Final Report:
Full Scale Wind Load Testing of Aluminum
Screen Enclosures
Forrest J. Masters, PhD, PE, Associate Prof. of Civil Engineering, University of Florida
Sungmoon Jung, PhD, Florida State University
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1
Presentation Outline
• Specimen selection process
• Full-scale testing
– Set up
– Design load (FBC) vs. applied load
– Key observations
• Material testing
• Comparison of test and analysis
• Implications to the code
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2
Selection of the “Generic” Specimen
• AAF acquired 35 signed and sealed, site-specific plans from the St. Johns
County Building Department and the City of Jacksonville.
• Ten designs with a mansard roof with approximate dimensions of 24 ft X 40
ft X 9 ft and a 48 in rise in the roof were selected, de-identified, and
forwarded to Dr. Jung (FSU) to review
• A design with average structural performance was selected
• In order to rank the candidate designs objectively, raking criteria were used
(performance of roof bracing, wall bracing, post, and other members)
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3
Generic Specimen
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4
Generic Specimen
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5
Generic vs. AAF Specimens
• AAF designed a second specimen (same size) following the 2010 AAF Guide to
Aluminum Construction in High Wind Areas.
• Significant differences between the “Generic” and the “AAF” specimens
– AAF has 8 additional 2 x 2 roof braces, whereas generic has none
– AAF has 2 x 8 roof beams, whereas generic has 2 x 6 roof beams
– AAF has 2 x 3 purlins, whereas generic has 2 x 2 purlins
–
–
–
–
–
AAF has a 5” super gutter, whereas generic has a 7” super gutter
AAF has a 2 x 3 + 1 x 2 eave rail, whereas generic has a 2 x 2 + 1 x 2 eave rail
AAF has 2 x 4 posts on the long wall, whereas generic has 2 x 5 posts
AAF does not have cable bracings on the side walls
Some AAF purlins require backing plates (at bracing bays)
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6
AAF Specimen
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7
AAF Specimen
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8
Preparation for the Testing
• Hartshorn Custom Contracting is fabricating both specimens
• AAF and FSU performed structural analysis to identify high
anticipated-to-allowable stress ratio and high tension. Visual Analysis
and SAP2000 were used (sample results: next slide)
• The information was forwarded to IBHS to install strain gauges
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9
High anticipated-to-allowable stress, moment (%)
High anticipated-to-allowable stress, buckling (%)
High tension (kips is shown)
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10
High anticipated-to-allowable stress, moment (%)
High anticipated-to-allowable stress, buckling (%)
High tension (kips is shown)
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11
Test Set Up
•
•
•
•
Tests were conducted at the IBHS Research Center
Generic specimen: assembled in April 23, tested in April 24
AAF specimen: assembled in April 25, tested in April 26
Both specimens used 18 ×14 × 0.013" fiberglass mesh
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14
Sensors: Generic
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15
Sensors: AAF
(A: axial, M: moment, C: cable)
Experimental Procedure
• Static pull tests (single point axial force) were conducted before wind tests.
Results were used for finite element model calibration.
• Wind tests: angle definition
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16
Experimental Procedure (cont’d)
• Wind tests
– Series I: 90 degree case over three wind speed intensities with and without
turbulence (Runs 1 to 6)
– Series II: repeated most of Series I across a range of wind angles (Runs 7 to 24)
– Series III: gradually increased the wind speed for 0 degree and 90 degree wind
angles (Runs 25 to 30)
– Series IV: tests at maximum wind speed for various scenarios (Generic: Runs 31
to 33, AAF: Runs 31 to 40)
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17
Design vs. Applied Wind Loading
• The following figures compare design wind loading (FBC) and applied wind loading
(IBHS)
– FBC: 120 mph, exposure B were used for both specimens
– IBHS: 90 mph, assumed a factor of 0.7 (includes gust effect, drag, screen)
• In principle, no failure should have occurred in the test
IBHS pressure @
33 ft = 14.5 psf
10
10
8
8
6
IBHS (90 mph)
4
FBC (ASD)
FBC (LRFD)
2
0
0
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5
10
15
Windward Pressure (psf)
IBHS pressure @
33 ft = 14.5 psf
12
Height (ft)
Height (ft)
12
6
IBHS (90 mph)
4
FBC (ASD)
FBC (LRFD)
2
0
20
0
5
10
15
Leeward Pressure (psf)
20
Key Observations During the Test
• Screens/attachments began to fail at 80 mph
Generic, max V = 80 mph
SLIDE
AAF, max V = 80 mph
Key Observations (cont’d)
• Several screen attachments failed at 90 ~ 100 mph
Generic, max V = 90 mph
Failed screens and/or screen
attachments (fully failed ones only),
after all 90 mph tests
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Key Observations (cont’d)
• Generic specimen lost one corner post at 90 mph
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Key Observations (cont’d)
• AAF specimen lost two corner posts at 100 mph
• The failure was due to the unbalanced loading (& failed attachment)
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Summary of the Tests
90 mph
100 mph
Retrofit
Generic
80 mph
• 100 mph @ 270 deg. and
0 deg., no substantial
damage
Structural failure of the corner post, and
failure of four screens and/or attachments
AAF
Retrofit
Partial failure of screen
attachments
• Unable to load @ 90 deg.
