COP v3.0:testing; method-resistance-wind-pressures-new-zealand

17.8 Method: Resistance To Wind Pressures For New Zealand 

1. SCOPE

This section sets out a test method for determining the resistance of sheet roof and wall cladding to wind pressures in New Zealand. (UDL)

2. REFERENCED DOCUMENTS

The following documents are referred to in this part of this Standard:
  • AS/NZS 1170 Minimum design loads on structures
  • AS/NZS 1170.2 Part 2: Wind loads

3. SUPPORTING STRUCTURE

The supporting structure must be as specified in section 15.3.

4. LOADING SYSTEM

  1. The test system used for UDL testing consists of two parts.
    • Part A Static Uplift Pressure Test: A sequential static uplift pressure is applied to the cladding assembly with pressure increments based on the fractional proportions, as specified in 6.2., to determine the maximum sustainable pressure before permanent deformation occurs. Pressure is returned to zero after each pressure increment to allow assessment of the onset of permanent deformation.

    • Part B Cyclic Uplift Pressure Test; The test is replicated on an identical cladding assembly with a series of cyclical pressure loadings, with pressure increments based on the fractional proportions, as specified in 6.2., of the factored pressure obtained during the static uplift test. The cyclic regime and number of cycles are specified in 6.4.

    Where failure due to cracking or other permanent damage from the repeated cyclic loading (Part B) occurs at a lesser pressure than that obtained from the factored Part A static pressure test, the cyclic pressure increment prior to the incidence of failure must be substituted as the performance load.
  2. The required cyclic wind pressure must be applied by an air box method that will provide a uniform distribution of uplift pressure appropriate to the part of the cladding being tested and maintain such distribution irrespective of the extent of deflection.
  3. A calibrated manometer must be used to monitor the applied air pressure and ensure the accuracy of the applied air pressure as measured by a transducer. Pressures must be determined to an accuracy of not less than ±2%.
  4. The cycling rate must be between 1 Hertz and 0.3Hertz (approximately 1-3 seconds).
  5. Where the measurement of the deflection of a cladding under load is required, measurement must be made with calibrated displacement transducers, measuring to an accuracy of not less than ±0.05 mm. Where such measurement is taken it must be by a three-point arrangement, to allow for movement of the ends of the span being measured.

5.TEST SPECIMEN

The test specimen must be as specified in section 15.3.

6. LOADING PROCEDURE

6.1.
To determine the static and cyclic target load for Uniformly Distributed load tests the Target loads (TL) must be those determined by:
the type of the material
the thickness of the material
the size of the fastener head or washer (if pierce fixed)
the maximum tributary area

For pierce fixed cladding the Tributary Area (TA) of a fastener must be determined by half the sum of the spacings between three adjacent fasteners*, multiplied by the sum of the distances between adjacent supports.

* NB these distances will not always be identical.

 

6.2.
The Static test load must be applied incrementally, held for a minimum of one minute and the pressure released to zero. Where a target load has been established the Static Test loads must be applied incrementally to the target load and zeroed after each cycle.

i.e.

1 @ 80% of the target load
1 @ 90% of the target load
1 @ 100% of the target load

Where a target load has not been established or where it has been exceeded the Static Test loads must be applied in conservative increments based on visual assessment under load.

A visual inspection must be made after the load has been removed to determine if permanent deformation has occurred. Where Load spreading washers are used these must be removed to determine if permanent deformation has occurred.

At the conclusion of each pressure increment, if there is no visible permanent deformation, the static test must be continued until permanent deformation is observed. The last test pressure to be applied prior to the cladding being assessed as having visible or measurable permanent deformation must be considered the passing static test pressure (P s )

 

6.3.
Where multiple tests are conducted at alternative spans and replication is attained as prescribed in section 15.1 (1.2), the Cyclic Load does not need to be applied to each of the cladding test configurations. In this instance, the cyclic test must be applied to only one of these tests and because it is a verification test the result is not required to be factored.
6.4.
Each cyclic test must consist of a series of sets, each containing 1000 cycles with the pressure within each cycle varying from not more than 50% to 100% of the test load pressure. At the completion of each 1000 cycle set and after all loading has been removed a visual inspection must determine if permanent deformation has occurred. Where Load spreading washers are used these must be removed to determine if permanent deformation or cracking has occurred. If there is no visible or measurable permanent deformation the next cycle must be commenced.

The maximum cycle pressure of the initial set of cyclic loading must be 80% of Ps as determined from 6.2, with subsequent sets being incremented by 10%

i.e.

1000 cycles at 80% of P s , cycling from 40% -80% P s
1000 cycles at 90% of P s , cycling from 45% -90% P s
1000 cycles at 100% of P s , cycling from 50% - 100% P s

Any observed initial onset of cracking or permanent deformation together with the presence of audible sound from the mechanical stress reversals of cladding materials must be recorded for each set.

N.B. P s may be substituted by TL as determined in 6.1.

 

6.5.
Serviceability limit state. The model must be subjected to the static and cyclic loads as prescribed in 6.2. and 6.4. Failure is deemed to have occurred when permanent deformation or cracking is visible around the fastener. Where cracking or permanent deformation occurs during a cyclic pressure test set at a pressure below the factored passing static test pressure Ps, this must be deemed the failure load. All static test results for that particular cladding and fastening arrangement must be multiplied by the same factor Pcy /Psf , - P min being the lowest value of the undamaged cyclic pressure sets. Roof and Wall cladding that is clip fixed is deemed to have failed if any of the performance criteria in section 15.1. (1.4.1). has occurred.

 

6.6.
Strength limit state. The model must be subjected to the specified static pressures for a period of not less than 1 minute. The behaviour of cladding, fastenings, supporting members and substructure must be observed and recorded. The maximum load is that which can be sustained irrespective of any permanent deformation.
N.B. There is no requirement for a cyclic test for strength limit state.

7. REPORT

The following information must be reported:

  1. The number of the report and the name of the client.
  2. The date and location of the test.
  3. The name of the testing officer.
  4. The type of test - UDL/ Cyclic / Serviceability/ Ultimate
  5. The test Procedure.
  6. Details of the material under test — Type/Profile/ Material/ thickness/ Spans.
  7. Substructure.
  8. Fastener type and fixing pattern
  9. Mode and point of failure- Permanent deformation at fastener, midspan buckling, pull-over,
  10. Pull-out, cracking.
  11. Deflection under load (if measured).
  12. Residual deflection (if measured).