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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%205

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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?