Masonry Wall Construction

[SteelPE]

I have a project that a client is asking me to prepare a proposal for. The building is a single-story building in an area with a wind speed of 131 mph. The building is anticipated to have an eave height of 20'-0" with dimensions of 146'x68' and utilize open-web steel joists and masonry bearing walls. The project is pretty straight forward with the exception that the client is looking to use 8" CMU.

Our company standards have us moving away from 8" CMU around 16'-0" to 18'-0". There is no real reason for our limit other than this is what has historically worked for us (other than the old h/t limit of 30 outlined in ACI 530 which limits 8" CMU to 20'-0" before you have to take a 75% reduction in axial capacity for the bearing wall). For this project we are trying to figure out a way to get the clients system to work before we put in a proposal. We are considering using the depth of the roof joists system (24" deep roof joists) and support the walls off the bottom chord of the joist. This would require a system of kickers and bridging in order to properly transfer this force up o the roof diaphragm. It's an unorthodox solution for us. Has anyone attempted to brace masonry walls in this manner before?

To me, as long as we can transfer the loads to the diaphragm properly, I don't see why it wouldn't work. Would it be cheaper than switching to 12" CMU.... unfortunately that is above my head.

 

[XR250]

Can you not get enough rebar in the wall to make 20 feet work? The diagonal bracing seems reasonable as well.

 

[XR250]

I worked on a local shopping center that had 20 ft, 8" CMU walls. They were not even fastened to the edge angle. The only thing bracing them was the 25 ft. O.C. I-beams. Wasn't a known issue until there was significant unrelated foundation settlement that caused the wall to start bowing outwards.

 

[driftLimiter]

I've done exactly what you have proposed with a 32" deep joist.

You could also coordinate w/ joist mfg and just tie the bottom chord to the anchors.

I used angle kickers to embed pl, then they come up to a perpendicular angle that is supported by the roof joists.

 

[SteelPE]

Can you not get enough rebar in the wall to make 20 feet work? The diagonal bracing seems reasonable as well.

I am not sure what we will be able to do as we are just trying to put together a scope of fees for the client and are investigating the feasibility of what the client is proposing. I am not sure where you are located (I can look that up after I type out this response) but 131 mph wind speed isn't anything to shake a stick at.

I've done exactly what you have proposed with a 32" deep joist.

You could also coordinate w/ joist mfg and just tie the bottom chord to the anchors.

I used angle kickers to embed pl, then they come up to a perpendicular angle that is supported by the roof joists.

I understand the coordination part. Going to require a bunch of effort there..... however, what you propose (attaching the bottom chord of the joist to the masonry wall) I would be nervous this would create a moment in the joist which would cause other issues. I have thought about possibly using a square end joist, but I am not sure if I can get that to work or not without inducing moment in the end of the joist.

 

[driftLimiter]

.....create a moment in the joist which would cause other issues. I have thought about possibly using a square end joist, but I am not sure if I can get that to work or not without inducing moment in the end of the joist.

Its unconventional but I'm told the joist MFG can account for this. But I had the same thought as you and opted to keep it conventional as possible.

 

[TRAK.Structural]

Its unconventional but I'm told the joist MFG can account for this. But I had the same thought as you and opted to keep it conventional as possible.

They can account for this, but the real question is WILL they account for it?

Personally I would push for 12" block, or even 10". Will be a lot less grouting and smaller bars. Remember that lift heights for the grout can become an issue with larger bars and lap lengths.

 

[SE2607]

I have a project that a client is asking me to prepare a proposal for. The building is a single-story building in an area with a wind speed of 131 mph. The building is anticipated to have an eave height of 20'-0" with dimensions of 146'x68' and utilize open-web steel joists and masonry bearing walls. The project is pretty straight forward with the exception that the client is looking to use 8" CMU.

Our company standards have us moving away from 8" CMU around 16'-0" to 18'-0". There is no real reason for our limit other than this is what has historically worked for us (other than the old h/t limit of 30 outlined in ACI 530 which limits 8" CMU to 20'-0" before you have to take a 75% reduction in axial capacity for the bearing wall). For this project we are trying to figure out a way to get the clients system to work before we put in a proposal. We are considering using the depth of the roof joists system (24" deep roof joists) and support the walls off the bottom chord of the joist. This would require a system of kickers and bridging in order to properly transfer this force up o the roof diaphragm. It's an unorthodox solution for us. Has anyone attempted to brace masonry walls in this manner before?

