A door opening (8'x4') at an existing tilt up concrete wall panel

[dcceecy]

We are going to cut a door opening (8'x4') at a tilt up concrete wall panel. the wall is about 7" thick and 32 feet tall (footing to roof), it is reinforced with #4@10" OC.

the wall support vertical load from roof and also act as shear wall (resist as in-plane shear)

I am thinking of attach steel plates to the concrete above the opening as header

any suggestions how to framing the openings?

Thank you.

 

[msquared48]

Thisw is normally done with internal tube columns to take the wind/seismic, with a tube steel beam in between, all periodically bolted to the panel.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[msquared48]

FYI, you would have receivede more answers by posting to the Structural Engineering Other Topics forum for this problem as it is a technical, not code issue, but don't do it now. That would be double posting and you would be redflagged.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[dcceecy]

Thank you for your advice. I always post my questions in that board. I think I posted the question here by mistake.

 

[structuresguy]

Well, where along the length of the wall is the opening? What percentage of the width of the wall will be removed? Can adjacent walls take additional shear after this wall is "weakened"? I say that in quotes, as it is my experience (having done lots of tilt) that shear wall behavior is very often not a limiting criteria for tilt walls. I have punched openings in existing walls many times, and usually have not done any external reinforcing to the wall.

 

[frv]

I agree with structuresguy..

I did a lot of tiltwall in my previous job and I never had shear as an issue.. usually wind at the parapets would control..

On a side note, I'm willing to bet the thickness of the wall is 7.25 in. Remember that tiltwall is framed with sawn lumber sizes, so unless they used (2) 2x4's (highly unlikely), it almost certainly was framed with a 2x8.

 

[dcceecy]

the wall height is about 32', width is about 28'.
the opening is about 4'wide, and 8' tall (it is a door)

the door is at the bottom of panel, about 9' from the edge (1/3 of 28')

by the way, the wall has no parapet.

frv, you may be right, I scaled the thickness from the drawing
the wall may be 7.25"

 

[structuresguy]

With the door near the middle third of the panel, I would say that the shear capacity of the wall probably has not been negatively impacted to any significant amount. You still have intact teh reinforcing at each end to resist the flexural component, and 4' out of 28' is a pretty small percentage. I would probably review connection to foundation and/or slab on grade, just to see if the panel connection at the base is impacted by cutting this hole. If so, I might add a new connection beside the door.

 

[msquared48]

I would not be worried about the shear either, but only the fact that, unless the openint is through a previously designed knockout panel, there is no vertical jamb steel from the foundation to the roof diaphragm to span out the lateral loads.

If the steel spans horizontally instead of vertically, the same woulod be true of the header steel.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[asixth]

I have done it a few times, I like to frame out the opening with a channel anchored above the opening and channels either side as strongbands. How wide is the panel, if it is 8' wide then you should be able to position the opening central to the panel.

Here is a thread I wrote a while back:

thread507-251820

 

[dcceecy]

Thank you for the reply.

in this job, the original panel was designed in 1988.

we put some door openings at previously designed knockout panels and some are not. A 6'-8"x12"x5/8" steel plate above the 4' width door opening as a header. the plate is anchored to concrete.

Now the reviewer (we submit for permit) wants us show the calculations to prove the in-plane and out-plane capacity of the panel with opening(even the opening is in previously designed knockout panels). we do not want to spend too much time on this. Any suggestions? Thank you.

 

[msquared48]

Considering the code changes for lateral forces over the years, I'm not surprised at the request for additional calculations, even for the knockput panels, as this is a major structural alteration.

Just run the calcs and show that the jamb steel is adequate.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask