huangyhg

vertical crack in fluted cmu
the building construction (built in 1989) is 12 inch fluted cmu bearing walls with pilasters (24"x24") at 10 feet on center. walls are 28'-0" tall and sit on a 6 feet tall concrete foundation wall. building dimensions are 57'-4" x 46'-8" with a 1 inch control joint at midspan of the 57'-4" wall. no control joint in the shorter wall. wall supports roof joists at 4'-0" on center supporting metal roof deck and membrane roof. no pilaster in corner. first pilaster is approximately 8 feet from corner in both directions.
crack starts at center of 3'-0" door lintel and stair steps over toward corner and then vertical along head joint closest to corner. the edge of door is located approximately 24 inches from the outside face of cmu. it appears that due to wall dimension, head joints for cmu at this location are approximately 2 to 4 inches apart. so the crack goes back and forth between the head joints. the crack is actually in the long wall (has control joint).
typical wall reinforcing consists of 6-#6 pilaster reinforcing and a #6@48 from centerline of each pilaster. which puts two bars 2'-0" apart centered between pilasters. horizontal reinforcing is #12 wire every other course. also, 1-#6 each side of opening and at corners. all bars centered in cells except pilasters, they are out at face.
this building is basically on the beach in outer banks of north carolina.
no signs of settlement in the foundation wall.
any thoughts on the cause of the crack and repair solutions? my thought was that it is due to expansion/contraction. did not verify that reinforcing was installed per above. since wall is primarily spanning horizontally between pilasters and corner wall, wasn't sure it that is actually the case for a vertical crack. would tuck pointing the crack be acceptable? would it just happen again? i wouldn't think you could put a control joint at the crack location since spans horizontal and not vertical.
any thoughts would be appreciated. thanks.
it sounds like a case of poor detailing and/or construction.
because you have head joints at 2" to 4" apart, you have stack bond (officially - other than running bond). in this case, the horizontal joint reinforcement is not spaced close enough. every othe course would be proper in an area such as this. the vertical steel does not effect shrinkage cracks. does the crack cross any vertical steel? - vertical steel next to the door may have been terminated at or just above the door lintel if it was not required for structural purposes.
the door defines a weak area along the length of the wall, so it is not surprising, the crack originated there. near a corner you can also get some very strange loading and stresses that could add to tensile stresses in the wall.
do you have any idea how old the crack is? it may be quite old and a close examination of the crack and any coating may give you a clue.
as an intial repair in light of no other damage, i would open up and tuck-point the joint. if all shrinkage has occurred, this may hold up well despite the nasty winds/storms that the wright brothers loved and put up with. make sure someone watches the joints/crack.
dick
concretemasonry,
thanks for the reply. same building there is a masonry screen wall. same wall construction...pilasters 10' on center, but free top. no drawings showning reinforcing. the wall is pulling away from the pilasters a good 1/2 inch. i can not see any reinforcing tieing the pilasters to the wall. i was going to suggest installing an angle on each side of the pilaster and bolt it to the wall. does that sound like a reasonable fix? or is there something we can do that is cheaper?
i have run into diagonal crack problems in concrete walls where the roof chord member failed during a seismic event allowing the wall to over deflect. from your description, i'm not sure if the crack pattern is the same, but, considering the frequency of hurricanes on the outer banks of the carolinas, maybe... at sometimeim the past 18 years...
when was it first noted?
mike mccann
mccann engineering

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