MODERN PRACTICESIN

FORMWORK FOR CIVIL ENGINEERINGCONSTRUCTION WORKS

MODERN PRACTICESIN

FORMWORK FOR CIVILENGINEERING

CONSTRUCTION WORKS

By

DR. JANARDAN JHAFormer Director

Amity Centre for Innovation & New ConceptsAmity University, NOIDA (U.P)

Ex. Professor and Head, Civil Engineering, Bihar Institute of TechnologySindri (Jharkhand)

&

PROF. S.K. SINHAVisiting Professor of Civil Engineering

Birla Institute of Technology, Patna (Bihar)Rtd. Professor and Head, Civil Engineering

Bihar Institute of TechnologySindri (Jharkhand)

UNIVERSITY SCIENCE PRESS(An Imprint of Laxmi Publications (P) Ltd.)

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JALANDHAR ∑ KOLKATA ∑ ∑LUCKNOW ∑

∑

MUMBAI RANCHI NEW DELHI INDIA USA GHANA KENYA ∑∑

∑

MODERN PRACTICES IN FORMWORK FOR CIVIL ENGINEERING CONSTRUCTION WORKS

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Printed and bound in India Typeset at Excellent Graphics

First Edition: 2014 UFC-9734-150-FORM CIVIL ENGG CONST-JHA

ISBN 978-93-83828-38-8

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v

Preface

Formwork and falsework are temporary structures that are built to support parts or the wholeof a permanent structure until it is self-supporting. Individual components of formwork andfalsework are assembled and form the temporary structure. In other words, Formwork meansthe surface, support and framing used to define the shape of the concrete until it is self-supporting.

• Formwork includes the forms on or within which the concrete is poured, the supportswhich carry the forms and the concrete, the bracing which may be added to ensurestability, as well as the foundations and footings.

• When complete, the formwork is sometimes referred to as the formwork assembly.• The formwork supports, bracing, foundations and footings are sometimes known as

falsework.Falsework means any temporary structure that is used to support a permanent

structure, material, plant, equipment and personnel until the construction of the permanentstructure has advanced to the stage that it is self-supporting.

• A temporary structural support system referred to as falsework includes the foundations,footings and all structural members supporting the permanent structural elements.

• Falsework is commonly used to support spanning or arched structures, such as bridges,while they are being constructed.

• The temporary support structures for formwork used to mould concrete to form a desiredshape and the scaffolding that might also give workers access to the structure beingconstructed is sometimes referred to as falsework.

There are three stages in the formwork operations:• Assembly and erection• Concrete placement• Stripping and dismantling

To be done safely, each of these operations requires planning, knowledge and skill fromboth supervisors and workers besides economy. Sometimes, the cost of formwork exceeds theactual cost of construction. The formwork and falsework may be assembled with timber, steel,alluminium, plastic coated steel or a combination of them.

Slipform technology is a new innovation in this field. Slipforming is a constructiontechnique which has been used for decades for production of concrete structures. Wide range

of structures are slipformed, typically, vertical structures such as towers, bridge columns andoffshore platforms and horizontal structures like rigid reinforced concrete pavement, canallining, etc. Apart from vertical structures with uniform thickness, slipforming technique isalso used where geometry of structure and wall thickness changes. Slipforming is a continuousworking operation (24 hours a day), which requires planned supply of materials, managementand supervision.

Shoring is a general term used in construction to describe the process of supporting astructure in order to prevent collapse so that construction can proceed.

At times, it is essential to replace or strengthen the foundation of an existing structure.The operation of providing new permanent foundations is known as underpinning.

Scaffolding is a temporary platform, either supported from below or suspended fromabove, on which workers sit or stand while performing tasks at heights above the ground. Itsupports men and materials for construction or repair works at height. Scaffolding involvessturdy connections of frames and planks by bolts and couplers, which come in many forms,depending on the size and shape of the desired framework. It is usually a modular system ofmetal pipes or tubes, although it can be from other materials.

