Smithfield Street Bridge - Pittsburgh, PA
N 40° 26.049 W 080° 00.165
17T E 584584 N 4476422
The Smithfield Street Bridge was the first bridge in America to use the lenticular - or lens-shaped - truss design; and it was one of the first major bridges in the U.S. built primarily with steel. It carries Smithfield St across the Monongahela.
Waymark Code: WM3KM1
Location: Pennsylvania, United States
Date Posted: 04/16/2008
Views: 47
From the ASCE
web site:
"Three rivers - the Allegheny, Monongahela, and Ohio - join in
Pittsburgh, making the city a natural site for the building of
bridges. But the Smithfield Street Bridge stands apart from other
Pittsburgh bridges for several reasons: it replaced structures by
two well-known bridge engineers, Lewis Wernwag and John A.
Roebling; it was the first use in America of the lenticular - or
lens-shaped - truss design; and it was one of the first major
bridges in the U.S. built primarily with steel.
The Smithfield Street Bridge also is significant because it was
designed by the renowned engineer and bridge designer Gustav
Lindenthal, who was only 32 years old when he conceived it. The
graceful appearance of the bridge's twin 360-foot spans
foreshadowed a new approach to bridge-building-when Lindenthal
became commissioner of bridges for the city of New York in 1902, he
initiated the formal practice of engineers and architects
collaborating on all major bridge projects.
Facts
Lindenthal originally specified Bessemer steel -- made in blast
furnaces -- for the Smithfield Street Bridge, but later decided on
open-hearth steel, manufactured locally, because it could be made
more uniformly and of higher quality. Other bridges for which
Lindenthal is known include the Hellgate Bridge over the East River
and the Queensborough Bridge, both in New York City.
The Smithfield Street Bridge was built on piers constructed in
1880 for a previous project that had been planned and then
abandoned by the company responsible for the constuction and
operation of the bridge. By building on the downstream side of
piers and designing a detachable sidewalk on the upstream side,
Lindenthal provided for the bridge's eventual expansion from its
original 48-foot width.
In 1889, a second deck was added to the Smithfield Street Bridge
to carry horse-drawn streetcars; ten years later, the deck was
widened to accommodate electric trolleys. In 1911, the tolls were
removed, and in 1915, the original wrought iron portals were
replaced with replicas made of cast steel.
A thorough renovation in 1933 replaced the bridge's steel floor
system with structural aluminum beams and prefabricated aluminum
decking.
A second renovation, in 1996, increased the bridge's load limit
from three to 23 tons. It also restored the bridge's original color
scheme -- including royal-blue trusses and sandstone-yellow portals
-- while replacing the six copper finials that crown the
elaborately decorated portals.
Another well-known bridge using the lenticular truss design in a
double span is the Saltash Railway Bridge across the River Tamar in
Cornwall, England, designed by noted engineer Isambard K. Brunel in
the late 1850s.