Introduction and types of Form Work in civil engineering
- 1. FORMWORK BUILDING MATERIAL AND CONSTRUCTION FACULTY:- (1) AR. VIREN MAHIDA (2) AR. NIRAV KHANDWALA BHAGWAN MAHAVIR COLLEGE OF ARCHITECTURE
- 2. • Formwork in construction is the use of support structures and moulds to create structures out of concrete which is poured into the moulds.Formwork can be made using moulds out of steel, wood, aluminium and/or prefabricated forms. • Formwork is an ancillary construction, used asa mould for a structure. Into this mould, fresh concrete is placed only to harden subsequently. • Theconstructionofformwork takestimeandinvolves expenditureupto20 to25%ofthecostofthestructure or evenmore. • The operation of removing the formwork is known as stripping. Stripped formwork can be reused. Reusable formsareknownaspanelformsandnon-usableare calledstationaryforms. What isFormwork? INTRODUCTI ON CATEGORI ES MATERI AL CHARECTRIS TICS CONST. DETAIL FAILURE OF FORMWORK Removal time
- 3. INTRODUCTI ON CATEGORI ES MATERI AL CHARECTRIS TICS CONST. DETAIL FAILURE OF FORMWORK A goodformworkshouldsatisfythefollowing requirements: • (1) Easyremoval • (2) Economy • (3) less leakage • (4) Quality (5) Rigidity (6) Smooth surface (7) Strength (8) Supports (1) Easy removal :Construction of formwork should permitremovalofvariouspartsin desiredsequenceswithout damage to theconcrete. (2) Economy :Material of the formwork should be cheap,easilyavailableandshouldbe suitablefor reuse (3) less leakage :The joints in the formwork should be tight againstleakage ofcementgrout. (4) Quality: Material of the formwork shouldnotwrappergetdistortedwhen exposed to the elements
- 4. A goodformworkshouldsatisfythefollowing requirements: • (5) Rigidity :Rigidly constructedandefficiently proppedand braced both horizontally and vertically, so as to retain its shape • sequenceswithout damage to the concrete • (6) Smooth surface : The formwork should besetaccuratelytothedesired line andlevelsshould have plane surface. • (7) Strength :Strong enough to withstandall typesofdeadandlive loads • (8) Supports : Aslight aspossibleandShould restonfirm base. INTRODUCTI ON CATEGORI ES MATERI AL CHARECTRIS TICS CONST. DETAIL FAILURE OF FORMWORK Removal time
- 5. Categoriesof formwork • Conventional: The formwork is built on site out of timber and plywood or moisture- resistant particleboard. It is easy to produce but time-consuming for larger structures, and the plywood facing has a relatively short lifespan.It is still used extensively where the labour costs are lower than the costs for procuring reusable formwork. It is also the most flexible type of formwork, so even where other systems are in use, complicated sections may use it. • Modern-Day Formworks:This formwork systems are mostly modular, which are designed for speed and efficiency. They are designed to provide increased accuracy and minimize waste in construction and most have enhanced health and safety features built-in. The main types of formwork systems in use noware: 1. Table form/flying form 2. System column formwork 3. Horizontal panel 4. Slip form 5. Tunnel form INTRODUCTI ON CATEGORI ES MATERI AL CHARECTRIS TICS CONST. DETAIL FAILURE OF FORMWORK Removal time
- 6. Categoriesof formwork Engineered/Pre-fabricated Formworks: • This formwork is built out of prefabricated modules with a metal frame (usually steel or aluminium) and covered on the application (concrete) side with material having the wanted surface structure (steel, aluminium, timber, etc.). The two major advantages of formwork systems, compared to traditional timber formwork, are speed of construction and lower life-cycle costs (barring major force, the frame is almost indestructible, while the covering if made of wood; may have to be replaced after a few – or a few dozen – uses, but if the covering is made with steel or aluminium the form can achieve up to two thousand uses depending on care and theapplications). INTRODUCTI ON CATEGORI ES MATERI AL CHARECTRIS TICS CONST. DETAIL FAILURE OF FORMWORK Removal time
- 7. Material usedin formwork (1) Steel formwork (2)Plywood formwork (3)Plastic formwork (1 (2 (3 ) (4)Aluminum formwork (4 INTRODUCTI ON MATERI AL CHARECTRIS TICS CATEGORIE S CONST. DETAIL FAILURE OF FORMWORK Removal time
