It is also not uncommon to find cracks at about 10-ft
spacing in long walls of liquid-containing basins. CRSI suggests that "the
natural shrinkage crack interval" is on the order of 10 to 15-ft. However,
the cracks typically initiate at the base of wall, where it is restrained by the
slab, and may not extend the full height of the wall.
Such walls typically have extra horizontal reinforcing
steel for crack control - the intent is to allow numerous fine cracks that don't
leak but to control wider cracks. This also improves appearance, since
tight cracks are less noticeable. Since the cracks initiate at the base
slab, another technique is to double up the area of horizontal reinforcement
near the base of wall to further control the cracks in this area.
William C. Sherman, PE
I've seen this
too. I no longer put joints in my walls. I just space the pvc
sleeves for the railing at wherever I want a relief crack to appear. I
studied one such wall for a period after construction; the crack started at
the sleeve at the top of the wall and over about a month, extended down the
wall, nice and straight, pretty as any control
Sent: Wednesday, March 22, 2006 4:41
Subject: Re: Joints in retaining
I too have seen similar cracks at
inserts - even at walls with joints. I have often wondered whether it
would be better to require core drilling for the railing posts and force
the shrinkage to occur more at the joints.
Kenneth S. Peoples, P.
Lehigh Valley Technical Associates,
----- Original Message -----
Tuesday, March 21, 2006 4:50 PM
Joints in retaining walls
FWIW I once saw a
cast concrete site retaining wall (i.e. not a building wall) somewhere in
California, about 6' or 7' tall, with a
fine, full-height vertical crack every 10', aligned with the inserts for a
metal railing. Not a "real" joint in sight!
message dated 3/21/06 1:41:03 PM, gloomis(--nospam--at)MasterEngineersinc.com
Handbook - Working Stress Design 1963 recommends contraction
about 25' and expansion joints at every 4th joint - 100'. The
CRSI 1996 states the same recommendations and also references
which is based on ACI 350.
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