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November 20, 2012
Wind and high-rise buildings by
Windtech
High-rise buildings are particularly prone to a range of wind
effects which are dependent on their height and form. In fact, the
taller the building, the more wind loads become the single most
important factor that will impact on the design of a tall building.
This article sheds some light on the workings behind the scene
during the design process to address the implications of wind
loads. This also furthermore looks into other issues that are
brought about by wind which can be of potential nuisance to the
owner/occupants and in the extreme case, cause catastrophic
effects.
The taller the building structure, the more significant its form
should be shaped due to the forces of the localised winds. Two
high-rise buildings situated at the same location and equal height
and volume, can experience very different wind forces depending
on their design and orientation. This is due to the fact that high-
rise buildings are in fact dynamic and not static structures. Their
motion is compounded by the way wind traverses around the
structure, applying varying pressures over the building surface.
Pressure loads experienced on a buildings’ surface varies due to
a number of factors, including the design of the building, its local
surrounds and local wind climate. Wind tunnel testing is used to
accurately establish the effect of these parameters on the actual
wind forces experienced. The measured wind loads on a building
can vary significantly due to different design that may be
employed. If this effect is not considered during the design
process, the cost of building the structure may become excessive,
and the project rendered unfeasible. For this reason, some
architects are considering and also modelling the effects due to
wind for a number of variations of the buildings concept,
optimising the form and orientation of the building for their specific
site.
The form of the building does not only impact the forces on the
structural framing that supports the building, but also on the
amount of motion that the structure exhibits. If the motion is
excessive then it can lead to a feeling of tiredness amongst
occupants in certain areas. A lot of research on this subject has
been undertaken over the past few years, particularly in Hong
Kong. It has been established that for a given level of
acceleration, the stiffer the building structure, the more likely that
occupants are to feel that same level of acceleration. This is
largely due to the fact that our bodies tend to respond to faster
oscillations of up to 1 to 2 cycles per second. This potential for
Shanghai World Financial Center,
Pudong, Shanghai - Height 492
meters, designed by KPF

2. occupant discomfort due to building motion can be accurately
predicted through detailed wind tunnel testing. In cases where the
oscillations become excessive, and there is little that can be done
to the structure’s design to reduce this, the installation of a
mechanical device called a damper can be considered. A tuned
damper is a device used to reduce the amplitude of the buildings
oscillating motion under wind loads. When installed, dampers are
located near the top of the building, and are often the most
effective method of reducing the discomfort due to the building’s
motion.
All high-rise buildings require lifts to transport occupants
throughout the building. Lift shafts however, not only provide a
void for lifts, but also act as a vent which allows airflow throughout
the height of the tower. Very tall lift shafts or vents can generate
an effect known as the stack effect. This effect occurs as a result
of the difference in temperature of the internal and external air
and openings connected to the shaft. This effect can be further
driven by internal cooling/heating in more extreme environments,
even in the case where the shaft seems to be sealed to the
outside. Small leakages such as from air intakes or exhausts can
expose the building to the effects of potentially high temperature
differences between the inside and outside air. In hot humid
climates, the difference in temperature between the inside and
outside of the building will tend to cause the heavier cooled air at
the top of the lift shaft to fall towards the base of the shaft. This
can generate a significant amount of air flow and pressure on the
lower level lift doors, resulting in discomfort for occupants in lift
lobbies, and in some cases can cause the lift doors to jam
resulting in significant disruption. Windtech have inspected such
situations on existing buildings, and have provided solutions to

3. mitigate this effect.
Another effect which cause lift doors to malfunction is the
issue of wind entry and pressurisation of entry/lift lobbies. This is
caused as a result of external openings located in different
pressure zones, directly connected to the lobby or lift shaft. There
are a number of different ways to eliminate this problem, with this
effect able to be recognised during the design phase through
wind tunnel testing. Mitigation can be achieved by providing
equalisation of the pressure across the lift door or to design
effective air-locks for the entries, which are generally the main
source of the high pressures in lobby spaces.
Wind-noise is another phenomenon known to occur in some
high-rise buildings. This effect can be generated from a range of
possible sources including facade detail and articulations.
Windtech Consultants have had extensive experience in both
identifying elements on a building façade or a facade detail that
can potentially generate excessive wind noise. It should be noted
that, although not common, it is also possible for internal details
to be a source for wind noise generation.
These are just some examples of wind effects that need to be
considered when designing a high-rise building. Examples of
other wind related effects include pedestrian comfort under strong
winds, wind pressures on the façade cladding and façade
attachments, dispersion of exhausts on air quality, natural
ventilation and wind-driven rain. (By Tony Rofail, Director,
Windtech Consultants, Sydney)
Contact Windtech Consultants
Website www.windtech.com.au
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