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Formwork

Animation depicting construction ofmulti-story building using aluminumhandset formwork.

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Formwork is the term given to either temporary orpermanent molds into which concrete or similar materialsare poured. In the context of concrete construction, thefalsework supports the shuttering molds.

Contents

1 Formwork and concrete form types

2 Slab formwork (deck formwork)2.1 History

2.2 Timber beam slab formwork

2.3 Traditional slab formwork

2.4 Metal beam slab formwork

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Modular steel frame formwork for afoundation

Timber formwork for aconcrete column

2.4 Metal beam slab formwork

2.5 Modular slab formwork

2.6 Table or flying form systems2.6.1 Structure

2.6.2 Support

2.6.3 Size

2.7 Tunnel forms

2.8 Cassette formwork

3 Climbing formwork

4 Flexible formwork

5 Usage

6 Gallery

7 See also

8 Literature

9 References

10 External links

Formwork and concrete form types [edit]

Formwork comes in several types:

1. Traditional timber formwork. The formwork is built on siteout of timber and plywood or moisture-resistantparticleboard. It is easy to produce but time-consuming forlarger structures, and the plywood facing has a relativelyshort lifespan. It is still used extensively where the labourcosts are lower than the costs for procuring

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Aluminum formwork system

Sketch of the side view of traditionaltimber formwork used to form a flight ofstairs

Placing a formwork component

reusable formwork. It is also the most flexible type offormwork, so even where other systems are in use,complicated sections may use it.

2. Engineered Formwork System. This formwork isbuilt out of prefabricated modules with a metalframe (usually steel or aluminium) and covered onthe application (concrete) side with material havingthe wanted surface structure (steel, aluminum,timber, etc.). The two major advantages of formworksystems, compared to traditional timber formwork,are speed of construction (modular systems pin,clip, or screw together quickly) and lower life-cyclecosts (barring major force, the frame is almostindestructible, while the covering if made of wood;may have to be replaced after a few - or a fewdozen - uses, but if the covering is made with steelor aluminium the form can achieve up to twothousand uses depending on care and theapplications).

3. Re-usable plastic formwork. These interlocking andmodular systems are used to build widely variable,but relatively simple, concrete structures. Thepanels are lightweight and very robust. They areespecially suited for low-cost, mass housingschemes.

4. Permanent Insulated Formwork. This formwork is assembled on site, usually out of

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insulating concrete forms (ICF). The formwork stays in place after the concrete has cured,and may provide advantages in terms of speed, strength, superior thermal and acousticinsulation, space to run utilities within the EPS layer, and integrated furring strip for claddingfinishes.

5. ″Coffor″ is a structural stay-in-place formwork system to build constructions in concrete. It iscomposed of two filtering grids reinforced by vertical stiffeners and linked by articulatedconnectors that can be folded for transport. A standard panel 1.10 m x 2.70 m (3' 8 x 9)weighs 32.7 kg (72 lbs) and can be carried by hand or by any means of machine. AfterCoffor is placed, concrete is poured between the grids: excess water of concrete iseliminated by gravity and air is also eliminated. Coffor remains in the construction afterconcrete is poured and acts as reinforcement. Any type of construction can be built withCoffor: individual houses, multi-story buildings including high-rise buildings, industrial,commercial or administrative buildings. Several types of civil works can be done with Coffor.Coffor is delivered completely assembled from the factory. No assembly is necessary on theconstruction site.

6. Stay-In-Place structural formwork systems. This formwork is assembled on site, usually outof prefabricated fiber-reinforced plastic forms. These are in the shape of hollow tubes, andare usually used for columns and piers. The formwork stays in place after the concrete hascured and acts as axial and shear reinforcement, as well as serving to confine the concreteand prevent against environmental effects, such as corrosion and freeze-thaw cycles.

