| Formwork has a dual function in concrete construction – it supports the plastic and hardening concrete |
| until it is sufficiently strong to support the actions/loads imposed upon it, and it imparts a finish to the |
| concrete surface. This Section describes the different types of formwork used in modern concrete |
| construction and outlines the requirements which must be met for formwork to perform satisfactorily. |
| The special requirements associated with the achievement of visually satisfying surface finishes are |
| discussed in Part V, Section 16 ‘Control of Surface Finishes’ in this Guide. |
| 7.2 UNDISTURBED SHORES............ 12 |
| CONTENTS |
| 7.3 RESHORING SYSTEMS .............. 13 |
| 1. INTRODUCTION ................................... 2 8. CONSTRUCTION OF FORMWORK ... 13 |
| 2. BASIC COMPONENTS OF 8.1 ERECTION .................................. 13 |
| FORMWORK ........................................ 3 8.2 PREPARATION FOR |
| 3. REQUIREMENTS FOR FORMWORK ... 4 CONCRETING ............................. 13 |
| 3.1 GENERAL ...................................... 4 8.3 EXTERNAL VIBRATION .............. 14 |
| 3.2 STRENGTH .................................... 4 8.4 STRIPPING FORMWORK............ 15 |
| 3.3 STIFFNESS .................................... 5 9. FORMWORK DOCUMENTATION ...... 15 |
| 3.4 ACCURACY ................................... 5 10. SUMMARY – CONSTRUCTION |
| CHECKLIST ....................................... 17 |
| 3.5 WATER-TIGHTNESS ..................... 5 |
| 11. RELEVANT AUSTRALIAN |
| 3.6 PERMEABILITY.............................. 5 |
| STANDARDS ..................................... 18 |
| 3.7 ROBUSTNESS ............................... 5 |
| 3.8 EASE OF STRIPPING .................... 6 |
| 1. INTRODUCTION |
| 3.9 STANDARDISATION ...................... 6 |
| 3.10 SAFETY ......................................... 6 |
| Formwork is the temporary structure which (a) |
| 4. MATERIALS FOR FORMWORK ........... 6 moulds concrete into the desired shape and (b) |
| holds it in the correct position until it is able to |
| 4.1 GENERAL ...................................... 6 |
| support the loads imposed upon it. It also |
| 4.2 CHOICE OF MATERIALS ............... 6 imparts the required surface finish. Importantly, |
| 4.3 FORM LINERS ............................... 7 formwork also provides safe working areas and |
| access ways for construction personnel. |
| 5. FORMWORK SYSTEMS ....................... 8 |
| Formwork and its supports (known as |
| 5.1 MODULAR FORMWORK ............... 8 falsework) is a structural system and must be |
| designed and built accordingly. The actions |
| 5.2 GANG FORMS ............................... 8 |
| (loads) imposed on it may be temporary, but |
| 5.3 TABLE FORMS............................... 8 |
| they can be extremely large. Frequently they |
| 5.4 JUMP/CLIMB FORMS .................... 9 are different in nature to those imposed on the |
| finished concrete structure. |
| 5.5 SLIP-FORMS.................................. 9 |
| 5.6 PERMANENT FORMWORK ......... 10 |
| Concrete is an extremely plastic and mouldable |
| material which will accurately reflect the shape, |
| 6. DESIGN OF FORMWORK ................... 10 |
| texture and finish of the surface against which it |
| 6.1 GENERAL .................................... 10 is cast. Any imperfection or inaccuracy in this |
| surface will be indelibly inscribed onto the |
| 6.2 LOADS ON FORMWORK ............. 10 |
| concrete surface. Form-face materials must |
| 7. FALSEWORK...................................... 12 |
| therefore be chosen both to achieve the |
| 7.1 DESIGN OF SUPPORT required surface finish and, in conjunction with |
| STRUCTURES ............................. 12 all the supporting elements, to maintain |
| PAGE 2 > Guide to Concrete Construction — Part IX-Section 27 – Formwork Version 1.0 |
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| accuracy and stability under all of the loads • Walers or bearers – which brace the |
| imposed during erection and placing – typically studs or support the joists and prevent |
| for at least several days into the life of the bulging or bowing in the other direction. |
| concrete structure. |
| | | | | | | | | An important | facet of formwork | design and | |
| | --- | --- | --- | --- | --- | --- | --- | -------------- | -------------------- | ------------ | |
| At early ages, the concrete will not be able to construction is the choice of spans (or centres) |
| support the loads imposed on it. Until the between studs, and also centres between |
| concrete is able to support the imposed loads |
| walers or bearers – both of which are important |
| the formwork (and falsework) will be the primary in preventing bulging and bowing. |
| loadbearing structure. Only when the concrete |
| | has | achieved | sufficient | | strength | can | the | | | | |
| | ---- | --------- | ----------- | --- | --------- | ---- | ---- | --- | --- | --- | |
| formwork be removed without detriment to the |
| safety or performance of the concrete structure. |
| Failure to meet accuracy, stability and strength |
| requirements will lead to formwork failures in |
| the form of bowing, warping or misalignment |
| which will be reflected in the final structure. |
| | Such | problems | could | | even | lead | to the | | | | |
| | ------------- | --------- | --------- | --- | ---------- | ----- | -------- | --- | --- | --- | |
| | catastrophic | | collapse | of | part (or | all) | of the | | | | |
| formwork. |
| | The | cost | of formwork | is | generally | | a very | | | | |
| | ---- | ----- | ------------- | --- | ---------- | --- | -------- | --- | --- | --- | |
| significant item in the overall cost of a project. |
| | The | formwork | system | should | be | the | most | | | | |
| | ---- | --------- | ------- | ------- | --- | ---- | ----- | --- | --- | --- | |
| Figure 27.1 – Wall Forms |
| | economical | | available | – | but cost | concerns | | | | | |
| | ----------- | ------ | ---------- | ---------- | ---------- | --------- | ---- | --- | --- | --- | |
| | should | never | be | permitted | to | overrule | the | | | | |
| criteria governing safety, strength and stability. |
| In reality, the initial cost of formwork may be a |
| very poor guide to its suitability for a project. |
| | Multiple | | uses of good | quality | formwork | | can | | | | |
| | --------- | --- | --------------- | -------- | --------- | --- | ---- | --- | --- | --- | |
| result in improved overall project economies. |
| | Formwork | | design and | selection | | of materials | | | | | |
| | --------- | --- | ------------ | ---------- | --- | -------------- | --- | --- | --- | --- | |
| should therefore always be approached on the |
| basis of ‘cost per use’. |
|
|
| 2. BASIC COMPONENTS OF |
| | | FORMWORK | | | | | | Figure 27.2 – Beam Form and Supports | | | |
| | --- | --------- | --- | --- | --- | --- | --- | ------------------------------------- | --- | --- | |
|
|
| The basic components of formwork for typical |
| concrete elements are shown in Figures 27.1 |
| to 27.4. |
| The basic structure of almost all formwork is the |
| same. It comprises: |
| • Form-face – which creates the surface |
| finish e.g. metal or plywood sheet, sawn |
| timber; |
| • Studs, or joists – lengths of sawn timber |
| | | or | (sometimes) | metal | sections | | which | | | | |
| | --- | --- | ------------ | ------ | --------- | --- | ------ | --- | --- | --- | |
| support the form-face and prevent it from |
| bulging or bowing in one direction; and |
| Figure 27.3 – Column Forms |
|
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| However, even metal components may become |
| loose fitting or broken due to wear. All formwork |
| materials and components must be checked |
| regularly to ensure that they are sound and |
| safe. |
| Table 27.1 – Requirements for Formwork |
| | | | | | | | Property | Purpose | |
| | --- | --- | --- | --- | --- | --- | ---------- | -------------------- | |
| | | | | | | | Strength | Carry imposed loads | |
| | | | | | | | Stiffness | Maintain specified | |
| shape and avoid |
| Figure 27.4 – Typical Soffit Forms and Falsework distortion of concrete |
| elements |
| (diagrammatic only; bracing not shown) |
| | | | | | | | Accuracy | Ensure shape and size | |
| | --------------------- | --- | --- | --- | --- | --- | --------- | ---------------------- | |
