Designing floor slabs on grade

289 Pages·9.75 MB·English

by  Boyd C.Ringo. Robert B. Anderson.

Designing
Floor Slabs
On Grade
Stfp-by-Sicp Procedures. Sample Solution*, and Commentary
Second Edition
(tmd C. Kin^o and Kohcrl K. Anderson
Designing
Floor Slabs
On Grade
Step-by-Step Procedures, Sample Solutions, and Commentary
Second Edition
Boyd C. Ringo and Robert B. Anderson
Technical Editor: Mary K. Hurd
= -= The Aberdeen Group*
426 S. Westgate St; Addison, Illinois 60101
Designing Floor Slabs on Grade
Step-by-Step Procedures, Sample Solutions, and Commentary
Second Edition
published by The Aberdeen Group
426 South Westgate
Addison, IL 60101
Book Editor Desine J. Hanford
Artist: Joan E. Moran
Copyright О 1996 The Aberdeen Group
Printed in the United States of America
Reproduction of any part of this work beyond that permitted by the 1976 United States Copyright Act without
permission of the copyright owner is unlawful. Requests for permission or further information should be addressed
to The Aberdeen Group. Library of Congress Catalog Number: 95-31988
10987654321
ISBN 0-924659-75-0,-
Item No. 3020
Library of Congress Cataloglng-tn-PubUcation Data
Ringo, Boyd C.
Designing floor slabs on grade : step-by-step procedures, sample solutions, and commentary. - 2nd ed.
p. cm.
Authors: Boyd C. Ringo and Robert B. Anderson
Includes index.
ISBN 0-924659-75-0 (pbk.)
1. Concrete slabs-Design and construction. 2. Floors, Concrete-Design and construction. I. Anderson, Robert B.
TA683J.S6R54 1996
624.1'8342-dc20 95-31988
CEP
ABOUT THE AUTHORS
Slab design experts and consultants, Boyd Ringo and Bob Anderson have
lectured worldwide on the design of slabs on grade. They have served together as
active members of the American Concrete Institute Committee 360, Design of Slabs
on Grade, and Committee 302, Construction of Concrete Floors. Now they join
forces to share their expertise in the how-to-do-it format of this versatile new design
handbook.
Boyd C. Ringo, a leading authority on plain and conventionally reinforced
concrete slabs on grade, has been involved as a professional engineer with design
and construction for more than 40 years. Now in private practice as a consulting
engineer in Cincinnati, he is a past chairman of ACI Committee 360, and was for
many years a professor of civil engineering at the University of Cincinnati. Ringo
has also worked as a structural designer and forensic investigator and has extensive
experience with industrial slabs on grade.
Robert B. Anderson, a pioneer in establishing the post-tensioned slab on grade,
helped in developing some of the early hardware as well as the design procedures
that are accepted today. Long active in the Post-Tensioning Institute, he is now
president of Robert B. Anderson Consulting Engineers, New Orleans. His practice
includes commercial, industrial, and residential design as well as conventional and
post-tensioned foundation design — with particular emphasis in dealing with
problems of expansive and compressible soils.
The Aberdeen Group, its employees and agents, and the authors are not engaged in the
business of providing architectural or construction services, nor are they licensed to do so.
The information in this book is intended for the use of builders, floor designers, and
contractors competent to evaluate its applicability to their situation, and who will accept
responsibility for the application of the information. The Aberdeen Group and the authors
disclaim any and all responsibility for the application of the information.
