Odd Base Plate Design

[grevs]

I'm new to base plate design and I'm only somewhat familiar with the AISC Steel Design Guide, which is helpful but mostly for standard base plates, unlike the one I'm finding myself analyzing now. I know the constraints seem ridiculous but, long story short, it's necessary. Please see the attached file to understand the layout. How in the heck should I analyze this? How would I determine the bearing length? Any help would be immensely appreciated.

Thanks.

 

[DaveAtkins]

I would do the statics--check P/A +/- M/S to see if that works. If not, use the angle under the base plate to prevent the left end of the base plate from lifting up.

DaveAtkins

 

[kslee1000]

Is the moment reversiable?

for the direction shown, I will simply perform analysis and design in 3 steps:

1. Assume the angle is rigid, perform analysis as usual, and design the base plate. (Ignore connection between the angle and plate)
2. Use pressure distribution obtained above to check the angle and anchorage. You may need to add stiffeners to stiffen the angle.
3. Design base plate - angle weld.

Detailing:
The weakness of this connection is the concrete. It tends to shear off from the right hand end of the base plate to the anchor holding the angle (assume one on the vertical leg). Therefore, pay attention to reinforcement arrangement, use of smaller size closely spaced L bars is preferable. Also, you may consider use anchorages preset in the concrete to fasten the base plate and the angle as opposed to use post installed anchors.

From sketch, the right hand column wall is right on the concrete nose, I would select a thiker plate than necessary, or use step plates (make true rigid plate), or provide stiffener, to better spread the force out farther. By doing so, the force in the angle would be dimished proportionally, which is desirable.

For moment in reverse, the steps and considerations are similar.

 

[BAretired]

M = 30,000"#. P = 1300#. ecc = 30000/1300 = 23"

Move P over a bit (in your mind) until the centerline of column lines with the edge of concrete. How far did you move it? About 1.5", right? So reduce M to 30,000 - 1300*1.5 = 28,050"#.

Lever arm = 0.9*6 = 5.4", so you need a compression of 28050/5.4 = 5194# at the end of the plate and a tension of 5194 - 1300 = 3894 at the edge of concrete.

Moment in plate = 5194*(5.6 - 0.6) = 25970"#.

Mf = 1.5M = 38955"#

0.9 Z Fy = 38955 so Z = 38955/(0.9*36000) = 1.20

8*t^2/4 = 1.20 so t = (1.2*4/8)^0.5 = 0.775"

Use 7/8" thick plate and anchor the 4 x 4 angle into the concrete to resist an uplift of 3894#. Be sure to tie it down so your anchors don't burst out of the concrete.


BA

 

[csd72]

I would be concerned about the corner of the concrete breaking off.

 

[JStructsteel]

You could weld a plate to the angle and extend the leg down to get more concrete cover if the uplift wants to break out the corner.

 

[PUEngineer]

My thought exactly, or use a bent plate instead of an angle and get a flare bevel weld between the bent plate and the flat plate. Of course that might invalidate BA's analysis based on what he assumed for the connection of the base plate to the angle.