| | 3. REQUIREMENTS FOR | | | | | | | of concrete elements; | |
| Ensure specified cover |
| FORMWORK |
| to reinforcement. |
| 3.1 GENERAL |
| | | | | | | | Watertightness | Avoid grout loss and | |
| | --- | --- | --- | --- | --- | --- | --------------- | --------------------- | |
| subsequent |
| | Although | formwork | is | constructed | | only to | | | |
| | --------- | --------- | --- | ------------ | --- | --------- | --- | --- | |
| honeycombing of the |
| | contain | and support | concrete | | until | the cast | | | |
| | -------- | ------------- | --------- | --- | ------ | ---------- | --- | --- | |
| concrete |
| | structure | is strong | enough | | to support | the | | | |
| | ---------- | ----------- | ------- | --- | ------------ | ---- | --- | --- | |
| imposed loads itself, it must provide a safe Permeability When used, permeable |
| formwork allows water |
| environment for all those working on or around |
| it. In addition to being strong enough, it must and air to be removed |
| also be stable against overturning, uplift, and from the formed surface |
| sideways movements. It must also meet all |
| statutory requirements for access ladders, Robustness Enable re-use |
| | guardrails, | working | platforms, | | etc. | Where | | | |
| | ------------ | -------- | ----------- | --- | ----- | ------ | ------------------ | ---------------- | |
| | | | | | | | Ease of stripping | Avoid damage to | |
| Importance Level II and Importance Level III |
| criteria (see AS 3610.1 – Appendix A) are met, concrete surfaces |
| formwork documentation that (a) sets out the |
| | | | | | | | Standardisation | Promote economy | |
| | --- | --- | --- | --- | --- | --- | ---------------- | ---------------- | |
| requirements of the formwork design, (b) states |
| | that the | design | conforms | | with AS | 3610 | | | |
| | ---------- | ------- | --------- | --- | --------- | ----- | ------- | ---------------------- | |
| | | | | | | | Safety | Ensure a safe working | |
| requirements, and (c) allows the formwork to be |
| | verified | and | inspected, | is | a mandatory | | | environment | |
| | ------------ | ---- | ----------- | ------ | ------------- | --- | --- | ------------ | |
| | requirement | of | AS 3610. | Where | proprietary | | | | |
| 3.2 STRENGTH |
| | formwork | systems | are | used, | | formwork | | | |
| | -------------- | -------- | ---- | -------- | ---------- | --------- | --- | --- | |
| | documentation | | can | contain | brochures | | | | |
| All components should be designed to cater for |
| | describing | the | formwork | – | provided | these | | | |
| | ----------- | ---- | --------- | --- | --------- | ------ | --- | --- | |
| the most severe loads that are likely to be |
| | contain | a suite | of information | | described | in | | | |
| | -------- | --------- | ---------------- | --- | ---------- | ---- | --- | --- | |
| AS 3610 (see also sub-section 9). imposed on the formwork. To achieve this, the |
| formwork design should be carried out by a |
| The general requirements for formwork are person experienced and competent in such |
| | summarised | | in Table | 27.1. | | Additional | design. | | |
| | ----------- | --- | ---------- | ------ | --- | ----------- | -------- | --- | |
| information is contained in AS 3610. |
| Care should then be taken to ensure that the |
| With new materials, these requirements may be design details are met and that the construction |
| readily met. With re-use, all materials (except loads imposed on the formwork are within the |
| perhaps metal components) may be weakened. |
| limits nominated by the designer. |
|
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| Sound materials should always be used. Re- 3.4 ACCURACY |
| used material may be satisfactory but should be |
| checked regularly to ensure it is in good In general, formwork should always be built to |
| condition and adequate for the job in hand. The an accuracy greater than that desired in the |
| strength of each item of formwork material finished concrete structure or element. All |
| contributes to the overall safety of the support structures should be sufficient to |
| temporary structure. ensure that this accuracy is maintained until the |
| concrete has hardened. |
| Particular care is required with formwork design |
| and application where flowing concrete (also The accuracy required may affect the selection |
| known as Super Workable Concrete or Self of the material from which the formwork is to be |
| Compacting Concrete – see Section 22 ‘Super- built, as some materials may be able to be |
| Workable Concrete’ in this Guide) as these assembled to tighter tolerances than others. |
| materials can exert full hydrostatic pressure on |
| the formwork, resulting in significantly higher |
| 3.5 WATER-TIGHTNESS |
| pressures on the formwork than are seen with |
| conventional ‘slumped’ concrete. This is |
| All joints should be sealed to stop grout (cement |
| particularly the case for formwork in vertical |
| and water) leaking from the formwork. Grout |
| structures such as columns and walls. |
| loss causes ragged edges, hydration staining |
| and honeycombing which can affect strength, |
| 3.3 STIFFNESS durability and appearance in the final structure. |
| These issues can be exacerbated when using |
| Formwork should not bow, bulge, sag or flowing concretes of the types described in sub- |
| otherwise move to the extent that the section 3.2. |
| completed concrete element falls outside the |
| tolerances specified for the work. |
| 3.6 PERMEABILITY |
| The formwork designer should detail the |
| formwork elements to have adequate stiffness, Systems using formwork with high permeability |
| but site personnel are responsible for ensuring have some advantages. There are several |
| that (a) the correct materials are used, (b) they systems available, but they may be as simple |
| are of adequate quality, and (c) they are used as a fabric material attached to plywood |
| in the proper manner. For example – plywood backing which contains drain holes. This type of |
| sheeting for general formwork use has a formwork allows ‘bleed’ water and air to escape |
| greater strength in one direction relative to the through the formed faces with the effects of (a) |
| other. It should always be used in the correct lowering W/C ratio in the areas adjacent (to a |
| orientation, as shown in Figure 27.5. depth of about 20 mm) to the formwork, (b) |
| increasing the strength and reducing sorptivity |
| and permeability in these outer areas, and (c) |
| improving the finish at these surfaces. |
| 3.7 ROBUSTNESS |
| Formwork should be robust enough to |
| withstand repeated stripping, storing and |
| erection. Re-use of formwork is an important |
| element in improving the overall economy of the |
| structure. The extent of possible re-use varies |
| with formwork materials – with ranges from ‘up |
| to 5 times’ for plywood to 20-30 times for |
| Figure 27.5 – Orientation of Plywood |
| fibreglass and 50-100 times for steel. For form |
| liners (see 4.3), re-use can vary from 1-20 times |
| PAGE 5 > Guide to Concrete Construction — Part IX-Section 27 – Formwork Version 1.0 |
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| for timber (with varying surface treatments) to The stripping procedures (see 8.4) specified |
| up to 100 times for rubber. must not be modified and limits placed on |
| stacked materials anywhere on the formwork |
|
|
| must not be exceeded. |
| 3.8 EASE OF STRIPPING |
|
|
| Formwork should be easy to remove – to avoid |
| 4. MATERIALS FOR FORMWORK |
| or minimise damage to the concrete and/or to |
| the forms. Consideration should therefore be |
| 4.1 GENERAL |
| given to providing adequate draw (taper) on |
| vertical faces and also to the movement which |
| Formwork can be constructed in a variety of |
| must be allowed in supports to facilitate easy |
| ways and from a number of materials. The size |
| removal of horizontal soffit forms and specialist |
| | | | | | | | | and nature | of | the | project | will most | likely | |
| | --- | --- | --- | --- | --- | --- | --- | ------------ | --- | ---- | -------- | ----------- | ------- | |
| systems such as table forms. |
| determine which materials and which systems |
| | | | | | | | | are likely to maximise technical and economic | | | | | | |