CONTENTS
INTRODUCTION...................................................................................................................xv
CHAPTER 1 Input values needed for design..................................................................1
1.1—Information about supporting soil.............................................................................1
1.1.1—Introductio n........................................................................................................1
1.1.2—Working with a soils specialist.........................................................................2
1.1.3—Limit risk with insufficient information ...........................................2
1.1.4—Working with limited soil information............................................................2
1.1.5—Summar y ...........................................................................................................4
1.2—Types of slab loadings.................................................................................................4
1.2.1—Introductio n.......................................................................................................4
1.2.2—Vehicle axle loads.............................................................................................4
1.2.3—Uniform loads with aisles.................................................................................5
1.2.4—Rack and post loads...........................................................................................6
1.2.5—Column loads.....................................................................................................7
1.2.6—Special or unusual loads...................................................................................7
13—Concrete for the slab...................................................................................................8
1.3.1 —Concrete strength properties for design..........................................................8
1.3.1.1 —Compression..........................................................................................8
1.3.1.2—Modulus of rupture.................................................................................8
1.3.1.3 —Shear strength.....................................................................................9
1.3.1.4—Surface durability...................................................................................9
1.3.2—Choosing the concrete mix...............................................................................9
1.3.2.1 —Cements................................................... 9
1.3.2.2—Aggregate s...........................................................................................10
1.3.2.3—Mix proportions....................................................................................10
IA—Safety factors..............................................................................................................10
1.4.1—Importance and meaning................................ 10
1.4.2—Common values for safety factor...................................................................10
13—Slab reinforcement....................................................................................................11
1.5.1 — Reinforcing steel ....................................................................................11
1.5.1.1—Genera l.................................................................................................11
1.5.1.2—Shrinkage crack control........................................................................11
1.5.1.3—Subgrade drag......................................................................................11
1.5.1.4—Temperature method.............................................................................12
1.5.1.5 — Equivalent strength method..................................................................13
1.5.1.6 — Slab with structurally active steel........................................................13
1.5.1.7 — Steel types and designations.................................................................13
1.5.2—Post-tensioning tendons...................................................................................14
1.5.2.1—Introduction 14
1.5.2.2—Crack control.......................................................................................15
1.5.2.3—Curl control/post-tensioned slabs..........................................................15
1.5.2.4 — Structural effectiveness.......................................................................15
1.5.2.5 — Tendon types......................................................................................15
1.6 — Fiber enhancement..................................................................................................16
CHAPTER 2 Slab types & design methods: The designer’s choice.....................17
2.1—Types of slab construction........................................................................................17
2.1.1—Introductio n.....................................................................................................17
2.1.2—Type A, plain concrete slab............................................................................17
2.1.3—Type B, slab with shrinkage control reinforcement.....................................18
2.1.4—Type C, slab with shrinkage-compensating concrete..................................18
2.1.5—Type D, slab post-tensioned for crack control.............................................19
2.1.6—Type E, lightly reinforced structural slab......................................................19
2.1.7—Type F, structurally reinforced slab..............................................................20
2.1.8 — Type G (Authors’ designation), fiber-enhanced concrete slab.................20
23—Methods of slab thickness determination..............................................................21
2.2.1 —Portland Cement Institute (PCA) method....................................................21
2.2.2—Wire Reinforcement Institute (WRI) method...............................................21
2.2.3—United States Army Corps of Engineers (COE) method............................22
2.2.4—Post-Tensioning Institute (PTT) method ..............................................22
2.2.5 — ACI Committee 223 (ACI223) method.......................................................22
2.2.6 — MATS (PCA) finite element analysis.........................................................22
2.2.7—Other methods................................................................................................22
2.2.8—Correlation of construction type with design method and
loading condition............................................................................................23
CHAPTER 3 Design for vehicle axle loads..................................................................25
3.1—Design objectives.......................................................................................................25
3.2—Using PCA charts to design for axle loading: AUTHORS’ CHOICE 26
3.2.1 — Single wheels, interior loading....................................................................26
3.2.2 — Dual wheels, interior loading......................................................................28
3.2.3 — Stress increases for loads at edges or joints................................................29
3.3—Design for axle loading using WRI charts.................................................... 29
3.4—Design for axle loading using COE charts............................................................31
3.4.1 — COE, light lift truck......................................................................................32
3.4.2 — COE, heavy lift truck...................................................................................33
3.4.3 — COE, outdoor paving areas..........................................................................34
3.5—Adapting PCA charts for use with swing vehicles................................................34
