Formwork for Concrete Structures About the Authors Robert L. Peurifoy (deceased) taught civil engineering at the University of Texas and Texas A&I College, and construction engineering at Texas A&M University and Oklahoma State University. He served as a highway engineer for the U. S. Bureau of Public Roads and was a contributing editor to Roads and Streets Magazine. In addition to authoring the McGraw-Hill publications Construction Planning, Equipment, and Methods and Estimating Construction Costs, 5th ed. , coauthored with Garold D. Oberlender, Mr. Peurifoy wrote over 50 magazine articles dealing with construction.

There's a specialist from your university waiting to help you with that essay.
Tell us what you need to have done now!


order now

He was a long-time member of the American Society of Civil Engineers, which presents an award that bears his name. Garold D. Oberlender, Ph. D, P. E. (Stillwater, Oklahoma), is Professor Emeritus of Civil Engineering at Oklahoma State University, where he served as coordinator of the Graduate Program in Construction Engineering and Project Management. He has more than 40 years of experience in teaching, research, and consulting engineering related to the design and construction of projects. He is author of the McGraw-Hill publications Project Management for Engineering and Construction, 2nd ed. and Estimating Construction Costs, 5th ed. , coauthored with Robert L. Peurifoy. Dr. Oberlender is a registered professional engineer in several states, a member of the National Academy of Construction, a fellow in the American Society of Civil Engineers, and a fellow in the National Society of Professional Engineers. Formwork for Concrete Structures Robert L. Peurifoy Late Consulting Engineer Austin, Texas Garold D. Oberlender Professor Emeritus Oklahoma State University Fourth Edition New York Chicago San Francisco Lisbon London Madrid Mexico City Milan New Delhi San Juan Seoul Singapore Sydney Toronto

Copyright © 2011, 1996, 1976, 1964 by The McGraw-Hill Companies, Inc. All rights reserved. Except as permitted under the United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the publisher. ISBN: 978-0-07-163918-7 MHID: 0-07-163918-7 The material in this eBook also appears in the print version of this title: ISBN: 978-0-07-163917-0, MHID: 0-07-163917-9. All trademarks are trademarks of their respective owners.

Rather than put a trademark symbol after every occurrence of a trademarked name, we use names in an editorial fashion only, and to the bene? t of the trademark owner, with no intention of infringement of the trademark. Where such designations appear in this book, they have been printed with initial caps. McGraw-Hill eBooks are available at special quantity discounts to use as premiums and sales promotions, or for use in corporate training programs. To contact a representative please e-mail us at bulksales@mcgraw-hill. com. Information contained in this work has been obtained by The McGraw-Hill Companies, Inc. “McGraw-Hill”) from sources believed to be reliable. However, neither McGraw-Hill nor its authors guarantee the accuracy or completeness of any information published herein, and neither McGraw-Hill nor its authors shall be responsible for any errors, omissions, or damages arising out of use of this information. This work is published with the understanding that McGraw-Hill and its authors are supplying information but are not attempting to render engineering or other professional services. If such services are required, the assistance of an appropriate professional should be sought.

TERMS OF USE This is a copyrighted work and The McGraw-Hill Companies, Inc. (“McGrawHill”) and its licensors reserve all rights in and to the work. Use of this work is subject to these terms. Except as permitted under the Copyright Act of 1976 and the right to store and retrieve one copy of the work, you may not decompile, disassemble, reverse engineer, reproduce, modify, create derivative works based upon, transmit, distribute, disseminate, sell, publish or sublicense the work or any part of it without McGraw-Hill’s prior consent. You may use the work for your own noncommercial nd personal use; any other use of the work is strictly prohibited. Your right to use the work may be terminated if you fail to comply with these terms. THE WORK IS PROVIDED “AS IS. ” McGRAW-HILL AND ITS LICENSORS MAKE NO GUARANTEES OR WARRANTIES AS TO THE ACCURACY, ADEQUACY OR COMPLETENESS OF OR RESULTS TO BE OBTAINED FROM USING THE WORK, INCLUDING ANY INFORMATION THAT CAN BE ACCESSED THROUGH THE WORK VIA HYPERLINK OR OTHERWISE, AND EXPRESSLY DISCLAIM ANY WARRANTY, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

McGraw-Hill and its licensors do not warrant or guarantee that the functions contained in the work will meet your requirements or that its operation will be uninterrupted or error free. Neither McGraw-Hill nor its licensors shall be liable to you or anyone else for any inaccuracy, error or omission, regardless of cause, in the work or for any damages resulting therefrom. McGraw-Hill has no responsibility for the content of any information accessed through the work.

Under no circumstances shall McGraw-Hill and/or its licensors be liable for any indirect, incidental, special, punitive, consequential or similar damages that result from the use of or inability to use the work, even if any of them has been advised of the possibility of such damages. This limitation of liability shall apply to any claim or cause whatsoever whether such claim or cause arises in contract, tort or otherwise. Contents Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix Abbreviations and Symbols . . . . . . . . . . . . . . . . . . . . xxi 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Purpose of This Book . . . . . . . . . . . . . . . . . . . . . . . . . . Safety of Formwork . . . . . . . . . . . . . . . . . . . . . . . . . . . Economy of Formwork . . . . . . . . . . . . . . . . . . . . . . . . Allowable Unit Stresses in Formwork Material … Care of Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Patented Products ………………………. Arrangement of This Book . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Economy of Formwork . . . . . . . . . . . . . . . . . . . . . . . . Background Information . . . . . . . . . . . . . . . . . . . . . . . Impact of Structural Design on Formwork Costs . . . Suggestions for Design . . . . . . . . . . . . . . . . . . . . . . . . Design Repetition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dimensional Standards . . . . . . . . . . . . . . . . . . . . . . . . Dimensional Consistency . . . . . . . . . . . . . . . . . . . . . . Economy of Formwork and Sizes of Concrete Columns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Beam and Column Intersections . . . . . . . . . . . . . . . Economy in Formwork and Sizes of Concrete Beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . Economy in Making, Erecting, and Stripping Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . Removal of Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . Building Construction and Economy . . . . . . . . . . . . Economy in Formwork and Overall Economy . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pressure of Concrete on Formwork . . . . . . . . . . . . . Behavior of Concrete . . . . . . . . . . . . . . . . . . . . . . . . . Lateral Pressure of Concrete on Formwork . . . . . . . Lateral Pressure of Concrete on Wall Forms . . . . . . Example 3-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example 3-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example 3-3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 2 2 2 3 3 3 6 7 7 7 9 10 10 11 11 12 13 14 15 16 19 20 21 21 22 23 24 25 26 2 3 v vi Contents Relationship between Rate of Fill, Temperature, and Pressure for Wall Forms . . . . . . . . . . . . . . . . . Lateral Pressure of Concrete on Column Forms . . . Example 3-4 . . . . . . . . . . . . . . . . . . . . . . . . . . . Example 3-5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example 3-6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . Relationship between Rate of Fill, Temperature, and Pressure for Column Forms . . . . . . . . . . . . . . Graphical Illustration of Pressure Equations for Walls and Columns . . . . . . . . . . . . . . . . . . . . . . . . . Effect of Weight of Concrete on Pressure . . . . . . . . . Vertical Loads on Forms . . . . . . . . . . . . . . . . . . . . . . . Example 3-7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example 3-8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example 3-9 . . . . . . . . . . . . . . . . . . . . . . . . . . . Placement and Consolidation of Freshly Placed Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wind Loads on Formwork Systems . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Properties of Form Material . . . . . . . . . . . . . . . . . . . General Information . . . . . . . . . . . . . . . . . . . . . . . . . . . Properties of Lumber . . . . . . . . . . . . . . . . . . . . . . . . . . Allowable Stresses of Lumber . . . . . . . . . . . . . . . . . . Adjustment Factor CD for Load-Duration . . . . . . . . Adjustment Factors CM for Moisture Content . . . . . Adjustment Factor CL for Beam Stability . . . . . . . . . Adjustment Factor CP for Column Stability . . . . . . . Adjustment Factors Cfu for Flat Use . . . . . . . . . . . . . . Adjustment Factors Cb for Bearing Area . . . . . . . . . . . Application of Adjustment Factors . . . . . . . . . . . . . . Example 4-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example 4-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plywood ……………………………… Allowable Stresses for Plywood . . . . . . . . . . . . . . . . . Plyform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . High-Density Overlaid Plyform . . . . . . . . . . . . . . . . . Equations for Determining the Allowable Pressure on Plyform . . . . . . . . . . . . . . . . . . . . . . . . Allowable Pressure Based on Fiber Stress in Bending . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Allowable Pressure Based on Bending De? ection . . . . Allowable Pressure Based on Shear Stress . . . . . . . . 28 31 31 32 33 33 33 36 36 38 38 38 39 39 39 41 41 41 44 46 46 51 51 52 52 53 53 53 54 55 55 60 60 62 63 63 Contents Allowable Pressure Based on Shear De? ection . . . Tables for Determining the Allowable Concrete Pressure on Plyform . . . . . . . . . . . . . . . . . . . . . . . . Maximum Spans for Lumber Framing Used to Support Plywood . . . . . . . . . . . . . . . . . . . . . . . . . . . Use of Plywood for Curved Forms . . . . . . . . . . . . . . Hardboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fiber Form Tubes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Steel Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aluminum Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plastic Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Form Liners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nails . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Withdrawal Resistance of Nails . . . . . . . . . . . . . . . . . Lateral Resistance of Nails . . . . . . . . . . . . . . . . . . . . . Toe-Nail Connections ……………………. Connections for Species of Wood for Heavy Formwork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lag Screws . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Withdrawal Resistance of Lag Screws ………..

