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?

 

[rb1957]

those are very valid points, but I doubt this bolt could become a "projectile". Yes, the tension preload ... but the bolt is most likely going to fail after yielding (and relaxing the preload). yes, it could become a projectile if it failed brittlely, like rapid crack growth from a small defect.

But "surely" people can't just come up to a crash barrier and slap up a signpost ? The crash barrier belongs to someone, probably the highway authority, who probably also control the adjacent ground (like up to the fencing along the highway).

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

 

[geesaman.d]

FWIW I'm seeing very springy structures. While they might in theory hold enough elastic energy to break a fastener, bolts aren't brittle and when they break they yield / stretch / crack before they fracture. So the clamping load would be released gradually and without fanfare other than losing clamping grip on the w-beam and sliding down the beam due to gravity.

Also the springiness of these is very beneficial to resisting vibration loosening. While it could still make sense to add anti-loosening features (double nut, loc-tite, ...) this seems to be a very low risk if the components are installed and properly torqued equally.