Introduction to formwork ppt introduction to
- 1. Formwork & Centering Design -facts and reality Presented by Mr. A.V. Ghogare Department of Civil Engineering, SRES’s Sanjivani College of Engineering, Kopargaon An Autonomous Institute, Dist: Ahmednagar, MH, India
- 2. CONTENT Introduction What is Formwork Difference between Formwork and Scaffolding Types of Formwork Elements of Formwork Design of Formwork Advancement in Formwork Precautions taken during and after constructions Case studies
- 3. INTRODUCTION Green Concrete is a fluid to semi solid material which takes time to achieve desired strength. To support the fresh concrete, form work plays vital role to give proper shape to the structural element. Formwork sustain weight of wet materials /concrete, workmen/labour load and machinery like vibrator, pump, trolley, etc. All loads are not static. The construction of formwork takes time.
- 4. INTRODUCTION Cost of formwork is up to 15 to 30% of the cost of the structure. But design of formwork make structure safe and economic. The operation of removing the formwork is known as stripping. Reusable forms are known as panel forms while non-usable are called stationary forms. Timber is the most common material used for formwork. The disadvantage with timber formwork is that it will warp, swell and shrink. Application of water impermeable coat to the surface of wood is necessary.
- 5. WHAT IS FORMWORK Formwork is a temporary structure which support fresh concrete and provide shape to concrete till it attained desired strength. Reusable forms are known as panel forms non-usable are called stationary forms.
- 7. OTHER RELATED TEMPORARY WORK Shoring:-construction of a temporary structure to support temporarily an unsafe structure. Scaffolding:- When the height of wall or column or other structural member of a building exceeds about 1.5m above ground level, temporary structures are needed to support the platform over which workmen can sit and carry on the constructions.
- 9. TYPES OF FORMWORK On the basis of materials used- Timber formwork Plywood formwork Steel formwork Aluminium formwork Plastic formwork
- 10. TYPES OF FORMWORK On the basis of structural elements- Slab Beam Column Footing Wall, Staircase Tunnel Retaining wall Water Tank
- 11. TYPES OF FORMWORK On the basis of Engineered formwork systems- Climbing form-work Flexible form-work On the basis of uses- Reusable form-work Permanent or stay in placed form-work
- 12. TIMBER FORMWORK It is easy to produce but time-consuming for larger structures. 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, It is used in complicated sections.
- 13. TIMBER FORMWORK 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.
- 14. If a smooth finished face is desired, wrought boarding should be specified. Where a fair finish face is desired under a roof slab, the upper surface of the supports may be covered with oiled soft building board or other water repellent packing material; oiled paper is not suitable. The sizes of timber sections for different components of formwork depend upon the span of the slab or beam, floor-to-floor height and the centre-to-centre spacing of the centering supports. The sizes of members for timber formwork for shuttering of 4.5 m span and 3.5 m height as mentioned in table.
- 15. For normal construction work where repetitive use of shuttering is possible, the quantity of timber shuttering can be worked out on the assumption that one set of shuttering can be used 10 to 12 times.
- 16. MAINTENANCE OF TIMBER FORMWORK Timber should be generally examined for any visible damage during use and be discarded or its safe capacity suitably reduced if any of the following is present: Signs of rot Cuts on the edge greater than 1/20 of the thickness of the section Bolt holes in the two outer third lengths or width Undue distortion of shape Any other mechanical damage Splitting
- 17. DISADVANTAGES OF TIMBER FORMWORK Even large floor heights are constructed using wooden or bamboo props without proper interconnection for the extended length or without proper bracing. These often result in serious failures. It is not recommended to use wooden props especially when floor heights are large requiring connecting one prop over the other. In any case the load carrying capacity of wooden or bamboo prop is often not known and difficult to ascertain depending on the type and quality of wood, its moisture content, size and shape.
- 18. PLYWOOD FORMWORK Plywood of different types and quality are used. It is usual to frame up the materials into largest size panels that can be handled by the available equipment on the site or is convenient for manual handling. The size will also depend on the shape of the structural member being cast. The plywood panels are suitable for large smooth areas like walls and floor. For complicated shapes, timber frames with plywood face are usually more economical than timber boards or other materials especially when high number of re-uses is required.
