[Oops, I am also aware that a paper was presented on the design of pipe at that time in the May 24, 1950 AWWA Annual Conference in Philadelphia, PA, and I guess a follow-up article was also published In the Nov. 1950 Journal AWWA by Mr. Hugh Kennison, at that time Chief Engineer of the Lock Joint Pipe Co. I saw that a sort of "Rubber and Steel Joint", that much resembles later versions, though it appeared in cross-sectional view with maybe some sort of extra, outer annular bell reinforcement outside the steel bell ring was in fact pictured in theat paper. I would assume you might still be able to get this paper from AWWA Publications.]