1 Prof. G G Schierle, PhD, FAIA Design of Fabric Structures Session T33, Thursday, 04/30, 2 – 3:30 PM Design of Fabric Structures This presentation is protected by US and International Copyright laws. Reproduction, distribution, display and use of the presentation without written permission of the speaker is prohibited.
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This presentation is protected by US and International Copyright laws. Reproduction, distribution, display and use of the presentation without written permission of the speaker is prohibited.
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Acknowledgements/Credits
This presentation includes book excerpts of
Structure and Design
http://www.universityreaders.com/titles/schierle/
Design of Fabric Structures
This program is registered with the AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to constitute approval, sponsorship or endorsement by the AIA of any method, product, service, enterprise or organization. The statements expressed by speakers, panelists, and other participants reflect their own views and do not necessarily reflect the views or positions of The American Institute of Architects or ofAIA components, or those of their respective officers, directors, members, employees, or other organizations, groups or individuals associated with them. Questions related to specific products and services may be addressed at the conclusion of this presentation.
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Learning Objectives
• Evaluate appropriate uses of fabric structures, i.e., select appropriate fabric structure types, and select and specify proper fabric material
• Design efficient fabric structures, design fabric structure details, and select and design proper fabric boundaries
• Evaluate the cost of fabric structures, day-lighting of fabric structures, and the appropriateness of fabric structures for various loads
Design of Fabric Structures
Saddle shape Wave shape Arch shape Pont shape
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Anticlastic Stability
• Two stressed strings stabilize a point in space
• Two sets of strings form a stable surface
• Without prestress, convex fiber gets slack, causing instability
• Flat fiber deforms greatly under load, causing instability
• Triangular panels are flat & unstable (AVOID)
Prestress Prestress (PS) effect on a stringF = force, P = load, Δ = deflection 1 Without prestress top link resists all
Assume: Δ = 12 With prestress Δ = 1/2
Top link increase: F=PS+P/2Lower link decrease: F=PS–P/2
3 Stress / strain diagram f/ΔA without prestressB with prestressC Prestress reduced to PS = 0D Prestressed string after PS = 0
Cable nets need about 50% prestressFabric structures need about 30% prestresshttp://www-classes.usc.edu/architecture/structures/papers/GGS-Yin.pdf
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Minimal SurfaceCriteria:• Minimum surface area• Equal stress throughout• Equal +- curvature at any point
Governing Equations (Schierle 1977*)*First published 1977 inJournal of Optimization Theory and Applications
F1/F2 = A/B
Y = F1(X/S1)K/F1+ X tan φY = F2(Z/S2)K/F2
K= F1+F2
Sm
all d
efle
ctio
n
P
rinci
pal c
urva
ture
Larg
e de
flect
ion
Stra
ight
gen
erat
ing
line
Fiber orientationGood Flawed
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Fabric Properties
8 to 20 kN/m46 to 114 lb/in
Permanent + mobileInternal + external
Flouro-polymer fabric
Coated or uncoated fabric*
40 to 100 kN/m228 to 571 lb/in
Permanent + mobileInternal + external
PTFE fabric(good qualities for sustainability)
Coated or uncoated fabric*
6 to 12 kN/m34 to 69 lb/in
PermanentInternal + external
Flouro-polymer foilETFE
Foil*
6 to 40 kN/m34 to 228 lb/in
Permanent internalTemporary external
PVC foilFoil
50 to 100 kN/m286 to 571 lb/in
Permanent Internal + external
Fine mesh fabricLaminated with PTFE film
Laminated fabric*
20 to 100 kN/m114 to 571 lb/in
PermanentInternal + external
Glass fiber fabricSilicone coating
Coated fabric
20 to 160 kN/m114 to 914 lb/in