3.6—Using shrinkage-compensating concrete for slabs subject to axle loads 36
3.7—Using post-tensloning tendons for a slab with axle loads...................................37
3.8—Designing structural reinforcement for a slab with vehicle loading.................37
3.9—Welded wire fabric as a structural element...................................................... 40
CHAPTER 4 Design of slabs for rack storage post loads.......................................43
4.1—Design objectives.......................................................................................................43
43 —Information needed to solve the post load problem............................................44
4.3—Using PCA charts to design for rack storage
post loading: AUTHORS’ CHOICE......................................................................44
4.4—Using PCA charts when actual к does not
equal chart к: AUTHORS’ CHOICE.................................................... 45
4.5—Using shrinkage-compensating concrete, post-tensioning tendons,
or active steel reinforcement...................................................................................48
CHAPTER 5 Slab design for column or wall loadings........................................49
5.1—Scope of the problem.................................................................................................49
5.2—Design objective..........................................................................................................50
53—Input values needed for design................................................................................50
5.4—Using equations to design for column loads: AUTHORS’ CHOICE 51
5 J —Adapting PCA charts to design for column loads on slabs ...............................53
5.6—Design for wall loading on slabs using the
ARMY-TM equations: AUTHORS’ CHOICE.....................................................54
5.7—ACI 318.1 Building Code Requirements for Structural Plain Concrete and
Commentary...............................................................................................................56
CHAPTER 6 Slab design for distributed uniform loading on both sides
of an aisle...........................................................................................................57
6.1—The design objective..................................................................................................57
6.2—Values needed to solve the problem........................................................................58
63—Using WRI charts to design for distributed
uniform loading on both rides of an aisle: AUTHORS’ CHOICE...................58
6.4—Using PCA tables to design for uniform loading on both rides of an aisle 60
63—Using shrinkage-compensating concrete for slabs with distributed
uniform loading on both rides of an aisle...............................................................62
6.6—Using post-tensioning tendons for slabs with distributed
uniform loading on both rides of an aisle..............................................................64
6.7—Using structurally reinforced concrete for slabs loaded uniformly on
both sides of an aisle..................................................................................................64
63-Use of fibers for concrete enhancement................................................................66
6.8.1 —Steel fiber ..............................................................................................67
6.8.2 —Synthetic (polymeric) fibers..........................................................................67
6.8.3—Joint treatment.................................................................................................68
6.8.4—Compatibilit y................................................... 69
CHAPTER 7 Design of slabs supported on plastic clays..........................................71
7.1—Introduction 71
73—Plastic clay conditions...............................................................................................71
73—The PTI method for slab design on plastic clay....................................................74
7.3.1 — Analysis of slab loads......................................................................................74
7.3.2—Values needed to solve the problem..............................................................75
7.3.3—Design objectives............................................................................................75
7.3.4—Computer solutions........................................................................................76
7.4—DESIGN EXAMPLE: Rectangular post-tensioned slab on
plastic clay with uniform and perimeter loads.....................................................76
7.4.1 —Symbols and notation.....................................................................................76
7.4.2—Hie problem and initial assumptions; materials data...................................77
7.4.3—Soils investigation..........................................................................................78
7.4.3.1 —Determine the predominant clay material in the soil..............................79
7.4.3.2—Find the constant suction value for the soil............................................80
7.4.3.3—Determine the average moisture movement velocity..............................81
7.4.3.4—Find edge moisture variation distance...................................................81
7.4.3.5—Determine expected differential swell for
edge lift and center lift conditions.........................................................82
7.4.4—Check preliminary beam sizes and tendon requirements,
Step 5 of Flow Chart 1 ..................................................................................86
7.4.4.1 — Preliminary determination, stiffening beam depth d,
edge lift condition.................................................................................86
7.4.4.2—Soil pressure under the beams (a subroutine for Step 5, Flow Chart 1).... 87
7.4.5—Determine section properties for full slab width, Step 6, Flow Chart 1.... 88
7.4.6—Calculate minimum number of tendons required, Step 7, Flow Chart I ... 89
7.4.7—Check design moments against allowable moments for edge lift
condition, Step 8, Flow Chart 1....................................................................90
7.4.8—Deflection calculations, edge lift condition, Step 9, Flow Chart 1.............92
7.4.9—Shear calculations for edge lift condition, Step 10, Flow Chart 1..............93
7.4.10—Center lift design..........................................................................................94
73—DESIGN EXAMPLE: Simple rectangle, uniform thickness post-tensioned
slab on plastic clay with uniform and perimeter load.........................................99
7.5.1 — Introduction.....................................................................................................99
7.5.2—Modeling the problem..................................................................................100
7.5.3—Determination of equivalent thickness........................................................101
7.5.4—Determine number of tendons required.......................................................101
7.5.5—Recheck design moments against allowable moment capacity.................102
7.5.6 —Check of shear capacity............................................................................104
7.5.7—Summary of results.......................................................................................104
7.6—DESIGN EXAMPLE: Simple rectangle, conventionally reinforced slab on
plastic clay with uniform and perimeter load.....................................................106
7.6.1—Introductio n...................................................................................................106
7.6.2—Modeling the problem, long direction.........................................................106
7.6.3—Values needed to solve the problem with conventional reinforcement... 107
