You can refer to the following URL and complete technical information about Hollow Structural Sections (HSS).
www.aisc.org/hss
Association for the institution's website,
American Institute of Steel Construction

AISC
www.modernsteel.com
Steel authority of U.S. law www.modernsteel.com journal's Web site (Modern Steel Construction (MSC this magazine that focuses on the specialized steel structures, part of emissions Institute AISC America. 

 
www.atlastube.com/hss
Atlas Tube Inc., one of the largest construction site sections and tube manufacturers in the United States

www.cidect.org
The Forum CIDECT the expertise to design and postgraduate Tubular deals.