7. Flexible formwork. In contrast to the rigid moulds described above, flexible formwork is asystem that uses lightweight, high strength sheets of fabric to take advantage of the fluidityof concrete and create highly optimised, architecturally interesting, building forms. Usingflexible formwork it is possible to cast optimised structures that use significantly lessconcrete than an equivalent strength prismatic section,[1] thereby offering the potential for

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Pantheon domeSchematic sketch of traditionalformwork

Modular formwork with deck forhousing project in Chile

significant embodied energy savings in new concrete structures.

Slab formwork (deck formwork) [edit]

History [edit]

Some of theearliest examplesof concrete slabswere built byRoman engineers.Because concreteis quite strong inresistingcompressive loads,

but has relatively poor tensile or torsional strength, theseearly structures consisted of arches, vaults and domes.The most notable concrete structure from this period is thePantheon in Rome. To mould this structure, temporaryscaffolding and formwork or falsework was built in thefuture shape of the structure. These building techniqueswere not isolated to pouring concrete, but were and arewidely used in masonry. Because of the complexity and thelimited production capacity of the building material,concrete’s rise as a favored building material did not occuruntil the invention of Portland cement (and developments

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Steel and plywood formwork forpoured in place concrete foundation

Traditional timber formwork on ajetty in Bangkok

by the Edison Portland Cement Company) and reinforcedconcrete.

Timber beam slab formwork [edit]

Similar to the traditional method, but stringers and joist arereplaced with engineered wood beams and supports arereplaced with metal props. This makes this method moresystematic and reusable.

Traditional slab formwork [edit]

On the dawn of therival of concrete inslab structures, building techniques for the temporarystructures were derived again from masonry andcarpentry. The traditional slab formwork technique consistsof supports out of lumber or young tree trunks, thatsupport rows of stringers assembled roughly 3 to 6 feet or1 to 2 metres apart, depending on thickness of slab.Between these stringers, joists are positioned roughly12 inches, 30 centimeters apart upon which boards orplywood are placed. The stringers and joists are usually 4

by 4 inch or 4 by 6 inch lumber. The most common imperial plywood thickness is ¾ inch and themost common metric thickness is 18 mm.

Metal beam slab formwork [edit]

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Hand setting modular aluminumdeck formwork

Handset modular aluminumformwork

Similar to the traditional method, but stringers and joist are replaced with aluminium formingsystems or steel beams and supports are replaced with metal props. This also makes this methodmore systematic and reusable. Aluminum beams are fabricated as telescoping units which allowsthem to span supports that are located at varying distances apart. Telescoping aluminium beamscan be used and reused in the construction of structures of varying size.

tertr

Modular slabformwork [edit]

These systemsconsist ofprefabricatedtimber, steel oraluminum beamsand formwork

modules. Modules are often no larger than 3 to 6 feet or 1 to 2 metres in size. The beams andformwork are typically set by hand and pinned, clipped, or screwed together. The advantages of amodular system are: does not require a crane to place the formwork, speed of construction withunskilled labor, formwork modules can be removed after concrete sets leaving only beams in placeprior to achieving design strength.

Table or flying form systems [edit]

These systems consist of slab formwork "tables" that are reused on multiple stories of a buildingwithout being dismantled. The assembled sections are either lifted per elevator or "flown" by cranefrom one story to the next. Once in position the gaps between the tables or table and wall are filled

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Flying formwork tables withaluminium and timber joists. Thetables are supported by shoesattached to previously poured columnsand walls

with "fillers". They vary in shape and size as well as their building material. The use of thesesystems can greatly reduce the time and manual labor involved in setting and striking theformwork. Their advantages are best utilized by large area and simple structures. It is alsocommon for architects and engineers to design building around one of these systems.

Structure [edit]

A table is built pretty much the same way as a beamformwork but the single parts of this system are connectedtogether in a way that makes them transportable. The mostcommon sheathing is plywood, but steel and fiberglass arealso in use. The joists are either made from timber, wood I-beams, aluminium or steel. The stringers are sometimesmade of wood I-beams but usually from steel channels.These are fastened together (screwed, weld or bolted) tobecome a "deck". These decks are usually rectangular butcan also be other shapes.

