As 3735-2001 Concrete Structures Retaining Liquids

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AS 3735

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AS 3735—2001

Australian Standard™

Concrete structures for retaining liquids

This Australian Standard was prepared by Committee CE-022, Concrete Structures for Retaining Liquids. It was approved on behalf of the Council of Standards Australia on 17 November 2000 and published on 13 March 2001.

The following interests are represented on Committee CE-022: Australian Pre-mixed Concrete Association Institution of Engineers Australia University of Queensland Water Services Association of Australia Additional interests participating in the preparation of this Standard: Association of Consulting Engineers Australia Australian Chamber of Commerce and Industry Australian Post Tensioning Association Licensed to Ishea A Bedding on 11 Jan 2005. 1 user personal user licence only. Storage, distribution or use on network prohibited.

Australian Water and Wastewater Association Brisbane City Council Department of Public Works and Services N.S.W. Melbourne Water National Precast Concrete Association Australia NSW Department of Land and Water Conservation Swimming Pool and Spa Association of N.S.W. Sydney Water Corporation University of New South Wales Water Corporation Western Australia

Keeping Standards up-to-date Standards are living documents which reflect progress in science, technology and systems. To maintain their currency, all Standards are periodically reviewed, and new editions are published. Between editions, amendments may be issued. Standards may also be withdrawn. It is important that readers assure themselves they are using a current Standard, which should include any amendments which may have been published since the Standard was purchased. Detailed information about Standards can be found by visiting the Standards Australia web site at www.standards.com.au and looking up the relevant Standard in the on-line catalogue. Alternatively, the printed Catalogue provides information current at 1 January each year, and the monthly magazine, The Australian Standard, has a full listing of revisions and amendments published each month. We also welcome suggestions for improvement in our Standards, and especially encourage readers to notify us immediately of any apparent inaccuracies or ambiguities. Contact us via email at [email protected], or write to the Chief Executive, Standards Australia International Ltd, GPO Box 5420, Sydney, NSW 2001.

This Standard was issued in draft form for comment as DR 99305.

AS 3735—2001

Australian Standard™

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Concrete structures for retaining liquids

Originated as AS 3735—1991. Second edition 2001.

COPYRIGHT © Standards Australia International All rights are reserved. No part of this work may be reproduced or copied in any form or by any means, electronic or mechanical, including photocopying, without the written permission of the publisher. Published by Standards Australia International Ltd GPO Box 5420, Sydney, NSW 2001, Australia ISBN 0 7337 3714 5

AS 3735—2001

2

PREFACE This Standard was prepared by the Standards Australia Committee CE-022, Concrete Structures for Retaining Liquids, to supersede AS 3735—1991. The objective of this standard is to provide designers of reinforced concrete structures used for retaining liquids at ambient temperatures with specifications for design and installation. For structures that specifically relate to concrete structures used for retaining liquids at ambient temperature, this Standard supplements and takes precedence over the requirements of AS 3600, Concrete structures. Statements expressed in mandatory terms in notes to tables are deemed to be requirements of this Standard.

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This draft Standard has been prepared from the previous edition of AS 3735—1991. The Standard is limited to concrete with a concrete stress limited in the range of 20 MPa to 50 MPa at 28 days. A Commentary, published as Supplement No. 1 to AS 3735, provides background information and explanation on the application of this Standard.

3

AS 3735—2001

CONTENTS Page

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SECTION 1 SCOPE AND GENERAL 1.1 SCOPE AND APPLICATION .....................................................................................4 1.2 REFERENCED DOCUMENTS ...................................................................................5 1.3 DEFINITIONS.............................................................................................................5 1.4 NOTATION .................................................................................................................5 1.5 USE OF ALTERNATIVE MATERIALS OR METHODS...........................................6 1.6 DRAWINGS AND SPECIFICATIONS .......................................................................7 SECTION 2 LOADS AND LOAD COMBINATIONS 2.1 GENERAL ...................................................................................................................8 2.2 LOADS AND OTHER ACTIONS ...............................................................................8 2.3 STABILITY DESIGN................................................................................................ 10 2.4 LOAD COMBINATIONS FOR SERVICEABILITY ................................................ 10 SECTION 3 DESIGN FOR SERVICEABILITY AND STRENGTH 3.1 GENERAL ................................................................................................................. 11 3.2 REINFORCED CONCRETE ..................................................................................... 11 3.3 PRESTRESSED CONCRETE.................................................................................... 13 SECTION 4 DESIGN FOR DURABILITY 4.1 GENERAL ................................................................................................................. 15 4.2 EXPOSURE CLASSIFICATION............................................................................... 15 4.3 REQUIREMENTS FOR CONCRETE ....................................................................... 16 4.4 REQUIREMENTS FOR COVER TO REINFORCEMENT (BARS AND TENDONS).......................................................................................... 16 4.5 DURABILITY OF METAL FIXTURES IN CONTACT WITH CONCRETE........... 18 4.6 DURABILITY OF WATERSTOPS, SEALANTS AND OTHER ASSOCIATED ITEMS .............................................................................................. 18 SECTION 5 MATERIAL AND CONSTRUCTION REQUIREMENTS 5.1 GENERAL ................................................................................................................. 19 5.2 CONCRETE............................................................................................................... 19 5.3 REINFORCEMENT................................................................................................... 19 SECTION 6 JOINTS, WATERSTOPS, JOINT FILLERS, AND SEALANTS 6.1 JOINTS ...................................................................................................................... 20 6.2 WATERSTOPS.......................................................................................................... 21 6.3 JOINT FILLERS ........................................................................................................ 21 6.4 SEALANTS ............................................................................................................... 21 6.5 CONTAMINATION OF WATER ............................................................................. 21 SECTION 7 TESTING 7.1 GENERAL ................................................................................................................. 22 7.2 TESTING FOR LIQUID-TIGHTNESS...................................................................... 22 7.3 TESTING OF LIQUID-RETAINING STRUCTURES............................................... 22 7.4 TESTING OF ROOFS ............................................................................................... 22

