Civil Engineering Reference
In-Depth Information
Howe truss (iron & wood)
Bollman truss
Howe truss (iron)
Warren truss
Pratt truss (with center counter)
Whipple truss
FIGURE 1.2
Truss forms used by railroads in the United States.
statically indeterminate and, therefore, many were built on early American railroads
without the benefit of applied scientific analysis.
The first railway bridge in the United States constructed entirely in iron was a
Howe truss with cast iron compression and wrought iron tension members built by
thePhiladelphiaandReadingRailroadin1845atManayunk,Pennsylvania.Following
this, iron truss bridges became increasingly popular as American railroads continued
their rapid expansion. Iron Howe trusses were also constructed by the Boston and
Albany Railroad in 1847 near Pittsfield, Massachusetts, and on the Harlem and Erie
Railroad in 1850. Early examples of Pratt truss use were the Pennsylvania Railroad's
cast and wrought iron arch-stiffened Pratt truss bridges of the 1850s. An iron railway
bowstring truss, also utilizing cast iron compression and wrought iron tension mem-
bers, was designed by Squire Whipple
∗
for the Rensselaer and Saratoga Railway in
1852. Fink and Bollman, both engineers employed by the B&O Railroad, used their
own patented cast and wrought iron trusses extensively between 1840 and 1875.
†
Noteworthy, iron trusses were also built by the North Pennsylvania Railroad in 1856
(a Whipple truss) and the Catasauqua and Fogelsville Railroad in 1857. The Erie
Railroad pioneered the use of iron Post truss bridges in 1865 and they remained a
standard of construction on the B&O Railroad for the next 15 years.
However, due to failures in the 30 years after 1840 occurring predominantly in cast
ironbridgemembers,theuseofcastironceasedandwroughtironwasusedexclusively
for railway girders and trusses. Isambard Kingdom Brunel used thin-walled wrought
iron plate girders in his designs for short and medium railway spans on the Great
Western Railway in England during the 1850s. Between 1855 and 1859, Brunel also
designed and constructed many noteworthy wrought iron lattice girder, arch, and
suspensionbridgesforBritishrailways.Inparticular,theRoyalAlbertRailwayBridge
across the Tamar River, completed at Saltash in 1859, is a significant example of a
∗
In 1847, Whipple published
A Treatise on Bridge Building
, the first book on scientific or mathematical
truss analysis.
†
The first all-iron trusses on the B&O were designed by Fink in 1853.
