Formwork for Concrete Structures, 4th Edition

543 Pages·2010·10.48 MB·english

by  Garold (Gary) Oberlender

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 high-
way 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. He was a
long-time member of the American Society of Civil En-
gineers, 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 ex-
perience in teaching, research, and consulting engineer-
ing 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

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Contents
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix
Abbreviations and Symbols . . . . . . . . . . . . . . . . . . . . . xxi
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Purpose of This Book . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Safety of Formwork . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Economy of Formwork . . . . . . . . . . . . . . . . . . . . . . . . 2
Allowable Unit Stresses in Formwork Material . . . 2
Care of Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Patented Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Arrangement of This Book . . . . . . . . . . . . . . . . . . . . . 3
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2 Economy of Formwork . . . . . . . . . . . . . . . . . . . . . . . . 7
Background Information . . . . . . . . . . . . . . . . . . . . . . . 7
Impact of Structural Design on Formwork Costs . . . 7
Suggestions for Design . . . . . . . . . . . . . . . . . . . . . . . . 9
Design Repetition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Dimensional Standards . . . . . . . . . . . . . . . . . . . . . . . . 10
Dimensional Consistency . . . . . . . . . . . . . . . . . . . . . . 11
Economy of Formwork and Sizes of Concrete
Columns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Beam and Column Intersections . . . . . . . . . . . . . . . . 12
Economy in Formwork and Sizes of
Concrete Beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Economy in Making, Erecting, and
Stripping Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Removal of Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Bui lding Construction and Economy . . . . . . . . . . . . 16
Economy in Formwork and Overall Economy . . . . 19
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3 Pressure of Concrete on Formwork . . . . . . . . . . . . . 21
Behavior of Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Lateral Pressure of Concrete on Formwork . . . . . . . 22
Lateral Pressure of Concrete on Wall Forms . . . . . . 23
Example 3-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Example 3-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Example 3-3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
v
vi Contents
Relationship between Rate of Fill, Temperature,
and Pressure for Wall Forms . . . . . . . . . . . . . . . . . 28
Lateral Pressure of Concrete on Column Forms . . . 31
Example 3-4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Example 3-5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Example 3-6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Relationship between Rate of Fill, Temperature,
and Pressure for Column Forms . . . . . . . . . . . . . . 33
Graphical Illustration of Pressure Equations for
Walls and Columns . . . . . . . . . . . . . . . . . . . . . . . . . 33
Effect of Weight of Concrete on Pressure . . . . . . . . . 36
Vertical Loads on Forms . . . . . . . . . . . . . . . . . . . . . . . 36
Example 3-7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Example 3-8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Example 3-9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Placement and Consolidation of Freshly Placed
Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Wind Loads on Formwork Systems . . . . . . . . . . . . . . 39
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
4 Properties of Form Material . . . . . . . . . . . . . . . . . . . 41
General Information . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Properties of Lumber . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Allowable Stresses of Lumber . . . . . . . . . . . . . . . . . . 44
Adjustment Factor C for Load-Duration . . . . . . . . . 46
D
Adjustment Factors C for Moisture Content . . . . . 46
M
Adjustment Factor C for Beam Stability . . . . . . . . . 51
L
Adjustment Factor C for Column Stability . . . . . . . 51
P
Adjustment Factors C for Flat Use . . . . . . . . . . . . . . 52
fu
Adjustment Factors C for Bearing Area . . . . . . . . . . . 52
b
Application of Adjustment Factors . . . . . . . . . . . . . . 53
Example 4-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Example 4-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Ply wood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Allowable Stresses for Plywood . . . . . . . . . . . . . . . . . 55
Plyform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
High-Density Overlaid Plyform . . . . . . . . . . . . . . . . . 60
Equations for Determining the Allowable
Pressure on Plyform . . . . . . . . . . . . . . . . . . . . . . . . 60
Allowable Pressure Based on Fiber Stress in
Bending . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Allowable Pressure Based on Bending Defl ection . . . . 63
Allowable Pressure Based on Shear Stress . . . . . . . . 63
Contents vii
Allowable Pressure Based on Shear Defl ection . . . . 63
Tables for Determining the Allowable Concrete
Pressure on Plyform . . . . . . . . . . . . . . . . . . . . . . . . 64
Maximum Spans for Lumber Framing Used to
Support Plywood . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Use of Plywood for Curved Forms . . . . . . . . . . . . . . 66
Hardboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Fiber Form Tubes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Steel Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Aluminum Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Plastic Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Form Liners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
Nails . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
Withdrawal Resistance of Nails . . . . . . . . . . . . . . . . . 75
Lateral Resistance of Nails . . . . . . . . . . . . . . . . . . . . . 75
Toe-Nail Connections . . . . . . . . . . . . . . . . . . . . . . . . . 77
Connections for Species of Wood for Heavy
Formwork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
Lag Screws . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
Withdrawal Resistance of Lag Screws . . . . . . . . . . . 78
