Tackling Concrete Problems
in
Old Buildings and their Control
by
Ir Prof Paul PANG
Assistant Director/Existing Buildings 1
Buildings Department
Why Concrete?
Advantages
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Durable
Economical
Environmentally friendly
Fire resistant
Easy maintenance
Versatile
Customized design
Building Stock
Building Stock Profile
Total number of private buildings around 42,000
12,000
No. of Buildings
11,000
10,000
9,000
8,000
7,000
6,000
5,000
4,000
3,000
2,000
1,000
0
< 11
11 to 20
21 to 30
31 to 40
Age
41 to 50
51 to 60
> 60
Common Problems
Factors Affecting Performance
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Design
Materials
Workmanship
Exposure
Usage and maintenance
Design
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Strength
Serviceability
Fire resistance
Durability
Ductility
Exposure conditions
Materials
Workmanship
Usage and Maintenance
2-storey UBW
overloading
change in use
Lack of Maintenance
Unauthorized Building Works
Consequences
Consequences
Accident
Investigation and Assessment
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To assess the overall condition
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To ascertain the extent and cause of problems
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To determine structural performance and integrity
Investigation & Assessment
Visual Inspection
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Physical Appearance
intact, loose, stained, cracked, deformed
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Concrete Colour
below 300℃
300 – 600 ℃
600 – 950 ℃
above 950 ℃
normal
pink to red
gray to buff
buff
Detailed Investigation
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In-situ Tests
destructive, non-destructive
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Structural Assessment
upon inspection/investigation results
Investigation & Assessment
visual inspection
detailed investigation
Diagnostic Tests
infrared thermography
half-cell potential mapping
cover-meter
resistivity measurement
tell-tale
carbonation depth
Diagnostic Tests
ground penetration radar
impact echo test
Schmidt hammer test
rebar tensile test
concrete coring
ultrasonic test
Investigation & Assessment
The Worst Credible Strength (WCS) is used for assessment
WCS = 1/n . Σfi (1-0.2/√n)
where
n = no. of samples (n ≥3)
fi = sample strength
Mitigation Measures
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Determine overall repair regime
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Stop at source
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Provide protection
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Replace defective concrete and re-bars
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Provide structural strengthening
Concrete Repair
patch repair
resin injection
injection grout
patch repair
spray concrete
recasting
Strengthening and Retrofitting
plate bonding
fiber wrapping
column encasement
strengthening
Proof Tests for Repair Works
Schmidt hammer test
cube test
pull off test
Control
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Legislation
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Enforcement
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Support and assistance to building owners
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Publicity and public education
Legislation
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Buildings Ordinance (B.O. s24, s26, s26A, s28)
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Minor Works Control System (MWCS)
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Mandatory Building Inspection Scheme (MBIS)
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Mandatory Window Inspection Scheme (MWIS)
Enforcement on Dilapidated Buildings
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Respond to reports from public & other parties
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Issue advisory letters and repair orders
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Prosecution
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Government contractor action
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Planned programmes (large scale operations)
Enforcement on Dilapidated Buildings
Statutory orders issued in the past 3 years
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Repair orders (building) – about 2 300
Repair orders (drainage) – about 1 500
Investigation orders – about 450
Demolition orders – about 10
Government contractor action on repair – about 1 350
Planned Programmes
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Operation Building Bright (OBB)
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Large Scale Operation on repair and investigation
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Mandatory Building Inspection Scheme (MBIS)
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Mandatory Window Inspection Scheme (MWIS)
Operation Building Bright
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One-off operation launched in
2009 by DEVB, HKHS and URA
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Financial and technical
assistance to owners
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About 1 500 Category 2
composite and domestic
buildings aged 30 or above will
benefit
Large Scale Operation
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Repair or Investigation of Buildings, for
Enhancement, with Age Under Thirty Years
(REIN-BEAUTY)
- 500 target buildings per year, aged below 30
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Inspection of buildings aged 50 or above
- about 4 000 buildings
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Inspection of cantilevered slab canopies
- about 3 700 buildings
MBIS and MWIS
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Preventive Measures
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Owners of target buildings are required to
inspect and repair their buildings and windows
regularly
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2 000 MBIS target buildings per year
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5 800 MWIS target buildings per year
MBIS
MBIS Features
Target Buildings
Inspection Items
Private buildings aged 30 years
or above (except domestic
buildings of 3 storeys or less)
Common parts of buildings
and features on the
External walls
Inspection Cycle
10 years
MWIS
MWIS Features
Target Buildings
Inspection Items
Private buildings aged 10 years
or above (except domestic
buildings of 3 storeys or less)
All windows of individual units
and common parts of buildings
Inspection Cycle
5 years
Minor Works Control System (MWCS)
Simplified System for the carrying out of
minor building works
Class 1: 44 items
Class 2: 40 items
Class 3: 42 items
Support and Assistance to Owners
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OBB
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MBIS
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Building Safety Loan Scheme
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Integrated Building Maintenance Assistance
Scheme
Publicity and public education
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Promotion via media
Leaflets and website
Seminars
Thank You