Making sense of minimum flexural reinforcement requirements for reinforced concrete members

Abstract

Part 1 N o single event was more instru mental in launching the pre stressed and precast concrete in dustry in North America than the construction of the Walnut Lane Bridge in Philadelphia in 1950 (see articles in Sept.-Oct.1976 PCI JOURNAL 1 ).*More than anything else, how ever, it was the charisma, dy namism, and engineering talent displayed by the man who designed the Walnut Lane Bridge, namely Professor Gustave Magnel of Bel gium, that gave the impetus neces Whatsoever a man soweth, that shall he also reap (Galatians 6:7) sary for the acceptance and de velopment of prestressed concrete in the United States.On the other hand, very few know how this came about, how the Belgian-American Educational Foundation, an American-sponsored organization founded in 1920 as an aftermath of World War I, was to be instrumental in bringing Professor Magnel to the United States in 1946.Nor is it known how many appar ently unconnected events and coin cidences which took place during that period, led to the construction of the Walnut Lane Bridge.This is an extraordinary and fas cinating story which I believe should be recorded for posterity.'I gLL 0" a -,',i '-C--/.i2'-2i7Io 3,, ,,r,/.,I tLJ7, -4<))-,c L ,c, CSai 4' //o & fig.9. Portion of an original calculation sheet in Magnel's own handwriting.Prestressed Concrete in America L Colt, a consulting engineer in New York, had developed.as consultant to John A. Roebling & Sons company, a pre' stressed concrete box girder of variable depth for a Walnut Lane Bridge using cables made up of galvanized strands provided with sockets and swage terminal for anchorages, and bridge saddles over transverse ctlaptrragms, similar to the cables used in suspension bridges.