Removing floor diaphragm at 2 story masonry wall

[NFExp]

I am working on a renovation at a 2-story church where the architect is removing the existing 2nd floor to create a volume space. The existing walls are 8" masonry and the reinforcement is unknown at this point but its assumed that the existing wall will need to be retro fitted... My suggestion would be to add steel columns and steel purlins attached to the masonry walls with steel angles and epoxy anchors.

I am reaching out to see if there are any other ways to retro fit the masonry worth exploring.

FYI
The walls are 22' high
The roof load is 1000plf
The wind load is 47.7psf (ultimate)
No seismic

Thanks in advance.

 

[structSU10]

What you choose might depend on if the wall will be stable at full height for construction loads. If this has to be installed prior to floor removal, that should be considered.

If it is unreinforced, you can knock out the face shells and reinforce. Its a tall wall so it might not work, and the sequence of install may be tricky.

You could also shotcrete the wall with a 4-6" shotcrete thickness on the inside.

Beyond that, a backup steel frame also makes sense. Installing the columns, assuming floor must stay while new support is erected, would be where the column is dropped straight down through a hole in the roof and floor. new girt placed above or below existing floor, then demo the floor.

 

[CANPRO]

I just finished the design of something almost identical and took the route structSU10 describes - install new columns through the existing floor, new girts above and below the floor, then demo the floor. Hasn't been built yet, so unfortunately I can't give you any feed back on the execution, but it seemed like the simplest solution - easy clean details, easy to construct, and fairly reliable. Obviously it depends on your specific situation - major consideration is what your lateral connection would look like to the existing structure at the top and bottom of new your columns.

 

[NFExp]

Thanks for the input.. I was thinking to suggest bracing the wall laterally from the outside. The bottom of the wind columns will be connected to the foundation. I haven't figured out the top yet.. The roof is framed with wood trusses.

 

[BridgeSmith]

Bracing from the outside would seem architecturally unappealing and more difficult to accomplish effectively in construction, since the wall would be pulling away from the columns, rather than pushing against them. You'll have to provide anchorage into the masonry adequate to resist the tension of the full wind load.

 

[CANPRO]

...more difficult to accomplish effectively in construction, since the wall would be pulling away from the columns, rather than pushing against them...

The wind might blow, but it sucks too...doesn't matter which side the bracing is on, the connections will be tension/compression. But I do agree that the reinforcing on the exterior side would be unwise.

Wood trusses might make the connection at the top a bit more difficult. What restrains the block wall laterally at the top now?

 

[charliealphabravo]

Bracing from the outside would seem architecturally unappealing

Well it is a church...

 

[BridgeSmith]

"The wind might blow, but it sucks too..."

I was under the impression that the inward design wind pressure on a building was considerably larger than outward pressure, unless the building has very large openings. I do bridge design, so I could very well be wrong on that.

 

[BridgeSmith]

"Well it is a church..."

Maybe if the proposal was to add flying buttresses, that would look nice. OTOH, it's a church, not an ancient cathedral, so they would not likely fit with the other architectural features.

 

[XR250]

You are doubling the load on the roof diaphragm so that needs to be considered..

 

[hokie66]

My first thought is like NFExp's, brace it on the outside. That way, you don't lose interior space, and I think steel is beautiful, so should enhance the appearance if done right.

 

[NFExp]

Does anyone think that adding pilasters would be better than a steel column?

 

[BridgeSmith]

Are you referring to concrete pilasters that would be made to be composite with the wall? If so, then yes, I think that could be very advantageous. Detailing so that it truly becomes composite with an existing wall would seem to be the tricky part. If the pilasters, be they steel or concrete, are not made composite with the wall, then it's no different structurally than a column, except perhaps the wall providing some lateral bracing if it's detailed for such.