Bolts coming loose or acting as a projectile 4

[Logan82]

Hi,

I want to bolt a structure to hold a road sign board to an existing W that is part of a vehicule guardrail on the side of a bridge.

Bolts have a diameter of 5/8 in. The plate has a thickness of 3/8 in.

My client has contacted an engineer specialized in bridges, and he told him that we can't drill through the W.

The initial concept from my client was to build a custom clamp using bended plate. We would leave a gap of 1/16" between the plates so that when the bolts are torqued, they clamp the W.

However, I am having 2 issues:
- Since torquing the bolt will deform the plates just like a spring, there will be energy stored there. If the bolt breaks for some reason after a while, I am wondering if the bolt will act as a projectile.
- I can't torque the bolt a lot since the 2 plates are not in a perfect contact. I can torque approximately 10 lbf*ft, which is not alot, so I worry that the bolts may come loose. Would red loctite be sufficient to prevent bolts from coming loose?

 

[SWComposites]

It would likely be less expensive to make the right side part a flat plate, and just have a single U shaped part on the left (with longer legs).
I doubt a 5/8 bolt is going to fracture before the other parts yield.
Suggest putting a second jam not on the bolt help prevent loosening.
I would be more worried about the U shaped parts yielding/deforming over time and loosening the joint.
Can you weld to the W?

 

[Logan82]

Thank you for your answer. It is a good idea to bend only 1 plate of metal. I can't weld the W either.

What does the torque procedure of the second nut look like?

 

[bones206]

Lindapter clamps are well suited for this type of application.

 

[Logan82]

Great find thanks

 

[rb1957]

did the other engineer object to drilling through the flanges of the W beam ? that certainly is more of an issue than drilling (and riveting?) through the web. ie ... did you propose to drill through the caps ? would he object to drilling through the webs ? how about welding ??

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[Logan82]

The other engineer didn't want to drill through the flanges or the web or weld on these. His reason is that this is a standardized vehicle guard rail, so it is advisable not to modify it.

 

[hokie66]

Seems to me that if this is a standard guardrail and a standard traffic sign, there would be a standard detail to connect the two.

 

[Logan82]

I have searched for a standard detail but I have found nothing.

 

[Logan82]

bones206, are the Lindapter beam clamps meant to stay outside during many years?

 

[stevenal]

Instead of a custom clamp, suggest a pair of square u-bolts. For longevity and road salt, stainless u-bolts can be specified. No projectiles involved unless you happen to break both sides at once. McMaster has a good selection.
To prevent loosening, suggest nylock nuts.

 

[BridgeSmith]

...suggest a pair of square u-bolts...No projectiles involved unless you happen to break both sides at once.

That's what we use for attaching bridge railing to the posts. Every bridge we touch that has toggle bolts for that connection gets upgraded to U-bolts.

 

[Logan82]

Thanks for the U-Bolt Idea!

 

[bones206]

are the Lindapter beam clamps meant to stay outside during many years?

Yes, I believe so. The available finishes are listed in the brochure linked below.

Lindapter bridge market brochure:

https://www.edgecs.com/documents/downloads/Bridge Market brochure.pdf

 

[MintJulep]

Why design a complicated, custom, expensive sign mount when simple, standard, cheap sign mounting systems exist?

https://youtu.be/6E9CGAsoDZk?si=CFy7mbBi3xqKzSOu

 

[Scuka]

Why bend the plate and not just use flat plates with a longer bolt?
What purpose do the bends achieve?
With flat plates, you can have the width of the bolt hole pattern just slightly larger than the W, which will minimize the deformation of the plate, which will minimize your projectile worries, while also making the whole thing cheaper. With this setup, you also don't have a limit on bolt torque.

 

[BridgeSmith]

Scuka, if I'm understanding your detail, that type of connection would almost certainly not be allowed. Nothing can protrude from the railing and create a snag point for vehicles or a hazard to the occupants.

 

[Scuka]

It's true that bolt head and nut would protrude, but OP already agreed above that one flat plate + one bent plate is an OK solution, so I'm not sure he's worried about protrusion.

Also, looking at the pictures of some guard rails (example), it seems it would be possible to hide the protrusions behind the sheet metal profile.

But anyway, the suggestion is here. OP will decide whether it's suitable based on all the other details and guard rail codes.

 

[Aesur]

I'm with BridgeSmith here, modifying a standard guardrail may put you and your company at liability due to the modification of a tested system should something happen. I would wand some kind of documentation from the jurisdiction allowing this before allowing such an alteration to a vehicle barrier.

 

[BridgeSmith]

Scuka, the attachment is to a post and beam bridge rail, which are nearly always approved based on crash testing. Deviation from the crash-tested configuration in even minor ways is not usually allowed. This includes adding anything protuding in front of the post. Even if it is behind the rail, it's still potentially a snag point for the body of a vehicle as it mashes into and wraps around the rail. It may seem like a small thing with a small potential to create a hazard, but those highway safety people are very particular about even the little stuff.