Reduction factor of seismic load case.

Hi all.

In case of following load case I've found some reduction facotr(0.714) of seismic load(U1).
OCC : W+P1+T1+D1+0.714U1

I have 2 questions for above load case.
1) Which code or standard indicate about above reduction factor?
2) Which case can I apply above reduction factor ?

Current project specification stated that seismic load calculation shall be in accordance with UBC 97 zone2A.

Thanks !

Which code? It's UBC 1997 you mentioned; in chapter 16 stated that if you used the allowable stress (elastic) design (i.e. not plastic design criteria) as it is the practice in piping being dictated by ASME B31 code, you have to divide the seismic load "E" by 1.4 (E/1.4). Hence, E/1.4 = 0.714E or in terms of seismic acceleration is 0.714U. This means that when verifying the OCC (operating and stress load cases), the seismic acceleration "U" calculated from UBC 1997 formulae shall be reduced by 0.714 factor. Hope this helps.

Thank you for provide useful information.

But I can't find about above contents in ASME B31.

Which para contains above contents (dictated by ASME B31 code, you have to divide the seismic load "E" by 1.4 (E/1.4). Hence, E/1.4 = 0.714E or in terms of seismic acceleration is 0.714U.) ?

It's not directly stated (dictated......is 0.714U.) in any para of ASME B31 code. You have to correlate both ASME B31 and UBC codes. Read first UBC 1997 sec 1612.3.1. Also refer to ASME B31E for seismic evaluation of piping.

ASCE 7 has a paragraph that addresses allowable stress design (ASD) and Load Resistence Factor Design (LRFD) - piping is by ASD and buildings are by LRFD. That paragraph states LRFD seismic loads are to be multiplied by 0.7. But watch out, B31 people are discussing this for change.