Column Located in the Corner of a Base Plate 1

[CES Eng.]

Hi All,

I am being asked to design an interesting base plate for a column that is located in one corner of the plate. The column is apart of a roof top pergola that needs to be located within the corner of the building parapet. The loads are pretty minor but I'm having some trouble proving that what is being designed is sufficient. Any help on the best method to tackle this plate design would be greatly appreciated.

Connection Information: Aluminum 6061-t6
Column: 6x4x1/4"
Base Plate: 12x12x3/4"

 

[jerseyshore]

Unless the loads are high, a 3/4" base plate like that should be fine. The anchors are usually controlling the design and layout, which it looks like you have started to design in Profis. You can also check the base plate in PROFIS FYI. There is an option to change the plate design from rigid to have the program check it as well.

 

[dik]

As long as the loading is axial, the area under the column should support it (unless it's a very heavy load) and I would not be concerned. If there is a moment applied, then it's a matter of dealing with it by fasteners and baseplate thickness. Depends on what your loads are.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[CES Eng.]

Hi Dik,

Yes, I have a minimal axial load of (650 lbs) and a moment of (9,264 in-lb). I'm wondering if that free corner below the column is going to be an issue when that moment is applied.

 

[dik]

Assuming a 3/8" base plate and 30ksi stuff, the plastic moment resistance is about 11,000 in-lbs, so a 3/4" will likely work. It's just a matter of designing the fasteners to accommodate the moment.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[phamENG]

Sadly Profis doesn't do aluminum. You can 'trick' it into doing something that is almost aluminum, but the limitations they put on either yield stress or modulus of elasticity prevents you from modeling it accurately. Combine that with the fact that it doesn't consider weld affected zones, you have to be really careful about interpreting the output to make sure it's not lying to you about deflections and that you're not exceeding the untempered yield stress around the weld (which is pretty likely as that's also the highest stressed part of the plate).

You could check it by hand by looking at a strip of base plate the width of the column in each direction for uplift, and one direction for moment. It would be conservative, but not overly so in this case. I doubt it will need much, and just for the sake of being able to make a good weld and prevent damage during shipping the conservative result will probably still be about where you want to be anyway.

 

[KootK]

1) Any axial probably needs to be dealt with concentrically below the column. The flexibility of the column means that it would just bend out of the way under eccentric axial.

2) Because of base plate flexibility, only the one anchor closes to the post (#4) will meaningfully participate in resisting bending moment. Your design needs to respect that.

3) Somewhat similar to phamENG's suggestion, a common and expeditious approach is to make this assumption: a thing that works if you remove inconvenient parts also works with those parts remaining. That isn't strictly true but is commonly done.

 

[Aesur]

From what I recall of 6061-T6, the weld affected zone will be in the range of 7 to 10 ksi. The only way I'm familiar with that will get you back to the original strength is to re-temper after welding, but as I'm sure you are aware this is expensive and sometimes hard to do.