Axial capacity of reinforced existing steel column 2

[AskTooMuch]

I have an existing steel column that has part of the flange missing due to corrosion.
I already had it sandblasted and will paint it with epoxy paint.
I know about needing to shore this column first or the plate will not resist dead load.

My question is about axial load, do I use the new Ax with plate on it resisting all the axial load?
If I use WT instead of plate (just saying as example), will all area (WF + Wt) resist the axial load?

Can I weld across the column flange (plate will be welded all around) for axial load?

 

[CANPRO]

If you're removing all of the load in the column prior to repair, the stress in the original section and the repair will depend on a few factors:

[ul]
[li]Is the connection between the existing and new steel sufficient to consider the section fully composite? More than likely the answer will be yes.[/li]
[li]The axial load will be split proportionately to the area of each section[/li]
[li]With a change in cross section, you will have some eccentricity at the transition between repaired and original condition. Might not be much but should be considered, especially if you're talking about using a WT section.[/li]
[li]Will depend on how well you can attach the repair plate to the baseplate[/li]
[/ul]

A couple other thoughts:

[ul]
[li]How difficult is it going to be to take the dead load off the column? I'd look at the repair option of not relieving the dead load from the column. You're right to identify that this would lock in the existing dead load stress in the reduced cross section, but maybe that isn't that big of a deal. Whatever dead load that is on there now is probably peanuts compared to the factored design load of the repair.[/li]
[li]What kind of loads are you talking about? Is it just axial?[/li]
[li]If one side is completey corroded, whats the condition of the opposite side? If you need to repair both sides, that may or may not change how you approach the repair[/li]
[/ul]

 

[Ron247]

From your sketch, it looks like your repair is near the base of your column. I think that lessens how critical you have to view this. One of the main reasons for fairly wide and "healthy" flanges on a W-shape column is to reduce kl/r. kl/r is far less critical at the base than it is at the middle of a column. kl/r is buckling related only to my knowledge. Not much chance of buckling at a base-plate. At the baseplate, a column can most likely take a higher axial load.

Along the lines of what Canpro noted, you will have some eccentricity at your plate for several reasons. 1) If you do not plate both flanges, you move the Neutral Axis at the plated area. 2) The loss of flange material also moves the Neutral Axis.

Anytime you have to check anything that has compression, you always have a minimum of 2 things to check. Will I overstress the material? Will the component become unstable due to buckling? I do not think buckling would be my concern so much at the base. But I also think you realistically may have a higher allowable stress at the base.