To me, as long as we can transfer the loads to the diaphragm properly, I don't see why it wouldn't work. Would it be cheaper than switching to 12" CMU.... unfortunately that is above my head.

You should look at slender walls if you haven't already. That approach eliminates the h/30 issue.

 

[SWComposites]

Send in two proposals, one for 8” CMU, one for 12” CMU. Make the former 10x cost of the latter.

 

[SE2607]

Send in two proposals, one for 8” CMU, one for 12” CMU. Make the former 10x cost of the latter.

Why? There isn't 10x more work or risk.

 

[XR250]

I am not sure where you are located (I can look that up after I type out this response) but 131 mph wind speed isn't anything to shake a stick at.

I am in a 115 mph so about 30% less pressure. Still seems possible though but maybe not practical.

 

[SteelPE]

Send in two proposals, one for 8” CMU, one for 12” CMU. Make the former 10x cost of the latter.

That would be nice, but knowing the players involved, I am not sure I would even want to deal with the headache.

Why? There isn't 10x more work or risk.

I understand what you are saying, but the way I see it, there certainly is more risk. For me, masons were the worst trade to deal with (that was until wood framers took over the top spot). In regards to masonry, anything out of "normal" for them (#9 ladder reinforcing @ 16" o.c. and #6@ 40" o.c.) is a tall order for them to do. So there is more risk involved and certainly more work on my end with getting the execution completed properly.

5 years ago, same players involved, same client wanted to push 12" CMU to 30' (lower wind speed as it was further inland). We reluctantly designed the system to support the required loads. Tons of reinforcing with lots of doubly reinforced cells around the openings placed in the perimeter of the building. When it came time to execute the design it was an uphill battle through the construction process. It wasn't a fun project with lots of headaches along the way.

 

[EZBuilding]

I agree with the recommendation to review the slender wall provisions for masonry design. If you consider the moments due to the wind load, little p-delta effect, and the joist bearing point eccentricity at the top of the wall I think you are good to go. I would tend to shy away from bracing the walls the joist bottom chord.

On a separate point, this seems to be a lot of the actual engineering work related with a bd task for a relatively small project. I would think the client should be paying you to evaluate this as an option - not having you preliminarily check their design before you get contracted.

 

[SteelPE]

On a separate point, this seems to be a lot of the actual engineering work related with a bd task for a relatively small project. I would think the client should be paying you to evaluate this as an option - not having you preliminarily check their design before you get contracted.

Have not even stuck a pencil on a single piece of paper yet. Most work I have done is to ask this question on this forum. When the client stated that they wanted 8" CMU @ 20'-0" tall that raised a red flag. Now it's either:

1) come up with a way to execute the design as the client wants
2) tell the client I'm not interested in the project

For the project outlined above (12" @ 30') I purchased some software from NCMA that will help with the analysis. It runs through the p-detla check outline above. I can probably get the wall to work, but when they start punching 10x10 OH door openings through the walls all bets are off. May need to just add pilasters each side of the openings.

 

[EZBuilding]

Yea, either a masonry return for the jamb. You might also be able to make a concrete tie column work for the jambs.

 

[SE2607]

May need to just add pilasters each side of the openings.

That's what I would do. I would also use pilasters at supports for any girders.

 

[bIockhead]

Send in two proposals, one for 8” CMU, one for 12” CMU. Make the former 10x cost of the latter.

I take some issue with this approach unless that is an accurate representation of the costs involved.

I can appreciate from other replies that this is a case where the client is gauging feasibility, but this strikes me the wrong way.

 

[XR250]

I am guessing #5 @ 24" O.C. would work for this. Openings would be an issue as you stated.

 

[dold]

I am guessing #5 @ 24" O.C. would work for this. Openings would be an issue as you stated.

Yeah I'm not seeing anything really out of the ordinary for 20' tall 8" block with 50psf wind. Jambs at openings probably have to be 3 cells each side with (2) #5. Again, nothing that can't be done. Certainly nothing that would cause me to 10x my fee... Just my $0.02

 

[strucbells]

Yeah this should all be feasible with 8" block using strength design, add pilasters at large garage door openings if needed.

A couple of methods to consider the 2nd order effects: https://www.structuremag.org/article/masonry-to-the-second-order/