| | --- | --- | --- | --- | --- | --- | --- | ---------------------------------------------- | --- | --- | --- | --- | --- | |
| imperatives. For example, on some projects, |
| 3.9 STANDARDISATION |
| | | | | | | | | particularly | small | ones, | | certain | formwork | |
| | --- | --- | --- | --- | --- | --- | --- | ------------- | ------ | ------ | --- | -------- | --------- | |
| As far as possible, formwork components elements are likely to be used only a relatively |
| small number of times. Considerable cutting |
| | should | be standardised | | | in size | to | avoid | | | | | | | |
| | ------- | ----------------- | --- | --- | --------- | --- | ------ | --- | --- | --- | --- | --- | --- | |
| unnecessary cutting. They should be able to be and fitting may be involved with consequent |
| | | | | | | | | wastage | of | materials. | The | use | of lower | |
| | --- | --- | --- | --- | --- | --- | --- | -------- | --- | ----------- | ---- | ---- | ---------- | |
| stripped, shifted and re-erected rapidly if speed |
| grade/cost materials may then be justified – |
| | of construction | | is | to be | maintained. | | This | | | | | | | |
| | ----------------- | --- | --- | ------- | ------------ | --- | ----- | --- | --- | --- | --- | --- | --- | |
| necessitates a system that comes apart easily, provided safety is not jeopardised. |
| | has a | minimum | of | elements | needing | | to be | | | | | | | |
| | ------- | -------- | --- | --------- | -------- | --- | ------- | --- | --- | --- | --- | --- | --- | |
| On larger projects, or with multiple projects, the |
| replaced (i.e. those damaged during removal) |
| use of specifically designed and constructed |
| | and is | easily | shifted | | with the | available | | | | | | | | |
| | ----------- | ------- | -------- | ----- | ---------- | ---------- | -------- | --------- | --------- | ---------------- | ---------- | --- | --------- | |
| | | | | | | | | formwork | elements | | can lead | to | improved | |
| | equipment. | On | small | jobs | this | will | involve | | | | | | | |
| | | | | | | | | economy. | | Standardisation | | | and | |
| ‘manhandling’, but on large jobs crane capacity |
| | | | | | | | | interchangeability | | then | become | particularly | | |
| | --- | --- | --- | --- | --- | --- | --- | ------------------- | --- | ----- | ------- | ------------- | --- | |
| may be used to improve efficiencies. |
| important selection criteria. |
| | Standardisation | | for | speed | of | construction | | | | | | | | |
| | ---------------- | --- | ---- | ------ | --- | ------------- | --- | --- | --- | --- | --- | --- | --- | |
|
|
| frequently requires more expensive formwork |
| 4.2 CHOICE OF MATERIALS |
| but, once re-use is taken into account, lower |
| overall project costs can be achieved. |
| | | | | | | | | Many materials | | may | be used | for formwork. | | |
| | ------------ | -------- | --------- | ------ | -------- | ------------- | -------- | -------------------------------------------- | ------------ | ---------- | -------------- | ---------------- | --------- | |
| | | | | | | | | Table 27.2 provides a brief overview of the | | | | | | |
| | 3.10 | SAFETY | | | | | | characteristics of those in common use. | | | | | | |
| | | | | | | | | Before | the final | selection | | of the | formwork | |
| | Formwork | must | provide | | a safe | | working | | | | | | | |
| | | | | | | | | material | is made | for | a particular | project, | a | |
| | environment | | for all | those | working | | on and | | | | | | | |
| | | | | | | | | number | of factors | | should | be considered, | | |
| | around | it. In | addition | to | being | of adequate | | | | | | | | |
| including: |
| | strength, | it | must | also | be stable | | against | | | | | | | |
| | ------------- | --- | -------- | ----- | ----------- | --- | -------- | --- | --- | --- | --- | --- | --- | |
| | overturning, | | uplift, | and | sideways | or | sliding | | | | | | | |
| • The size of the forms; |
| | movements. | | Properly | | guarded | walkways | | | | | | | | |
| | ----------- | --- | --------- | --- | -------- | --------- | --- | --- | --- | --- | --- | --- | --- | |
| • The shape of the forms; |
| | should | be | provided | around | | all areas | of | | | | | | | |
| | ------- | --- | --------- | ------- | --- | ----------- | --- | --- | --- | --- | --- | --- | --- | |
| • The surface finish quality required; |
| suspended work to provide safe access to them |
| • The accuracy required; |
| during construction, as should a safe means of |
| • The number of re-uses required; |
| | withdrawal | as | concreting | | progresses. | | All | | | | | | | |
| | ----------- | --- | ----------- | --- | ------------ | --- | ---- | --- | --- | --- | --- | --- | --- | |
| • The handling methods proposed; |
| statutory requirements must be met. |
| • The methods of compaction proposed; |
| The tightness of all components must be • The methods of curing proposed; and |
| thoroughly checked prior to pouring concrete. |
| • Safety. |
|
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| The weighting given to each factor will vary from textures and patterns on the concrete surface – |
| project to project. On small projects, where typically a scene or portrait. |
| multiple uses of formwork elements are unlikely |
| and a great deal of cutting and fitting may be |
| required, timber sections may well be |
| appropriate. On major projects, where |
| standardised components can be employed |
| and multiple re-use achieved, heavier steel |
| sections may well be warranted. Modular units |
| may also be viable in such circumstances. In |
| the final analysis, the choice of formwork |
| materials is a matter of cost, suitability and |
| availability. Most of the commonly accepted |
| materials can be made to work in most |
| situations. The quality of the finish required, and |
| the overall cost of the formwork, are likely to be |
| the principal determinants in choosing |
| materials. |
| (a) |
| 4.3 FORM LINERS |
| Form liners are effectively a mould placed on |
| the inside of formwork and are used to create |
| simple or complex designs or textures on the |
| surface of concrete (Figure 27.6). The use of |
| form liners has expanded the architectural |
| applications of concrete hugely, and it is really |
| open to the designer to create as complex a |
| pattern as can reasonably be imposed on a |
| concrete surface. When combined with |
| coloured concrete the architectural scope |
| expands even further. A wide variety of |
| materials can be used as form liners, with |
| important considerations being (a) the |
| complexity of the design required, and (b) the |
| extent of re-use of the form liner that is required. (b) |
| For low levels of re-use materials like |
| Figure 27.6 – Variety of Textures and Patterns achieved |
| cardboard, rigid plastics, polystyrene or by Using Form Liners |
| tempered hardboard have been used. These |
| will generally only provide one or two castings. Detailed information on the use of form liners |
| For high levels of re-use, rubbers and synthetic and their range of applicability is given in the |
| polymers are common. Patterns can also be CCAA Briefing 06 ‘Form Liners – Achieving |
| created when form liners are coated (partially) Surface Relief and Texture’ (June 2002). |
| with a retarding agent to create different |
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| Table 27.2 – Formwork Materials |
| Material Uses |
| Timber Commonly used for studs, bearers, joists, walers etc. as it is readily available and |
| easily worked with conventional tools. Has good load-carrying capacity and some |
| suitable species are relatively light-weight, e.g. Oregon. Australian hardwoods tend to |
| be heavier and more susceptible to warping. Some species of pine also tend to |
| splinter or split when nailed. |
| Steel Steel sections are used in formwork framing, particularly in patented systems. Strong |
| and robust, steel-framed formwork is capable of multiple re-uses but requires a |
| degree of standardisation to warrant its additional cost. It is commonly used in |
| precasting yards, particularly for repetitive work. |
| Coated plywood Commonly used for soffits or as form liners in beams, columns and similar elements. |
