flexural strength of exterior metal building wall assemblies with rigid insulation

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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

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OUTLINE:

IntroductionSuction/Uplift LoadingDesign MethodsExperimentsOngoing Study

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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.

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Wind loading: Gravity/Pressure

Gravity

Pressure

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Wind loading: Uplift/Suction

Uplift

Suction

Our focus!

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Inside of the building:

Primary frame

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Purlins (Roof)

Girts (Wall)

Inside of the building:

Primary frame

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Purlins (Roof)

Sheathing

Girts (Wall)

Sheathing

Inside of the building:

Primary frame

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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

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LOADING: Wall/Suction

AA

Section A-A

screw

Wallpanel

girt

Wallpanel

girt

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LOADING: Wall/SuctionBending + Rotation

X

X

Wallpanel

girt

Wallpanel

girt

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LOADING: Roof/Uplift

Roof PanelB

B

Section B-B

X X

Bending + Rotation

kФ

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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.

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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

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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.

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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)

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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

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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.

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Test setup:Girts

Girts

Rigid insulation

Rigid insulation

Panel

Panel

Vacuum

Vacuum

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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

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Failure mode-1: Panel failure

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Failure mode-2: Panel pull over

• Thick rigid board = “Washer”. • Can prevent panel pull over.

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• 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

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• The girt is too thin to clamp the screw.

Failure mode-3: NOT for slender girt

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Rotation + Yielding Rotation + Local Buckling

Failure mode-4: Girt/Purlin failure

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Slender Z-section, 50mm rigid board(Video)

http://www.youtube.com/user/drcrismoen

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• 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

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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

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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

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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.

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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

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4Failure modes:1. Panel failure2. Panel pull over3. Screw failure4. Girts failure

ye

t

FSMR

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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

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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.

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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

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Summary:

• Bare panel:

• Rigid insulation:

• Slender cross-section:• Stocky cross-section:

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Summary:

• Bare panel:

• Rigid insulation:

• Slender cross-section:• Stocky cross-section:

Panel pull over

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Summary:

• Bare panel:

• Rigid insulation:

• Slender cross-section:• Stocky cross-section:

Panel pull over Prevent panel pull over Screw bending/fracture Lower kФ

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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

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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

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ONGOING STUDY (Limit State Design):

1. Panel failure:

2. Panel pull over:

3. Screw bending/fracture:

4. Girt/Purlin failure:

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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.

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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

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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.

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ONGOING STUDY (Limit State Design):

1. Panel failure:

2. Panel pull over:

3. Screw bending/fracture:

4. Girt/Purlin failure:

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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

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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%

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Questions

This presentation is @ www.moen.cee.vt.edu