Lateral Resistance of Lag Screws . . . . . . . . . . . . . . . . Timber Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . Split-Ring Connectors . . . . . . . . . . . . . . . . . . . . . . . . . Shear-Plate Connectors . . . . . . . . . . . . . . . . . . . . . . . . Split-Ring and Shear-Plate Connectors in End Grain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Penetration Requirements of Lag Screws . . . . . . . . . Form Ties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concrete Anchors ………………………. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Design of Wood Members for Formwork . . . . . . . . General Information . . . . . . . . . . . . . . . . . . . . . . . . . . . Arrangement of Information in This Chapter . . . . . Lumber versus Timber Members . . . . . . . . . . . . . . . . Loads on Structural Members . . . . . . . . . . . . . . . . . . Equations Used in Design . . . . . . . . . . . . . . . . . . . . . . Analysis of Bending Moments in Beams with Concentrated Loads . . . . . . . . . . . . . . . . . . . . . . . . Analysis of Bending Moments in Beams with Uniformly Distributed Loads . . . . . . . . . . . . . . . . Bending Stress in Beams . . . . . . . . . . . . . . . . . . . . . . Stability of Bending Members . . . . . . . . . . . . . . . . . . 63 64 64 66 66 72 72 73 73 74 74 75 75 77 78 78 78 79 82 82 83 84 84 85 85 86 87 87 87 88 89 89 90 91 92 93 vii viii Contents Examples of Using Bending Stress Equations for Designing Beams and Checking Stresses in Beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example 5-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example 5-2 ……………………… Example 5-3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . Horizontal Shearing Stress in Beams . . . . . . . . . . . . .

Example 5-4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example 5-5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . Modi? ed Method of Determining the Unit Stress in Horizontal Shear in a Beam . . . . . . . . . . . . . . . . . . Example 5-6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example 5-7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . De? ection of Beams . . . . . . . . . . . . . . . . . . . . . . . . . . . De? ection of Beams with Concentrated Loads . . . . De? ection of Single-Span Beams with Concentrated Loads . . . . . . . . . . . . . . . . . . . . . . . . Example 5-8 . . . . . . . . . . . . . . . . . . . . . . . . . . . Multiple-Span Beam with Concentrated Loads . . . . De? ection of Beams with Uniform Loads . . . . . . . . . Single-Span Beams with Uniformly Distributed Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example 5-9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . De? ection of Multiple-Span Beams with Uniformly Distributed Loads . . . . . . . . . . . . . . . . . . . . . . . . . . Table for Bending Moment, Shear, and De? ection for Beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Calculating De? ection by Superposition . . . . . . . . Example 5-10 . . . . . . . . . . . . . . . . . . . . . . . . . . . Example 5-11 . . . . . . . . . . . . . . . . . . . . . . . . . . . Allowable Span Length Based on Moment, Shear, or De? ection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Allowable Span Length for Single-Span Members with Uniformly Distributed Loads . . . . . . . . . . . . Allowable Span Length for Multiple-Span Members with Uniformly Distributed Loads . . . . . . . . . . . . Stresses and De? ection of Plywood . . . . . . . . . . . . . . Allowable Pressure on Plywood Based on Bending Stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example 5-12 . . . . . . . . . . . . . . . . . . . . . . . . . . . Example 5-13 . . . . . . . . . . . . . . . . . . . . . . . . . . . Example 5-14 . . . . . . . . . . . . . . . . . . . . . . . . . . . Allowable Pressure on Plywood Based on Rolling Shear Stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example 5-15 . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 95 96 97 98 99 99 100 102 103 104 105 106 107 108 109 109 110 111 111 113 113 114 115 116 116 117 118 120 120 121 121 122 Contents Allowable Pressure on Plywood Based on De? ection Requirements . . . . . . . . . . . . . . . . . . . Allowable Pressure on Plywood due to Bending De? ection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example 5-16 . . . . . . . . . . . . . . . . . . . . . . . . . . . Allowable Pressure on Plywood Based on Shear De? ection . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example 5-17 . . . . . . . . . . . . . . . . . . . . . . . . . . . Tables of Equations for Calculating Allowable Span Lengths for Wood Beams and Plywood Sheathing . . . . . . . . . . . . . . . . . . . . . . . . . Compression Stresses and Loads on Vertical Shores . . . . Example 5-18 . . . . . . . . . . . . . . . . . . . . . . . . . . Table for Allowable Loads on Wood Shores . . . . . . . Bearing Stresses Perpendicular to Grain ……… Design of Forms for a Concrete Wall . . . . . . . . . . . . . Lateral Pressure of Concrete on Forms . . . . . Plywood Sheathing to Resist Pressure from Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . Studs for Support of Plywood . . . . . . . . . . . . Wales for Support of Studs . . . . . . . . . . . . . . . Strength Required of Ties . . . . . . . . . . . . . . . . Design Summary of Forms for Concrete Wall . . . . Minimum Lateral Force for Design of Wall Form Bracing Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . Bracing for Wall Forms . . . . . . . . . . . . . . . . . . . . . . . . Example 5-19 . . . . . . . . . . . . . . . . . . . . . . . . . . . Example 5-20 . . . . . . . . . . . . . . . . . . . . . . . . . . . Design of Forms for a Concrete Slab . . . . . . . . . . . . . Loads on Slab Forms . . . . . . . . . . . . . . . . . . . . Plywood Decking to Resist Vertical Load . . . . Joists for Support of Plywood . . . . . . . . . . . . . Stringers for Support of Joists . . . . . . . . . . . . . Shores for Support of Stringers . . . . . . . . . . . Minimum Lateral Force for Design of Slab Form Bracing Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . Minimum Time for Forms and Supports to Remain in Place . . . . . . . . . . . . . . . . . . . . . . . . . . . . Minimum Safety Factors for Formwork Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Shores and Scaffolding . . . . . . . . . . . . . . . . . . . . . . . General Information . . . . . . . . . . . . . . . . . . . . . . . . . . . Shores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix 123 123 125 125 126 27 127 131 132 132 135 136 136 138 140 142 143 144 144 146 148 149 150 151 152 154 156 159 159 160 162 163 163 163 x Contents Wood Post Shores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Patented Shores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ellis Shores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Symons Shores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Site Preparation for Shoring . . . . . . . . . . . . . . . . . . . . Selecting the Size and Spacing of Shores . . . . . . . . . Tubular Steel Scaffolding Frames . . . . . . . . . . . . . . . Accessory Items for Tubular Scaffolding . . . . . . . . . Steel Tower Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . Safety Practices Using Tubular Scaffolding . . . . . . . Horizontal Shores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shoring Formwork for Multistory Structures . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Failures of Formwork . . . . . . . . . . . . . . . . . . . . . . . . . General Information . . . . . . . . . . . . . . . . . . . . . . . . . . . Causes of Failures of Formwork . . . . . . . . . . . . . . . . Forces Acting on Vertical Shores . . . . . . . . . . . . . . . Force Produced by Concrete Falling on a Deck . . . . Example 7-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . Motor-Driven Concrete Buggies . . . . . . . . . . . . . . . . Impact Produced by Motor-Driven Concrete Buggies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design of Formwork to Withstand Dynamic Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Examples of Failure of Formwork and Falsework . . . . Prevention of Formwork Failures . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Forms for Footings . . . . . . . . . . . . . . . . . . . . . . . . . . . General Information . . . . . . . . . . . . . . . . . . . . . . . . . . . Forms for Foundation Walls . . . . . . . . . . . . . . . . . . . . Example 8-1 ……………………… Procedure for Erection of Forms for Footings . . . . . Forms for Grade Beams . . . . . . . . . . . . . . . . . . . . . . . . Forms for Concrete Footings . . . . . . . . . . . . . . . . . . . . Additional Forms for Concrete Footings . . . . . . . . . Forms for Stepped Footings . . . . . . . . . . . . . . . . . . . . Forms for Sloped Footings . . . . . . . . . . . . . . . . . . . . Forms for Round Footings . . . . . . . . . . . . . . . . . . . . . Placing Anchor Bolts in Concrete Foundations . . . . Forms for Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General Information . . . . . . . . . . . . . . . . . . . . . . . . . . . De? nition of Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . Designing Forms for Concrete Walls . . . . . . . . . . . . . 165 166 166 168 170 170 174 177 177 179 180 182 183 185 185 185 186 187 189 190 191 193 193 194 195 197 197 197 198 202 204 204 205 207 208 208 210 211 211 212 213 8 9 Contents Physical Properties and Allowable Stresses for Lumber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Physical Properties and Allowable Stresses for Plyform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table of Equations for Calculating Allowable Span Lengths for Wood Beams and Plywood Sheathing . . . . . . . . . . . . . . . . . . . . . . . . . Design of Forms for a Concrete Wall . . . . . . . . . . . . . Lateral Pressure of Concrete on Forms . . . . . Plyform Sheathing to Resist Pressure from Concrete . . . . . . . . . . . . . . . . . . . . . . . . Summary of Allowable Span Lengths for the Sheathing . . . . . . . . . . . . . . . . . . . . . . . . . . Studs for Support of Plyform . . . . . . . . . . . . . Bearing Strength between Studs and Wale . . . . Size of Wale Based on Selected 24 in. Spacing of Studs . . . . . . . . . . . . . . . . . . . . . . Strength Required of Ties . . . . . . . . . . . . . . . . Results of the Design of the Forms for the Concrete Wall . . . . . . . . . . . . . . . . . . . . . . . . Tables to Design Wall Forms . . . . . . . . . . . . . . . . . . . . Calculating the Allowable Concrete Pressure on Plyform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Allowable Pressure Based on Fiber Stress in Bending . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Allowable Pressure Based on Bending De? ection . . . . Allowable Pressure Based on Shear Stress . . . . . . . . Allowable Pressure Based on Shear De? ection . . . . Maximum Spans for Lumber Framing Used to Support Plywood . . . . . . . . . . . . . . . . . . . . . . . . . . . Using Tables to Design Forms . . . . . . . . . . . . . . . . . . Forms for Walls with Batters . . . . . . . . . . . . . . . . . . . . Forms for Walls with Offsets . . . . . . . . . . . . . . . . . . . Forms for Walls with Corbels . . . . . . . . . . . . . . . . . . . Forms for Walls with Pilasters and Wall Corners . . . Forms for Walls with Counterforts . . . . . . . . . . . . . . Forms for Walls of Circular Tanks . . . . . . . . . . . . . . . Form Ties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Snap Ties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Coil Ties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Taper Ties …………………………….. Coil Loop Inserts for Bolt Anchors . . . . . . . . . . . . . . Prefabricated Wood Form Panels . . . . . . . . . . . . . . . . Commercial, or Proprietary, Form Panels . . . . . . . . . Gates Single-Waler Cam-Lock System . . . . . . . . . . xi 215 215 215 220 222 222 224 225 226 227 229 229 230 231 233 234 235 235 235 240 240 241 242 243 243 244 246 246 247 249 250 251 253 253 xii Contents Forms for Pilasters and Corners . . . . . . . . . . . . . . . . . Ellis Quick-Lock Forming System . . . . . . . . . . . . . . . Jahn System for Wall Forms . . . . . . . . . . . . . . . . . . . . Forms for a Concrete Wall Requiring a Ledge for Brick . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Forms for a Stepped Concrete Wall . . . . . . . . . . . . . . Modular Panel Systems ………………….. Hand Setting Modular Panels . . . . . . . . . . . . . . . . . Gang-Forming Applications . . . . . . . . . . . . . . . . . . . . Gang Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Forms for Curved Walls . . . . . . . . . . . . . . . . . . . . . . . . Jump Form System . . . . . . . . . . . . . . . . . . . . . . . . . . . . Self-Lifting Wall-Forming System . . . . . . . . . . . . . . . Insulating Concrete Forms . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Forms for Columns . . . . . . . . . . . . . . . . . . . . . . . . . . . General Information . . . . . . . . . . . . . . . . . . . . . . . . . . Pressure on Column Forms . . . . . . . . . . . . . . . . . . . . . Designing Forms for Square or Rectangular Columns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sheathing for Column Forms . . . . . . . . . . . . . . . . . . . Maximum Spacing of Column Clamps Using S4S Lumber Placed Vertical as Sheathing . . . . . . . . . . Example 10-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . Plywood Sheathing with Vertical Wood Battens for Column Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tables for Determining the Maximum Span Length of Plyform Sheathing . . . . . . . . . . . . . . . . Maximum Spacing of Column Clamps Using Plyform with Vertical Wood Battens . . . . . . . . . . . Example 10-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . Column Clamps for Column Forms . . . . . . . . . . . . . Design of Wood Yokes for Columns . . . . . . . . . . . . . Example 10-3 . . . . . . . . . . . . . . . . . . . . . . . . . . . Example 10-4 . . . . . . . . . . . . . . . . . . . . . . . . . . . Steel Column Clamps with Wedges . . . . . . . . . . . . . Example 10-5 . . . . . . . . . . . . . . . . . . . . . . . . . . . Concrete Column Forms with Patented Rotating Locking Device . . . . . . . . . . . . . . . . . . . . . . . . . . . . Column Forms Using Jahn Brackets and Cornerlocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Modular Panel Column Forms . . . . . . . . . . . . . . . . . . Adjustable Wraparound Column Forms . . . . . . . . . . All-Metal Forms for Rectangular Forms . . . . . . . . . . 255 257 260 269 269 269 272 272 274 276 278 280 281 282 283 283 283 284 286 286 287 288 290 292 293 296 296 298 299 300 301 303 305 306 308 308 Contents Fiber Tubes for Round Columns . . . . . . . . . . . . . . . . Steel Forms for Round Columns . . . . . . . . . . . . . . . . One-Piece Steel Round Column Forms . . . . . . . . . . Plastic Round Column Forms Assembled in Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Spring-Open Round Fiberglass Forms . . . . . . . . . . . One-Piece Round Fiberglass Column Forms . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Forms for Beams and Floor Slabs . . . . . . . . . . . . . . . Concrete Floor Slabs . . . . . . . . . . . . . . . . . . . . . . . . . . . Safety of Slab-Forming Systems . . . . . . . . . . . . . . . . . Loads on Concrete Slabs . . . . . . . . . . . . . . . . . . . . . . . De? nition of Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . Design of Forms for Concrete Slabs . . . . . . . . . . . . . . Spacing of Joists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example 11-1 …………………….. Use of Tables to Determine Maximum Spacing of Joists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Size and Span Length of Joists . . . . . . . . . . . . . . . . . . Example 11-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . Example 11-3 . . . . . . . . . . . . . . . . . . . . . . . . . . . Use of Tables to Determine the Maximum Spans for Lumber Framing Used to Support Plywood . . . Stringers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ledgers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Forms for Flat-Slab Concrete Floors . . . . . . . . . . . . . Forms for Concrete Beams . . . . . . . . . . . . . . . . . . . . . Spacing of Shores under Beam Bottoms . . . . . . . . . . Example 11-4 . . . . . . . . . . . . . . . . . . . . . . . . . . . Example 11-5 . . . . . . . . . . . . . . . . . . . . . . . . . . . Example 11-6 . . . . . . . . . . . . . . . . . . . . . . . . . . . Forms for Exterior Beams . . . . . . . . . . . . . . . . . . . . . Form Details for Beams Framing into Girders . . . . . Suspended Forms for Concrete Slabs . . . . . . . . . . . . Designing Forms for Concrete Slabs . . . . . . . . . . . . . Design of Formwork for Flat-Slab Concrete Floor with Joists and Stringers . . . . . . . . . . . . . . . . . . . . . Loads on Slab Forms . . . . . . . . . . . . . . . . . . . . Plywood Decking to Resist Vertical Load . . . Joists for Support of Plyform . . . . . . . . . . . . . Stringers for Support of Joists . . . . . . . . . . . . . Shores for Support of Stringers . . . . . . . . . . . Design Summary of Forms for Concrete Slab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311 312 314 315 316 317 318 319 319 320 320 321 322 322 324 325 327 330 331 332 337 338 338 340 341 341 343 346 348 349 350 351 353 354 354 356 358 360 361 xiii xiv Contents Minimum Lateral Force for Design of Slab Form–Bracing Systems . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Patented Forms for Concrete Floor Systems . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ceco Flangeforms ………………………. Adjustable Steel Forms . . . . . . . . . . . . . . . . . . . . . . . . Ceco Longforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ceco Steeldomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ceco Fiberglassdomes . . . . . . . . . . . . . . . . . . . . . . . . . Ceco Longdomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plastic Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Corrugated-Steel Forms ………………….. Cellular-Steel Floor Systems . . . . . . . . . . . . . . . . . . . . Selecting the Proper Panel Unit for Cellular-Steel Floor Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Horizontal Shoring ………………………