- 8. (1)Steelformwork •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. INTRODUCTI ON CATEGORI ES MATERI AL CHARECTRIS TICS CONST. DETAIL FAILURE OF FORMWORK Removal time
- 9. Steelformwork • It can be used for a no. of times. • It is non absorbent. • Smooth finish surface obtained. • No shrinkage of formwork occurs. • Easy to use. • Its volume is less • Its strength is more. • Limited size or shape • Excessive loss of heat • A very smooth surface will be produced which would give problems for finishing process • Limited fixing Advantag es Disadvantag es INTRODUCTI ON CATEGORI ES MATERI AL CHARECTRIS TICS CONST. DETAIL FAILURE OF FORMWORK Removal time
- 10. INTRODUCTI ON CATEGORI ES MATERI AL CHARECTRIS TICS CONST. DETAIL FAILURE OF FORMWORK (2)plywoodformwork Sheeting for slabs, beam, column side and beam bottom 25 mm to 40mm thick Joints, ledges 50 x 70 mm to 50 x 150 mm Posts 75 x 100mm to 100 x 100 mm Timber for formwork should satisfy the following requirement: It should be •well seasoned •light in weight •easily workable with nails without splitting •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. Removal time
- 11. INTRODUCTI ON CATEGORI ES MATERI AL CHARECTRIS TICS CONST. DETAIL FAILURE OF FORMWORK (3)Plasticformwork - Glass reinforced plastics (GRP) and vacuum formed plastics are used when complicated concrete shapes are required (e.g. waffle floors). - Although vacuum formed plastics will always need support, GRP can be fabricated with integral bearers making it self supporting. - Like steel, plastic formwork can be re-used many times, as long as care is taken not to scour the surface whilst vibrating the concrete. Removal time
- 12. INTRODUCTI ON CATEGORI ES MATERI AL CHARECTRIS TICS (4)Aluminumformwork • Often used in pre-fabricated formwork, that is put together on site. • Aluminium is strong and light, and consequently fewer supports and ties are required. • The lighter sections will deflect more, but this can be avoided by simply following the manufacturers recommendations. • Advantage 1. It can be used repeatedly with low average use-cost. 2. Construction is Convenient and Effective. 3. Saving on Construction Time. 4. Wide Application. 5. No construction Garbage on Site. C C O O N N S S T T . . D D E E T T A A I I L L FAILURE OF FORMWORK Removal time
- 13. FORMWORKFORWALL It consists of • Timber sheeting • Vertical posts • Horizontal members • Rackers • Stakes • Wedges After completing one side of formwork reinforcement is provided at the place then the second side formwork is provided. INTRODUCTI ON CATEGORI ES MATERI AL CHARECTRIS TICS CONST. DETAIL FAILURE OF FORMWORK Removal time
- 14. FORMWORKFORCOLUMN • It consists of the following – Side & End Planks – Yoke – Nut & Bolts • Two end & two side planks are joined by the yokes and bolts. INTRODUCTI ON CATEGORI ES MATERI AL CHARECTRIS TICS CONST. DETAIL FAILURE OF FORMWORK Removal time
- 15. Erectionsequencefor a column Prior to positioning column formwork check that steel for the colum n has been inspected and cleared for casting. - Position formwork for the column from predetermined grids. - Plumb formwork both ways and securely support using adjustab le steel props. - The propping angle should be 45° to the floor. - Ensure the steel props are safely secured to the column formwo rk and the floor, and that adjustment for pushing and pulling is operational. - Set out the positions of column clamps from a storey rod. - Transfer the column clamp positions from the storey rod on to - column formwork. - Use nails to support the arms of column clamps while wedging. - Position and wedge the bottom, middle and top clamps sets. - Check the formwork at the top for square. - Position and wedge the remainder of the column clamps. INTRODUCTI ON CATEGORI ES MATERI AL CHARECTRIS TICS CONST. DETAIL FAILURE OF FORMWORK Removal time
