Removing interior columns in an existing PEMB
Removing interior columns in an existing PEMB
(OP)
I've got a project where the existing PEMB has frames at 20' on center. Out-to-out of PEMB frame is 120' with interior columns approximately 20' from the exterior column. The owner wants to remove the interior columns. Has anyone done this?






RE: Removing interior columns in an existing PEMB
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Removing interior columns in an existing PEMB
RE: Removing interior columns in an existing PEMB
RE: Removing interior columns in an existing PEMB
RE: Removing interior columns in an existing PEMB
I wouldn't be surprised if the cost wound up being about as much as a new building.
RE: Removing interior columns in an existing PEMB
RE: Removing interior columns in an existing PEMB
RE: Removing interior columns in an existing PEMB
RE: Removing interior columns in an existing PEMB
RE: Removing interior columns in an existing PEMB
I have done something similar a few times, but on a smaller scale and with just one frame (sounds like you have to do this for a more than a few). First question is - do they need the full 120' clear on the inside? If they can lose a bit of space each side of the building that means you can put new columns/foundations adjacent to the existing, inside the building. That shortens your span, simplifies the foundation work and reduces the reinforcing.
When I did this, I turned the roof beams into the top chord of a new truss. For one design, I used back-to-back channels for the bottom chord and sandwiched the existing post, which became vertical members of my truss. This way the whole truss can be built in place without shoring, and when the truss is complete the existing columns can be cut below the bottom chord. The back-to-back channels on the bottom chord also make fitting up the new web members easier since they don't have to be cut to exact lengths.
RE: Removing interior columns in an existing PEMB
RE: Removing interior columns in an existing PEMB
1. Beam geometry and web/flange thicknesses
2. Steel testing to verify Fy of both flanges and welds (in PEMB's they sometimes are different)
3. Connection information including verifying bolt types/grades and diameters.
4. Verification of roof purlin sizes and connections to the beam - they brace the top chord so this must be verified.
5. Capacity of the roof purlins to also accept diagonal strut bracing of the bottom chords.
6. Capacity of the existing end columns for the higher loading - need to stiffen or strengthen?
7. Capacity of the base plates of those columns and the anchor rods.
8. Steel grade of the anchor rods.
9. Embedment of the anchor rods to work with the higher loadings.
10. Footing size verification.
I'm sure there's other things as well. All perhaps do-able (CANPRO did it after all).
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RE: Removing interior columns in an existing PEMB
As a side note, as mentioned above, the span of the frames on my jobs were considerably less (in the range of 70'-80'). And I think the key to making this feasible, is installing new columns/footings adjacent to the existing.
EDIT - I should also note that another important factor here is making sure it is okay to lose the headroom involved with installing the truss. If you can make the truss deep enough, the stress in the existing beam/new top chord (and the demand on the purlins acting as a brace) could be less than the current configuration
RE: Removing interior columns in an existing PEMB
RE: Removing interior columns in an existing PEMB
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Removing interior columns in an existing PEMB
RE: Removing interior columns in an existing PEMB
RE: Removing interior columns in an existing PEMB
The existing PEMB was built in the early 80's. Its an existing church that had classrooms around the perimeter with the sanctuary in the middle portion. Now the sanctuary is expanding to the out-to-out dimensions. There will be (2) existing frames that will be modified. The truss idea from CANPRO may be more feasible engineering-wise, but economics may win out. The other option will be to buy (2) new PEMB frames, existing foundation modification, a new roof and re-using existing roof purlins and wall girts (possibly).
RE: Removing interior columns in an existing PEMB
RE: Removing interior columns in an existing PEMB
RE: Removing interior columns in an existing PEMB
Shoot, if that's what it's for just remove the interior partitions (assuming they don't have any shear-wall function) and live with the interior columns. Even some of the grandest cathedrals in the world have interior columns in their main sanctuaries.
Anything else is a waste of money and is foolish vanity. Remind them of the parable about the rich man who kept building larger barns. (Luke 12:13-21)
RE: Removing interior columns in an existing PEMB
RE: Removing interior columns in an existing PEMB
Building was likely designed with reduced RLL as well.
RE: Removing interior columns in an existing PEMB
If you choose to ignore my and hokie66's advice to run away from this, think of this: What will you do, after all the measuring, analysis and assumptions, if you can't get the building to work as is? How do you break it to the owner, that it can't take the code prescribed loads of 2017, 1997, or 1977? You've got to tell them. It's an ethical responsibility.
Some scabs are not worth picking at.
RE: Removing interior columns in an existing PEMB
Hate to bring up an Architect, but has one been consulted to check all the crap they do? Interior space, exterior elevations, etc.
RE: Removing interior columns in an existing PEMB
Some projects are ridiculous and should be avoided.
Please listen...
Mike McCann, PE, SE (WA)
RE: Removing interior columns in an existing PEMB
Based on the opinions expressed about how the potential high cost, you can remind them of another parable (Luke 14:28) "Suppose one of you wants to build a tower. Won't you first sit down and estimate the cost to see if you have enough money to complete it? BTW - that's what we're doing.
RE: Removing interior columns in an existing PEMB
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Removing interior columns in an existing PEMB