Grouting deep masonry beam
Grouting deep masonry beam
(OP)
I have a project with a 40" deep (5 courses) reinforced masonry beam. The mason is proposing to build this and grout this one course at a time. He would build it like 5 bond beams on top of each other. I cannot find any notes in ACI 530 regarding grouting beams in multiple separate pours. Is this allowed? Am I crazy for expecting this to be poured together to avoid "cold joints" through the depth of the beam?






RE: Grouting deep masonry beam
RE: Grouting deep masonry beam
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Grouting deep masonry beam
Normally, for large openings (like doors on a high-walled industrial location or gymnasium). The proper way is to use conventional bond beams (closed bottom) and block that allows any vertical horizontal steel to be placed as the units are laid and the wall grouted. This pushes a smart contractor towards this type of construction and promotes the use of plant mixed grout.
It is best to have some sort of detail or notes on the drawings to guide the contractors.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: Grouting deep masonry beam
RE: Grouting deep masonry beam
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Grouting deep masonry beam
I think you would use a lintel block with a closed bottom, as concrete masonry suggested, for the first course of the deep beam. The other courses could be knock out blocks as depicted on the right in your diagram. These are not "standard" blocks, which would require sawing the webs.
RE: Grouting deep masonry beam
Don't mess with Canada.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Grouting deep masonry beam
Thanks again!
RE: Grouting deep masonry beam
You'll have to look at the geometry to ensure it fits, but I may even consider spec'ing 180-deg hooks at the top and bottom of the vertical bars to force engagement with your horizontal bars in the highest and lowest course.
RE: Grouting deep masonry beam
I wold be specifying knock out blocks for everything but the bottom course, it can be a standard lintel block. As a happy medium with the contractor I would likely be comfortable with him doing it in 2 lifts, say 3 courses the first grouting, and 2 on the second. I would not allow him to use 5 layers of lintel blocks.
RE: Grouting deep masonry beam
In many or most areas, the "knock-out" blocks are very very common. There are also block that are delivered and made without the upper 1/3 or 2/3 of the webs. I work for a company that sold manufacturing equipment to the concrete products industry domestically and internationally and we had a "library" of configurations that were common. In some markets the block were supplied with the top of the webs not knocked out because contractors could use the knocked out section to plug the cores, eliminating the mesh and handling/disposal.
The block producer I worked for for 20 years carried the knock-out units in stock for both plain face block and for split face architectural block configurations. We also made these configurations in higher strength block.
Check what is possible in the area you are designing for. - It is a big world.
enginerding -
The grouting of these deep masonry beams with the knock-out units is very similar to the grouting of an ordinary reinforced grouted masonry wall as far as procedure, lifts and and topping off to account for normal absorption of the excess water needed for a usable grout mix. For 5 courses, there would be no need to waiting, but it would be prudent to top off the last course after the consolidation to provide a smooth top better bearing for anything that is set on the walls. The concept of using 5 individual courses of solid bottom block would produce and inferior wall.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: Grouting deep masonry beam
Not sure why you directed that comment at me. I tried to make the same points as you did. Maybe it is in the translation...
RE: Grouting deep masonry beam
Isn’t there also a “H” shaped block which has a center cross shell, but no end cross shells, which opens up the cores a bit, and doesn’t make the head joint area so tough to grout full? Those poorly filled head joint areas would be particularly bad in a deep beam action. The 5 courses of 8" bond beam block is an awful idea. The bond at each horiz. joint is not very good in terms of transmitting horiz. shear, and it is very difficult to get any vert. shear reinf’g. from top to bottom. It’s akin to claiming that 5-2x6's stacked atop each other, with no glue, makes a laminated wood beam. The individual 2x6's slide past each other when the deep beam tries to work, no hoirz. shear strength, no shear flow tying the pieces together to form the deep beam. The filled/grouted vert. cores and vert. reinf. serve this same function, tying the deep beam together over its depth, and providing a good compression block at the top. I would make the bot. course a 16" deep lintel block, set the rebar (horiz. and vert.), and grout it to within an inch or so of the top, leaving the grout fill rough. Set the next 3 courses of “H” blk. being careful to minimize mortar dropping, or removing them, set some top reinf’g., then grout the top 3 courses.
RE: Grouting deep masonry beam
I did suggest H blocks in my first post. Where I am, we tend to use them extensively when you want full grouting. Not sure about availability where the OP works, but H blocks should be a standard shape in reinforced concrete masonry.
