intended to stop anything physically, but are usually psychological barriers only

OR

they are meant to be a sacrificial element intended to warn a truck backing up that it has hit something prior to actually hitting the more precious building beyond it.

AASHTO only knows how to create guardrails against impact through actual physical testing.

F = ma doesn't do you much good since you don't know the decelleration value of a to get F. The decelleration could be almost any value depending on the "hardness" of the elements of the truck - If it hits on a bumper "a" is different than if it hits on the bumper between bumper-struts, etc.

 

[bridgebuster]

JAE is correct about the function of bollards.

Anyway, here's a link to a site that will help you calculate the force.

http://hyperphysics.phy-astr.gsu.edu/hbase/carcr.html#cc3