thickness of breakaway plate for a traffic sign

[rteja]

The company i just joined is fabricating traffic signs with breakaway connection, where the plate thickness is 10mm. They have already finished the fabrication.
Now the consultant is insisting to consider a design wind speed of 160 kmph which results in a plate thickness of 14mm or more.

I want to know if adding an extra plate of 8mm thick to the existing top plate of breakaway (by using countersunk bolts) is a reasonable solution? (i attached a picture of typical breakaway connection for reference)

Thanks.

 

[BridgeSmith]

Assuming you're referring to a system to designed to breakaway from a vehicle impact, I offer the following caution: (If it's to breakaway some some other reason, this may not be applicable)

I don't know much about the internal design of the breakaway systems, but I know that a serious amount of dynamic modeling and testing goes into making them break and fall in a specific way (direction and timing). Changing the strength of a planned failure point could alter how it performs, with possibly fatal results. I would urge caution in making changes without thorough investigation of the effect it will have on the dynamic performance.

 

[dik]

Was the 160kph part of the original design. If the engineer wants it raised, then there is a legitimate extra to contract if it wasn't. Did anyone sign off on the design loading? Can you cut an annular groove in the body of the bolt and test them. By cutting a groove, the failure loading is much better defined.

Dik

 

[ACtrafficengr]

Make sure the regulating agency is okay with changing the design. If they require crash testing of modified designs, the client's requires may not be reasonable.

My glass has a v/c ratio of 0.5

Maybe the tyranny of Murphy is the penalty for hubris. -

http://xkcd.com/319/

 

[rteja]

Here the thickness of base plate does not affect the intended performance of breakaway system.
Since the baseplate is failing in bending, is it okay to increase the thickness of base plate by adding another plate using countersunk bolts? (Welding is not allowed on-site. So it has to be a mechanical connection)