Simplified design of prestressed concrete tanks for potable water

This document provides guidelines for the planning, design and construction of a cylindrical tank constructed on the ground with prestressed concrete (PC) for use with potable water tank. This document is applicable to PC tanks for potable water with a capacity of 30 000 m3 or less and the diameter-to-height ratio (D/H) from 1,0 to 3,0. NOTE When designing and constructing a tank not covered by this document (reinforced concrete tanks, underground tanks, elevated tanks, etc.), a designer can refer to this document for common elements where possible.

Conception simplifiée du réservoir pour l'eau potable en béton pré-armé

General Information

Status
Published
Publication Date
23-May-2018
Current Stage
6060 - International Standard published
Start Date
24-May-2018
Completion Date
24-May-2018
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ISO 18407:2018 - Simplified design of prestressed concrete tanks for potable water
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INTERNATIONAL ISO
STANDARD 18407
First edition
2018-05
Simplified design of prestressed
concrete tanks for potable water
Conception simplifiée du réservoir pour l'eau potable en béton pré-
armé
Reference number
ISO 18407:2018(E)
ISO 2018
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ISO 18407:2018(E)
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© ISO 2018

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Published in Switzerland
ii © ISO 2018 – All rights reserved
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ISO 18407:2018(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................vi

Introduction ..............................................................................................................................................................................................................................vii

1 Scope .................................................................................................................................................................................................................................1

2 Normative references ......................................................................................................................................................................................1

3 Terms and definitions .....................................................................................................................................................................................1

4 Symbols ..........................................................................................................................................................................................................................4

5 Design principles ..............................................................................................................................................................................................12

6 Load .................................................................................................................................................................................................................................13

6.1 General ........................................................................................................................................................................................................13

6.2 Deadweight .............................................................................................................................................................................................13

6.3 Imposed load .........................................................................................................................................................................................13

6.4 Hydrostatic water pressure ......................................................................................................................................................14

6.5 Prestress ....................................................................................................................................................................................................14

6.5.1 General...................................................................................................................................................................................14

6.5.2 Prestressing force immediately after prestressing .........................................................................14

6.5.3 Effective prestressing force .................................................................................................................................18

6.5.4 Indeterminate forces due to prestress .......................................................................................................19

6.6 Creep and drying shrinkage of concrete ........................................................................................................................19

6.7 Effect of temperature ......................................................................................................................................................................19

6.8 Seismic action .......................................................................................................................................................................................20

6.9 Wind load ..................................................................................................................................................................................................20

6.10 Snow load .................................................................................................................................................................................................20

6.11 Earth pressure ......................................................................................................................................................................................21

6.12 Uplift pressure force ........................................................................................................................................................................22

6.13 Other loads ..............................................................................................................................................................................................22

7 Structural analysis ...........................................................................................................................................................................................22

7.1 Calculation of member force ....................................................................................................................................................22

7.2 Concrete .....................................................................................................................................................................................................22

7.2.1 Strength ................................................................................................................................................................................22

7.2.2 Modulus of elasticity..................................................................................................................................................23

7.2.3 Poisson’s ratio .................................................................................................................................................................23

7.2.4 Drying shrinkage ..........................................................................................................................................................23

7.2.5 Creep .......................................................................................................................................................................................23

7.3 Steel ...............................................................................................................................................................................................................25

7.3.1 Strength ................................................................................................................................................................................25

7.3.2 Modulus of elasticity..................................................................................................................................................26

7.3.3 Relaxation ...........................................................................................................................................................................26

7.4 Calculation of tensile reinforcement .................................................................................................................................26

8 Stress limit ...............................................................................................................................................................................................................27

8.1 General ........................................................................................................................................................................................................27

8.2 Stress limit of reinforced concrete members .............................................................................................................28

8.2.1 Stress limit of concrete ............................................................................................................................................28

8.2.2 Stress limit of reinforcement ..............................................................................................................................28

8.3 Stress limit of prestressed concrete members .........................................................................................................28

