Cladding University
Founded 1997
Testing 101 - Introduction to Mockups
Instructor: Steve Strebel, ALT Cladding and Design
There are two two basic types of mockups commonly used in the cladding industry: Visual
mockups (Testing 102) and mockups used to test the cladding
design and implementation (this class).
Class Syllabus
Purpose of the mockup
Mockup specimen
Common tests
It's not just testing
Contractor's approach
Purpose of the Mockup
Mockup tests are quite common when a custom curtain wall is to be used on a building. The mockup serves several purposes including:
- Test the wall for air tightness
- Test the wall for water tightness
- Insure that the wall is structurally sound
- Verify the wall can accommodate the required seismic movement.
- Verify that washer tieback attachments are adequate.
- Expose flaws in the design.
- Verify the wall can be quickly and easily assembled.
- Verify the wall can be quickly and easily erected.
- Educate a few of workers that will install the wall at the job by letting them "practice" the erection on the mockup.
- Check the quality of the fit and finish of the cladding contractor's work.
- A final visual check of the design.
Mockup Specimen
The mockup specimen is usually a full scale portion of the typical wall. The size of the specimen varies greatly depending upon the number of systems on the job and the complexity of each system. Generally, the mockup should be no less than three bays wide by two typical floor heights tall. This size allows all of the typical joints in the typical wall to be tested for weatherability and provides enough size to reasonably test the wall structurally. See sketch below.
It is highly desirable to test at least one corner condition in the mockup.
Ideally, the typical outside and inside corners (if applicable) will be included in the
specimen. Special features should be tested if they will occur on the wall in
quantity.
Some building require a much larger mockup as shown in the photo to the left. This mockup has two outside corners, an inside corner, several different wall types, and a large fin element feature.
The mockup is a significant investment in both it's cost and it's implications for a successful curtain wall. It is important that you have ALT Cladding and Design choosing an effective and appropriate specimen for your job.
Common Tests
Mockups are usually tested for:
- Air infiltration
- Water penetration
- Structural Adequacy
- Seismic movement
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Air infiltration
tests measure the amount of air that can pass through the wall. This is an important
factor when considering the heating and cooling loads on the building.
Air infiltration is also a rough indication of the acoustic performance of the wall too. Although there are many important considerations in assessing acoustic performance, a simple rule of thumb is that a tight wall will transmit less noise than a wall where air can pass through easily.
The photo to left shows a mockup specimen in the process of being tested for air infiltration. The view is from side standing at ground level. As part of this test, the specimen is covered with plastic which can be seen in the photo. The vertical red bar (left center) is part of the spray rack, which is not used in the air infiltration test.
Water penetration is the most obvious test for curtain walls. While a tenant will probably never notice if a wall leaks a little too much air, they will certainly notice if the wall leaks any water.
Leaking water is very expensive for the building owner. It can damage expensive tenant furnishings as well as the cladding system itself. Leaking water usually requires expensive remedial work to patch the leak. It is therefore important to reduce the likelihood of leaks by testing the wall in a mockup.
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There are two basic types of
water tests: dynamic and static. The dynamic test simulates the pulsing or driving
action of a rain storm. This is done by either blowing air and water at the wall
with a big fan (an airplane engine) or by pulsing the pressure applied to the wall while
spraying water. The photo to the left shows a typical dynamic test in progress.
Some dynamic testing is done by pulsing the chamber pressure rather than using an airplane engine.
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In a static water test, water is sprayed on the mockup while a negative
pressure is applied to the inside of the wall. The photo at the left shows a static water
test in progress. Note that the water is simply being sprayed on the wall from the
outside. There is no fan or pulsing action "blowing" the water. The
negative pressure on the inside is the force driving the water to the inside.
The primary structural test in curtain wall testing is to test the strength of the wall against the expected maximum wind load. To do this test the specimen is pressurized with a static pressure to see if it can withstand the load.