Support [edit]

All support systems have to be height adjustable to allow the formwork to be placed at the correctheight and to be removed after the concrete is cured. Normally adjustable metal props similar to(or the same as) those used by beam slab formwork are used to support these systems. Somesystems combine stringers and supports into steel or aluminum trusses. Yet other systems usemetal frame shoring towers, which the decks are attached to. Another common method is to attachthe formwork decks to previously cast walls or columns,thus eradicating the use of vertical propsaltogether. In this method, adjustable support shoes are bolted through holes (sometimes tieholes) or attached to cast anchors.

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Size [edit]

The size of these tables can vary from 70 to 1,500 square feet (6.5 to 139.4 m2). There are twogeneral approaches in this system:

1. Crane handled: this approach consists of assembling or producing the tables with a largeformwork area that can only be moved up a level by crane. Typical widths can be 15, 18 or20 ft. or 5 to 7 metres but their width can be limited, so that it is possible to transport themassembled, without having to pay for an oversize load. The length might vary and can be upto 100 ft. (or more) depending on the crane capacity. After the concrete is cured, the decksare lowered and moved with rollers or trolleys to the edge of the building. From then on theprotruding side of the table is lifted by crane while the rest of the table is rolled out of thebuilding. After the centre of gravity is outside of the building the table is attached to anothercrane and flown to the next level or position.

This technique is fairly common in the United States and east Asian countries. The advantages ofthis approach are the further reduction of manual labour time and cost per unit area of slab and asimple and systematic building technique. The disadvantages of this approach are the necessaryhigh lifting capacity of building site cranes, additional expensive crane time, higher material costsand little flexibility.

2. Crane fork or elevator handled:

By this approach the tables are limited in size and weight.Typical widths are between 6 and 10 ft or 2 to 3 meters,typical lengths are between 12 and 20 ft or 4 to 7 metres,though table sizes may vary in size and form. The majordistinction of this approach is that the tables are lifted

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Formwork tables in use at abuilding site with more complicatedstructural features

either with a crane transport fork or by material platformelevators attached to the side of the building. They areusually transported horizontally to the elevator or cranelifting platform singlehandedly with shifting trolleysdepending on their size and construction. Final positioningadjustments can be made by trolley. This technique enjoyspopularity in the US, Europe and generally in high labor cost countries. The advantages of thisapproach in comparison to beam formwork or modular formwork is a further reduction of labor timeand cost. Smaller tables are generally easier to customize around geometrically complicatedbuildings, (round or non rectangular) or to form around columns in comparison to their largecounterparts. The disadvantages of this approach are the higher material costs and increasedcrane time (if lifted with crane fork).

Tunnel forms [edit]

Tunnel forms are large, room size larger than your bedrooms and uses electromagnetic ultramechanic machines which utilize all forms of energy. That allows walls and floors to be cast in asingle pour. With multiple forms, the entire floor of a building can be done in a single pour. Tunnelforms require sufficient space exterior to the building for the entire form to be slipped out andhoisted up to the next level. A section of the walls is left uncasted to remove the forms. Typicallycastings are done with a frequency of 4 days. Tunnel forms are most suited for buildings that havethe same or similar cells to allow re-use of the forms within the floor and from one floor to the next,in regions which have high labor prices.

Cassette formwork [edit]

See structural coffer.

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Climbing formwork [edit]

Main article: Climbing formwork

Climbing formwork is a special type formwork for vertical concrete structures that rises with thebuilding process. While relatively complicated and costly, it can be an effective solution forbuildings that are either very repetitive in form (such as towers or skyscrapers) or that require aseamless wall structure (using gliding formwork, a special type of climbing formwork).

