q107/random_k2/random_1.md

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
4. RELEVANT AUSTRALIAN 3.6 PERMEABILITY.............................. 5 STANDARDS ..................................... 18 3.7 ROBUSTNESS ............................... 5 3.8 EASE OF STRIPPING .................... 6
5. INTRODUCTION 3.9 STANDARDISATION ...................... 6 3.10 SAFETY ......................................... 6 Formwork is the temporary structure which (a)
6. 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.
7. 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,
8. 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
9. 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

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

PAGE 3 > Guide to Concrete Construction — Part IX-Section 27 – Formwork Version 1.0

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.

PAGE 4 > Guide to Concrete Construction — Part IX-Section 27 – Formwork Version 1.0

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

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 PAGE 7 > Guide to Concrete Construction — Part IX-Section 27 – Formwork Version 1.0

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. PAGE 8 > Guide to Concrete Construction — Part IX-Section 27 – Formwork Version 1.0

						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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PAGE 9 > Guide to Concrete Construction — Part IX-Section 27 – Formwork

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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PAGE 10 > Guide to Concrete Construction — Part IX-Section 27 – Formwork

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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PAGE 11 > Guide to Concrete Construction — Part IX-Section 27 – Formwork

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: PAGE 13 > Guide to Concrete Construction — Part IX-Section 27 – Formwork Version 1.0

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

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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.

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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?

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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