Chapter 8 formwork Bách Khoa

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Construction methods and management

Chapter 8 Concrete

formwork

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8.5 Concrete form design

8.6 Formwork inspection and acceptance

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formwork

• Improper or inadequate shoring

• Inadequate bracing of members

• Lack of control of rate of concrete placement

• Improper vibration or consolidation

of concrete

• Improper or inadequate connections

• Improper or inadequate bearing

details

4

source: Peurifoy và Oberlender, 1996, tr.156

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Causes of failures of

formwork

• Premature stripping of formwork

• Errors in placement of reshoring

• Improper or lack of design of formwork

• Inadequate strength of form material

• Failure to follow codes and standards

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GENERAL REQUIREMENTS FOR FORMWORK

Chapter 8 Concrete formwork

6

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Formwork/concrete life

cycle

7

source: Hanna, 1999

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Objectives in building and designing formwork

• Quality— must be designed and built with sufficient stiffness and accuracy so the

size, shape, position, and finish of the cast concrete are attained within the required

tolerances.

• Safety— must be built with sufficient

strength and factors of safety so they are capable of supporting all dead and live

loads without collapse or danger to workers and to the concrete structure.

• Economy— must be built efficiently,

minimizing time and cost in the construction process

8

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Principles in building and

designing formwork

Each component of the forms must be

able to support its load from two points

of view:

• Strength: based on the physical

properties of the material used

• Serviceability: the ability of the selected sections to resist the anticipated loads without exceeding deflection limits

9

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General requirements for

formwork

• Be strong enough to withstand the

pressure of plastic concrete and to

maintain their shape during the concrete placing operation

• Be tight enough to prevent wet concrete from leaking through joints and causing unsightly fins and ridges

• Be simple to build

• Be easy to handle on the job

10

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General requirements for

• Be designed such that the form may be

removed without damage to the concrete or

to themselves

• Be made so that workers can handle them with safety

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CLASSIFICATION OF

FORMWORK

12

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Formwork classification

13

Formwork classification

The material

used

The structural component molded

The way of using

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source: doosong vina

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catio

Plywood and lumber

Source: HCMUT student

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19

Specification Wood Metal Aluminum Plastic(FUVI)

Reusability 5 – 10 times 20 – 50 times Over 100 times Over 100 times

Surface quality Good , degrades

rapidly

Good, degrades (rust

& deformation) Excellent Excellent Weight/manage

ability Average(10 kg/m²) Heavy(+/- 31kg/m²)

Lightweight (+/- 20kg/m²)

Very lightweight (7kg/m²) Safety Average Dangerous Good Excellent Maintenance

cost N/A High Average Low

Recyclability

Cannot be wasteful and difficult

Store inwarehouse to prevent weathering

Store inwarehouse

to prevent weathering

No warehouse required

source:http://www.fuvicoppha.com/vietnam/whyfuvi.html

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• Forms for beams

• Forms for floor slabs

• Forms for walls

• Forms for columns

• Forms for footings

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• Flying deck forms

• Formwork for architectural concrete

21

The

way of

using

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Built-in-place forms

22

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Prefabricated panel

systems

23

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Formwork for architectural concrete

24

source: http://www.icfinfo.org.uk/

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source: http://slipformwork.com

Slip forms

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Slip forms

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Slip forms

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A rail

climbing

system

Climbing forms

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source:http://www.nationalforming.com/jb240.html

A rail

climbing

system

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Climbing forms

40

source: KHK scaffolding and formwork L.L C

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Jumping forms

42

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Flying deck forms

43

source: Peri

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Flying deck forms

44

source: Peri

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TYPICAL FORMWORK

45

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Forms for column footings

46

source:Hurd, 1995

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47

source:Hurd, 1995

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source:Hurd, 1995

Stepped

column

footings

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source:Hurd, 1995

Sloped

footing

forms

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Forms for wall footings

source:Hurd, 1995

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Forms for wall footings

source:Hurd, 1995

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Forms for wall

52

source:Hurd, 1995

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Forms for wall

53

source:Hurd, 1995

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Forms for wall

c)

d)

e)

f)

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Forms for wall

55

Prefabricated

panel

systems

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Form for curved walls

source:Hurd, 1995

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Forms for column

57

source:Hurd, 1995

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59

source:http://upload.wikimedia.org/wikip edia/en/c/c5/Formwork-tie-bolts.jpg Source:HCMUT student

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60

source:http://img.directindustry.com/images_d i/photo-g/column-formwork-387120.jpg

Prefabricated

form system

for columns

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Forms for beam and slab

construction

61

source:Hurd, 1995

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construction

62

source:Nunnally, 1995

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source:Hurd, 1995

construction

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construction

source:Hurd, 1995

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Forms for beam and slab construction

65

source:Hurd, 1995

Spandrel beams

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construction

66

source:http://upload.wikimedia.org/wikipe dia/en/3/35/Formwork-trad-beam.png

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Forms for beam and slab construction

67

Source: ACI347-04

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construction

68

source:http://www.builderbill-diy-help.com/image-files/v-form.gif

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construction

69

source:http://www.ischebeck.de/assets/images/schalungssysteme /alu-deckenschalung/alu-deckenschalung-titan-hv.jpg

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construction

70

source: Doka

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construction

71

source:http://lh5.ggpht.com/_LL1XswgWVBY/ScHH3KFPfaI /AAAAAAAANuI/PqMa6bf1eyU/DSC_0034.JPG

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Forms for stairway

72

source:Hurd, 1995

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Forms for stairway

73

source:http://www.sawformwork.com/form_steel/Formed-Stairs.jpg

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SHORES AND SCAFFOLDING

74

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Shores and scaffolding

• working platform: where workers stand/walk on

to work above the ground

• shores: support for formwork

• scaffolding: support for working platform and formwork

75

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Single-post and combination steel shore

76

source:http://www.ngochungltd.com/upl

oads/imgproducts/1260721760.GIF source:http://www.thienhoaan.com/images/CC -giao-Anh-To.jpgCCTH462L.jpg

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Single-post steel shore

77

Source: Dong Duong Ltd.

