Originally Posted By: rmeyers
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Unfortunately, a close up of the crack doesn't tell us much about the causes. It's the surrounding conditions and the potential forces at work that we need to see! (Or better yet, an engineer needs to see!)
I think Michael is on the right track. Added courses of block need to be secured to the cast-in-place wall with properly designed re-bar and in-fill. In addition, long anchor bolts should have been used that were embedded into the c.i.p. wall and extended up through the block cores to properly secure the framing and foundation systems together.
The hinge type rotation of the block may result from several different forces at work. The concrete wall may be moving inward due to exterior pressures on the wall. (Not clear if I'm seeing a vertical crack to the left side of the photo?)
The floor system could be expanding and exerting an outward thrust on the top of the wall (Unlikely). However, the floor system will be a stabilizing outward force attempting to hold the top of the wall in position, hence the potential for basement wall inward bulges.
Has the condition existed through a seasonal cycle to determine if there are thermal or moisture factors that are coming into play as they relate to seasonal changes. (Expansion & contraction of the framing and floor systems or soils, etc.)
How wide is the sill plate in relation to the block width and again, is it anchored to only the block with short anchor bolts? If the floor and wall loading is concentrated to the outside edge of the plate and block, there could be torque forces at work lifting the inside edge of the block off of the top of the poured wall. (Per Michael)
Whatever the scenario, the main problem appears to be the inadequate connection or anchoring of the block course to the top of the c.i.p. wall.
This condition has the potential to develop into a major structural issue if the load factors involved are not identified and properly addressed in a timely manner. There will likely be further opening of the crack which may be accompanied by shifting of the block in relation to the top of the c.i.p. wall.
A structural engineer should be brought in to evaluate the situation and make recommendations as to needed repairs to control the problem. Working now with a creative structural engineer to design a re-enforcing repair may be money well spent toward avoiding major structural repairs in the future.
Just my thoughts! Good Luck!
HAVE A GREAT DAY!!!