RE: Grouting deep masonry beam
Yup... I thought I had read that in this thread, but then I couldn’t find it. Then you also said a fair share of what I repeated, but in few words. See how good I listen, learn and mimic?
RE: Grouting deep masonry beam
RE: Grouting deep masonry beam
RE: Grouting deep masonry beam
RE: Grouting deep masonry beam
I guess there may have been a difference of terms. Every marketplace/area has different terms. There is a divergence of the description for a block with 2 face shells and one cross web - In some areas, it is an "H" block and in other areas, while it is an "I" block, but just depends on how you orient it.
We made the 8x8x16 with two webs at 8" on center in both knock-out webs AND some with the top 2/3 of the webs not existing, because of the contractor and engineers requests.
All special units may have problems meeting the ASTM C90 requirements for structural, especially those with reduced web heights. - This has happened numerous times when we wrote the ASTM C90 standard that has a requirement for the "equivalent web thickness per liner dimension" of the unit. Fortunately, that can be resolved if the wall is partially reinforced.
In the real world, all block actually have a top and bottom and it is preferred to lay the preferred block with the top of the face shell that usually has a flair (extra 1/4") to make the unit easier to handle and spread a good uniform mortar bed with minimum mortar droppings in cores that are not good for grouting. - This is often requested by engineers and contractors.
Keep in mind the strength of the mortar and grout have minimal effect on the wall strength of the actual wall. - I have see engineers place a maximum on the grout strength to insure stress distribution through the wall that reflects the code and specifications for tall masonry walls (over 10' or so).
Cheers!!!
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: Grouting deep masonry beam
The only "out" that I can think of is if the mortar in the bed joints, acting on it's own without help from the grout, could supply the required horizontal shear capacity. In that regard, multiple lintel courses might actually help (more mortar). As Hokie mentioned, however, I think that the rational thing to do here is maximize grout volume.
This does have me wondering about the analagous situation with walls. With walls, we'll add in the shear strength of grouted cores and not worry about the cold/construction joints. Often there are vertical bars present that could be used for shear friction but not always.
Lastly, I have a research paper that concluded that horizontal shear transfer in unreinforced concrete beam cold joints is quite good. I know of no code based way to take advantage of that but it's reassuring none the less.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Grouting deep masonry beam
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Grouting deep masonry beam
The codes and all research for 50 to 90 years ago is based the wall behavior and not individual components. - That is why there are specifications for the properties/performance of individual items (mortar, cement, aggregate, masonry units to develop standards) of the materials types used in a walls.
With concept of treating the section as a series of individual 8" high beams over the large opening would lead you into untested waters because you are looking a and individual mortar joint the is really in direct compression and there very little virtually no testing to analyze such a small element of a wall. The mortar is bonded horizontally to masonry units before the preceding course has really cured. The folly of friction is meaningless, especially when the mortar is really in confined compression.
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: Grouting deep masonry beam
I'm not really sure what you're getting at here. For the beam under consideration, there has to be shear transfer across the horizontal cold joint for composite flexural behaviour. If shear friction is the wrong term for that, what's the right term?
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Grouting deep masonry beam
With respect, I think you are wrong. The same philosophy you espouse for walls does not apply to beams. Reinforced masonry beams work the same as reinforced concrete beams.
RE: Grouting deep masonry beam
You are correct it is an unusual procedure that requires or encourages improper construction, especially if there are stirrups or vertical steel. Is the remainder of the building vertically reinforced?
Kook, Hokie, - I will forward your concerns at the next technical meeting to others also involved in the writing of the ACI 530 standard. The problem exists that it is unusual to not build the wall on the same day for such a small wall section, which would removing and reinstalling the scaffolding to provide valuable access to the interior area of the building. Possibly, the engineers and contractors on the codes and standards group may offer some alerts in CI 530 for the design engineers regarding the possible problems for an apparent unique situation. This could also include a decision whether a common mortar joint between masonry units laid in running bond ("other than stack bound") is a "cold joint". I don't think there are any concrete beams in this situation since it is apparently a reinforced concrete masonry situation without discontinuities.
In general, I have a hard time seeing a situation where a contractor would build each course of the wall and fill the CMU cores course by course. Doing that, would assume mortar would likely be used in place of a mixing a proper grout of 8"-11" slump for reinforce masonry when there is a solid bottom bond beam in place. - Every situation has it own unique features, but if there is only one situation in a building, it could be done if there is access to both sides of the wall during the support of the deep lintel during strength development.