7.6.4—The reinforced concrete solution for slab on plastic clay..........................108
7.6.5—Short direction section with conventional reinforcement..........................109
CHAPTER 8 Design of slabs on compressible clays................................................113
8.1—Introductio n.............................................................................................................113
8.2—What is compressible clay?....................................................................................113
83—PTI method for designing slabs supported on compressible clays.................116
8.3.1 — Analysis of slab loads...................................................................................116
8.3.2—Values needed to solve the problem............................................................116
8.3.3—Design objectives.........................................................................................117
8.3.4—Computer solutions......................................................................................118
8.4—DESIGN EXAMPLE: Rectangular post-tensioned slab on compressible
clay with uniform and perimeter loads...............................................................118
8.4.1 — Symbols and notation...................................................................................118
8.4.2—The problem and initial assumptions; materials data.................................119
8.4.3—Soils investigation........................................................................................120
8.4.3.1 — Determine the predominant clay material in the soil
(Step 5, Flow Chart 4).........................................................................121
8.4.3.2—Constant soil suction value for soil.....................................................122
8.4.3.3—Velocity of moisture flow...................................................................123
8.4.3.4—Determine edge moisture variation distance, em..................................123
8.4.3.5—Estimated differential movement (swell)............................................124
8.4.4—Preliminary beam sizes, tendon requirements............................................125
8.4.4.1 — Estimate the required depth d of stiffening beams................................125
8.4.4.2—Soil bearing pressure under beams......................................................126
8.4.5—Determine section properties for full slab width: Step 7, Flow Chart3.. 127
8.4.6—Calculate minimum number of tendons required, Step 8, Flow Chart 3... 128
8.4.7—Check design moments against allowable moments for edge lift
conditions, Step 9, Flow Chart 3................................................................129
8.4.8—Deflection calculations, edge lift condition................................................131
8.4.9—Shear calculations for edge lift condition....................................................132
8.4.10—Center lift design........................................................................................134
83—DESIGN EXAMPLE: Simple rectangle, conventionally reinforced slab on
compressible clay with uniform and perimeter load, Step 12A, Flow Chart 3... 139
8.5.1—Introduction 139
8.5.2—Modeling the problem, long direction................................................ 139
8.5.3—Values needed to solve the problem with conventional reinforcement... 140
8.5.4—The reinforced concrete solution for slab on compressible clay...............141
8.5.5—Short direction section with conventional reinforcement..........................142
CHAPTER 9 The hybrid post-tensioned slab: combining stiffening
elements with regions of uniform thickness....................................145
9.1—Introduction 145
93—Plastic clay conditions..............................................................................................145
93—The PIT method for slab design on plastic clay..................................................148
9.3.1 —Analysis of slab loads....................................................................................148
9.3.2—Values needed to solve the problem.............................................................148
9.3.3—Design objectives..........................................................................................149
9.3.4—Computer solutions.......................................................................................149
9.4—DESIGN EXAMPLE: Post-tensioned slab combining stiffening
elements with uniform thickness on plastic clay with uniform
and perimeter loads.................................................................................................151
9.4.1—Symbols and notation....................................................................................151
9.4.2—The problem and initial assumptions; materials data.................................152
9.4.3—Soils investigation.........................................................................................153
9.4.3.1—Determine the predominant clay mineral in the soil.............................154
9.4.3.2—Find the constant suction value for the soil..........................................155
9.4.3.3—Determine the average moisture movement velocity............................156
9.4.3.4—Find the edge moisture variation distance............................................156
9.4.3.5—Determine the expected differential swell for edge lift and
center lift conditions..........................................................................157
9.4.4—Check slab thickness based on loading requirements................................159
9.4.5—Check preliminary beam sizes, Step 6 of Flow Chart 5.............................161
9.4.5.1 —Preliminary determination, stiffening beam depth d,
edge lift condition...............................................................................161
9.4.5.2—Soil pressure under the beams (a subroutine for
Step 6, Flow Chart 5).........................................................................161
9.4.6—Determine section properties for full slab width
Step 7, Flow Chart 5......................................................................................163
9.4.7—Determine adequacy of stiffened section in relation
to the p distance chosen................................................................................164
9.4.8—Calculate minimum number of tendons required, Step 9, Chart 5............165
9.4.9—Check design moments against allowable moments for edge
lift condition, Step 10, Flow Chart 5............................................................166
9.4.10—Deflection calculations, edge lift condition, Step 11, Flow Chart 5.......168
9.4.11—Shear calculations for edge lift condition, Step 12, Flow Charts 168
9.4.12—Center lift design.........................................................................................169
CHAPTER 10 Supporting design information...........................................................173
10.1 —Dowels for floor slabs on grade.......................................................................173
10.1.1 —Purpose and function of dowels.................................................................173
10.1.2—Types of dowels..........................................................................................173
10.1.3—Size and spacing of dowels........................................................................174
103—Joints in slabs on grade.........................................................................................174
10.2.1 —Purpose of joints..........................................................................................174
10.2.2—Types and functions of joints.....................................................................175
10.2.3—Shear transfer...............................................................................................176
10.2.4—Joint spacings..............................................................................................176