Foundations For Highrise Buildings.pdf

CIVL 1100 Discovering Civil and Environmental Engineering

Unit 10. Foundations for High-rise Buildings Buildings

Professor Limin Zhang, PhD, FASCE Department of Civil and Environmental Engineering The Hong Kong University of Science and Technology

• • • •

Types of foundations Design requirements Layout of foundations for high-rise buildings Geotechnical lab session

Hong Kong ranks first in the world in both skyscraper and high-rise count, with at least 52 skyscrapers over the height of 200 m, and more than 7,687 highrise buildings. A highrise is defined as a structure at least 35 m or 12 stories tall.

• • • •

Types of foundations Design requirements Layout of foundations for high-rise buildings Geotechnical lab session

Hong Kong ranks first in the world in both skyscraper and high-rise count, with at least 52 skyscrapers over the height of 200 m, and more than 7,687 highrise buildings. A highrise is defined as a structure at least 35 m or 12 stories tall.

Amazing Buildings Around the World Chicago Spiral

CCTV Beijing

The Nest, Beijing

Beijing Olympic Stadium Dubai Rotating Tower

Shanghai World Financial Center (492m)

828 m (2,716 ft)

Every single building must be supported on a solid founda foundation. tion. Types of foundations? Design requirements? Common layout of foundations for high-rise buildings?

Types of Foundations • Foundation  – As a structural member that connects the superstructure with the ground  – As a system member transferring loads to soils/rocks

• Foundation types  – Shallow foundations  – Deep foundations  – Offshore foundations

Shallow Foundations • Square • Rectangular • Circular • Continuous • Combined • Ring

Shallow Foundations

Shallow foundations, where applicable, are often the most economic.

HKUST Enterprise Center

Shallow Foundations Eiffel Tower Each of the four legs of Eiffel Tower is supported by a footing. Once the tallest structure in the world (1889), its foundation has not experienced any HKUST Enterprise Center

HKUST 10-story student hostel

excessive settlement.

Deep Foundations

Shaft friction f s

Toe resistance qb

Electricity Transmission towers (due to wind and broken cable)

Deep Foundations – Driven Piles • Prefabricated members driven into ground

Deep Foundations - Jacked Piles

Deep Foundations – Bored Piles/Drilled Shafts • Drill cylindrical hole, install reinforcement cage, and pour concrete

Bored Pile Construction: Flight Auger

Bored Pile Construction: Grab and Chisel

2.3 m diameter casing and grab

Bored Pile Construction: Drilling in Rocks

 A 2.3 m diameter drill bit

15

Bored Piles in Rocks: Bellout of Pile Toe D

D

f s

Soil

Bedrock < 30

qb = 5 –10 MPa Without bellout

< 1.5D

With bellout, 1.5D

The shaft resistance in soil layers is often ignored in Hong Kong, but is the primary resistance for piles when bedrock cannot be reached.

Bored Piles: Reinforcement Cage

Offshore Foundations vs. Water Depth

 Anchors Jacket

Risers Vertical risers Wellheads

Pipeline

Manifold

Subsea wellhead

Offshore Piles for Wind Turbines Gravity base, water depth < 25m

Monopile, water depth < 35 m

Jacket structure

Floating platform

Foundations used to support offshore wind turbines. The cost of foundations can represent up to 50% of the development cost for an offshore wind farm.

• • •

Types of foundations Design requirements

Layout of foundations for high-rise buildings

Performance Requirements • Strength requirements • Geotechnical strength: the ability of the soil or rock to accept the loads imparted by the foundation without failing (bearing failure) • Structural strength: the foundation’s structural integrity and its ability to safely carry the applied loads

• Serviceability requirements • Both total settlement and differential settlement must be smaller than their allowable values

• Constructability requirements • The foundation must be designed such that a contractor can build it without having to use extraordinary methods or equipment

• Economic requirements • Economic, but more conservative than superstructures

Consequences of failure (to future engineers like you?) If a builder builds a house for a man and does not make its construction firm, and the house he has built collapses and causes the death of the owner of the house, that builder shall be put to death. From

The Code of Hammurabi, Babylon, CIRCA 2000 B.C.