- 16. Circular andoctagonalcolumn • Fabricated steel, usually two piece, and of ten with a hinge. • Fibre cement pipes which are left in place as permanent formwork. • Timber sheathing tied with standard colu mn clamps. Corners need to have infill pie ces. Alternatively, metal strap can be use d without the need for corner infills. INTRODUCTI ON CATEGORI ES MATERI AL CHARECTRISTICS Circular column formwork CONST. DETAIL FAILURE OF FORMWORK Removal time
- 17. Erectionsequencefor a column INTRODUCTI ON FAILURE OF FORMWORK CHARECTRIS TICS CATEGORI ES MATERIAL CONST. DETAIL Removal time
- 18. Columnbracingformwork • Column formwork bracing performs two functions: • It must maintain the accuracy of the column form position and plumb so that it is within tolerance. •Withstand results of forces acting on either the column formwork or the bracing. Th e forces may be wind or impact. These impact forces can occur from the collision of concrete buckets or cranes hoisting materials INTRODUCTI ON CATEGORI ES MATERI AL CHARECTRIS TICS CONST. DETAIL FAILURE OF FORMWORK Removal time
- 19. Erectionsequencefor a column • Beam soffit must be thickened timber or strengthe ned plywood. • Beam sides 18mm plywood or 25mm boards, with studs (cleats) at 500 to 600mm centres. • Deep beams (over 600mm) should have walkers an d ties. • Use angle fillets in the beam side to soffit joint wh ere possible. • Allowance must be made for height adjustment of the props or false work. Erection sequence for constructing beam formwork includes • Position of sole plates; •Marking out and setting heights for false works; •Assemble and position props, adjustable head jacks, false works , bearers and Spreaders; •Construct and erect side walls and beam soffit. INTRODUCTI ON CATEGORI ES MATERI AL CHARECTRIS TICS CONST. DETAIL FAILURE OF FORMWORK Removal time
- 20. Formworkfor stairs •Points to consider when designing stair form work: Stair formwork must support the weight of concrete the weight of the throat of the stair and the steps will have to be supported. Because of the slope of the stair, some of the force i s transmitted sideways. All formwork must be well tied together to prevent sideway movement. Consider the finish of the stair treads and type of no sing. Space may have to be left for purpose made n osing. INTRODUCTI ON CATEGORI ES MATERI AL CHARECTRIS TICS CONST. DETAIL FAILURE OF FORMWORK Removal time
- 21. INTRODUCTI ON CATEGORI ES MATERI AL CHARECTRIS TICS CONST. DETAIL REMOVAL TIME FAILURE of FORMWORK TimeofRemovalof formwork • Time of formwork removal depends on the following factors 1. Type of Cement :Rapid hardening cements require lesser time as compared to OPC (Ordinary Portland Cement) 2. Ratio of concrete mix :Rich ratio concrete gain strength earlier as compared to weak ratio concrete. 3. Weather condition :Hydration process accelerates in hot weather conditions as compared to cold and humid weather conditions. Sr. No Structural Member OPC (Ordinary Portland Cement) Rapid Hardening Cement 1 Beam sides, walls & Columns 2-3 Days 2 Days 2 Slab (Vertical Supports remains intact) 4 Days 3 Days 3 Slab (Complete Formwork removal) 10 Days 5 Days 4 Beams (Removal of Sheeting, Props remains intact) 8 Days 5 Days 5 Beams & Arches (Completeformwork removal) (up to 6 m span) 14 Days 5-8 Days 6 Beams & Arches (Completeformwork removal) (more than 6 m span) 21 Days 8-10 Days
- 22. INTRODUCTI ON TimeofRemovalof formwork CHARECTRISTI CS CATEGORIE S MATERI AL CONST. DETAIL Removal time FAILURE OF FORMWORK
- 23. Formwork failures are the cause of many accidents and failures that occur during concrete construction which usually happen when fresh concrete is placed Generally some unexpected event causes one member to fail, then others become overloaded or misaligned and the entire formwork structure collapses Improper stripping and shore removal Inadequate bracing Vibration Unstable soil under mudsills, shoring not plumb Inadequate control of concrete placement Lack of attention to formwork details Inadequate cross bracing and horizontal bracing of shores Forms sometime collapse when their shores/ jack are displaced by the vibration caused by: passing traffic movement of workers & equipment on the formwork FAILURE OF FORMWORK INTRODUCTI ON CATEGORI ES MATERI AL CHARECTRIS TICS CONST. DETAIL FAILURE OF FORMWORK Removal time