- 19. PLYWOOD FORMWORK Resin bonded plywood sheets are attached to timber frames to make up panels of required sizes. The cost of plywood formwork compares to timber shuttering is cheaper in certain cases- It is possible to have smooth finish, cost of surface finishing can be saved. By use of large size panels it is possible to effect saving in the labour cost of fixing and dismantling. Number of reuses is more as compared with timber shuttering. For estimation purpose, number of reuses can be taken as 20 to 25.
- 20. Ply surfaces get easily damaged hence adequate care has to be taken during assembly, erection, casting, striking and storage. The soft surfaces and edges are more prone to damage than other surfaces and therefore they need to be protected. Plywood conforming to IS 4990 may be used for form lining, sheathing and panel. Use of plywood instead of timber planks is getting popular these days. In this case resin bonded plywood sheets are attached to timber frames to make up panels of required sizes. Plywood shuttering ensures quality surface finish and is specially recommended in large flat areas exposed to concrete are to be constructed like floor slabs, retaining walls etc.
- 21. ADVNTAGES OVER TIMBER FORMWORK It is possible to have perfectly plain and smooth surface. Thus the expenditure on surface finishing can be saved. By use of large size panels it is possible to effect saving in the labour cost of fixing and dismantling. Number of re-uses as more as compared with timber shuttering. For estimation purposes, number of re-uses can be assumed as 20 to 25.
- 22. STEEL FORMWORK It consists of panels fabricated in 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 numbers in any desired modular shape or size. Steel forms are largely used in large projects or in situations where large number reuses of the shuttering is possible. This type of shuttering is considered most suitable for circular or curved structures.
- 23. The usual size for wall and slab panel varies from 600 mm X 600 mm to 600 mm X 1200 mm. Steel sheet plates conforming to IS 2062 or IS 8500 or IS 1977 may be used for form lining. Rolled sections and tubes conforming to IS 2062 or IS 8500 or IS 1161 may be used for steel forming and bracings. Steel forms are mostly used in large construction projects or in situations where large numbers of re-uses of the same shuttering are possible. This type of shuttering is considered most suitable for circular or curved shaped structures such as tanks, columns, chimneys etc. and for structures like large sewer, tunnels and retaining walls.
- 24. There are two ways steel is used in formwork and false work. 1) Proprietary formwork: These systems are available in different forms, some of which are listed below: Steel framed panels with either steel plate or plywood facing Telescopic supporting trusses Adjustable props (tubular) Yokes and fastening devices Tie rods and spacers Clamps and bracings (tubular)
- 25. 2) Purpose made formwork These formworks are specially designed for a particular type of job work as in case of linings inside tunnels, culverts, slip formwork for tall structures and other jobs, which have unusual shape.
- 26. MAINTENANCE OF FORMWORK Formwork, which is to be reused, should be carefully cleared and properly repaired between uses. Concrete or mortar film sticking to the form face or the joining surface should be completely removed after each use when not required for use; The formwork material should be properly stored. The component should be cleaned and painted periodically. Threaded parts should be oiled, greased after thorough clearing and removal of dirt or slurry. Free movement of the telescopic components should be ensured by periodic cleaning/oiling.
- 27. COMPARISON BETWEEN STEEL & TIMBER FORMWORK Steel forms are stronger, durable and have longer life Steel forms can be reuses many times (2000 Nos.) 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.
- 28. PLASTIC FORMWORK Plastic form work is generally used for quick pouring of concrete. The formwork is assembled either from interlocking panels It is not as versatile as timber formwork due to the pre- fabrication requirements. It is best suited for low-cost, repetitive structures such as mass housing schemes. Prefabricated fibre-reinforced plastic is used. It is used for concrete columns. It has good resistance to environmental damage for both the concrete and reinforcing bars.
