Old Bldg. suddenly cracking 1

[HeavyCivil]

I was asked for a proposal on analysis of a building, roughly 24X60, walkout style, which has suddenly begin to form cracks or widen existing cracks. Diagonal in CMU walls (although one major vertical crack from foundation to roof diaphragm cracks through middle of every second course of block - running bond). Suspended slab has "new" cracks up to 0.060". No steel deck, but does have I-beams cast in - pretty old building - and one-way reinforcing (both rusted badly and spalling cover).

They park on grade at the first floor level (surcharge) and we've had a terribly wet summer and winter is coming late and the rain keeps coming.

You can see clear through the wall at some of the diagonal cracks in the CMU wall and they go from foundation to roof some as wide as 3/8".

Any ideas without seeing pictures? Differential settlement? Fines washed out of soil undermining ftg's? Sinkholes? Sudden lateral earth pressure from failed ftg rain and wet summer?

 

[cntw1953]

Carefully examine visible foundation element and columns to see if there is indication of movement. Sudden speed up on deterioration over existing wounds in conjuction with new defects surely is caused by the recent event - excessive water.

 

[SlideRuleEra]

Agree with cntw1953. The excessive rain that you mention has likely changed (raised) the water table. ANY significant change in the water table (either higher or lower) can cause foundation settlement in many soils. When/if the water table stabilizes (long term) the settlement will probably stop as unexpectedly as it began.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[Ron]

Rain is probably contributing factor. Look at the long side of the building. If cracks near center are wider at top than bottom, you might have some swelling clays under the building. If opposite, I would look at settlement issues, rubble, or buried pipes under building.

With large volume of recent rainwater, is there a chance that there are underlying stormwater lines that are allowing soil infiltration at the joints, thus causing loss of soil under the building? Same could be true of rubble or trash under building.

More investigation is obviously required.

 

[jike]

I would also investigate the possibilty of a broken underground pipe.

 

[unclesyd]

I would get a few core samples around the building to see what your building is setting on.

Not my area of knowledge, I just saw this done at my stepdaughters house. $200,000 house + $35,000 foundation remediation.

 

[dik]

If your building is 'suddenly' cracking and has been around in reasonable condition for a century, you want to make sure you determine the cause of the cracking.

Repair can be problematic... if the cracking is due to excessive moisture washing away the lime material; repair is most difficult. There are several other causes as noted above. Check Sliderules' site for information on Historic Masonry (Brick?). It has outlined a few pitfalls with masonry repair and some of the problems encountered.

Dik

 

[HeavyCivil]

Thanks for the input.

I'd like to get some borings done. Also would like to install surface mounted strain gauges or simply measure stationing on cracks with calipers on regular basis. If it cracks continue to open we will probably recommend they vacate.

To put any serious money into this structure would be polishing the proverbial turd. This building has served its useful life and no longer meets their needs. I am more worried about safety and how long they have before relocating operations.

 

[msucog]

if the cracks are rather isolated to one portion of the building i'd focus on soil washing/sinkhole/etc. however if highly plastic soils are present, maybe they could be swelling. a raise in water table likely wouldn't kick off new "fill/surcharge induced" settlement. if you got retaining walls maybe the backfill is now saturated. lots of ifs for such an old and relatively small building.

 

[dicksewerrat]

Get cost estimate and time frame for new bldg, same size. It will probably take less time to put up a new bldg. than repairing the old one. Less money also.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[vandede427]

I disagree with sewerrat. It will cost less money to repair the existing one than to demo, design, and build a new one.