| Readily worked, coated plywood (properly handled) is capable of multiple re-uses. |
| Cardboard Has been used in column and waffle forms. |
| Normally suitable for one-off use only. |
| Glass reinforced concrete Commonly used as permanent formwork, where it provides a decorative finish, or in |
| (GRC) or plastic moulds to achieve intricate shapes – particularly for precast elements. Generally, it is |
| relatively durable and capable of multiple re-uses. |
| Concrete Precast concrete elements are used as permanent formwork – where the precast |
| element is exposed to view in the completed structure. Also used to provide |
| permanent forms in precast concrete factories where it is very economical for |
| standard elements or components. |
| Rubber, thermoplastic and Used as form liners to provide intricate effects and for decorative finishes. Rubber and |
| polystyrene materials thermoplastic sheeting are used for decorative finishes and are suitable for multiple |
| uses. |
| 5. FORMWORK SYSTEMS Adequate cranage is essential for handling |
| gang forms but the cost of the cranage is offset |
| 5.1 MODULAR FORMWORK by the increased speed of construction offered |
| by moving large units of formwork from one |
| A number of formwork systems comprising location to another. |
| modular units are available on a sale or hire |
| 5.3 TABLE FORMS |
| basis. The systems generally incorporate |
| modular panels so that they can be re-used on |
| Table forms are a type of gang form used to |
| a wide variety of jobs. Panels may use a steel |
| form soffits. Large sections of soffit form, |
| frame with plywood facing which can be |
| complete with propping and bracing elements, |
| replaced when necessary. Generally, such |
| can be fabricated into a single unit which, after |
| systems incorporate simple but effective means |
| use, can be lowered from the soffit, transported |
| of support and fixing. |
| to the edge of the floor, lifted to the next level |
| 5.2 GANG FORMS by the crane and realigned ready for the next |
| concrete placement (Figure 27.7). |
| Gang forms are individual components, often |
| modular, made up into large panels that are |
| then tied and braced so that they can be moved |
| as a complete unit. |
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| | | | | | | | free from | the slipform. | Slip-forming | | can be | |
| | --- | --- | --- | --- | --- | --- | ----------- | --------------- | ------------- | ------ | ------------ | |
| | | | | | | | undertaken | either | vertically | (e.g. | for silos, | |
| towers and lift shafts) or horizontally (e.g. for |
| roads and safety barriers). |
| Figure 27.7 – Typical Use of Table Forms |
|
|
| A 'transporter' is often used to wheel the table |
| forms to the edge of the building, where a |
| special rig enables the crane to handle them |
| efficiently. |
| Table form systems are of particular use in |
| Figure 27.8 – Typical Self-climbing Formwork System |
| multi-storey building construction where speed |
|
|
| is important, adequate cranage is available and |
| the initial cost of formwork can be offset by |
| On vertical elements, the slipform has shutters |
| multiple re-uses. |
| on both faces that are lifted vertically, at a |
|
|
| | | | | | | | predetermined | rate | by a | series | of hydraulic | |
| | --- | --- | --- | --- | --- | --- | -------------- | ----- | ------ | ------- | -------------- | |
| 5.4 JUMP/CLIMB FORMS jacks (Figure 27.9). Typical rates of slip- |
| forming vary from 300-400 mm per hour. Some |
| Jump or climb forms are gang forms for casting |
| projects are slip-formed continuously, whilst on |
| vertical elements such as walls and shafts. others the free-standing height is limited to a |
| | They are | equipped | with | simple | and | rapid | | | | | | |
| | ---------- | --------- | ----- | ------- | ---- | ------ | --- | --- | --- | --- | --- | |
| few storeys. |
| | mechanical | means | of | handling, | require | a | | | | | | |
| | ----------- | ------ | --- | ---------- | -------- | --- | --- | --- | --- | --- | --- | |
| Slip-forming is not recommended where a high |
| | minimum | of labour | and | do | not rely | on the | | | | | | |
| | -------- | ----------- | ---- | --- | ---------- | -------- | --- | --- | --- | --- | --- | |
| availability of cranage (Figure 27.8). degree of colour control on the finished surface |
| is necessary as colour banding is very difficult |
| | The system strips the form, shifts it to the new | | | | | | to avoid. | | | | | |
| | ------------------------------------------------- | ---------- | ---------- | --- | ---------- | --------- | ---------- | --- | --- | --- | --- | |
| | position | and then | re-aligns | | it using | its own | | | | | | |
| On horizontal construction, it can be used in its |
| inbuilt jacking system. Daily casting cycles are |
| | common. | | | | | | most simple | form | to construct | | kerbs and | |
| | -------- | --- | --- | --- | --- | --- | ------------- | ----- | -------------- | --- | ----------- | |
| channels and, in the more sophisticated form, |
| Jump or climb form systems are capable of to construct roads or channel linings. Horizontal |
| producing a high-quality finish with good colour |
| paving rates of up to 2 km per day have been |
| control. |
| achieved on large projects but an average rate |
| of 300-500 m per day is more common. No |
|
|
| edge forming is generally used for this work and |
| 5.5 SLIP-FORMS |
| the concrete must be made to a consistency |
| sufficient to avoid slumping once it is free of the |
| | Slipform | systems | incorporate | | continuously | | | | | | | |
| | --------- | -------- | ------------ | --- | ------------- | --- | --------- | ------------- | --- | ---------- | --------- | |
| | | | | | | | machine. | Slip-forming | is | discussed | in more | |
| moving formwork to speed construction and to |
| detail in Section 19 ‘Slip-formed Concrete’ of |
| eliminate the need for large areas of formwork. |
| this Guide. |
| | The concrete | being | | 'extruded' | must | have | | | | | | |
| | ------------------------------------------------ | ------ | --- | ----------- | ----- | ----- | --- | --- | --- | --- | --- | |
| | adequate stiffness to hold its shape once it is | | | | | | | | | | | |
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| Precast concrete and glass reinforced concrete |
| | (GRC) | are commonly | | used for permanent | | |
| | ------ | -------------- | --- | --------------------- | --- | |
| formwork – the former being used where the |
| form takes part of the structural loads and the |
| | latter | where decorative | | finishes | only are | |
| | ---------- | ------------------ | -------- | ---------- | ---------- | |
| | required. | The | use of | permanent | forms | |
| minimises subsequent finishing operations and |
| | often reduces | the scaffolding | | and | falsework | |
| | --------------- | ---------------- | --- | ---- | ---------- | |
| required for these operations. |
|
|
| 6. DESIGN OF FORMWORK |
| 6.1 GENERAL |
| The design of formwork, particularly on large |
| projects, calls for a considerable degree of skill |
| and experience. Not only can the loads on it be |
| | both | large and | complex, | but | stripping | |
| | ----- | ----------- | --------- | ---- | ---------- | |
| procedures, and the way they cause loads to be |
| transferred to the concrete structure, are of |
| considerable complexity and importance. |
| | Whilst | the actual | design | should always | be | |
| | ------- | ------------ | ------- | --------------- | --- | |
| Figure 27.9 – Slip-forming a Vertical Element |
| undertaken by a specialist formwork designer, |
|
|
| all involved with either the erection or removal |
| 5.6 PERMANENT FORMWORK of formwork on the construction site should be |
| | aware | of the | factors | which affect | its | |
| | ------ | -------- | -------- | -------------- | ---- | |
| Permanent formwork is a type of formwork performance, and in particular its strength and |
| which is left in place to become part of the stability – and hence its safety. AS 3610.1 sets |
| | out requirements | | for | the design | and | |
| | ------------------ | --- | ---- | ------------ | ---- | |
| finished structure (Figure 27.10). It may assist |
| in taking some of the structural load or simply construction of formwork which are aimed at |
