25 framed tube

7/27/2019 25 Framed Tube

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24 Framed tube Copyright G G Schierle, 2001-06 Press Esc to end, for next, for previous slide 1Framed Tube


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24 Framed tube Copyright G G Schierle, 2001-06 Press Esc to end, for next, for previous slide 2

Framed tube

Framed tubes have narrowly spaced exterior

columns that, combined with spandrel beams,

form rigid frames to resist lateral load.

1 Framed tube

2 Framed tube with core

3 Shear lag in framed tube


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Large drift

(unglued boards resist independently)

Small drift

(glued boards resist in synergy

shear joins tension & compression)

Gue-lam beam anlogy


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Framed tube

Framed tubes have narrowly spaced exterior

columns that, combined with spandrel beams,

form rigid frames to resist lateral load.

1 Framed tube

2 Framed tube with core

3 Shear lag in framed tube

4 Framed tube with outriggers5 Prefab framed tube

6 Prefab framed tube element

A Shear lag at mid faade

B Shear peak at cross walls

C Joint at inflection point of zero bending


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Column buckling K-factor review

Pin support Flag pole Moment frame column

K = 1

K = 2

K = 1

(theoretic, assumesperfectly rigid joints)

K ~ 1.2 (recommended,includes a safety factor

due to semi-rigid joints)


6/1524 Framed tube Copyright G G Schierle, 2001-06 Press Esc to end, for next, for previous slide 6

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 tower

2 Floor framing

3 Prefab steel element

4 Typical column cross section



CBS Tower New York

Architect: Eero Saarinen

The 38-story CBS tower has a framed tube of concrete

columns that are triangular on the upper floors and diamondshaped on the ground floor.

The columns have niches for mechanical ducts that decrease

with decreasing duct sizes from mechanical floor on top but

not from the second floor mechanical room.A Top floor columns

B 2nd floor columns

C 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: 155x125x494 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 Angeles

Architect: I M Pei

Engineer: CBM

Framed tube exterior

combined with braced core

AMP Tower Melbourne

Architect/Engineer: SOM

Framed tube tower,

flanked by L-shapedlow-rise wing



Sears tower ChicagoArchitect/Engineer: SOM

The Sears tower is a bundled tube structure

Bundled tubes have interior walls to transfer shear from

tension to compression side to avoidshear lag

1 Bundled tubes reduce shear lag

2 Large shear lagin single tube

3 Framing plan (3x3x75x75)

4 Architectural plan5 2-module top floors

6 5-module floors

7 7-module floors

8 9-module floors

9 Axon

Bu

ndle

d

tu

be


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B h



HVAC floor

HVAC floor

Lobby

Spandrel beamsV=(M0-M1)/B=(192821-174641)/110 V = 165 k

M=V L/2 = 165 (5x12) M = 9,900 k

S = M/Fb = 9900/22ksi S = 450 in3

Use W18x234 466 > 450

Base shear

V= 30psf x75x 414/1000 V = 932 k

Overturn moments

M0 = 30psfx75x4142/(2x1000) M0 = 192,821 k

M1 = 30psfx75x3942/(2x1000) M1 = 174,641 k

Vc =(L/2) V/B = 5x932/110 Vc = 42 kMc = Vc h/2 = 42x10x12 Mc = 5040 k

Gravity load

P = 30 floors x252x100/(3x1000) P = 625 k

Lateral load

P=M0

/ B = 192,821/110 P= 1753 k

P = 625+1753 P = 2378 k

Ptot = P+MBx =2378+5040x0.17 Ptot = 3235 k

Use W14x665 3372 > 3235

Mid-wall-columns

Vc = L V/B=10x932/110 Vc = 85 k

Mc = Vc h/2= 85x10x12 Mc = 10200 kAxial load (gravity)

P =30 floors x100x10x15/1000 P = 450 k

Ptot=P+MBx =450+10200x0.175 Ptot = 2235k

Use W14x500 2490 > 2235

Framed TubeAssume

30-story steel office building.

