Detailed questionWe are a residential engineering and design company in Central Florida, and have several builders inquiring about removing as many grouted filled cells as possible to reduce cost. They comment that we are more conservative than our competitors. We have completed our own wall calculations based on TMS 402-13 (and confirmed with NCMA software), and are comfortable with our grout filled cell spacing calculations; however, the code is less clear about filled cell requirements around openings. Some of our competitors only place a filled cell (typically with (1) vertical #5 bar) on one end of shorter window and door openings. I’ve heard several engineers cite FBC 2121.2.2.2 (see below), but of course this is only for High Velocity Hurricane Zones, and that section has several other requirements for “tie columns;” namely 2121.2.2.3 & 2121.2.2.4. In my view you can’t follow one section of the code, and ignore the others. I’ve spoken to plans examiners and inspectors, who cite Figure R606.11(1) showing reinforced filled cells on both sides and above and below openings; however, this section is prescriptive, deals with anchorage, and has unclear requirements (“Wind loads less than 30 psf,” is that design or ultimate pressure?). The most relevant code citations I can find are in R301.2.1.1, which points me to FBC, Section 2107: Allowable Strength Design, which references back to TMS 402-13. I can’t find any clear-cut requirements about reinforced filled cell placement around openings. Assuming we don’t need the reinforced filled cell for the loading requirements, or buck fastening, is there a code citation, construction guide, white paper, or other source we can reference regarding filled cell requirements around openings. If not, what is your view as far as best practices or typical industry standards. Referenced code section: 2121.2.2.2 When openings are between 3 and 8 feet (914 mm and 2.4 m) in width, such openings shall have one #5 vertical reinforcing bar at each side. The vertical bars shall be placed in concrete filled cells and shall extend into footings and into tie beams. All such bars shall be continuous from footing to tie beam. All splices, where needed, shall be 30 inches (762 mm) minimum. 2121.2.2.3 Tie columns shall be not less than 12 inches (305 mm) in width. Tie columns having an unbraced height not exceeding 15 feet (4.6 m) shall be not less in thickness than the wall or less than a nominal 8 inches (203 mm), and, where exceeding 15 feet (4.6 m) in unbraced height, shall be not less in thickness than 12 inches (305 mm). The unbraced height shall be taken at the point of positive lateral support in the direction of consideration or the column may be designed to resist applicable lateral loads based on rational analysis. 2121.2.2.4 Tie columns shall be reinforced with not less than four #5 vertical bars for 8 inch by 12 inch (203 mm by 305 mm) columns nor less than four #6 vertical bars for 12 inch by 12 inch (305 mm by 305 mm) columns nor less reinforcing steel than 0.01 of the cross-sectional area for columns of other dimension nor less than may be required to resist axial loads or bending forces. Vertical reinforcing shall be doweled to the footing and splices shall be lapped 30 bar diameters. Columns shall be tied with #2 hoops spaced not more than 12 inches (305 mm) apart. Detailed AnswerGreat question: Short answer - up to the registered engineer or architect - not specifically addressed in any code that would usurp the judgement of the design professional....Period.
Very Long Answer: Lets start with section 2121 of the 6th Edition FBC - Building. These are historic prescriptive requirements and there has ALWAYS been confusion as to where and how they apply. Thus, we inserted the following section into 2122 - Reinforced Unit Masonry - to try and drive home that 2121 just does not apply to masonry designed in accordance with the provisions of TMS 402/602: 2122.1Standards. The provisions of TMS 402/ACI 530/ASCE 5 and TMS 602/ACI 530.1/ASCE 6 are hereby adopted as a minimum for the design and construction of reinforced unit masonry. In addition to TMS 402/ACI 530/ASCE 5 and TMS 602/ACI 530.1/ASCE 6, reinforced unit masonry structures shall comply with Sections 2122.2 through 2122.10. 2122.2General. 2122.2.1 Section 2121 shall not apply where design and construction are in accordance with the provisions of this section. Thus you are completely correct that the provisions of 2121 are unique and independent and offer no guidance in properly designing your masonry structure - unless you want to use them in their entirety in designing your structure. Ok, now to the residential code. Not much help there. As you indicated, Figure R606.11(1) shows some interesting stuff but nothing that gives you the guidance you, as a designer, are looking for. The provisions calling for steel girding all openings is a seismic provision dealing primarily with shear. For shear in residential wind design you are generally going to distribute your shear to solid wall sections depending on their stiffness and utilizing only the un-reinforced value of masonry. If your un-reinforced shear value of the individual solid panels is not sufficient and you have to design a reinforced masonry shear wall you would absolutely be reinforcing around all sides of openings --- but --- that is almost never going to be the case with residential design - and is rarely the case with low-rise commercial design. Bottom line is you are generally not going to see masonry under an opening unless it is there of crack control (not structural reasons). R301.2.1.1 references the ICC 600 in which section 405.3.2 "Openings in Masonry Walls" gives some common sense guidance to put a bar on either side of openings over 6' wide and to make sure that any bars interrupted by the opening get distributed to both sides. For openings in residential structures this is about as good as it gets. For large openings you have to make sure that the wall segment on either side will take the load from 1/2 the opening width. Where you have a number of large openings in a row this can be challenging. Hope this helped. Obviously, you are always going to put a bar over the opening.
