Unit 5.pptx
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This document discusses techniques for repairing, rehabilitating, and retrofitting structures. It covers strengthening structural elements, repairing structures damaged by corrosion, fire, leakage, or earthquakes. Specific techniques addressed include repairing fire-damaged concrete, sealing leaks, repairing cracks, jacketing structural members, and dry packing. The document also covers engineered demolition methods like mechanical demolition, implosion, and deconstruction for taking down structures.
Unit 5.pptx
- 1. UNIT V REPAIR, REHABILITATION AND RETROFITTING OF STRUCTURES PREPARED BY MYTHILI D AP CIVIL EXCEL ENGINEERING COLLEGE
- 2. Strengthening of Structural elements, Repair of structures distressed due to corrosion, fire, Leakage, earthquake – DEMOLITION TECHNIQUES - Engineered demolition methods - Case studies.
- 3. Need for Strengthening • Load increases due to higher live loads, increased wheel loads, installations of heavy machinery or vibrations • Damage to structural parts due to aging of construction materials or fire damage, corrosion of the steel reinforcement, and impact of vehicles • Improvements insatiably for use due to limitation of deflections, reduction of stress in steel reinforcement and reduction of crack widths • Special Modification of structural system due to the elimination of walls/columns and openings cut through slabs. • Errors in planning or construction due to insufficient design dimensions and insufficient reinforcing steel.
- 7. Restoration of fire Damaged Elements • The eccentrically loaded columns fail when reinforcement bars in tension heat up. • The fire resistance of such elements can be increased by increasing the thickness of protective layer. • Heat transmission and temperature of bottom reinforcement are keys to the behavior of reinforced concrete slab exposed to fire. • The reinforcing bars are assumed to retain one half of their original strength. Carrying capacity of slabs can be enhanced by increasing their thickness. For beams, depth and width can be increased.
- 8. Restoration of fire Damaged Elements • It should be kept in mind that in beams, weakening of bond between transverse reinforcement and concrete on account of heating reduces the residual shear load carrying capacity considerably. The carrying capacity of axially loaded depends upon the cross section of the column coefficient of change in strength of concrete under high temperature and corresponding critical temperature. The carrying capacity can be restored by increasing the cross section with suitable increase in the longitudinal steel.
- 9. Leakages in the concrete structures • It causes inevitable damage to the reinforcement. Construction joints, shrinkage and restraint cracks may form leak paths. The amounts of water involved vary from damp-patches which tend to evaporate as they are formed, to running –leaks which may eventually form undrained surfaces. • Damp patches may also be formed when water passes through the voids along reinforcing bars formed due to plastic settlement. The other common routes for larger volume leaks are honeycombed concrete, movements joints like expansion and contraction joints. In case of water-retaining structures, the extent of leakage may be measured by monitoring loss of liquid from the structure.
- 10. Techniques • Conventional leak-sealing methods • Leak-sealing by injection techniques
- 11. Conventional leak-sealing methods • Surface preparations • Filling of surface imperfections with resin- based grouts • Application of primer • Application of two coats of high-build paint
- 12. Injection Sealing • From liquid flow and pressure considerations the simplest and most cost effective way is to seal the leakage from the water-retaining side of the structure. When the wet side is inaccessible, the leakage must be tackled from the dry side which is considerably more difficult.Successfull leak sealing requires injection of sealant to fill water passages completely, and it is necessary to attain a relatively high flow velocity to achieve this, because of short pot-life or working time of the typical repair material.
- 13. Marine exposure • Durability of concrete exposed to sea-water again stresses that of all chemical and physical properties, permeability of concrete is the most important factor influencing performance. Concrete are achieved by using mixes having high cement contents and low water: cement ratios, through consolidation and control of thermal and shrinkage cracking, and limiting cracks due to mechanical loading.
- 14. techniques required for repairing cracks • Bonding with epoxies • Routing and sealing • Stitching • Blanketing • External stressing • Grouting • Autogenous healing
- 15. Bonding with epoxies • These are organic compound which when activated with suitable hardening agents form strong chemically resistant structures having excellent adhesive properties. They are used as binders or adhesives to bond new concrete patches to existing surfaces or hand together cracked portions. Once hardened, this compound will not melt, flow or bleed. Care should be taken to place the epoxy within the pot life period after mixing.
- 16. Routing and sealing • This method involves enlarging the cracks along its exposed surface, filling and finally sealing it with a suitable material. This is the simplest and most common technique for sealing cracks and is applicable for sealing both fine pattern cracks and larger isolated.
- 17. Stitching • The tensile strength of a cracked concrete section can be restored by stitching in a manner similar to sewing cloth.
