if you dont mind..
select all intersecting lines and polylines and explode..
purge and save it as dwg file...
Save it again but as a dxf file...
Open staad pro..
import/export dxf..
Structure Convention, chose Y Up..
Choose appropriate Units..
Select all lines in staad pro..
in Geometry Tab select INTERSECT SELECTED BEAMS..
in the File Tab selct IMPORT/EXPORT..
Export as 3D DXF File..
Provide File name for the dxf file..
in Structure convention, chose Z UP..
Open in autocad the generated dxf file from staad and remove all unnecessary text..

may it helps you..