civl 11

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  1. Common Types of Building Defects
    • Foundation issues
    • Cantilever structures
    • Water seepage
  2. Causes of soil movement
    • Moisture –volume of soil changes with moisture contents
    • Pressure –soil consolidate under pressure/loading
    • Vibration –traffic, piling, earthquake, etc.
    • Faulty foundation design / construction
    • Settlement of reclaimed / landfill site
  3. Settlement and reclaimed land - All reclaimed land will settle, Allow for … years generally for settlement, the faster the settlement, ……; Speed and amount depends on…
    • 5-7; the faster the construction can begin
    • fill materials (e.g. sand) and the seabed material
  4. TKO building settlement – cause
    • reclaimed land
    • Strategic sewage discharge program-sewage tunnel built under TKO; inflow of ground water into the tunnel → ground water level drops → further settlement
  5. TKO building settlement –consequence
    • superstructure generally not affected
    • joints between building and roads may crack appearance
    • underground services e.g. burst pipes
  6. Type of piles and settlement
    • Friction piles –more problematic: likely to sink with soil together
    • end-bearing piles: loads transferred to bedrock → building itself is stable (doesn’t settle)
  7. TKO building settlement –remedies
    • seal up the cracks
    • use flexible joints
    • On-site testing to ensure quality of piles (e.g. ultrasonic test)
  8. Cantilevered Structures – reason for collapse
    • Tension on top → main reinforcement on top; Cracks more likely on surface under tension
    • Main reinforcement on top may be lower than designed, eg. Workers walking on top during construction strength weakened
    • The top may often get wet (cracks on slab surface)corrosion
    • Excessive loading, eg. Wind load, extra loading
  9. Cantilevered Structures-remedies for collapse
    • Avoid premature removal of props supporting the formwork (min. 28 days)
    • Precast balcony –better quality control
  10. Common Mechanisms of Water Penetration
    • Gravity (Gravity force pulls water down the face of a wall and into possible openings)
    • Wind-driven
    • Capillary action and surface tension (Water can flow against gravity and in narrow spaces)
  11. Buildings Elements Vulnerable to Water Seepage
    • Flat Roofs
    • Windows
    • Floor Slabs
    • Partition Walls
  12. Buildings Elements Vulnerable to Water Seepage- Flat Roofs-why
    • Weather attack: rain, heat, wind
    • Building services (大廈管理)
    • Misuse/Illegal Structure
  13. Problems with flat roofs
    • Poor Roof Maintenance
    • Ponding 1: Improper Grade of Slab Surfaces(deflected beam) + insufficient fall + drain at high point
    • Ponding 2: Blockage of drainage outlets; use dome-shaped drainage outlets
    • Additional works on top of roof; Shock absorber for ac
  14. Flat roof- Common materials involved
    • Waterproof Membranes(sheet form+liquid form)
    • Asphalt
  15. Defects of Asphalt
    • Surface crazing (minor cracks)-Due to sun exposure
    • Fractures (Deep cracks throughout the asphalt thickness)-Due to excessive bending
    • Blistering(Asphalt softened under solar heat)- Due to expansion of entrapped water
  16. Good Flat Roof Design
    • Adequate movement joints
    • Avoid too many openings
    • Avoid overloading
    • Allow sufficient fall (1:40 recommended)
    • Install sufficient floor drains, use dome-shaped drainage outlets
    • Shock absorber for ac
  17. Buildings Elements Vulnerable to Water Seepage- Windows-why
    • Gap too wide for grouting
    • Waterproof coating applied to concrete surface (before grouting)
  18. Buildings Elements Vulnerable to Water Seepage- Windows-remedies
    • Projections over window
    • Drip groove under projections to break surface tension
    • Set-back of Window
    • Non-shrinkage cement grout to fill up the gap
    • Waterproof coating on grout surface
    • Series of water tests conducted before and after grouting
    • Applying sealant around window
  19. Weakness of aluminum windows and regulations
    • corrosion of screws/rivets window sash falls apart
    • Mandatory Window Inspection Scheme –inspection every 5 years for buildings 10 years or older

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Author:
yhliuaa
ID:
320283
Filename:
civl 11
Updated:
2016-05-19 16:16:16
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civl 11
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