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[SEAOC] Re: [SEAOC] Re: [SEAOC] Concrete cracks

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About concrete cracks - I don't think anyone's mentioned all the crack
characteristics which tell a story about the cause. For example:

-A tapered vertical crack in a beam or a wall, which does not extend full
height, indicates  flexure. If it's a beam, the bending could indicate an
excessive load. If it's a foundation wall, it usually means there's been
uneven settlement of the subsoil. The crack shape and location will indicate
what part of the wall has settled. And, of course, we all know what a
diagonal crack means in a beam, near a support, if it slopes down and away -
shear deformation.

-Cracks of uniform width extending full height of a foundation wall, if
they're  at a regular spacing (often every tenty feet), indicates shrinkage.
This is common and not usually a concern (unless you're trying to keep a
head of water out).

-Shrinkage cracks in floor slabs are also usually at a regular spacing,
although they tend to radiate from corners of openings, or columns or the
ends of walls which extend through the slab.

-And, as already noted, an out - of - plane displacement of one side of the
crack relative to the other indicates a shear deformation which has gone as
far as separating the two sides. In the slab on grade, one side has settled
or been pushed down by a heavy load.

The idea is to see the crack as an indication of movement - usually
perpendicular to the crack. If we can figure what force or strain might have
caused tension across the crack, we can usually come up with a theory about
the cause.

Jim Warne
Vancouver


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