- 18. Blanketing • This is the simplest and most common technique for sealing cracks and is applicable for sealing both fine pattern cracks and larger isolated. The cracks should be dormant unless they are opened up enough to put in a substantial paten in which case the repair may be more property termed as “Blanketing”.
- 19. External stressing • Development of cracking in concrete is due to tensile stress and can be arrested by removing these stresses. Further the cracks can be closed by including a compressive force sufficient to over come the tension a residual compression.
- 20. Grouting • Grouting can be performed in a similar manner as the injection of an epoxy. However the use of an epoxy is the better solution except where considerations for the resistance of cold weather prevent such use in which case grouting is the comparable alternative.
- 21. Autogenous healing • The inherent ability of concrete to heal cracks within “autogenous healing”. This is used for sealing dormant cracks such as precast units cracked in handling of cracks developed during the precast pilling sealing of cracks in water hands and sealing of cracks results of temporary conditions.
- 22. Jacketing • It consists of restoring or increasing the section of an existing member by encasing it in a new concrete. This method is useful for protection of section against further deterioration by providing additional to in member.
- 23. Dry packing • Dry packing is the hand placement of a very dry mortar and subsequent tamping or ramming of the mortar into place producing an intimate contact between the old and new concrete work.
- 24. causes of cracks • Use of unsound material • Poor & bad workmanship • Use of high water-cement ratio • Freezing & thawing • Thermal effects • Shrinkage stresses
- 25. types of cracks • a) Class-1: Cracks leading to structural failure b) Class-2: Cracks causing corrosion • c) Class-3: Cracks affecting function • d) Class-4: Cracks affecting appearance
- 26. Demolition techniques • Non Engineering Demolition Manual Demolition • Engineering Demolition Mechanical Method Implosion Deconstruction Method
- 27. Non Engineering Demolition • This is normally carried out by contractors using manual tool which is portable, tools used are Sledge Hammer, Jack Hammers and Drillers.
- 28. Jack Hammer Sledge Hammer Driller
- 29. Engineering Demolition • Wrecking Ball Method • Pusher Arm technique • Thermic Lance Technique • Non – Explosive Demolition • Concrete Sawing Method • Deliberate Collapse Method • Pressure Jetting
- 30. Wrecking Ball Method • A Steel ball anti spin device which is suspended by a steel rope and swung by a drag rope, the weight of the ball is around 500 to 1000 Kg used with suitable fittings attached to a crane of adequate capacity, the building is dismantled by making the steel ball to hit the structure this method is much faster than manual method
- 32. Pusher Arm Technique: • A Hydraulically powered pusher arm machine is mounted on tracked or wheeled chassis, this method is not recommended for large building but it is good for small masonry structure, the building is demolished by using the pusher arm. •
- 34. Thermic Lace Technique • Flame is produced by having supply with pure oxygen with a temperature of 2500 degree centigrade to melt the reinforcement.
- 36. Non- Explosive Demolition • A Number of holes is drilled along the desired line of separation and are filled with slurry which is a special material when the slurry is filled in the holes water is poured into the drilled holes after few hours the slurry expands as a result cracking will appear on the structures which help in easy demolition of structure.
- 37. Concrete Sawing Method • Using the concrete saw the structure is been demolished which works on a high power supply helps in destruction of structure in an easy way.
- 39. Deliberate Collapse Method • The Collapse is usually achieved by either by removing key structural elements (e.g. with explosive charges) or by wire rope pulling at a high level of overturn this method is not suitable for pre stressed concrete structures.
- 40. Pressure Jetting • The Jet heads are generally small and so action of jet is mainly to loosen the aggregate by washing out softer mortar (water with high pressure).
- 42. Implosion • Collapsing the structure inward, gravity makes the structure to collapse. If the supporting structure of a building at a certain point is removed the building may get damaged and the structure can be easily demolished. The procedure is followed by analysing the blue print of the building and the explosives is used on the key components of the building at different level from bottom to top i.e. from explosion should take place from lower level internal component then step by step to the top level by sequential order which result in demolition of building.
- 44. Deconstruction Method • A slow and careful process that is almost the reverse process of construction. Non Structural Method: Dismantling of doors, windows, flooring etc. • Structural Method: Dismantling of beams, Columns, Floors, walls.
- 45. House Demolition • Step 1: Get the building inspected. • Step 2: Acquire the necessary permits. • Step 3: Disconnect existing services. • Step 4: Tear down the house. • Step 5: Haul away the debris. • Traditional Mechanical Demolition. • Deconstruction.