8.3.1 Stress limit of concrete ............................................................................................................................................28

8.3.2 Tensile stress limit of prestressing steel ..................................................................................................29

8.3.3 Stress limit of reinforcement ..............................................................................................................................29

8.3.4 Augmentation of tensile stress limit of concrete...............................................................................29

9 Verification of safety against earthquake ................................................................................................................................29

9.1 Principles of seismic design ......................................................................................................................................................29

9.1.1 General...................................................................................................................................................................................29

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ISO 18407:2018(E)

9.1.2 Ground motion levels ................................................................................................................................................29

9.1.3 Levels of earthquake resistance ......................................................................................................................29

9.1.4 Effects of earthquake.................................................................................................................................................30

9.1.5 Seismic design procedure .....................................................................................................................................30

9.2 Input earthquake motion ............................................................................................................................................................30

9.2.1 Seismic design method ............................................................................................................................................30

9.2.2 Design seismic coefficients for the seismic coefficient method for Level 1

ground motion ................................................................................................................................................................31

9.2.3 Design seismic coefficients for the seismic coefficient method for Level 2

ground motion ................................................................................................................................................................32

9.2.4 Seismic input for design by dynamic analysis .....................................................................................33

9.3 Verification of structural safety .............................................................................................................................................33

9.3.1 Effects of earthquake.................................................................................................................................................33

9.3.2 Combination of loads ................................................................................................................................................37

9.3.3 Calculation of member forces ............................................................................................................................38

9.3.4 Safety verification ........................................................................................................................................................47

9.4 Investigation for foundation .....................................................................................................................................................54

10 General structural details ........................................................................................................................................................................54

10.1 Prestressing steel ...............................................................................................................................................................................54

10.1.1 Clear distance ..................................................................................................................................................................54

10.1.2 Concrete cover ................................................................................................................................................................55

10.1.3 Arrangement of curved prestressing steel .............................................................................................56

10.1.4 Arrangement of anchorages and couplers ..............................................................................................56

10.1.5 Protection of anchorage zone ............................................................................................................................56

10.1.6 Reinforcement of concrete near anchorages ........................................................................................56

10.2 Steel reinforcement ..........................................................................................................................................................................56

10.2.1 Clear distance ..................................................................................................................................................................56

10.2.2 Concrete cover ................................................................................................................................................................57

10.2.3 Bend configurations of reinforcement .......................................................................................................57

10.2.4 Splices in reinforcement .........................................................................................................................................59

10.2.5 Anchoring of reinforcement ................................................................................................................................60

10.2.6 Welded wire fabric ......................................................................................................................................................61

10.3 Concrete joints .....................................................................................................................................................................................61

10.3.1 Construction joints ........................................................................................................................................... ...........61

10.3.2 Joints between precast concrete members ............................................................................................62

10.4 Reinforcement for opening ........................................................................................................................................................62

11 Design of members..........................................................................................................................................................................................63

11.1 Method of calculating member force ................................................................................................................................63

11.1.1 Analysis method ............................................................................................................................................................63

11.1.2 Analysis model ................................................................................................................................................................63

11.2 Component division .........................................................................................................................................................................65

11.3 Roof ................................................................................................................................................................................................................65

11.3.1 Structural types..............................................................................................................................................................65

11.3.2 Design in general ..........................................................................................................................................................66

11.4 Tank wall ...................................................................................................................................................................................................72

11.4.1 Structural types..............................................................................................................................................................72

11.4.2 Design in general ..........................................................................................................................................................74

11.5 Base slab ....................................................................................................................................................................................................91

11.5.1 Structural types..............................................................................................................................................................91

11.5.2 Design in general ..........................................................................................................................................................92

12 Materials ....................................................................................................................................................................................................................96

12.1 Quality of materials ..........................................................................................................................................................................96

12.1.1 General...................................................................................................................................................................................96

12.1.2 Concrete materials ......................................................................................................................................................96

