This is not a SFA software-related problem. But this limit has to be set manually when we use SFA.
But I didn't find any provisions for it in US codes.
In VERIFICATIONMANUAL, 75% is used.
It is currently not based on any code. The user is free to specify any value between 0 and 100..
Answer Verified By: ZHAO BIAO
Thank you for your reply. I have another question.
When there is tensile stress under footing, SFA adjusts pressures at corners.
But "the base pressures reported do not include the effect of buoyancy.", why?
We should consider buoyancy when we calculate corner pressures. Then we adjust the maximum and minimum values in case Pmin<0.
Since water table is usually a transient effect, meaning, its level depends on the season - high water table during the wet season, low water table during dry season - the effect of water table is included in only those calculations where its effect makes things worse.
For example, if the column reaction force causes uplift on the footing, the buoyant force is included because when combined with the column force, it leads to a smaller net downward load and thus a lower factor of safety in sliding.
But when we calculate the maximum soil pressure when the footing is fully in contact with soil, the buoyancy effect ought to be excluded because that is what causes the downward load to be the maximum and thus leads to a higher pressure on the soil.
If buoyancy is not included, SFA calculates the total downward force as selfweight of footing + soil weight + force from column + surcharge load
If buoyancy is included,
Total downward force = selfweight of footing + soil weight + force from column - buoyant force
Surcharge load too is treated as a transient effect, meaning its effect is included only in those calculations where it increases the "demand" on the foundation