Foundation beams design with Winkler springs - stiffness value???
Foundation beams design with Winkler springs - stiffness value???
(OP)
I am designing a one-storey RC house, the foundation is a raft foundation 45cm thick, with foundation beams (45cm height) (fully embedded inside the raft) interconnecting the frame columns.

1. The superstructure was designed with fully fixed supports at column bases but the foundation beams will be designed with winkler beams at column supports.
Support definition at column bases is:
UX - fixed
UY - fixed
UZ - spring with stiffness - RELEASED
RX - spring with stiffness - RELEASED
RY - spring with stiffness - RELEASED
RX - fixed
So now how do i choose the stiffness value for the 3 releases?

1. The superstructure was designed with fully fixed supports at column bases but the foundation beams will be designed with winkler beams at column supports.
Support definition at column bases is:
UX - fixed
UY - fixed
UZ - spring with stiffness - RELEASED
RX - spring with stiffness - RELEASED
RY - spring with stiffness - RELEASED
RX - fixed
So now how do i choose the stiffness value for the 3 releases?
RE: Foundation beams design with Winkler springs - stiffness value???
UX - fixed
UY - fixed
UZ - spring stiffness, KZ = 65876.60kN/m
RX - spring with stiffness - RELEASED
RY - spring with stiffness - RELEASED
RX - fixed
My question now is: do i also need to calculate the HX and HY values for the rotation stiffness or Robot will use the value from KZ stiffness to automatically determine the HX and HY stiffnesses?
RE: Foundation beams design with Winkler springs - stiffness value???
https://forums.autodesk.com/t5/robot-structural-an...
The workaround in 2013 and 2014 release is replacing HX elastic ground along bars by nodal elastic supports in rotation distributed along bars.
RE: Foundation beams design with Winkler springs - stiffness value???
I'm not an expert in Robot. Unfortunately, I don't know that you're going to find too many Robot users on Eng-Tips. It's just not that widely used of a program in North America.
That being said, I have some comments:
1) You need to understand what your program is doing internally. I suspect it's merely converting the subgrade modulus into a vertical springs based on the area of the footing. But, that is merely a guess.
2) If the program is adding vertical springs along the length of the grade beam, then YOU need to investigate this a little deeper to determine if it gives you the behavior you're looking for. Start with simple models and see if the results agree with what you think they should be.
3) Now if you want to convert the subgrade modulus and footing area into a rotational spring, then how would you do this? I've done it by assuming a unit rotation of the footing and then calculating the soil reactions induced by that unit rotation. Note: I assume the soil can take tension and compression for simplicity in calculating the rotational reaction.
RE: Foundation beams design with Winkler springs - stiffness value???