(no screen at the corner
due to the damage)
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Partial failure of screen
attachments
Failure of two screens and/or attachments
Structural failure of two
corner posts
Material Testing
• Material testing was conducted to confirm the material performance
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Material Testing (cont’d)
• Specified: 6005-T5 (E = 10,100 ksi, 𝜎𝑦 = 35.0 ksi, 𝜎𝑢 = 38.0 ksi)
• Actual performance: E = 9,300 ksi, 𝜎𝑦 = 27.8 ksi, 𝜎𝑢 = 34.0 ksi
– 𝜎𝑦 and 𝜎𝑢 are estimated statistically
– 𝜎𝑦 : N = 12, mean = 32.3 ksi, standard deviation = 1.2 ksi
– 𝜎𝑢 : N = 12, mean = 37.5 ksi, standard deviation = 0.9 ksi
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Model Calibration
• Using the results from pull tests, three different modeling
assumptions were compared
Model A: baseline
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Model B: boundary
conditions prevent
rotation
Model C: Model B + frame
end-releases are fixed except
purlins and corner bracings
Model Calibration (cont’d)
9.0E-2
6.0E-2
Axial Analysis (kips)
• Finite element results were
compared to sensor readings
• Model C was chosen for
further analysis
• Sample results on the right:
axial forces, AAF, pull 01
-6.0E-2
3.0E-2
Model A
Model B
0.0E+0
-3.0E-2 0.0E+0
Model C
3.0E-2
-3.0E-2
-6.0E-2
Axial Experiment (kips)
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6.0E-2
9.0E-2
Comparison of Design vs. Test
1.0E+0
5.0E-1
Data Lower Than Analysis
Axial Analysis (kips)
• For 80 mph and 90 mph tests, test
results (x-axis) were compared to the
analysis results (y-axis)
• Analysis used FBC loading. Therefore,
in principle, all test results should be
lower than analysis results.
• Marked notable locations (a sample
comparison is shown on the right)
-1.5E+0
-1.0E+0
-5.0E-1
0.0E+0
0.0E+0
-5.0E-1
-1.5E+0
Axial Experiment (kips)
28
5.0E-1
1.0E+0
80 mph
-1.0E+0
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Data Higher Than Analysis
90 mph
Summary of Notable Members: Generic
• One corner bracing exceeded the allowable stress
• High moment correlated well with screen attachment failure
M-9
A-6
M-10
M-12
M-21
A-14
M-8
M-20
M-19
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M-18
A-16
M-17
A-15
M-7
A-13
A-5
M-11
Actual to Allowable Stress Ratio
1.2
1.0
0.8
0.6
Max
Avg
0.4
0.2
0.0
A-15 (0) M-17 (0) M-18 (0) A-1 (90) A-2 (90) M-17
(90)
M-21
(90)
Summary of Notable Members: AAF
• Two posts exceeded the allowable stress (one of which actually failed
during the testing)
M-8
M-7
A-14
A-5
A-11
M-17
M-20
M-19
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30
A-13
A-4
Actual to Allowable Stress Ratio
M-21
M-9
M-18
M-10
A-6
A-12
1.4
1.2
1.0
0.8
Max
0.6
Avg
0.4
0.2
0.0
A-6 (0) M-8 (0) M-9 (0) A-4 (90) M-9 (90) M-18
(90)
M-21
(90)
Implications to the Code
• Although the wind loading did not exceed the design loading, failures
were observed:
– Screens began to fail at 80 mph
– Some screen attachments failed at 90 to 100 mph
– Some of the failed screen attachments fluttered while attached to the structural
member, contributing failure of it
– One vertical post failed due to the unbalanced loading (one side had screen but
the other side lost the screen)
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Implications to the Code (cont’d)
• The failure of screen attachments and unbalanced loading have direct
implications on the rule on removing the screen (Rule 61G20-1.002).
If some screens are cut but not others, unbalanced loading may
accelerate the failure of the post. Code changes should be considered
to either require removal of all screens above the chair rail, or, devise
a more secure fastening of screen attachments to prevent partial
failure and unbalanced loading.
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Implications to the Code (cont’d)
• The tensile ultimate strength and tensile yield strength of the
aluminum extrusions, based on the testing of coupons harvested from
the specimens, were lower than the specified values. To ensure that
the aluminum meets or exceeds the specified performance levels, the
building code should require that material certification be submitted
to the building official.
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Implications to the Code (cont’d)
• The tested specimens received very thorough inspection and quality
control. However, it is well known that the real-world plan review and
inspection may not reach such a level, and therefore, likely experience
much more severe failure due to the hurricane. The code
requirement on this issue would greatly reduce potential failure of
screen enclosures due to the hurricane.
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