Soil Springs
Soil Springs
(OP)
Can't I just model a spring stiffness as related to my soil sub-grade modulus of reaction, and review the results to determine if I'm having any uplift forces, instead of "jumping through hoops" to create tension/compression only springs/links?
Is this not correct? I'm trying to get loads that are to be carried down to my 'mat' foundation under my shear wall frames.
Let me know if this is not correct.
Thanks.
Is this not correct? I'm trying to get loads that are to be carried down to my 'mat' foundation under my shear wall frames.
Let me know if this is not correct.
Thanks.
RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke
www.tbastructures.com





RE: Soil Springs
Even if your mesh changes, ETABS should automatically handle those area springs as you assigned them
RE: Soil Springs
However, when applying the reaction to different size areas per Terzaghi's research, we found conflicting formulas for how you apply this. Do you know what the formulas are? I have a Bowles foundation book, as well as a 5th edition Das Foundation book. One states to multiply the sub-grade reaction by the width and one states to divide by it. I feel like it should be somewhere in the middle. Which one is correct?
Thanks.
RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke
www.tbastructures.com
RE: Soil Springs
CSI has a special purpose program for design and analysis of foundations called SAFE.
RE: Soil Springs
Yes, I agree k is a pressure vs. deformation relationship ksi/in, or whatever units you want to use. This relationship of the k value with the shape and size of the foundation, as discussed in Das' Foundation Engineering, 5th Edition, doesn't have a linear relationship, as one would assume. Das claims that Terzaghi found a relationship with different areas (because k is based on a 1'x1' plate and this could change as the size of the footing changes) and in Das this relationship is stated as k*(1/B) where B is the width of the footing (ft). In Bowles' 2nd Edition book, it states the relationship is k*B, where B is the width.
In both texts, they claim the formulas are derived from Terzaghi's research in the 50s.
Does anyone know which formula is correct?
Thanks.
Also, if you want to design your shear walls correctly, the footings in etabs should have soil properties below to allow for shear to be transferred to the floor slab diapraghms and not all to the footing. This also helps reduce the possibility of having uplift on the your footings because most of the load on your walls is then transferred to the diaphragm and basement walls as a result of the allowed movement in the footing below your design in ETABS. We do utilize SAFE for footings once we have the controlling loads on them from the ETABS analysis.
Thanks for your help.
RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke
www.tbastructures.com