CHAPTER 6 - FALSEWORK, FORMWORK AND CONCRETE FINISH · PDF fileFalsework, Formwork and...

Falsework, Formwork and Concrete Finish 6-1

CHAPTER 6 - FALSEWORK, FORMWORK AND CONCRETE FINISH

DS Temple

6.1 SCOPE

This section covers the inspection and monitoring of Falsework, Formwork and Concrete Finish as per

the applicable chapter of the Specifications. It also includes special attention which must be given to

materials used, design and erection of falsework and formwork to be checked by the engineer’s

monitoring staff.

6.2 MATERIALS

The engineer’s monitoring staff should confirm the suitability of proposed materials:

6.2.1 Falsework

• Steel Grade to be provided in accordance to Design Requirements.

• Timber Grade to be provided in accordance to Design Requirements.

Condition of all materials to be used should be checked by the engineer’s monitoring staff to ensure that the materials are fit for purpose.

6.2.2 Formwork

The most commonly used materials for the manufacture of formwork are steel and timber. The

monitoring staff should ensure that the surfaces of forms are clean and free of defects to ensure that

the required surface finishes can be obtained. In order to obtain a good quality finish in accordance

with the specifications, high quality materials must be used and attention to details and workmanship

cannot be over-emphasized.

6.3 DESIGN

The monitoring staff should ensure that the contractor submits (within the period specified in the

Project Specification) designs, drawings and calculations where required, for all falsework and

formwork for review by the engineer. The design of all temporary works should be undertaken by the contractor, and the engineer through his representatives on site should only scrutinize the plans and

pass comment on issues that may be non-compliant in terms of the specifications. No approval should

be given for any temporary works as this could attract liability to both the employer and the engineer.

Copies of all falsework and formwork designs should be placed on the safety file on site prior to the

work being carried out.

The following matters should receive attention:


6.3.1 Falsework

6.3.1.1 Foundations

• Allowable bearing capacity of founding material for falsework supports to be confirmed by the

contractor (Dynamic Cone Penetrometer or other suitable means).

• Allowance should be made for the wetting of the foundation material when determining the

allowable bearing capacity of the founding material.

• Actual design bearing pressure for falsework supports to be provided by the contractor.

• Ensure all falsework for the erection of decks and slabs is provided with jacks for adjustment

for line and level.

• For river bridges the stability of foundations under minor flood events should be considered.

• Falsework should always rest on sound founding material which is properly compacted and

leveled to ensure no standing water will occur during rain.

• The adequacy of safety of the falsework should be signed off by the CCP.

6.3.1.2 Load Capacity

The load capacity and technical specifications of all elements making up the falsework including

jacks, clamps and fittings should be provided with temporary works design. Ensure jack extension limits specified by the manufacturer of the particular type of jack in use are not exceeded.

6.3.1.3 Settlements

The contractor should provide with his calculations the expected settlements of the falsework due to

elastic deformation of the founding material and falsework.

6.3.1.4 Deflections

Levels for the construction of falsework for the construction of slabs and decks should allow for

precambering for expected long term/creep deflections due to dead loads, prestressing and

superimposed dead loads. This provision should be in accordance with the design drawings and is especially important for very skew reinforced concrete decks. The monitoring staff should liaise with

the design office to confirm requirements, and in instances where no precamber is specified, should

ensure that this is confirmed by the designer.

• Reinforced Concrete

The total deflection can normally be assumed to be 3 times the elastic deflection under Dead

and Superimposed Dead Loads.

• Prestressed Concrete

The monitoring staff should note that the precambering for prestressed concrete decks could be negative (in downward direction). The long-term deflection in prestressed concrete decks will

generally continue in the direction of the initial deflection.

6.3.1.5 Overall Stability and Bracing

The monitoring staff should ensure that the contractor’s design deals adequately with the overall

stability and bracing of the proposed falsework taking into account wind loading and other horizontal

actions as required.