- 29. OTHER MATERIALS There are several other types of materials that may be used in falsework such as aluminium, PVC, reinforced plastics, high- density polyethylene, poly-propylene, ferro-cement and polythene sheet for lining, etc. In certain applications, masonry, concrete and earthwork may be used as part of falsework. Although these types of formwork faces offer many uses, additional care has to be taken while placing and vibrating concrete in order to avoid damage to the form face. Cleaning also needs to be done immediately after de-shuttering. Wet cloth cleaning is necessary and to be done immediately after de-shuttering to remove dust and cement concrete paste sticking to the surface.
- 30. COMPARISON OF FORMWORK Sr. No. Description Timber/ Plywood Formwork Steel Aluminium Plastic 1 Strength Low to moderate High High Low 2 Durability 10-20 > 1500 > 2000 > 2000 3 Handling easy easy easy easy 4 Finishing Good Good V. Good V. good 5 Cost low High V. High High 6 Modification in shape possible difficult difficult difficult 7 Accuracy For any complicated structure More suitable for standard dimensions More suitable for similar and Repetitive use More suitable for similar and Repetitive use 8 Deflection moderate less less More 9 Load Heavy Heavy Light V. Light Suitable for Small and complicated work Big and standard dimensions Big and repetitive or similar work Vertical and repetitive or similar work
- 31. FORMWORK FOR STRUCTURAL ELEMENTS Slab Beam Column Footing Staircase Wall
- 32. SLAB FORMWORK Slab formwork is designed as per the depth of concrete slab. The loads on plywood are usually considered as being uniformly distributed over the entire surface of the formwork. The slab is supported on 25mm thick sheathing laid parallel to the main beams The sheathing is supported on wooden battens which are laid between the beams. In order to reduce the deflection, the battens may be propped at middle of the span through joists.
- 33. SLAB FORMWORK
- 34. BEAM FORMWORK The side forms of the beam is 30mm thick sheathing while bottom sheathing may be 50 to 70 mm thick. The ends of the battens are supported on the ledger which is fixed to the cleat throughout the length. Cleats 100mm X20 to 30mm are fixed to the side forms. The beam form is supported on a head tree. The shore or post is connected to head tree through cleats. At bottom of the shore, two wedges of hard wood are provided over a sole piece.
- 35. BEAM FORMS
- 36. BEAM FORMS
- 37. FORMWORK FOR COLUMNS Sheathing all around the column periphery, 2 Side yoke and end yoke, 4 Wedges, 2 bolts and 4 washers. Two side yokes are comparatively heavier sections and are connected together by two long bolts of 16mm dia. The sheathing are nailed to the yoke. Ex. Square, rectangular, circular or any other shape, etc
- 38. COLUMN FORMWORK Column forms should be capable of being stripped easily. In tall forms it is desirable to provided windows at appropriate levels on at least one face to facilitate inspection, concrete placement and vibration. Any method (standard or patented) such as adjustable clamps, bolts, and purpose made yokes, etc. to hold the panels in place may be used. The spacing and size of these clamps should depend upon the lateral pressure of fresh concrete.
- 40. FORMWORK FOR FOUNDATIONS It depends on whether sides of foundations are vertical or inclined (slopped). For vertical sides, construct hollow box open at top and bottom as shown in figure. It should be rigid when filled with concrete. Ex. Square, rectangular or Box footing, combined footings, Raft foundation, etc For slopped footing, up to 150-200mm, box is prepared, over which trapezoidal forms should be fixed to provide required slopes. Yokes of size 75mmX100mm and Bolts are used to secure the boards at suitable interval (300-600mm)
- 42. WALL FORMWORKS The boarding may be 40-50mm thick for wall up to 4m height. The boards are fixed to 50mmX100m posts known as studs, about 0.7 to 1m apart. Horizontal walling of size 75mm X 100mm are fixed to the post at 1 to 1.25m interval. The whole assembly is than strutted using 75mmX100mm struts.
