Civil Engineering Reference
In-Depth Information
after construction due to concerns about the strength of wrought iron bridges under
increasing railroad loads.
1.3 STEEL RAILWAY BRIDGES
Steel is stronger and lighter than wrought iron, but was expensive to produce in the
early nineteenth century. Bessemer developed the steel-making process in 1856 and
Siemens further advanced the industry with open-hearth steel making in 1867. These
advances enabled the economical production of steel. These steel-making develop-
ments, in conjunction with the demand for railway bridges following the American
Civil War, provided the stimulus for the use of steel in the construction of railway
bridges in the United States. In the latter part of the nineteenth century, NorthAmeri-
can and European engineers favored steel arches and cantilever trusses for long-span
railway bridges, which, due to their rigidity, were considered to better resist the effects
of dynamic impact, vibration, and concentrated moving railway loads.
The first use of steel in a railway bridge
∗
was during the 1869 to 1874 construction
of the two 500 ft flanking spans and 520 ft central span of the St. Louis Bridge (now
named the Eads Bridge after its builder, James Eads
†
) carrying heavy railroad loco-
motives across the Mississippi River at St. Louis, Missouri. Eads did not favor the use
of a suspension bridge for railway loads
‡
and proposed a cast steel arch bridge. Eads'
concern for stiffness for railway loads is illustrated by the trusses built between the
railway deck and the main steel arches of the St. Louis Bridge
(Figure 1.12)
.
The Eads
BridgefeaturesnotonlytheearliestuseofsteelbutalsootherinnovationsinAmerican
railway bridge design and construction. The construction incorporated the initial use
of the pneumatic caisson method
§
and the first use of the cantilever method of bridge
construction in the United States.
∗∗
It was also the first arch span over 500 ft and
incorporated the earliest use of hollow tubular chord members.
††
The extensive inno-
vations associated with this bridge caused considerable skepticism among the public.
In response, before it was opened, Eads tested the bridge using 14 of the heaviest
locomotives available. It is also interesting to note that the construction of the Eads
Bridge almost depleted the resources of the newly developed American steel-making
industry.
The initial growth of theAmerican steel industry was closely related to the need for
steelrailwaybridges,particularlythoseoflongspan.TheAmericanrailroads'demand
∗
The first use of steel in any bridge was in the 1828 construction of a suspension bridge in Vienna,
Austria, where open-hearth steel suspension chains were incorporated into the bridge.
†
Eads was assisted in design by Charles Pfeiffer and in construction by Theodore Cooper.
‡
A suspension bridge was proposed by John Roebling in 1864.
§
This method of pier construction was also used by Brunel in the construction of the RoyalAlbert Bridge
at Saltash, England, in 1859.
∗∗
The cantilever method was proposed in 1800 by Thomas Telford for a cast iron bridge crossing the
Thames at London and in 1846 by Robert Stephenson for construction of an iron arch railway bridge in
order to avoid falsework in the busy channel of the Menai Straits. Eads had to use principles developed
in the seventeenth century by Galileo to describe the principles of cantilever construction of arches to
skeptics of the method.
††
The tubular arch chords used steel with 1.5-2% chromium content providing for a relatively high
ultimate stress of about 100 ksi.
