shearwall failure? 1

[calculor1]

Hi I'm curious for some feedback. I've been parking at this building for the past 8 years and Monday I just noticed these cracks in the attached photos. Being a little nosy I went to the city building planning department to take a look at the permit drawings. The building was constructed in 1982; the building is 8 stories reinforced concrete. The foundation consists of a 3'-6" thick mat slab with one level of underground parking. Shear failure?

 

[KootK]

If you're sure that the cracks are new then yeah, maybe. Has there been a big wind storm or anything lately? Shear cracking doesn't necessarily mean shear failure. In theory, one would need to crack the concrete in shear before even engaging the horizontal bars.

With eight up, one down, and a raft slab, the building would be a prime candidate for backstay shear amplification/reversal issues in the basement.

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.

 

[calculor1]

I agree, I think there is a backstay effect here. After looking thru the structural drawings it would seem that these walls were not intended to be part of the LFRS, they are only 8" thick with minimum reinforcement. I have attached another photo which shows more extensive cracking.

 

[KootK]

The cracks in the new photo are pretty vertical to be shear.

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.

 

[Ingenuity]

Are the floors post-tensioned?

 

[calculor1]

I have another photo that shows them 45 deg. That last photo is causing the confusion where the cracks appear to be mostly vertical.

Ingenuity the floors are not post tensioned. The floor above the park axe is quite thick to accommodate a bank vault.
Looking at the drawings, it looks like the only shear walls would have been a bank of elevators ( c shaped) with quite a bit of eccentricity. I'm wondering if the 8 inch walls are taking some lateral load.

 

[KootK]

Do the 8" walls extend the full height of the building?

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.

 

[calculor1]

No they only appear to be at the lower level

 

[TehMightyEngineer]

Definitely appears to warrant closer inspection though. Those definitely appear related to structural loading in nature and not just normal cracking from everyday use.

How do the ends of the shearwall look? With a typical shearwall I would expect we'd see some cracking at the chords due to the flexure of the wall.

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com

 

[KootK]

It's hard to imagine a one story wall, surrounded by basement walls, drawing a lot of wind shear. How sure are you that the cracks are recent developments?

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.

 

[calculor1]

Honestly, I have no idea on the timeline for the cracks. I've been parking here for the past 8 years and just noticed the cracks. I assumed the diagonal cracking indicated there might be a shear issue. I'm more curious than anything. It would appear that the 8 inch walls surround the core of the building and they are the only ones showing the diagonal cracking. I have attached another photo showing more cracks.

 

[allgoodnamestaken]

Could be torsional cracking, if its around the core only?

 

[msquared48]

That was what I was just thinking too...

Mike McCann, PE, SE (WA)

 

[hokie66]

It depends on where this is located within the building footprint. If near the extremity, likely the wall served as an anchor to slab shrinkage, and the slab won.