I found some information from Wahoo Decks. See the links belowhttp://www.wahoodecks.com/dryjoist/howitworks.phphttp://www.wahoodecks.com/resf...DryJoistBrochure.pdfhttp://www.wahoodecks.com/resf...alInformationPDF.pdf
The material is an engineered metal product, like an I-beam. The metal is tested (to conform to AA ADM standards) and the values are then given to the engineer for design.
AA ADM stands for Aluminum Association Aluminum Design Manual, 2005 Edition
Hope this helps