Removing existing building column 2

[CTW]

I'm evaluating a request from a client to remove the bottom half of an existing column from a building. The bays of the building are 17'-4" currently, and the owner would like one 34'-8" wide bay. The two bays where the column is located are configured as shown.

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The request is to remove the bottom half of the middle column of the two bay arrangement shown above.

To me, the most logical option is to place a new beam directly under the cut off point of the column to pick up the load from the column. I would like to avoid adding new columns for this beam, but I think this might be inevitable. I would prefer to anchor the beam ends to the existing columns, but I'm still contemplating the feasibility of this. The existing columns are old built-up members of angles and plate. The columns have had concrete added to them over the years and adequate drawings do not exist.

There is a 60 ton crane in the building and the new beam will also have to support the roof loads.

Any suggestions or comments on supporting the load from the cut off column?

 

[whyun]

I've once done a crazy space frame above the roof which spans across the columns that are cut. There were hanger rods at the removed columns to transfer the original column load to the space frame.

Space frame itself had to be analysed as well as checking for the existing columns and footings for the space frame reaction.

Columns had to be strengthened and footings had to be underpinned and enlarged. Very expensive solution but there was no alternative.

 

[SperlingPE]

The remaining two columns have been encased in concrete?
Don't forget to check the foundations.
Can the existing upper beam be reinforced to take the new load? By welding additional steel to it?

 

[CTW]

The remaining columns have concrete around them. Without having any existing drawings on the columns/concrete, I can't really classify them as encased in concrete. It appears that heavy plates were riveted to the existing column flanges (for added protection) and concrete was cast between the flanges.

Existing foundations are definitely a concern and will be checked if additional load is added to them.

The upper most beams are two simple span runway giders. I would rather leave these alone. The lower beam is truly encased in concrete. However, I don't have any information on the reinforcing around the beam or the size of the steel beam encased in concrete. So I was trying to avoid utilizing that beam.

That's how I arrived at the present idea of using a steel beam header to take the load from the column slated for removal.

 

[dbuzz]

Can you modify the bracing to transfer the gravity load from the central column to the adjacent columns? I've done something similar before.

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[JAE]

CTW -
The first thing I thought of was that of lateral instability. Is this an issue here with a new beam? Would the new beam have any type of floor or other lateral stiffening entity? If you cut off the lower half of the middle beam, and the new beam is placed at that level, I doubt there would be any type of lateral constraint and that would be a big issue in my book.

I would second the idea dbuzz presented, using the upper level to form a large story-high truss system. Each existing piece of the remaining structure would have to be thoroughly checked and this may mean really closely inspecting the existing beams and columns. The load would of course be dumped to the adjacent columns and footings and I would expect that they are inadequate.

Also, with an existing crane - there is also the issue of fatigue to review. And any time you replace a column with a flexural member, you have the issue of deflections. At the moment the column is cut, there is an immediate re-distribution of load and there would most likely be an immediate deflection. This will be difficult to calculate, but with a bridge crane, the tolerance for out-of-level rails is fairly tight so some means of adjusting the crane rails would be required. Some temporary jacking or phasing of jacking might be required to insert some camber into the system to account for this.

 

[CTW]

dbuzz-
Nice idea. I'll look into that. This may be a little more difficult to do since the existing columns have concrete around them, but I like the idea.

JAE-
The lateral stability was one of the reasons I was seeking some other options for this design. The existing columns and footings will be checked. The building used to have (2) 60 ton cranes in it, but one of the cranes has since been removed. So I expect the existing columns and ftgs to check out ok. Fatigue should not be much of an issue in this case. The crane used to see continuous use but it is now only used as a service crane for the main operations.

Good point about the deflection immediately after removing the column. This is a good reason to seriously consider dbuzz's idea.

 

[LPPE]

As usual, I agree with JAE. I think dbuzz has a good idea, too.

 

[JAE]

Well, "my" idea was to agree with dbuzz....but thanks anyway!

 

[dbuzz]

Good point though from JAE about the increased load on the two "outer" columns and associated footings. The tributary area will be effectively doubled. It's unlikely there is that much "fat" in the original design.