Ask CAD files - Tekla Structures

I have a problem importing 3d object (.dwg) to Tekla Structures (BIM)
Some previous 3d object was created using AutoCAD and now to be used as object on Tekla, i import it but seems not as expected, Tekla read 3d object ( . dwg) as a series of line, not a solid
Try has been made by converting .dwg files to IFC and then go in Tekla, but process consume a lot of time
Welcome any sugggests