I wanted to change the orientation of Local X and Y axes in plate without changing the Local z axis. (All plates should be rotated 90 degrees or 270 degrees w.r.t Local z)
So that the outcome should be look like the below image.
The orientation of the local x and local y axis of the plate depends on how that plate element was created. The local x axis will always be parallel to the plate edge which is formed by connecting the start and 2nd node of that plate. So when you manually create the plate, you first click on one node and then on the 2nd node to draw the first plate edge. Local X axis will be parallel to that edge. So to change the orientation of these axis, you will need to change the order of element incidences. Regretfully, but there is no automatic tool for this and you would need to perform this task manually in the STAAD Editor or create an OpenSTAAD macro to automate this task.