| provide a permanent decorative finish. ensuring its effectiveness and safety. |
|
|
| 6.2 LOADS ON FORMWORK |
| Formwork should be designed to support both |
| | the vertical | and | horizontal | loads which | are | |
| | -------------- | ---- | ----------- | ------------- | ---- | |
| imposed on it whilst it is being erected and while |
| it is in position. In supporting these loads, the |
| | formwork | should | not | deflect excessively, | | |
| | --------- | ------- | ---- | ---------------------- | --- | |
| buckle, bulge or otherwise move out of position. |
| The most severe loading generally occurs when |
| the concrete is being placed. However, this is |
| | not always | the | case, so | it is common | to | |
| | ------------ | ---- | ---------- | --------------- | --- | |
| consider the loads on formwork at three stages |
| of construction: |
| During Erection – Loads on formwork during |
| erection can arise from two principal sources, |
| Figure 27.10 – Precast Permanent Formwork used |
| for an Edge beam of a Multi-storey Building (a) the weight of material, equipment etc. which |
| may be stacked on it prior to concreting; and (b) |
|
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| the effect of wind which may exert both vertical on the formwork, and particularly on the props |
| and horizontal forces on the formwork and its supporting lower floors (see 7.3). |
| supports. Care should therefore be taken to |
| Of prime importance, however, is the lateral |
| | avoid excessive | load | concentrations | and | to | | | | | | |
| | ----------------- | ----- | --------------- | ---- | --- | --- | --- | --- | --- | --- | |
| pressure exerted on side forms during and after |
| | ensure that | bracing | is installed | as early | as | | | | | | |
| | ------------- | -------- | -------------- | ---------- | --- | --------- | ------------ | ---------- | ---------- | ---- | |
| | | | | | | concrete | compaction. | Vibration | liquefies | the | |
| possible, and certainly before the formwork is |
| concrete and increases the pressure exerted on |
| used as a working platform (Figure 27.11). |
| | | | | | | the forms | (Figure | 27.13). | Due | allowance | |
| | --- | --- | --- | --- | --- | ----------- | -------- | -------- | ---- | ---------- | |
| should be made for this, particularly with deep |
| pours, such as columns. |
| Figure 27.11 – Loads on Formwork prior to |
| Construction |
|
|
| During Concreting – During concreting, the |
| concrete itself imposes a considerable dead |
| weight on the forms. In addition, the weight of |
| men and equipment on the platform should be |
| Figure 27.13 - Lateral Pressures on Formwork |
| taken into account. At this stage, lateral stability |
| during Compaction |
| should also be considered. The formwork with |
|
|
| its load of plastic concrete is inevitably top- |
| heavy and therefore particularly susceptible to |
| The lateral pressure exerted by fluid concrete |
| sideways movement. The possibility of impact during compaction is by far the most severe |
| | arising from | a wayward | concrete | bucket | or | | | | | | |
| | ---------------- | ----------- | --------- | ----------- | --- | --------- | ------------ | ----- | ---------------- | ------- | |
| | | | | | | loading | experienced | by | vertical | forms. | |
| | similar mishap | should | also be | considered | | | | | | | |
| | | | | | | Problems | such as | form | liners bulging | and | |
| (Figure 27.12). deflecting between supports frequently arise |
| because the magnitude of the lateral pressure |
| is underestimated. This is particularly the case |
| | | | | | | with deep | narrow | forms, | where it | is often | |
| | --- | --- | --- | --- | --- | ----------- | ------- | ------- | ---------- | ---------- | |
| assumed the loads will be less than in (say) |
| heavy columns. In fact, the width of formwork |
| has little influence on lateral pressure, with the |
| principal consideration being the height of the |
| | | | | | | fluid concrete. | Factors | | influencing | lateral | |
| | --- | --- | --- | --- | --- | ----------------- | -------- | --- | ------------ | -------- | |
| pressure are set out in Table 27.3. |
| In general terms, any factor which increases the |
| fluidity of the concrete, or the height of fluid |
| Figure 27.12 – Loads on Formwork during concrete, increases the lateral pressure on the |
| | Construction | | | | | formwork (see also comments about flowing | | | | | |
| | ------------- | --- | --- | --- | --- | ---------------------------------------------- | -------- | ------- | -------- | -------- | |
| | | | | | | concrete in sub-section 3.2). Conversely, any | | | | | |
| | | | | | | factor which | reduces | these, | reduces | lateral | |
| After Concreting – On multi-storey projects, it |
| pressure (Figure 27.13 and Table 27.3). |
| is usual for work to proceed on upper floors |
| | while the concrete structure below is still gaining | | | | | | | | | | |
| | ---------------------------------------------------- | -------------- | ------- | ---------- | --- | --- | --- | --- | --- | --- | |
| | strength. | Consideration | should | therefore | be | | | | | | |
| | given to these additional loads being imposed | | | | | | | | | | |
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| Table 27.3 – Formwork Materials during the placing activities. Problems during |
| reshoring operations and premature falsework |
| Effect on |
| or formwork removal have also been significant |
| | Factor | | | lateral | | | | | | | | | |
| | -------------------- | --- | --- | ---------- | --- | --- | ------------------------------- | -------- | --- | ------- | --- | ----------- | |
| | | | | pressure | | | causes of structural failures. | | | | | | |
| | Increasing concrete | | | Increases | | | | | | | | | |
| | | | | | | | All support | systems | | should | be | adequately | |
| density |
| | | | | | | | braced | to | ensure | stability | and | prevent | |
| | --- | --- | --- | --- | --- | --- | ------- | --- | ------- | ---------- | ---- | -------- | |
| Increased rates of Increases progressive collapse. Bracing should be |
| | placing | | | | | | provided in two directions at right angles to | | | | | | |
| | -------- | --- | --- | --- | --- | --- | ---------------------------------------------- | --- | --- | --- | --- | --- | |
| each other and be provided near the edges of |
| | Increased heights of pour | | | Increases | | | | | | | | | |
| | -------------------------- | --- | --- | ---------- | --- | --- | --- | --- | --- | --- | --- | --- | |
| the system where concrete placement is likely |
| Internal vibration Increases to commence. All bracing should be between |
| 30° and 60° to the horizontal. |
| | Increased slump | | | Increases | | | | | | | | | |
| | ---------------- | --- | --- | ---------- | --- | --- | --- | --- | --- | --- | --- | --- | |
| Design of falsework systems should also take |
| Increased fluidity, e.g. Increases account of the final support conditions (e.g. the |
| flowing concrete |
| | | | | | | | ground) | and | detail | the | size | of base | |
| | ------------------- | --- | --- | ---------- | --- | --- | ---------------- | ---- | ------- | ------- | ----- | ---------- | |
| | | | | | | | plates/spreader | | beams | needed | to | take the | |
| | Increased concrete | | | Decreases | | | | | | | | | |
| loads without sustaining excessive deflections. |
| temperatures |
| | | | | | | | In multi-storey | | construction, | | the | propping | |
| | ----------------------- | --- | --- | ---------- | --- | --- | ----------------- | ------- | -------------- | -------------- | ---- | ----------- | |
| | Faster setting cements | | | Decreases | | | | | | | | | |
| | | | | | | | should | extend | down | a sufficient | | number of | |
| (including use of |
| floors to ensure the loads are supported without |
| accelerators) |
| | | | | | | | excessive | stress | on, | or | deflection | of, the | |
| | --- | --- | --- | --- | --- | --- | ---------- | ------- | ---- | --- | ----------- | --------- | |
|
|
| recently cast structure. This design should take |
| 7. FALSEWORK account of the rate of concrete strength gain |
| with age and the effect that local environmental |
| conditions may have on it (e.g. concrete gains |
| 7.1 DESIGN OF SUPPORT |
| strength more slowly in cold weather). |
| STRUCTURES |