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I am building a 16 ft tall masonry wall with a bond beam at the top and it supports hollow core slabs. The superintendent says that the code requires an intermediate horz. bond beam at 8 ft. Is that correct? No, that is incorrect. There is no code, state or national, that requires a bond beam at 8 ft in non-seismic zones. The FBC 6th Ed. specifically exempts Florida from ANY seismic considerations so the seismic issue cannot apply. Florida's seismic category would not require intermediate bond beams in any case.
A designer might choose to include bond beams at an intermediate location but that would be a design choice NOT a codes issue. A building official is requiring a UL lable the block I am using. The producer is saying UL lables on masonry units are not available in Florida. What is going on? The question on whether masonry units can be required to carry a UL lable has been around for many years. The answer your producer gave is the correct one - UL labled block are not available in Florida. Additionally, your Building Official cannot require one (your architect CAN require it in his specification - but he will pay the price). Your Building Official MUST accept block manufactured under Section 722.3 of the 6th Ed. FL Building Code, Building. This section specifies the fire rating of a concrete masonry unit by aggregate type and equivalent thickness.
My architect is questioning my ability to obtain a light weight block with a compressive strength of 3500 psi. Can you clarify? First you need to make sure you understand what is being required. We are assuming we are discussing a individual block with a net area compressive strength of 3500 psi. If that is the case then there is no problem. Lightweight high strength block in that range are manufactured every day.
On the other hand, if an f'm=3500psi is what the specifier has in mind the answer would be no. Not available in any weight block, light or not. And not recommended if it was. f'm=3500 psi is literaly "off the chart"! That is the chart in Table 2 of TMS 602-16 which is the current masonry code in the FBC 6th Ed. Hi, I want to build a two story building with concrete block filled with concrete and rebar. As you know, Florida is hot and the UV rays heat up a concrete wall big time. Do you folks have any experts on staff who have experience applying materials and paints to exterior concrete blocks to create 'cool' walls? The most common way to insulate your home in Florida is to use a foil type insulation spread between the furring strips on the inside face. Using a 1 5/8" furring strip rather then a 3/4" furring strip allows you to slightly increase your interior insulation value of the available foil products.
The maximum recommended insulation for Florida homes is a 3/4" polyiso board with a reflective side. The board is glued or nailed to the inside face of the masonry wall with the foil face pointing inward. 3/4" furring strips are then attached over the board and the drywall attached to the furring strips. This gives you a through wall insulation value for a typical block wall of R10 or an added insulation value of R7.8 (insulation value of the 3/4" board plus the insulation value of a 3/4" reflective air space). Normally block walls are either painted, sealed or stucco'd on the outside and none of these adds any appreciable energy efficiency to the home. The truth is that masonry homes require very little insulation in the Florida climate. We proved this with extensive research done at the Pacific NW Labs, one of the top energy research labs in the Country. Results from that testing are attached to this blog and clearly show that your typical foil interior insulation is the best value for money. The actual energy $ savings between the minimum R4 foil interior insulation and R20 super insulation is only about $100 per year (not per month - per year). This is for a 2000 sf one story home in Miami. The $ difference in Central and Northern portions of the State is even less because of the cooler evenings which makes the masonry thermal mass work better. You can super insulate all you want but you will never recoup your investment with energy saving. That is because the opaque exterior walls just don't contribute that extensively to the overall energy use of the home. Things like efficient hot water heaters and air conditioners, extra attic insulation and better infiltration packages make a HUGE difference your energy bill. The opaque portions of exterior walls just don't contribute that much to your energy use. Thus, there is only a minor gain in heaping insulation on these walls and your return on investment drops off to almost nothing after a modest amount of insulation is added. Does solid grouting of your cells in a masonry wall help to reduce the movement of water and water vapor through the wall? The short answer is yes but not by much and it is not discussed as a way to water proof masonry walls. Integral waterproofing agents in the block, concave tooled mortar joints, exterior sealants applied to the block face, weeps and flashing and control of cracking by properly placed control joints are the prescribed methods of limiting water and vapor movement through the wall. Solid grouting can improve the structural capacity of your wall but improvement of water tightness is not an acknowledged benefit. There are just too many other more effective and less costly ways to address wall leakage. Pleaase see the attached article that addresses creating water tight masonry walls. Additional information:
Keeping your Single Wythe Masonry Building Dry https://ncma.org/resource/design-for-dry-single-wythe-walls/ Block made with Florida limestone normally has a density per cubic foot of 120 to 124#. This puts it in the upper end of the C90 classification of Medium Weight block (Table 2 - C90-14). NCMA TEK Note 13-01C gives an STC rating of 47-48 for an 8" hollow unit with a density of between 115 and 125 #/CF. Links to additional documentation:
https://ncma.org/resource/sound-transmission-class-ratings-for-concrete-masonry-walls/ You helped me earlier with a spec sheet for our 8in block. It shows meeting the C90 spec, but do you have one showing the block meet the C129 spec also? This is for a project on a local military base. They are requesting the same specs for the following products, 8in part, 8in halves, lintels, bond beams, and jambs. They are also specifying a block strength of 2800 psi. Is this something you could help me with? he C129 spec is a less restrictive version of the C90 spec. Any unit meeting the C90 spec will also meet the C129 spec. Additionally, the individual block strength of 2800psi is a pretty much meaningless number. In editions of the TMS 602 prior to the 2013 edition the 2800psi block strength gave you an f'm=2000psi. In editions of the TMS 602-13 the required strength of block to achieve f'm=2000 reduced to 2000psi (one to one). A block with a strength of 3250psi now yields an f'm=2500psi - which is now the new high strength block. A standard block (every C90 block) is now an f'm=2000psi. The required individual block strength for C90 has increased from 1900psi to 2000psi which, again, yields an f'm=2000psi. Specifying an individual block strength of 2800psi means that the specifier is looking at the OLD code. This is explained again in the blog below. Good luck with your project! Call if you have questions. The specifier is welcome to call me also.
Detailed Question: We have had several jobs recently specifying “high Strength Block”. Some has listed 2500 psi another I believe was 2800. Looking at C90 it seems to be open to interpretation and maybe job specific? We have a HS block but just trying to make sure we are fine. Is there a specified strength for this classification? Detailed Answer: There are generally two block strengths that are readily available to the structural designer. For the sake of simplicity I will call them ""normal"" and ""high"" strength. The strengths have changed dramatically since January 1st, 2018. The new strength values for masonry come from either the 2013 or the 2016 edition of the TMS 602 specifications section 1.4B.2.b.Table 2. The Florida Building Code, 6th Edition, references the 2016 TMS 602 but the strength values are the same in both editions (and will be in future editions). The compressive strength of an individual block of ""normal"" strength is 2000 psi which can be used to build a wall with an f'm=2000 psi. An individual ""high"" strength block would have a compressive strength of 3,250 psi and would result in a wall with an f'm=2500 psi. This ""high"" strength block is stocked on some yards but is readily available on demand from most manufactures with minimal delay and only a slight increase in cost. Walls designed with an f'm=2750 psi require that the individual block unit has a compressive strength of 3900 psi. These block are available from manufactures throughout Florida but are going to result in longer lead times (because they are almost never stocked). You can expect significant additional cost and longer holding times after manufacture to make sure they will achieve the required strength. I would not recommend specifying masonry with a compressive strength f'm=3000psi. This strength requires an individual block with a strength of 4500 psi. This strength is closing on the natural limit of masonry produced with Florida aggregate. If you require a masonry unit of this strength consult with your block supplier on cost and availability. You will most like find that you are going to be better off specifying a "normal" strength 12" wide unit which is available off the shelf everywhere. This was a comment by a Florida Building Official on waterproofing block walls. "Masonry is by it's nature porous and is not a good vapor barrier. My assumption is that in addition to the Tyvek, some sort of siding, brick or other finished material is planned other than stucco. " What are your thoughts? You would never put tyvek on a masonry wall. I have never heard or seen such a thing. The code does not require a “vapor barrier” on cmu . Your block either has integral water repellent in combo with an exterior sealant/paint ----- or ------ it is stucco’d in which case the stucco and paint in combo with the cmu becomes the water/vapor barrier ------ or---------- you put brick on the outside with a roll on barrier ------ or---------- if you are using direct adhered stone or thin brick you use a product that seals the wall and adheres the stone or thin brick.
In all cases, other than at cracks - which need to be addressed in the design, the wall is water tight and sufficiently vapor tight to keep the interior dry. Question on the apparent conflict between the section of the Fl code in 2122 requiring attachment of masonry to adjacent columns and beams and the requirements of TMS 402 B.3.2 prohibiting attachment of masonry walls for participating infill. The prohibition to connecting infill masonry to the surrounding frame in TMS 402-16 Section B.3.2 only applies to in-plane forces in participating infills. The reason is explained in the commentary for that sections which explains that this is to prevent the connectors from causing ""premature damage along the boundaries of the infill under in-plane loading (Dawe and Seah (1989a))"".
The Florida code is requiring connection for out of plane loading from wind which is also required by Section B.3.3 of TMS 402. |
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