1 i •_; ! 1 1 • ■ i j. I mi Harpers Ferrv bridgi as completed aftei the Civil War. 

 It was used by the Baltimore and Ohio until 1894, and as ,1 highway bridge 

 until [936. (Photo 6go, Baltimore and Ohio Collection, Museum oi History 



and I ei hnoli 



"much satisfaction." He went on at some length to 

 praise the "valuable mechanical features" embodied 

 therein, and expressed great confidence that iron 

 would become as important a material in the field of 

 civil engineering as it was in mechanical engineering. 

 The cost of this first major Bollman bridge was 

 523,825.00. Its span was 76 feet. Latrobe's confi- 

 dence was well placed. The Savage span and 

 another at Bladensburg in.i\ be considered successful 

 pilot models, for, in spite of a certain undercurrenl of 

 mistrust of iron bridges within the engineering pro- 

 fession due mainly to a number of failures of im- 

 properly designed spans — Latrobe felt there was 

 siiilirirnt justification for the unqualified adoption 

 of iron in all subsequent major bridge structun 

 the B. & O. 



\liiiiist immediatel) following completion of the 

 Savage Bridge, Bollman undertook the design of 

 replacements for the large Patapsco River span at 

 Blysville (now Daniels). Maryland, and the so-called 

 Winchester span of the B. & O.'s largest and most 

 important bridge, that over the Potomac at Harpers 

 Ferry. Harpers Ferry bridge, a timber structure, 

 had been designed by Latrobe and built in 1 836— 

 1837 by the noted bridge constructor I .ev is W ernv ag. 

 It was peculiar in having a turnout, near the Virginia 



shore, whereb) .1 subsidiary road branched "it to 

 Winchester (see fig. 6). Only the single span on 



this line. -iiu. iicd between the inidi iver switch and 



the shore, wa> slated for replacement, as the other 

 seven spans of the bridge bad been virtually recon- 

 structed in the decade or so of their hi-tor\ and were 

 in sound condition at the time. 



The Winchester span (fig. 8), which was the first 

 Bollman truss to embody sufficient refinement of 

 detail to be considered a prototype, was completed 

 in 1851. Bollman was extremely proud of the work, 

 with perfect justification it ma) be said. The 124- 

 foot span was fabricated in the railroad's extensive 

 Mount Clair shops. It was subdivided into eight 

 panels l>\ seven struts and seven pairs of truss rods. 

 An interesting difference between this span and 

 Hcillin. m's succeeding bridges was bis use of granite 

 rather than cast iron for the towers. The span con- 

 of three parallel lines of trussing to accommo- 

 (1 ue a common road in addition to the single-track 

 Winchester line. 



1 he distinctive feature of the Bollman system was 

 the previously mentioned series oi diagonal truss links 

 in combination with a cast-iron compression chord, 

 which Bollman called the "stretcher." I he spacing 

 between the chord and the junction of each pair of 



PAPER 36: 1\(.IM i-rim; CON 1 RIBIIK INS Ol- WLNDKI BOl I MAN 



89 