How hard can the wind blow? In typhoon areas, wind pressures of over 5 kPa are not uncommon. This is a pressure of 5 kilo-Newtons (~500 kilograms) per square meter or about 100 pounds per square foot. If a single light of glass is one meter wide by two meters tall, the load on just this one piece of glass is 10 kilo-Newtons or 1,000 kilograms or 2,100 pounds. The load on a single anchor connecting the curtain wall to the building can easily reach 20 kN (~2,000 kg or ~4,200 lbs). To demonstrate a safety factor, mockup testing is usually goes up to 1.5 times design load.
If your building is in a typhoon region, it is especially important to have a consultant experienced in such high loads. ALT Cladding and design, with offices in Manila and previously in Taipei, is very experienced in Typhoon loading.
Other structural tests that may be required include window washer tie back brackets, window sill foot loads, and missile impact loads.
Seismic mockup tests usually are designed to insure the wall can handle the expected lateral floor to floor displacement that will result when the building experiences an earthquake. When an earthquake hits the building, it will start to sway. As it sways, each floor deflects a little bit relative to the floors above and below it. This deflection is typically in the range of 6 to 20 mm per floor. The mockup test insures that the curtain wall can accommodate these movements without damaging itself.
Note, the layman may think the answer to make the curtain wall handle seismic loads is to make the wall stronger. This is not the way to do it. The curtain wall can never be made strong enough to resist the movement of the building. Therefore, the answer is to allow the curtain wall to move with the building so as to minimize the loads it will see. This is the type of design specialization that ALT Cladding and Design excels in.
It's Not Just Testing
As mentioned above, the mockup serves as more than just a test specimen. The mockup is where the typical design is tested and verified with respect to assembly and erection. Custom curtain walls give each building a unique look. However, it is this same uniqueness that means that each wall is being designed and built for the first (and last) time.
It is very important to verify that this one-of-a-kind wall system can be put together and constructed properly and efficiently. The mockup provides an excellent opportunity to insure this. It is not uncommon to refine the design or erection procedure based on how well the mockup goes together.
The mockup should be looked at as both a test specimen and a learning tool. Ideally, the curtain wall manufacturer will have one or two supervisors assembling the mockup from the factory crew that will be assembling the cladding systems in the factory. Probably, more important, the contractor should have one or two foreman crew from the crew that is going to install the curtain wall on the job erect the mockup. It is a always a plus when the people who will be responsible for constructing the wall get a chance to see the problems and "practice" on the mockup before the job begins.
The mockup serves as the final chance to insure the visual intent of the architect is realized. Only when the real full size components are all assembled together, can the true visual impact of the wall be appreciated. Minor changes improving the aesthetics may be requested after the mockup, by the architect, to correct things not foreseen until the mockup is assembled.
Fit and finish of the wall system is also established at the mockup. However, because the mockup parts are usually short run components done just for the mockup, some mockups have a lower quality than required for the job. These items need to be identified by a qualified consultant and noted so that the contractor is held to the highest possible standard for the job material. ALT Cladding and Design routinely documents the assembly, and erection of mockups for our clients to fulfill this need.
The Contractor's Approach
As explained above, the mockup is an important process in the design and creation of a quality wall system. Smart contractors will use the mockup as a learning experience to maximize the efficiency of the design. The mockup can identify problems such as water leakage that will cost both the contractor and building owner time and money. In addition, it can identify assembly and erection problems that, if not corrected, could lead to production problems, quality problems, or delays in the erection of the curtain wall.
Unfortunately, many, not all, curtain wall contractors look at the mockup as just something they have to pass in order to continue with the project and keep billing the owner. Sad but true. We have seen contractors caulk areas that are not supposed to be caulked, weld brackets where there is no weld called on the drawings, sneak gaskets and sponges in splice joint, and on and on. Many of these things are not a problem so long as the "modifications" are noted and carried through to the job. Too often, this is not the intent of the contractor who just wants to pass the mockup.
It is not enough to have the consultant witness the test. Today's building owners need to have a trained eye watch and document the construction of the test specimen in addition to the test itself. If you don't know exactly what you are testing, the test does not have much value. ALT provides this service to building owners throughout Asia.