Exterior columns resist gravity

and lateral loads

Design Ground floor

Column KL=1.2x20 KL= 24

Wind pressure P = 30 psf

DL = 80 psf

LL = 30 psf (beams @ 60%)

LL = 20 psf (columns @ 40%) = 110 psf (beams)

= 100 psf (columns)

B h



HVAC floor

HVAC floor

Lobby

Joists

M=wL2/8=(110psf x10/1000)x302/8 M = 124 kS = M/Fb = 124kx12/22ksi S = 68 in3

Use S18x54.7 89.4 > 68

Spandrel beamsV=(M0-M1)/B=(192821-174641)/110 V = 165 k

M=V L/2 = 165/(5x12) M = 9,900 k

S = M/Fb = 9900/22ksi S = 450 in3

Use W18x234 466 > 450

Base shear

V= 30psf x75x 414/1000 V = 932 k

Overturn moments

M0 = 30psfx75x4142/(2x1000) M0 = 192,821 k

M1 = 30psfx75x3942/(2x1000) M1 = 174,641 k

Vc =(L/2) V/B = 5x932/110 Vc = 42 kMc = Vc h/2 = 42x10x12 Mc = 5040 k

Gravity load

P = 30 floors x252x100/(3x1000) P = 625 k

Lateral load

P=M0

/ B = 192,821/110 P= 1753 k

P = 625+1753 P = 2378 k

Ptot = P+MBx =2378+5040x0.17 Ptot = 3235 k

Use W14x665 3372 > 3235

Mid-wall-columns

Vc = L V/B=10x932/110 Vc = 85 k

Mc = Vc h/2= 85x10x12 Mc = 10200 kAxial load (gravity)

P =30 floors x100x10x15/1000 P = 450 k

Ptot=P+MBx =450+10200x0.175 Ptot = 2235k

Use W14x500 2490 > 2235

Framed TubeAssume

30-story steel office building.

Exterior columns resist gravity

and lateral loads

Design Ground floor



DL = 80 psf


LL = 20 psf (columns @ 40%) = 110 psf (beams)

= 100 psf (columns)



Steel structure weight

Structure 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 stories

B 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 only

F Structure weight for gravity and lateral optimized

G Structure weight for gravity and lateral not optimized

H Empire State building New York

I Chrysler building New York

J World Trade center New YorkK Sears tower Chicago

L Pan Am building New York

M United Nations building New York

N US Steel building Pittsburgh

O John Hancock tower Chicago

P First Interstate building Los AngelesQ Seagram building New York

R Alcoa building Pittsburgh

S Alcoa building San Francisco

T Bechtel building San Francisco

U Burlington House New YorkV IDS Center Minneapolis

W Koenig residence Los Angeles


14/1524 Framed tube Copyright G G Schierle, 2001-06 Press Esc to end, for next, for previous slide 14Tragedy at World Trade Center

E i 20th t h


15/1524 Framed tube Copyright G G Schierle 2001-06 Press Esc to end for next for previous slide 15

Exercise

Design 20th-story columns

Assume



DL = 80 psf


LL = 20 psf (columns @ 40%)

= 110 psf (beams) = 100 psf (columns)

20th story shear

V= V = k

Overturn moments

M20 = M20 = k

Column shear (B = 110, L=10)

Vc = (L/2) V/B = Vc = k

Column bending (in k)

Mc = Vc h/2 Mc = k

Gravity load

P = 11 floors x252x100 psf /(3x1000) P = k

Lateral load

P= P = k

Gravity + lateral load

P = P = 441 kTotal load (Ptot = P+ Mc Bx)

Ptot = Ptot = 659 k

Use W14x ____> 659

HVAC floor

HVAC floor

Lobby

9.5x

13+20=1

44

25 framed tube

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