Various types of climbing formwork exist, which are either relocated from time to time, or can evenmove on their own (usually on hydraulic jacks, required for self-climbing and gliding formworks).

Flexible formwork [edit]

There is an increasing focus on sustainability in design, backed up by carbon dioxide emissionsreduction targets. The low embodied energy of concrete by volume is offset by its rate ofconsumption which make the manufacture of cement accountable for some 5% of global CO2emissions.[2]

Concrete is a fluid that offers the opportunity to economically create structures of almost anygeometry - we can pour concrete into a mould of almost any shape. This fluidity is seldom utilise,with concrete instead being poured into rigid moulds to create high material use structures withlarge carbon footprints. The ubiquitous use of orthogonal moulds as concrete formwork hasresulted in a well-established vocabulary of prismatic forms for concrete structures, yet such rigidformwork systems must resist considerable pressures and consume significant amounts ofmaterial. Moreover, the resulting member requires more material and has a greater self-weightthan one cast with a variable cross section.

Simple optimisation methods[3][4][5] may be used to design a variable cross section member in

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which the flexural and shear capacity at any point along the element length reflects therequirements of the loading envelope applied to it.

By replacing conventional moulds with a flexible system composed primarily of low cost fabricsheets, flexible formwork takes advantage of the fluidity of concrete to create highly optimised,architecturally interesting, building forms. Significant material savings can be achieved.[6] Theoptimised section provides ultimate limit state capacity while reducing embodied carbon, thusimproving the life cycle performance of the entire structure.

Control of the flexibly formed beam cross section is key to achieving low-material use design. Thebasic assumption is that a sheet of flexible, permeable fabric is held in a system of falseworkbefore reinforcement and concrete are added. By varying the geometry of the fabric mould withdistance along the beam, the optimised shape is created. Flexible formwork therefore has thepotential to facilitate the change in design and construction philosophy that will be required for amove towards a less material intensive, more sustainable, construction industry. Its potential isfurther demonstrated in work by Lee.[7]

Further information can be found online.

Professor Mark West - http://www.umanitoba.ca/cast_building/ The Second InternationalConference on Flexible Formwork - http://www.icff2012.co.uk

Usage [edit]

For removable forms, once the concrete has been poured into formwork and has set (or cured),the formwork is struck or stripped (removed) to expose the finished concrete. The time betweenpouring and formwork stripping depends on the job specifications, the cure required, and whetherthe form is supporting any weight, but is usually at least 24 hours after the pour is completed. Forexample, the California Department of Transportation requires the forms to be in place for 1–7

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Formwork stripped exposing the setconcrete

days after pouring,[8] while the Washington State Department of Transportation requires the formsto stay in place for 3 days with a damp blanket on the outside.[9]

Spectacular accidents have occurred when the forms wereeither removed too soon or had been under-designed tocarry the load imposed by the weight of the uncuredconcrete. Less critical and much more common (though noless embarrassing and often costly) are those cases inwhich under-designed formwork bends or breaks duringthe filling process (especially if filled with a high-pressureconcrete pump). This then results in fresh concreteescaping out of the formwork in a form blowout, often inlarge quantities.

Concrete exerts less pressure against the forms as ithardens, so forms are usually designed to withstand a number of feet per hour of pour rate to givethe concrete at the bottom time to firm up. For example, wall or column forms are commonlydesigned for a pour rate between 4–8 ft/hr.[citation needed] The hardening is an asymptotic process,meaning that most of the final strength will be achieved after a short time, though some furtherhardening can occur depending on the cement type and admixtures.

Wet concrete also applies hydrostatic pressure to formwork. The pressure at the bottom of theform is therefore greater than at the top. In the illustration of the column formwork to the right, the'column clamps' are closer together at the bottom. Note that the column is braced with steeladjustable 'formwork props' and uses 20 mm 'through bolts' to further support the long side of thecolumn.