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Forms for Thin-Shell Roof Slabs . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Geometry of a Circle . . . . . . . . . . . . . . . . . . . . . . . . . . Example 13-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . Locating Points on a Circle . . . . . . . . . . . . . . . . . . . . . Elevations of Points on a Circular Arch . . . . . . . . . . Example 13-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . Forms for Circular Shell Roofs . . . . . . . . . . . . . . . . . Design of Forms and Centering for a Circular Shell Roof . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Space the Joists . . . . . . . . . . . . . . . . . . . . . . . . . Space the Ribs ……………………. Design the Ribs …………………… Determine the Load on the Shores …….. Determine the Elevations of the Top of the Decking ……………………. Determine the Slope of the Decking at the Outer Edges . . . . . . . . . . . . . . . . . . . . . . . . . Centering for Shell Roofs . . . . . . . . . . . . . . . . . . . . . . . Use of Trusses as Centering . . . . . . . . . . . . . . . . . . . Decentering and Form Removal . . . . . . . . . . . . . . . . Forms for Architectural Concrete . . . . . . . . . . . . . . . Forms for Architectural versus Structural Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concrete Coloring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363 364 365 365 365 366 367 369 370 370 371 373 373 374 375 379 381 381 381 382 383 385 386 386 387 387 388 388 390 391 391 391 392 394 395 395 396 13 14 Contents Stained Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stamped Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . Form Liners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sealing Form Liner Joints . . . . . . . . . . . . . . . . . . . . . . Smooth-Surfaced Concrete . . . . . . . . . . . . . . . . . . . . . Hardboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wetting and Oiling Forms . . . . . . . . . . . . . . . . . . . . . . Nails for Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Form Ties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Construction Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . Detailing Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Order of Erecting Forms for a Building . . . . . . . . . . . Order of Stripping Forms . . . . . . . . . . . . . . . . . . . . . . Wood Molds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plaster Waste Molds . . . . . . . . . . . . . . . . . . . . . . . . . . . Plastic Molds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Metal Molds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Forms for Corners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Forms for Parapets . . . . . . . . . . . . . . . . . . . . . . . . . . . . Forms for Roof Members . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Slipforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sheathing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wales or Ribs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Yokes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Working Platform . . . . . . . . . . . . . . . . . . . . . . . . . . . . Suspended Scaffolding . . . . . . . . . . . . . . . . . . . . . . . . Form Jacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Operation of Slipforms . . . . . . . . . . . . . . . . . . . . . . . . Constructing a Sandwich Wall . . . . . . . . . . . . . . . . . . Silos and Mills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tall Bridge Piers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Towers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concrete Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . Linings for Shafts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Slipforms for Special Structures . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Forms for Concrete Bridge Decks . . . . . . . . . . . . . . Wood Forms Suspended from Steel Beams . . . . . . . Example 16-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . Wood Forms for Deck Slab with Haunches . . . . . . . 396 397 397 399 399 399 400 400 400 401 402 402 405 405 406 408 408 410 411 411 413 415 415 415 418 418 418 419 419 419 422 422 423 424 425 426 428 429 430 431 431 431 437 v 16 xvi Contents Wood Forms for Deck Slab Suspended from Concrete Beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . Forms for Overhanging Deck Constructed on Exterior Bridge Beams . . . . . . . . . . . . . . . . . . . . . . . Deck Forms Supported by Steel Joists . . . . . . . . . . . . Example 16-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . Deck Forms Supported by Tubular Steel Scaffolding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Adjustable Steel Forms for Bridge Decks . . . . . . . . . All-Steel Forms for Bridge Structures . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Flying Deck Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Advantages of Flying Forms . . . . . . . . . . . . . . . . . . . . Form-Eze Flying Deck Forms . . . . . . . . . . . . . . . . . . . Versatility of Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . Patent Construction Systems . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Dimensional Tolerances for Concrete Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Guidelines for Safety Requirements for Shoring Concrete Formwork . . . . . . . . . . . . . . . . . . . . . . . . . . . OSHA Regulations for Formwork and Shoring Conversion of Units of Measure between U. S. Customary System and Metric System … 438 438 439 444 446 447 449 450 451 451 451 454 456 460 463 465 471 493 505 507 513 A B C D E …… Directory of Organizations and Companies Related to Formwork for Concrete . . . . . . . . . . . . . . Index …………………………………

Preface T his book is written for architects, engineers, and constructors who are responsible for designing and/or building formwork and temporary structures during the construction process. It is also designed to serve either as a textbook for a course in timber and formwork design or as a reference for systematic self-study of the subject. A new chapter on the design of wood members for formwork and temporary structures has been added to this edition. Numerous example problems have been added throughout the text to illustrate practical applications for calculating loads, stresses, and designing members.

