10 framed tube

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Framed tube Prof Schierle 1

Framed Tube


Framed tubeFramed tubes have narrowly spaced exterior columns that, combined with spandrel beams, form rigid frames to resist lateral load.

1 Framed tube2 Framed tube with core3 Shear lag in framed tube


Large drift(unglued boards resist independently)Small drift (glued boards resist in synergyshear joins tension & compression)

Gue-lam beam anlogy

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Framed tubeFramed tubes have narrowly spaced exterior columns that, combined with spandrel beams, form rigid frames to resist lateral load.

1 Framed tube2 Framed tube with core3 Shear lag in framed tube4 Framed tube with outriggers5 Prefab framed tube6 Prefab framed tube element

A Shear lag at mid façadeB Shear peak at cross wallsC Joint at inflection point of zero bending


Column buckling K-factor review

Pin support Flag pole Moment frame column

K = 1K = 2

K = 1 (theoretic, assumes perfectly rigid joints)

K’ ~ 1.2 (recommended,includes a safety factordue to semi-rigid joints)


World Trade Center New YorkArchitect: Minoru Yamasaki Engineer: Skilling / Robertson

The World Trade center had a Framed Tube structure,composed of closely spaced columns (~ 1 meter). Moment resisting beam / column joints formed a lattice wall to resist gravity and lateral loads.

1 Axonometric view of one tower2 Floor framing3 Prefab steel element4 Typical column cross section

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CBS Tower New YorkArchitect: Eero Saarinen

The 38-story CBS tower has a framed tube of concretecolumns that are triangular on the upper floors and diamondshaped on the ground floor.

The columns have niches for mechanical ducts that decreasewith decreasing duct sizes from mechanical floor on top butnot from the second floor mechanical room.

A Top floor columnsB 2nd floor columnsC Ground floor columns

Concrete floors span between core and framed tube:

• One-way rib slabs face the core• Two-way waffle slabs at corners

Size: 155’x125’x494’ high (47x38x151m) Typical story height: 12’ (3.66m)Floor-to-ceiling height: 8.75’ (2.67m)Height/width ratio 3.9


First Interstate Bank Los AngelesArchitect: I M PeiEngineer: CBM

Framed tube exteriorcombined with braced core

AMP Tower MelbourneArchitect/Engineer: SOM

Framed tube tower, flanked by L-shaped low-rise wing


Sears tower ChicagoArchitect/Engineer: SOMThe Sears tower is a bundled tube structureBundled tubes have interior walls to transfer shear from tension to compression side to avoid shear lag

1 Bundled tubes reduce shear lag2 Large shear lag in single tube3 Framing plan (3x3x75’x75’)4 Architectural plan5 2-module top floors

6 5-module floors7 7-module floors8 9-module floors9 Axon

Bu

nd

led

tu

be

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Fazlur Khan high-rise concepts

http://en.wikipedia.org/wiki/Fazlur_Khan


Mid-wall-columnsVc = L V/B=10x932/110 Vc = 85 kMc = Vc h/2= 85x10’x12” Mc = 10200 k”Axial load (gravity)P =30 floors x100x10x15/1000 P = 450 kPtot=P+MBx =450+10200x0.175 Ptot = 2235kUse W14x500 2490 > 2235

Framed TubeAssume 30-story steel office building.Exterior columns resist gravityand lateral loads

Design Ground floorColumn KL=1.2x20’ KL= 24’Wind pressure P = 30 psfDL = 80 psfLL = 25 psf (beams @ 50%)LL = 20 psf (columns @ 40%) = 105 psf (beams) = 100 psf (columns)

Base shearV= 30psf x75’x 414/1000 V = 932 kOverturn momentsM0 = 30psfx75’x4142/(2x1000) M0 = 192,821 k’M1 = 30psfx75’x3942/(2x1000) M1 = 174,641 k’

Vc =(L/2) V/B = 5’x932/110’ Vc = 42 kMc = Vc h/2 = 42x10’x12” Mc = 5040 k”Gravity loadP = 30 floors x252x100/(3x1000) P = 625 kLateral loadP=M0 / B = 192,821/110 P= 1753 k P = 625+1753 P = 2378 kPtot = P+MBx =2378+5040x0.17 Ptot = 3235 kUse W14x665 3372 > 3235

HVAC floor

HVAC floor

Lobby

42

4-1

0 =

41

4’

42

4-3

0 =

39

4’


HVAC floor

HVAC floor

LobbySpandrel beamsV=(M0-M1)/B=(192821-174641)/110 V = 165 kM=V L/2 = 165 (5’x12”) M = 9,900 k”S = M/Fb = 9900/22ksi S = 450 in3

Use W18x234 466 > 450






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HVAC floor

HVAC floor

Lobby

JoistsM=wL2/8=(105psf x10’/1000)x302/8 M = 118 k’S = M/Fb = 118k’x12”/22ksi S = 64 in3

Use S18x54.7 89.4 > 64

Spandrel beamsV=(M0-M1)/B=(192821-174641)/110 V = 165 kM=V L/2 = 165/(5’x12”) M = 9,900 k”S = M/Fb = 9900/22ksi S = 450 in3

Use W18x234 466 > 450







Steel structure weightStructure weight per floor area defines efficiency of steel structures. For gravity load alone, the weight increase only slightly with height.Lateral load, however, accelerates the increase at a non-linear rate.

1 Structural weight vs. building height by Fazlur Kahn2 Structural weight per floor area of actual buildings

A Number of storiesB Structure weight in psf (pounds per square foot)C Structure weight in N/m2

D Structure weight for floor framing onlyE Structure weight for gravity load onlyF Structure weight for gravity and lateral optimizedG Structure weight for gravity and lateral not optimizedH Empire State building New YorkI Chrysler building New YorkJ World Trade center New YorkK Sears tower ChicagoL Pan Am building New YorkM United Nations building New YorkN US Steel building PittsburghO John Hancock tower ChicagoP First Interstate building Los AngelesQ Seagram building New YorkR Alcoa building PittsburghS Alcoa building San FranciscoT Bechtel building San FranciscoU Burlington House New YorkV IDS Center MinneapolisW Koenig residence Los Angeles


Tragedy at World Trade Center

10 framed tube

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