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

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What I would like to know is, are ANY cracks in concrete serious? I remember
a through crack at a 45 degree angle in a wall, from top to bottom. The
engineer said it was ok. I remember a through crack in a waffle slab, from
the drop panel corner to the column. Engineer said no problem. If these are
not problems, what are, excluding the obvious seismic crushing of freeway
columns? In other words, are cracks in concrete stress relief?

>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