Foundation for Bollards 1

[molen]

I'm trying to design the foundation/anchorage for pipe bollards under pretty high loads. I'm designing for a 5500# truck at 45 mph (per aviation specs) and an allowance of 30 degree give on the bollard. Assuming crumpling of the truck, I'm looking at a 95,000# horizontal load at 18" above the sidewalk. When I analyze the foundation system, I'm coming up with gigantic footings which will not work on the site. If I look at adding piles, the depth required for the piles is insane. Can anyone offer a little guidance? Is there something I can do to reduce the load? Is there some other method of analysis that will simplify the foundation system?

I also have some bollard that will require a shallow foundation due to underground utilities. These will have a "sled" system that I'm also struggling with. Same loading.

Thanks!

 

[cancmm]

Are you designing the bollard to survive such an impact completely unscathed? Or are you considering the fact that it may need to be repaired/replaced afterward? There's a big difference between analyzing dynamic impact vs. static loads.

 

[molen]

Relatively unscathed. We are allowed a 30 degree yield on the 8" steel bollard. It's an airport project, so they want to completely keep vehicles away. Not just slow them down.

 

[JAE]

This has been discussed a bit in the past here at Eng-Tips. Do a search for other threads.

The jist of the discussions, though, was that "highway" guardrails, and the associated posts, are generally designed based upon actual field tests of such posts (per AASHTO oversight) and not mathematically.

Angle of impact, velocity, density of the vehicle, crushing characteristics of the vehicle, soil properties, height of impact, etc. are some of the mutlitude of variables that exist and make a definitive calculation very very difficult.

 

[JStephen]

My first thought was that you'd want to tie multiple posts together to spread the load, but that gets you into the highway guardrail mentioned above.

Another option would be the concrete barriers like they use temporarily or permanently to separate lanes, etc.

It seems like if the foundation was large enough, then including the mass and acceleration of the bollard and foundation could remove a good bit of the loading applied to the soil.

http://www.rsaprotect.com/antiram.php

 

[vmirat]

I design these things all the time for DoD. I'm assuming you are doing the same ATFP requirement for the FAA. I calculate the kinetic energy of the vehicle and then the lateral point load based on a 30 inch height above grade. Then, I use the same formulas for calculating pier depth for a light pole or flag pole. Attached is a spreadsheet that I developed which determines the size of the pier based on vertical soil bearing and lateral soil bearing.

 

[molen]

Thanks for the help everyone. I did use KE to determine the lateral impact load. I was trying to avoid it, but it looks like I'll have to design piers and pier caps for each bollard. Thanks for the spreadsheet, vmirat.

 

[hokie66]

For that much impact loading, I would think you would try to absorb some of the load rather than trying to stop it in its tracks.

 

[racookpe1978]

Rather than a single bollard to stop the truck "cold" as you put it .... Why not a double row of bollards: First row (the truck might only hit one bollard) is offset from the second row so the second row only sees a 10 or 15 mph "bouncing shredded bent up non-driveable" vehicle.

Thus, the first row doesn't have to take all the kinetic force by itself. from your description, you don't need to remove the posts or have a "gate" for the bollards.