The software was completely retired in December 2017.
Autodesk now recommends Autodesk Advance Steel for steel detailing and Autodesk Revit for concrete and rebar detailing. How to Access/Download ASD Today Download AutoCAD aSD
Because the product is retired, you cannot buy a new license or download a trial. However, there are specific ways existing users can still access it: AutoCAD Structural Detailing discontinued - Autodesk The software was completely retired in December 2017
It is important to note that in 2015.