Photo 6.1: Well designed falsework and bracing

6.3.1.6 Temporary Works Vertical and Horizontal Clearance

The minimum vertical and horizontal clearances as prescribed by the roads authority and employer should be adhered to by the contractor in his preparation of the temporary works design to be carried

out by the contractor. Generally the clearances as specified in the SANRAL Code of Procedure for the

Planning and Design of Highway and Road Structures in South Africa should be used. However, where these clearances cannot be achieved the monitoring staff should refer to the engineer for final

verification. Temporary guardrails, concrete barriers and other protection should be used to protect

the temporary support work.

6.3.2 Formwork

6.3.2.1 Load Capacity

The proposed formwork should be capable of sustaining the loads due to wet concrete and superimposed loads due to construction activities and equipment without excessive deflection.

6.3.2.2 Deflection

The engineer’s monitoring staff should ensure that the expected deflection of the forms as provided in

the formwork design falls within the specified tolerances for surface regularity.

6.3.2.3 Grout Seals

Grout seals should be incorporated into the joints between individual formwork panels in all instances

where the panels do not fit together with sufficient tightness to prevent leakage of fines.


6.3.2.4 Permanent Formwork

• On beam and slab decks using permanent formwork special attention should be given to bearing

length.

• All permanent formwork should be designed to carry the loads resulting from the wet concrete

and superimposed loads due to construction activities and equipment. The deflection under

permanent loading should not exceed 50% of the construction tolerance.

• The strength and bracing of circular void formers should be sufficient to prevent distortion and

resist all the loads they will be subjected to, and must comply with the requirements of the

drawings and Specifications. The adequacy of the formers and bracing should be signed off by

the CCP.

• Void formers must be tied down to the formwork bearers and should not be tied to or be

supported on the reinforcement.

• In voided deck slabs the concrete should be cast in layers to reduce the effects of buoyancy and

to reduce the movement of void formers.

Photo 6.2: Precast concrete permanent formwork in

position before casting.


Figure 6.3: Bracing and installation of void formers

6.3.2.5 Stripping

Minimum stripping times for falsework and formwork must be in

accordance with the Specifications. Any deviation in stripping

times should be approved by the engineer.

6.4 INSPECTION

The engineer’s monitoring staff should inspect the falsework and formwork at the completion of

erection and prior to the placing of concrete, and should insure that the CCP has signed off before

concreting. The concrete finish should be inspected on final completion of each structural element

(Refer to Chapter 8).

6.4.1 Falsework

(a) Confirm compliance with the design.

(b) Setting out - This is a very important aspect as it is fundamental to successful construction of

the structure.

(c) Safe access - Should be inspected regularly as a part of the ongoing Site Safety.

(d) Foundations - Foundation conditions should be inspected before erection of falsework. All

falsework should be inspected as soon as possible after inclement weather or flood event.

(e) Support elements - Should be inspected on completion of erection. Special attention should

be given to connections, details and areas of transfer of stress and the provision of adequate

bracing in accordance with the design. These should include the clamping of bracing and the safe reach of screw jacks.

(f) Line and level - Alignment and levels should be in accordance with the contractor’s design.

(g) Falsework should be maintained in position for the times as prescribed in the specifications. Back propping after early removal of falsework should not be permitted.

WARNING Inadequately braced void

formers may collapse resulting

in deck cross sections which do

not conform to the design. This

is likely to require demolition

and reconstruction of the deck.


(h) When the concrete is placed in the forms special care must be taken to ensure that no overloading of the formwork or falsework takes place due to the dumping of large piles of

concrete in one particular position.

6.4.2 Formwork

(a) Confirm compliance with design requirements as specified on the drawings and

specifications.

(b) Setting out, line and level to be confirmed.

(c) Condition of forms - Ensure forms are fit for purpose, sealed around edges where required and shutter release agent applied prior to fixing of reinforcement.

(d) Workmanship of shuttered areas (especially with reference to gaps where grout leakage may

occur).

(e) Where high quality surface finishes are required i.e. F2 and F3, the use of grout seals is

recommended.

(f) Permanent formwork - Confirm adequate support especially with regard to the holding down and bracing of circular voids.

(g) Removal of formwork - Ensure methods for removal of formwork are such that no damage

occurs to the freshly cast concrete.

(h) Chamfers on exposed surfaces should be formed using new materials and be adequately

secured in position during concreting.

