FORMWORK for Civil Engineering Construction Works Dr V

FORMWORK for Civil Engineering Construction Works Dr V Srinivasa Reddy Professor of Civil Engineering GRIET Lecture 1 1

Code Standards on Formwork • INTERNATIONAL STANDARDS • ACI 347 r-94 - guide to formwork for concrete • ACI SP-4 - formwork for concrete. • OHSAS - Occupational Health and Safety Act standards • BS 5975 - British standards • CAN/CSA - S 269. 3 - Canadian standard • SAA 1509 - 1974 - Australian standards • DIN 4420 - German standards The above standards covers all topics in detail, including lateral pressure of concrete, superimposed loads like P&M (plants and Machinery)loads, impact loads and environmental loads like wind loads etc. • INDIAN STANDARDS • IS - 14687 - 1999 , Indian Standard - False work for Concrete Structures - Guidelines • The other code available for reference “IRC 87 - 1984 - Guidelines on design and erection of formwork for road bridges” is derived from the British and American codes. The above codes do not elaborate on design factors and special applications when compared to the treatise of international codes. The code itself was made available only in 1999. 2

3

Definition of Formwork: When concrete is placed, it is in plastic state. It requires to be supported by temporary supports and castings of desired shape till it becomes sufficiently strong to support its own weight. This temporary casing is known as the formwork or forms or shuttering. Formwork also carries the weight of freshly placed concrete and itself besides live load due to materials, equipment and workmen In the Construction of any building concreting and reinforcement binding is the main activity after that to hold them in their position Formwork is most important 4

• Formwork is a classic temporary structure in the sense that: • it is erected quickly • highly loaded for a few hours during the concrete placement • and within a few days disassembled for future use • The term "Temporary Structures" may not fully imply the temporary, since some forms, tie hardware, and accessories are used hundreds of times, which necessitates high durability and maintainability characteristics and design that maximizes productivity • Unlike conventional structures, the formwork disassembly characteristics are severely restricted by concrete bond, rigidity, and shrinkage, which not only restricts access to the formwork structure but causes residual loads that have to be released to allow stripping from the concrete which initiates disassembly. 5

• In 1908 the use of wood versus steel formwork was debated at the ACI convention. Also, the advantages of modular panel forming with its own connecting hardware, and good for extensive reuse were realized. • By 1910 steel forms for paving were being produced commercially and used in the field n Today modular panel forming is the norm. 6

Why Formwork • For the different construction activities like • Brick work above 5 ft • Surface finishing works like plastering, painting, walling etc. • Renovation, repair and alteration works. • Roof and slab pouring Some temporary nature supports and structures are required like • Formwork (Supporting Structure) • Scaffoldings (arrangement for working plate forms) • Shoring (supporting method for unsafe structure) • Underpinning (Method of strengthening an existing structure’s footing) 7

8

9

10

Form work : All arrangement done to support the green concrete till it attains the strength is known as form work or temporary work. Form work determines the geometry, shape, size and finish of the form work. Centering : Part of the form work which supports the horizontal surface is called centering for example slab bottom , beam bottom etc. Shuttering : Part of the form work which supports the Vertical surface is called Shuttering for example column sides, beam sides, slab side , wall side etc. Staging : That portion which support centering & shuttering is called Staging. Pipes/Props/Jacks Scaffolding : That arrangement which is meant to be a supporting platform for people ( labor , supervisor, mason , fitter, painter, carpenter etc. ) is known as scaffolding. Scaffolding is nothing but a fixed/movable platform which can be used for working at 11 heights. They are usually used for activities such as plastering, painting, brick work

There are various types of scaffolding : 1. Tube and Coupler Scaffolding: Assembled using tubes and couplers at joints. 12

