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Basement Wall Cracking

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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