footing rotation

[nitnelion]

Given a spread footing and a soil subgrade reaction modulus, does anybody know how to calculate the amount of rotation (degrees) a footing will rotate under a moment reaction from a fixed column base plate?

 

[civilperson]

Assume the movement at the zero pressure location is zero. Find the amount of vertical movement at the maximum pressure edge and find the distance between the zero and the maximum. Either assume the footing is rigid or subtract the edge deflection of the footing due to soil pressure from the soil movement, trig will give the angle.

 

[dgkhan]

Nittany lion,
You are not trying to get your PSU assignment solved here and you did not graduated yet. Ethics is also apart of engineering.

 

[nitnelion]

I graduated a while ago. This is a real world problem for a real world job that I have to stamp. I'm trying to determine the seismic deflection of a rigid frame to determine if it meets code. In the past, for moment frames supported by spread footings, I've used a deflection that is the average of the pinned base and fixed base deflections. I know a spread footing typically will not act as a full fix, but I also know a spread footing is more than just a pin. I want to try and do it more accurately. Thanks to civilperson.

 

[kslee1000]

The real world answer is there is no simple solution to determine the rotation of a footing given the very complicate nature of the underlaying soil. For moment over the spread footing, I will try first to eliminate, or minimize the moment by ties or anything that works. Second, to ensure the resulting maximum pressure exerted on soil not to exceed the allowable bearing strength, in such case, your settlement will be within conventional tollerance.

 

[UcfSE]

Check the PCI Design Handbook, 6e. It has some information.