What is a typical Florida bond beam and how is it built?
Florida masonry bond beams are usually 1 or two courses of bond beam block grouted solid. Bond beam block differs from regular block in that the center webs are cut down to receive horizontal steel. One course bond beams must be tied down at a closer spacing than 2 course bond beams because they don't have as much strength. The masonry industry recommends the two course bond beam for several reasons: Larger allowable spacing between vertical tie downs and a longer embedment length for vertical tie down bars are the main structural reasons.
Cost wise there is not much difference between the one and two course bond beams, especially when bars are only called for in the top course. The mason can lay his block all the way to the top of the wall without stopping. He simply puts in his grout stop under the second course then finishes laying his wall up and places his steel in the top. The second course can be built out of regular block so the only additional cost is about a cubic yard for grout for a typical 2000 sf home.
The steel is more effective in the top of the bond beam because of the uplift forces on the roof from wind.
To summarize, the most common bond beam used in Florida and the bond beam recommended by the masonry industry is a 2 course solid grouted bond beam with a single bar in the top course. The top course would be bond beam block and the second course would by regular block. Vertical wall steel should hook into the top of the bond beam. The spacing of vertical wall steel will vary depending on your height of wall, span of roof and wind speed.
ICC 600 gives specific instruction all of these issues and is accepted by the current 6th Ed, 2017 Florida Building Code, Residential.
The architect is specifying the product DRY-BLOCK by gcp applied technologies as an integral waterproofing admix to be added to the block that are to be covered with a direct applied stucco. Is this what the industry would recommend?
The masonry industry and the stucco manufactures in Florida clearly DO NOT recommend the use of an integral waterproofing agent in masonry to be covered with direct applied stucco. This is not specific to the DRY-BLOCK product but applies to ANY integral waterproofing agent added to the block during the manufacturing process.
The reason is simple - integral waterproofing agents negatively effect the bond between the block unit and the stucco coating. This bond is one of the most important aspects direct applied stucco coatings. The problem is that good stucco bond depends on absorption of cement and water, out of the stucco, into the pores of the block. The integral waterproofing agents are an excellent product for preventing exactly this type of water movement.
Integral waterproofing in the masonry is highly recommended for single-wythe masonry walls which are not covered with direct applied stucco. They would also be appropriate for masonry covered with stucco attached to lath that is then mechanically attached to the block.
In the case of direct applied stucco, the stucco itself is the primary waterproofing barrier protecting the wall. Stucco has proven itself an effective waterproofing barrier by both experience and testing.
Can 6" masonry be used to satisfy the impact resistance criteria in Florida?
The FBC, 6th edition, Building, Section 1626.4.1 allows for 8" hollow masonry to meet the impact criteria for the HVHZ (Dade and Broward). Although there is no mention of 6" masonry 1626.4.4 allows for 2" of reinforced concrete to meet the requirements also.
Common sense would grant that solid grouted 6" masonry is going to perform better than 2" of poured concrete but again it is not mentioned directly.
That being said, FEMA P-320 Safe Room Const Plans specify 6" masonry with a #5 bar in a grouted cell at 16" o/c.
The more stringent FEMA P-361, Safe Rooms for Tornadoes and Hurricanes, 3rd Ed, March 2015 allows solid grouted 6" masonry with a #4 bar at 32" o/c.
As a side note, we plan to submit a code change to include solid grouted 6" masonry in the "deemed to comply" list under 1626.4 in the 7th Edition FBC. It is not currently listed simply because the issue of its use rarely comes up.
In summary, I can see no good reason why a building official would reject solid grouted 6" masonry as specified in P-361 as being acceptable for missile impact requirements in the HVHZ.
I have an 8' freestanding masonry screen wall adjacent to a building. Should the building be connected or not to the enclosure wall? In one location there is a doorway in the screen wall almost adjacent to the building with only an 8" piece of masonry between the building and the door opening. This 8" piece of masonry sits on the building foundation. Should this also be connected to the building or not?
If the wall is supported by an independent foundation I would definitely recommend putting a full separation control joint between the wall and the building to account for differential settlement of the two foundations.
The short section of wall sitting on the building foundation is trickier. Since it sits on the building foundation it is unlikely that there would be any vertical movement between the wall and the masonry door jam. In this case I would recommend solidly attaching the door jam to the building wall. This would also give the wall some additional out of plane strength to resist wind loads applied to it from the door. This will, unfortunately, create a stress build up at the underside of the lintel where it sits on this short section of wall. The stress is from the screen wall changing length from moisture loss or temperature change OR the foundation supporting the screen wall settling at a different rate than the building foundation.
This control joint would be a standard joint at the corner of opening that runs under the lintel bearing horizontally for 8" then turns and runs up to the top of the wall or the underside of the bond beam, whichever works structurally. If there is a vertical bar adjacent to the opening it can pass through the horizontal plane of the control joint (slip joint) without completely negating the value of the joint.
Links to additional information:
NCMA TEK 10-2C - http://ncma-br.org/pdfs/130/TEK%2010-02C1.pdf
How do Interpret Table 2 in TMS 602-16 in order to get the required net area compressive strength of an individual block for a specified f'm?
I have included an article below explaining the increased block strength. It includes a copy of Table 2 so that you can reference it as you read this.
The values of f'm are listed in the left most column and are labeled "Net area compressive strength of concrete masonry". Values are given in psi.
The right hand two columns give the required Net area strength of the individual unit to achieve the given f'm. The far right column is to be used if Type "N" mortar is used to lay up the wall and the middle column is used if Type M or S mortar is used in the wall.
Thus, an individual block with a net area strength of 2000 psi gives you an f'm = 2000 psi.
An individual block with a net area strength of 3250 psi gives you an f'm = 2500 psi.
And an individual block with a net area strength of 3900 psi gives you an f'm = 2750 psi.
Links to additional information:
Update on Increased Design Strength of CMU 1-3-18 with Attachment 1.pdf
We are bidding a job where the project engineer is requiring a 2500 psi block to meet an f'm of 1500 psi. We know that the new code allows a 2000 psi block to have an f'm of 2000 psi. What can we do?
Lets be clear, the project engineering can call for any strength block they desire - as long as it is called out in the project specs that are bid with the job. So if your project specs call for a 2500 psi individual block strength and an f'm of 1500 the 2500 wins and that is what you need to supply to the job.
On the other hand, if the specs ONLY call out for a masonry unit that meets 2000 psi f'm they MUST accept the current code and accept a 2000 psi individual unit strength. Requiring a higher strength unit than is required by the code, and not called out in the bid documents, would constitute a change to the project.
Don Beers, PE, GC