CMU Bond Beam in FL

[rmartinat]

Hello fellows,

This question is related to masonry construction in Florida (specially south FL). Please feel free to chime in if you have any experience with the FBC. I have seen plans (specially for housing developments) where the EOR specifies a 8x8 CMU bond beam at the roof level (2 story structure) and a 8x16 CMU bond beam at the 2nd fl level. I know developers love using this instead of a CIP tie beam because its more budget friendly. I have not been able to find anything on the FBC that would allow this specific CMU bond beam situation. The only section that talks about it and allows something similar (only for 1-story R-3 occupancy) is FBC 2121.2.3.2.

Am I missing another chapter or section of interest? Is this maybe an old design practice that is being carried over and it's being overlooked by design professionals and plan reviewers?

Any help or comments would be greatly appreciated.

Thank you!

 

[phamENG]

That section of the code is applicable only to Broward and Dade counties (high velocity hurricane zones), right? So if you're there, you'd have to take it up with the AHJ. Anywhere else....as long as the construction is strong enough to meet the demand I don't see a reason not to do it. Standard CMU construction.

 

[JedClampett]

There's a prescribed design method in Section 2121.1. It's not bad for residences, but a little too prescribed for my taste. But you're allowed to engineer it yourself per 2122. I usually use a mixture of the tie beams and columns method plus a touch of JedClampett from 2122 goodness added in.

 

[rmartinat]

Thank you for your responses. This project is in Broward County. So, it is within the high velocity hurricane zone. That means that the tie columns spaced at 16' o.c. from 2121.2.2 is also applicable. Again thank you for your time and responses.

 

[phamENG]

Looks like Jed has the better answer. If you design to 2122 (which is just saying use TMS 402), then 2121 doesn't apply. I don't believe there are any mentions of tie beams in 2122.

 

[StrEng007]

The FBC does not do a very good job of explaining the intent (rather history) behind these two sections. Section 2121 is a detailing residual that is left over from the South Florida Building Code. If you follow section 2121, you're essentially providing CMU infill that is considered non-load bearing for the purpose of gravity loads. The only reinforcing requirement specified here for the actual CMU is the horizontal joint reinforcement that is to be embedded in each tie-column. This was/is viewed as a concrete frame where the CMU was analogous to a curtain that was placed within the opening.

Here are some images from the 1984 South Florida Building Code:

Per Section 2703 ALLOWABLE UNIT STRESSES IN MASONRY:

Regarding tie-beam:

You'll notice that some of this language closely follows section 2121 of the current 2023 FBC.

This is all to say that, no you're not required to have this 16'x16' grid of cast-in-place tie-beams and tie-columns so long as you design your CMU per TMS402/602. CMU bond beams can be used.