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Tackling Concrete Problems in Old Buildings and their Control

by Ir Prof Paul P ANG Assistant 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

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Tackling Concrete Problems in Old Buildings and their Control

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  1. by Ir Prof Paul PANG Assistant Director/Existing Buildings 1 Buildings Department Tackling Concrete Problems in Old Buildings and their Control

  2. Why Concrete?

  3. Advantages • Durable • Economical • Environmentally friendly • Fire resistant • Easy maintenance • Versatile • Customized design

  4. Building Stock

  5. Total number of private buildings around 42,000 Building Stock Profile

  6. Common Problems

  7. Factors Affecting Performance • Design • Materials • Workmanship • Exposure • Usage and maintenance

  8. Design Strength Serviceability Fire resistance Durability Ductility

  9. Exposure conditions

  10. Materials

  11. Workmanship

  12. 2-storey UBW overloading change in use Usage and Maintenance

  13. Lack of Maintenance

  14. Unauthorized Building Works

  15. Consequences

  16. Consequences

  17. Accident

  18. To assess the overall condition To ascertain the extent and cause of problems To determine structural performance and integrity Investigation and Assessment

  19. 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 Testsdestructive, non-destructive Structural Assessmentupon inspection/investigation results Investigation & Assessment

  20. Investigation & Assessment visual inspection detailed investigation

  21. half-cell potential mapping Diagnostic Tests infrared thermography cover-meter resistivity measurement tell-tale carbonation depth

  22. Diagnostic Tests ground penetration radar Schmidt hammer test impact echo test ultrasonic test rebar tensile test concrete coring

  23. 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

  24. Determine overall repair regime Stop at source Provide protection Replace defective concrete and re-bars Provide structural strengthening Mitigation Measures

  25. Concrete Repair resin injection spray concrete patch repair patch repair injection grout recasting

  26. Strengthening and Retrofitting column encasement plate bonding fiber wrapping strengthening

  27. Proof Tests for Repair Works cube test Schmidt hammer test pull off test

  28. Control • Legislation • Enforcement • Support and assistance to building owners • Publicity and public education

  29. Legislation Buildings Ordinance (B.O. s24, s26, s26A, s28) Minor Works Control System (MWCS) Mandatory Building Inspection Scheme (MBIS) Mandatory Window Inspection Scheme (MWIS)

  30. 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)

  31. 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

  32. Planned Programmes • Operation Building Bright (OBB) • Large Scale Operation on repair and investigation • Mandatory Building Inspection Scheme (MBIS) • Mandatory Window Inspection Scheme (MWIS)

  33. 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

  34. 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

  35. 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

  36. MBIS

  37. MWIS

  38. 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

  39. Support and Assistance to Owners • OBB • MBIS • Building Safety Loan Scheme • Integrated Building Maintenance Assistance Scheme

  40. Publicity and public education • Promotion via media • Leaflets and website • Seminars

  41. Thank You

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