Civil Engineering Reference
In-Depth Information
through development of the equilibrium equation at the intersection of two truss
members. James Clerk Maxwell
∗
and Culmann
†
both published graphical methods
for truss analysis. Culmann also developed an analysis for the continuous beams and
girders that were often used in the 1850s by railroads. Later, in 1866, he published
a general description of the cantilever bridge design method.
‡
In subsequent years,
Culmann also developed moving load analysis and beam flexure theories that were
almost universally adopted by railroad companies in the United States and Europe.
Bridge engineers were also given the powerful tool of influence lines for moving load
analysis, which was developed by E. Winkler in 1867.
The effects of moving loads, impact (from track irregularities and locomotive ham-
mer blow), pitching, nosing, and rocking of locomotives continued to be of interest to
railway bridge engineers and encouraged considerable testing and theoretical investi-
gation. Heavier and more frequent railway loadings were also creating an awareness
of,andinitiatingresearchinto,fatigue(notablybyA.WohlerfortheGermanrailways).
North American engineers recognized the need for rational and scientific bridge
design, and J.A.L. Waddell published comprehensive topics on steel railway bridge
design in 1898 and 1916. Furthermore, Waddell and others promoted independent
bridge design in lieu of the usual proprietary bridge design and procurement practice
of the American railroad companies. The Erie Railroad was the first to establish this
practice and only purchased fabricated bridges from their own scientific designs,
which soon became the usual practice of all American railroads.
1.4.2 R
AILWAY
B
RIDGE
D
ESIGN
S
PECIFICATIONS
Almost 40 bridges (about 50% of them iron) were collapsing annually in the United
States during the 1870s. This was alarming as the failing bridges comprised about
25% of the entire American bridge inventory of the time. In particular, between 1876
and 1886 almost 200 bridges collapsed in the United States.
Most of these bridges were built by bridge companies without the benefit of inde-
pendent engineering design. As could be expected, some bridge companies had good
specifications for design and construction but others did not. Therefore, without inde-
pendent engineering design, railroad company officials required a good knowledge of
bridge engineering to ensure public safety. This was not always the case, as demon-
strated by the Ashtabula collapse where it was learned in the subsequent inquiry that
the proprietary bridge design had been approved by a railroad company executive
without bridge design experience.
§
Many other proprietary railway bridges were also
failing, primarily due to a lack of rigidity and lateral stability. American engineers
∗
Truss graphical analysis methods were developed and improved by J.C. Maxwell and O. Mohr between
1864 and 1874. Maxwell andW.J.M. Rankine were also among the first to develop theories for steel sus-
pension bridge cables, lattice girders, bending force, shear force, deflection, and compression member
stability.
†
Culmann published an extensive description of graphical truss analysis in 1866.
‡
Sir Benjamin Baker also outlined the principles of cantilever bridge design in 1867.
§
Therewerealsomaterialqualityissueswiththecastironcompressionblocks,whichwerenotdiscovered
as the testing arranged by the Lake Shore and Michigan Southern Railroad Co. was inadequate.
