Wind Loads for 19th Century Bridges:Design Evolution, Historic Failures,and Modern Preservation 2007

Preservation of 19th century truss bridges can be accomplished by
rehabilitation into pedestrian bridges.But most vehicular truss
bridges from the 19th and early 20th centuries were designed for
much lower wind pressure than mandated today.Engineers trying
to rehabilitate such bridges often find insufficient lateral resis-
tance in the historic structures.Engineers involved with suchre-
habilitation projects follow the Guide Specifications for Design of
Pedestrian Bridges (AASHTO1997),which basically mandatesa
wind pressure of 3.59 kPa (75psf).How did his requirement
originate?This paper will explore 19 th and early 20 th century
event significant to the development of standards for design wind
pressure.
The success of the patent truss bridge in the 19 th century had
its roots in the westwardex pansion of the United States,which
created a demand for bridges of increasing span and capacity in
ever-increasing numbers.The principal advantages of trusses,
whether they are timber,iron,or steel,are economy and speedof
construction.However,these advantages are not attained without
trade-offs:light weight trusses were—andare—susceptible to
wind.
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