Masonry cracking 1

[SteelPE]

I have a client who asked me to look at an existing building that has developed some cracks. The customer is concerned that the cracks pose a structural risk to the building.

The building was constructed 11 years ago. The building is 100’ wide x 200’ long x 26’ tall steel framed with 8” masonry walls used as infill. I visited the site over the weekend and took a few pictures. The building is oriented in such a way that the 200’ side faces the east and west direction. Some of the cracks (which have already been repaired) occur on the each 200’ long side but not the 100’ long sides.

A few things I noticed:
-Masonry contraction joints are at 40’ o.c..
-no visible contraction joints were observed in the foundation wall (only construction joints).
-Masonry joints do not align with construction joints.
-Cracks are concentrated at the bottom 3-4 courses of masonry and are above foundation cracks.
-The building is constructed in an area that tends to have a lot of sand (I don’t know this for certain).

The cracks almost look like shrinkage cracks…..but the building has been in place for 11 years so unless the cracks are just opening up now…. Or nobody ever saw them before, I don’t know.

Does anyone have any idea on what the cracks might be cause by?

 

[KootK]

I vote thermal cracking in the foundation telegraphing up into the masonry. Any chance there's been an extra cold winter recently? Or the building was left unheated for a spell?

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.

 

[SteelPE]

KootK

The building is in the North East which had tons of snowfall (which would insulate the foundation against thermal fluctuations). The building has also been occupied since it was built by the same owner and is very well taken care of. As I visited on the weekend I was not able to go inside. Also, on the west side, the foundation is only exposed for 6-8" on the east side the grade changes a little more allowing for exposure of the foundation (you can see some parging on the foundation wall in the pictures I attached).

I was thinking possible thermal movements of the masonry in relation to the foundation.

 

[KootK]

Are you proposing that thermal masonry expansion may have initiated the foundation cracking?

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.

 

[SteelPE]

I'm not proposing anything, I have only been asked if the cracks pose a structural problem (which they do not). However, to further my education, and beat them to the punch, I would like to know some theories on why the cracks appeared.

 

[KootK]

Do we know anything about the steel? Column spacing? Cross bracing versus moment frames? Is the foundation strip/pad footings as opposed to piles and grade beams? Hopefully Ron and/or ConcreteMasonry chime in on this.

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.

 

[SteelPE]

I wasn't the engineer who designed the original building ,he passed away a few year ago, so I don't the answer to those questions yet. I was told that the building is steel framed with the masonry walls used for LFR similar to a B-18 of table 12.2-1 of ASCE7-05.

 

[concretemasonry]

In my opinion, the cracks in the masonry are old shrinkage cracks due to the 40' panel length and no control joint in the panel. They are old and the original cracks are at the head joints and also went through the center of the original architectural CMUs in every other course. The repairs to the units themselves are very evident. and there are no newer cracks in the repaired units.

They are not structural. - Probably due to a lack of enough joint reinforcement or no intermediate bond beam for a 26' high wall.The original cracks probably occurred in the first year or so after construction. For the 100' long walls, they may not be not be 40' long panels

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[SteelPE]

concretemasonry

The repairs you can see in the photos are new (less than a year old). From what I have been told, there is a horizontal bond beam at elevations 13' and 26'. I have yet to see the drawings so I don't know if there was any joint reinforcing or what the spacing was. The description of the structure would lead you to believe that there is horizontal joint reinforcing at a minimum of 16"o.c. Typical reinforcing for the area is #9 ladur reinforcing at 16"o.c. (every other course).

I found other cracks that were not repaired, maybe they were too small as I had a hard time seeing them. Took me 10 min to figure out what they client was talking after visiting the site. So the cracks are small.

So is it masonry shrinkage, concrete foundation shrinkage or a combination of the two?

 

[oldestguy]

Owner must be a "fuss-budget". With a 40 ft wall length with no control joints, they ought to feel blessed with such good performance so far. I suppose they feel a concrete floor should not crack either with a 40 ft. joint spacing.. dreamers.

 

[Ron]

Cracks are shrinkage cracks. Check to see if walls recently painted, change in HVAC that would increase dehumidification, etc. Cracks are not structurally significant.