| The design of support structures should also |
| | All propping, | bracing | and | fixing | elements | | | | | | | | |
| | --------------- | -------- | ---- | ------- | --------- | --- | --- | --- | --- | --- | --- | --- | |
| consider the method to be used for stripping the |
| (collectively the ‘falsework’) that support the formwork. It is normal practice to strip soffit |
| formwork and transmit load to the supporting formwork in two stages – (1) the sheet/form- |
| foundation (usually the ground) – should be face elements which are to be re-used quickly, |
| considered as part of the total formwork and (2) the support structure which is to remain |
| system. |
| in place until the concrete can carry the loads. |
| | NOTE: The term ‘shoring’ used below refers to the | | | | | | | | | | | | |
| | -------------------------------------------------- | ---------------- | ----------- | --- | ------------ | --- | --- | --- | --- | --- | --- | --- | |
| | process | of temporarily | supporting | | a building | or | | | | | | | |
| 7.2 UNDISTURBED SHORES |
| | structure | with ‘shores’ | or | props | to prevent | the | | | | | | | |
| | ---------- | ----------------- | ------- | ------ | ------------- | ---- | --- | --- | --- | --- | --- | --- | |
| | structure | from collapsing | during | | construction | or | | | | | | | |
| Proprietary systems are available that enable |
| renovation. |
| the support structure to remain in place while |
| | Falsework | must also | be | able | to resist | any | | | | | | | |
| | ---------- | ----------- | --- | ----- | ----------- | ---- | --- | --- | --- | --- | --- | --- | |
| the form-face materials are removed for re-use. |
| tendency to overturn, i.e. the formwork system |
| must be kept stable during erection and In these systems the props (or shores) extend |
| concrete placement. Assessments of falsework from the base to the soffit of the concrete slab |
| and the deck system is removed around them. |
| | failures | during construction | | show | that | the | | | | | | | |
| | --------- | --------------------- | --- | ----- | ----- | ---- | --- | --- | --- | --- | --- | --- | |
| majority of failures occur during concrete This is a preferred system, as the props remain |
| untouched until removal at an appropriate later |
| placement. These failures can be a result of |
| date. Thus, the risk of deflection and stress |
| | designers | not properly | estimating | | the | loads | | | | | | | |
| | ---------- | -------------- | ----------- | --- | ---- | ------ | --- | --- | --- | --- | --- | --- | |
| (both live and dead loads) that the falsework changes in the concrete slab during reshoring |
| is eliminated. It also ensures that the props for |
| structure must support – including additional |
| successive storeys remain in vertical alignment |
| loads and vibration effects that are experienced |
| | | | | | | | and there | is | no | chance | of props | being | |
| | --- | --- | --- | --- | --- | --- | ----------- | --- | --- | ------- | ---------- | ------ | |
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| overtightened, causing reverse stresses in the • Limitations on the stacking of materials |
| concrete slab. on either partially completed formwork, |
| completed formwork, or on freshly placed |
| 7.3 RESHORING SYSTEMS |
| concrete. These loads can be substantial |
| and, unless controlled, can lead to |
| Reshoring systems involve the removal of a |
| overloading of partially completed |
| section of the formwork and support structure, |
| structures; |
| following which the support structure is then |
| • Limitations on the bracing of formwork |
| replaced once the formwork is clear. With |
| against concrete elements of the |
| proper control and good supervision these |
| permanent structure. Depending on the |
| systems can give acceptable results. Props |
| age of such elements they may not be |
| must be replaced in the original pattern and not |
| able to support such loading without |
| overtightened to avoid causing undesirable |
| damage; |
| stresses in the concrete. |
| • Protection of surface finishes on existing |
| The three usual methods of reshoring are: work; |
| • Safety – The maintenance of a safe |
| • Secondary reshoring – in which shores |
| working environment is the responsibility |
| are placed before any formwork or props |
| of all involved with the project. Attention |
| are moved. They are placed under the |
| may therefore need to be given to such |
| soffit form as close as possible to the |
| matters as (a) the provision of access |
| original props. The original props and |
| ladders, guardrails and working |
| forms are then removed, taking care to |
| platforms; (b) safe-load areas and |
| mark the location of the original elements |
| overhead protection for those working |
| – as the final step is to replace the original |
| below; and (c) suitable lighting and |
| props and remove the secondary props; |
| similar facilities. |
| • Partial reshoring – in which the soffit is |
| stripped, bay by bay, and props are |
| replaced on the correct grid and 8.2 PREPARATION FOR CONCRETING |
| retightened. Typical bays are 2-3 m in |
| width; Cleanliness – Once the formwork is erected |
| • Total reshoring – which involves complete and set in the correct position, all enclosed |
| stripping of the soffit and subsequent areas and surfaces should be cleaned of all |
| replacement of the props. This is the least foreign debris that may affect the finished |
| desirable method as it can impose severe surface, including timber, reinforcing steel, tie |
| stresses on the relatively immature wires, sawdust, sand, mortar etc. This may |
| concrete and give rise to excessive necessitate a 'window' at the base of the form |
| deflections. through which such material can be discarded. |
| Where form faces will be inaccessible after |
| 8. CONSTRUCTION OF erection (e.g. wall forms) release agents should |
| be applied to them before they are erected. |
| FORMWORK |
| Immediately formwork has been stripped, it |
| 8.1 ERECTION |
| should be cleaned without damaging the form |
| face. If necessary, any repairs should then be |
| On many projects the formwork is supplied and |
| made to restore the surface. Formwork should |
| erected by a specialist subcontractor. While this |
| be stored to avoid damage and should be |
| has many advantages, it can also cause some |
| stored/stacked to enable easy retrieval. |
| problems if there is not good communication |
| between the project designer, the main Release Agents – Most surfaces require the |
| contractor and the formwork contractor. application of a release agent to allow the |
| formwork to part easily from the concrete after it |
| Specific matters to which attention should be |
| has hardened – without damage to either |
| given include: |
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| surface. However, there are a few specialist • The forms are clean; |
| plastic form-liners that may not need a release |
| • Repairs have been completed; |
| | agent. | | | | | | | | • The correct release agent has been used | | | |
| | ------- | --- | --- | --- | --- | --- | --- | --- | ------------------------------------------- | --- | --- | |
| and properly applied to vertical forms; |
| Release agents permit easy separation of the |
| and |
| | formwork | | from | the concrete | | and | help to | | | | | |
| | --------- | --- | ----- | -------------- | --- | ---- | --------- | --- | --- | --- | --- | |
| • Joints have been sealed. |
| preserve the formwork. In selecting a release |
| agent for a given project, care should be taken |
| Before concreting commences it is important to |
| to check that it will not: |
| check that: |
| • Cause unacceptable discolouration to the |
| • The line, level and plumb are correct; |
| concrete surface; and/or |
| • Dimensions are correct; |
| | | • Leave | any | material | | on the concrete | | | | | | |
| | --- | --------- | ---- | --------- | --- | ------------------ | --- | --- | --- | --- | --- | |
| • All ties are at correct centres and tight; |
| | | surface | | which will | prevent | bonding | of | | | | | |
| | --- | -------- | --- | ------------ | -------- | -------- | --- | --- | --- | --- | --- | |
| • Props and supports are in the correct |
| subsequent coatings (e.g. Render, paint). |