New summary tables have been added to assist the reader in understanding the concepts and techniques of designing formwork and temporary structures. This fourth edition has been developed with the latest structural design recommendations by the National Design Specification (NDS 2005), published by the American Forest & Paper Association (AF&PA). In writing this edition, an effort has been made to conform to the intent of this reference document. The material presented is suggested as a guide only, and final responsibility lies with the designer of formwork and temporary structures.

Many patented systems and commercial accessories are available to increase the speed and safety of erecting formwork. Numerous figures and photographs are presented to introduce the reader to the available forming systems for walls, columns, beams, and slabs. Garold D. Oberlender xvii This page intentionally left blank Acknowledgments he author would like to thank the many manufacturers for permission to use the contents of their publications and technical information, and the many suppliers of formwork materials and accessories for providing illustrative material that is contained in this book.

Many individuals, agencies, and manufacturers have assisted the author in obtaining and presenting the information contained in this book. The author expresses his sincere thanks for this assistance. The author would like to thank Carisa Ramming for her careful review, helpful comments, and advice in the development of this fourth edition, in particular the new chapter on design of wood members for formwork. The author also wishes to recognize the late Robert L. Peurifoy for his pioneering work as an author and teacher of construction education.

Throughout the author’s career, Mr. Peurifoy was an inspiration as a role model, mentor, and colleague. Finally, the author greatly appreciates the patience and tolerance of his wife, Jana, and her understanding and support during the writing and editing phases of the fourth edition of this book. T xix This page intentionally left blank Abbreviations and Symbols A ACI b c cu ft cu yd d ? E F f fbm ft h I Ib/Q in. L l lb M NDS P p area American Concrete Institute width of a beam, in. distance from neutral axis of beam to extreme ? ber in bending, in. ubic feet cubic yard depth of a beam, in. de? ection of a member, in. modulus of elasticity, lb per sq in. allowable unit stress, lb per sq in. applied unit stress, lb per sq in. feet board measure, of lumber feet height of form, ft moment of inertia of a beam about its neutral axis, in. 4 rolling shear constant, in. 2 inches length of a beam or column, ft length of a beam or column, in. pounds bending moment of a beam, in. -lb National Design Speci? cation, for wood total concentrated load, lb unit pressure produced by concrete on forms, lb per sq ft xi xxii Abbreviations and Symbols PCA psf psi R S S4S sq ft sq in. T V v W w ? // Portland Cement Association pressure or weight, lb per sq ft stress, lb per sq in. rate of ? lling forms, ft per hour section modulus, in. 3 lumber that is surfaced on all four sides square feet square inches temperature, degrees Fahrenheit total external shear force on a beam, lb velocity, ft per sec total load uniformly distributed along a beam, lb uniformly distributed load, lb per lin ft denotes a perpendicular direction denotes a parallel direction

Formwork for Concrete Structures This page intentionally left blank CHAPTER 1 Introduction Purpose of This Book This book presents the principles and techniques for analysis and design of formwork for concrete structures. Because each structure is unique, the formwork must be designed and fabricated based on the specific requirements of each job. The level of effort required to produce a good formwork system is as important as the level of effort required to produce the right combination of steel and concrete for the structural system of the structure.

Formwork for concrete structures has a significant impact on the cost, time, and quality of the completed project. Formwork is important because it is a major cost of the concrete structure. Too often the designers of concrete structures devote considerable time in selecting the minimum amount of concrete and steel for a structure without devoting adequate attention to the impact of the formwork that must be constructed to form the concrete. For most structures, more time and cost are required to make, erect, and remove formwork than the time and cost to place the concrete or reinforcing steel.

For some structures, the cost of formwork exceeds the cost of the concrete and steel combined. This book presents the methods of analyses of various components of formwork, to assist the designer in developing a formwork system for his or her project. The purpose of formwork is to safely support the reinforced concrete until it has reached adequate strength. Thus, formwork is a temporary support for the permanent steel and concrete. The designer is responsible for producing a forming system that is safe, economical, and easily constructible at the jobsite.

The overall quality of the completed project is highly dependent on the formwork. Many articles and papers have been written related to the design, fabrication, erection, and failure of formwork. At the end of each chapter of this book, references of other publications are provided to assist the reader in better understanding the work that others have produced related to formwork. 1 2 Chapter One Safety of Formwork The failure of formwork is a major concern of all parties involved in a construction project; including the owner, the designer, and the contractor.

Although the principles, concepts, and methods that are contained in this book provide the basics for the analysis and design of formwork, it is the responsibility of each designer of formwork to ensure that the forms are designed adequately. This requires a careful analysis of the job conditions that exist at each jobsite, a determination of the loads that will be applied to the formwork, and the selection and arrangement of suitable forming materials that have adequate strength to sustain the loads. It is the responsibility of the workers at the jobsite to fabricate and erect the formwork in accordance with the design.

A careful check of the design and inspection of the work during construction are necessary to ensure the safety and reliability of the formwork. Safety is everyone’s responsibility, and all parties must work together as a team with safety as a major consideration. Economy of Formwork Economy should be considered when planning the formwork for a concrete structure. Economy involves many factors, including the cost of materials; the cost of labor in making, erecting, and removing the forms, and the cost of equipment required to handle the forms.

Economy also includes the number of reuses of the form materials, the possible salvage value of the forms for use elsewhere, and the cost of finishing concrete surfaces after the forms are removed. A high initial cost for materials, such as steel forms, may be good economy because of the greater number of uses that can be obtained with steel. An analysis of the proposed formwork for a given project usually will enable the job planner to determine, in advance of construction, what materials and methods will be the most economical. Allowable Unit Stresses in Formwork Material

In order to attain the maximum possible economy in formwork, it is desirable to use the highest practical unit stresses in designing forms. It is necessary to know the behavior of the pressures and loads that act on forms in determining the allowable unit stresses. When concrete is first placed, it exerts its maximum pressure or weight on the restraining or supporting forms. However, within a short time, sometimes less than 2 hours, the pressure on wall and column forms will reach a maximum value, and then it will decrease to zero.

Thus, the forms are subjected to maximum stresses for relatively short periods of time. Introduction Within a few hours after concrete is placed for girders, beams, and slabs, it begins to set and to bond with the reinforcing steel, thereby developing strength to support itself. Although the forms are usually left in place for several days, magnitudes of the unit stresses in the forms will gradually decrease as the concrete gains strength. Thus, the maximum unit stresses in the formwork are temporary and of shorter duration than the time the forms are left in place.

The allowable unit stresses specified for lumber are generally based on a full design load that is applied for a normal load duration of approximately 10 years. If the duration of the load is only a few hours or days, such as with formwork, the allowable unit stress may be adjusted to a higher value. For loads that are applied for a short duration, less than 7 days, the allowable unit stresses may be increased by 25%. The examples and tables contained in this book are based on using increased allowable unit stresses, assuming loads are applied for a short duration. Care of Forms Forms are made of materials that are subject to considerable damage through misuse and mishandling. Wood forms should be removed carefully, then cleaned, oiled, and stored under conditions that will prevent distortion and damage. At periodic intervals, all forms should be checked to determine whether renailing, strengthening, or replacing parts is necessary. Patented Products There are numerous patented products for concrete structures that have been produced by companies in the construction industry.

Many of these products are contained in this book. However, it is not practical to include all of the products that are currently available. Inclusion of the products of some manufacturers and the exclusion of similar products of others should not be interpreted as implying that the products included in this book are superior to those not mentioned. The products described in this book are intended to illustrate only the types of products available for use in concrete formwork.

For most of the products that are included in this book, the manufacturers’ specifications, properties, dimensions, and other useful information are given in tables. Arrangement of This Book There are 17 chapters in this book. The following paragraphs briefly describe each one. 4 Chapter One Chapter 1, Introduction, provides an introduction to this book, including its purpose, the importance of safety, and general information related to allowable stresses for form materials and patented products that are available for forming concrete structures.

Chapter 2, Economy of Formwork, provides information related to the importance of economy in formwork. Because formwork is a major cost of concrete structures, planning and designing the formwork system is an integral part of the process of designing and constructing concrete structures. There are decisions that must be made during the design process that will have major impacts on the construction process and the cost of the structure. Chapter 3, Pressure of Concrete on Formwork, presents information related to the pressure that concrete exerts on the formwork.

When concrete is placed in the forms, it applies vertical loads due to its weight as well as horizontal loads because it is in a liquid state and has not gained sufficient strength to support itself. In addition to the loads on the formwork from concrete and reinforcing steel, the designer must consider the live loads that are applied to the forms due to workers and equipment that are used to place the concrete. Chapter 4, Properties of Form Material, provides information related to the properties of form materials.

