Foundation Settlement C.I.P. Beam Stress

[G87]

Hello,
I have a question regarding settlement of shallow foudations and the redistribution of stress in a cast-in-place beam and the cast-in-place slab it supports. I want to relocate the position of some existing columns which support the cast-in-place beam. I am concerned about the redistribution of the stresses in the beam. I plan on inserting a new beam beneath the existing beam and supporting it, before the existing columns are removed to add additional support. However I am also concerned the new foundations will settle and cause some additonal deflection in the beam. I have considered jacking up the existing beam slightly to help make up for some of the settlement in the new foundations. The height of the columns is 24ft unbraced.

 

[kslee1000]

Can you post an elevation view?

 

[G87]

I have attached an elevation of the completed building. The majority of the columns are behind a new curtain wall that will be installed.

 

[kslee1000]

You have a tall order at hand. If there is clear indication of settlement, the first thing is to get a geotech on board to find out the root problem. Your thinking is correct, without fixing/strengthen the existing foundation, anything you do from top could be a waste, or even make things worse.

The other difficulty is to jack up tall concrete structure, it needs proper planning and excution. Try to line up experienced contractors and have conversation with them to gain ideas, and learn the pit falls to avoid.

Good luck. Once you are done with above, come back if you have further questions.

 

[RHTPE]

I agree with kslee1000 - you do have a challenge in front of you. You will certainly need to examine the existing reinforcing in the beam and determine if it is compatible with the new support locations. It also appears that the new columns will be round and perhaps considered architecturally exposed, thus creating construction challenges with regard to their connection to the existing concrete beam. The forms for these columns will need to be split vertically into 2 half-round sections, and someone will have to determine how to place concrete into them.

All of the above will impacted by the geotechnical challenges as well.

I seem to recall an application for a tall monopole sign that utilized telescoping steel "pipe" sections and was raised to its final height by pumping grout inside the pole. Whether or not the concept is applicable here remains to be determined.

I would also like know the final outcome once you get there.


Ralph
Structures Consulting
Northeast USA