| locations; |
| • All bracing systems are in place; |
| In the case of wall and column forms, release |
| agents should be applied to clean formwork • All wedges are nailed; |
| • All clamps are tight; |
| before it is erected. In the case of soffit forms, |
| • All bolts, jacks etc are tight; |
| | release | | agents | are | applied | before | the | | | | | |
| | -------- | --- | ------- | ---- | -------- | ------- | ---- | --- | --- | --- | --- | |
| reinforcing steel is placed (Figure 27.14). The • The supports are founded on a solid |
| | release | | agent(s) | can | be applied | by | spray, | | base; | | | |
| | -------- | --- | --------- | ---- | ------------ | --- | ------- | --- | ------ | --- | --- | |
| brush, roller, squeegee etc., depending on its • All foreign material has been removed |
| | characteristics, but on no account should it be | | | | | | | | from forms; | | | |
| | ------------------------------------------------ | --- | --- | --- | --- | --- | --- | --- | ------------ | --- | --- | |
| allowed to coat reinforcing steel or any • Release agent has been correctly applied |
| | construction joint. | | | | | | | | to soffits; and | | | |
| | -------------------- | --- | --- | --- | --- | --- | --- | --- | ---------------------------------------- | --- | --- | |
| | | | | | | | | | • Joints are sealed and cramped/wedged | | | |
| tight. |
| During concreting checking is required for: |
| • Line, level, and plumb maintenance; |
| • Any settlement; |
| • Any leakage; and |
| • Any loosening of wedges, bolts, nails. |
|
|
| 8.3 EXTERNAL VIBRATION |
| In some circumstances, external vibration may |
| Figure 27.14 – Release Agent being applied to Soffit |
| Form before Reinforcement is placed |
| be applied to formwork – e.g. in some precast |
|
|
| operations, or when placing concrete in thin |
| sections. In these situations, both the formwork |
| Inspection – Formwork must be set accurately |
| and the concrete are vibrated. Where external |
| | in | plan | and be | capable | of | maintaining | the | | | | | |
| | --- | ----- | -------- | -------- | --- | ------------ | ---- | --- | --- | --- | --- | |
| vibration is used, it is important that (a) the |
| correct line, level, plumb, shape and tolerance |
| concrete is placed in controlled lifts so that |
| | during | | concreting | and | until | the hardened | | | | | | |
| | ------- | --- | ----------- | ---- | ------ | -------------- | --- | --- | --- | --- | --- | |
| when vibrated, the air can be expelled from the |
| | concrete | | can | take the | required | loads. | This | | | | | |
| | --------- | --- | ---- | ---------- | --------- | ------- | ----- | --- | --- | --- | --- | |
| concrete, and (b) the formwork be very rigid and |
| | requires | | a detailed | inspection | | procedure | to | | | | | |
| | --------- | --- | ------------ | ----------- | --- | ---------- | --- | ----- | --------------------- | --------------- | --- | |
| | | | | | | | | leak | free. The formwork | designer must | be | |
| ensure that all elements of the formwork are |
| aware of the need to use external vibration |
| | adequate, | | clean, | in the | correct | place | and | | | | | |
| | ---------- | --- | ------- | -------- | -------- | ------ | ---- | --- | --- | --- | --- | |
| when doing the design. External vibration can |
| wedged/bolted tight. |
| be used to obtain high quality off-form finishes |
| Before the formwork is assembled it is and also when low slump concrete is being |
| | necessary to check that: | | | | | | | placed. | | | | |
| | ------------------------- | --- | --- | --- | --- | --- | --- | -------- | --- | --- | --- | |
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| Vibrating tables constitute a form of ‘external desired to leave vertical formwork in place, |
| vibration’. In these situations, the formwork is either to assist in curing the concrete, or |
| attached to the vibrator (and not the vibrator to because it suits the construction sequence to |
| the formwork as above). The use of vibrating do so, it is desirable to ease the forms from the |
| tables is common in the manufacture of concrete surface as soon as possible to |
| concrete products (e.g. concrete blocks) and in minimise colour variations. |
| | precast | operations | and | is used | to obtain | a | | | | | | | |
| | -------- | ----------- | ---- | --------- | ----------- | --- | ------------- | --- | ------------- | --- | --- | ----------- | |
| | | | | | | | Multi-storey | | Construction | | – | While the | |
| consistent level of compaction. |
| | | | | | | | Standards | provide | some | guidance | | on the | |
| | --- | --- | --- | --- | --- | --- | ---------- | ---------- | ----- | --------- | --------- | -------- | |
| | | | | | | | minimum | stripping | | times | required | for | |
| multistorey construction, they also point out that |
| 8.4 STRIPPING FORMWORK |
| | | | | | | | the construction | | and | stripping | of | formwork | |
| | --- | --- | --- | --- | --- | --- | ------------------ | --- | ---- | ---------- | --- | --------- | |
| systems which involve reshoring should be in |
| General – The project designer is normally |
| required to provide a schedule of stripping accordance with the project and formwork |
| times for formwork which is in accord with the documentation. Consequently, it is incumbent |
| | | | | | | | on the | project | designer | | to provide | this | |
| | --- | --- | --- | --- | --- | --- | -------- | -------- | --------- | --- | ------------ | ----- | |
| requirements of AS 3600. Reference is also |
| made in AS 3600 to the requirements for information. Reshoring is a hazardous |
| stripping detailed in AS 3610, and it notes that operation which, unless carried out in a correct |
| | | | | | | | and systematic | | manner, | | can | lead to | |
| | --- | --- | --- | --- | --- | --- | ---------------- | --- | -------- | --- | ---- | --------- | |
| where stripping requirements in AS 3600 are |
| more stringent than in AS 3610, then the unacceptable loads being placed on the |
| AS 3600 requirements will prevail. The concrete at an early age. |
| nominated times are minimum stripping times |
| This is particularly so for prestressed concrete |
| designed to ensure that the structure remains |
| as the stressing operations can cause quite |
| secure from collapse (under its own weight plus |
| | | | | | | | substantial | loads | to | be transferred | | to the | |
| | --- | --- | --- | --- | --- | --- | ------------ | ------ | --- | ---------------- | --- | -------- | |
| that from any additional super-imposed loads) |
| | | | | | | | shores, | re-shores, | back-props | | | and other | |
| | --- | --- | --- | --- | --- | --- | -------- | ----------- | ----------- | --- | --- | ----------- | |
| and from damage which might affect its later |
| temporary supports. |
| performance (e.g. cracking or deformation in |
| excess of that anticipated by the designer). The advice of the project designer should |
| Stripping must be carried out in a planned and therefore always be sought for both reinforced |
| controlled manner to ensure the proper and and prestressed concrete construction before |
| | controlled | transfer | of | loads | from | the | | | | | | | |
| | ----------- | --------- | --- | ------ | ----- | ---- | --- | --- | --- | --- | --- | --- | |
| specified procedures are changed in any way. If |
| formwork/falsework to the permanent or specific procedures are not provided in the |
| existing structure. project documentation, they should be sought. |
| AS 3610.1 also provides guidance on stripping |
| 9. FORMWORK DOCUMENTATION |
| times, which, while compatible with AS 3600, |
| refines the requirements to take account of the |
| AS 3610.1 contains a number of requirements |
| specified class of surface finish (Table 27.4). |
| | | | | | | | in relation | to | documentation | | including | (a) | |
| | --- | --- | --- | --- | --- | --- | ------------- | --- | -------------- | --- | ---------- | ---- | |
| The stripping times for formwork removal noted documentation requirements will vary |
| depending on the complexity of the project, (b) |
| in AS 3600 and shown in Table 27.4 shall be |
| it is expected that all aspects of the formwork |
| | increased where L | | s /D > 280/(D +100) (where | | | | | | | | | | |
