Safe working load vs ultimate capacity

[JStructsteel]

Im trying to find an insert for a project to cast into concrete that has a ultimate capacity of 16K. Every manufacture I look at has safe working loads. What factors do you use to convert? Multiply by factor of safety and then use a phi factor on that number? Seems reasonable to me, but not sure what else to consider.

 

[dik]

Do you have the load as a DL and LL? If so, can you divide them by the respective load factors? If not, use the load factor for dead load.

Dik

 

[JStructsteel]

Its all live load. I need 16K ultimate shear. Its a AASHTO code, so 16K/1.75?

 

[WARose]

What I've typically done: safe working load= Ult. load/(max load factor in combinations/Φ)

 

[JStructsteel]

Ok, thanks. 16K/1.75/0.75=12.2K. Not a huge difference.

 

[WARose]

Something is wrong with your math (I get 6.85). I think you forgot about the ( ) in my equation.

 

[JStructsteel]

Yes, I missed that, that makes more sense. Fits in line with one manufacturer saying ultimate load is SWL X F.S.

 

[TehMightyEngineer]

Phi is 0.9 for shear under AASHTO.

I usually go about this a different way; if I have a insert that has a safety factor of 4 and they give me a safe working load; I multiply their safe working load by the safety factor to get ultimate capacity, multiply the ultimate capacity by the failure mode phi factor, and then compare to my factored loads.

Worked out in equation form:

(SWL)(Safety Factor)(Φ) ≥ (Factored Load)

Ian Riley, PE, SE
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[TehMightyEngineer]

I should clarify; concrete shear has Φ = 0.90

Dowels and anchor bolts and other items cast into the concrete reference ACI 318-05 appendix D (per AASHTO LRFD 7 article C6.13.2.12 and C14.8.3.1.) which would use Φ = 0.45 thru 0.75 depending on failure mode.

Ian Riley, PE, SE
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[JStructsteel]

I was going with 0.75 from the PCI manual.