What is the contractor's responsibility in specifying the strength of concrete? For example, would 2,500 PSI High Strength achieve the wind loads and 20ft wall heights? Or would 3,000 PSI CMU be needed for 20’ walls grouted 8” o.c.? That is why you hire a structural engineer! It depends... on the location, height of the wall section, vertical load, fixity of end conditions, openings, lateral support, etc. You're not designing the wall section, simply offering advice on the availability and cost of materials along with potential problems with the use of various materials. Without designing the wall section myself - which would include understanding the entire structure that the wall is a part of - it isn't possible to challenge or advise him on the design.
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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. We have a customer that is looking for a video on jobsite safety and best practices in masonry construction. Can any of you guide me to this? The Masonry Contractors Association of America www.masoncontractors.org has the best selection of job site safety videos and training. 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 Why do we mortar the cross webs on either side of a poured cell? If the cross webs aren't mortared what can be done after the fact, that is, after the wall is laid up but prior to it being grouted? The short answer is the obvious answer - the cross webs are mortared to keep the grout from leaking out of the cell being filled. We don't want the grout leaking out for a number of reasons. The important structural reason is that the fluid paste surrounding the pea rock would leak out during the filling and vibrating of the cells leaving the pea rock behind with empty void spaces around the rock at each joint. These void spaces, where the paste is gone and only the rock is left, are commonly know as "honeycombs" in construction. Honeycomb severely weakens hardened grout or concrete where it occurs. This would only apply to course aggregate grout mixes that contain pea rock. High slump fine aggregate grout mix, that contains only sand and aggregate, is going to simply flow through the joints with little or no segregation between the cement and the sand. This uncontrolled leaking of fine aggregate grout does not present a structural problem as much as a construction problem. The fine aggregate grout will actually fill the adjacent cells, costing the contractor more money for grout. The contractor will surely be more reluctant to vibrate the grout after initial water loss as the level of fine aggregate grout would continue to drop as the grout leaks out. Unfortunately, this code required final vibration is essential to make sure that grout bridging in the cell has not formed a hollow areas under the bridged area (see below). Also, the extra grout will increase the weight of the wall. Extra weight, other then in tall multi story buildings, is usually not a problem but should be verified with the designer. So, to answer the second part of the question directly, if the cross webs are not mortared the wall should be grouted with a fine aggregate grout with the proper slump (8" to 11"). It is essential that this fine aggregate grout be re-consolidated after the initial water loss to collapse any void areas. This will require additional topping off of the wall. Section 3.3 B. 4.b.2 of the TMS 602-16 code clearly calls out for the cross webs to be mortared. Fine aggregate grout should not and cannot become a substitute for proper construction. Links to additional documentation:
Grouting Concrete Masonry Walls http://ncma-br.org/pdfs/130/TEK%2003-02A.pdf What is the current code required geometry for a grade 60 #5 bar used in concrete masonry? Table 6.1.8 in the current TMS 402-16 (current referenced edition by the 6 Ed FBC) call for Grade 60 reinforcing for a #3 through a #8 bar to have an inside bend diameter of 6 db and an extension of 12 db. For a #5 bar the tip of the extension would then be 15 db or 9.37" from the face of the bar.
The project engineer has requested that ALL intersecting walls be laid up with 50% of the units overlapping at the corner. There are MANY intersecting walls and this prevents any wall from being run in an economical way as you have to continually stop and build your lead for the intersecting wall. What does the code require? An engineered masonry structure built in Dade or Broward is covered under the High Velocity Hurricane Zone section of the code, specifically section 2122. Section 2122.10 requires that "intersecting walls shall comply with TMS 402 section 5.1.1."
The referenced section gives three equivalent ways that intersections can be tied together. The first is that 50% of the units are overlapped at the corner. The second is that the wall shall be tied with a 28" long heavy steel "Z" anchor spaced at 48" vertically up the wall. The third method is to place a bond beam with .4 square inches of steel spaced at 48" vertically up the wall (you could use (2) #4 bars or (1) #6 bar). Since the plans and specs did not call out specifically for the 50% overlapping, any of the three methods would meet the requirements of the job and the code. I have a customer who wants to know what is the maximum height of wall he can pour at one time? Stated another way - what is the maximum drop for grout going down a wall? The grouting height table occurs in two location in the TMS code. In the TMS 402-16 code it appears as Table 3.2.1 and in the TMS 602-16 specifications it appears as Table 6 (same table in both locations).
The table gives the allowable height than you can drop the grout down the wall based on whether the grout is a fine grout (sand only) or a course grout (contain pea rock) along with the clear dimensions of the net opening down through the wall that will be receiving grout. The tables allow for grout to be dropped a maximum of 24' for both fine and course grout. Realistically, it is rare that walls are grouted at heights above 12' - 8" because of the need of substantial bracing for an un-grouted wall 24' in height. Also, typically there is a bond beam around the 12' level which makes it a natural location to grout the wall. The 6th Ed FBC, Building HVHZ Section 2122 simply references the TMS 402/602-16 code for grouting requirements and has no other specific requirements other than a maximum age of 1 1/2 hours after the addition of mix water. I have included with this post a portion of the Masonry Association's Masonry Certification Workshop slides pertaining to Grouting. |
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