Building collapse in Shanghai due to foundation failure, 5:30 am, 27 June 2009 Photocredit: Pei Xing

Short Pile Scandal at Shatin, 1999 • 21 of the 36 large diameter bored

piles were 2-15 m shorter than required • 11 were founded in soil instead of bedrock • The two buildings were demolished in 2000 when constructed up to 33rd and 34th floors. • Total loss: HK$605 million

http://ihouse.hkedcity.net/~hm1203/li nks/hk-yu-chui.htm

Short Pile Scandal at Tin Shui Wai, 1999 • • • • •

Short piles found in 1999 Foundation retrofitted Over HK$100 million for maintenance Vacant for 13 years, sold in 2013 Loss of over HK$500 million + reputation

天頌苑兩幢大廈在九九年被揭發出現短樁問 題，房署其後斥資一億五千萬元為兩幢大廈 進行加固地基工程，當年房委會亦要賠償訂 金和利息開支予有關居屋的準買家，以及承 擔一千二百八十個單位延遲出售的損失，加 上七千萬元的訴訟費，涉及的金額高達六億 二千多萬元，但房署早前只獲保險公司賠償 兩億多元，因此事件令房署損失四億多元。 The Sun, 25 Jan. 2007

房委會推出這批居屋貨尾單位，主要集中於 當年爆出短樁醜聞的天水圍天頌苑的兩幢居 屋，事隔至今已十多年，房委會一直未有推 售這批單位. 東方電視, 5 Feb. 2013

5 Feb. 2013

Limit States A limit state is a condition beyond which a structural component ceases to fulfill the function for which it is designed.

• Strength limit states (ultimate limit states) 

Geotechnical resistance



Structural resistance

• Service limit states (function of structure under expected service loads) 

Deformations, vibration, cracking, local damage, deterioration

Some Ultimate Limit States for Foundations

Modes of Building Settlement

(a)

Uniform

(b)

Tilting without distortion

(c)

Distortion

Global Factor of Safety

Geotechnical resistance

Deformation

 Rn  FS 

  Qi

di  dn

Rn = Ultimate bearing capacity FS = Factor of safety Qi = Nominal load effect di = Estimated displacement under the nominal service load effect dn = Tolerable displacement

Recommended Factor of Safety

Allowable toe resistance of piles on rock (Code of Practice for Foundations 2004) Greater design values acceptable if verified by load tests. Piles can be founded in soils if with proper justifications.

Example: Capacity of Bored Piles on Rock D

D

≤ 1.5D

Without bellout

With bellout, 1.5D

qult = 10 MPa

qult = 10 MPa

Quiz Which of the following is NOT one of the basic requirements for designing a proper foundation? A. Strength B. Founding on bedrock C. Constructability D. Serviceability

In the Shatin short pile scandal, what was the major reason that threatened the safety of the buildings concerned? A. The pile diameter was too small to take the load B. The pile material was too weak to provide adequate strength C. The piles had not reached the bedrock to provide enough bearing capacity D. The design requirements were too high to achieve

Damage due to Differential Settlement

Tolerable Foundation Settlement for Structures on Sand (Eurocode 1, 1993)

Total settlement Isolated foundation

25 mm

Raft foundation

50 mm

Differential settlement between adjacent columns Open frames

20 mm

Frames with flexible cladding or finishes

10 mm

Frame with rigid cladding or finishes

5 mm

Relative rotation (angular distortion) 

1 / 500

Allowable Post-construction Settlement for High-speed Railways (Chinese Ministry of Railways 2007)

New passenger train, design speed (km/h)

General roadbed

Bridge approach

(mm)

(mm)

200-250

100

50

250-300

50

20

300-350

15

5

Ballast Subbase I Subbase II

Roadbed

The Leaning Tower of Pisa project 



1173-1178: 19.6 m diameter ring-shape footing & 3.5-story tower. Tilting started. 1360-1370: constructed to the belfry, about 56 m tall, tilting 3  toward south 1838: 2.5 m settlement. Construction of the trench (to see the beautiful carvings) added 0.5 m settlement. End of 20th century: 5.5 tilting, top 5.2 m off plumb. 1997-2001: soil extraction, back to 5 . °







°

°

37

Correcting the Tower Using Soil Extraction

Soil extraction (1997-2001): Back to 5.0 . There was no intention to correct the tower to perfectly vertical.