2. Bamboo/Wooden Scaffold : It is made using bamboo materials. It is considered unfit for industrial use. 13

3. Suspended Scaffold : It is used for cleaning glass at malls usually. 14

Shuttering/Formwork the falsework supports the shuttering moulds 15

Objectives of Form Building • Basic objectives in form building are three fold: • Quality - In terms of strength, rigidity, position, and dimensions of the forms • Safety - for both the workers and the concrete structure • Economy - the least consistent with quality and safety requirements • Cooperation and coordination between engineer / architect and the contractor are necessary to achieve these goals. • Economy is a major concern since formwork costs constitutes up to 60 percent of the total cost of concrete work in a project. • In designing and building formwork, the contractor should aim for maximum economy without sacrificing quality or safety. 16

How Formwork Affects Concrete Quality • Size, shape, and alignment of slabs, beams, and other concrete structural elements depend on accurate construction of the forms. • The forms must be: • Sufficiently rigid under the construction loads to maintain the designed shape of the concrete, • Stable and strong enough to maintain large members in alignment, and • Substantially constructed to withstand handling and reuse without losing their dimensional integrity. • The formwork must remain in place until the concrete is strong enough to carry its own weight, or the finished structure may be damaged. 17

Causes of Formwork Failure • The main causes of formwork failure are: • - Improper stripping and shore removal • - Inadequate bracing • - Vibration • - Unstable soil under mudsills*, shoring not plumb • - Inadequate control of concrete placement • - Lack of attention to formwork details. *Mudsill: A plank, frame, or small footing on the ground used as a base for a shore or post in formwork. 18

• Formwork failures are the cause of many accidents and failures that occur during concrete construction which usually happen when fresh concrete is being placed. • Generally some unexpected event causes one member to fail, then others become overloaded or misaligned and the entire formwork structure collapses. • Forms sometimes collapse when their supporting shores or jacks are displaced by vibration caused by: • passing traffic • movement of workers and equipment on the formwork • the effect of vibrating concrete to consolidate it. • Diagonal bracing can help prevent failure due to vibration. 19

Causes of Failure Improper Stripping and Shore Removal Case study: Too early shore removal at Bailey's Crossroads in Virginia (1972): 26 -stories + apartment building Forms were supported by floors 7 -days old or older Failure occurred on the 24 th floor, where it was shored to the 5 -day-old 23 rd floor. The overloaded 23 rd floor failed in shear around one or more columns, triggering a collapse that carried through the entire height of the building. • Premature stripping of forms, premature removal of shores, and careless practices in reshoring can produce catastrophic results. 20

Inadequate Bracing • The more frequent causes of formwork failure, however, are other effects that induce lateral force components or induce displacement of supporting members. • Inadequate cross bracing and horizontal bracing of shores is one of the factors most frequently involved in formwork accidents. • Investigations prove that many accidents causing thousands of dollars of damage could have been prevented only if a few hundred dollars had been spent on diagonal bracing for the formwork support. • Diagonal bracing improves the stability of such a structure. • Suppose a worker accidentally rams or wheelbarrow into some vertical shores and dislodges a couple of them. This may set up a chain of reaction that brings down the entire floor. • One major objective of bracing is to prevent such a minor accident or failure from becoming a disaster. 21

Inadequate Control of Concrete Placement • The temperature and rate of vertical placement of concrete are factors influencing the development of lateral pressures that act on the forms. • If temperature drops during construction operations, rate of concreting often has to be slowed down to prevent a build up of lateral pressure overloading the forms. If this is not done, formwork failure may result. • Failure to regulate properly the rate and order of placing concrete on horizontal surfaces or curved roofs may produce unbalanced loadings and consequent failures of formwork. 22

23

Qualities of formwork • It should be according to ACI document SP-4 • It should be water tight • It should be strong • It can be reusable • Its contact surface should be uniform • It should be according to the size of member. 24

Requirements of a Good Formwork The essential requirements of formwork or shuttering are: a) It should be strong enough to take the dead and live loads during construction. b) The joints in the formwork should be rigid so that the bulging, twisting, or sagging due to dead and live load is as small as possible. Excessive deformation may disfigure the surface of concrete. c) The construction lines in the formwork should be true and the surface plane so that the cost finishing the surface of concrete on removing the shuttering is the least. • A formwork should be easily removable without damage to itself so that it could be used repeatedly 25

