I'm analyzing the bolted connection at the base of a drilling mast. It's a symmetrical 4-bolt connection. There is tension (uplift) and a moment. There's also shear, but it doesn't significantly influence the allowable interaction equation. This is not the typical steel base plate bolted to a concrete foundation, but rather a steel plate bolted to another steel plate. I found a method in the red AISC Connection Design book (I think that's what it's called), but that method only deals with moment + shear. It involves finding the neutral axis for the moment, by balancing the "tension area" and the "compression area". The "tension area" is the area of the bolts; the "compression area" is an assumed area of bearing between the 2 base plates. In my situation, the neutral axis is quite far away from the centerline of the bolt group.
Would I just use this method to get a max bolt tension due to the moment, and then get the bolt tension due to the uplift by dividing the uplift load by the number of bolts, and then add the 2 together? My boss suggested that perhaps we can count the "compression area" in distributing the uplift load. In other words, take the uplift load and divide it by the area of the 4 bolts + the area of the "compression area".
Do I have to do something fancier with the uplift load, since it is applied eccentric to my neutral axis?
Reply To This Thread
Posting in the Eng-Tips forums is a member-only feature.