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Gallery [edit]

Coal tunnel constructedusing handset aluminumconcrete forms.

Concrete poolconstruction usingaluminum concreteforms.

Soffit formwork to a flightof concrete stairs.

Stair formwork showingthe use of strongbacks tosupport the risershutters.

Sketch showing the usetimber props for beamforms.

Coal silo constructionusing radius concreteformwork.

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Detail of an alternative tocolumn clamps for largercolumns. Twin steelwalers and tie bolts, asused in wall forms.

An example ofpermanent formwork. Acolumn using spiralducting.

An example ofpermanent formwork, asuspended house slabon roll formed galvanizedsteel. The formwork inthis case is alsostructural, being bondedto the slab.

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Concrete fenceconstruction using ashlarstone aluminum concreteforms.

Concrete housingconstruction inVenezuela usingaluminum concreteformwork.

Concrete construction inBrazil using handsetaluminum concreteformwork.

Concrete construction inMoscow metro usingspecial aluminumconcrete formwork

Engineered FormworkSystem in Moscowmetro

Engineered FormworkSystem in Moscowmetro

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See also [edit]

PERI

MEVA Formwork System

Outinord

PASCHAL Formwork

Doka Group

Climbing formwork (formwork that climbs up the rising building during the construction)

Concrete cover (depth of the concrete between reinforcing steel and outer surface)

Moladi (plastic formwork system)

Slip forming (construction method in which concrete is poured into a continuously moving form)

Mould release agent for formwork

GHI Formwork

Literature [edit]

Matthias Dupke: Einsatzgebiete der Gleitschalung und der Kletter-Umsetz-Schalung: EinVergleich der Systeme. 2010, Verlag Diplomarbeiten Agentur, Hamburg, ISBN 978-3-8386-0295-0.

The Concrete Society, Formwork: A guide to good practice

References [edit]

1. ^ Orr, J. J., Darby, A. P., Ibell, T. J., Evernden, M. C. and Otlet, M., 2011. Concrete structures usingfabric formwork. The Structural Engineer, 89 (8), pp. 20-26.

2. ^ WRI (2005) Carbon Dioxide Emissions by Source 2005. Earthtrends Data Tables: Climate andAtmosphere, Available online

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V · T · E ·

3. ^ Orr JJ, Darby AP, Ibell TJ, et al (2011) Concrete structures using fabric formwork. The StructuralEngineer 89(8): 20-26. http://opus.bath.ac.uk/23588/

4. ^ Kostova K, Ibell T, Darby AP and Evernden M (2012) Advanced composite reinforcement for fabricformed strutural elements. In Second International Conference on Flexible Formwork (Orr JJ, DarbyAP, Evernden M and Ibell T. (eds)). University of Bath, Bath, UK. www.icff2012.co.uk

5. ^ Garbett J, Darby AP and Ibell TJ (2010) Optimised beam design using innovative fabric-formedconcrete. Advances in Structural Engineering 13(5): 849-860.

6. ^ Orr JJ, Darby AP, Ibell TJ and Evernden M (2012a) Optimisation and durability in fabric cast'Double T' beams. In The Second International Conference on Flexible Formwork (Orr JJ, Darby AP,Evernden M and Ibell T. (eds)). University of Bath, Bath, UK http://opus.bath.ac.uk/30078/

7. ^ Lee, DSH (2010) Study of construction methodology and structural behaviour of fabric formed form-efficient reinforced concrete beam. PhD Thesis, University of Edinburgh, Edinburgh.

8. ^ [Section 90-7] from the Caltrans Standard Specifications, 2006

9. ^ [Section 6-02.3(11)] from the WSDOT Standard Specifications, 2006

External links [edit]

Stripping time of form work as per india standards

An illustrated glossary of the terms used in temporary types of construction work. Formwork,scaffolding etc.

[1]

Formwork,Scaffolding and Shoring Definition and productivity.

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