Classification of Formwork The different categories in which formwork can be classified are: a) According to size. b) According to location of use. c) According to materials of construction. d) According to nature of operation. e) According to brand name of the product. 26

• Classification according to size In practice, there are only two sizes formwork; small-sized and large-sized. Any size which is designed for operation by workers manually is small-sized. At present, the most common systems are made of timber and aluminium, and are usually in the form of small panels. There is seldom medium-sized formwork. In cases in which large-sized formwork is used, the size of the form can be designed as large as practicable to reduce the amount of jointing and to minimize the amount of lift. The stiffness required by large-sized formwork can be dealt with by the introduction of more stiffening components such as studs and soldiers. The increase in the weight of the formwork panels is insignificant as a crane will be used in most cases. 27

• Classification according to the location of use 1. Foundations 2. Wall 3. Column 4. Slabs & beams 5. Stairs • Classification according to materials of construction Timber in general is still the most popular formwork material for its relative low initial cost and adaptability. Steel, in the form of either hot-rolled or cold-formed sections and in combination with other sheeting materials, is another popular choice formwork materials. In the past two to three years, full aluminium formwork systems have been used in some cases but the performance is still being questioned by many users, especially in concern to cost and labor control 28

• Classification according to nature of operation Formwork can be operated manually or by other power-lifted methods. Timber and aluminium forms are the only manually-operable types of formwork. They are designed and constructed in ways that they can be completely handled independently without the aid of any lifting appliances. 29

• Classification according to brand name of the product Several patented or branded formwork systems have successfully entered the local construction market in the past decade. Each of these firms offers its own specialized products, while some can even provide a very wide range of services including design support or tender estimating advice. As the use of innovative building methods is gaining more attention from various sectors in the community, advanced formwork systems are obviously a promising solution. VSL FORMWORK (Source Raymond, 2001) 30

31

Minimum Plank Thickness for Formwork 18 mm is the minimum for small formworks and requires closer cross planks 20 – 24 mm is the standard Thin planks can give way to the pressure of the concrete 32

Nail Size • 1 1/2” = 40 mm nails are too week and cannot stand the pressure of the concrete • The standard length for nails is 2 ½ “ = 65 mm 33

Column Formwork Sizing of Panels Column +2 X thickness Column 34

• Nail all edges with 2 1/2” nails • Join the braces as well 35

Verticality • Use a plum bob • Mark the centre • Check verticality and straightness • Do this in both directions and secure the position 36

Cutout in Column Cut out in outer dimension of formwork Support for beam 37

Erect and align the column 38

Set up support Beams and Props for the Beam Prop 39

Insert Panels one by one if they are large. . and fix them Double support Prop 40

Fair face Columns and Brickwork No Bond! 42

Column added to brickwork • Build first the walls • Add the column for maximum bond Formwork 43

Column Groove for Mortar 44

Fair Face Formwork • Rough planks do not provide a smooth surface • Plywood or steel sheets make a smooth surface for concrete • Fair face formwork is designed for easy removal and reuse 45

Apply Formwork Oil Mix Oil and Grease 1: 2 46

• Formwork oil prevents the formwork from sticking to the concrete. It eases dismantling • Formwork oil gives the concrete a fine finish • Never use burnt engine oil. It will blacken the concrete and spoil the formwork 47

Column Footing • After excavation a screed of 5. . 10 cm concrete is laid to provide a clean ground • Next comes the footing, a large block of concrete that provides a base for the column 48

TIMBER FORMWORK Timber Formwork : For The Slab 49

Timber Formwork: After Concrete Was Poured 50

ADVANTAGES OF TIMBER FORMWORK a) Easy handling because it’s light weight b) Easy to disassemble c) Damaged parts can be replaced with new one d) Very flexible DISADVANTAGES OF TIMBER FORMWORK a) Can’t be used for long. Have limited re-use. Can only be re-used 5 or 6 times b) If the timber is dry, it will absorb moisture from wet concrete which could weaken the resultant concrete member. c) Timber with high moisture content (more than 20 % moisture content), wet concrete will shrink & cup leading to open joints & leakage of grout. 51

