History and Development of Steel Railway Bridges - Design of Modern Steel Railway Bridges - page 18

Baltimore truss
Petit truss
FIGURE 1.7 Baltimore trusses (the inclined chord truss is also called Petit truss).
rapid erection of railway bridges in remote areas of the United States. The princi-
pal exception was the New York Central Railroad, which used riveted construction
exclusively for its iron railway bridges.
In 1863, the Pennsylvania Railroad successfully crossed the Ohio River using a
320 ft iron truss span. The railroad used the relatively rigid Whipple truss for such
long spans. This construction encouraged greater use of longer span iron trusses to
carry heavy freight railroad traffic in the United States.Another notable wrought iron
railway truss was the 390 ft span built by the B&O Railroad at Louisville, Kentucky,
in 1869.
In the 1870s the Pratt truss (patented in 1844) became prevalent for short- and
medium-span railway bridges in the United States. Pratt trusses are statically deter-
minate and their form is well suited for use in iron bridges. Whipple, Warren, and
Post trusses were also used by U.S. railroads in the 1870s. The Bollman truss bridge,
patented in 1852 and used by the B&O and other railroads until 1873, was an example
of the innovative ∗ use of wrought iron in American railway bridge construction. For
longer wrought iron railway bridge spans, the Baltimore or Petit truss was often used
(Figure 1.7). † The first use of a Baltimore truss (a Pratt truss with subdivided panels)
was on the Pennsylvania Railroad in 1871.
Large railway viaduct bridges were also constructed in wrought iron. The 216 ft
high and 1300 ft long Viaduc de la Bouble was built in France in 1871. In 1882
the Erie Railroad completed construction of the 300 ft high and over 2000 ft long
wrought iron Kinzua Viaduct in Pennsylvania ( Figure 1.8) . Also in France, Gustave
Eiffel designed the wrought iron Garabit Viaduct, which opened to railroad traffic in
1884 ( Figure 1.9) .
A large number of iron railway bridges built after 1840 in the United States and
England failed under train loads. It was estimated that about one-fourth of railway
∗ Bollman trusses used wrought iron tension members and cast iron compression members. The redundant
nature of the truss form reduced the possibility of catastrophic failure.
† The Petit truss was used extensively by American railroad companies.