The principal materials used for forms include wood, steel, plywood, fiberglass, plastics, aluminum, and other materials. The designer must know the physical properties and the behavior of the materials that are used in building forming systems for concrete structures. Accessories used to attach the components of form materials are also an important part of formwork. The accessories used to fasten the form materials include nails, screws, bolts, form ties, column clamps, and other parts too numerous to mention.

Chapter 5, Design of Wood Members for Formwork, presents the fundamental concepts and equations that are used to design formwork and temporary structures during construction. The design of formwork involves determining the pressures and loads from the concrete placement during construction, analysis of the loads to determine the distribution of the loads through the formwork system, and selecting the sizes of members to sustain the loads adequately.

The formwork must be designed with sufficient strength to resist loads that are applied and to restrict the deflection of the forms within an allowable tolerance. Safety, economy, and quality must be major considerations in designing formwork. Chapter 6, Shores and Scaffolding, provides information related to shores and scaffolding for formwork. Patented shores are often used to support formwork. If patented shores are used, it is important that placement and spacing of the shores be in accordance with the manufacturer’s recommendations.

In some situations, shores are fabricated by workers at the jobsite. If job-built shores are used, it is important that a qualified person be involved in ensuring the safety of the shoring system because failure of shores is a common cause of Introduction formwork failure. Similarly, scaffolding is important for the safety of workers and their efficiency. Chapter 7, Failures of Formwork, addresses the important issue of the safety of formwork systems. Formwork failure is costly, in terms of both the physical losses at the jobsite and injuries to orkers. Physical losses include the loss of materials that are destroyed in the failure and the time and expenses that must be incurred to clean up and reinstall the forms. Injuries and loss of life of workers create suffering of people and can lead to costly legal actions. Chapter 8, Forms for Footings, provides information related to the design and construction of forms for footings and the fundamental equations that can be used in the design process. Information is also included for placing anchor bolts in concrete foundations.

Chapter 9, Forms for Walls, addresses the design of forms for concrete walls. Equations and tables are presented to facilitate the design of continuous walls and for walls with corbels. Due to the height of walls, the pressure at the bottom of the forms is significant. Therefore, the designer must carefully evaluate the loads that are applied to wall forms to ensure that the forms have sufficient strength to resist the applied load. Accessories for walls including snap ties, coil ties, and form clamps are also presented.

Chapter 10, Forms for Columns, addresses the design of forms for concrete columns. Included in this chapter are square, rectangular, round, and L-shaped columns. Column forms may be made of wood, steel, or fiberglass. Because columns are generally long in height, the pressure of the concrete at the bottom of the forms is an important consideration in the design of forms for concrete columns. Chapter 11, Forms for Beams and Floor Slabs, presents relevant information on that subject. The size, length, and spacing of joists are addressed considering the strength and deflection criteria.

Spacing of shores under beam bottoms and details for framing beams into girders are also presented. Chapter 12, Patented Forms for Concrete Floor Systems, is devoted to such patented forms. Patented forms are commonly used for floor systems because considerable savings in labor cost can be derived by simply erecting and removing standard forms, rather than fabricating forms at the jobsite. Chapter 13, Forms for Thin-Shell Roof Slabs, addresses thin-shell roof slabs. Roofing systems that consist of thin-shell reinforced concrete provide large clear spans below the roof with efficient use of concrete.

These types of roofs also produce aesthetically pleasing appearances for the exterior of the structures. Chapter 14, Forms for Architectural Concrete, considers architectural concrete. There are numerous techniques that can be applied to forms to produce a variety of finishes to the concrete surface after the forms are removed. For concrete buildings, the appearance of the completed structure is often a major consideration in the design of 5 6 Chapter One the structure. Forms for architectural concrete can apply to both the interior and the exterior of the building.

Chapter 15, Slipforms, addresses the slipform techniques that have been used successfully to form a variety of concrete structures. Slipforms can be applied to horizontal construction, such as highway pavements and curb-and-gutter construction, as well as to vertical construction of walls, columns, elevator shafts, and so on. Chapter 16, Forms for Concrete Bridge Decks, discusses the decking of bridges, which are continuously exposed to adverse weather conditions and direct contact with wheel loads from traffic.

The deck portion of bridges generally deteriorates and requires repair or replacement before the substructure or foundation portions of the bridges. Thus, there is significant time and cost devoted to formwork for bridge decking. Chapter 17, Flying Deck Forms, describes the use of flying forms for concrete structures. Flying forms is the descriptive name of a forming system that is removed and reused repetitively to construct multiple levels of a concrete structure. This system of formwork has been applied successfully to many structures.

Appendix A indicates dimensional tolerances for concrete structures that can be used by the workers at the jobsite to fabricate and erect forms that are acceptable. Appendix B provides recommended guidelines for shoring concrete formwork from the Scaffolding, Shoring, and Forming Institute. Appendix C presents information related to safety regulations that have been established by the United States Occupational Safety and Health Act (OSHA) of 2009. Appendix D provides a table of multipliers for converting from the U. S. customary system to metric units of measure.

Appendix E contains a directory of organizations and companies related to formwork. This directory contains addresses, phone numbers, fax numbers, and websites to assist the reader in seeking formworkrelated information. References 1. APA—The Engineered Wood Association, Concrete Forming, Tacoma, WA, 2004. 2. ACI Committee 347, American Concrete Institute, Guide to Formwork for Concrete, Detroit, MI, 2004. 3. ANSI/AF&PA NDS-2005, American Forest & Paper Association, National Design Specification for Wood Construction, Washington, DC, 2005. 4.

Design Values for Wood Construction, Supplement to the National Design Specification, National Forest Products Association, Washington, DC, 2005. 5. U. S. Department of Labor, Occupational Safety and Health Standards for the Construction Industry, Part 1926, Subpart Q: Concrete and Masonry Construction, Washington, DC, 2010. 6. American Institute of Timber Construction, Timber Construction Manual, 5th ed. , John Wiley & Sons, New York, 2005. CHAPTER 2 Economy of Formwork Background Information Formwork is the single largest cost component of a concrete building’s structural frame.

The cost of formwork exceeds the cost of the concrete or steel, and, in some situations, the formwork costs more than the concrete and steel combined. For some structures, placing priority on the formwork design for a project can reduce the total frame costs by as much as 25%. This saving includes both direct and indirect costs. Formwork efficiencies accelerate the construction schedule, which can result in reduced interest costs during construction and early occupancy for the structure. Other benefits of formwork efficiency include increased jobsite productivity, improved safety, and reduced potential for errors.

Impact of Structural Design on Formwork Costs In the design of concrete structures, the common approach is to select the minimum size of structural members and the least amount of steel to sustain the design loads. The perception is “the least amount of permanent materials in the structure will result in the least cost. ” To achieve the most economical design, the designer typically will analyze each individual member to make certain that it is not heavier, wider, or deeper than its load requires. This is done under the pretense that the minimum size and least weight result in the best design.

However, this approach to design neglects the impact of the cost of formwork, the temporary support structure that must be fabricated and installed to support the permanent materials. Focusing only on ways to economize on permanent materials, with little or no consideration of the temporary formwork, can actually increase, rather than decrease the total cost of a structure. To concentrate solely on permanent material reduction does not consider the significant cost of the formwork, which often ranges 7 8 Chapter Two from one-third to one-half of the total installed cost of concrete structures.

The most economical design must consider the total process, including material, time, labor, and equipment required to fabricate, erect, and remove formwork as well as the permanent materials of concrete and steel. Table 2-1 illustrates the impact of structural design on the total cost for a hypothetical building in which the priority was permanent material economy. The information contained in this illustration is an excerpt from Concrete Buildings, New Formwork Perspectives [1]. For Design A, permanent materials are considered to be concrete and reinforcing steel.

The total concrete structural frame cost is $10. 35 per square ft. For Design B, the same project is redesigned to accelerate the entire construction process by sizing structural members that are compatible with the standard size dimensions of lumber, which allows for easier fabrication of forms. The emphasis is shifted to constructability, rather than permanent materials savings. The time has been reduced, with a resultant reduction in the labor cost required to fabricate, erect, and remove the forms. Note that for Design B the cost of permanent materials has actually increased, compared to he cost of permanent materials required for Design A. However, the increase in permanent materials has been more than offset by the impact of constructability, that is, how easy it is to build the structure. The result is lowering the cost from $10. 35 per square ft to $9. 00 per square ft, a 13% savings in cost. Cost Item Formwork Temporary material, labor, and equipment to make, erect, and remove forms Concrete Permanent material and labor for placing and finishing concrete Reinforcing steel Materials, accessories, and labor for installation of reinforcing steel Total cost TABLE 2-1

Emphasis on Emphasis on Permanent Constructability, Material, Design A Design B $5. 25/ft2 51% $3. 50/ft2 39% Percent Increase (Decrease) (33) $2. 85/ft2 27% $3. 00/ft2 33% 5 $2. 25/ft2 22% $2. 50/ft2 28% 11 $10. 35/ft2 100% $9. 00/ft2 Concrete Structural Frame Cost 100% (13) Economy of Formwork 9 Suggestions for Design Economy of concrete structures begins in the design development stage with designers who have a good understanding of formwork logic. Often, two or more structural alternatives will meet the design objective equally well.

However, one alternative may be significantly less expensive to build. Constructability, that is, making structural frames faster, simpler, and less costly to build, must begin in the earliest phase of the design effort. Economy in formwork begins with the design of a structure and continues through the selection of form materials, erection, stripping, care of forms between reuses, and reuse of forms, if any. When a building is designed, consideration should be given to each of the following methods of reducing the cost of formwork: 1.

Prepare the structural and architectural designs simultaneously. If this is done, the maximum possible economy in formwork can be ensured without sacrificing the structural and architectural needs of the building. 2. At the time a structure is designed, consider the materials and methods that will be required to make, erect, and remove the forms. A person or computer-aided drafting and design (CADD) operator can easily draw complicated surfaces, connections between structural members, and other details; however, making, erecting, and removing the formwork may be expensive. 3.

