Applies To
	Product(s):	STAAD.Pro
	Version(s):	All
	Environment:	N/A
	Area:	STAAD.Pro Analysis Solutions
	Subarea:	Seismic Analysis
	Original Author:	Abhisek Mandal, Bentley technical Support Group

 I am applying a UBC seismic load on a bridge. The analysis engine reports an error message which says that:
EITHER NA OR NV FACTOR HAS NOT BEEN SPECIFIED WHILE SEISMIC ZONE HAS BEEN SPECIFIED AS 4. ?

This is due to the fact that, for your model, STAAD looks at the data under the DEFINE UBC LOAD command and concludes that you intend to analyse the structure per the UBC 1997 code. It then checks whether all the required parameters have been specified for that code, and detects that NA and NV are missing. You perhaps have an input similar to the one below :

DEFINE UBC LOAD
ZONE 0.4 I 1 RWX 12 RWZ 12 STYP 1.2 PX 0.2626 PZ 0.2626

For Zone 4, Na and Nv are two of the fundamental parameters necessary to calculate the base shear. If you look at Tables 16-Q and 16-R on pages 2-34 & 2-35 of the UBC 1997 code, you will find that for Zone 4, the coefficients Ca and Cv are dependent on Na and Nv.

So, specify the NA and NV parameters, so that the commands look similar to the one below :

DEFINE UBC LOAD
ZONE 0.4 I 1 RWX 12 RWZ 12 STYP 1.2 NA 1.6 NV 1.6 PX 0.2626 PZ 0.2626