vertical seismic force

Dear friends,
I put 0.3g in lateral(Fx,Fz) direction(zone 4),
is it necessary i put any coefficient in Y direction?(vertical)
thanks

That depends on your project specifications. However, you can find a host of publications (ASCE #7 for example) that recommend a vertical seismic load.

Generally piping system consider lateral direction only for seismic unless otherwise asked for special case(example; when hydraulic mass need to considered because of submerged pipe in a liquid). You can find it the design criteria or guid of nuclear power plants per US NRC Regulation and ASME III NB/NC.

.............and you might want to look at this:

http://www.americanlifelinesalliance.org/pdf/Seismic_Design_and_Retrofit_of_Piping_Systems.pdf

Thanks John!