H/t for Masonry Fence

#1

I am designing an 8" CMU, 10 ft. tall masonry fence. Only self weight, seismic and wind loads. NCMA wants to limit it to 8 ft tall or about h/t = 12.5 (or 25 for a pinned -pinned, full height wall). Seems pretty darn conservative as the axial and wind loads are not huge. I hate to switch to 10" or 12" CMU since the contractor is already complaining about cost.

Thanks!

#2

XR250:
Those kinds of walls/fences are pretty common in the SW U.S.A., and they do have fairly high h/t ratios. Apparently, the design philosophy is basically that people don’t live near or under them and if/when they fall over they just fall in someone’s back yard. The self-weight and prevailing winds are not great or the real problem, but I’d worry about wind gusts and EQ’s. One of the biggest problems is that they act like dams in rains w.r.t. water back-up behind them and they can scour out under the found. Many Metro areas and Counties have a sort-of preapproved design and details and a tabulation of h/t’s and panel lengths, etc. They’ve been around (some designs and details) for a long time, have proven themselves over that time and are kinda grandfathered in, without exactly meeting todays codes. Generally, they consist of pilasters/posts every 8-10’, which are reinforced and grout filled. Then, the infill panels are only 4 or 6” thick, 8x16” conc. blk., with bed joints mortared and reinforced with ladder type joint reinforcing. The head joints are not mortared, they are just laid loose against each other, and the pilaster blocks are “H” shaped so the panel blocks fit into them on each side of the pilaster. The founds. can be as simple as a trench with drilled deeper holes at the pilasters, and then the whole trench filled with concrete or even flowable fill. In your case, the difference btwn. 8 and 10” conc. blk. should be that big a deal when labor and all else is considered.

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#3

I had a *.pdf by the NCMA… but, cannot upload it.

I found the link at:

There are references to numerous TEK publications.

Dik

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#4

Thanks dhengr and DIK. i may not have specified but this is going to be reinforced 8" CMU without pilasters (for aesthetics). There won’t be any hydrostatic load as it is a flat area. I think I will simply ignore the h/t for this one. It is really no different than an 8 ft. tall wall with more wind load. I can’t imagine a buckling failure happening! !0" CMU is hard to come by here and they def. don’t want to use 12"

#5

You can also do serpentine walls in plan or ‘staggered’ by a foot or so every 10’-12’ to provide stability and not affect aesthetics.

Dik