huangyhg

high strength masonry
i'm considering using some high strength masonry on a job. my initial calcs suggest an f'm of 4000 psi would be required.
what i can't seem to find is the required net strength of the cmu units to get me there. all the tables i've found only go up to f'm=3000 psi, but i've found plenty of information on the net that says 4000 psi is possible.
anyone have any ideas?
find a job or post a job opening
arkeng,
assuming the design is in accordance with ibc and not ubc, compliance with f'm for new engineered masonry construction is usually verified by one of two methods:
1. unit strength method ibc sec 2105.2.2.1, or
2. prism test method ibc sec 2105.2.2.2
the f'm max value of 3000 psi for cmus is when the unit strength method is used for complaince with f'm. ibc table 2105.2.2.1.2 or msjc spec table 1, page s-10
imo, you'll have to go with the prism testing method wherein the whole assemblage(blocks, grout and mortar minus the rebar) is tested.
i would also check with your local cmu manufacturers to see if you can get blocks of the required strength. i wanted to use f'm=2000 psi on a project once, and this caused a controversy with the local block mfrs because using f'm greater than 1500 psi in my area is almost never done.
if you actually require this strength of masonry, why not use precast or cip concrete? i've never heard of 4000 psi masonry before.
motorcity,
funny you should ask that: this job was originally cip concrete and working comfortably with 10" walls (at 4500 psi). contractor has convinced the owner there's time and money to be saved by going to masonry. i've had to go to 12" cmu and the bottom story is 4000 psi.
i suspect (hope) they may change their mind when they see the details.
arkeng,
i think you should proceed with your work, with an eye toward demonstrating whether or not, and where any cost savings would be. from your description, i believe you may find none. complex details and hard-to-supply masonry units both should translate to higher than average costs for the masonry option... you just might find that the concrete is cheaper after all.
regards,
chichuck
i had something similar come up where i wanted to use concrete and they had the money saving conversation without me regarding cmu. i would have so much reinforcing and plus those high strength units, that i didn't even go to the effort that you are and just told them no, it wouldn't work and it would be about as much money if i was able to get the cmu wall to work. i am tired of spending all my budget (which is too little to begin with) trying to do something extraordinary to save somebody else 50 cents.

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