Is there any technical reference how the base pressure in staadpro or staad foundation is calculated? This is in relation to my observation that the base pressure seems to be a function of the thickness of the mat (plate). The thicker the plate you assign the lower the base pressure becomes this is even under constant uniform pressure load and neglecting self weight of mat.
My understanding is that the base pressure is a function of the soil spring stiffness which is also a function of the influence area and the total load which is this case both are constant since self weight of the plate is neglected.
Can anybody from the support shed some light on the matter.
Thanks
Hi Kirk,
It seems to me you are trying to model soil-structure interaction. If that is the case, the stiffness of your plates matters, and so the thicker they are, the stiffer they get.
Hope this helps.
Hi Hean,
Yes I am doing a mat foundation analysis supported with springs and I do understand that the thicker the plate gets the stiffer it is also but how is it correlated to the soil base pressure? In what sense does the soil stiffness be affected by the thickness of the plate?
Think of it this way: Suppose that you have a rectangular mat with a point load in the middle. If your plate is thick and stiff, the load will be spread out to most of the area of soil below, and hence the base pressure you get will be lower. On the other hand, if your mat is very flexible, the point load will be able to pass through the mat more easily and most of the load will be concentrated by a relatively small area under the mat, and so you will get a higher base pressure.
Hean, thanks for the explanation however I am still interested to know how or what formula has been used to derive the base pressure in relation to the plate and soil stiffness.
Have a look at Foundation Analysis and Design by bolwes. I don't have the book with me right now, but there's a section that talks about modelling of flexible foundation.
Most engineering introductory books make the assumption of rigid foundation, and a triangular or rectangular upward pressure distribution from the soil. I am not not aware of any book that has a derivation of the type of formula you want. Perhaps you will need to search through the literature, or see if anybody else can shed some light on it.