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CMU Horizontal Reinforcement Ties - Florida Building Code Section 2122 High-Velocity Hurricane Zones

CMU Horizontal Reinforcement Ties - Florida Building Code Section 2122 High-Velocity Hurricane Zones

CMU Horizontal Reinforcement Ties - Florida Building Code Section 2122 High-Velocity Hurricane Zones

(OP)
I am working on a project in a HVHZ in Florida for the first time. The structure is a reinforced concrete moment frame with reinforced CMU infill walls spanning vertically between beams. I am currently wading through the FBC trying to understand all of the requirements for reinforced masonry. I'm trying to meet the requirements of Section 2122 in order to avoid using tie beams and tie columns as required by Section 2121.

Section 2122.2.3 states:

Minimum No. 9 gauge ladder-type hot-dipped galvanized, stainless steel, or epoxy coating horizontal joint reinforcing at every alternate course [16-inch (406 mm) spacing], for reinforced masonry shall be provided. This reinforcement shall be tied to structural columns with approved methods. In addition, horizontal joint reinforcement shall comply with TMS 602/ACI530.1/ASCE 6 Sections 2.4C thru 2.4F and Section 3.4B.10.

What constitutes an approved method for tying horizontal ladder-type reinforcement to structural reinforced concrete columns? Also, what is the fundamental reason for tying horizontal reinforcement to columns?

RE: CMU Horizontal Reinforcement Ties - Florida Building Code Section 2122 High-Velocity Hurricane Zones

When I do this, i just continue the ladder reinforcing into the column. And every other design I've seen did it the same way.
As far as the why, if supporting the CMU infill top and bottom is good, then top, bottom and on each side is better.
But I'm confused, if you're trying to avoid the tie beams and columns, why follow 2122? Doesn't the code say something like that masonry designed by an engineer doesn't have to follow this section?

RE: CMU Horizontal Reinforcement Ties - Florida Building Code Section 2122 High-Velocity Hurricane Zones

(OP)
Jed, thanks for sharing your experience. That makes perfect sense to me if the column is poured after the wall is built, but how do you manage this detail when you construct a moment frame first and then infill with CMU?

From what I understand from researching past threads, Section 2121 with the tie beam/tie column requirements is a holdover from the predecessor South Florida Building Codes and Section 2122 was added to provide an alternative method exclusively using reinforced masonry without concrete tie beams and tie columns. As far as I can tell, I have to follow the requirements of one of these 2 sections for masonry design in a HVHZ.

RE: CMU Horizontal Reinforcement Ties - Florida Building Code Section 2122 High-Velocity Hurricane Zones

Embedded plates in the columns to field weld #3 horizontal bars to? Could get congested in the column though...

Mike McCann, PE, SE (WA)


RE: CMU Horizontal Reinforcement Ties - Florida Building Code Section 2122 High-Velocity Hurricane Zones

(OP)
Mike, not a bad idea, but I'm trying to minimize cost for this municipal client and I'd prefer to avoid potential issues from mixing trades and having a welder on stand by.

RE: CMU Horizontal Reinforcement Ties - Florida Building Code Section 2122 High-Velocity Hurricane Zones

I've thought about this a lot and I'm pretty sure that the CMU infill goes in first, then they pour the concrete Columns first, then beams) using the CMU as a form. So they just leave the ladder reinforcing sticking out and the concrete gets poured around it. I've done a bunch of these, but unfortunately have never been there during this stage.
As a practical matter, if you poured the concrete first, it would be very, very (two verys) difficult to install the CMU. The mortar joint against the concrete columns would be very iffy and there would be a lot of trimming of the block, not to mention the installation of the ladder reinforcing and the vertical reinforcing.
As far as this method of construction, you're probably right. I think it's a mix of prescriptive requirements and engineering. But I stopped fighting it a while back. It seems hell for stout and all the Florida contractors can do it and expect it.

RE: CMU Horizontal Reinforcement Ties - Florida Building Code Section 2122 High-Velocity Hurricane Zones

It is typical to see dovetail slots and matching straps or other anchors be specified to match the spacing of the ladder reinforcement. Whether they get installed properly on the field is another issue altogether.

It would not be typical for the CMU infill to be placed first in non-load bearing construction as you would not be able to control your load path to the foundation. It is rare to see moment frame construction in HVHZ - most projects would go straight to shear walls.

RE: CMU Horizontal Reinforcement Ties - Florida Building Code Section 2122 High-Velocity Hurricane Zones

(OP)
This is good to know. I'll proceed with the design with this construction sequence in mind. As long as the contractors are used to it, I have no problem with using the infill walls as partial forms for the columns and beams.

Although I'm doing the design work, another SE based in Florida is supervising the design and ultimately sealing the drawings. His recommendation was to provide dovetail slots in the columns and use a brick tie of sorts every other course along the height of the wall. I contacted Hohmann & Barnard about and they do not recommend his approach or have a product specifically designed for tying horizontal reinforcement into concrete columns, which is what lead me to pose the question here on the forum. Thanks again for your insight.

RE: CMU Horizontal Reinforcement Ties - Florida Building Code Section 2122 High-Velocity Hurricane Zones

(OP)
Unfortunately, the building I am "designing" is a carbon copy of an existing building built in 2012 and designed by another firm. We are making it a bit larger in a plan, adjusting some bay spacings and elevating it for future sea-level rise, but otherwise I am tasked with staying as faithful as possible to the original design. On the other hand, the 2017 Florida Building Code is in effect for this new structure, so I need to make sure that the old design meets the current code requirements. If I went with dovetail slots and brick ties, how can I justify that as an "approved method" per the FBC HVHZ requirements? Intuitively, I don't see dovetail connections doing much good against a hurricane unless the wall has already deflected quite a bit.

The original design has massive 24" and 30" square columns and the general notes refer to the CMU walls as "filler walls", so I don't believe the CMU was counted on for load bearing. EZBuilding's point about the load path being uncontrolled is well taken. In my mind, isolating the filler walls from the frame for gravity loads is the conventional way to go, but I get the sense that things are done a bit differently in this hurricane prone area.

RE: CMU Horizontal Reinforcement Ties - Florida Building Code Section 2122 High-Velocity Hurricane Zones

Seems to me that if you tie the infill walls to the moment frame columns, you are negating the moment frame action. In other words, your moment frame acts more like a shear wall than a moment frame due to its stiffness. Big change to the lateral system

RE: CMU Horizontal Reinforcement Ties - Florida Building Code Section 2122 High-Velocity Hurricane Zones

(OP)
I believe I can detail the CMU wall as either participating or non-participating infill per ACI 530 Appendix B and provide some sort of tie to satisfy FBC 2122.2.3. Either way, any ties to the bounding frame must be detailed to not transfer in-plane forces to satisfy Appendix B, correct?

My preference is to detail it as non-participating, but that's where I run into the construction sequence questions. Plus, it is a departure from the original building design, which I am being encouraged to avoid. Are there any dovetail-type ties on the market designed for and approved for use as a horizontal reinforcement connector in a HVHZ? If not, I feel like I'm stuck with treating the CMU as a participating infill wall and employing the construction sequence Jed described.

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