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.
Zhao,
Your question:
Dead weight factor. Is this factor defined for Gk(selfweight of footing, pedestal and soil above footing)?
Answer:
Yes, correct.----------------------------------------------Your question:
If we enter SFA from Staad Pro, there exist load combinations we use for structures.For example, 1.2DL+1.4LL. Gk is dead load.Here should we specify this factor to be 1.2(load factor for dead load)?
Answer :
Yes you have to. If you enter SFA from STAAD.Pro, or, import a STAAD.Pro model from SFA, the dead load factor (1.2 in your example) has to be manually entered in the "Selfweight and deadweight factor" table.------------------------------------------------You question:
Could SFA idenfify Gk to be dead load for all combinations?
Only if you generate load combinations from within SFA. But if the data is imported from a STAAD.Pro model, SFA cannot currently identify the load type (Dead, Live, Wind, etc.). A new version of the program that will be available by the end of this year will be able to identify the load type on its own for data that comes in from a STAAD.Pro model.
But what made us confused is special rules for mat foundation. In previous version of SFA, weight of soil is not considered for mat foundation as it is not designed as rigid foundation.
As far as I remember, all versions of SFA have considered the weight of soil as an additional load on mat. In older versions, the soil weight was applied by converting it to an equivalent selfweight of the mat. You can find the details here.
https://communities.bentley.com/products/ram-staad/f/ram-staad-forum/103571/selfweight-of-mat-foundations-in-staad-foundation-advanced/599428#599428
In the current version, the program applies the soil weight as a pressure load on the mat. For each load case, the pressure is calculated as
dead load factor * Unit weight of soil * height of soil on top of mat
SFA creates a STAAD.Pro file (.STD file) containing the finite element model of the mat. If you open that model in STAAD.Pro, you can see the pressure value applied as an element pressure load for each load case on all the elements that constitute the mat.
-----------------------------------
In the following picture, it says SFA checks soil bearing capacity under load combinations of service ultimate state. But in calculation report, SFA also checks it for strength ultimate cases.Is this step intended to get the net soil reaction presussure?
We agree that we need to mention in the manual that the recent versions of the program check the soil pressure for strength load cases too. The pressure needs to be calculated for the strength load cases because the bending moments and shear force on the footing are based on the soil pressure.