the abbreviated reign of “neon” leon spinks

IGNORE THE PAST AT YOUR PERIL 55
suspension bridges were severely damaged or destroyed by the wind be-
tween 1818 and 1889.
By the late 19th century, bridge engineers were building less fl ex-
ible and heavier bridges to avoid problems with wind. John Roebling, for
example, had incorporated the lessons of the past into his landmark 1883
Brooklyn Bridge, which he consciously designed to handle strong wind.
But by the early 20th century, those earlier lessons were fading. Princeton
civil engineering professor David P. Billington wrote that Roebling’s
“historical perspective seemed to have been replaced by a visual preference
unrelated to structural engineering.” A major suspension bridge
hadn’t failed since 1889, but as Petroski points out, “the absence of failure
does not prove that a design is flawless. . . . it appears to be a trait of human
nature to take repeated success as confirmation that everything is
being done correctly.”
It wasn’t. By the 1930s, even the massive Golden Gate Bridge, for
which Moisseiff had been a consulting engineer, was behaving badly on
windy days. Its chief engineer reported a 1938 incident in which a cluster
of ripples traveled along the bridge’s roadway like an incoming set of surfable
waves. That landmark bridge eventually was retrofitted to make it
more stable.
Moisseiff was aware that wind posed a problem, but according to
Hobbs he believed, like most other engineers at the time, that wind was
far less a factor in stressing a bridge than heavy traffic and poor workmanship.
He’d even tempted fate by designing the Tacoma Narrows Bridge
with an impermeable, eight-foot-high side panel running along the outside
of the roadway that acted like a sail, maximizing the wind’s impact.
Bridge designers knew that wind occasionally moved bridges from side to
side, and they usually adjusted their designs for that lateral movement, or
deflection—a theory credited mostly to Moisseiff, who claimed his Tacoma
Narrows design would withstand a broadside wind of 120 miles per
hour, and could deflect twenty feet.