Figure an. — Two views of Bollman-built "water-pipe truss" that carrie 

 Lombard Street over Jones Falls in Baltimore. Built in 1877. 



in complex fabrications. The normal practice at the 

 time was to use cast compression members in iron 

 bridges and structures, with their sectional area 50 

 proportioned to the length that a state of tension 

 could not exist. In the case of lonn members, this 

 naturally meant that an excessive amount of material 



was used. 



Bollman was conscious of the problem from his 

 experience with the stretchers and stint-, of his truss, 



and he must have been aware of the great advantage 

 which would be obtained by a practical method of 

 forming such members in wrought iron, the tensile 

 resistance of which is equivalent to the compressive. 

 1 [e eventually developed the forerunner of what came 

 to be known as the Phoenix form by having special 

 segmental wrought-iron shapes rolled by Morris, 

 rasker and Company of Philadelphia, these shapes 

 being combined into a circular section with out- 



94 



BULLETIN 240: CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