| | ----------------- | --- | ---------------------------- | --- | --- | --- | --- | --- | --- | --- | --- | --- | |
| L is the span between formwork supports and design, fabrication, stripping etc. will be |
| s |
| included in the documentation which is to be |
| D is the overall depth of the member); and the |
| prepared by ‘competent persons’ (as defined in |
| superimposed construction load is >2.0 kPa. |
| section 1.5.1.5 of AS 3610.1), and (c) where |
| Subject to these general provisions, stripping of elements of the design are done by different |
| formwork should be done at the earliest time – |
| | | | | | | | persons, | or where | proprietary | | information | is | |
| | --------- | ---------- | --------- | --- | --------------- | --- | --------- | ---------- | ------------ | --- | ------------ | --- | |
| | provided | that the | concrete | | has developed | | | | | | | | |
| included, all elements need to be collected and |
| sufficient strength to prevent damage to the collated into a single comprehensive document |
| surface of the element. For vertical surfaces, if |
| that fully describes formwork requirements. |
| formwork is stripped less than 18 hours after |
|
|
| casting then special care needs to be taken to |
| | ensure the surface is not damaged. Where it is | | | | | | | | | | | | |
| | ----------------------------------------------- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | |
|
|
| | | | | | | | | | | | | Version 1.0 | |
| | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ------------- | |
| PAGE 15 > Guide to Concrete Construction — Part IX-Section 27 – Formwork |
|
|
| Table 27.4 – Minimum Formwork Stripping Times – In-situ Concrete (from AS 3600 and AS 3610.1) |
| Surface finish Hot conditions Average conditions Cold conditions |
| Formed surface |
| | | classification | > 20°C | 20°C ≥ x > 12°C | 12°C ≥ x > 5°C | |
| | --------------- | ----------------- | -------- | ---------------- | --------------- | |
| | Vertical faces | Classes 1, 2, 3* | 1 day | 2 days | 3 days | |
| | | | | | | |
| | | Classes 4, 5 | 9 hours | 12 hours | 18 hours | |
| A minimum of one day applies to the stripping of vertical faces where frost damage is likely. |
| Beam and slab Formwork removal of beams and slab soffits must be in accordance with AS 3600 section |
| soffits elements – 17.6.2.3 and 17.6.2.4 (and not less than 3 days) as well as conforming to AS 3610.1 |
| | reinforced slabs of | Appendix C3. | | | | |
| | -------------------- | ------------- | --- | --- | --- | |
| | Normal Class | | | | | |
| | concrete | | | | | |
|
|
| NOTE: *Where colour control on surface finishes has been specified it is advisable to strip forms early, subject to the limitations |
| given. |
| |
| Version 1.0 |
| PAGE 16 > Guide to Concrete Construction — Part IX-Section 27 – Formwork |
| |
| 10. SUMMARY – CONSTRUCTION CHECKLIST |
| | • Loads | | | • | Watertightness | | | | |
| | --------- | --- | --- | --- | --------------- | --- | --- | --- | |
| − What are the stacked load limits at all stages? − Are all joints properly sealed and cramped? |
| − Are the stacked materials on spreaders? − Are the construction joints sealed? |
| | | − Will the loads be exceeded by any construction | | | | | | | |
| | --- | -------------------------------------------------- | --- | --- | --- | --- | --- | --- | |
| procedure? |
| • Reinforcing Steel/Inserts |
| |
| − Is the reinforcement correct? |
| • Materials − Are all inserts/blockouts in the correct location? |
| | | − Are the correct form materials being used? | | | | | | | |
| | --- | ---------------------------------------------- | ------------ | ----------------- | --- | --- | --- | --- | |
| | | − Is the form face | appropriate | for the finish | | | | | |
| • Concrete/Concreting |
| required? |
| | | | | | − Is | the mix design | in accordance | with the | |
| | --- | --- | --- | --- | ------ | ----------------- | --------------- | ---------- | |
| specification? |
| | • Position | | | | − What | is the maximum | | rate of placement | |
| | ------------ | ------------------------------------------ | --- | --- | ----------- | ----------------- | --- | -------------------- | |
| | | − Are the forms in the correct location? | | | permitted? | | | | |
| − Are they to dimension and within tolerance? − Are the forms maintaining line, level, plumb, |
| − Are they accurate to line, level and plumb? shape etc. during concreting? |
| | | | | | | | | | |
| | ---------- | --- | --- | --- | ---------- | --- | --- | --- | |
| | • Fixing | | | • | Stripping | | | | |
| − Is the nailing/screwing adequate? − What are the minimum stripping times? |
| − Are the ties the correct type? − Has the project designer permitted modification |
| | | − Are they on the correct grid? | | | of these? | | | | |
| | --- | --------------------------------- | --- | --- | ---------- | --- | --- | --- | |
| − Are all ties, clamps and bolts tight? − Do the procedures enable stripping without |
| damage to form or concrete? |
| | | − Are wedges tight and nailed? | | | | | | | |
| | --- | -------------------------------- | --- | --- | ------- | ---------------- | ----------- | ----------------- | |
| | | | | | − Are | the provisions | consistent | with the re-use | |
| times required? |
| • Bracing/Props |
| − Has the crane the necessary slings etc. to move |
| | | − Are the props plumb? | | | the forms quickly? | | | | |
| | --- | ------------------------ | --- | --- | ------------------- | --- | --- | --- | |
| − Are all loads centrally placed? − What curing methods are to be used once the |
| − Are supported elements wedged and nailed? formwork is removed? |
| − Are props straight? − Is the storage area for the formwork properly |
| | | − Are base plates on adequate foundations? | | | organised? | | | | |
| | --------------- | -------------------------------------------- | --- | --- | ---------------------------------- | ---------------- | ------------ | ----------- | |
| | | − Is the bracing correct? | | | | | | | |
| | | − Is the bracing firmly connected? | | | | | | | |
| | | | | • | Safety | | | | |
| | | | | | − Are | there adequate | guardrails, | handrails, | |
| | • Cleanliness | | | | walkways, signs etc. in position? | | | | |
| | | − Are the form faces cleaned? | | | | | | | |
| | | − Is any damage correctly repaired? | | | | | | | |
| • Inspection |
| | | − Is the correct release agent in use? | | | | | | | |
| | --- | ---------------------------------------- | --- | --- | --- | --- | --- | --- | |
| − Are there enough experienced inspectors on the |
| | | − Is it being correctly applied? | | | | | | | |
| | --- | ---------------------------------- | --- | --- | --- | --- | --- | --- | |
| job to provide appropriate supervision? |
| | | − Has all debris been removed from within the | | | | | | | |
| | --- | ----------------------------------------------- | --- | --- | --- | --- | --- | --- | |
| |
| form? |
| |
| | | | | | | | | | |
| | --- | --- | --- | --- | --- | --- | --- | --- | |
| |
| PAGE 17 > Guide to Concrete Construction — Part IX-Section 27 – Formwork Version 1.0 |
| |
| 11. RELEVANT AUSTRALIAN STANDARDS CCAA OFFICES |
| 1) AS 3600 – Concrete structures |
| 2) AS 3610.1 – Formwork for concrete, Part 1: NATIONAL OFFICE (NSW) |
| Specifications Level 10 |
| 163 -175 O’Riordan Street |
| Mascot NSW 2020 |
| POSTAL ADDRESS |
| PO Box 124 |
| Mascot NSW 1460 |
| Telephone: (02) 9667 8300 |
| QUEENSLAND |
| Level 14, 300 Ann Street, |
| Brisbane QLD 4000 |
| Telephone: (07) 3227 5200 |
| VICTORIA |
| Suite 910/1 Queens Road |
| Melbourne VIC 3004 |
| Telephone: (03) 9825 0200 |
| WESTERN AUSTRALIA |
| 45 Ventnor Avenue |
| West Perth WA 6005 |
| Telephone: (08) 9389 4452 |
| SOUTH AUSTRALIA |
| Level 30, Westpac House |
| 91 King William Street |
| Adelaide SA 5000 |
| Telephone: (02) 9667 8300 |
| TASMANIA |
| PO Box 1441 |
| Lindisfarne TAS 7015 |
| Telephone: (03) 6491 2529 |
| ONLINE DETAILS |
| www.ccaa.com.au |
| Email: info@ccaa.com.au |
| Since the information provided is intended for general |
| guidance only and in no way replaces the services of |
| professional consultants on particular projects, no legal |
| liability can be accepted by Cement Concrete & Aggregates |
| Australia for its use. |
| © Cement Concrete & Aggregates Australia |
| PAGE 18 > Guide to Concrete Construction — Part IX-Section 27 – Formwork Version 1.0 |
