[Fifteenth progress report] : Investigation of prestressed -reinforced concrete for highway bridges / prepared as a par-t of an investigation conducted by the Engineering Experime-ntal Station University Illinois ; in cooperation with the -Division of Highways State of Illinois and U.S. Department- of Commerce Bureau of Public Roads. 

 - Urbana, Ill. : University of Illinois 
 - [104]p. 
 - Progress report ; no. 15 .