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Re: Unreinforced foundation walls

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At 09:42 AM 2/2/2005 -0600, you wrote:
I've seen plenty of non-reinforced HCMU basement walls in Iowa and
Illinois and virtually all of them have a chest-high crack, some opened more
than others.  Realtors used to call me for a report on "sale-pending"
basement wall cracks, but they finally figured out I always say repair is
necessary; and they quit calling.
     Another troubling thing about non-reinforced HCMU basement walls is
that the first course was/is often not a full mortar bed.  The result is
that if water appears on the basement floor in the northeast corner it may
be entering the wall at the southwest corner, no way to know.
     My rule is (and this may have come from a code or something else I
read) all below-grade HCMU should be fully grouted, all cells.  I can live
with that.
John P. Riley

Show me an unreinforced HCMU basement wall, and I'll show you a crack. I won't design them, but I see them in real estate transactions regularly. Instead of failing every one of them (most are 30 to 50 years old), I usually let anything less than 3/16" go with a warning to verify grading and drainage, and to monitor the crack on a regular basis. Bigger, and we're looking at a fix.

What I've found more interesting is that the crack usually occurs one to three courses _above_ the mid-height. It's worth noting, as it means that the wall is not in a pinned-pinned condition, as usually assumed in design texts, but is fixed-pinned. Fixed-pinned has the maximum moment occur at (no surprise) about 0.55H above the fixed end. If i were fixed-fixed (the sill & floor) or pinned-pinned, you should be seeing the tension crack about 1/3 or 2/5 from the bottom of he wall. But now I'm just rambling....


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