3d bracing modeling

huangyhg

3d bracing modeling
i'm designing a steel plate girder bridge.  i don't have a problem with the main member except the bracing. i found in a textbook shown that each girder is splited to 3 beams (2 beams for top and bottom flange and the other is for web). this method allow me to model full depth bracing.  my question is how am i going to input the properties such as ix, iy for each beams (or constraint command in sap software)??