< Basic of Bracing

< Braced Panels Arrangements

< Trussing to Reduce Story Drift

< Tabular Frame Concept

Timber and Steel DesignTimber and Steel Design

Mongkol JIRAVACHARADETS U R A N A R E E INSTITUTE OF ENGINEERINGUNIVERSITY OF TECHNOLOGY SCHOOL OF CIVIL ENGINEERING

Lecture Lecture 1166 Lateral Resisting SystemLateral Resisting System

Wind & Building Pressure

windward(+)

leeward(-)

eleva

tor sh

aft

Wind pressure “pushes” outdoor air into the windward side of the building and “pulls” indoor air from the leeward side

Windward columns in tension

Leeward columns in compression

Sidesway of Buildings

Basic of BracingH H

∆

h

Story Drift:

H

Tens

ion

H

Compr

essio

n

H

Tens

ion

HTension

Dual-functioning Bracing:

X-bracing:

Single-story Multi-bay Bracing:

Bracing multistory buildings:

Opening

Vertical bracing

Vertical bracing

Ver

tical

bra

cing

Ver

tical

bra

cing

Bracing Around Floor Opening

H1

H2

H3

4.0 m

4.0 m

4.5 m

4.0 m

4,480 kg

6,000 kg

3,400 kg

13,880

30,575 30,575

14,9

60 T

30,5

75 C

20,89

2 T

13,880 C14

,821 T

14,9

60 T

14,9

60 C

10,480 C6,3

36 T

0

4,48

0 C

4,480 C

Bracing to Resist Wind Load

Building Frame to Resist Lateral LoadsTo dissipate energy in the moment-frame beams and to avoid soft story mechanisms

Earthquake

Beam-sway mechanism

Earthquake

Column-sway mechanism

“Soft-story”failure mode

Building Collapse in KOBE Earthquake (1995)

5th floor

Bracket-type Bracing:

Eccentrically Braced Frames (EBF)To dissipate energy in the shear or moment links and protect theremainder of the frame from inelastic action.

D-Braced EBF

e

Split-K-Braced EBF

e

V-Braced EBF

e e

Split-K is the best because large moments are avoided near the column

Forces in EBFD-Braced EBF Split-K-Braced EBF

e

M

V

P

e

M

V

P

EBF with W-Shape Bracing

Link length e

C of bracemust intersectC of beam at edge or insidelink

L

L

Stiffener plates bothsides with continuousfillet welds to weband flange

Intermediate stiffenerplate both sides forlink length e > 62.5 cm

Concentrically Braced Frames (CBF)To dissipate energy in yielding and buckling braces.

Diagonal braced CBF Inverted V-braced CBF V-braced CBF

X-braced CBF K-braced CBF

Braced Panels Arrangements

Trussing to Reduce Story Drift

(a) Bracing around Elevator Shaft

(b) Hat Truss (c) Belt Truss

Tabular Frame Concept Solid-wall tube

(a) (b)

World Trade Center - New York

Height: 417 and 415 meters

Ground Breaking: August 5, 1966

Opened: April 4, 1973 Terrorist attack: September 11, 2001

Typical Floor Plan of the World Trade CenterThe central core is designed to carry part ofthe vertical loads only.

The closely spaced tabular perimeter columnsact like a hollow tube supporting part of verticalloads and all the horizontal loads.

Sears Tower - ChicagoWorld's Tallest Building Until 1996

Height: 442 meters

Build: 1973

Terrorist attack: not yet

Actually nine 23-by-23 meters towers bundled together

World's Top 10 BuildingsRank Name City Country Feet Metres Stories

1 Petronas Tower 1 Kuala Lumpur Malaysia 1483 452 882 Petronas Tower 2 Kuala Lumpur Malaysia 1483 452 88

3 Sears Tower Chicago USA 1450 442 1104 Jin Mao Tower Shanghai China 1380 421 88

**5 Citic Plaza Guangzhou China 1,283 391 80

6 Shun Hing Square Shenzhen China 1,260 384 69

7 Empire State New York USA 1250 381 102

8 Central Plaza Hong Kong China 1227 374 78

9 Bank Of China Hong Kong China 1209 369 70

10 The Center Hong Kong China 1148 350 79

11 T & C Tower Kaohsiung Taiwan 1140 348 85

12 Aon Center Chicago USA 1136 346 80

13 John Hancock Chicago USA 1127 344 100

14 Burj al Arab Hotel Dubai UAE 1,053 321 60

15 Baiyoke Tower II Bangkok Thailand 1,050 320 90

Bundled Tube Structure

The Sears Tower is a bundled-tube structural design. The rigid outer walls act like the walls of a hollow tube. The Sears Tower is actually a bundle of nine tubes, and is considered one of the most efficient structures designedto withstand wind.

4.6 m typ.

3 @ 23 m = 69 m

3@

23m

=69

m

Typical Framing Plan

The Petronas TwinTowers were thetallest buildings in theworld from April 15th,1996 until October17th, 2003 whenTaipei 101 (FinancialCenter) was toppedout at 508m (1676ft).

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FUTURE TALLEST?Planned Shanghai tower may rise 500 meters.

MEGAFRAME Perimeter tube has columns,

belt trusses, bracing.