(i) Kickers should be formed and cast monolithically with foundation concrete. Height to be

between 75 and 100mm. The kickers should be of the class of concrete of the element

above.

(j) At horizontal construction joints ensure the existing concrete surface is free from all grit and loose material prior to casting.

Photo 6.4: Unacceptable formwork & ferule pop out


6.4.3 Concrete Finish

The inspection of concrete finish should be undertaken on removal of forms to ensure compliance with

specifications.

Where areas of substandard surface finish have been identified,

remedial measures must be carried out in accordance with the

Project Specifications and as directed by the engineer. Method

statements for the expected repair of surface defects, e.g.

honeycombing, etc. should be in place before any concreting commences to ensure that remedial measures can be implemented

timeously.

Photo 6.5: Very poor ferule patching

Unformed surfaces should be checked in terms of conformance to the surface finish as specified on the

drawings and in the specifications.

Photo 6.6: Very poor workmanship

NOTE

Bad formwork = bad finish Good formwork & good

concrete practice result in

good finish


6.4.4 Conformance with Project Specifications

The monitoring staff should also ensure that all Project Specifications regarding formwork are

complied with.

6.5 FALSEWORK, FORMWORK AND CONCRETE FINISH - CONSTRUCTION

MONITORING CHECK LIST

The monitoring staff should use the “Falsework, Formwork and Concrete Finish - Construction

Monitoring Check List” as far as possible to ensure the quality of the formed concrete surfaces.


INDEX TO APPENDICES

6A - FALSEWORK, FORMWORK AND CONCRETE FINISH CONSTRUCTION MONITORING CHECK LIST


CONSTRUCTION MONITORING CHECKLIST

PROJECT NO. / NAME: .......................................................................................................................................

INSPECTOR’S NAME(S): ....................................................................................................................................

STRUCTURE: ........................................................... ELEMENT: ..............................................................

ACTIVITY AND DETAILS APPROVAL

SIGNED DATE Y/N N/A Comment

1. APPROVED DESIGN AND

DRAWINGS AVAILABLE

1.1 Design drawings

1.2 Method statement

1.3 Falsework design required

1.4 Falsework drawings

2. SETTING OUT

2.1 Platform co-ordinates

2.2 Platform / Bench dimensions

2.3 Platform / Bench levels

2.4 Layout of bases and supports

3. EARTHWORKS

3.1 DCP Tests

3.2 Compaction tests

3.3 Allowable bearing capacity

3.4 In-situ support conditions wet/dry

3.5 Adequacy of bearers

3.6 Drainage of platform

4. FALSEWORK

4.1 Base jacks provided

4.2 Base jack extensions

4.3 Type of supports per drawing

4.4 Alignment of supports

4.5 Number of supports

4.6 Bracing provided

4.7 Connections in order

4.8 Top jacks provided

4.9 Top jack extensions

4.10 Main bearers / Girders

4.11 Line level and position

4.12 Safe access for traffic

4.13 Clearances for access (traffic)

4.14 Protection for safe access (barriers)

Check list continues on next page…

FALSEWORK, FORMWORK AND

CONCRETE FINISH CHECK LIST (1/2)

APPENDIX 6A


ACTIVITY AND DETAILS APPROVAL

SIGNED DATE Y/N N/A Comment

5. FORMWORK

5.1 Setting out of element

5.2 Dimensions of element

5.3 Type of formwork

5.4 Condition of forms

5.5 Cleanliness of box

5.6 Chamfers

5.7 Bracing of forms

5.8 Sealing of forms

5.9 Joint water tightness

5.10 Ferrules, ties and cones

5.11 Whalers

5.12 Contraction joints and chamfers

5.13 Access to placement point

6. PERMANENT FORMWORK

6.1 Type of formwork

6.2 Support and tiedowns

6.3 Bracing in circular void formers

6.4 Connections

6.5 Drainage of voids

7. CONCRETE FINISH

7.1 Honeycombing

7.2 F1 Finish achieved

7.3 Patching / Repairs required

7.4 F2 Finish achieved (Fin removed,

etc.)


7.6 F3 Finish achieved (rubbed)


FALSEWORK, FORMWORK AND

CONCRETE FINISH CHECK LIST (2/2)

APPENDIX 6A

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