Applying Seismic Loads in Vessel Design by COMPRESS

[StaticPressure]

Does any body know why COMPRESS decreases the earthquake load for vertical vessels by 1/3, but does not do it for horizontal vessels (for example when NBC 2005 has been chosen)? I have noticed for both vertical and horizontal vessels, COMPRESS increases the allowable stresses as per UG-23(d) for combination of pressure and wind/seismic. So why again we need to decrease the earthquake load by 1/3 for vertical vessels?

I appreciate any answer that can give more light on it.

 

[mqadir]

Friend

thats the moment arm 1/3 (L) we need to multiply the force with factor to get moment.

Thanks