If patented forms are to be used, design the structural members to comply with the standard dimensions of the forms that will be supplied by the particular form supplier who will furnish the forms for the job. 4. Use the same size of columns from the foundation to the roof, or, if this is impracticable, retain the same size for several floors. Adopting this practice will permit the use of beam and column forms without alteration. 5. Space columns uniformly throughout the building as much as possible or practicable. If this is not practicable, retaining the same position from floor to floor will result in economy. . Where possible, locate the columns so that the distances between adjacent faces will be multiples of 4 ft plus 1 in. , to permit the unaltered use of 4-ft-wide sheets of plywood for slab decking. 7. Specify the same widths for columns and column-supported girders to reduce or eliminate the cutting and fitting of girder forms into column forms. 8. Specify beams of the same depth and spacing on each floor by choosing a depth that will permit the use of standard sizes 10 Chapter Two of lumber, without ripping, for beam sides and bottoms, and for other structural members.

It is obvious that a concrete structure is designed to serve specific purposes, that is, to resist loads and deformations that will be applied to the structure, and to provide an appearance that is aesthetically pleasing. However, for such a structure, it frequently is possible to modify the design slightly to achieve economy without impairing the usability of the structure. The designer can integrate constructability into the project by allowing three basic concepts: design repetition, dimensional standards, and dimensional consistency.

Examples of these concepts, excerpted from ref. [1], are presented in this chapter to illustrate how economy in formwork may be affected. Design Repetition Any type of work is more efficient if it is performed on a repetitive basis. Assembly line work in the automobile manufacturing industry is a good example of achieving efficiency and economy by repetition. This same concept can be applied to the structural design of concrete structures. Repeating the same layout from bay to bay on each floor provides repetition for the workers.

Similarly, repeating the same layout from floor to floor from the lower floor levels to the roof provides repetition that can result in savings in form materials and in efficiency of the labor needed to erect and remove forms. Dimensional Standards Materials used for formwork, especially lumber and related wood products such as plywood, are available in standard sizes and lengths. Significant cost savings can be achieved during design if the designer selects the dimensions of concrete members that match the standard nominal dimensions of the lumber that will be used to form the concrete.

Designs that depart from standard lumber dimensions require costly carpentry time to saw, cut, and piece the lumber together. During the design, a careful selection of the dimensions of members permits the use of standard sizes of lumber without ripping or cutting, which can greatly reduce the cost of forms. For example, specifying a beam 11. 25 in. wide, instead of 12. 0 in. wide, permits the use of a 2- by 12-in. S4S board, laid flat, for the soffit. Similarly, specifying a beam 14. 5 in. wide, instead of 14 in. wide, permits the use of two 2- by 8-in. boards, each of which is actually 7. 25 in. wide.

Any necessary compensation in the strength of the beam resulting from a change in the dimensions may be made by modifying the quantity of the reinforcing steel, or possibly by modifying the depth of the beam. Economy of Formwork 11 Dimensional Consistency For concrete structures, consistency and simplicity yield savings, whereas complexity increases cost. Specific examples of opportunities to simplify include maintaining constant depth of horizontal construction, maintaining constant spacing of beams and joists, maintaining constant column dimensions from floor to floor, and maintaining constant story heights.

Repetitive depth of horizontal construction is a major cost consideration. By standardizing joist size and varying the width, not depth, of beams, most requirements can be met at lower cost because forms can be reused for all floors, including roofs. Similarly, it is usually more cost efficient to increase the concrete strength or the amount of reinforcing material to accommodate differing loads than to vary the size of the structural member. Roofs are a good example of this principle. Although roof loads are typically lighter than floor loads, it is usually more cost effective to use the same joist sizes for the roof as on the floors below.

Changing joist depths or beam and column sizes might achieve minor savings in materials, but it is likely that these will be more than offset by higher labor costs of providing a different set of forms for the roof than required for the slab. Specifying a uniform depth will achieve major savings in forming costs, therefore reducing the total building costs. This will also allow for future expansion at minimal cost. Additional levels can be built after completion if the roof has the same structural capabilities as the floor below.

This approach does not require the designer to assume the role of a formwork planner nor restricts the structural design to formwork considerations. Its basic premise is merely that a practical awareness of formwork costs may help the designer to take advantage of less expensive structural alternatives that are equally appropriate in terms of the aesthetics, structural integrity, quality, and function of the building. In essence, the designer needs only to visualize the forms and the field labor required to form various structural members and to be aware of the direct proportion between complexity and cost.

Of all structure costs, floor framing is usually the largest component. Similarly, the majority of a structure’s formwork cost is usually associated with horizontal elements. Consequently, the first priority in designing for economy is selecting the structural system that offers the lowest overall cost while meeting load requirements. Economy of Formwork and Sizes of Concrete Columns Architects and engineers sometimes follow a practice of reducing the dimensions of columns every two floors for multistory buildings, as the total loads will permit.

Although this practice permits reduction 12 Chapter Two in the quantity of concrete required for columns, it may not reduce the cost of a structure; actually, it may increase the cost. Often, the large column size from the lower floors can be used for the upper floors with a reduction in the amount of the reinforcing steel in the upper floor columns, provided code requirements for strength are maintained. Significant savings in labor and form materials can be achieved by reusing column forms from lower to upper floors.

If a change in the column size is necessary, increasing one dimension at a time is more efficient. The column strategy of the structural engineer has a significant impact on formwork efficiency and column cost. By selecting fewer changes in column size, significant savings in the cost of column formwork can be achieved. Fewer changes in sizes can be accomplished by adjusting the strength of the concrete or the reinforcing steel, or both. For example, to accommodate an increase in load, increasing concrete strength or the reinforcing steel is preferable to increasing column size.

Columns that are placed in an orientation that departs from an established orientation cause major formwork disruptions at their intersections with the horizontal framing. For example, a column that is skewed 30° in orientation from other structural members in a building will greatly increase the labor required to form the skewed column into adjacent members. A uniform, symmetrical column pattern facilitates the use of high-productivity systems, such as gang or flying forms for the floor structural system. Scattered and irregular positioning of columns may eliminate the possibility of using these costeffective systems.

Even with conventional hand-set forming systems, a uniform column layout accelerates construction. The option to use modern, highly productive floor forming systems, such as flying forms or panelization, may not be feasible for certain column designs. The designer should consider adjacent structural members as a part of column layout and sizing. Column capitals, especially if tapered, require additional labor and materials. The best approach is to avoid column capitals altogether by increasing reinforcement within the floor slab above the column.

If this is not feasible, rectangular drop panels, with drops equivalent to the lumber dimensions located above columns, serve the same structural purpose as capitals, but at far lower total costs. Beam and Column Intersections The intersections of beams and columns require consideration of both horizontal and vertical elements simultaneously. When the widths of beams and columns are the same, maximum cost efficiency is attained because beam framing can proceed along a continuous line. When beams are wider than columns, beam bottom forms must be notched Economy of Formwork to fit around column tops.

Wide columns with narrow beams are the most expensive intersections to form by far because beam forms must be widened to column width at each intersection. 13 Economy in Formwork and Sizes of Concrete Beams Cost savings can be accomplished by selecting beam widths that are compatible with the standard sizes of dimension lumber. Consider a concrete beam 18 ft long with a stem size below the concrete slab that is 16 in. deep and 14 in. wide. If 2-in. -thick lumber is used for the soffit or beam bottom, it will be necessary to rip one of the boards in order to provide a soffit that has the necessary 14. in. width. However, if the width of the beam is increased to 14. 5 in. , two pieces of lumber, each having a net width of 7. 25 in. , can be used without ripping. Thus, two 2- by 8-in. boards will provide the exact 14. 5 in. width required for the soffit. The increase in beam width from 14. 0 to 14. 5 in. — an additional 0. 5 in. —will require a small increase in the volume of concrete as shown in the following equation: Additional concrete = [(16 in. ? 0. 5 in. )/(144 in. 2/ft2 )] ? [18 ft] = 1. 0 cu ft Because there are 27 cu ft per cu yard, dividing the 1. 0 cu ft by 27 reveals that 0. 37 cu yards of additional concrete are required if the beam width is increased by 0. 5 in. , from 14. 0 to 14. 5 in. If the cost of concrete is $95. 00 per cu yard, the increased concrete cost will be only $3. 52. The cost for a carpenter to rip a board 18 ft long will likely be significantly higher than the additional cost of the concrete. Also, when the project is finished, and the form lumber is salvaged, a board having its original or standard width will probably be more valuable than one that has been reduced in width by ripping. There are numerous other examples of economy of formwork based on sizes of form material.

For example, a 15. 75-in. rip on a 4-ftwide by 8-ft-long plywood panel gives three usable pieces that are 8 ft long with less than 1 in. of waste. A 14-in. rip leaves a piece 6 in. wide by 8 ft long, which has little value for other uses. With 6 in. of waste for each plywood panel, essentially every ninth sheet of plywood is thrown away. This is an area in which architects and engineers can improve the economy in designing concrete structures. Designs that are made primarily to reduce the quantity of concrete, without considering the effect on other costs, may produce an increase rather than a decrease in the ultimate cost of a structure.

Additional savings, similar to the preceding example, can be achieved by carefully evaluating the dimension lumber required to form beam and column details. 14 Chapter Two Economy in Making, Erecting, and Stripping Forms The cost of forms includes three items: materials, labor, and the use of equipment required to fabricate and handle the forms. Any practice that will reduce the combined cost of all these items will save money. With the cost of concrete fairly well fixed through the purchase of ready-mixed concrete, little, if any, saving can be affected here.

It is in the formwork that real economy can be achieved. Because forms frequently involve complicated forces, they should be designed by using the methods required for other engineering structures. Guessing can be dangerous and expensive. If forms are over-designed, they will be unnecessarily expensive, whereas if they are under-designed, they may fail, which also can be very expensive. Methods of effecting economy in formwork include the following: 1. Design the forms to provide the required strength with the smallest amount of materials and the most number of reuses. 2.

