Tackling Concrete Problems in Old Buildings and their Control by Ir Prof Paul PANG Assistant Director/Existing Buildings 1 Buildings Department 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 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 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 Investigation and Assessment To assess the overall condition To ascertain the extent and cause of problems To determine structural performance and integrity Investigation & Assessment Visual Inspection Physical Appearance intact, loose, stained, cracked, deformed Concrete Colour below 300℃ 300 – 600 ℃ 600 – 950 ℃ above 950 ℃ normal pink to red gray to buff buff Detailed Investigation In-situ Tests destructive, non-destructive 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 Determine overall repair regime Stop at source Provide protection Replace defective concrete and re-bars 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 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 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 OBB MBIS Building Safety Loan Scheme Integrated Building Maintenance Assistance Scheme Publicity and public education Promotion via media Leaflets and website Seminars Thank You