APPLIED ARCHITECTURAL STRUCTURES:...
Transcript of APPLIED ARCHITECTURAL STRUCTURES:...
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F2009abn
thirteen
membrane, net &
shell structuresMembrane, Nets & Shells 1
Lecture 13
Applied Architectural Structures
ARCH 631
lecture
Denver Airport – Birdair.com
APPLIED ARCHITECTURAL STRUCTURES:
STRUCTURAL ANALYSIS AND SYSTEMS
ARCH 631
DR. ANNE NICHOLS
FALL 2014
Membrane, Nets & Shells 2
Lecture 12
Architectural Structures III
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Membrane and Net Structures
• form followspressure or
tension
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Lecture 12
Architectural Structures III
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Membrane and Net Structures
• types
– fabric
– cables
– pneumatic
– inflated
http://nisee.berkeley.edu/godden
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Lecture 12
Architectural Structures III
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Membrane and Net Structures
• sensitive to aerodynamic effects of wind
– fluttering
• stabilization
– rigid supporting framework
– prestressing of surface
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Lecture 12
Architectural Structures III
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Membrane and Net Structures
• tensile stress andtangential shear stresses occur
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Lecture 12
Architectural Structures III
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Pneumatic Structures
• internal pressure
– air-supported:
entire volume
– air-inflated: cavities
• ribs
• dual walls
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Lecture 12
Architectural Structures III
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Air-Supported Structures
• pressure slightly higher than atmospheric
• light loads
• greater spans than air-inflated
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Lecture 12
Architectural Structures III
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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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Architectural Structures III
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Membrane Stresses
• pressure is constantly applied stress
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Architectural Structures III
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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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Lecture 12
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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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Lecture 12
Architectural Structures III
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Air-Inflated Members
• prestressed in tension
• structural stresses added
• increase in tension
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Lecture 12
Architectural Structures III
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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
Membrane, Nets & Shells 16Lecture 12
Architectural Structures IIIARCH 631
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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)
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Lecture 12
Architectural Structures III
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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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Lecture 12
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Shells
• similar to membranes, domes & vaults
• THIN
• rigid
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Lecture 12
Architectural Structures III
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Shells
Empire State Performing Arts Center, Ammann & Whiney
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Architectural Structures III
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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
Membrane, Nets & Shells 27Lecture 12
Architectural Structures IIIARCH 631
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Meridional and Hoop Forces
• meridional force per unit length:
• hoop force per unit length:
φφ 2
2 sinRπ
WN =
+
+−= φ
φcos
cosRwN
θ
1
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Membrane, Nets & Shells 28Lecture 12
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Distribution and Concentrated Forces
• size distributions
• concentrated force causes
R.
R)'cos(
620
4951
=
°
∞→φN
0.6
2 R
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Lecture 12
Architectural Structures III
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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
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Architectural Structures III
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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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Architectural Structures III
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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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Lecture 12
Architectural Structures III
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Annunciation Greek Orthodox Church
• Wright, 1956
http://www.bluffton.edu
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Annunciation Greek Orthodox Church
• Wright, 1956
Membrane, Nets & Shells 34Lecture 12
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Cylindrical Shells
• can resist tension
• shape adds “depth”
• not vaults• barrel shells
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Kimball Museum, Kahn 1972
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Kimball Museum, Kahn 1972
• outer shell edges
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Lecture 12
Architectural Structures III
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Kimball Museum, Kahn 1972
• skylights at peak
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Architectural Structures III
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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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Architectural Structures III
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Anticlastic Shell Behavior
• edge conditions offer restraint
– tie rods useful
– shears
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Lecture 12
Architectural Structures III
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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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Architectural Structures III
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Heilmajer Memorial Bandstand
• Kramer, 2002
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Architectural Structures III
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Heilmajer Memorial Bandstand
• Kramer, 2002