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Wen Dazhi, BSc, PhDPE, PE(Geo), AC(Geo), CE, MICE, MIEAust, CPEng
BUILDING DAMAGE ASSESSMENT
amage ca egor es
Basis of damage assessment
Staged design approach and design assumptions
Case studies of buildings on mixed foundations
GeoSS 10112009 2
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DAMAGE CATEGORIES
1) Visual appearance or aesthetics;
2) Serviceability or function; and
GeoSS 10112009 3
3) Stability.
DAMAGE CATEGORIESCategory Typical crack
width (mm)Effects
Negligible 0.1mm Hairline cracks only
25mm Beams lose bearing, walls requireshoring. Windows broken withdistortion. Danger of instability.
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DAMAGE CATEGORIES
Category Typical crackwidth (mm)
Repair
Negligible 0.1mm Hairline cracks only
V. Slight 25mm Major repairing work involvingpartial or complete rebuilding.
AS2870 DAMAGE CLASSIFICATION
FOR WALLS
Description of typical damage and required repair Approximatecrack width limit
Damagecategory
Hairline cracks
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AS2870 - DAMAGE CLASSIFICATION
FOR CONCRETE FLOORS
Description of typical damage Approximate crack width limitin floor
Changein offset
Damagcate or
Hairline cracks, insignificantmovement of slab from level.
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Not economic to restrict to no damage.
DAMAGE CATEGORIES
Typically allow up to slight damage for
most structures.
Restrict to very slight damage for
GeoSS 10112009 9
significance, such as heritage buildings.
BASIS OF BUILDING DAMAGE
ASSESSMENT
r er on or onse o v s e crac ng:
Limiting tensile strain.
Local strain at onset of cracking much
GeoSS 10112009 10
sma er an m ng ens e s ra n.
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MODES OF MOVEMENT
- NOT DAMAGING
GeoSS 10112009 11
UNIFORM
SETTLEMENTUNIFORM TILT
RIGID BODY TILT
GeoSS 10112009 12
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MODES OF MOVEMENT
- DAMAGING
GeoSS 10112009 13
BENDING/SHEARHORIZONTAL
EXTENSION
MODES OF MOVEMENT - DAMAGING
AND
SHEARSTRAINS
THAT
GeoSS 10112009 14
DAMAGE
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LIMITING TENSILE STRAIN VS DAMAGE
CATEGORIES FOR MASONRY BUILDINGS
Limiting tensile Damage Class Typical crackstrain (%) width (mm)
0.0 - 0.05 Negligible
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TOTAL CALCULATED STRAINS
Horizontal strain and the bending strain
Horizontal strain combined with diagonal
strain using a Mohrs circle of strain.
GeoSS 10112009 17
INTERACTION DIAGRAM, /L, h & L/H
GeoSS 10112009 18
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Stage 1 - if settlement
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ASSUMPTIONS FOR STAGE 2
Building simply follows the green fieldsettlement.
Building is made of masonry.
Settlements due to consolidation are even,and do not induce bending or horizontal
strain.
GeoSS 10112009 21
First two assumptions are consideredconservative i.e. they over-predict strainand damage.
STAGE 3 ASSESSMENT
Refinement of Stage 2 assessment.
Foundation details are considered.
Ground beams will reduce horizontalextension to a negligible value.
Piles will reduce settlements and
GeoSS 10112009 22
.
Continuous foundations, e.g. strip
footings or rafts are less prone to
damaging differential settlements.
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STAGE 3 ASSESSMENT
ec s o so -s ruc ureinteraction: building stiffness will
modify Green Field settlements,
typically making them wider and
GeoSS 10112009 23
.
BUILDING DAMAGE ASSESSEMENT SUMMARY SHEET
Project/ Contract Number
Name of Building:
Address:
Description of Structure:
PHOTO
Description of Foundations
Drawings available YES/NO
Result of Preliminary AssessmentMaximum settlement:Maximum slope:
Second stage assessment required YES/NO
Summary
Sheet
GeoSS 10112009 24
Maximum settlement:Maximum ground slope:Maximum tensile strain:
Detailed evaluation required YES/NO
Detailed Assessment attached YES/NOProtection measures needed YES/NO
Protection measures proposed:
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BUILDING DAMAGE ASSESSMENT
The theory works well in buildings on
uniform foundations.
Reliance should not be placed on
theoretical assessment alone.
Careful inspection of buildings should be
carried out. There would be tell-tale si ns
GeoSS 10112009 25
that indicate problems in the buildings.
Detailed structural assessment will be
necessary for those buildings.
CONSOLIDATION SETTLEMENTS -
COMMON ASSUMPTIONS
Consolidation settlements are generally
relatively uniform if the depth and
compressibility of the soft soils are uniform.
If uniform,consolidation settlements do not
GeoSS 10112009 26
cause tensile strain and do not cause damage.
Consolidation settlements commonly assumed
to have negligible effect.
