Height Alert Barrier

[dik]

I have a project with a 24'x16' high HSS portal... likely 6x6 verticals and 5x8 horizontal. Its only purpose is to support a 'plank' allowing a 13'6" vehicle to pass underneath... The portal will support a 'plank' that will be supported at 1/5 points... spans 5', 15', and 5' (approx). Do you know of an easy way to determine if a 2x8 PSL will span 15' with 5' (approx) cantilevers and not buckle?

Almost no load, other than the PSL plank.
Dik

 

[Ganesh Persaud]

Dik a sketch would help out much more than you know it.

 

[oldestguy]

So9metims these so called vehicle height limit things are made so the actual limit thing hangs on a more sturdy beam thing. This allows an over height vehicle to hit the lower easily moved limit thing , yet does not knock the whole device down. The lower "thing" can be a pole hung on cables or chains from the higher solid "beam thing" you are designing..

 

[KootK]

1) could do it as a true lifting beam problem if you feel fancy.

2) could use woodworks, forte, etc to model a double cantilever with rotational supports at the hangers (not quite true).

3) could use one of the two models shown below which are even less true.

Technically, neither #2 nor #3 is truly correct but, for something with near zero consequences, I'd consider any of these good enough. Or you could just go with a 3.5" wide piece and think on it no more.

 

[dik]

KootK has it... but forces in opposite direction W/2 are the hanger loads... I think I'll contact a PSL supplier to see what they think... I don't think it's a problem... just want to know for sure... and yes, it's moveable so if a vehicle comes in contact with it, it will move... not break.

OG... it hangs from the portal frame.

 

[dold]

For something like this I think my analysis would consist of "I've picked up a 20ft(25ft...a long board) 2x8 before, in the middle, and it didnt do anything but bend a little bit, even when bending weak axis." Not going to buckle, unless a group of hooligans comes by and hangs on it.

What's the attachment to the cable? Might go beefier on the headache bar to get a more durable connection.

 

[r13]

Your hanger (a chain, I guess) will have more chance to be damaged than the beam, as it suffers dynamic (impact) force in a random manner. I think the supplier will have some suggestions.

 

[dik]

Thanks retired13... I was thinking of a cable with closed loops, but a chain with open eyes might work better.

Dik

 

[r13]

Here is an idea.

 

[dik]

I'd put the hangers on an angle to resist lateral movement.


Dik

 

[r13]

It warrants a dynamic analysis Joking aside, I have seen V shape hanging chains. You may chose more flexible chains that will break with a run over truck, instead of the entire frame been pulled with it. I am overthinking here, but replace a chain is much cheaper than the frame, isn't it?

 

[IRstuff]

The infamous bridge was raised 8 inches, but its barrier continues to eat trucks:

http://11foot8.com/

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[dik]

Something to remember...


Dik

 

[EngineeringEric]

Don't use a PSL outside. Use regular PT lumber, or something else. Regular PSL/LVL/LSL and wet exposure with a critical single through bolt connection isn't a great long term element. Even though they make a PSL-PLUS that is good for exterior, i have reservations but maybe could be sold on that product. Also, i'd recommend through bolts vs lags, personal preference

 

[dik]

Yes... not exposed to the elements... but no PWF treatment... thanks... bolts maybe a better idea...


Dik