by the wind tunnel tests. Softening the corners of the structure such as the unique
“double stair step corner façade” in Taipei 101 in Taiwan, can dramatically reduce the
crosswind oscillations. In Petronas towers in Kuala Lumpur, tapering and in Shanghai
Center in China, tapering along with twisting of the structure were done to confuse the
wind to lose its consistence. Creating corner slots in the building to allow the wind to
bleed through as in 151 Incheon tower in South Korea, can suppress the vortex shedding while reducing the base moment.
Apart from the above mentioned shape strategies, special damping systems can be
installed in the tall structures. Through these systems, the energy resulting from the
oscillations due to vortex shedding can be drawn out. Taipei 101 uses such a damper
to prevent damages due to strong winds.
Although vortex shedding is a common mode of structural failure of tall structures,
it is slightly overlooked due to the complexity of analysis. Analyses can be carried
out through theoretical formulations, numerical algorithms, wind tunnel tests, full
scale experiments and code provisions. Accurate analyses of this problem can only be
achieved by the joint application of all these techniques. Since, vortex shedding is a
dynamic process, in order to get realistic structural responses to this phenomenon, it
is important to be simulated dynamically. With the vast growth of tall structures, concentration of tall structures will increase in the urban cities in the future. Ultimately,
the population will expand and grow around these concentrated areas. Therefore, it is
of utmost importance to identify the impact of vortex shedding to prevent the failure
the phenomenon of resonance will occur
resulting in crosswind oscillations of the
structure. Thus, stiffening the building to
increase the natural frequency, thereby
reducing the risk of resonance can be
done. Although the approach is suitable
for moderately tall structures, for super
tall structures, this is not practicable and
is costly. This is because; it requires a considerable amount of steel and concrete
to make a very tall structure much stiffer.
Therefore, several other approaches have
been identified.
of a structure that can lead to catastrophic damages for nearby structures and most
crucially the lives of people.
KANCHANI BASANAYAKE
Department of Civil Engineering
(Fourth Year)
References:
1. Thompson,J.,Vortex Shedding & Tall Structures – The Uncertainties of Wind
Loading, (online) Available at: www.spartaengineering.com
2. Giosan, I. ,Vortex Shedding Induced Loads on Free Standing Structures ,(online)
Available at: hwww.wceng-fea.com/vortex_shedding.pdf
3. Irwin, P.A., Wind Issues In The Design Of Tall Buildings, (online)
Available at: http://peer.berkeley.edu/tbi/wp-content/uploads/2010/09/Irwin.pdf
The simplest approach is to create turbulence so that the fluid flow cannot
form a vortex sheet. A disturbance on
the structure in the form of spirals will
facilitate the breaking of vortices, creating turbulence. This is commonly seen
being applied at the upper parts of chimney stacks. Another technique is to vary
the cross section of the structure along
its height. This strategy was successfully
implemented in the construction of Burj
khalifa, and its successfulness was proven
Petronas towers, Kuala Lumpur • Source: en.wikipedia.org
Gauge Newsletter
University of Peradeniya
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