I am looking at the maximum beam moments in the post processing mode and also looking at my steel design in the analysis output file. The design seems to completely ignore the higher moments that I see in the post processing mode and is designing for less critical cases. What could be the issue ?
Most likely you are using a LOAD LIST command before the design, in which case the design would consider only those cases which are included as part of the LOAD LIST. For example, if the commands are defined as shown next, the design would consider the load cases 20 to 35 for the design.
…LOAD LIST 20 TO 35PARAMETER 1CODE AISC UNIFIED 2005METHOD ASDTRACK 2 CHECK CODE ALL…
You may want to check and ensure that the load case with the higher moments is part of the LOAD LIST, if you would like STAAD.Pro to consider the load case for design.
Another possibility is, although a particular load case may have a higher value of moment, a different load case with a lesser value of moment, may actually end up being reported as the most critical case for design, as it may end up with a higher ratio due to interaction of bending & axial or torsion & shear. So check out the critical condition being reported for design too.