Grouting deep masonry beam 4

[enginerding]

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?

 

[KootK]

Above, I expressed a lack of concern for the horizontal cold joints. I've changed my mind. Like a cold joint in a concrete beam, I now feel that the joint should be analyzed using shear friction principles and that the result of that should be vertical bars developed on either side of the cold joints. This would be similar to what FoxSE and Jayrod have proposed. Having multiple course grout pours at the top and bottom of the beam would be preferable for bar development purposes.

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.

 

[KootK]

Link

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.

 

[concretemasonry]

I think you can get in trouble by misleading yourself when analyzing specific parts selected and materials in a masonry walls. - It is not like a steel or concrete beams or welds. - Especially when the cementitious materials in the wall are fresh and not fully cured (except the block that are cured enough to build with and will cure before design loads are applied.

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.

 

[KootK]

The folly of friction is meaningless, especially when the mortar is really in confined compression.

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.

 

[hokie66]

concretemasonry,
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.

 

[concretemasonry]

enginerding -

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.