Lateral Resistance of Lag Screws . . . . . . . . . . . . . . . . 79
Timber Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
Split-Ring Connectors . . . . . . . . . . . . . . . . . . . . . . . . . 82
Shear-Plate Connectors . . . . . . . . . . . . . . . . . . . . . . . . 83
Split-Ring and Shear-Plate Connectors in
End Grain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
Penetration Requirements of Lag Screws . . . . . . . . . 84
Form Ties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Concrete Anchors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
5 Design of Wood Members for Formwork . . . . . . . . 87
General Information . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Arr angement of Information in This Chapter . . . . . 87
Lumber versus Timber Members . . . . . . . . . . . . . . . . 88
Loads on Structural Members . . . . . . . . . . . . . . . . . . 89
Equations Used in Design . . . . . . . . . . . . . . . . . . . . . . 89
Analysis of Bending Moments in Beams with
Concentrated Loads . . . . . . . . . . . . . . . . . . . . . . . . 90
Analysis of Bending Moments in Beams with
Uniformly Distributed Loads . . . . . . . . . . . . . . . . 91
Bending Stress in Beams . . . . . . . . . . . . . . . . . . . . . . . 92
Stability of Bending Members . . . . . . . . . . . . . . . . . . 93
viii Contents
Examples of Using Bending Stress Equations for
Designing Beams and Checking Stresses
in Beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Example 5-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Example 5-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Example 5-3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
Horizontal Shearing Stress in Beams . . . . . . . . . . . . . 98
Example 5-4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
Example 5-5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
Modifi ed Method of Determining the Unit Stress in
Horizontal Shear in a Beam . . . . . . . . . . . . . . . . . . 100
Example 5-6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
Example 5-7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Defl ection of Beams . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Defl ection of Beams with Concentrated Loads . . . . 105
Defl ection of Single-Span Beams with
Concentrated Loads . . . . . . . . . . . . . . . . . . . . . . . . 106
Example 5-8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
Multiple-Span Beam with Concentrated Loads . . . . 108
Defl ection of Beams with Uniform Loads . . . . . . . . . 109
Single-Span Beams with Uniformly Distributed
Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
Example 5-9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
Defl ection of Multiple-Span Beams with Uniformly
Distributed Loads . . . . . . . . . . . . . . . . . . . . . . . . . . 111
Table for Bending Moment, Shear, and Defl ection for
Beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
Calculating Defl ection by Superposition . . . . . . . . . 113
Example 5-10 . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Example 5-11 . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
Allowable Span Length Based on Moment, Shear, or
Defl ection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Allowable Span Length for Single-Span Members
w ith Uniformly Distributed Loads . . . . . . . . . . . . 116
Allowable Span Length for Multiple-Span Members
with Uniformly Distributed Loads . . . . . . . . . . . . 116
Stresses and Defl ection of Plywood . . . . . . . . . . . . . . 117
Allowable Pressure on Plywood Based on
Bending Stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
Example 5-12 . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Example 5-13 . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Example 5-14 . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
Allowable Pressure on Plywood Based on Rolling
Shear Stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
Example 5-15 . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
Contents ix
Allowable Pressure on Plywood Based on
Defl ection Requirements . . . . . . . . . . . . . . . . . . . . 123
Allowable Pressure on Plywood due to Bending
Defl ection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
Example 5-16 . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
Allowable Pressure on Plywood Based on
Shear Defl ection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
Example 5-17 . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
Tables of Equations for Calculating Allowable
Span Lengths for Wood Beams and
Plywood Sheathing . . . . . . . . . . . . . . . . . . . . . . . . . 127
Compression Stresses and Loads on Vertical Shores . . . . 127
Example 5-18 . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
Table for Allowable Loads on Wood Shores . . . . . . . 132
Bearing Stresses Perpendicular to Grain . . . . . . . . . 132
Design of Forms for a Concrete Wall . . . . . . . . . . . . . 135
Lateral Pressure of Concrete on Forms . . . . . 136
Plywood Sheathing to Resist Pressure from
Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
Studs for Support of Plywood . . . . . . . . . . . . 138
Wales for Support of Studs . . . . . . . . . . . . . . . 140
Strength Required of Ties . . . . . . . . . . . . . . . . 142
Design Summary of Forms for Concrete Wall . . . . 143
Minimum Lateral Force for Design of Wall Form
Bracing Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
Bracing for Wall Forms . . . . . . . . . . . . . . . . . . . . . . . . 144
Example 5-19 . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
Example 5-20 . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
Design of Forms for a Concrete Slab . . . . . . . . . . . . . 149
Loads on Slab Forms . . . . . . . . . . . . . . . . . . . . 150
Plywood Decking to Resist Vertical Load . . . . 151
Joists for Support of Plywood . . . . . . . . . . . . . 152
Stringers for Support of Joists . . . . . . . . . . . . . 154
Shores for Support of Stringers . . . . . . . . . . . 156
Minimum Lateral Force for Design of Slab Form
Bracing Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Minimum Time for Forms and Supports to
Remain in Place . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Minimum Safety Factors for Formwork
Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
6 Shores and Scaffolding . . . . . . . . . . . . . . . . . . . . . . . 163
General Information . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
Shores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163