cracks develop in building

huangyhg

cracks develop in building
i am investigating a building in baton rouge that developed (pre-katrina) a sudden & audible separation of partition walls between two separate adjacent additions.  the separation is between partition walls that are at an expansion joint of two additions that were done in the early 1980鈥檚 (about 5 years apart). the building is a single story steel framed structure with metal deck over steel bar joists.  exterior walls are on cmu, interior walls on steel wide flanges.  there are several additions to the original building that together make up the wing where the problem was first noticed and the movements are most pronounced.  all of these structures are over 20 years old and have had problems with wall cracking before, but not at this exact location.  judging from fact that these light buildings are on drilled shafts, it is likely that the soil is not good at the site.  the slab is grade supported, though, and the outside brick veneer shows no foundation settlement-type cracks.   the main deal is that this event was sudden and resulted in a new separation of almost 戮鈥?at the top of the wall intersection.  
as best we could in a working building, we have looked at the structure everywhere around the most pronounced area (i.e. bearing walls & beams and joists in the adjacent wings) and see nothing out of the ordinary.  the weather the day it happened (august, 2005) was hot but not as hot as it had been all summer.  the joints in the buildings are logically arranged and the covering over the roof joint shows no distress (roof is more recent than structure).
we put crack monitors up but have seen very little further movement (still ongoing investigation obviously).  
the only out of the ordinary thing that might be related is that the building interior had recently been renovated.  this renovation (repair of interior clay block joints, replacement of portions of clay block walls with metal stud) may have tightened up the structure鈥檚 normal breathing and caused it to do this, but the concentration of the release seems surprising to me.   the fact that these walls existed in their former state for 20 years and suddenly felt the need to separate points to something being really different.
any ideas or similar experiences?
tw
you state that "the separation is between partition walls that are at an expansion joint". it sounds like there was expansion joint put in the structure but none in the partition wall. sounds like an oversight by either the architect or the contractor. if this is the case i am not surprised that something cracked, settled or made a noise.
i have seen a similar experience in an older building where an expansion joint was placed in the structure and quarry tile was placed over it with no joint. on a day of 30 degrees below zero, the tile raised up (like a snake) over a 15 minute period of time until it exploded! this was 20 or 30 years after the building was built.
im not exactly what seperated from what and in what direction it moved from your post but i did notice you said that some block walls were replaced with stud walls. is it possible that the vertical or lateral connections of the stud walls were not as strong as the connections of the original walls and snapped under the same expansion stresses the building has alwalys seen?