In this book authors have tried to explain the various and latest techniques of formwork,shoring, underpinning and scaffolding practiced all over the world. The book should provevery useful to the civil, architecture engineering undergraduate students and practicingengineers. A large number of figures and photographs have been provided to explain the actualworking. Any suggestion to improve upon is most welcome.

Dr. Janardan JhaProf. Suresh Kumar Sinha

vi PREFACE

Preface (v–vi)

1. Introduction to Formwork 1–14

1.1 Introduction ............................................................................................................................ 11.2 Objectives of Form Building .................................................................................................. 11.3 Technical Terms ..................................................................................................................... 21.4 How Formwork Affects Concrete Quality ............................................................................ 61.5 Causes of Formwork Failure ................................................................................................. 6

1.5.1 Safety ........................................................................................................................ 71.6 Planning for Formwork ......................................................................................................... 71.7 Areas of Cost Reduction......................................................................................................... 71.8 Requirements of Formwork ................................................................................................... 81.9 Economy in Formwork ........................................................................................................... 81.10 Materials of Formwork .......................................................................................................... 91.11 The Size of Form Section ....................................................................................................... 91.12 Types of Formwork ................................................................................................................ 91.13 Indian Standards on Formwork (IS:456–2000) ................................................................. 121.14 Treatment of Formwork ...................................................................................................... 131.15 Summary............................................................................................................................... 13

2. Principles of Formwork Design 15–26

2.1 Design Considerations ......................................................................................................... 152.2 Structural Design ................................................................................................................. 162.3 Introduction to Design Principles ....................................................................................... 16

2.3.1 Design of Formwork for Slab ................................................................................ 172.3.2 Vertical Loads ........................................................................................................ 17

2.4 Example of Slab Formwork Design .................................................................................... 182.4.1 Example .................................................................................................................. 182.4.2 Lateral Pressure of Fresh Concrete ..................................................................... 19

( vii )

Contents

2.5 Form Design ......................................................................................................................... 202.5.1 Lateral Loads ......................................................................................................... 212.5.2 The Wall Form Design .......................................................................................... 212.5.3 Example for Slab Form Design ............................................................................. 22

2.6 Summary............................................................................................................................... 26

3. Timber and Timber Derived Materials for Formwork 27–59

3.1 Introduction .......................................................................................................................... 273.2 Functional and Load Requirements of Formwork............................................................. 27

3.2.1 Formwork Functions ............................................................................................. 273.2.2 Basic Principles of Formwork Making ................................................................. 28

3.3 Elements of Formwork ........................................................................................................ 293.3.1 The Formwork Sheeting ........................................................................................ 293.3.2 The Formwork Bearers ......................................................................................... 303.3.3 The Elements of False-work Structures .............................................................. 30

3.4 Defects Commonly Found in Formwork ............................................................................. 303.5 Timber Forms ....................................................................................................................... 31

3.5.1 Plywood ................................................................................................................... 333.6 Construction of Formwork .................................................................................................. 34

3.6.1 Propping and Centering ........................................................................................ 353.6.2 Shuttering .............................................................................................................. 353.6.3 Order and Method of Removing Formwork ......................................................... 363.6.4 Nailing Formwork ................................................................................................. 363.6.5 Treatment of Formwork ........................................................................................ 373.6.6 Removal of Formworks .......................................................................................... 37

3.7 Forms for Foundations ........................................................................................................ 373.8 Forms for Walls .................................................................................................................... 38

3.8.1 Ties .......................................................................................................................... 413.9 Formwork .............................................................................................................................. 43

3.9.1 Forms for Columns ................................................................................................ 433.9.2 Forms for Lintels and Simple Beams ................................................................... 463.9.3 Forms for Staircase ............................................................................................... 473.9.4 Forms for Slab or floor .......................................................................................... 493.9.5 Best Practices for Conventional Wood System.................................................... 553.9.6 Limitations of Conventional Wood System ......................................................... 553.9.7 Advantages of Conventional Wood System ......................................................... 56

