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types of formwork.pdf

  1. Formwork Presented by aglaia
  2. Formwork • It is used as a mould for a structure in which fresh concrete is poured only to harden subsequently. • Types of concrete formwork construction depends on formwork material and type of structural element. • Formworks can also be named based on the type of structural member construction such as slab formwork for use in slab, beam formwork, column formwork for use in beams and columns respectively etc. • The construction of formwork takes time and involves expenditure upto 20 to 25% of the cost of the structure or even more.
  3. • Design of these temporary structures are made to economic expenditure. • The operation of removing the formwork is known as stripping. Stripped formwork can be reused. • Reusable forms are known as panel forms and non-usable are called stationary forms.
  4. Requirements of a formwork • It should be strong enough to withstand all types of dead and live loads. • It should be rigidly constructed and efficiently propped and braced both horizontally and vertically, so as to retain its shape. • The joints in the formwork should be tight against leakage of cement grout. • Construction of formwork should permit removal of various parts in desired sequences without damage to the concrete. • The material of the formwork should be cheap, easily available and should be suitable for reuse.
  5. • The formwork should be set accurately to the desired line and levels should have plane surface. • It should be as light as possible. • The material of the formwork should not warp or get distorted when exposed to the elements. • It should rest on firm base.
  6. Types of Formwork 1. Timber Formwork 2. Steel formwork 3. Plywood formwork
  7. Timber Formwork • It should be 1. well seasoned 2. light in weight 3. easily workable with nails without splitting 4. free from loose knots • Timber used for shuttering for exposed concrete work should have smooth and even surface on all faces which come in contact with concrete.
  8. Advantages • Easy handling because it’s light weight. • Easy to disassemble. • Damaged parts can be replaced with new one. • Very flexible. Disadvantages • Can’t be used for long. • If the timber is dry, it will absorb moisture from wet concrete which could weaken the resultant concrete member. • Timber with high moisture content ,wet concrete will shrink & cup leading to open joints & leakage of grout.
  9. Plywood Formwork • Resin bonded plywood sheets are attached to timber frames to make up panels of required sizes. • The cost of plywood formwork compares favourably with that of timber shuttering and it may even prove cheaper in certain cases in view of the following considerations: • It is possible to have smooth finish in which case on cost in surface finishing is there. • By use of large size panels it is possible to effect saving in the labour cost of fixing and dismantling. • Number of reuses are more as compared with timber shuttering. For estimation purpose, number of reuses can be taken as 20 to 25.
  10. Advantages • Plywood can also be cut into required size easily. • Plywood Strong, durable and light in weight. • Provides smooth finish on the surface. • Very Large size plywood sheets are available which makes the construction of formwork quicker and easier. • Curved formworks can also be prepared using plywood. • When compared to timber, it gives more number of reuses. Disadvantages • When compared to timber it is costly. • Thin plywood sheets cannot sustain the weight of concrete they may bow out if proper thickness is not provided.
  11. Steel Formwork • This consist of panels fabricated out of thin steel plates stiffened along the edges by small steel angles. • The panel units can be held together through the use of suitable clamps or bolts and nuts. • The panels can be fabricated in large number in any desired modular shape or size. • Steel forms are largely used in large projects or in situation where large number reuses of the shuttering is possible. • This type of shuttering is considered most suitable for circular or curved structures.
  12. Advantages • Very strong and able to carry heavy load. • Easy to be fixed. • Uniform size and surface. • Can be used for a very long time. Disadvantages • Limited size or shape. • Excessive loss of heat. • A very smooth surface will be produced which would give problems for finishing process.
  13. Steel forms compared with timber formwork • Steel forms are stronger, durable and have longer life than timber formwork and their reuses are more in number. • Steel forms can be installed and dismantled with greater ease and speed. • The quality of exposed concrete surface by using steel forms is good and such surfaces need no further treatment. • Steel formwork does not absorb moisture from concrete. • Steel formwork does not shrink or warp.
  14. Aluminum Formwork • It is used often for pre-fabricated formworks. • It is getting more popular because of its light weight and good strength. • It requires fewer supports and ties.
  15. Advantages • Easy to fix and easy to dismantle. • It can be handled easily because of its light weight. • It can be re-used for many times. • The walls and slabs of structures can be casted simultaneously. • Monolithic crack free structures can be built using aluminum formwork. Disadvantages • When the load reaches its maximum limit, the lighter sections may deflect. • Architectural modifications are not possible when aluminum formwork is used.
  16. Plastics Formwork • Plastic is another type of formwork material which is used for small concrete structures or for complex portions of the structure. • It is light in weight and durable for long periods. For complicated concrete structures, Glass reinforced plastics (GRP) and vacuum formed plastics are used.
  17. Advantages • Plastic is light in weight and can be easily handled. • Formwork for complex shaped structures can be prepared easily. • Good resistant against water. • The damaged plastic sheets can be recycled and useful to make new sheets. • Good quality plastic has great re-usability. Disadvantages • Plastic is weak against heat. • It is costly material. • It does not take much load when compared with others.
  18. Magnesium Formwork • Magnesium is another metal element which is used for formwork. • Magnesium is not directly used for formwork and is used with the combination of oxygen atoms which forms magnesium oxide, usually called magnesia or MgO. • Magnesium oxide boards or MgO boards are famous in some countries because of their multiple applications. • MgO boards are available in required sizes and grades.
  19. Advantages • Mgo boards are light in weight and easy to handle. • They are fire proof and waterproof. • Bio friendly boards cause no harm to the environment. • They are strong to resist heavy loads. Disadvantages • When Mgo boards meet wet concrete, the magnesium chloride present in MgO boards may dissolve and cause corrosion to the reinforcement. • Skilled supervision is required for installation. • MgO boards cannot sustain in humid conditions.
  20. Fabric Formwork • Fabric formwork is the modern technology in construction sector. • Fabric can be mold into any required shapes which makes it more famous formwork for architectural purposes.
  21. Order and Method of Removing Formwork: • The sequence of orders and method of removal of formwork are as follows: • Shuttering forming the vertical faces of walls, beams and column sides should be removed first as they bear no load but only retain the concrete. • Shuttering forming soffit of slabs should be removed next. • Shuttering forming soffit of beams, girders or other heavily loaded shuttering should be removed in the end. • Rapid hardening cement, warm weather and light loading conditions allow early removal of formwork.
  22. • The formwork should under no circumstances be allowed to be removed until all the concrete reaches strength of at least twice the stresses to which the concrete may be subjected at the time of removal of formwork. • All formworks should be eased gradually and carefully in order to prevent the load being suddenly transferred to concrete.
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