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Air, Water, Structural - Mock-up



Q:

What is a pre-construction mock-up?

A:

A pre-construction mock-up is a full-size representation of the proposed exterior wall system built before the exterior wall design is completed in order to study proposed construction details, test for performance and possibly judge appearance of the exterior wall system.

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Q:

Why performance test a pre-construction mock-up?

A:

Construction professionals use mock-ups in an attempt to reverse the old adage that there is never enough time to do things right, but there's always time to do them over. Mock-ups are great tools not only to verify design but for logistics of project installation procedures and QC. It is imperative to utilize the same construction personnel to build the mock-up that will be at the project site. With proper planning, costs associated with mock-up testing generally are a minimal impact to overall project costs and is money well spent compared to fixing an entire building after the fact. Mock-up testing can be a very inexpensive insurance policy and valuable learning tool.

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Q:

What types of wall systems has Architectural Testing tested?

A:

The systems tested by Architectural Testing include but are not limited to stick built systems, unitized systems, unit and mullion systems, column cover and spandrel systems, window wall and slab cover systems, cavity walls, point supported glass, structurally glazed walls, cable supported glass walls, rain screen pressure-equalized wall systems, skylights and more. Since the mid 1980's ATI has conducted thousands of tests on mock-ups from all over the world.

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Q:

What size should a curtain wall mock-up be?

A:

A curtain wall mock-up can range from 100 ft2 to over 2,000 ft2. The size of the building, various building conditions, can all be factors used in determining the size of the curtain wall mock-up. The architects, consultants, building owners, and manufacturers determine what building conditions need to be tested in the case of specific projects. Minimum size requirements are specified in the test specimen section of ASTM E 283, E 330, E 331, and E 547. For multi-story buildings, most conditions can be included in mock-ups that are two stories high and three units wide per AAMA 501-94.

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Q:

What are the referenced ASTM and AAMA test methods for conducting air infiltration, water penetration and structural performance on exterior wall mock-ups?

A:

Air infiltration is conducted in accordance with ASTM E 283-91, Standard Test Method for Determining the Rate of Air Leakage Through Exterior Windows, Curtain Walls, and Doors Under Specified Pressure Differences Across the Specimen. Static water penetration is conducted in accordance with ASTM E 331-00, Standard Test Method for Water Penetration of Exterior Windows, Curtain Walls, and Doors by Uniform Static Air Pressure Difference. Dynamic water penetration is conducted in accordance with AAMA 501.1-94, Standard Test Method for Exterior Windows, Curtain Walls and Doors for Water Penetration Using Dynamic Pressure. Structural performance is conducted in accordance with ASTM E 330-97, Standard Test Method for Structural Performance of Exterior Windows, Curtain Walls, and Doors by Uniform Static Air Pressure Difference.

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Q:

What other tests are exterior wall mock-ups subjected to?

A:

Many curtain wall mock-ups are subjected to vertical and horizontal interstory movement. Simulated floor slab conditions are mechanically fastened to permit hydraulic jacking side to side and up and down. The purpose of these movements is to simulate wind induced movement of multi-story buildings and live load conditions. Horizontal movements due to seismic events are performed on occasion as well. Thermal cycling and condensation evaluations are also performed frequently on curtain wall systems. Stud wall chambers covered with foam insulating board are erected on the exterior of the mock-up. The curtain wall mock-up is subjected to alternating hot and cold cycles maintained for two hours per cycle. Window washer anchorage load tests, supplemental water resistance following sealant removal, negative load sealant bonding tests are performed when specified.

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Q:

What is a basic test procedure?

A:

The following is a basic procedure or test sequence:

1. Preload @ 50% D.P.
2. Air infiltration
3. Static water resistance
4. Dynamic water resistance
5. Structural performance @ D.P.
6. Structural performance @ 1.5 x D.P.

D.P. = Design wind pressure
S.T.P. = Structural test pressure = 150% D.P.
W.T.P. = Water test pressure = 20% D.P.

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Q:

What is a complex test procedure?

A:

The following is a complex procedure or test sequence:

1. Preload @ 50% D.P.
2. Air infiltration
3. Static water penetration
4. Dynamic water penetration
5. Structural performance @ D.P.
6. Repeat air infiltration
7. Repeat static water penetration
8. Repeat dynamic water penetration
9. Interstory movement displacement (vertical)
10. Repeat air infiltration
11. Repeat static water penetration
12. Repeat dynamic water penetration
13. Condensation evaluation
14. Thermal cycle
15. Repeat air infiltration
16. Repeat static water penetration
17. Repeat dynamic water penetration
18. Supplemental static water penetration
19. Structural overload at 75% and 150% D.P.
20. Supplemental negative structural load
21. Seismic (lateral displacement)

D.P. = Design wind pressure
S.T.P. = Structural test pressure = 150% D.P.
W.T.P. = Water test pressure = 20% D.P.

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Q:

How does the project specific mock-up typically progress?

A:

A pre-construction mock-up test should be scheduled well in advance of the final production schedule for a building. A timely mock-up test will identify design, fabrication, and installation deficiencies with ample opportunity to make corrections relatively easily and less expensively. A properly executed mock-up test program provides relatively inexpensive insurance that the exterior wall being tested will perform as intended.
A successful pre-construction mock-up test requires cooperation, coordination, and understanding of the responsibilities between the architect, general contractor, curtain wall manufacturer, installer, and testing laboratory.
The contract documents must include specifications and drawings for the pre-construction curtain wall mock-up. The specification writer must clearly identify what tests are to be performed, the methodology for performing the test, and the performance criteria. It is very important that the architects for the project prepare a schematic drawing of the architectural mock-up, which should include a dimensioned elevation and plan view of the mock-up. The curtain wall manufacturer must also prepare detailed drawings of the mock-up, which are inclusive of glazing, anchorage, and sealant details.
ATI utilizes the architect's and curtain wall manufacturer's drawings to prepare a drawing of the building frame representation (test chamber design), where the building structure is typically simulated with structural steel beams and columns.
Once approval is given of the test chamber design, ATI constructs the test chamber and schedules a mock-up install date. The mock-up is then erected by the appropriate personnel and upon completion of the installation and adequate sealant cure time, the mock-up is performance tested.

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Q:

What are some common mistakes made?

A:

Architectural Testing has tested hundreds of mock-ups. We find most mistakes are workmanship related and are a result of not following recommended application or installation details. This is also relative to understanding and adhering to the project specifications. Some specific mistakes are as follows:
-         Improper sealant selection/application
-         Not providing adequate details at gutters or flashing terminations
-         Gutters and flashings are installed without end dams or proper splice seals
-         Failure to coordinate a second line of defense against water penetration from one contractors' work to another
-         Inadequate design and installation of the system including anchorage and working joints, to effectively accommodate fabrication/construction tolerances and building/thermal movements
-         There is at times a tendency to make modifications to a system during performance testing that are not practical for job application or are not carried through in the field
Again, over the years, ATI has been witness to remediation to mock-ups resulting mostly from workmanship issues. This is best learned in the laboratory setting so it can be taken to the project site. Although not the majority, design changes are also made as a direct result of the performance testing process. Identifying and correcting these mistakes can be thought of as a reprieve from costly problems down the road.

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