Florida Building Code Tie Beams in CMU construction

[E M]

New to cmu residential construction and have some questions related to tie beams.
Have a structural engineer helping me with this that I have never used before so doing a little due diligence to see if my ideas truly will not meet code for Florida.
See attached in in progress wall section.

Hurricane zone 2
1 story residential structure
CMU/ CBS construction
All Hip roofs/ Trusses

Short Question:
Can I use 12" tie beams at truss bearing in Florida?

Long Discussion/ Questions/ Comments:
What I want to do is have a continuous tie beam around the perimeter of the house that is a total of 12"+/- high.
This would be half high open bottom bond beam as top course = truss bearing with another 8" open bottom bond beam below this for total of 12". At masonry openings would like to use 8" deep reinforced precast lintels with 1/2 height open bottom bond beam above for total of 12" at window, door & garage door heads. So, all exterior window and doors to have 8/0 rough openings +/- with 12" of tie/ bond beams above.

My engineer is telling me that Florida building code requires 2- 8" course tie beams minimum (16" total) so there is no way I can use 12" no matter what kind of reinforcing I put in the walls.

FBC references TMS 602 Article 2.3 but I don't have access to this. Pulled up some older Florida building codes prior to this reference and seems like 12" minimum tie beams are allowed.

One of the reasons I started down this path is because on local (Tampa Florida) Precast manufacturer website they are showing span tables for this precast & pre-reinforced built up lintel type. Seems down and dirty to me just want to get clarification as to why this is not possible from an engineering standpoint.

Another thing I would like to do with this setup is to use precut wood studs. If 12" tie beams are allowed (crossing my fingers)then I would really like to have top 1/2 course be cut to get to precut stud height which would technically be 5-1/8" high required. This would require cutting all the top cmu open bottom bond beams full perimeter. More work for masons = less work for framers and sheetrockers.... so would be interested in thoughts about this. My thinking is the masons will be happy enough with using precast lintels and sills to make up for only cutting those block.

But first things first. Can I use 12" tie beams at truss bearing in Florida?

 

[StrEng007]

Yes, you could use a 12" tie beam if you're referring to Florida terminology (tie-beams are cast-in-place concrete beams at the top of a CMU wall).

The section you want to reference is 2020 FBC Section 2121.2.3.
[ul]
[li]Concrete tie beam: 8x12 minimum[/li]
[li]"U" type beam block (bond beam): Must have at least 14" vertical and 4 1/2" horizontal width of poured-in-place beam cross-section.[/li]
[/ul]
The actual width of an 8" U-block is 7 5/8". So if 4 1/2" is poured inside the U-block, that would leave you with approximately 1 9/16" of face shell thickness. They vary by manufacturer but this is close to standard.

The same logic goes for the vertical pour inside the bond beam. U-blocks are 7 5/8" tall, and need to account for the bed joint thickness. If the lower U-block is closed bottom, there is another thickness dimension to account for.

The 8x16 bond beam is industry standard and satisfies the code.

 

[SWComposites]

OP - you refer to “my engineer”. Are you an Architect or Contractor or what?

 

[E M]

StrEng007. Thanks for the response. That section looks like the section I saw in the old Florida Building Code I was able to pull up on line.... where I found the 12 is ok.

Understand the nominal vs actual on the bond beams/ tie beams.

Not following the part where it says 14" for U-Block. This project technically want to use precast lintels so not sure that technically qualifies as a a typical ublock. Regardless not following why 14" mentioned there and 12 elsewhere.....

SW. I'm not a licensed architect but practice architecture and work for an architectural design/ build firm.

 

[phamENG]

E M - the difference is terminology. The tie beam you're referring to is, everywhere else, referred to as a CMU bond beam. When the code refers to 'a tie beam of reinforced concrete', they are NOT referring to masonry units. They are referring to attaching forms to the top of the wall and pouring concrete, NOT grout. It also appears that they want U-blocks, not bond beam blocks if you use those which would require you to use 16" tall U-blocks. Besides, the U-blocks are limited to 7' spans, and it looks like you have 8'?

