Source
r/AskEngineers•
Freefall84

Eccentric loads and the use of multiple fixings

Mechanical

I'm working on a project with some offset connections to a structure using steel brackets similar to the image linked below, (they're 100mm tall for scale)

https://imgur.com/a/hjkwXSj

the bracket itself has around 7kN of load through a bolt spanning the "fork" section of the bracket, pulling away from the structure perpendicular to the face with the two holes (we'll call these holes structure holes). As well as 2kN of force pulling downwards.

Looking at the calculations I've been given, the company who has produced the bracket has calculated the pullout of the bolts as 7kN divided by two (half per hole) and then added the 2kN of deadload in the exact same manner. They're using a pair of M10 anchor bolts into the structure, with an M12 through bolt through the forks

It's as if they've ignored that neither the bracket, nor the connection between the secondary building elements are not infinitely rigid. Is this a suitable approximation or is it way off?

Also there's some instances where the brackets are fixed using 4no Tech screws into the steel operating on the exact same basis. But to me those Tech screws just seem too, well flimsy.

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Posted Dec 8, 2023, 3:16 PM UTC

22
unafraidrabbit•

For simpler designs, a ridged analysis is fine. Factors of safety account for any deviation from the exact loads.

2
PA2SK•

If you're concerned about the bracket you could ask them if they've done an analysis on it. I would usually do an fea analysis to determine if it's strong enough. For structural stuff like this where weight and size are not a concern it's common to simply overbuild things so you don't need to do any analysis. Assuming this is a reputable shop and they know what they're doing that's probably what they did, and at that point all they really need to worry about is the bolts. It doesn't hurt to send an email and get them on record stating the bracket is strong enough though. It's a good cya just in case something does fail later.

1