IBC2000 (RESPONSE SPECTRUM / SEISMIC LOAD) 1

[hagi10]

Let me note what I have first;
- 3D model
- moment frames in both directions
- steel building
- seismic design category C
- IBC 2000

What I did;
- I did response spectrum analysis w/ the response spectrum given in soil report. *I have only one response spectrum for both directions.
- I applied the response spectrum in orthogonal directions and calculated seismic forces in each direction, EQx and EQy to use in static analysis.
- I used the load factors in IBC 2000 Section 1605.2.1 w/ 100% EQx and 100%EQy seperately.
eg; - 1.2DL + 1.0EQx + 1.0LL
- 1.2DL + 1.0EQy + 1.0LL

What I want to know;
- Is that load combination is acceptable? (in seismic design category C)
- Do I have to apply 100% in most critical direction and 30% percent of ground motion in the orthogonal direction (see IBC2000 Section 1623.3.5.2)?

PLEASE COMMENT w/CODE REFERENCES.
THANKS,
O.

 

[prsconsultant]

You need to do a 100% + 30% combinations only when the building has non-parallel lateral systems (see IBC 2000 Table 1616.5.1 & 1620.2.2)

Load combinations per 1605.2 are adequate. Make sure the earth quake load E is as defined in section 1617 with appropriate values of rho & omega0.

Also the modal base shear shall be scaled per 1618.7