Unless otherwise required by design, all tie beams shall have four #3 ties at 12 inches (305 mm) on center at corners and at each bend and at 48 inches (1219 mm) on center elsewhere. A tie beam shall be not less in dimension or reinforcing than required for the conditions of loading nor less than the following minimums: a tie beam shall have a width of not less than a nominal 8 inches (203 mm), shall have a height of not less than 12 inches (305 mm) and shall be reinforced with not less than four #5 reinforcing bars placed two at the top and two at the bottom of the beam except that a tie beam using “U” type beam block may be used with the following limitations:
1. Limited to one-story Group R3 occupancy.
2.Limited to unsupported spans of 7 feet (2.1 m).
3.Beam block shall be reinforced with one #7 bar in the top and one #7 bar in the bottom of the pour.
4.Beam block shall provide not less than 14 inches (356 mm) vertical dimension or less than 41/2 inches (114 mm) horizontal dimension of poured-in-place beam cross-section.
5.Where beam blocks are used, consideration of resistance to uplift caused by wind forces shall be based on only that portion of the dead load above the topmost mortar joint in the wall.

ref: Link

 

[StrEng007]

Pham, one thing I've seen accepted a lot is the BO allowing 8x16 bond beams (8" width x 16" total height, achieved with 2 courses) with bond beam blocks, where lath is placed below the bond beam (as to create a stop for the grout pour). This also allows continuity of the vertical wall reinforcing to hook into the bond beam. I haven't seen too many cut sheets on the 16" tall U-blocks... how do they handle holes for vertical reinforcing to maintain uplift continuity?

E M - Another thing to sort out with terminology is bond beam vs lintel. The bond beam provides horizontal reinforcing in the wall that ties the structure together. Bond beams can span over openings, but as pham mentioned it has a limitation. If you're specifically looking to use CMU type components to span over larger openings, that's where you consider the pre-cast lintel system. Of course, all of this has to be designed for gravity, uplift, and lateral loads. Cast-Crete is a commonly specified system in Florida.

https://www.castcrete.com/products/

 

[E M]

StrENG & phamENG-
Recently moved to Florida and the terminology scrambles my brain sometimes.... Playing catch up in that arena. First exposure was CBS. Everyone talking CBS and nobody knew what CMU was. Then it's the tie beam term differences.Coming from commercial cmu detailing, yes I'm accustomed to "bond beams" open bottom, header, and lintel blocks. So when I'm talking to the engineer it all gets kind of scrambled.

For purposes of this discussion, I would like to have open bottom bond beams 1 + 1/2 courses (nominal 8X12) high at entire building perimeter at the top. This gets tied into all the vertical reinforcing and filled cells below. No lintel blocks at these locations.... and maybe screen at course below so it gets filled as well. Then, I want to have a 8" high x 8" wide (nominal) continuous precast u shaped lintel over all the openings with a half high open bottom bond beam above that which would effectively make for 8x12 nominal headers over all the openings.

So, in everyones mind can I do this?

The way I'm reading it now seems like no.
Looks like the only way to get by with 12" is if use cast in place tie beams around perimeter and the same for headers.

Otherwise will need 14" min high POURED/ Filled u-shaped bond beam blocks top and bottom (to account for the thickness of the bond beam materials prior to filling. Wondering if this means 2 stacked u shaped blocks or 1 u- shaped block at bottom and one open bottom bond beam at top.

Between the 2 of you think I'm understanding now and appears my engineer is correct. Right?

 

[E M]

StrEng---- was typing when you posted.....

 

[E M]

Yes, I was the system you are describing with screen below the bond beam course (open bottom not U-shaped is what I was thinking as well. Wanted to use that system with 12" up top, screen at course below which effectively would be 20" tall....
then precast lintels above doors but would end up with only 12" overall height lintels no matter what I do which doesn't appear to code.

Any ideas? reaally want coursing at top of windows and doors to line up with 8/0 heads and all block/ precast above.
May just need to take walls up another 4".... but not what I want to do.

Maybe I'll call castcrete and get their take on this. Thanks for the link StrENG

 

[EZBuilding]

Masonry design is really confused by the combinations of unreinforced vs reinforced, ASD vs LRFD and empirical versus engineered design methodologies.

Florida construction used to have empirical provisions of the code as the biggest driver in it's selection. Over times, the difference between the empirical and engineered sections have gotten meshed together and caused a ton of confusion.

Section 2121 is an empirical based requirements. Section 2122 is the engineered based requirements and allows the empirical sections of 2121 to be waived. Construction of masonry walls with masonry bond beams at the top of walls and precast lintels at the top of openings is acceptable should they meet the engineering requirements of the TMS.

2122.2General.
2122.2.1
Section 2121 shall not apply where design and construction are in accordance with the provisions of this section.