3.10 Modular Slab Formwork ...................................................................................................... 563.10.1 Table or Flying Form Systems ............................................................................. 563.10.2 Structure ................................................................................................................ 563.10.3 Support ................................................................................................................... 573.10.4 Size .......................................................................................................................... 573.10.5 Crane Handled ....................................................................................................... 573.10.6 Crane Fork or Elevator Handled .......................................................................... 57

3.11 Summary............................................................................................................................... 58

viii CONTENTS

4. Steel and Aluminium Formwork 60–92

4.1 Introduction .......................................................................................................................... 604.1.1 Concrete Construction ........................................................................................... 604.1.2 Concrete Formwork ............................................................................................... 60

4.2 Steel Formwork .................................................................................................................... 624.2.1 Elements and Accessories of Steel Formwork ..................................................... 644.2.2 Strength and Durability of Formwork ................................................................. 784.2.3 Formwork Materials affect Construction Duration ............................................ 784.2.4 Formwork Materials affect Quality of Concrete ................................................. 794.2.5 Labour Requirement ............................................................................................. 794.2.6 Formwork Economy ............................................................................................... 80

4.3 Aluminium Formwork ......................................................................................................... 804.3.1 Slab Construction .................................................................................................. 814.3.2 Aluminium Formwork for Walls .......................................................................... 844.3.3 Aluminium Formwork for Column ....................................................................... 854.3.4 Aluminium Formwork for Stairs .......................................................................... 874.3.5 Formwork for Domes and Shell Roofs .................................................................. 87

4.4 Table or Flying Form Systems ............................................................................................ 884.5 Easy Stripping Construction Formwork System ............................................................... 914.6 Summary............................................................................................................................... 92

5. Stripping of Formwork 93–104

5.1 Introduction .......................................................................................................................... 935.2 Stripping the Formwork and False-work ........................................................................... 955.3 Knock–down Slab System ................................................................................................... 975.4 Built-in-place Wall Forms ................................................................................................... 985.5 Hydraulic Rams used in Dismantling Formwork .............................................................. 995.6 Stripping Time ................................................................................................................... 1005.7 Allowable tolerances .......................................................................................................... 1005.8 Competent Person Sign-off Prior to Stripping ................................................................. 102

5.8.1 Bond Reduction .................................................................................................... 1035.8.2 Exclusion Zone ..................................................................................................... 1035.8.3 Drop Stripping ..................................................................................................... 1035.8.4 Dismantling False-work ...................................................................................... 103

5.9 Occupational Health and Safety Requirements .............................................................. 1035.10 Risk Controls ...................................................................................................................... 1045.11 Summary............................................................................................................................. 104

6. Slip-Form Construction 105–129

6.1 Introduction ........................................................................................................................ 1056.2 Slip Form Technology ........................................................................................................ 106

6.2.1 Slip Forming Process ........................................................................................... 1066.2.2 Advantages of Slip-form Construction ............................................................... 1076.2.3 Economics of Slip Form Construction ................................................................ 1086.2.4 Safety .................................................................................................................... 109

CONTENTS ix

6.2.5 Other Considerations .......................................................................................... 1096.2.6 Sustainability Features of Slip Form Construction .......................................... 1106.2.7 Strategic Application to Concrete Structures ................................................... 1106.2.8 Pre-construction Services .................................................................................... 1106.2.9 Project Planning .................................................................................................. 1106.2.10 Design liaison ....................................................................................................... 1116.2.11 Procurement ......................................................................................................... 1116.2.12 Construction ......................................................................................................... 1116.2.13 Quality Assurance and Control .......................................................................... 1116.2.14 Cost Control ......................................................................................................... 111

6.3 Design of Slip Formwork ................................................................................................... 1116.3.1 Types of Construction .......................................................................................... 1116.3.2 Vertical Slip Form ............................................................................................... 1186.3.3 Tapered Slip Forming .......................................................................................... 1236.3.4 Why Choose Slip Forming ................................................................................... 124

6.4 Before Choosing Slip Forming Some of the Factors to Consider ................................... 1256.4.1 Assembling Formwork for Slip form Methods of Construction ....................... 1256.4.2 General Structure of Slip Form .......................................................................... 1256.4.3 Removal of Formwork ......................................................................................... 126

