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Re: Basement Wall Cracking

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Thor:

The position, pattern and width of the cracks make me believe the cracks are structural in nature. Your comment about the pattern being "like the tributary area load
distribution for a two-way slab" may have some validity, although I would have put it another way......."similiar to yield line cracking" (this may make more sense, if you are familiar with that theory).

Are there drawings of the original construction? The wall height seems low, which makes me think that this is a home and not a commercial structure. If it is a home, it is standard practice (in this part of the country) to use plain concrete (unreinforced) to span that distance. How do the stresses check out for the unreinforced section? Are there unusual loadings at that point on the outside of the structure? What type of material did they backfill with? Is the drainage adequate?

Your idea of the rebar (if any) being misplaced is a reasonable one. Over the years, I have discovered that there may be so many possibilities for the reason why something cracked that it is difficult to speculate on exactly what the cause may have been. About the only thing you can do is suggest several possibilities unless you carry the investigation far enough to actually find out.

Jim Kestner, P.E.
Green Bay, Wi.

vicpeng wrote:

 We have a basement wall in a building that has been in service since 1977.  The problem is that it has cracked along a 55 ft section close to one corner. Wall clear height     8'-0"Wall thickness        8"Main 2.5mm crack at 5' above floor slab.Length of main crack    about 14'Crack width maximum 2.5mm Bifurcating cracks run off at about 30 degrees to contact floor and ceiling slab respectively about 20' away.  Crack width decreases from the 2.5mm to 0 over about 20' each end of main crack.  There are other secondary cracks but the main pattern is so much like the tributary area load distribution for a two-way slab. ____________________________________________   \                                        /     \   1mm                          /0.5mm       \                               /         \                           /           \         2.5mm    /                          1mm             \-------------------/- - - - - - - - - - - - - - -- - - - - - -          /                      \       \       / 1mm                   \        \     /                                \         \   /                                    \          \ /                                         \          \________________________________\________  The scales are grossly out of proportion but the pattern is as shown.  5'-0" dimension on bottom half. My numbers suggest that if the wall rebar was in the centre of the wall instead of at the inside face then I can expect about 1.5mm crack width?  This, from elementary geometry means an out of plane deformation of about 7mm, which is not much different from tolerances for waviness etc in concrete.  Would appreciate any comments or ideas on what could be causing this in an otherwise sound wall for the remaining perimeter.

Thor Tandy  P.Eng  MCSCE
Victoria BC
Canada
vicpeng(--nospam--at)vtcg.com

 

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