Hold down bolt tensile loading

[adiem]

I am looking at the design of hold down bolts on a four legged tank with a blast loading. I have calculated the overturning moment due to the blast loading and I need to calculate the uplift loading on the bolts. Do I divide the moment by half the pitch of the hold down bolts to calculate the tensile loading on the bolts or am I doing something wrong?

 

[TomBarsh]

Is there one bolt per leg? Or more?

I don't understand why the screw thread pitch would have anything to do with this. The axial force in the leg/bolt cluster will be the overturning moment divided by the distance between the legs (and consider the directionality of this also; eg: take the distance between diagonally opposite legs as well as adjacent legs), then divide this force by the number of legs involved (1 when considering "on the diagonal", 2 when considering legs in pairs on opposite sides of the neutral axis. This gets more complicated when there are more than 4 legs involved.

You could get really fancy and treat the bottom of the leg as a fixed connection to the base plate/foundation with more than 1 anchor bolt. Similar principles would apply here as well

 

[adiem]

TomBarsh

Thanks for your reply, I think I got it right but there seems to be a little misunderstanding, perhaps I have used the wrong terminology. When I say 'pitch' I mean the distance between the hold down bolts 'not' the actual tread pitch.

Yes, there is one bolt per leg.

Thanks again

Adiem

 

[TomBarsh]

sorry, my misunderstanding. Yes, I agree that you have the correct solution method.

 

[desertfox]

adiem

Relative to the axial direction of the bolt thread axis is the blast loading, if the blast loading force is at 90 degrees to the bolt axis then you need a different method
because if the frame is trying to tip over on one side, the bolts furthest away from the pivoting side will see the greatest load.

regards desertfox