Existing Masonry Wall and sliding foundation
Existing Masonry Wall and sliding foundation
(OP)
The hillside along the south wall of a big box supermarket is sliding away. The geotechnical engineers are stabilizing the hillside. We are analyzing an existing 12" load-bearing reinforced concrete masonry unit wall that is 20 feet high and is 5.5" out of plumb to determine if the wall is safe. The construction tolerance for the wall is 0.5" for variation from plumb. When we analyze the wall, the stresses fall within the allowable range. However, it just doesn't feel right. A variation from plum of 5.5" in a 20 foot high wall is a lot. I am afraid that the wall will collapse below the allowable stress range. Am I being too cautious? What would you say to the owner? I am thinking of telling him to rebuild the wall even though my analysis shows the wall is understressed.






RE: Existing Masonry Wall and sliding foundation
Dick
RE: Existing Masonry Wall and sliding foundation
RE: Existing Masonry Wall and sliding foundation
A couple of thoughts here:
1. Can the footings be underpinned and jacked back into place? Many times simply re-setting the footings back to their original location will solve the problem. Helical piling can be used, or resistance piling, to underpin the footings and then they can be hydraulically jacked upwards.
If there is lateral sliding of the footings - that is a whole different (and more challenging) problem. For this helical piling can also be used laterally to pin the footing back into the soil.
2. If the wall is out of plumb, is the whole building also out of plumb? If so, then you might have a lot more PΔ thrust than you think.
3.
RE: Existing Masonry Wall and sliding foundation
RE: Existing Masonry Wall and sliding foundation
HOWEVER, THAT DOES NOT SOLVE THE P DELTA PROBLEM. That's a totally different issue and gets into the repairability of the structure. I would be concerned with the connections at the roof of the structre, checking all of them for structural integrity, even with this small degree of rotation, to include the chord ties.
If this is in a seismiclly active area, I would ask the geotech if there is any danger of liquefaction during a major event, that could lead to more rotation. If so, then rebuild the wall and install pin pile too as a precautionary measure. If not, I would have to ask myself if I want to assume the liability should the wall not be repaired and fail later. I know what my answer would be.
Mike McCann
MMC Engineering
RE: Existing Masonry Wall and sliding foundation
One question here, if only the south wall has slided with 5.5" out of plumb (assuming lateral movement occurred on top only), wouldn't be the joists/beams/girders have teared apart, fell off the support seatings, or the wall has cracked below the roof support level? If so, why save the wall?
RE: Existing Masonry Wall and sliding foundation
As I read Vincent's problem, it is the bottom of the wall that has moved out, not the top.
Vincent,
I agree with others that the wall should be rebuilt following rectification of the embankment and footing.
RE: Existing Masonry Wall and sliding foundation
RE: Existing Masonry Wall and sliding foundation
The wall has moved from the bottom; i.e. the footing has slid with the hillside. I checked the joist bearing connections as well as I could. The joist seats are grouted into the wall. There were no signs of distress at the grout pockets or the surrounding CMU. This is not a seismically active area. But nevertheless, the stresses are within acceptable limits but I am still uncomfortable with this amount of distortion to the original design. Masonry is not steel. It seems most of you are thinking along the same lines as I am.
RE: Existing Masonry Wall and sliding foundation
www.idecharlotte.com
RE: Existing Masonry Wall and sliding foundation