The Latitude parameter(IBC 2012) is being incorrectly set to zero when defined using the GUI
Steps to Reproduce
Suppose you add a seismic definition as per IBC 2012 using the GUI and specify the zip code as 97317. You will see the latitude, longitude, Ss, and S1 values correctly reported inside the dialog box. However, if you add the definition and go into the Editor you'll find the latitude incorrectly defined as "0" as shown next:
DEFINE IBC 2012 LAT 0 LONG 33.8845 I 1 RX 3 RZ 4 SCLASS 4 TL 12
This means that when the analysis is performed, Ss and S1 values corresponding to the wrong location are specified and thus the loading will be incorrect.
If you manually input the correct latitude and longitude in the Editor then the analysis will be correct only so long as the model isn't saved from the GUI. As soon as you save from the GUI, however, the seismic definition will revert back to the incorrect state in which LAT is "0"
The only way to ensure consistent and correct results is to avoid using the parameter Latitude and directly define Ss and S1 in the input file like this:
DEFINE IBC 2012 SS 2.24787 S1 0.817423 I 1 RX 3 RZ 4 SCLASS 4 TL 12
You may find out the SS and S1 value from the GUI when you enter the value of Latitude and Longitude as shown next
The problem will be addressed in the upcoming release of STAAD.Pro Connect Edition