Cladding University
Founded 1997
Testing 201 - Intermediate Mockups
Instructor: Steve Strebel, ALT Cladding and Design
The typical cladding mockup consists of several important tests. These tests are explained in detail in this class.
Class syllabus
Air infiltration tests
Water leakage tests
Structural tests
Seismic tests
Air Infiltration Tests
Air infiltration tests are the first tests conducted on the mockup. The purpose of the tests is to measure how much air passes through the wall under a certain amount of pressure. There is always a pressure differential between the outside and inside of the building that tries to drive air through the wall to equalize the pressure. This pressure differential is caused by wind and the operation of the building's mechanical systems such as air conditioning.
There are two basic air infiltration tests. One to measure the air passing through the typical wall and one to measure the air passing through the operating windows. Due to the nature of operating windows, they will tend to leak more air than typical fixed lights of glass.
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The air infiltration of the curtain wall is measured by covering the specimen
with plastic sheet and measuring the chamber air leakage.
The photo to the left shows a plastic sheet being installed over the mockup specimen. The edges of the sheet are sealed with tape.
Since the plastic sheet is air tight, the leakage at this point is assumed to be entirely from the test chamber. After this reading is recorded, the plastic sheet is removed and the air leakage is measured again. This time the leakage is the gross leakage of the specimen and the chamber. By subtracting the first reading (the chamber leakage), the net leakage of the curtain wall is determined.
Operating windows are tested similarly. However, instead of covering the window with plastic sheet, only the joints around the perimeter of the window are covered with tape. The tape seals the window joints. By measuring the air infiltration with the tape on and then the tape removed, the net infiltration though the operating window is determined.
Water Leakage Tests
Water leakage is measured in two ways. Static water tests and dynamic water tests. In both cases a spay rack is positioned in front of the test specimen to spray water on the wall while it is being tested. The spray racks are designed to cover the wall with a specified quantity of water per minute per area of wall to be tested.
The dynamic test simulates the driving or
pulsing action of a rain storm. The most common method to do this is to run an
airplane engine while the wall is being sprayed with water. The engine is mounted on
a frame - it is not in the airplane. The photo to the left shows a dynamic test in
progress. Note the spray racks in front of the wall being tested. In this
case, the airplane is positioned to test the corners of the mockup. Normally, it is
positioned directly in front of a flat wall mockup. Sometimes, on large mockups,
several tests must be performed in order to move the airplane engine so that all walls are
properly tested.
Dynamic tests can also be done by pulsing air with large pistons while spraying the face of the wall with water. When the walls are tested like this, the mockup chamber is constructed such that the exterior of the wall is in the chamber.
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The other type of water test is the static test. See photos above. The photo on the left is a view from the side of the mockup. The photo on the right is a close-up of the water being sprayed on the mockup. Note that water is being applied to two surfaces at this corner. It is important to apply a proper amount of water at an appropriate rate and distribution pattern to have a meaningful test.
In a static test, the wall is again sprayed with water. However, instead of a dynamic wind, a static (constant) pressure is applied to the specimen. The static pressure is either an external positive pressure or an internal negative pressure that draws air and water into the wall.
To achieve the pressure difference, air on the inside of the mockup chamber above was pumped out of the chamber creating a negative pressure on the interior of the building. Note that this pressure differential occurs on real buildings and is a major cause of hard to find leaks. It is vital to have your wall designed to stop leaks under pressures like this.
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In both cases, the tests
are successful if no uncontrolled water penetrates the wall. Note that
water can enter some areas on the interior side of the wall and be controlled such that it
is retained in these specially designed areas where it can be drained to the exterior.
The photo to the left shows an example of uncontrolled water leakage. In this case, water has leaked from a joint in the rail above and has run down the jamb forming a small puddle of water on the window sill rail. (In the corner next to the glass.) Often, where you see the water is not at the location of the leak.
The "rough" surfaces on the very left of the picture are the mockup chamber closure as this leak occurred at the side of the mockup.
Our True Stories page shows some more dramatic examples of water leakage.
Structural Tests
The primary structural test is to apply a
static load to the mockup simulating the maximum load it will see on the building.
In typhoon areas, the load can be very large. The photo to the left shows the glass
of a mockup being deflected by the structural test. The pipes and bars of the spray
rack can be seen in front of the wall. The reflections of these pipes are curved as the
glass is deflected. Without the load, the reflections will be strait
lines.
Usually, there will be six structural wind load tests. Loading at 50%, 100%, and 150% of the positive design load. And loading at 50%, 100%, and 150% of the negative design load. Positive load is load that pushes the wall toward the interior of the building and negative load tries to suck the wall off the building. Before each test, a partial load is applied in the direction to be tested, to take slack out of the system.
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Deflections of the
curtain wall framing members, glass, and panels are measured at the 50% and 100%
loading. These deflections must be within the specified criteria in order for the
test to pass.
The photo to the left shows a typical arrangement to measure glass deflection. The measuring instrument. called a dial gage, is positioned in the center of the glass and the deflection of the glass is being measured relative to the supporting horizontal rails. Note that the red bar spanning from top rail to bottom rail is what the gage is attached to.
The photo also shows a gage measuring the lower horizontal rail. Framing member measurements are usually taken at the center of spans, at cantilevers, and at anchors.
Excessive deflection must be avoided in cladding design to avoid damage to the wall. In addition consideration must be given so that large deflections in the wall do not unnecessarily alarm the occupants of the building.
The most common other structural test is the window washer tie-back or window
washer track test. Window washer tie-backs sockets in the wall where a pin with a
cable to the basket can be inserted. They are not intended to hold up the window
washer basket. They are used to keep the basket from swinging excessively in wind gusts.
Washer tracks are tracks built into the mullions (vertical framing members). When these are used, the washer basket moves up and down the building with rollers captured in these tracks. Again, the tracks are intended to keep the basket from being swayed in a wind gust.
The photo shows a window washer tie-back being tested by pulling it with a cable and a specified load.
Seismic Tests
Seismic tests are done on the mockup to verify that the wall can take the expected building movement that will occur during an earthquake. When an earthquake happens, the floors of the building move slightly sideways from the floors above and below. The curtain wall must be able to accommodate this movement.
To test this, one floor (floors are simulated) of the mockup is designed to be movable. This floor is shifted back and forth a specified distance by hydraulic cylinders. In this way the relative movement between floors that will occur during an earthquake is simulated.