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F2018abnMembrane, Nets & Shells 1

Lecture 13

Applied Architectural Structures

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thirteen

membrane, net &

shell structures

lecture

Denver Airport – Birdair.com

APPLIED ACHITECTURAL STRUCTURES:

STRUCTURAL ANALYSIS AND SYSTEMS

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DR. ANNE NICHOLS

FALL 2018


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Membrane and Net Structures

• form follows

pressure or

tension


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• types

– fabric

– cables

– pneumatic

– inflated

http://nisee.berkeley.edu/godden


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• sensitive to aerodynamic effects of wind

– fluttering

• stabilization

– rigid supporting framework

– prestressing of surface


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• tensile stress and

tangential shear stresses occur


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Pneumatic Structures

• internal pressure

– air-supported:

entire volume

– air-inflated: cavities

• ribs

• dual walls


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Air-Supported Structures

• pressure slightly

higher than

atmospheric

• light loads

• greater spans than

air-inflated


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Air-Inflated Structures

• higher degree of

pressurization

• pressure doesn’t

directly balance

loads

• buckling or folding

results in collapse

• flexibility in space


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Loads & Behavior

• snow accumulation

– shape

– heat loss

• avoid large

concentrated loads

• wind loads

– suction

– tension

– “buckling”


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Membrane Stresses

• pressure is constantly applied stress


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Membrane Stresses• enough pressure to prevent folding

• large radius, large stress


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Supports

• air-supported

– need airtight

seal

– resists uplift

and thrust

– “inverted” arch

– containment

rings


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Profile Selection

• lower profile

– higher stresses

– lower air volume

– can be used to avoid

wind pressure effects


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Air-Inflated Members

• prestressed in

tension

• structural stresses

added

• increase in tension


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Punctures

• fracture or rip from redistribution of

stresses

• air-supported

– low pressure

– gradual deflation

• air-inflated

– isolated cells deflate

• design in suspension


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Net and Tent Structures

• low curvatures, high stress (big radius)

• avoid flat areas

• carefully place high & low points

Basic Types of Tensile Structures (© Tentech)

http://www.tentech.nl/


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Support Conditions

• compression masts

• uplift at ground

• free edges can

be stiffened with

cables

• stress reduction

at high points

by a cable ring


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Form Development

• modeling

• software


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Materials

• strength

– tear resistant

– bi-directional

• durability

– ultraviolet

effects

– creep

– corrosion in metals


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Shells

• similar to membranes, domes & vaults

• THIN

• rigid


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Shells

Empire State Performing Arts Center, Ammann & Whiney


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Shell Types

• shape classifications

– developable: • singly curved (vault)

– synclastic• doubly curved

• same direction

– anticlastic: • doubly curved

• opposite curvature

– free form


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Synclastic

• surface of revolutions


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Shell Stresses

• in-plane

– tension

– compression

– shear

• insignificant

bending

• suitable for distributed loads

• can’t handle concentrated loads well


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Spherical Shells

• arch of revolution

• compression

• some tension

– “bow”


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Forces in Spherical Shells

• similar to plates

– two directions of forces

– shear

– maintain curvatures

• meridional– arch direction

• hoop – radial direction

– can see tension

• holes redistribute stresses

– edges need reinforcement


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Meridional and Hoop Forces

• meridional force per unit length:

• hoop force per unit

length:

22 sinRπ

WN

cos

cosRwN θ

1

1


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Distribution and Concentrated Forces

• size distributions

• concentrated force

causes

R.

R)'cos(

620

4951

N

0.6

2 R


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Support Conditions

• absorb horizontal thrust

– tension ring

– being pushed out

– need to be continuous

– can be used as foundation

• top (crown) rings

– in compression

../animations/dome_ten_comp.mov


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Support Conditions

• buttresses

• edge restraint effects

– deformations different

– fixed edges• bending stress

• deep section

– pinned edges• still induces bending

– post-tensioning helpsstiffen


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Buckling & Lateral Loading

• instability

– compression

– moment of inertia

– low stress levels

• local

• snap-through

• lateral loading

– shear


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Annunciation Greek Orthodox Church

• Wright, 1956

http://www.bluffton.edu


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Annunciation Greek Orthodox Church

• Wright, 1956


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Cylindrical Shells

• can resist tension

• shape adds “depth”

• not vaults

• barrel shells

../animations/barrel_stresses2.mov


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Kimball Museum, Kahn 1972


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• outer shell edges


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• skylights at peak


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• saddle or “ruled” shapes

• surface generated with straight lines

• tension follows “cable drape”

• compression follows “arch”

Anticlastic Shells (Hyperbolic Paraboloid)


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Anticlastic Shell Behavior

• edge conditions offer restraint

– tie rods useful

– shears

../animations/hyperbolic_tent.mov


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Zarzuela Hippodrome, Torroja 1935

http://www.arch.mcgill.ca


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Zarzuela Hippodrome, Torroja 1935


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Heilmajer Memorial Bandstand

• Kramer, 2002


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• Kramer,

2002


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• Kramer, 2002

F2018abn

Videos

Membrane, Nets & Shells 45

Lecture 13


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BC Place roof replacement

Canada Place roof rehabilitation

http://vimeo.com/24829903

http://youtu.be/tdTsdaZc_d8

https://youtu.be/bB696JWgCBQ

https://youtu.be/rkhxiShx0U8

https://youtu.be/XO1WqsGmnOg?t=4m20s

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