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Raul Jimenez
Senior Project Manager
Asked a question last year

How to design Formwork?

What is the procedure of designing the formwork?

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Ross Kim
Geotechnical engineer

Column Formwork

Before erecting column formwork, make sure the steel is checked and ready for casting.

  1. Place the formwork for column from predetermined grids.
  2. Plumb it from both sides and support it securely using adjustable steel props.
  3. The angle of propping should be 45° to the floor.
  4. Make sure the props are secured properly to the column formwork and floor, adjustment for pulling and pushing is operational.
  5. Start the position of column clamps from a storey rod.
  6. Transfer the clamps position to formwork from rod.
  7. During wedging, use nails to support arms of column.
  8. Place and wedge the base, center and top clamp sets.
  9. Check the formwork, looks square or not from the top.
  10. Place and wedge the remaining of the column clamps.
  11. Place a plumb bob hanged from a gauge block, plumb the column.

Make a final check for plumb if the formwork is safely propped and column alignment before and right after the concrete is poured and vibrated.

Beam formwork
1 Thicken timber of strengthening plywood must be provided to beams soffit.
2. Beams side – 18 mm plywood, 25 mm boards, studs 500 to 600 mm centers.
3. Walkers and ties over 600 mm must provide
4. If possible, use angle fillets to soffit joints.
5. For calls work allowance made for height adjustment.

Constructing beam framework erections sequence is
1.Mark sole plates position
2. Setting heights of falsework
3. Erect side walls and construct beam soffit.
4. Take the proper position of the soleplate.

Staircase Formwork

Points to be considered

  • The formwork should support the concrete weight. The weight of the throat of both stair and step should be upheld.
  • Formwork should be tied very tightly together to hold the sideways movement because of the slope the force is transferred sideways.
  • Consider the finish of the stair treads and type of nosing.
    Space may have to be left for the purpose made nosing.

Hi,

For the design of homework, virtually a basic understanding of how the Concrete behaves on a particular time. How much pressure it exerts on formwork is necessary.

Following are some properties for the designing of formwork

  1. Rate of a pour of Concrete: during pouring of Concrete, the weight of Concrete is directly proportional to the rate, which is it pours by transit mixer.in19 this case, the two conditions will love the Concrete will start hardening during pouring, which leads to less pressure developed on formwork, but if the Concrete does not start hardening, then pressure develops greater on formwork.
  2. Weight of concrete poured:  pressure exerted on formwork is directly proportional to the weight of concrete.if the weight of concrete is less than the pressure exerted is also less.
  3. Height of framework required for Concrete: the height of Concrete is the most important aspect because height and weight are directly proportional to the pressure applied on formwork. If the height of the casting member is is more than pressure develops on homework is also large.
  4. Cement type used for concreting: type of cement is related to the rate of hardening of the cement. If Concrete harder and faster, which allows a faster poor rate.so26 that is site engineer at just the polling rate of Concrete.
  5. The method adopted for vibrating: there are two types of vibrating techniques used, internal and external vibration. If internal vibrating is used with the help of a vibrating needle, then concrete acts like a pure liquid. So pressure act on formwork is large. (ACI recommends if external vibration used then reduce 10% in pressure formula).
  6. Water to cement ratio of Concrete that is a slump of Concrete: if a slump value of Concrete is more than concrete acts like a liquid which exerts a large pressure on formwork.
  7. External admixtures or additives used: chemical admixtures effects on hardening time of concrete. Basically, it acts as a retiring agent or plasticizer. Which also affects on formwork design.

Hi, For the design of formwork as per technical and legal specifications, please refer IS 456: 2000. These codes describe the detail of formwork and their applications. Thank you.

Daniel Kelley
Junior Civil Engineer

Formwork is the term used for the process of creating a temporary mould into which concrete is poured and formed. Traditional formwork is fabricated using timber, but it can also be constructed from steel, glass fibre reinforced plastics and other materials.

There are three types of formwork :-

-Beam formwork :-
Formwork for beams takes the form of a three-sided box which is supported and propped in the correct position and to the desired level. The removal time for the formwork will vary with air temperature, humidity and consequent curing rate. Typical striking times are as follows (using air temperature of 7-16 ºC):

i) Beam sides: 9-12 hours.
ii) Beam soffits: 8-14 days.
iii) Beam props: 15-21 days.

-Column formwork :-
This consists of a vertical mould of the desired shape and size of the column to be poured. As a means of keeping the formwork material thickness to a minimum, horizontal steel or timber clamps (or yokes) are used at equal centres for batch filling and at varying centres for filling that is completed in one pour.

The head of the column formwork can be used to provide support for the beam formwork, but while this gives good top lateral restraint it can make the formwork complex. Alternatively, the column can be cast to the underside of the beams. Later on, a collar of formwork can be clamped around the cast column to complete the casting and support the incoming beam formwork.

-Plastic formwork :-
Re-usable plastic formwork is generally used for quick pours of concrete. The formwork is assembled either from interlocking panels or from a modular system and is used for relatively simple concrete structures. It is not as versatile as timber formwork due to the prefabrication requirements and is best suited for lost-cost, repetitive structures such as mass housing schemes.

Stay-in-place structural formwork is generally assembled on site using prefabricated fibre-reinforced plastic. It is used for concrete columns and piers and stays in place, acting as permanent axial and shear reinforcement for the structural member. It also provides resistance to environmental damage for both the concrete and reinforcing bars.

Proprietary systems are used to support vertical formwork while concrete cures, consisting of a series of tubes and ties.