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CASE STUDIES OF BUILDINGS ON
MIXED FOUNDATION
For buildings on mixed foundations orfounded over varying depths of soft clay, the
common assumptions:
That it is conservative to assume that the
building moves with the ground
That consolidation settlements do not induce
GeoSS 10112009 27
significant differential settlement or tensilestrain
ARE NOT APPLICABLE
FOOCHOW METHODIST CHURCH
GeoSS 10112009 28
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Sunda
FOOCHOW METHODIST CHURCH
School
Newkindergartensection
Old Church,wrapped inextension
GeoSS 10112009 29
Farrer Park StationLittleIndiaStation Cut & cover tunnel
RaceCourseRoadRotan Lane
FOOCHOW METHODIST CHURCH
Foochow Methodist ChurchKerbau Road RaceCourseLane Kinta Road Robert LaneRoad
N
LittleIndiaStation Farrer Park StationCut & Cover TunnelBored Tunnel Bored Tunnel
GeoSS 10112009 30
Old Alluvium
Kallang Formation
J urong Formation
90.00
70.00
80.00
100.00
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FOOCHOW
METHODIST
CHURCH
GeoSS 10112009 31
17.5m
105
-40 -20 0 20 40 60 80 100
Deflection (mm)
l
-10 0 10 20 30 40 50 60
Deflection (mm)
FOOCHOW METHODIST CHURCH
75
85
95
Red
uced
Leve
90
100
Reduced
Level
GeoSS 10112009 32
55
65
PredictedMeasuredFormation Level
70
80
PredictedMeasuredFormation Level
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1ststrut00
FOOCHOW METHODIST CHURCH
Consolidation settlement
2ndstrut3rdstrut
4thstrut
5thstrut
6thstrut
5
10
15
20
25
50
100(mm)
Settlement at final excavation level
GeoSS 10112009 33
30
35
(m)
40 20 0 (mm)
Wall deflection at finalexcavation level
base slab
FOOCHOW METHODIST CHURCH
0
20
40
1 10 100 1000Days
t(mm Excavation at 3rdstrut level
60
80
100
120
Settlemen Excavation resumed
from 3rdto 4thstruts
Excavation at finalformation
-212-Sep-9
8
11-Nov-9
8
10-Jan-9
9
11-Mar-9
9
10-May-9
9
09-Jul-99
07-Sep-9
9
06-Nov-9
9
05-Jan-0
0
05-Mar-0
0
04-May-0
0
03-Jul-00
01-Sep-0
0
31-Oct-0
0
30-Dec-0
0
28-Feb-0
1
29-Apr-01
28-Jun-0
1
27-Aug-0
1
GeoSS 10112009 34
0
2
4
6
8
10
Drawdown(m
GWP3071 GWP3081 GWP3051-1 GWP3051-2 GWP3051-3
Excavation completed and baseslab cast
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FOOCHOW METHODIST CHURCH
RaceCourseRoadStruts for cut & covertunnel
Kindergartenon H-steel piles
3-storey sanctuaryon pad footings
ton to t esanctuary on H-steelpiles
. m
GeoSS 10112009 35
RotanLane
Sunday Schoolon Bakau piles
Chander L ane
FOOCHOW METHODIST CHURCH
Moderate toComputer
Severe
damage
(12mm crack)
at 15mm
settlement,
Room
GeoSS 10112009 36
e ore
excavation
started
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FOOCHOW METHODIST CHURCH
GeoSS 10112009 37
Computer Room
-Nov-98
-Dec-98
-Jan-99
-Feb-99
-M
ar-99
-Apr-99
-M
ay-99
-Jun-99
-Jul-99
-Aug-99
-Sep-99
-Oct-99
-Nov-99
-Dec-99
m)
FOOCHOW METHODIST CHURCH
0
10
20
30
05
05
05
05
05
05
05
05
05
05
05
05
05
05
lSettlement/Cra
ckwidth(
GeoSS 10112009 38
40
50Differentia
CME404 CME405 CMA3641 CMD3772 Differential Settlement
Second Floor Third Floor First Floor First Floor Between L351 / L381
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FOOCHOW METHODIST CHURCH
0.00E+00
5.00E-04
1.00E-03
05-Nov
-98
05-Dec
-98
05-Jan-9
9
05-Feb
-99
05-Mar
-99
05-Apr
-99
05-May
-99
05-Jun-99
05-Jul-9
9
05-Aug
-99
05-Sep
-99
05-Oct-99
05-Nov
-99
05-Dec
-99
otation(Radiant)
GeoSS 10112009 39
. -
2.00E-03
R
Rotation (Radiant) TM3211
FOOCHOW METHODIST CHURCH
GeoSS 10112009 40
Junction of Sunday
School and
Kindergarten
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FOOCHOW METHODIST CHURCH
Original building
pos onNeighbouring
unit
GeoSS 10112009 41
For buildings in a terrace, rigid body tilting will lead to
tearing at the junction with the neighbour unit.
posi tion
148 RACE COURSE ROAD
GeoSS 10112009 42
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148 RACE COURSE ROAD
No 148 Race
Course Road
No 146
GeoSS 10112009 43Shirlaw, Wen, Algeo & Patterson-Kane (2003)
148 RACE COURSE ROAD
Settled by 107mmNo 146, piled
GeoSS 10112009 44
Building tilting away
from the adjacent
structure
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148 RACE COURSE ROAD
GeoSS 10112009 45
148 RACE COURSE ROAD
GeoSS 10112009 46
Adjacent buildings on different foundations: Old buildings on footings
butted against newer buildings on deep foundations.
