6 / coNjECTURAi section of Bollman's segmental wrought-iron 



colun i the standard Phoenix i olum 



Phoenix column as used in truss-bridgi i om] members 



I \ VII \ I ION OF THE TRUSS 



By the late I850's iron was well established as .1 

 bridge material throughout the world. Once the 

 previous fears of iron had been stilled and the atten- 

 tion of engineers was directed to the interpretation 

 of existing and new spanning methods into metal, 

 the Bollman truss began to Miller somewhal from the 

 comparison. Although its components were simple 

 in fabricate and its analysis and design were straight- 

 forward, it was less economical oi materia] than the 

 more conventional panel trusses such as the Pratt 

 and Whipple types. Additionally, there was the req- 

 uisite amount ol secondary metal in lower chords and 

 braces necessary for stability and rigidity. 



A fat in! difficult to assess is Bollman's handling of 

 his patent, which was renewed in 1866. There is 

 sufficient evidence to conclude that he considered 

 the patent valuable because it was based upon a 

 sound design. Therefore, he probably established a 

 high license fee which, with the truss's other short- 

 comings, was sufficient to discourage its use l>\ other 

 railroads. As patron, the B. & O. had naturally had 



full rights to its use. 



An additional detect, acknowledged even by Boll- 

 man , a 1 ox,- because ol the unequal length of the links 

 tup except the center one. 1 his caused an 

 unevenness in the 1 hernial expansion and contraction of 

 the framework, with the result that the bridges were 

 difficult to keep in adjustment. This had the prac- 

 tical effect of virtually limiting the system to inter- 

 mediate span lengths, up to about 150 feet. For 

 longer spans the B. & < >. employed the truss ol another 



ol Latrobe's assistants, German-born and technically 



trained Allien 1 ink. 



The Fink truss was evolved contemporaneously with 



Bollman's and was structurally quite similar, being a 

 suspension truss with no lower chord. I he prii 

 difference was the symmetry ol I ink's plan, which 

 was achieved l>\ carrying the individual panel loads 

 from the panel pomts to increasingly longer panel 

 units before having them appear at the end bearings 

 I in i liminated the weakness ol unequal strains. The 

 design was basically a more rational one. and it came 

 to be widelv used in spans ol up to nerally 



i leck-type truss i see fig. 11). 



\V. Bollman and Company 



Bollman resigned from the Baltimore and Ohio in 

 1858 to form, with John II. ["egmeyer and John 

 ('lark, two of his former B. & ( >. assistants, a bridge- 

 building In in in Balti re known as W. Bollmai 



Company. This was apparently the first organiza- 

 tion in the United States to design, fabrii 



erect iron bridges and structures, pi :ering in what 



2^ veais later had In-come an immense industry. 

 I he firm had its foundation at least as early as 

 1855 when advertisements to supply designs and esti- 

 mates for Bollman hrid [es appealed over I ejmever's 

 name in seva i) railroad journals see fig. 12). 



Bollman's separation from the B. & < '. was not a 



Complete one. I he railroad continue I its program 



of replacing timber bridges with Bollman trusses, and 



at ted with W. Bollman and ( omp.uiv for design 



PAPER 36: ENGINEERING Ci i\ 1 KI1U riOXS Ol \VI\DII ItOI.I.MAN 



91 



