Struct123ure
Structural
- May 16, 2023
- 52
I am located in Canada and abide by OBC additionally follow the Canadian-Foundation-Engineering-Manual if that matters.
I want to know what the "right" approach is to converting ASD bearing capacity to LRFD so that I can put it on a report/drawings.
Approach 1: and commonly used from my experience most geotechnical companies simply put a 1.5*SLS so if SLS=200kPa, ULS=300kPa, but I see that as an simplification, without any code backing.
Here is my two approaches.
Approach 2: CFEM formula 6.1 Ψ*ϕ_gu*R_u > Σα*F. Ψ*ϕ_gs*R_s > Σα*F for serviceability.
R_s=SLS/Ψ*ϕ_gs
R_s=200kPa/(1.0*0.8)
R_s=250kPa
ULS=R_s/Ψ*ϕ_gu
ULS=250kPa/(1.0*0.5)
ULS=500kPa This approach makes the most sense to me since we are removing any factor on SLS bearing (getting back to the tested capacity) and then applying the ULS factor. But I am uncomfortable with it being so high.
Approach 3:
SLS=Ψ*ϕ_gu*ULS
ULS=SLS/Ψ*ϕ_gu
ULS=200kPa/(1.0*0.5)
ULS=400kPa This uses the correct factor from CFEM, and seems more correct since ULS is closer to SLS.
Any advice from someone who works in Geotechnical and prepares reports would be greatly appreciated.
I want to know what the "right" approach is to converting ASD bearing capacity to LRFD so that I can put it on a report/drawings.
Approach 1: and commonly used from my experience most geotechnical companies simply put a 1.5*SLS so if SLS=200kPa, ULS=300kPa, but I see that as an simplification, without any code backing.
Here is my two approaches.
Approach 2: CFEM formula 6.1 Ψ*ϕ_gu*R_u > Σα*F. Ψ*ϕ_gs*R_s > Σα*F for serviceability.
R_s=SLS/Ψ*ϕ_gs
R_s=200kPa/(1.0*0.8)
R_s=250kPa
ULS=R_s/Ψ*ϕ_gu
ULS=250kPa/(1.0*0.5)
ULS=500kPa This approach makes the most sense to me since we are removing any factor on SLS bearing (getting back to the tested capacity) and then applying the ULS factor. But I am uncomfortable with it being so high.
Approach 3:
SLS=Ψ*ϕ_gu*ULS
ULS=SLS/Ψ*ϕ_gu
ULS=200kPa/(1.0*0.5)
ULS=400kPa This uses the correct factor from CFEM, and seems more correct since ULS is closer to SLS.
Any advice from someone who works in Geotechnical and prepares reports would be greatly appreciated.
