Thank you for posting your idea. When considering the structural behaviour of steel frames, typically it is only the frame members that is of concern. Checker plates and gratings are typically not considered because their impact on the analysis/design is minimal however including them would mean the design is now reliant on them for stability. If the client removed say for maintenance and some minor mods and the structure failed, then that would seem unreasonable. This is secondary framework which means it can be taken away without undermining any primary structure. However, saying that STAAD.Pro can account for such a plate, just assign it a suitable thickness and material value.