PermanentInternal + external
Glass fiber fabric PTFE coating
Coated fabric*
40 to 200 kN/m228 to 1142 lb/in
Permanent + mobile Internal + external
Polyester fabric PVC coating
Coated fabric*
Tensile strengthCommon useMakeupType
* Self-cleaning
> 25 yearsUp to 90 %++++
> 25 years15 to 40 %++++
> 25 yearsUp to 96 %++++
15 to 20 yearsinternally
Up to 90 %+0
> 25 years35 to 55 %++++
> 20 years10 to 20 %++++
> 25 years4 to 22 %++++
15 to 20 years0 to 25 %++
DurabilityTranslucencyUV light resistance++ very good+ good
Fire rating++ incombustible+ low flammability0 none
Maximum spansAssuming: Live load LL = 20 psfSafety factor Sf = 4Span/sag ratio L/f = 10
Fabric breaking strength Max. span600 pli (lb/in) ~ 60 ft800 pli (lb/in) ~ 80 ft
Costs Type Cost / sq. ftPrefab PVC $15 to $20Custom PVC $30 to $60PTFE Teflon-coated fiberglass $60 to $180Note: costs exclude foundations
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RL
RR
H
H
TR
TL
W= w L
w
h
RL
RR
L/2L
f
f H
Symmetric suspensionHorizontal reaction H = w L2/(8f)Vertical reaction R = w L/2Max fabric tension T = 1.35 w L
Asymmetric suspensionVector methodTotal load W = w LFabric tensions TR TLHorizontal reaction HVertical reactions RL RR
w
Design / AnalysisRadial loadEdge cable tension T = R p
Lateral LoadSeismic (not critical)V = Cs WV = seismic base shearCs = Seismic coefficient W = mass (dead load)Example (V / ft2, Cs = 0.2, w = 1 psf)V = 0.2 x1 V = 0.2 psf
LDG: Lateral Design Graph Sample: 100’ x 50’ x 20’
Wind (critical)Velocity• 90 mph (most USA)• 150 mph (Golf coast)Gust factors (G= 0.85 for rigid structures)G ~ 1.5 for fabric structuresExample (V per ft2, p = 20 psf ~ 90 mph)V = p G = 20 x 1.5 V = 30 psf
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Acoustics• Thin fabric provides little sound insulation • Micro-perforated foils absorb sound(suspended under structural fabric)
• Form may be used to control acoustics• Anticlastic forms disperse sound• Synclastic forms focus sound
Expo ‘64 LausanneArchitect: Saugey / SchierleEngineer: Froidevaux et Weber
26 restaurant pavilions: • Featured Swiss regional cuisines• Symbolizing sailing and mountains
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R=100’
L=120’
f=12’
A A
B
BSection B-B
Design example
Assume:
Wind pressure p = 30 psf
Allowable fabric stress Fa= 200 pli
Available canvass stress Fa= 50 pli
Wind load (normal to fabric)
T = p R = (30)(100) T = 3000 #
Fabric stress per inch
f = 3000/12 f = 250 pli
Fabric NOT OK 250 > 200 > 50
Cable net was required
Assume: Same allowable stressGravity load w = 20 psfGraphic method
Total LoadW = w L = 20 (120’) W = 2400 #Horizontal reaction H = 3000 #Vertical reaction RL= 2400 #Fabric tension T = 3720 #Fabric stress (#/in)f = 3720#/12” f = 310 pliGravity load not OK 310>200>50Cable net was required
L=120’
f=12’
A A
B
B
h=40
’
HRL
f RL=2400#
H=3000#
W= 2400#T=3720#
w = 20 psf
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Wave shapes
Computer model
San Diego Convention CenterArchitect: Arthur EricksonEngineer: Horst BergerFabric design: Horst Berger
Concrete pylons at 60’ supportridge, valley, and guy cables thatspan 300’ between pylons
Watts Towers Cultural Center (2002)Architect: Ado / SchierleEngineer: ASI
Removable fabric and cable truss
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Stadium Oldenburg GermanyArchitect: Kulla, Herr und Partner Engineer: Schlaich Bergermann
Anticlastic fabric panels suspended from cantilever cable trusses
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Grid Shell Mainz, GermanyArchitect: Mutschler / Otto Engineer: Ove ArupGrid shell of 50 cm square, 50 mmtwin slats form rhomboids in space; covered with translucent fabric.
Form-finding model
Millennium Dome LondonArchitect: Richard RogersEngineer: Buro Happold
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anticlasticfabric
Cur
ved
wal
l to
resi
st w
ind
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Speaker
Prof G G Schierle, PhD, FAIAUSC - School of ArchitectureLos Angeles, CA 90089-0291