1
Flexural Strength of Exterior Metal Building Wall Assemblies with Rigid Insulation
Tian Gao and Cris Moen
The Charles E. Via, Jr. Dept. of Civil & Environmental Engineering Virginia Tech
www.moen.cee.vt.edu
SSRC Annual ConferenceGrapevine, Texas, April 18, 2012
2
OUTLINE:
IntroductionSuction/Uplift LoadingDesign MethodsExperimentsOngoing Study
3
INTRODUCTION: Metal building
Metal Building
Metal Building
Metal BuildingMetal
Building
• Low rise, light weight and long span building.• Many cold-formed steel members are used.
4
Wind loading: Gravity/Pressure
Gravity
Pressure
5
Wind loading: Uplift/Suction
Uplift
Suction
Our focus!
6
Inside of the building:
Primary frame
7
Purlins (Roof)
Girts (Wall)
Inside of the building:
Primary frame
8
Purlins (Roof)
Sheathing
Girts (Wall)
Sheathing
Inside of the building:
Primary frame
9
Purlins (Roof)
Sheathing
Simple
Girts (Wall)
Sheathing
Continuous
Inside of the building:
Primary frame
Continuous
Simple
Through-fastened
Standing seam
Zee
Cee...
Purlin
Girt
Design variables:
None
Fiber glass
Rigid board
Uplift/Suction
Gravity/Pressure
X
XX
X
X
In this study, we will cover:
Purlin
Girt
Zee
Cee...
None
Fiber glass
Rigid board
Through-fastened
Standing seam
Uplift/Suction
Gravity/Pressure
Continuous
Simple
X
XX
X
X
12
LOADING: Wall/Suction
AA
Section A-A
screw
Wallpanel
girt
Wallpanel
girt
13
LOADING: Wall/SuctionBending + Rotation
X
X
Wallpanel
girt
Wallpanel
girt
14
LOADING: Roof/Uplift
Roof PanelB
B
Section B-B
X X
Bending + Rotation
kФ
15
DESIGN METHODS: Analytical approach
Peköz’s model
EuroCode
q
w K
Peköz, T.B., and Soroushian, P. (1982). “Behavior of C- and Z-purlins under wind uplift.” Proc., 6th International Specialty Conference on Cold-Formed Steel Structures, Rolla, MO.
16
DESIGN METHODS: Analytical approach
Peköz’s model
EuroCode
q
w K
Peköz, T.B., and Soroushian, P. (1982). “Behavior of C- and Z-purlins under wind uplift.” Proc., 6th International Specialty Conference on Cold-Formed Steel Structures, Rolla, MO.
kФ
???Test
17
DESIGN METHODS: Analytical approach
Peköz’s model
EuroCode
q
w K
Peköz, T.B., and Soroushian, P. (1982). “Behavior of C- and Z-purlins under wind uplift.” Proc., 6th International Specialty Conference on Cold-Formed Steel Structures, Rolla, MO.
kФ
???Test
Gao, T., and Moen, C.D. (2012). “Rotational restraint prediction method for through-fastened metal building wall girts and roof purlins.” Thin-Walled Structures.
18
DESIGN METHODS: Experimental approach R-factor method
AISI AS/NZS
ye
t
FSMR
Fully braced girt/purlin capacity
Wall/roof flexural capacity in a full scale test (Vacuum Test)
19
AISI R-factor:
Depth Range, in. (mm) Profile R
d ≤ 6.5 (165) C or Z 0.70
6.5(165) < d ≤ 8.5 (216) C or Z 0.65
8.5 (216) < d ≤ 11.5 (292) Z 0.50
8.5 (216) < d ≤ 11.5 (292) C 0.40
d
CZ
20
50 VACUUM TESTS @ VT:
• Motivation: Energy efficiency (*ASHRAE-90.1).• Determine the R-factor for the case when the rigid
board insulation is used.
Girts
Metal panel
25mm Rigid Board 50mm 100mm
Girts
Metal panel
Girts
Metal panel
* ASHRAE-90.1. (2010). American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., Atlanta, GA.
21
Test setup:Girts
Girts
Rigid insulation
Rigid insulation
Panel
Panel
Vacuum
Vacuum
22
1. Failure modes (4) failure modes
2. Effect of cross-section local slenderness Stocky (200 mm deep, 2.5 mm thick) Slender (250 mm deep, 1.5 mm thick)
3. R-factors
Results: Stocky
Slender
23
Failure mode-1: Panel failure
24
Failure mode-2: Panel pull over
• Thick rigid board = “Washer”. • Can prevent panel pull over.
25
• If the rigid board insulation is used, and the girt is thick enough to clamp the screw.
Failure mode-3: Screw bending/fracture
Thickness BoardThickness
26
• The girt is too thin to clamp the screw.
Failure mode-3: NOT for slender girt
27
Rotation + Yielding Rotation + Local Buckling
Failure mode-4: Girt/Purlin failure
28
Slender Z-section, 50mm rigid board(Video)
http://www.youtube.com/user/drcrismoen
29
• Slender cross-section: the connection becomes not that important, because all action happens in the girts.• Stocky cross-section: connection failure.
