Bending on preloaded bolt

[YaadRam]

Hello,

What is the most accurate way to calculate the failing point of a preloaded bolt connecting between a fixed metal roof and a cantilevered beam. See image attached.

Thank you in advance.

 

[rb1957]

i would react the moment as "heel and toe" ... a distributed load between the roof and the beam, triangular, peaking towards the free end of the beam, as one load of the couple and bolt tension as the other ... couple force = moment/(2/3*bolt edge distance).

there would be a small moment in the bolt, but reasonly negligible IMHO.

you could take it all out as bolt bending, bolt loading is then a combination of tension and bending, i'd suggest Rt+Rm = 1/RF or you could go with Rt^2+Rm^2 = 1/RF^2 or variations on a theme.

 

[YoungTurk]

I concur with rb; however, I'd add that the heel toe reaction requires a high level of rigidity in the beam and firm support from the metal roof. If either of these is not the case, the heel-toe reaction distance shortens and the bolt tension and bending loads increase. What you've drawn is effectively the extreme opposite of the heel toe where the contact area is totally ineffective and the bolt takes all the bending.

Since we don't have roofs on airplanes, you might get a more practical answer by asking the civil guys over in the structural forum.

 

[YaadRam]

"there would be a small moment in the bolt, but reasonly negligible IMHO."

The beam is more than a meter long and the force reaches about
1 Kgf.

Dont you think the moment needs to be addressed ?

When you say "Rt+Rm = 1/RF"
what does Rt,Rm,RF mean ?

 

[rb1957]

the same bending is happening on the plate on the load side of the bolt, so if the plate is considered to be too flexible to load up the reaction, it'll be too flexible at the load as well.

mind you, it does look like a diving board ...

 

[YoungTurk]

Good point, but there is usually some sort of backup structure at the fasteners.