Bollards - ICYC 12

[dik]

Didn't know that...

https://steeltubeinstitute.org/reso...ent=ReadArticle_Link--R6X97&mc_cid=16add1e0bb

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

I only use baseplates for small impacts and the plate thickness is generally 5/8" so that it deforms, generally before doing in the anchor rods... I also generally spec weldable anchor rods so that they can easily be 'fixt'.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Ron]

Good info dik...thanks.

 

[DayRooster]

Dik,

I guess I am looking for more reasoning into the base plate thickness selection with regards to work-energy formulas. I think you will find this out in your calculations but as Steve mentioned there is a massive amount of energy to be absorbed to cut down the loads to a reasonable number. Last I ran the numbers I was getting very little energy absorption between the rigid fork truck and rigid bollard. Which resulted in very high forces that easily went beyond the properties of the standard bollard. Specifically with regards to fork trucks where the intent is to guard the structure. Sacrificing a baseplate is fine. But the bollard should hold and not allow the fork truck to pass through to damage a building or enter a pedestrian alleyway. This is where I have heard “near miss” stories.

Again I just want to point out that I’m talking rigid fork trucks and not road approved vehicles with built in collision frames for energy absorption. I feel the equations presented in the article are straight forward for the road approved vehicle cases. If the vehicle is big and is driving fast then run the numbers and put in a massive monolith of concrete.

 

[DayRooster]

Let me ask this question for all those familiar with the euro code provision. Does the vehicle stiffness apply to fork trucks too? Is this trying to say that a passenger vehicle with a road tested collision system has the same stiffness as a fork truck with no collision system?

“A vehicle equivalent stiffness of 300 kN/m is adopted in Eurocode 1 Part 1.7 (CEN, 2006), for all types of vehicles and velocities at impact.”

 

[dik]

Does anyone know what the 'theta' value represents? The CSA S16 code has a similar recursive (first time I've used SMath for recursive calc and it seems to work OK) calculation and returns a similar value. If you use 5 iterations, you end up with the same value and it takes more than twice as long. I've set it to a fixed variable to use in future calculations, else it seems to do the recursive calc each time the variable is used.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

I cannot find the error... it seems like the Canadian code uses a lesser component of the added concrete... maybe someone else can find an error if it's there. Feel free to use and/or modify.

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1634743749/tips/Steel-Bollard_rmegjj.pdf[/url]

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/raw/upload/v1634743749/tips/Steel-Bollard_bikxbt.sm[/url]

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[bones206]

Bones - I am interested about the energy absorption of a traditional baseplate. In theory that is what the slow stop bollard does at its core. It is a special baseplate that has an engineered amount of energy absorption. So I can wrap my head around the idea of a special designed baseplate that would function as a energy dissipation device. I guess my question is what does that calculation look like for a standard base plate? How much energy would be absorbed in a hit before the baseplate shears or tears?

If I was to do the calc, I'd start by assuming a yield line distribution in the base plate, then developing a resistance-deflection function based on the flexural resistance of the yield lines. UFC 3-340-02 Chapter 3 has a really good breakdown of how to do all that stuff.

You could probably do something with Hilti Profis now that they have a plastic strain output based on FEA of the plate, anchors, attachment and weld. Just keep iterating the paramters until you reach a result where the anchors work and the weld works and the plate exhibits sufficient plastic strain to absorb the kinetic energy.

 

[DayRooster]

Bones - That is very interesting. I would be very interested in seeing how much energy absorption could be handled by various baseplate configurations. Know of any grad school students looking for a project?

 

[dik]

The problem is you want to make it weak enough that it sustains the design load, and 'bends' but not fails the anchor rods... that's what I like about soil embedded bollards.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[bones206]

Just for fun I did a run in Profis with a 6" bollard section welded to a 5/8" plate, subject to a 10 kip lateral load with a 3 ft lever arm. I'd have to dig deeper into their analysis methodology to fully interpret the results, but it is helpful in that it indicates the plate's ductility ratio, which can be compared to an ultimate allowable ductility ratio. Also gives a good sense of where the yield lines are.

 

[DayRooster]

Bones - I like where your going with this one.

Few thing I will share is that load would be lower to the ground with a fork truck. If I’m not mistaken it can be within a foot for the case of the rigid frame backing up into the bollard. Also there is not much deflection of the bollard and very little crush distance of vehicle since it is a heavy steel frame. Last I saw this equates to forces higher than 10 kips. That being said maybe the forces could be reduced because I never factored in the work-energy that would occur due to a baseplate yielding and undergoing strain hardening. The force of a loaded fork truck impact (going let’s say maximum 10 mph) comes out to a energy. But it does take quite a bit of energy between yield and the failure of a steel plate. I would be curious if it could be quantified and compared against the fork truck energy to determine the residual force left over that the strain hardened base plate would still need to handle.

 

[dik]

I've occasionally repaired columns that have been struck by forklift traffic and the damage is occasionally up a couple of feet.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[DayRooster]

Dim - I would agree that it is more common for the forks to hit. Just natural based on sight lines. But I would think you would have to design for all cases if we are doing a complete analysis.

 

[bones206]

Know of any grad school students looking for a project?

Nope. I have lots of nieces and nephews in college or about to graduate high school. They are evenly split between computer science and life sciences/healthcare career pursuits. I guess they aren't as fascinated by bollards as we are

The loads I used in the Profis run were meant to be order of magnitude guesstimates, just to see what kind of results Profis would spit out.

 

[DayRooster]

Bones - That makes sense about the loads you used. I do think the answer probably lies somewhere in that region like you mentioned. I guess until then the general engineering community will keep taking SWAGs at bollard designs.

 

[dauwerda]

Unless installed as antiterrorist type devices I would argue most bollards aren't designed or expected to stop vehicles (car, truck, forklift, etc.). They are intended to provide enough resistance that an operator feels the impact and stops, so as to prevent further damage. I would say this is especially true in warehouses and such.