6.5 Theoretical Details of Concrete Hardening in the Slip Form......................................... 1266.6 Slip Form Works by Concrete Pump ................................................................................ 1266.7 Self Consolidating Concrete .............................................................................................. 128

6.7.1 Chemical Admixture ............................................................................................ 1286.7.2 Self Consolidating Concrete Compared to Ordinary Concrete ........................ 1286.7.3 Tests on Self Concrete Consolidating ................................................................ 129

6.8 Summary............................................................................................................................. 129

7. Shoring, Underpinning and Scaffolding 130–169

7.1 Introduction ........................................................................................................................ 1307.2 Types of Shoring ................................................................................................................. 131

7.2.1 Raking Shores ...................................................................................................... 1317.2.2 Horizontal or Flying Shores ................................................................................ 1337.2.3 Dead Shores ......................................................................................................... 1357.2.4 Trench Shoring or Timbering ............................................................................. 136

7.3 Aluminium Shores ............................................................................................................. 1387.3.1 Trench Jacks ........................................................................................................ 1387.3.2 Aluminium Waler Systems ................................................................................. 1387.3.3 Hydraulic Bracing Systems ................................................................................ 1407.3.4 Lifting Chains ...................................................................................................... 1417.3.5 Pipe Lifters ........................................................................................................... 142

7.4 Underpinning ..................................................................................................................... 1427.4.1 Methods of Underpinning ................................................................................... 143

7.5 Scaffolding .......................................................................................................................... 1487.5.1 General Requirements of Scaffold ...................................................................... 1507.5.2 Basic Scaffolding .................................................................................................. 150

x CONTENTS

7.5.3 Scaffold Platform may be Classified as Follows ................................................ 1517.5.4 Types of Scaffolds ................................................................................................ 152

7.6 Fittings and Accessories .................................................................................................... 1657.6.1 Salient Features .................................................................................................. 168

7.7 Summary............................................................................................................................. 169

Index 171–174

Colour Photograph 175–184

CONTENTS xi

1.1 INTRODUCTIONThe concrete is such a wonderful material which acquires exact shape of the mould in which itis placed. Formwork is the term given to either temporary or permanent moulds into whichconcrete or similar materials are poured. In the context of concrete construction, the falsework supports the shuttering moulds. In other words, shuttering or formwork is the term usedfor temporary timber, plywood, metal, plastic or other material used to provide support tofresh concrete mix till it gets strength for self support. It provides supports to horizontal,vertical and inclined surfaces or also provides support to cast concrete according to requiredshape and size. The formwork also produces desired finish to concrete surface.

The cost of concrete also includes the cost of the formwork which is required to support theconcrete until it attains sufficient strength to support itself. Sometimes, the cost of formworkis higher than the cost of concrete alone. Hence, any effort to effect economy in concrete structureshould be directed primarily on reducing the cost of formworks.

The construction of a concrete structure requires formwork to support the slabs (HorizontalFormwork) as well as columns and walls (Vertical Formwork). Formwork is the contact surfaceand structural backing needed to contain fresh concrete until it can safely support itself. If itis not removed, it is called permanent formwork. If it has to be supported from below, thestructural support is called false work. The exact distinction between formwork and falsework is not very important, but it is usual to call all material and equipment used to cast wallsformwork. This is because the system of loads is self-contained, while for concrete memberssuch as slabs or beams, false work is used to take the loads to the ground below or to a similarsupport. For such members, the actual surface material and its immediate support is consideredto be formwork.

1.2 OBJECTIVES OF FORM BUILDINGForms mould the concrete to desired size and shape and control its position and alignment.But formwork is more than a mould; it is a temporary structure that supports its own weight,plus the freshly placed concrete, plus construction live loads (including materials, equipment,and personnel).Basic objectives in form building are:

1. Quality — In terms of strength, rigidity, position, and dimensions of the forms2. Safety — For both the workers and the concrete structure

Introduction to Formwork1

Modern Practice In Formwork For CivilEngineering Construction Works

Publisher : Laxmi Publications ISBN : 9789383828388 Author : Janardan Jha

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