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”
