can you give me a tip about how to create solid plate
in sap2000?
i have already create this in sap90.
Also, how can i create solid element in sap2000, generally?
If you already have SAP90 input file, you can import it into SAP2000.
The best way to create SOLID elements in SAP2000 is to create DXF file using AutoCAD (or similar). Note that you have to draw solids as 3D Mesh elements - type 3D command (see SAP help).
The other, much slower way, is to write .s2k input file. Details could be found in SAP manuals.