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Combination steel shore

78

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Frame scaffolding

79

fc.com/content/images/materials/Scafolding/scaffolding01_mid.jpg

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80

Source: HCMUT student

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Horizontal shores

82

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Shoring and reshoring for multistory buildings

83

Source: Andres and Smith, 1998

For a typical multi

story building with

are usually required

for progress at the

rate of one story

per week.

Shoring and reshoring sequence in a multistory building

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CONCRETE FORM DESIGN

Chapter 8 Concrete dômrk

84

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Concrete form design – Vertical loads

Vertical loads consist of dead and live loads

• D (dead load): The weight of formwork, the weight of the reinforcement and freshly placed concrete

• LL (live load): the weight of the workers, equipment, material storage, runways, and impact.

• The formwork should be designed for a live load of not less than 2.4 kPa When motorized carts are used, the live load should not be less than 3.6 kPa

• The design load for combined dead and live loads should not be less than 4.8 kPa or 6.0

ACI

standard

347-04

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Concrete form design – Lateral pressure

For concrete having a slump of 175 mm or less and placed with normal internal

vibration to a depth of 1.2 m or less,

− pmax = maximum lateral pressure, kPa;

− R = rate of placement, m/h;

− T = temperature of concrete during placing,

°C;

− C w = unit weight coefficient per Table 2.1;

− C c = chemistry coefficient per Table 2.2

, 7 [

C

p w c

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Concrete form design –

Lateral pressure

• For walls with a rate of placement of

less than 2.1 m/h and a placement

height not exceeding 4.2 m

87

] 8 , 17

785 2

, 7 [

C

p w c

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Concrete form design Lateral pressure

-• For walls with a placement rate less than 2.1 m/h where placement height exceeds 4.2 m, and for all walls with a placement rate of 2.1 to 4.5 m/h

• with a minimum of 30C w (kPa), but in no case greater than ρgh.

244 8

, 17

1156 2

, 7 [

C C

p w c

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-Unit weight coefficient C w

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-Unless the above conditions are met,

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-• the assumed value of horizontal load due to wind, dumping of concrete,

inclined placement of concrete, and equipment acting in any direction at each floor line should be not less than 1.5 kN/m of floor edge or 2% of total dead load on the form distributed as a uniform load per linear meter of slab edge, whichever is greater

92

ACI

standard

347-04

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• Recommended minimum lateral design load for wall form

• wf: wind force prescribed by local code but minimum of 0,72 kPa.

93

Wall height h (m)

Design lateral force applied at top

of form (kN/m)

h < 2,4 (h x wf)/2 2,4 < h < 6,7 1,46, but at least (h x wf)/2

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FORMWORK INSPECTION AND APPROVAL

94

source:http://img.directindustry.com/images_ di/photo-g/slab-formwork-366844.jpg

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Formwork inspection

• Forms should be inspected and checked before the reinforcing steel is placed to ensure the concrete quality and shape

o Inspect the location, dimension, and shape

o Inspect the joints, the faces in contact with concrete

o Inspect the strengh and stability of

formwork system, shores and

scaffolding

95

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Concrete form design

-DESIGN PRINCIPLES

• The design of concrete formwork that

has adequate strength to resist failure

and will not deflect excessively when the forms are filled is a problem in structural design

design

– Unless commercial forms are used, this will usually involve the design of wall, column, or slab forms

constructed of wood or plywood

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Concrete form design

-DESIGN PRINCIPLES

• In such cases, after the design loads have been established, each of the

primary form components may be

analyzed as a beam to determine the maximum bending and shear stresses

maximum bending and shear stresses and the maximum deflection that will occur.

– Vertical supports and lateral bracing are then analyzed for compression and tension loads.

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METHOD OF ANALYSIS

1 span 2 spans 3 spans

1 span 2 spans 3 spans Bending moment (Nm)

wl EI

∆ =

4

185

wl EI

∆ =

4

145

wl EI

∆ =

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METHOD OF ANALYSIS

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SLAB FORM DESIGN

• Method of Analysis

– The procedure for applying the equations of Tables 13-5A to the design of a slab form is first to consider a strip of sheathing of the specified thickness and 1 m wide (see

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SLAB FORM DESIGN

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Table 13-6 Section properties of

Table 13-6 Section properties of plywood.* (Created by author with data from APA—the Engineered Wood Association)

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Table 13-8 Typical values of allowable stress for lumber

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FIGURE 13-2 Slab form, Example 13-1.

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Design the formwork for an elevated concrete floor slab 152mm thick Sheathing will be nominal 25mm lumber while 50x200mm

lumber will be used for joists Stringers will

be 100x200mm lumber Assume that all

members are continuous over three or

more spans Commercial 17.8kN shores

will be used It is estimated that the weight

of the formwork will be 0.24KPa The

adjusted allowable stresses for the lumber being used are as follows:

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