Do not specify or require a high-quality finish on concrete surfaces that will not be exposed to view by the public, such as the inside face of parapet, walls or walls and beams in service stairs. 3. When planning forms, consider the sequence and methods of stripping them. 4. Use prefabricated panels where it is possible to do so. 5. Use the largest practical prefabricated panels that can be handled by the workers or equipment on the job. 6. Prefabricate form members (not limited to panels) where possible. This will require planning, drawings, and detailing, but it will save money. . Consider using patented form panels and other patented members, which frequently are less expensive than forms built entirely on the job. 8. Develop standardized methods of making, erecting, and stripping forms to the maximum possible extent. Once carpenters learn these methods, they can work faster. 9. When prefabricated panels and other members, such as those for foundations, columns, walls, and decking, are to be reused several times, mark or number them clearly for identification purposes. 10. Use double-headed nails for temporary connections to facilitate their removal. 11.

Clean, oil, and renail form panels, if necessary, between reuses. Store them carefully to prevent distortion and damage. Economy of Formwork 12. Use long lengths of lumber without cutting for walls, braces, stringers, and other purposes where their extending beyond the work is not objectionable. For example, there usually is no objection to letting studs extend above the sheathing on wall forms. 13. Strip forms as soon as it is safe and possible to do so if they are to be reused on the structure, in order to provide the maximum number of reuses. 14. Create a cost-of-materials consciousness among the carpenters who make forms.

At least one contractor displayed short boards around his project on which the cost was prominently displayed. 15. Conduct jobsite analyses and studies to evaluate the fabrication, erection, and removal of formwork. Such studies may reveal methods of increasing productivity rates and reducing costs. 15 Removal of Forms Forms should be removed as soon as possible to provide the greatest number of uses but not until the concrete has attained sufficient strength to ensure structural stability and to carry both the dead load and any construction loads that may be imposed on it.

The engineer-architect should specify the minimum strength required of the concrete before removal of forms or supports because the strength required for the removal of forms can vary widely with job conditions. The minimum time for stripping forms and removal of supporting shores is a function of concrete strength, which should be specified by the engineering/architect. The preferred method of determining stripping time is using tests of job-cured cylinders or tests on concrete in place. The American Concrete Institute ACI Committee 347 [2] provides recommendations for removing forms and shores.

The length of time that forms should remain in place before removal should be in compliance with local codes and the engineer who has approved the shore and form removal based on strength and other considerations unique to the job. The Occupational Health and Safety Administration (OSHA) has published standard 1926. 703(e) for the construction industry, which recommends that forms and shores not be removed until the employer determines that the concrete has gained sufficient strength to support its weight and superimposed loads.

Such determination is based on compliance with one of the following: (1) the plans and specifications stipulate conditions for removal of forms and shores and such conditions have been followed, or (2) the concrete has 16 Chapter Two been properly tested with an appropriate American Society for Testing and Materials (ASTM) standard test method designed to indicate the compression strength of the concrete, and the test results indicate that the concrete has gained sufficient strength to support its weight and superimposed loads.

In general, forms for vertical members, such as columns and piers, may be removed earlier than horizontal forms, such as beams and slabs. ACI Committee 347 suggests the following minimum times forms and supports should remain in place under ordinary conditions. Forms for columns, walls, and the sides of beams often may be removed in 12 hours. Removal of forms for joists, beams, or girder soffits depends on the clear spans between structural supports. For example, spans under 10 ft usually require 4 to 7 days, spans of 10 to 20 ft require 7 to 14 days, and spans over 20 ft generally require 14 to 21 days.

Removing forms for one-way floor slabs also will depend on clear spans between structural supports. Spans under 10 ft usually require 3 to 4 days, spans 10 to 20 ft usually require 4 to 7 days, and spans over 20 ft require 7 to 10 days. Building Construction and Economy Careful planning in scheduling the construction operations for a building and in providing the forms can assure the maximum economy in formwork and also the highest efficiency by labor, both of which will reduce the cost of formwork. Consider the six-story building in Figure 2-1, to be constructed with concrete columns, girders, beams, and slabs.

The floor area is large enough to justify dividing the floor into two equal or approximately equal areas for forms and concreting. A construction joint through the building is specified or will be permitted. If the structure is symmetrical about the construction joint, the builder will be fortunate. If the building is not symmetrical about the construction joint, some modifications will have to be made in the form procedures presented hereafter. Each floor will be divided into equal units for construction purposes. Thus, there will be 12 units in the building.

One unit will be completely constructed each week, weather permitting, which will include making and erecting the forms; placing the reinforcing steel, electrical conduit, plumbing items, etc. , and pouring the concrete. The carpenters should complete the formwork for unit 1 by the end of the third day, after which time some of them will begin the formwork for unit 2 while others install braces on the shores and other braces, if they are required, and check; if necessary, the carpenters will adjust the elevations of girder, beam, and deck forms.

One or two carpenters should remain on unit 1 while the concrete is being placed. This will consume one week. Economy of Formwork 17 FIGURE 2-1 Construction schedule for concrete frame of building. During the second week, and each week thereafter, a unit will be completed. Delays owing to weather may alter the timing but not the schedule or sequence of operations. Figure 2-1 shows a simplified section through this building with the units and elapsed time indicated but with no provision for lost time owing to weather.

Forms for columns and beam and girder sides must be left in place for at least 48 hours, whereas forms for the beam and girder bottoms, floor slab, and vertical shores must be left in place for at least 18 days. However, concrete test cylinders may be broken to determine the possibility of a shorter removal time of shores. Formwork will be transferred from one unit to another as quickly as time requirements and similarity of structural members will permit.

Table 2-2 will assist in determining the number of reuses of form units and total form materials required to construct the building illustrated in Figure 2-1. Although the extent to which given form sections can be reused will vary for different buildings, the method of analyzing reusage presented in this table can be applied to any building and to many concrete structures. If the schedule shown in Table 2-2 will apply, it will be necessary to provide the following numbers of sets of forms: for columns and beam and girder sides, two sets and for beam bottoms, slab decking, and shores, three sets. 8 Chapter Two Units 1 Total Elapsed Time at Start of Unit, Week 0 Forms for Columns Beam sides Beam bottoms Slab decking Shores Columns Beam sides Beam bottoms Slab decking Shores Columns Beam sides Beam bottoms Slab decking Shores Columns Beam sides Beam bottoms Slab decking Shores Columns Beam sides Beam bottoms Slab decking Shores Columns Beam sides Beam bottoms Slab decking Shores Columns Beam sides Beam bottoms Slab decking Shores Columns Beam sides Beam bottoms Slab decking Shores

Source of Forms New material New material New material New material New material New material New material New material New material New material Unit 1 Unit 1 New material New material New material Unit 2 Unit 2 Unit 1 Unit 1 Unit 1 Unit 3 Unit 3 Unit 2 Unit 2 Unit 2 Unit 4 Unit 4 Unit 3 Unit 3 Unit 3 Unit 5 Unit 5 Unit 4 Unit 4 Unit 4 Unit 6 Unit 6 Unit 5 Unit 5 Unit 5 2 1 3 2 4 3 5 4 6 5 7 6 8 7 TABLE 2-2 Schedule of Use and Reuse of Formwork for a Building Economy of Formwork 19 Units 9 Total Elapsed Time at Start of Unit, Week 8

Forms for Columns Beam sides Beam bottoms Slab decking Shores Columns Beam sides Beam bottoms Slab decking Shores Columns Beam sides Beam bottoms Slab decking Shores Columns Beam sides Beam bottoms Slab decking Shores Source of Forms Unit 7 Unit 7 Unit 6 Unit 6 Unit 6 Unit 8 Unit 8 Unit 7 Unit 7 Unit 7 Unit 9 Unit 9 Unit 8 Unit 8 Unit 8 Unit 10 Unit 10 Unit 9 Unit 9 Unit 9 10 9 11 10 12 11 TABLE 2-2 Schedule of Use and Reuse of Formwork for a Building (Continued ) If structural sections such as columns, girders, beams, and floor panels in odd-numbered units 1 through 11 are similar, and those in the even-numbered nits 2 through 12 are similar, but those in units 1 through 11 are not similar to those in units 2 through 12, it will be necessary to move form sections to higher floors above given units. For example, forms for unit 1 cannot be used in unit 2, or those from unit 3 in unit 4, and so on. Under this condition, it will be necessary to provide one set of columns and beam and girder sides for unit 1 and another set for unit 2, which will be sufficient for the entire building.

It will be necessary to provide a set of forms for the beam and girder bottoms, slab decking, and shores for unit 1 and another one for unit 3, and similarly for units 2 and 4. Economy in Formwork and Overall Economy The specifications for some projects require smooth concrete surfaces. For such projects, it may be good economy to use form liners, such as thin plywood, tempered hardboard, or sheet steel. Although the cost of the forms will be increased, reduction in the cost of finishing the surfaces will be reduced or eliminated. The small fins that sometimes 0 Chapter Two appear on concrete surfaces opposite the joints in the sheets of lining material can be reduced or eliminated by sealing the joints with putty or some other suitable compound prior to placing the concrete. Numerous papers have described materials and methods of construction for forming economical concrete buildings. The American Concrete Institute, the Portland Cement Association, and other organizations involved in concrete structures have sponsored international conferences on forming economical concrete buildings.

The proceedings of these conferences have been published and are available from these institutions as shown in the references at the end of this chapter. References 1. Ceco Concrete Construction Co. , Concrete Buildings, New Formwork Perspectives, Kansas City, MO, 1985. 2. ACI Committee 347, American Concrete Institute, Guide to Formwork for Concrete, Detroit, MI, 2004. 3. “Forming Economical Concrete Buildings,” Proceedings of the First International Conference, Portland Cement Association, Skokie, IL, 1984. 4. Forming Economical Concrete Buildings,” Proceedings of the Second International Conference, Publication SP-90, American Concrete Institute, Detroit, MI, 1986. 5. “Forming Economical Concrete Buildings,” Proceedings of the Third International Conference, Publication SP-107, American Concrete Institute, Detroit, MI, 1988. 6. US Department of Labor, Occupational Safety and Health Standards for the Construction Industry, Part 1926, Subpart Q: Concrete and Masonry Construction, Washington, DC, 2010. CHAPTER 3 Pressure of Concrete on Formwork Behavior of Concrete

Concrete is a mixture of sand and aggregate that is bonded together by a paste of cement and water. The five basic types of cement used in concrete mixtures are Type I—Ordinary portland cement Type II—Modi? ed low heat, modi? ed sulfate resistance Type III—Early high strength, rapid hardening Type IV—Low heat of hydration Type V—Sulfate resisting Admixtures are commonly used in concrete mixes. Additives include liquids, solids, powders, or chemicals that are added to a concrete mix to change properties of the basic concrete mixture of water, cement, sand, and aggregate.