• • •

Types of foundations Design requirements Layout of foundations for high-rise buildings

International Commerce Center 2002-2010 • 118 floors, 484 m above ground • 241 closely spaced shaft-grouted friction barrettes • Founding level: – 60 mPD to -96 mPD

Foundation for International Commerce Center

Bank of China Tower

1985-1990

Main column

Wall

Drainage Basement Diaphrag wall Grouting Grouting

Caisson

Caisson

Load (MN) D

D+L

Bell-out +/- W

Diameter (m)

 AA

327

380

131

10.5

BB

277

322

93

9.5

DD

180

209

98

8.2

EE

142

164

79

7.2

The Centre

1995-1998

The Center used four 24 m diameter caissons of an average depth of 45 m as the principal foundation.

Shanghai Jinmao Tower 1994-1999

• • •

88 story /360 (420) m high Clay /silt 429 driven steel tube piles, d=914 mm, t =20 mm, L=83 m

The Shanghai World Financial Center (left) 45

Taipei 101 508 m high

Taipei 101: Evenly Distributed Bored Piles  A

B

C

D

E

F

G

H

H.5

J

K

L

M

N

P

Q

R

S

T

1

• Tower

1.6

 – 380 bored piles

2 3

 – 1.5 m diameter

4

 – 62 – 81 m length

5

6

 – Socket into bedrock

7

8

Podium

 – 15 – 33 m (Avg. 23 m)

9

• Podium

10

 – 167 bored piles

11

12

 – 2.0 m diameter

13

 – 57 – 81 m length

14

15

 – Socket into bedrock

16

 – 5 -29 m (Avg. 15 m)

17

18

19

Tower

Burj Khalifa, Dubai 2004-2010 Height: 828 m

Tower area • 196 bored piles • D = 1.5 m, L = 47.45 m • Raft at -7.55 m, thickness = 3.7 m Podium Area • D = 0.9 m, L = 30 m • Raft at -4.85 m, thickness = 3.7 m

Introduction to the Geotechnical Engineering Laboratory Session Building collapse due to liquefaction in 1964 Niigata earthquake

In 1971, the upstream of  the lower San Fernando dam in California failed about a minute after the end of an earthquake, an interesting punctuation mark to the liquefaction debate at that time.

Soil Liquefaction • A phenomenon where a saturated soil substantially loses its strength and stiffness in response to an applied shear stress, usually earthquake shaking, causing it to behave like a liquid. • The phenomenon is most often observed in saturated, loose sandy soils.

Sand boils in liquefaction

Your Geotechnical Laboratory: Laboratory Soil Liquefaction Tests

Water table

• Prepare saturated sand beds of different densities • Shake the sand beds at different intensities • Observe soil liquefaction

Test Objectives • To gain insight into soil liquefaction and to identify the key factors that influence soil liquefaction

Shaking intensity

Frequency

Duration

Water content Soil density

Geotechnical Lab Session Week

Date 17 Nov 2015

12 19 Nov 2015

24 Nov 2015 13 26 Nov 2015

Time

Session

Group

13:00-14:50

LA 3

C1-C4

17:00-18:50

LA 2

B1-B4

9:00-10:50

LA 4

D1-D4

13:00-14:50

LA 1

A1-A4

13:00-14:50

LA 3

C5-C8

17:00-18:50

LA 2

B5-B8

9:00-10:50

LA 4

D5-D8

13:00-14:50

LA 1

A5-A8

Refer to “Lab Groups and Name Lists for Geotechnical Engineering Experiments”