12.1.3 Concrete ...................................................................... ..........................................................................................................97

12.1.4 Prestressing steel .........................................................................................................................................................97

12.1.5 Steel reinforcement ....................................................................................................................................................97

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ISO 18407:2018(E)

12.1.6 Welded wire fabric ......................................................................................................................................................97

12.1.7 Anchorages and couplers ......................................................................................................................................97

12.1.8 Sheath .....................................................................................................................................................................................97

12.1.9 Coating materials for protecting prestressing steel .......................................................................98

13 Tank appurtenances ......................................................................................................................................................................................98

13.1 Ladders/stairs and handrails ..................................................................................................................................................98

13.2 Manhole and water pilot hole .................................................................................................................................................99

13.3 Ventilators ................................................................................................................................................................................................99

13.4 Lightning rods .......................................................................................................................................................................................99

13.5 Piping ...........................................................................................................................................................................................................99

13.6 Catch basin............................................................................................................................................................................................100

13.7 Water-level gauge ...........................................................................................................................................................................100

13.8 Rainwater treatment ....................................................................................................................................................................100

13.9 Protection equipment .................................................................................................................................................................100

Annex A (informative) Reference design flow .....................................................................................................................................101

Annex B (informative) Design seismic coefficients for the seismic coefficient method ..........................103

Annex C (informative) Seismic input for design by dynamic analysis ........................................................................106

Annex D (informative) Example of material specifications ...................................................................................................108

Annex E (informative) Example of design calculation .................................................................................................................112

Bibliography .........................................................................................................................................................................................................................174

© ISO 2018 – All rights reserved v
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ISO 18407:2018(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see the following

URL: www .iso .org/iso/foreword .html.

This document was prepared by Technical Committee ISO/TC 71, Concrete, reinforced concrete and

prestressed concrete, Subcommittee SC 5, Simplified design standard for concrete structures.

vi © ISO 2018 – All rights reserved
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ISO 18407:2018(E)
Introduction

The aim of this document is to provide rules for the design and construction of prestressed concrete

water tanks to be built in less-developed areas of the world. The design rules are based on simplified

worldwide-accepted strength models. This document is self-contained; therefore actions (loads) and

simplified analysis procedures are included, as well as minimum acceptable construction practice

guidelines.

A great effort was made to include self-explanatory tables, graphics and design aids to simplify the

use of this document and provide procedures. Notwithstanding, the economic implications of the

conservatism inherent in approximate procedures as a substitution to sound and experienced

engineering should be a matter of concern to the designer who employs this document and to the owner

who hires him.

A prestressed concrete tank for potable water generally comprises the roof, wall and base slab. The roof

is made to entirely cover the top of the cylindrical wall so as to protect the water from contamination

with rainwater, etc. In many cases, it is made in the form of a dome shaped like a convex disc cut off

from a sphere. The wall is a vertical cylinder that forms a container for water in combination with

the flat disc base slab. Normally, only the wall of a prestressed concrete water tank is made with

prestressed concrete, while the roof and base slab are made with reinforced concrete. Prestress is

generally applied to the wall using prestressing steel in the vertical and circumferential directions, but

in some cases prestress is applied only to the circumferential direction. For this reason, this document

defines a prestressed concrete cylindrical tank as a structure having prestressing steel at least in the

circumferential direction of the wall to apply prestress, so as to cover both types. Therefore, the roof,

base slab and wall in the vertical direction may not necessarily be of prestressed concrete construction

but may be of reinforced concrete construction.

A prestressed concrete water tank construction is generally adopted to preserve a water storage

facility with the aim of preventing severe secondary disasters and allowing the standing water to be

used as an emergency water supply. For this reason, it is required to be designed as a rule as a high

degree of importance.

The minimum dimensional provisions contained in this document are intended to account for

undesirable side effects that will require more sophisticated analysis and design procedures. Material

and construction provisions are aimed at site-mixed concrete, as well as ready-mixed concrete and

steel of the minimum available strength gra
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