Local slenderness
Slender Z-sectionStocky Z-section
30
R-factors for Z-section, bare panel
Slender
Failure modes:1. Panel failure2. Panel pull over3. Screw failure4. Girts failure
2 2 22
4 4
ye
t
FSMR
31
R-factors for Z-section, bare panel
• Panel pull over dominates for locally stocky Z-sections.
Stocky
Failure modes:1. Panel failure2. Panel pull over3. Screw failure4. Girts failure
2 2 22
4 4
ye
t
FSMR
32
R-factors for Z-section, rigid board
4 4 4 4Failure modes:1. Panel failure2. Panel pull over3. Screw failure4. Girts failure
ye
t
FSMR
• For slender Z250, No reduction in R-factor.
33
R-factors for Z-section, rigid board• For slender Z250, No reduction in R-factor.• For stocky Z200, R-factor is reduced from 0.65 to 0.5.
4 4 4 42 2
34
34
4Failure modes:1. Panel failure2. Panel pull over3. Screw failure4. Girts failure
ye
t
FSMR
34
R-factors for Z-section, rigid board• For slender Z250, No reduction in R-factor.• For stocky Z200, R-factor is reduced from 0.65 to 0.5.
4 4 4 42 2
34
34
4
kФ
LOW!Failure modes:1. Panel failure2. Panel pull over3. Screw failure4. Girts failure
Gao, T., Moen, C.D. (2011). “Flexural strength of exterior metal building wall assemblies with rigid Insulation.” Virginia Tech Research Report No. CE/VPI-ST-11/01, Blacksburg, Virginia.
35
R-factors for C-section, rigid board• For slender C250, No reduction in R-factor.• For stocky C200, R-factor is reduced from 0.65 to 0.4.
44 4 4
223
3 34
Failure modes:1. Panel failure2. Panel pull over3. Screw failure4. Girts failure
ye
t
FSMR
36
Summary:
• Bare panel:
• Rigid insulation:
• Slender cross-section:• Stocky cross-section:
37
Summary:
• Bare panel:
• Rigid insulation:
• Slender cross-section:• Stocky cross-section:
Panel pull over
38
Summary:
• Bare panel:
• Rigid insulation:
• Slender cross-section:• Stocky cross-section:
Panel pull over Prevent panel pull over Screw bending/fracture Lower kФ
39
Summary:
• Bare panel:
• Rigid insulation:
• Slender cross-section:• Stocky cross-section:
Panel pull over Prevent panel pull over Screw bending/fracture Lower kФ
Girt/Purlin body
40
Summary:
• Bare panel:
• Rigid insulation:
• Slender cross-section:• Stocky cross-section:
Panel pull over Prevent panel pull over Screw bending/fracture Lower kФ
Girt/Purlin body Connection
41
ONGOING STUDY (Limit State Design):
1. Panel failure:
2. Panel pull over:
3. Screw bending/fracture:
4. Girt/Purlin failure:
42
ONGOING STUDY (Limit State Design):
1. Panel failure:
2. Panel pull over:
3. Screw bending/fracture:
4. Girt/Purlin failure:
• Use Direct Strength Method (DSM) to predict the panel flexural capacity.
DSM is using the buckling strengths (local, distortional and global) to predict the capacity.
43
ONGOING STUDY (Limit State Design):
1. Panel failure:
2. Panel pull over:
3. Screw bending/fracture:
4. Girt/Purlin failure:
• Panel-flange connection study.• Panel connection failure.
Gao, T., and Moen, C.D. (2012). “Rotational restraint prediction method for through-fastened metal building wall girts and roof purlins.” Thin-Walled Structures.
AISI E4.2.2. Pull-Over
44
ONGOING STUDY (Limit State Design):
1. Panel failure:
2. Panel pull over:
3. Screw bending/fracture:
4. Girt/Purlin failure:
• Board-flange connection study.• Flange thickness & screw.• Fastener bending study.
Gao, T., Moen, C.D. (2011). “Flexural strength of exterior metal building wall assemblies with rigid Insulation.” Virginia Tech Research Report No. CE/VPI-ST-11/01, Blacksburg, Virginia.
45
ONGOING STUDY (Limit State Design):
1. Panel failure:
2. Panel pull over:
3. Screw bending/fracture:
4. Girt/Purlin failure:
46
ONGOING STUDY (4. Girts/Purlin failure):
kϕ
Finite strip analysis
• (Mcrl, Mcrd, Mcre)Mn
DSM
• EuroCode• Peköz
Gao, T., and Moen, C.D. (2012). “Rotational restraint prediction method for through-fastened metal building wall girts and roof purlins.” Thin-Walled Structures.
Gao, T., Moen, C.D. (2011). “Flexural strength of exterior metal building wall assemblies with rigid Insulation.” Virginia Tech Research Report No. CE/VPI-ST-11/01, Blacksburg, Virginia.
Bare panel
Rigid insulation
47
Primary results: DSM prediction• 46 simple span Vacuum Tests, uplift/suction loading.• Z and C-sections, bare panel only, girt/purlin failure.
Mean=1.01COV=19%