Aerodynamics and Aeroelasticity
The limits of the capacity of structures are constantly being verified and
In this development the high strength of the materials of today is usually
utilized, which enables us to design slender structures with long spans and
Wind acting on structures becomes more and more important in this connection in
more than one way. Longer spans in themselves often cause the wind load to be
the dominant load. In addition the dynamic characteristics of the structure
become important for the response of the structure under the wind action.
The last-mentioned condition, determined by the aerodynamic behaviour of the
structure, often sets the limit for the possible designs of the structure
expressed by e.g. the span or the height. The structure may show an unacceptable
performance - either by showing direct aerodynamic instability
(flexural-torsional flutter as known from the legendary Tacoma bridge), or by
giving comfort or fatigue problems. In the worst case phenomena causing
inexpediencies or directly threatening safety may appear at low wind velocities.
ES-Consult has worked with these problems in detail in relation to projects and
in research and development works.
Certain aerodynamic phenomena can be encountered by special features of the
design. An example is vibrations caused by vortex shedding. The phenomenon,
which is known from chimneys and bridges, is very dependent on the natural
damping of the structure. It is specially noticeable if the damping of the
structure is small and if the structure is flexible, whereby the frequency of
the vortex shedding may be locked in an interval to which the structure is
sensitive. To overcome this the structure may be built with "appendages", which
eliminate the damaging rhythmic vortex shedding, or the structure may be
equipped with tuned mass dampers.
ES-Consult has worked on these problems in relation to various projects: The
Great Belt Bridge, fatigue assessment of slender steel chimneys, etc.
Staff members in ES-Consult have written several papers on the subject. A
list of the papers is available.