I have a continuous beam, and all members have the same E and same properties. I run it once with one set of member properties. I double the depth of the members and run it a second time. The results of the second run (midspan moment, reactions, etc.) do not match those from the first run. Shouldn't the results stay the same as the EI remains constant for both the beams?
The difference is due to shear deformation. Instead of specifying properties as YD and ZD (which would trigger a shear deformation calculation), provide the values as
AX, IX, IY and IZ
and check the results. They should stay the same.
Or, if you are running STAAD.pro 2004 or later, specify the command
on the second line of your input file. This will forcibly switch off shear deformations from the calculations.
Now, changing just YD or ZD should have no effect on the results.