Which American Code contains clauses for minimum contact area limit between footing and soil？

Question

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.

Kris Sathia · Accepted Answer

It is currently not based on any code. The user is free to specify any value between 0 and 100..

Kris Sathia · Answer

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.

Kris Sathia · Answer

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

Kris Sathia · Answer

Zhao, 
 Your question: 
 When checking footing shear capacity and calculating reinforcement area, net soil reaction is used. That is the reason why SFA calculates Pmax under ultimate load combinations (Then minus the pressure induced by selfweight of soil and footing). 
 Answer: 
 That is correct. 
 ----------------------------------------------------------- 
 Your question: 
 But should we compare Pmax with soil bearing capacity in order to conclude if dimension of footing is enough? I don't think so. 
 Answer: 
 That is a choice left to the user. We agree that in most engineers do not check the ultimate soil pressures against a bearing capacity (factored by a number between 1 and 2 typically). But some companies do. So, we have provided that option. 
 -------------------------------------------------------------- Your question: 
 And there is also no need to calculate contact area percentage under ultimate load combinations. 
 Answer: 
 This too is the user's choice. Some users have told us that for ultimate load cases too, they want to ensure that the loss of contact is within a reasonable limit, especially if the structure is supporting costly equipment like turbines. If it is not a matter of concern to you, you can ignore it. --------------------------------------------------------------- Your question: 
 But if Chinese Code is selected, this step is not included in calculation sheet. This is a bit confusing. 
 Answer: 
 We will look into it.

Kris Sathia · Answer

Yes, these are compulsory checks at present. However, in order to ensure that they do not govern, specify a large number (2 or greater) as the multiplying factor, and a small value like 5% for contact area for ultimate load cases. Later this year, we will have a version of the program where these checks are optional. You do not need to create 2 separate models.

Kris Sathia · Answer

In SFA version 9.7.1.139 that was released last week, the program is able to perform the concrete design of combined footings with partial loss of contact of upto 50%.

Kris Sathia · Answer

If you install the latest version of STAAD.Pro which was released 2 weeks ago, SFA 9.7.1.139 will get automatically installed with it. 
 You must have received a notification in Connection Client about the latest version of STAAD.Pro available for installing. Follow those prompts. If you haven't received such a notification, use the procedure described here. https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/40058/procedure-for-downloading-staad-pro-ce

Which American Code contains clauses for minimum contact area limit between footing and soil？

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