Formwork For Structural Member. Formwork Engineeringpptx

Formwork

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. Formwork for structural elements Slab Beam Column Footing Staircase Wall

3. 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.

4. Slab Formwork

5. 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.

6. Beam forms

7. Beam forms

8. 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

9. 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.

10. 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)

11. 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.

12. Wall Formworks

13. 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.

14. Form work for tank wall

15. 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.

16. 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).

17. 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.

18. 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.

19. 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.

20. 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.

21. Process involved in Concrete Formwork This normally involves the following operations: Propping and centring Shuttering Provision of camber Cleaning and surface treatment

22. 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

23. 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.

24. 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 15 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

25. Stripping time

26. Order and Method of Removing Formwork The sequence of orders and method of removal of formwork are as follows: The vertical faces of walls beams and column sides should be removed first as they bear no load. 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. All formworks should be eased gradually and carefully in order to prevent the load being suddenly transferred to concrete.

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