Chapter 6
AEROELASTICITY IN CIVIL
ENGINEERING
Certain types of civil engineering structures can be subjected to aero-
dynamic forces generated by structural motions. These motions, called
self-excited, are in turn affected by the aerodynamic forces they gener-
ate. Behavior associated with self-excited motions is called aeroelastic.
The flutter of the Brighton Chain Pier Bridge (Fig. 6.1) and, more than
one century later, the original Tacoma-Narrows Bridge (Fig. 6.2) are
notorious examples of aeroelastic behavior. Tall chimneys and buildings
may also respond aeroelastically and need to be designed accordingly.
The John Hancock building in Boston, which has a relatively flat shape
in plan (Fig. 6.3), has experienced across-wind and torsional motions
of sufficient severity to warrant the installation of a large tuned-mass
damper system at its top. These motions may have been due to aeroelas-
tic effects
∗
. Under certain conditions power lines experience aeroelastic
behavior referred to as galloping .
Aeroelastic phenomena of interest in civil engineering differ from those
studied in aeronautical engineering in two important ways. First, civil
engineering structures are typically bluff, although in modern suspended-
span
†
bridge design streamlined box-like deck shapes are increasingly
being used. Second, unlike flows typically considered in aeronautical
engineering, the flows in which civil engineering structures are immersed
are in most cases turbulent. Atmospheric turbulence depends upon the
∗
Recent research on tall buildings with relatively large ratio between depth and width suggests
that this was indeed the case - see Section 6.6.2. To the writers’ knowledge, for legal or other
reasons, detailed technical reports on the wind-induced behavior of the John Hancock building
are not available in the public domain.
†
The term “suspended-span bridge” covers both suspension bridges and cable-stayed bridges.
299
