Steel Column Reinforcement

[CameronEC]

See attached sketch for planned reinforcement (Existing W-shape with 4 angles)

We are reinforcing some steel columns to increase their weak axis buckling resistance. There is currently alot of existing beams that are connected into the W-shape column, so rather than having to cut back all the beams to allow for the reinforcement, we are proposing to add angles at the flanges so there is not interference with the current structure.

I was just wondering on what checks I should be make other than just the built-up section resistance? I am also not totally sure how to check the class of the attached section.

 

[hokie66]

When designing your reinforcements, consider the amount and position of required field welding. The location of angles as your sketch shows makes for very difficult welds inside the column flanges. I would try to do the reinforcement all on one side rather than both, possibly using two angles rather then four.

 

[JAE]

First off I'm not sure how you can get a weld stick inside the web area of the column and point backwards to the fillet weld that would be required. Perhaps possible but check it out to see about the constructability of the detail. Typically fillet welds need a 30 degree angle of attack on the stick to work.

The analysis of the column would fall under Chapter E of AISC (if you are US) - you'd just have to check against local buckling of the angle legs - perhaps make them thick enough so local buckling doesn't control.

One other thought is that to increase buckling resistance, you wouldn't have to extend the reinforcing through or past the intersecting beams. Just reinforce up to the beams such that the stiffened section of column between the beams will be improved. The small section of existing column at the beams can remain as is as I would assume the yielding of that column in that area won't control the overall design of the column.

 

[structSU10]

I agree with JAE. If a complete buckling analysis is done on a partially reinforced section, you see that the effective length for the column is below 1. In a study i did, with a 40% increase in MOI, my effective length factor became 0.9 if the column was reinforced for the middle 70% of the column.

A paper from AISC discusses reinforcing loaded columns called "Reinforcing Loaded Steel Compression Members" from J.H. Brown. It outlines a design procedure that may be helpful as well.

 

[CameronEC]

Thanks for the replies. I agree that the weld could cause some problems, and we will have to look into this a little further.

And, reinforcing only a portion of the column still casues problems, as many of the supportted beams do not provide adequate lateral resistance to act as a brace point.

Thanks again!