huangyhg

cracks in masonry wall
i am evaluating cracks in a 100 foot tall brick structure. the brick encases a steel structure. 30 foot long vertical cracks through the brick work are apparent at two of the corners (approx 3' from the corner).
i am looking for masonry engineering references particularly related to older structures. does anybody have any info on this?
thank you.
i think i have seen this before,but first let me ask,
when you say through the brick you mean,
1.the cracks are in the morter joint?
2.the cracks are splitting bricks?
3.the cracks are running the joints and splitting some bricks here and there along the way?
next,how are the bricks applied to the steel.
by decking?
last,
lets say we are looking at your building from above it,and say it is square.
from the front door side of the building we will call that side (1).
going counter clockwise we will assign each side a #, 1 thru 4.this way you can tell me which corners are affected by saying corners 1/2 or 2/3 or 3/4 or corner 4/1.get the idea?
this will tell you alot like are the cracks on one side of the building and how are they related if at all.
also this can narrow down things like steel,foundation,and roof load problems.
sounds like there were no expansion (movement) joints near the corners, and the brick created its own movement joints.
daveatkins
vbi- sight along a head joint a few meters from a cracked corner and you will be able to tell pretty easily if the corners are getting pushed laterally as dave atkins mentions.
if no movement such is obvious, there could be many other causes such as corrosion behind the wall, movement in the foundations etc. consider removing a few brick at one crack. its not uncommon in older structures for the exterior portion of the steel frame to be relatively unprotected, that is, the steel is in contact with the brick but may only be primed. as you are probably aware the steel will expand quite a bit as it corrodes and that could push the brick out and potentially cause the cracks you are describing.
i am sorry. i was out of the office a few days but thank you for your responses.
first- i somewhat expected this to be caused by the corroding (expanding) steel underlying the brick. but i am now concerned it is something more.
to answer your question 37ed...a big crack is located at outside corner 2/3 (4' from corner on wall of 2). it is almost straight running through every brick. on the inside, verical (straight) cracks are located at each corner 1/2, 2/1, 2/3, 3/2 etc. the tower is 100' tall (40' square). it almost apears as though the bricks are over stressed and cracking. big ornamental limestone is located at the top of the tower at each corner.
thanks for your feedback...
it sounds like it could possibly be brick lateral expansion with no provision for lateral expansion near the corners although on a 40 foot square structure there can't be that much expansion unless the brick is very porous.
that being said there are many other things which should also be looked at before a final determination is made. what is the backup material for the brick? how is the steel frame braced? what is the calculated sway? is the steel isolated from the masonry? how is the brick tied to the structure? is there any problem with corrosion? how often is the brick supported vertically? is vertical expansion of the brick a problem?
just a few things to look at....
mind you i can't see you building from here,but sounds like a loading issue from above.your limestone seems to be playing a factor.
also could be some steel issues.check for weep holes in the walls.if you don't feel like you see enough than knock a hole in the wall at ground level.
this will tell the tell about possible water damage in connection to possible steel damage.
i have done this in the past and watch gallon upon gallon flow out of old brick walls.water will form in "pocket" between colunms,and concrete peirs at the lowest point in the wall and stay there until it weeps or not.in winter it will freeze and expand.and keep in mind we may be talking about an area of 2ft by 10ft or greater.that is alot of water.
this will cause what you are saying.cracking bricks.
if rust has occured then you know what happens next,lateral problems will add to the mix,and sounds like it already has.
good luck
ed
thanks ed,
you seemed to make a contradiction though. your first line points to a loading condition from the limestone above.
the water/rust/expansion is what i originally thought. now i am leaning toward a loading stress condition. do you know of any masonry reference guides that might be helpful. that is, how much weight can a brick wall support onto itself.
vb
sorry if i am being confussing,but i am trying to give you all the possible situations based on what i am hearing from you.
i have found that in ever stuctural problem it is always a chain of events that leads to a given situation.
i do have some load charts and will forward.
reguards
ed
look at the way the masonry has been supported from the steel structure. sometimes steel shelf (or relieving) angles are placed at each floor, or every other floor. typically in older sructures, these shelf angles stopped at the columns. this causes the unsupported brick to act as a tall, thin column and you get a vertical crack that is a consistent in width, without tapering or stepping.
if this sounds like the condition have, repair usually consists of making the crack an expansion joint (routing and filling with backer rod and sealant, and, attaching the brick at the column in some fashion. you can use short sections of shelf angle welded to the steel column or there are a variety of dovetail and specialty anchors used for this purpose.
i looked through my references and mostly what i use are reprints of publications that were provided at seminars. bia (brick industry associates) and ncma (national concrete masonry association) have on-line references free of charge.
"if you are going to walk on thin ice, you might as well dance!"
sometimes the shelf angles at corners are cut square near columns as opposed to being mitered which provides continuous support; with square cut angles the brick is supported by the mortar. check out the book by robert drysdale.

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