Cracking in Brick Gable
Cracking in Brick Gable
(OP)
I'm looking at a church built in 1922. The exterior walls are 3 wythes of unreinforced brick. Near the top of the front gable is a 36" diameter circular window. There is a perfectly horizontal crack in the grout at the CL of the small window extending the entire width of the gable at that location. There is no other sign of significant cracking in the brick in this wall. My first guess at the cause would be wind loading (very low seismic area). The dead load up there isn't big and the tensile stress (fatigue?) in the mortar from out of plane bending is the cause. Anybody care to offer an opinion?






RE: Cracking in Brick Gable
I'm thinking a scenario like - Window frame is metal and heats up quicker than the surrounding brick, there is no relief and little dead load so the frame pushes up and out on the brick. I'd think this would be more of a diagonal crack though.
Or - the roof has a tension tie on the inside of the wall. The wall, due to a long term thermal gradient expands through the day with the roof, but the roof contracts quicker at night putting a horizontal compression on the gable with perpendicular tension. - If the roof isn't tied/restrained near the gable then this one can be thrown out.
Could be wind if the roof has a shallow slope and produced uplift.
RE: Cracking in Brick Gable
The window frame is wood and there is a wood tie on the inside of the wall. See attached photo
RE: Cracking in Brick Gable
Just my thoughts.
RE: Cracking in Brick Gable
I don't think its thermal because the crack is still open which suggests the load is still acting. Same with out of plane bending - I wouldn't expect to see through the crack - one side should be closed in compression.
Swelling of the window frame? Does the crack close towards the outside edges? Looks like there are some slight cracks stepping up to the ridge.
If it were window swelling I would check for a wet frame. Check if the frame is tight. Looks like the frame is rigid enough for some decent loading. Check if there is anything else holding the gable up.
RE: Cracking in Brick Gable
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Cracking in Brick Gable
1) Do we know anything about the age of the cracks?
2) Is there any reason to believe that the humidity environment in the building would have recently changed?
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Cracking in Brick Gable
RE: Cracking in Brick Gable
RE: Cracking in Brick Gable
- Is the crack the same/similar on the outside?
- Did the window go with it or is there a separation? I doubt it's the window that is lifting that peak. Looks like I can see a gap over the window, towards the left.
- Any embedded steel? What is the green flash reflection on the left? Also something sticking out of the wall at the far left, iron?
RE: Cracking in Brick Gable