 

[E M]

EZBuilding. Thanks for the interest and info.
"FBC references TMS 602 Article 2.3 but I don't have access to this"
Wrote above in my original post. Is there anything that you (or anyone else) is aware of in that article (or elsewhere) that would allow me to use the system I'm describing?
"Engineered vs empirical" design methodologies.... Kind of like prescriptive vs performance in my arena sounds like.

 

[EZBuilding]

TMS is the masonry design code, the old ACI 530. It is a material specific building. Think AISC or ACI for masonry.

Prescriptive versus performance could be a way to look at it. In our field performance tends to indicate looking at a specific issue to meet certain performance targets which strays away from just minimum building code requirements.

I think your system is allowed, but I don't know if it would have sufficient capacity. There are a lot of variables that could affect that answer - roof span, wind pressure, roof type, etc - which is where the building specific engineering should come in.

 

[phamENG]

StrEng007 - I agree. I've seen 16" u-blocks, but masons hate them because they're easy to break. I would prefer bid beam blocks all day but I was trying to read the code s closely s possible.

Full disclosure: in a Tampa Bay native but got my Engineering training and experience in Virginia. I still speak enough Florida Man to figure our the peculiarities, though.

One thing to keep in mind, a lot of engineers use prescriptive standards as minimums. If something goes wrong, it's a lot harder to prove it was your fault...

 

[E M]

OK. Went out to look at ACI530 and all it did was make my head explode. Just when I think I should have been an engineer again, I'm put right back into reality!
Hurricane zone 2
5/12 roof slope
all hips and trusses
2/0 overhangs
9/0 +/- bearing.

Not asking anyone to engineer but just curious if you could see this working. My "guess" is biggest issue is going to be the garage door header..... 20/0 8" precast lintel with "only" 4" open bottom bond beam above.

Really want a clean design for this that I can use precut studs with that I can replicate for future projects.

My guess is contractors are going to balk at forming and pouring 12" deep tie beams all the way around at the top only and they will pass a substantial cost on to me/ my client..... right? Not to mention it's probably not the "easy" way to go about doing this. But all things considered sure seems easier to me than having all different kinds of system elsewhere....

Everyone's perspective appreciated. Should I just roll with what my engineer is telling me? 2 8" block courses at the top and work everything else out? Forget precut studs?

 

[EZBuilding]

StrEng007 - I agree. I've seen 16" u-blocks, but masons hate them because they're easy to break. I would prefer bid beam blocks all day but I was trying to read the code s closely s possible.

Are U-blocks lintels? Or bond beam blocks without openings in the bottom? If so I do prefer the precast lintels for openings with additional bond beams above if needed to form a deeper beam section

One thing to keep in mind, a lot of engineers use prescriptive standards as minimums. If something goes wrong, it's a lot harder to prove it was your fault...

Good point - but I think there is typically enough dollars involved with the framing of the tie beam that it becomes beneficial. It does feel nicer to have the cast-in-place tie beam.

Not asking anyone to engineer but just curious if you could see this working. My "guess" is biggest issue is going to be the garage door header..... 20/0 8" precast lintel with "only" 4" open bottom bond beam above.

I usually have the hardest times making any of the girder trusses connections to work to the masonry wall assembly. Depending on demands you may need some of the ugly and beefy Simpson straps that come down the side of the wall. With a 40 inch masonry beam I think you should be able to make the garage door header work - again, though, not knowing spans, layout and loading we can only speak in generalities.

 

[E M]

Thanks EZBuilding (and everyone) for the help.
Passing along what I found out following a call back from "CAST-CRETE". Thanks StrENG07 for the "connection". Great pdf's of different shapes etc this website as well.
So here's the way the rep says things are done in the Tampa area.
"All" wall heights either 8/0, 9/4 or 10/0 to work with block coursing.
All open bottom bond beams at top course for entire perimeter of house.
Course below is normal full height cmu course with screen below to catch grout.... effectively creating a 16" high bond beam course (or whatever you want to call it.
Precast lintels at head height (8/0 in this case) with open bottom bond beam at top (just like the rest of the wall).
At sliding doors same 8/0 RO as windows.
At man doors 8/2 RO and a special shaped precast header is used that effectively removes 2" from botoom of the precast header.

Straight forward and the least expense imaginable.

Only question now is how to work some sort of precast studs into the equation but he assures me that there are precut studs available that work with this setup.