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masonry wall reinforcement detail
i have seen some engineers call for a reinforced bond beam with 2- #4 or #5 bars continuous as the first course of cmu atop a continuous concrete spread footing which also contains continuous reinforcement. i have seen other engineers not require a bond beam at this location. my question is, whether there is some prescriptive requirement or logical design reason for this reinforcement? under the ibc code, would a seisic design category c or d have any effect on the answer? i have seen ncma (national concrete masonry association) details that depict this reinforcement and others that do not, without giving any mention of its reqirement, that i have found.
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good question! i had an engineer that worked for me that insisted on doing this. i never did this since i figured the concrete footing is much stronger than a masory bond beam.
if you are having anything bearing on the wall, then you need a solid bearing area. in most cases, a bond beam is preferable, but for some construction soild 4" high units are also adequate.
the use of a bond beam is just good construction to provide continuity, good load distribution and added strength during and after construction.
in many cases, it is not required by code, but that does not mean the omission of it is good. - "if you go by the code, you are not wrong, but you may not be right".
i would not design or build a wall without a bond beam at the top.
"concretemasonry" you've apparently got it upside down, i'm refering to the bottom course of cmu, which is directly atop of the concrete footing, being a bond beam. of course i agree the top course should be a bond beam.
for me, i look at the concrete spread footing as just a base where the cmu sit. a lot time i dont even reinforce the spread footing so i put the 2 rebars at the top and bottom.
but if you design the wall to resist moment at the bottom then i would put reinforced spread footing with enough dowels into the cmu wall. i dont think the bottom 2 rebars would be necessary anymore since the footing act as one with the cmu.
i hope i am making any sense.
never, but never question engineer's judgement
i see no need to have a bond beam directly above a continuous footing. if all below grade cells are fully grouted (which they should be), what benefit is there to require the bond beam. i will typically show a bond beam at finish floor elevation though.
dlong -
i admit that i automatically assumed it was the top course instead of the unusual situation in the first course.
is this a common basement or a more substantial structure with unique loadings?
if it is a common basement, reinforcement is not even required in most areas and applications. the footing is just a means to provide a level area to build a basement under the prescriptive design requirements of the irc or the empirical methods of aci 530. - in these cases, as an engineer, i feel a detailed design usually not required. for a basement, in many cases a bottom bond beam or even full mortar bedding distrupts many moisture control methods.
some engineers may prefer the approach you mentioned for some reason.
if there is any vertical reinforcement, a reinforced footing with appropriate dowels for the reinforcement would be the preferred method. adding a bond beam on top of this would serve no purpose and only complicates the constructability and reliability of the wall.
dick
it is redundant and unnecessary to place both a bond beam as first course and reinforce the foundation in the longitudinal direction with dowels connecting the wall to the foundation. extra steel is better placed vertically with those reinforced cells grouted.
early in my career, i worked for an engineer who always detailed his cmu walls with a reinforced bond beam first course. when i asked him about it, he said it was for crack control. i always followed his example since he had 30 years experience at that time. over the last 15 years, i saw other engineers detail the walls without the first course as a reinforced bond beam. i have inspected several cmu walls over time and have yet to see a difference between a first course that is reinforced and one that is not. i continue to detail the first course as reinforced. in my opinion, it acts as a shear collector for shear walls transferring the horizontal shear into the footing.
bond beam is the answer....agreed
all you're talking about is a couple of #3 or #4 bars continuous - a small price to pay for extra insurance at your foundation connection.
mike mccann
mccann engineering

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