IBC 2006/ASCE 7-05 Load combo question
IBC 2006/ASCE 7-05 Load combo question
(OP)
Hi, question about code interpretation.
In ASCE 7-05 Section 12.4.2.3 discusses seismic load combinations where Sds and rho are included. In reviewing IBC 2006, I do not see anything that says we need to use the combos in section 12.4.2.3 for seismic design. I only see discussion about load combos with the overstrength factors. How do you interpret IBC06? Should these load combos from ASCE 7-05 be used in lieu of the standard 1.2D+L+1.0EQ and 0.9D+1.0EQ?
Any help is greatly appreciated.
In ASCE 7-05 Section 12.4.2.3 discusses seismic load combinations where Sds and rho are included. In reviewing IBC 2006, I do not see anything that says we need to use the combos in section 12.4.2.3 for seismic design. I only see discussion about load combos with the overstrength factors. How do you interpret IBC06? Should these load combos from ASCE 7-05 be used in lieu of the standard 1.2D+L+1.0EQ and 0.9D+1.0EQ?
Any help is greatly appreciated.
RE: IBC 2006/ASCE 7-05 Load combo question
IBC definition of E: "Combined affect of horizontal and vertical earthquake-induced forces as defined in Section 12.4.2 of ASCE 7" (Section 1602)
ASCE says E = Eh + Ev
Eh = rho*QE and Ev = .2*SDS*D (ASCE 12.4.2)
So:
1.2*D + 1.0*E + L
= 1.2*D + 1.0*(rho*QE + 0.2*SDS*D) + L
= 1.2*D + 1.0*rho*QE + 1.0*0.2*SDS*D + L
= 1.2*D + 1.0*0.2*SDS*D + 1.0*rho*QE + L
= (1.2 + 0.2*SDS)*D + 1.0*rho*QE + L ----> Which is ASCE 12.4.2.3
I think the other equations fall out the same way.
If you are in a lower seismic zone, it really doesn't matter too much……
For example, say Seismic Design Category = C and SDS = .20
Then:
rho =1.0 (ASCE 12.3.4.1) and Eh = QE = normal horizontal effects from V
Ev =.2*SDS*D = .04*D.
So the horizontal E just equals Eh and the vertical E is just adding 4% to the Dead Load…..
Now if your really in a low seimsic zone and SDS <= .125, Ev can = 0 and your really back to 1.2*D + 1.0*E + L where E just equals Eh
RE: IBC 2006/ASCE 7-05 Load combo question