- 43. WALL FORMWORKS
- 44. FORM WORK FOR STAIRS The sheathing or decking for the deck slab is carried on cross joists which are in turn supported to raking ledgers. The ledger is generally of 75mm X 100mm size. The cross joist may be of 50mm X 100mm size. The riser planks are 40-50mm thick and width equal to the riser. A stiffener joist of size 50mmX100mm is placed along the middle of the riser planks.
- 48. FORM WORK FOR TANK WALL
- 49. MONOLITHIC FORMWORKS walls, columns, slabs, beams and stairways are realized using the monolithic construction method. The system offers a suitable and fast solution for forming frequently repetitive floor plans - horizontally or vertically. The individual panels can be easily moved and transported by hand. Through the use of special wedge couplers, the wall and slab panels are assembled in a very short time. The individual panels are produced according to project specifications . As a result, all structural dimensions and building shapes are possible.
- 50. CLIMBING FORMWORKS It is a special type formwork for vertical concrete structures that rises with the building process. While relatively complicated and costly, it can be an effective solution for buildings that are either very repetitive in form (such as towers or skyscrapers) or that require a seamless wall structure . Various types of climbing formwork exist, which are either relocated from time to time, or can even move on their own (usually on hydraulic jacks, required for self-climbing and gliding formworks).
- 51. GUIDELINES FOR FORMWORK Type of concrete and temperature of the concrete are important for selecting formwork as they exert pressure. The formwork sides must be capable of resisting the hydrostatic pressure of the wet concrete depending on the rate of setting and curing. The formwork base must be capable of resisting dead and live load of the wet concrete, workmen and machinery. Once the concrete as gained sufficient strength, the formwork can be removed. A minimum of 5 MPa strength of concrete can be achieved before striking vertical formwork. Both shuttering and formwork in its various forms will be supported by false work.
- 52. REQUIREMENTS OF GOOD FORMWORK It should be strong enough to carry all types of dead and live loads. It should be rigidly constructed and efficiently propped and braced both horizontally and vertically, The joints in the formwork should be stiff so that the deformations caused by loads shall be minimum. The joints in the formwork should be water tight. 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. 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.
- 53. MATERIAL SELECTION The type of material to be used for formwork depends upon the nature of construction as well as the availability and cost of material. Formwork can be made out of timber, steel, plywood, pre-cast concrete or fibre-glass, used separately or in combination. Timber and plywood are the most commonly used materials for formwork because these can be cut or assembled easily on site. Use of wooden props (ballies) and bamboo props are still persisting in many construction works.
- 54. With the introduction of steel forms, use of timber formwork is getting reduced especially in case of major construction projects. Large numbers of re-use of the same forms are possible then steel, aluminium and plastic forms are used. However, for small works involving less number of re-uses, timber formwork proves economical. Formwork commercially available may be fabricated at site, or partially or wholly prefabricated and may be used.
- 55. PROCESS INVOLVED IN CONCRETE FORMWORK This normally involves the following operations: Propping and centring Shuttering Provision of camber Cleaning and surface treatment
- 56. TOLERANCE IN SHAPE, LINES & DIMENSIONS The formwork shall be designed and constructed so as to remain sufficiently rigid during placing and compaction of concrete, and shall be such as to prevent loss of slurry from the concrete. The tolerances on the shapes, lines and dimensions shown in the drawing shall be within the limits given in table given in IS 456-2000
- 58. CLEANING & TREATMENT OF FORMWORK All rubbish, particularly, chippings, shavings and sawdust, shall be removed from the interior of the forms before the concrete is placed. The face of formwork in contact with the concrete shall be cleaned and treated with form release agent. Release agents should be applied so as to provide a thin uniform coating to the forms without coating the reinforcement.
- 59. STRIPPING TIME Forms shall not be released until the concrete has achieved a strength of at least twice the stress to which the concrete may be subjected at the time of removal of form work. While the above criteria of strength shall be the guiding factor for removal of formwork, in normal circumstances where ambient temperature does not fall below 150 C and where ordinary Portland cement is used and adequate curing is done, following stripping period may deem to satisfy the guideline given in IS 456-2000
- 60. STRIPPING TIME