Formwork (formwork) in concrete construction is used as a form for the structure, into which fresh concrete is poured to subsequently harden. The types of concrete formwork construction depend on the material of the formwork and the type of structural element.
Formwork can also be named according to the type of construction of the structural member, such as plate formwork for use in slab, beam formwork, column formwork for use in beams and columns, etc.
Formwork construction takes time and involves spending up to 20-25% of the construction cost or more. The design of these temporary structures is economically costly. The operation of removing formwork is known as stripping. Removed formwork can be reused. Reusable molds are known as panel molds and non-reusable molds are called stationary molds.
Wood is the most common material used for formwork. The disadvantage of wooden formwork is that it will warp, swell and shrink. Applying a waterproof coating to the surface of the wood mitigates these defects.
Requirements permanently formwork
It should be strong enough to confront to all types of dead and live loads. It should be solidly constructed and effectively supported and braced both horizontally and vertically to retain its shape.The joints within the formwork should be tight against leakage of cement mortar.
The formwork design should allow the removal of the numerous parts in the desired order without damaging the concrete.Formwork material should be cheap, easily available and suitable for repeated use.The formwork should be set exactly on the required line and the levels should have a flat surface. It should be as light as possible.
Formwork material shouldn't warp or warp when exposed to the weather.It should rest on a solid base. Economy in formwork to save formwork costs, the next points must be observed: The construction plan should include the minimum number of deviations in room size, floor area, etc., to allow for reuse of formwork.The design should be perfect so that the slim parts can only be used in the most economical way.
Minimal sawing and cutting of wood pieces should be wiped out order that the material can be reused many times. the number of surface treatment depends on the quality of the formwork. Formwork are often made from wood, plywood, steel, precast concrete or fiberglass, individually or together . Steel molds are utilized during a situation where a large amount of reuse of the same molds is required. Wooden formwork is compatible for little jobs. Fiberglass made from precast concrete and aluminum is used in cast structures such as slabs or elements with curved surfaces.
.jpg)
1. Wooden formwork Timber for formwork should meet the next requirements: It should be: Well seasoned Low weight Easy to work with nails without splitting No loose knots Wood used for formwork for work with fair-faced concrete should have a smooth and even surface on all surfaces that inherit contact with the concrete.
2. Normal element sizes for timber formwork reinforcement for slabs, beam, column side and beam bottom 25mm to 40mm thick Joints, cornices 50 x 70 mm to 50 x 150 mm Posts 75 x 100 mm to 100 x 100 mm
3. Plywood formwork Resin-glued plywood sheets are attached to wooden frames to form panels of the required sizes. the price of plywood formwork compares favorably with wooden formwork and can even be cheaper in some cases, taking into account the following considerations: It is possible to have a smooth surface, during this case it's the cost of surface treatment. By using large-sized panels, it's possible to influence the saving of labor costs for fastening and dismantling. The number of reuses is higher than with wooden formwork. For estimation purposes, the quantity of reuses can be taken as 2to 25.
4. Steel formwork It consists of panels made up of thin steel plates reinforced along the edges with small steel angles. Panel units are often held together using suitable clamps or bolts and nuts. Panels are often produced in large numbers in any modular shape or size. Steel forms are widely utilized in large projects or during a situation where a large amount of reuse of formwork is possible. this type of closure is considered most suitable for circular or curved structures. Comparison of steel and wooden formwork Steel formwork is stronger, more durable and features a extended life than wooden formwork and its reuse is increasing. Steel forms are often installed and dismantled with greater ease and speed. The surface quality of fair-faced concrete when using steel forms is nice , and such surfaces don't have to be further modified.
Steel formwork doesn't absorb moisture from concrete.Steel formwork doesn't shrink or deform.Construction of concrete formwork this usually involves the next operations: Support and centering Shielding Providing elevation Cleaning and surface treatment The order and method of removing formwor Order order and formwork removal method are as follows:
First, the formwork forming the vertical surfaces of the walls, beams and sides of the column must be removed, because they're doing not carry any load, but only hold the concrete.Furthermore, the formwork forming the soffit of the boards must be removed.
Formwork forming a soffit made up of beams, joists or other heavily loaded formwork should be removed if necessary.Fast-hardening cement, warm weather and light-weight loads allow timely removal of formwork.
Under no circumstances should the formwork be allowed to be removed until all concrete has reached a strength of a minimum of twice the strain to which the concrete may be subjected at the time the formwork is removed. All formwork should be relieved gradually and punctiliously to avoid sudden load transfer to the concrete.
S. No. Component Description Duration
(1) Vertical sides of walls, columns and beams 1-2 days
(2) slab plate 3 days and immediately refixed prop jack
(3) Beam bottom 7 days and immediately refixed prop jack
Slabs
(a) For slabs with a span up to 4.5 m 7 days
(b) For slabs with a span greater than 4.5 m 14 days
( 5)Removal of beam and arch supports
(a) For spans of 6 m Up to 14 days
(b) Span 6m or more 21 days
No comments:
Post a Comment
thanks for read this artical