concrete form pressure on existing wall

[structSU10]

I am looking at a condition where a cast in place concrete wall was cast against an existing wall one floor at a time. The existing wall is a multi-wythe masonry wall. I am getting more info but assume they had form ties between the inside formwork and the existing wall.

I want to see if this concrete placement damaged the wall but need to see what makes sense for analyzing the 'locked in' wall stress due to this effort. We get a pressure from the concrete during placement and the wall deflects due to that pressure so I would think at least some - or all - of that stress 'stays' in the masonry as the wall never rebounds as the concrete took the shape of the deformed wall. If that is the case as you move to the next level of placement there would be a compounding affect from the previous form pressure and the next lift. For the next lift the composite wall assembly (existing masonry tied to concrete) resists the new pressure and I combine the original wall stress with the composite wall stresses.

I want a sanity check that I am not overcounting the concrete placement forces effect on the wall. Any thoughts / comments?

 

[phamENG]

I'm a little confused - do you want to determine if it was damaged or do you want to determine if the stresses likely exceed some level? Calculations can give you a good idea of the stress, but not damage. Damage would need to be assessed either visually or through testing.

I wouldn't analyze it as being composite unless there is a well defined connection between the brick and the concrete to make it act so - form ties wouldn't cut it in my book. I'd look at the fluid pressures for each lift, and cut them off at each lift. Once the concrete sets up and begins to cure, the vertical forces are going to stay in the concrete (assuming it's capable of resisting the axial loads), and the fluid pressures will 'reset.'

 

[le99]

If I understand correctly, you've raised two questions here:

1. The existing masonry wall is to be utilized as a concrete form during construction. For this, you shall analyze the strength of the wall to resist the pressure exerted by the concrete in the plastic state (similar to fluid and ensure it would not damage.

2. Composite action is ascertained only if the concrete and masonry interface is capable of resisting the resulting shear stress. I doubt it can be achieved in this case without the help of shear devices.

 

[Tomfh]

I would only consider the triangular force from the current lift. I wouldn't apply a saw tooth pressure pattern from each and every lift, which is what you seem to be getting at. The wall cannot deflect further from subsequent lifts without the force from the prior lift dissappearing.

If the wall is now complete and the brick is still straight I wouldn’t worry about it.

 

[Celt83]

You may have a larger issue of your CIP structure now being bonded to your neighbors multi-wythe brick wall.

I'm making a thing:

http://www.thestructuraltoolbox.com

(It's no Kootware and it will probably break but it's alive!)

 

[BAretired]

Or larger still if your neighbors multi-wythe brick wall collapses during the pour.

BA

 

[structSU10]

This was work done to an existing wall (a seismic retrofit) and I want to understand if it is a cause for distress I am seeing.

This was a 4 story wall placed one level at a time. My thought is I run an analysis for each level and account for the stresses the wall saw from the previous lower pour so its a series of models that I combine the stress. for example I would run the first level on a full height wall strip then run the next level with loads off the first, combine the stresses of the analyses all the way through the construction sequence to determine the final stress in the wall after the pours were completed. My thought with composite action was to rely on the anchors they defined between the concrete wall and masonry wall for sections already poured to check the masonry stresses through the construction sequence so each wall model has different stiffness at the lower pours.

 

[Tomfh]

What is the distress you are seeing?

What are the anchors they added?

 

[le99]

If you allow sufficient time between pours, the second pour has very little effect on the first pour which may have started to set. Although you can't visualize the condition of the masonry wall, you can tell there is a problem if the concrete quantity far exceeds the calculated volume.