Curtain
Wall
 Structural
Integrity |
Wind Pressure
The wind pressure is critical
in the structural design particular in the tall building. The framing
members, panels and the thickness of glass, are determined by maximum wind
loads. The pressures and vacuums alternately created by high winds
subject framing members and glass to stress reversal. The structure should
always be subjected to pressure acting first in one direction, then reverse
in direction. On high-rise buildings the negative pressure may often
be much higher than the positive pressure. The structural members
and wall anchors should be designed to withstand these forces.
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A 64-storey building model
triangular in plan which
was tested in wind tunnel |
Test result: Distribution
of positive wind load |
Test result: Distribution
of negative wind load |
Dead Load
Unlike the wind forces,
the self weight of the curtain wall is static and constant. Because
of the materials used in curtain walls is relatively light in weight, it
is a force of secondary significance. It is less significant as wind
in the design.
Temperature Effect
The effect of temperature
changes uniquely significant due to the high coefficient of expansion of
aluminum. But the other causes including wind action, gravity forces and
by deformations and displacements of the building frame should be taken
into consideration as well.
Movement may take in the
following location:
|
Movement within the wall
components themselves |
|
Relative movement between
between the components |
|
Relative movement between
the wall and the building frame |
In the design, provision of
movement for the above connections should also be taken into consideration.
| Weathertightness |
It is necessary to protect
against both water leakage and excessive air infiltration. The wathertightness
of the window system is closely related to proper joint and seal design.
The pressures and vacuums alternately created by high winds cause rain
to defy gravity, flowing in all directions over the wall face which contribute
to potential water leakage. The forces acting to move water through
an opening can be summarized in the following diagrams:
In the early design, it tried
to provide all joints at their outer surface with a permanently waterproof
seal. However, this approach was essentially impossible and abandoned
due to the continual movement of the members. To solve the
problem, an internal drainage system is made which provide a guide to collect
the water and drain it away from the joints. In the modern technology,
"pressure equalization" method may be used as well. "Pressure equalization"
method is based on the "rain screen principle". The "rain screen
principle" is to eliminate the pressure differential on the different sides
of the curtain wall. The "pressure equalization" quote
the 1962 Norwegian publication, "The only practical solution [to preventing
water leakage] is to design the exterior rain-proof finishing so open that
no super-pressure can be created over the joints or seams in the finishing.
This effect is achieved by providing an air space behind the exterior finishing,
but with connection to the outside air. The surges of air pressure
created by the gusts of wind will then be equalized on both sides of the
exterior finishing". This is not simply a ventilated space, in which
air currents may occur due to pressure differences within the space. To
be effective it must be a confined air space, and it is this essential
that imposes many of the design complexities encountered in the application
of the rain screen principle.
| Other
Considerations |
| |
Thermal insulation |
| |
Sound insulation |
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