"The new  iron viaduct erected by a railroad construction crew that summer, contrasted sharply with its predecessor. The 235-foot-long structure stretched from Valley Street on the north to Market Street on the south, sloping slightly uphill along its length. The viaduct featured a pin-connected Pratt through truss over the railroad tracks, flanked on both sides by 60-foot and 43-foot plate girder deck approach spans. Fabricated by the Lassig Bridge & Iron Works of Chicago, using members rolled in Pittsburgh by Carnegie, the truss was made up entirely of built-up wrought iron components.
"City Engineer Emmet Steece determined that the steep approach on the viaduct's norht end needed to be reconfigured. Steece had drawn a steel structure comprised of three 36-foot girder spans supported by steel columns on concrete pedestals. With their built-up flanges, through-deck configuration and upper chords radiused continuously to form the end posts, the structures resmbled most girders of the time. What made these girders noteworthy was their patticed webs. Instead of solid plates, which was the industry standards, the webs of Steece's girders were made up of angle sections, riveted into a series of triangles with curved gusset plates - resembling a Vierendeel Warren truss...the Sixth Street Viaduct is the only such open-web girder known to exist in Iowa."
Carl W. McWilliams