Timber formwork used for the construction of 2 nd and the 3 rd floor. 52

ADVANTAGES OF STEEL FORMWORK a) Very strong and able to carry heavy load b) Easy to be fixed c) Uniform size and surface d) Can be used for a very long time DISADVANTAGES OF STEEL FORMWORK a) Limited size or shape b) Excessive loss of heat c) A very smooth surface will be produced which would give problems for finishing process 53

STEEL FORMWORK 54

The first floor circular columns were constructed using steel column forms. The steel column form should be oiled before concreting. 55

After concreting to the first floor columns, the steel column forms were dismantled easily. 56

ADVANTAGES OF GLASS REINFORCED PLASTIC FORMWORK a) Very useful for complex shape and special features b) Easy to disassemble c) Light (not heavy) d) Damages on the formwork can be easily be repaired DISADVANTAGES OF GLASS REINFORCED PLASTIC FORMWORK a) Expensive 57

Formwork systems in India A formwork system refers to the moulds used to hold and support wet concrete until it cures, which is pretty much a vital element in concrete construction. formwork systems have evolved from being customized timber-based to preengineered systems made of steel, aluminium, manufactured timber, plywood and plastics. This advancement, especially in the case of high-rise projects has translated into faster implementation with lesser labour, implying enhanced productivity while delivering a better finished product The only IS code available is IS 14687: 1999 which only provides guidelines on the usage of formwork and these too are very vague. Hence, standards that are followed for the designing of its formwork and scaffolding systems are ACI SP-4 58

Formwork detail for different structural members In concrete construction , formwork is commonly provided for the following structural members. • • • Foundations Wall Column Slabs & beams Stairs 59

Formwork for Foundations • Wall foundations It consists of • Plywood Sheeting • Struts 60

Formwork for Foundations • Column Foundations It consists of • Side Supports • Side Planks • Cleats Side Support Side Planks 61

Formwork for Wall • It consists of • Timber sheeting • Vertical posts • Horizontal members • Rackers • Stakes • Wedges Struts • After completing one side of formwork reinforcement is provided at the place then the second side formwork is provided. 62

Formwork for Column • It consists of the following • Side & End Planks • Yoke • Nut & Bolts • Two end & two side planks are joined by the yokes and bolts. 63

Column formwork 64

65

Formwork for Slabs & beams • It consists of • Sole plates • Wedges • Props • Head tree • Planks • Batten • Ledgers • Beam formwork rests on head tree • Slab form work rests on battens and joists • If prop height are more than 8’ provide horizontal braces. 66

Lintel or Beam Formwork 67

Formwork for Stairs • It consists of • Vertical & inclined posts • Inclined members • Wooden Planks or sheeting • Stringer • Riser Planks 68

69

Removal of formwork Time of formwork removal mainly depends on the following factors 1. Type of Cement 1. Rapid hardening cements require lesser time as compared to OPC (Ordinary Portland Cement) 2. Ratio of concrete mix 1. Rich ratio concrete gain strength earlier as compared to weak ratio concrete. 3. Weather condition 1. Hydration process accelerates in hot weather conditions as compared to cold and humid weather conditions. 70

Time of Removal of formwork Sr. No Structural Member OPC (Ordinary Portland Cement) Rapid Hardening Cement 2 -3 Days 2 Days 1 Beam sides, walls & Columns 2 Slab (Vertical Supports remains intact) 4 Days 3 Slab (Complete Formwork removal) 10 Days 5 Days 4 Beams (Removal of Sheeting, Props remains intact) 8 Days 5 Beams & Arches (Complete formwork removal) (up to 6 m span) 14 Days 5 -8 Days 6 Beams & Arches (Complete formwork removal) (more than 6 m span) 21 Days 8 -10 Days 71

Maintenance of formwork • Due to continuous use wooden planks & steel plates surfaces become uneven and require maintenance. • For wooden formwork use cardboard or plastic fiber board. Bolt hole places must also be repaired. • For steel formwork plates must be leveled by mallet and loose corners must be welded. 72