Is it possible to create a hole in reinforced concrete beam?
Depends on what level of accuracy you are looking for.
Highest level - Every component of the beam - the flanges, webs, etc. would have to be modeled using solid elements or plate elements. Hence, instead of modeling the beam as a line member, it would be a mesh of solid elements or plate elements. The exact location of the opening, its shape, size etc. could then be modeled to a high level of precision.
Intermediate to Low level - Specify the beam as a series of line segments. Segments which do not contain the opening have the full cross section properties, others have a reduced section due to the hole. For the ones with the hole, calculate the section properties manually at the location where the material available is the least, meaning, a section cut through the diameter for a circular hole. The properties required are : Cross section Area (AX), moments of inertia (IY and IZ), and Torsion constant (IX). Specify them in the STAAD model by using the "PRISMATIC" member property type.