03-01-2013, 12:29 PM
IMPLICATIONS OF SOLID-WALLED BALCONIES ON WIND LOADING
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INTRODUCTION
Balconies are a common feature on tall buildings, especially when the
building is facing an ocean or a lake. The key function of a balcony is to provide accessibility to the outdoor environment for pleasure. However, solid-walled balconies can have a significant influence on local cladding pressures and the overall wind-induced response of tall buildings.
Although the impact is often beneficial in reducing wind loads, there are some situations where balconies can actually increase wind loading. Beneficial or otherwise, wind loads on solidwalled balconies are not addressed in building codes. While they can be measured in a wind tunnel study, there are some broader implications that RWDI considers.
IMPLICATIONS OF CORNER BALCONIES ON LOCAL
CLADDING PRESSURES
For a building with sharp corners, high suctions can
normally be expected due to the flow separations and
reattachments and the associated vortices. With the presence
of corner solid-walled balconies, these flow patterns
can be altered dramatically. Table 1 provides a comparison
of the peak suctions (negative pressures) at several measurement
locations near the corners for one building
studied by RWDI. For this building, the influence of the
balconies was investigated by constructing and testing a
second model without the balconies. The reductions
attributed to the presence of the balconies are very
evident, reducing the peak suctions by an average of
approximately 30%.
Figure 2 shows the reduction in wind tunnel pressure coefficients
caused by the presence of balconies at the measurement
locations B2 and B3 from Table 1.
PRACTICAL IMPLICATIONS OF BALCONIES
Buildings with several individual solid-walled balconies
create unique challenges in predicting structural wind
loading using code analytical methods and may affect the
choice of methods used in wind tunnel testing.
Building codes do not typically address the influence of
balconies on cladding or structural wind loads. For
cladding this means that, without a wind tunnel test, the
code-prescribed “hot spots” must be considered despite
the knowledge that they will most likely be reduced by the
presence of the balconies. For overall structural design, it
is left up to the designer to decide how to treat the additional
surface area from the balconies. This decision can
get quite difficult when there are many balconies in line
sheltering each other. As is apparent from the previous
section the assumptions made by the designer may not
necessarily be conservative.
For these same reasons, the presence of balconies can
influence the choice of the wind tunnel testing method.
Although the pressure integration technique offers practical
and theoretical advantages over the force balance
technique, the presence of balconies will often make the
latter a more practical choice. It is worth noting that, from
a practical standpoint, the force balance technique remains
a valid and reliable approach for predicting the response
of tall buildings to wind.
SUMMARY
• Building codes tend not to address the impact of balconies,
yet they can have significant effect on wind loading.
• Solid-walled, corner balconies tend to act not only as an
architectural feature, but also as a passive aerodynamic
device reducing wind loading in many situations.
• In general, corner balconies act to disrupt the coherent
formation of strong vortex shedding, thereby reducing
wind loads acting on tall buildings .
• Local cladding pressures, overall across-wind loads, and
torsional loads can be reduced by approximately 0-35%, 5-
35%, and 15-45% respectively with the presence of corner
balconies. The amount of reduction is dependent on the
size of the balconies.
• When there is a wide face (large after-body), the torsional
loading can increase significantly when balconies are present.