Post on 03-Jun-2018
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Guest Lecturer:
Bruce Kaskel, SE, RAPrincipal
Wiss, Janney, Elstner Associates, Inc.
CE 479
CURTAIN WALL STRUCTURES
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OBJECTIVES AND DISCUSSION TOPICS
1.What are curtain walls?
2.Are they architecture? Or engineering?
3.Two basic curtain wall systems
4.Curtain wall framing concepts5.Infill panels
6.Glass
7.Special problems in structural behavior8.Temperature effects
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WHAT ARE CURTAIN WALLS?
1.Lightweight wall systems installed outside
of building structure. Often not the design
of the Structural Engineer of Record (EOR)2.Designed to resist wind and rain. Must also
accommodate building drift and seismic
movements without distress
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CLASSIC CURTAIN WALLS
The Inland Steel Building 1957Skidmore, Owings & Merrill Chicago
1. Commonly aluminum-
framed
2. Repetition of elements
for economy and design
simplicity
3. Infill panels float in
framing4. Glass as a unique infill
panel
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ARCHITECTS WANT A LOOK
ING Bank Building 1995Frank Gehry Prague-Czech Republic
1. The engineering is
left to others, often
the manufacturer?
2. Usually design is
performed by SEs
working for sub-
contractors to theGeneral Contractor
for the building
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MATERIALS USEDALUMINUM FRAMING
1. Alloyed aluminum 6061-T5 or 6063-T6
2. Yield strengths comparable to mild steel
3. Modulus of elasticity 1/3 of steel4. Principal design load - wind. Loads either
determined
5. Deflection often governs design
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ALUMINUMS ADVANTAGES FOR CURTAIN WALL FRAMING
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ALUMINUMS PROPERTIES
Aluminum Design Manual 2005
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WIND LOADS
1. Wind is the principal structural
design load (rain and thermal
resistance uses other principles)
2. Loads determined from codeeither by SER or curtain wall SE
3. Usually ASCE 7 based
4. Wind tunnel modeling is used
for significant buildings5. Other loads - missile impact
during hurricane, bomb blast
loads
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BASIS FOR WIND LOAD DESIGN
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1:100 scale models
Instrumented with
pressure taps Placed in Wind-
tunnel and
subjected to windsfrom each direction
WIND TUNNEL TESTING TO DETERMINE WIND LOADS
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Category IV
Storm
140 mph gustsat landfall
Eye passed 50
miles east ofNew Orleans
HURRICANE KATRINACASE STUDY
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HURRICANE KATRINACASE STUDY
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HURRICANE KATRINACASE STUDY
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TESTING GLASS FOR RESISTANE TO DEBRIS (MISSILES)
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Testing at White Sands, New Mexico
GLASS EXPOSED TO EXTREME FORCES
Courtesy: 3M Corp.
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Glass-Shattering with
Impact
Glass with Safety Film-
Bending with Impact
Courtesy: 3M Corp.
HOW GLASS AND FRAME RESIST BLAST FORCE
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ALUMINUM SECTIONS
1. Sections optimized for in-plane bending
efficiency
2. Extruded aluminum sections optimized for
efficiency
3. Manufacturers have standard dies and
sections
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SLENDER BEAM ELEMENTS
Aluminum Design Manual 2005
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THERMAL BREAKS IN FRAMING
1. Sections can have thermal breaks to
reduce thermal conductivity2. Engineered sections include performance
of plastics bonded to aluminum
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Historic Photo of 860-880
Lake Shore Drive
BASIC CURTAIN WALL ASSEMBLIES
1. Two basic ways to
assemble curtain wall
systems
2. Stick: Piece-built andglazed on site
3. Unitized: Pre-built with
glazing in a shop. Erected
on site4. Selection may be specified.
Often decision is based on
contractors cost analysis
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1.Anchors
2.Mullion3.Horizontal Rail
4.Spandrel Panel
5.Vision Glass
CURTAIN WALL COMPONENTS
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FRAMING CONCEPTS
1. Vertical elements: Mullions
2. Horizontal elements: Rails (sometimes
mullions) - typically frame short distance
from mullion to mullion and transfer
gravity weight of glass to mullions
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Shear block
Joint plug /
zone dam
Thermal
isolator
Glazing pressure
plate
Cover
CURTAIN WALL INTERNAL CONSTRUCTION
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ISOMETRIC OF PRESSURE PLATE SYSTEM
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VERTICAL MULLIONS
1. Typically span from floor to floor
2. Two-story stick possible due to ease of
extruding 25 foot long sections3. Anchorage to slab edge requires
integration with SEs system
4. SE remains responsible to carry curtain
wall loads imposed at anchor through
structure
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TYPICAL WIND LOAD TRIBUTARY AREAS
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ANCHORS
1. Gravity anchors
2. Wind anchors necessary for two-story
systems3. Adjustability and ease of erection issues
4. Unitized panel anchors must
accommodate setting large panels
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JOINTS
1. Design must account for thermal
expansion of aluminum
100 F 300 x 0.00128 = 3/8 Silicone sealant + 50% joint
necessary
2. Slip joints may need to transfer shear ormoment
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INFILL PANELS
1. Metal or glass are conventionally used
2. Architects are very sensitive to design ofinfill panels
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GLASS
1. Glass design to resist loads is unique
2. Glass behaves as elastic thin-plate under
out of plane loading; however,3. Glass is a brittle material without a well-
defined characteristic breakage strength
4. Glass is designed usually probability theory
and relatively large factor of safety
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ASTM E1300
1. Current national standard for structural
design of glass infills
2. Plug and chug with charts; or,
3. Proprietary computer program
http://localhost/var/www/apps/conversion/tmp/Program%20Files%20(x86)/Standards%20Design%20Group,%20Inc/Window%20Glass%20Design%205http://localhost/var/www/apps/conversion/tmp/Program%20Files%20(x86)/Standards%20Design%20Group,%20Inc/Window%20Glass%20Design%205http://localhost/var/www/apps/conversion/tmp/Program%20Files%20(x86)/Standards%20Design%20Group,%20Inc/Window%20Glass%20Design%2058/11/2019 Kaskel2012
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GLASS (cont.)
SAP analysis for
complex glass
geometry
Stress risers occur at
glass with
connection holes
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SPECIAL PROBLEMS IN CURTAIN WALL STRUCTURES
1. Compression fiber bracing?
2. Adequate resistance to rotation of
individual members
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EXAMPLE OF INADEQUATE ROTATION RESISTANCE
Laboratory Structural Overload Test
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RECAP
1. Curtain walls are unique engineered
systems
2. Curtain walls may come in many
appearances; but,
3. Engineering principles rely on basic statics
4. Aluminum is a predictable material for
flexural members;5. Glass in not
6. The devil is in the details
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QUESTIONS?