unsymmetric column- anchor loads

[ToadJones]

I have a column with a cap channel on one side so that it is singly symmetric. Obviously the neutral axis is pulled toward the side with the cap channel.
The column has an axial load and a strong axis moment.

The column is resting on a loose baseplate with brackets from the flanges to the bolts.
I am trying to determine the anchor pullout force (if there is any).

My questions are:

1). Where do you consider the axial load to act?
2). Is it safe to assume the column rotates about the neutral axis for determining the anchor bolt loads?

 

[msquared48]

I assume this is a wide flange column? Can you post a sketch? (I actually beat BA to the request!)

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Lion06]

The axial load always acts at the centroid of the cross-section, right?

As for the bolt force.......... can you post a sketch of the base assembly? I have a picture in my mind, but want to make sure it's what you have.

 

[ToadJones]

sorry, it appears to be sideways.

This is not exactly what I have, but basically the same idea

 

[ToadJones]

...I don't have my Blodgett with me, but I am guessing there is something in there.

 

[hokie66]

I would just find a notional stress gradient at the base P/A +/- M/S. Then counteract any uplift with a couple between the bolts on the tension side and the compression flange.

 

[slickdeals]

Toad,
For uplift loads, you will have lateral moment + uplift * eccentricity.
For gravity loads, I would consider no eccentricity.

 

[ToadJones]

hokie-
not sure what you mean by "counteract any uplift with a couple between the bolts on the tension side and the compression flange"

I started out using P/A +- M/S but I think I started to over think it.
For the case shown in the sketch, the entire baseplate is in compression, so no tension in the bolts.

Slick-
Not sure I follow your post.
How can you ignore "e" for gravity loads when there is a moment?

 

[hokie66]

I thought that was your question...how to determine the tension in the bolts. If you know there is no tension, then what is the question?

 

[ToadJones]

Hokie-
Sorry for the confusion.
You are talking about "uplift" in the bolts resulting from moment, correct?
I thought you were talking about direct uplift from a column axial load.
I guess my question was, in determining the tension in the bolts due to moment, would you assume the column rotates about it's neutral axis or some other spot. My inclination is that it would rotate about a location near the compression flange.
I was approaching this by moving my axial load in the column some distance eccentricity "e" from the line of the axial load. e=M/P.
My other question was, would the "e" distance be measured from the column centerline or the NA...again, I was thinking it would be measure from the N.A.

 

[graybeach]

I think your e should be measured from the neutral axis.

 

[graybeach]

The location of the resultant force is M/P away from the neutral axis of the column. With this you can calculate the anchor bolt M and P relative to the centroid of the anchor bolt pattern.