Buckling Stress Concentration

We are working on a steel girder where we want to cut a void in the web, and replace the portion with a new plate. The hole is next to the bearing stiffener. When running the model in STAAD, we get a high buckling stress concentration, right at the top corner of the void. Effectively, in two 1" elements, the stress dissipates to tolerable levels. The only way to reduce this concentration is to put a horizontal stiffener plate at the top of the cut. Is there any way to ignore the high stress concentration in the analysis, and state that the system is stable? If not, is there any other remedy that could reduce the stress right at this point?
Thanks for any information.