Modeling an incorrect foundation wall 1

[BadgerPE]

Hey all. I am working on a problem right now for a local contractor who incorrectly poured a foundation. The design called for a 5 foot deep frost wall with the finished floor grade and exterior grade at the top of the foundation. However, due to the presence of bedrock, the foundation was raised such that the floor is now 4.5 feet below the top of the wall sitting directly on top of the footing and the finished grade is still at the top of the foundation. The structure being placed on the foundation is an open garage type building with no interior walls to resist earth and wind forces.
My question is, how do you appropriately model this situation? I understand that modeling it like a retaining wall would be an option, however I'm not sure how to account for the strength at the corners of the wall where the other frost walls attach. Right now my largest concern is overturning. Currently I have about 850 ft-lb/ft of resisting moment while my overturing moment is more like 3250 ft-lb/ft. One thought I had was installing deadman anchors along the lenght of the wall, but I am not sure how to quanitfy the amount needed. Any help would be greatly appreciated.

 

[ishvaaag]

The best way to exact the present mechanical strength is to model it wholly 3D with solids in Autocad or a FEM program and had it loaded and analyzed for the standing loads. Inventor, Algor, Visual Nastran 4D, any of the big FEM programs, SAP 2000 and RISA 3D can account of this kind of model. From the behaviour you can see what is happening for the loads, and at what safety factor the structure remains stable against attempted overturning.

 

[msquared48]

Installing deadmen is your best course here since the wall is already constructed.

To get the force to be resisted per foot, just look at the wall as a beam resisting a uniformly varying load. If the deadmen are placed, say 2 feet from the top, it is a propped cantilever analysis, and there are equations to get the reaction per foot the deadmen will have to generate. Place the deadmen at 4 to 8 foot spacings and extend back to indisturbed ground, using the passive pressure to resist the force.

Simple. No worries.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask