by

Ir Prof Paul PANGAssistant Director/Existing Buildings 1

Buildings Department

Tackling Concrete Problems in

Old Buildings and their Control

Why Concrete?

Advantages

Durable Economical Environmentally friendly Fire resistant Easy maintenance Versatile Customized design

Building Stock

Building Stock Profile

Total number of private buildings around 42,000

Common Problems

Factors Affecting Performance

Design Materials Workmanship Exposure Usage and maintenance

Design

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

To assess the overall condition

To ascertain the extent and cause of problems

To determine structural performance and integrity

Investigation and Assessment

Visual Inspection

Physical Appearance intact, loose, stained, cracked, deformed

Concrete Colour below 300℃ normal 300 – 600 ℃ pink to red

600 – 950 ℃ gray to buff above 950 ℃ buff

Detailed Investigation

In-situ Tests destructive, non-destructive

Structural Assessment upon inspection/investigation results

Investigation & Assessment

Investigation & Assessment

visual inspection detailed investigation

Diagnostic Tests

carbonation depthtell-taleresistivity measurement

infrared thermography half-cell potential mapping cover-meter

Diagnostic Testsground penetration radar impact echo test Schmidt hammer test

rebar tensile test concrete coring ultrasonic test

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

Investigation & Assessment

Determine overall repair regime

Stop at source

Provide protection

Replace defective concrete and re-bars

Provide structural strengthening

Mitigation Measures

Concrete Repair

injection groutresin injectionpatch repair

recastingspray concretepatch repair

Strengthening and Retrofitting

plate bonding fiber wrapping column encasement strengthening

Proof Tests for Repair Works

Schmidt hammer test pull off testcube test

Control

Legislation Enforcement Support and assistance to building

owners Publicity and public education

Legislation

Buildings Ordinance (B.O. s24, s26, s26A, s28)

Minor Works Control System (MWCS)

Mandatory Building Inspection Scheme (MBIS)

Mandatory Window Inspection Scheme (MWIS)

Enforcement on Dilapidated Buildings

Respond to reports from public & other parties

Issue advisory letters and repair orders

Prosecution

Government contractor action

Planned programmes (large scale operations)

Enforcement on Dilapidated Buildings

Statutory orders issued in the past 3 years

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

Operation Building Bright (OBB)

Large Scale Operation on repair and investigation

Mandatory Building Inspection Scheme (MBIS)

Mandatory Window Inspection Scheme (MWIS)

Operation Building Bright

One-off operation launched in 2009 by DEVB, HKHS and URA

Financial and technical assistance to owners

About 1 500 Category 2 composite and domestic buildings aged 30 or above will benefit

Large Scale Operation

Repair or Investigation of Buildings, for Enhancement, with Age Under Thirty Years (REIN-BEAUTY)

- 500 target buildings per year, aged below 30

Inspection of buildings aged 50 or above - about 4 000 buildings

Inspection of cantilevered slab canopies - about 3 700 buildings

MBIS and MWIS

Preventive Measures

Owners of target buildings are required to inspect and repair their buildings and windows regularly

2 000 MBIS target buildings per year

5 800 MWIS target buildings per year

MBIS

MBIS Features

Target BuildingsPrivate buildings aged 30 years

or above (except domestic buildings of 3 storeys or less)

Inspection ItemsCommon parts of buildings

and features on theExternal walls

Inspection Cycle10 years

MWIS

MWIS Features

Target BuildingsPrivate buildings aged 10 years

or above (except domestic buildings of 3 storeys or less)

Inspection ItemsAll windows of individual units and common parts of buildings

Inspection Cycle5 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

OBB MBIS

Building Safety Loan Scheme

Integrated Building Maintenance Assistance Scheme

Publicity and public education

Promotion via media Leaflets and website Seminars

Thank You