question on equation K2-2 of AISC 13th edition manual
question on equation K2-2 of AISC 13th edition manual
(OP)
I want to know if anyone has information on some of the variables in this equation. I am unsure what they are exactly. The equation is
U=Pr/(Ag*Fc)+Mr/(S*Fc)
where
Pr= required axial strength in chord
Mr= required flexural strength in chord
Fc= Available stress
S= chord elastic section modulus
Ag=gross area
What I want to know is what are Pr, Mr, and Fc? And where do I get these values?
U=Pr/(Ag*Fc)+Mr/(S*Fc)
where
Pr= required axial strength in chord
Mr= required flexural strength in chord
Fc= Available stress
S= chord elastic section modulus
Ag=gross area
What I want to know is what are Pr, Mr, and Fc? And where do I get these values?






RE: question on equation K2-2 of AISC 13th edition manual
Just read down a bit.
RE: question on equation K2-2 of AISC 13th edition manual
RE: question on equation K2-2 of AISC 13th edition manual
I went through the text to where each part was referenced and Pr= Pnt+B2*Plt but how would you get B2 and Plt and Pnt?
RE: question on equation K2-2 of AISC 13th edition manual
We are Virginia Tech
Go HOKIES
RE: question on equation K2-2 of AISC 13th edition manual
RE: question on equation K2-2 of AISC 13th edition manual
They use this general term, "required", because they cover both ASD and LFRD design with the same equation.
ASD: Pr = Pa = load resulting from controlling service level load commbination
LRFD: Pr = Pu = load resulting from controlling factored load combination
same for Mr...= Ma, or Mu
RE: question on equation K2-2 of AISC 13th edition manual
Rn=5.5*Fy*t^2*(1+0.25*N/D)*Qf
Qf=1-.3*U*(1+U)
U=Pr/(Ag*Fc)+Mr/(S*Fc)
Or am I overlooking something?
So if I have to assume a load being lifted then do a force analysis to get loads and moments on the structure then determine the nominal strength based on specification provisions to see if they exceed those that the assumed load imparted on the structure....How do I do this if those same assumed loads are in the calculation that is needed to determine safety?
I apologize if this is a trivial issue and I am over looking something, but to me the equations to analyze I-beams and welds and bolts are a lot different then HSS members, which this is my first time working with.
RE: question on equation K2-2 of AISC 13th edition manual
For LRFD:
Mu <= phi*Mn
Mu is the moment resulting from factored loads from analysis.
Mn is the nominal or theoretical moment capacity of the beam.
Phi= a reduction factored for various reasons
Meaning, the factored moment on the beam from analysis must be less than the theoretical moment capacity of the section multiplied by a reduction factor.
The same principles to moments, forces, axial...whatever.
They call it Mu, Ru, Pu etc.
RE: question on equation K2-2 of AISC 13th edition manual
Ru=Pu=1.2*D+1.6*L <= Rn=5.5*Fy*t^2*(1+.25*N/D)*[1-.3*(Pr/(Ag*Fc)+Mr/(S*Fc)]
?
RE: question on equation K2-2 of AISC 13th edition manual
RE: question on equation K2-2 of AISC 13th edition manual
Thank you for your responses though.
RE: question on equation K2-2 of AISC 13th edition manual
The chord stress interaction factor Qf is based on the utilization ratio U, equal to |Pr/(Ag Fc)+Mr/(S Fc)|. The Pr and Mr here are the force and moment in the HSS member itself. These are different than the Pu you're applying perpendicularly to the HSS member.
RE: question on equation K2-2 of AISC 13th edition manual
RE: question on equation K2-2 of AISC 13th edition manual