Concrete Filled Pipe Bollards 1

[vmirat]

How do you analyze the bending capacity of a steel pipe filled with concrete? For example, I need to evaluate the capacity of an 8-inch double extra strong steel pipe filled with concrete that is 2'-8" tall, embedded in the ground. I thought of converting the steel pipe to concrete via transformation, but that didn't seem right.

 

[steve1]

NASCAR tracks have a barrier that keeps the race cars from crashing into the stands. I think that I saw somewhere that their cable system is anchored by mass concrete buried in the ground (similiar to cable bridge anchorage).

 

[jjeng2]

I saw something in a post that got me thinking on another concept. If the purpose of the bollards is to stop a threat and then be replaced if they are too damaged, you might need to think more in terms of energy absorption instead of static strength. If you can sacrifice the bollard as long as it stops a threat, then you should be maximizing energy absorption, which many times means maximum deformation.

 

[LPPE]

I had to check concrete light pole bases for impact from a truck at 5mph. From the equations of kinematics and allowing the concrete base to only deflect a small amount, the impact force was friggin HUGE. I'd love to hear what your final design was to stop 5kips going 30mph with a 8" bollard.

 

[FalsePrecision]

LPPE,
Read the info posted by vmirat, about half way up. Bollards at 10' on center. 2 wire ropes. End posts to take direct impact or tension in ropes. (I assume the end posts are something other than these 8" dia. pipes) Theory - would the vehicle deflect the ropes, to produce a catenary effect, thus absorbing a large amount of energy (the bollards would be "rotated" out of plumb by a large amount). The tension in the ropes would be very large, to produce a more gradual full deceleration of the vehicle. See the other posts above mentioning cables and energy absorption.

 

[LPPE]

What if the vehicle hits the bollard directly instead of cables? Accidents rarely happen where you want them to. (not that you want accidents to happen...). Overall, would it be safe to say, then, that the bollards are only used once per impact? They'd slow the car in a safe manner, but be completely destroyed in the process?

 

[FalsePrecision]

If each bollard was part of the cable "network", then if a car hit a bollard head-on, then the bollard would be deflected, plus the cables would be tensioned -the net effect is to provide maximum stopping power without using a larger bollard. That was the architect's request - to keep bollard size to 8" maximum. Since this is for security, I am assuming that the damage to the car and occupants is not an issue.

 

[theonlynamenottaken]

I would design these like harbor bumpers and use an energy technique. The energy of the vehicle is easy... (.5mv^2). The energy capacity of the bollard is the area under the load-deflection curve. Where to take the area up to is a matter of judgment. Not letting the pipe yield is nuts (a triangular area, while above yield is ~rectangular... where the real energy capacity comes from is plastic deformation). Letting it deflect until extreme fibers approach ultimate is the failure point. I'd take it 50-70% of the way towards ultimate from yield. Also depends on the max. bumper height you have to consider (duh).

 

[flamby]

Wow! A fused liveware in a truck determined at high speed to break in and blow it apart and you guys want to stop him with a bollard!

Make it with solid steel then.

Ciao.