They can accelerate or retard setting times, decrease water permeability, or increase strength, air content, and workability. Admixtures include pozzolans such as silica flume, blast-furnace slag, and fly ash. The pressure of concrete on formwork depends on the type of cement and admixtures in the concrete mix. When concrete is first mixed, it has properties lying between a liquid and a solid substance. It is best described as a semiliquid and is usually defined as a plastic material. With the passage of time, concrete loses its plasticity and changes into a solid.

This property of changing from a plastic to a solid makes concrete a valuable building material because it can be easily shaped by forms before attaining its final state. The ability to change from a semiliquid (or plastic) to a solid state appears to be the result of two actions within the concrete. The former 21 22 Chapter Three Compressive strength, psi Compressive strength, psi 5000 Air-entrained concrete 6000 Non-air-entrained concrete 4000 28 day 28 day 3000 4000 5000 3000 2000 7 2000 3 1000 1000 1 0 0. 4 0 0. 5 0. 6 0. 4 0. 5 0. 6 0. Water-cement ratio, by weight Water-cement ratio, by weight 1 3 7 FIGURE 3-1 Relationship between age and compressive strength of concrete for Type I portland cement. Notes: (1) Courtesy, Portland Cement Association. (2) Data based on compressive tests of 6- by 12-in. cylinders using Type I portland cement and moist-curing at 70°F. action is the result of the setting of the cement, which may begin within 30 min after the concrete, is mixed under favorable conditions, namely, a warm temperature. This action may continue for several hours, especially if the temperature is low.

The latter action is the development of internal friction between the particles of aggregate in the concrete that restrains them from moving freely past each other. The magnitude of the internal friction is higher in a dry concrete than in a wet one, and it increases with the loss of water from a concrete. Figure 3-1 gives illustrative relationships for age-compressive strength of laboratory cured air-entrained and non–air-entrained concrete with different water-cement ratios using Type I portland cement, when the concrete is moist cured at 70°F.

Lateral Pressure of Concrete on Formwork The pressure exerted by concrete on formwork is determined primarily by several or all of the following factors: 1. Rate of placing concrete in forms 2. Temperature of concrete Pressure of Concrete on Formwork 3. Weight or density of concrete 4. Cement type or blend used in the concrete 5. Method of consolidating the concrete 6. Method of placement of the concrete 7. Depth of placement 8. Height of form The American Concrete Institute [1] has devoted considerable time and study to form design and construction practices.

ACI Committee 347 identifies the maximum pressure on formwork as the full hydrostatic lateral pressure, as given by the following equation: Pm = wh where Pm = maximum lateral pressure, lb per sq ft w = unit weight of newly placed concrete, lb per cu ft h = depth of the plastic concrete, ft For concrete that is placed rapidly, such as columns, h should be taken as the full height of the form. There are no minimum values given for the pressures calculated from Eq. (3-1). (3-1) 23 Lateral Pressure of Concrete on Wall Forms

For determining pressure of concrete on formwork ACI 347 defines a wall as a vertical structural member with at least one plan dimension greater than 6. 5 ft. Two equations are provided for wall form pressure. Equation (3-2) applies to walls with a rate of placement less than 7 ft per hr and a placement height of 14 ft or less. Equation (3-3) applies to all walls with a placement rate of 7 to 15 ft per hr, and to walls placed at less than 7 ft per hr but having a placement height greater than 14 ft. Both equations apply to concrete with a 7 in. aximum slump, and vibration limited to normal internal vibration to a depth of 4 ft or less. For walls with a rate of placement greater than 15 ft per hr, or when forms will be filled rapidly, before stiffening of the concrete takes place, then the pressure should be taken as the full height of the form, Pm = wh. For wall forms with a concrete placement rate of less than 7 ft per hr and a placement height not exceeding 14 ft: Pm = CwCc[150 + 9,000R/T] where Pm = maximum lateral pressure, lb per sq ft Cw = unit weight coefficient as shown in Table 3-1 Cc = chemistry coefficient as shown in Table 3-2 R = rate of fill of concrete n form, ft per hr (3-2) 24 Chapter Three T = temperature of concrete in form, degrees Fahrenheit Minimum value of Pm is 600Cw, but in no case greater than wh. Applies to concrete with a slump of 7 in. or less Applies to normal internal vibration to a depth of 4 ft or less For all wall forms with concrete placement rate from 7 to 15 ft per hr, and for walls where the placement rate is less than 7 ft per hr and the placement height exceeds 14 ft. Pm = CwCc[150 + 43,400/T + 2,800 R/T] (3-3) here Pm = maximum lateral pressure, lb per sq ft Cw = unit weight coefficient Cc = chemistry coefficient R = rate of fill of concrete in form, ft per hr T = temperature of concrete in form, °F Minimum value of Pm is 600Cw, but in no case greater than wh. Applies to concrete with a slump of 7 in. or less Applies to normal internal vibration to a depth of 4 ft or less Values for the unit weight coefficient Cw in Eqs. (3-2) and (3-3) are shown in Table 3-1 and the values for the chemistry coefficient Cc are shown in Table 3-2.

For concrete placed in wall forms at rates of pour greater than 15 ft per hr, the lateral pressure should be wh, where h is the full height of the form. ACI Committee 347 recommends that the form be designed for a full hydrostatic head of concrete wh plus a minimum allowance of 25% for pump surge pressure if concrete is pumped from the base of the form. Example 3-1 A wall form 12 ft high is filled with 150 lb per cu ft concrete at a temperature of 70°F. The concrete is Type I without a retarder.

Concrete will be placed with normal internal vibration to a depth of less than 4 ft. The rate of placement is 5 ft per hr. From Table 3-1, the value of Cw is 1. 0 and from Table 3-2 the value of Cc is 1. 0. The rate of placement is less than 7 ft per hr and the placement height does not exceed 14 ft, therefore Eq. (3-2) can be used to calculate the lateral pressure as follows. Pm = CwCc[150 + 9,000R/T] Pm = CwCc[150 + 9,000R/T] = (1. 0)(1. 0)[150 + 9,000(5/70)] = 793 lb per sq ft Pressure of Concrete on Formwork 25

Weight of Concrete Less than 140 lb per cu ft 140 to 150 lb per cu ft More than 150 lb per cu ft TABLE 3-1 Value of Cw 0. 5 [1 + (w/145 lb per cu ft)], but not less than 0. 8 1. 0 w/145 lb per cu ft Values of Unit Weight Coefficient, Cw Cement Type or Blend Types I, II, and III without retarders? Types I, II, and III with a retarder Other types or blends containing less than 70% slag or 40% fly ash without retarders? Other types or blends containing less than 70% slag or 40% fly ash with a retarder? Blends containing more than 70% slag or 40% fly ash ? Value of Cc 1. 1. 2 1. 2 1. 4 1. 4 Retarders include any admixture, such as a retarder, retarding water reducer, retarding mid-range water-reducing admixtures, or high-range water-reducing admixture (superplasticizers), that delay setting of concrete. TABLE 3-2 Values of Chemistry Coefficient, Cc Checks on limitations on pressures calculated from Eq. (3-2): Limited to greater than 600Cw = 600(1. 0) = 600 lb per sq ft Limited to less than Pm = wh = 150(12) = 1,800 lb per sq ft The calculated value from Eq. (3-2) is 793, which is above the minimum of 600 and below the maximum 1,800.

Therefore, use 793 lb per sq ft lateral pressure on the forms. The 793 lb per sq ft maximum pressure will occur at a depth of 793/150 = 5. 3 ft below the top of the form as shown in Figure 3-2. Example 3-2 A wall form 8 ft high is filled with 150 lb per cu ft concrete at a temperature of 60°F. The concrete is Type I with a retarder. Concrete will be placed with normal internal vibration to a depth of less than 4 ft. The concrete rate of placement will be 10 ft per hr. 26 Chapter Three FIGURE 3-2 Distribution of concrete pressure for Example 3-1.

From Table 3-1 the value of Cw is 1. 0 and from Table 3-2 the value of Cc is 1. 2. The rate of placement is between 7 and 15 ft per hr and the placement height does not exceed 14 ft. Using Eq. (3-3) to calculate the lateral pressure. Pm = CwCc[150 + 43,400/T + 2,800R/T] = (1. 0)(1. 2)[150 + 43,400/60 + 2,800(10/60)] = 1,608 lb per sq ft Checks on limitations on pressures calculated from Eq. (3-3): Limited to greater than 600Cw = 600(1. 0) = 600 lb per sq ft Limited to less than Pm = wh = 150(8) = 1,200 lb per sq ft The calculated value from Eq. 3-3) is 1,608 lb per sq ft, which is above the limit of 600Cw. However, the calculated value 1,608 is greater than the limit of Pm = wh = 1,200 for an 8-ft-high wall. Therefore, the maximum design concrete lateral pressure is 1,200 lb per sq ft. Figure 3-3 shows the lineal distribution of pressure. Example 3-3 A concrete wall is 9 ft high, 15 in. thick, and 60 ft long. The concrete will be placed by a pump with a capacity of 18 cu yd per hr at a temperature of 80°F. The concrete density is 150 lb per cu yd with Type I cement without additives or blends; therefore, Cw and Cc = 1. 0.

Leave a Reply

Your email address will not be published. Required fields are marked *