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Original building
148 RACE COURSE ROAD
posi tion
Settled building
GeoSS 10112009 47
Racking action causes damage, in particular at door /
window frames / arches.
Masjid Wak Tanjong
GeoSS 10112009 48
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Masjid Wak Tanjong
GeoSS 10112009 49
Masjid Wak Tanjong
Cross
Walls
GeoSS 10112009 50
CCL Paya Lebar
Station D/W Layout
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Masjid Wak Tanjong
GeoSS 10112009 51
Interface between Kallang Formation and OA
Excavation Level: RL85.7m
Masjid Wak Tanjong
Typical
Excavation
Sequence16.7m
GeoSS 10112009 52
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Masjid Wak Tanjong
GeoSS 10112009 53
Masjid Wak Tanjong
GeoSS 10112009 54
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Masjid Wak Tanjong
in piezometric level:
At 9m below ground: 1.5m
At 15m below ground level: 3m
GeoSS 10112009 57
27m below ground level: 6m
20/03/03 01/08/04 14/12/05 28/04/07 09/09/08
Masjid Wak Tanjong
-70.00
-60.00
-50.00
-40.00
-30.00
-20.00
-10.00
0.00
GeoSS 10112009 58
-90.00
- .
505 519 520
Building Settlements
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Masjid Wak Tanjong
GeoSS 10112009 59
Masjid Wak Tanjong
GeoSS 10112009 60
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Masjid Wak Tanjong
GeoSS 10112009 61
Part of the building on piles and part on footings
Damaging at small differential settlements.
Other Examples
GeoSS 10112009 62
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GeoSS 10112009 63
Annex structureon footings
abutting buildings
on piles
PiledFootings
GeoSS 10112009 64
CIRCLELINESTAGE 1
Nicoll Highway Station
FILL (6.5m THICK)
SOFT MARINE CLAY
(33m THICK)
OLD ALLUVIUM
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GeoSS 10112009 65
Singsation
GeoSS 10112009 66
.
SOFT MARINE CLAY
(33m THICK)
SANDY OLD ALLUVIUM
SETTLEMENT
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STAR SINGSATION KTV CLUB
GeoSS 10112009 67
GeoSS 10112009 68
Walkway - piled
Main load bearing
column - shallow
foundations
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No 7 CANTONMENT ROAD
136mm 72mm 55mm 20mm 9mm72mm
No 7 No 9
GeoSS 10112009 69
Fill & Organic clay Weathered Jurong Formation
Shirlaw, Wen, Algeo & Patterson-Kane (2003)
No 7 CANTONMENT ROAD
GeoSS 10112009 70Shirlaw, Wen, Algeo & Patterson-Kane (2003)
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No 7 CANTONMENT ROAD
Party Wall
to No 9
GeoSS 10112009 71Shirlaw, Wen, Algeo & Patterson-Kane (2003)
Buildings over varying depths of soft
clay - usually a terrace problem
GeoSS 10112009 72
Pocket of soft clay
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GeoSS 10112009 73
GeoSS 10112009 74
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POSSIBLE MEASURES
o en y u ngs a are unusua ysensitive to settlement
To carry out protective measures
GeoSS 10112009 75
IDENTIFICATION
To identify buildings on mixed foundations -
A&A drawings
To identify locations of variation in geology, in
particular along terrace houses
GeoSS 10112009 76
A general walk around the site building
inspection
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IDENTIFICATION
Look at the geological profile / soilinvestigation data - consolidation often
(marine/estuarine)
Sensitive buildings often show some signs ofdamage or repair - existing cracks / spalling
Watch out for additions to old buildings or new
GeoSS 10112009 77
buildings abutting old buildings With terrace houses, signs of local dips in theroof line, local settlements in the road outside
or local damage to drains / aprons
PROTECTIVE MEASURES
Recharge wells to control consolidation-
tight wall and with wells installed before
excavation starts)
Separate the parts of the structure on differentfoundations
GeoSS 10112009 78
Prop (where necessary for safety) and repairafterwards
Underpinning
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Methods of Mair, Taylor and Burland to be
CONCLUSIONS
.
Stage 1 - if < 10mm, no need to considerfurther
Stage 2 - green field assessment. Assumes
GeoSS 10112009 79
Stage 3 - Detailed evaluation, taking intoaccount building stiffness and foundations
CONCLUSIONS
Buildings on mixed foundations are
extremely sensitive to settlement and more
susceptible to damage than other buildings.
GeoSS 10112009 80
foundations are required.
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THANKS
GeoSS 10112009 81