AS 3735—2001

4

STANDARDS AUSTRALIA Australian Standard Concrete structures for retaining liquids

S E CT I ON

1

S COP E

AND

G E N ERAL

1.1 SCOPE AND APPLICATION 1.1.1 Scope This Standard specifies requirements for concrete structures and members that include reinforcing steel or tendons, or both, used for retaining liquids at ambient temperature.

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The Standard supplements and takes precedence over the requirements of AS 3600. The principles of concrete design and construction embodied in this Standard apply to structures and members made of concrete— (a)

with a characteristic compressive strength at 28 days (f ′ c) in the range of 20 MPa to 50 MPa; and

(b)

of saturated, surface-dry density in the range of 1800 kg/m3 to 2800 kg/m3.

The Standard does not apply to the design of— (i)

dams;

(ii)

aqueducts, hydraulic tunnels or similar structures;

(iii) small septic tanks (see AS 1546.1); (iv)

portable precast concrete water tanks of less than 25 000 L capacity;

(v)

fibre-impregnated concrete that does not comply with the design requirements and procedures of AS 3600; or

(vi)

precast concrete pipes (pressure and non-pressure) (see AS 4058).

1.1.2 Application This Standard applies to concrete structures for the storage of liquids where the exposure conditions for concrete are within the specified limits. Such structures include those retaining water or sewage, public swimming pools, and swimming pools the area or overall length of which are greater than that specified in AS 2783. However, where applicable, the specifications of the relevant authority shall be used. NOTE: It is intended that the design of a structure or member to which this Standard applies, be carried out by, or under the supervision of, an engineer as defined in Clause 1.6.2.

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AS 3735—2001

1.2 REFERENCED DOCUMENTS The following documents are referred to in this Standard:

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AS 1012 1012.13

Methods of testing concrete Part 13: Determination of drying shrinkage of concrete for samples prepared in the field or in the laboratory

1170 1170.1 1170.2 1170.4 1379

Minimum design loads on structures Part 1: Dead and live loads and load combinations Part 2: Wind loads Part 4: Earthquake loads Specification and supply of concrete

3582

Supplementary cementitious materials for use with portland (and blended) cement Part 1: Fly-ash Part 2: Slag—Ground granulated iron blast-furnace Part 3: Silica fume

3582.1 3582.2 3582.3 AS/NZS 1546 1546.1

On-site domestic waste water treatment units Part 1: Septic tanks

2783 2841

Use of reinforced concrete for small swimming pools Galvanized steel wire strand

3600 3610 3735

Concrete structures Formwork for concrete Concrete structures for retaining liquids—Commentary

4058 4680 HB 79

Precast concrete pipes (pressure and non-pressure) Hot-dipped galvanised (zinc) coatings on fabricated ferrous articles Alkali Aggregate reaction—Guidelines on minimising the damage to concrete structures in Australia

NZS 3106

Code of practice for concrete structures for the storage of liquids

ASTM A 775M

Specification for epoxy-coated reinforcing steel bars

1.3 DEFINITIONS For the purpose of this Standard, the definitions given in AS 3600 apply. 1.4 NOTATION Unless a contrary intention appears the following applies: (a)

The symbols used in this Standard shall have the meanings ascribed to them below, with respect to the structure, or member, or condition to which a clause is applied.

(b)

Where non-dimensional ratios are involved, both the numerator and denominator are expressed in identical units.

(c)

The dimensional units for length, force and stress in all expressions or equations are to be taken as millimetres (mm), Newtons (N) and megapascals (MPa) respectively.

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AS 3735—2001

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Quantity symbol

Definition

Ac, eff

=

effective concrete area (see Figure 3.1)

As

=

the cross-sectional area of reinforcement

a 1, a 2

=

a distance (see Figure 3.1)

D

=

the overall depth of a cross-section in the plane of bending

db

=

the nominal diameter of a bar, wire, or tendon

Fep

=

the earth pressure load

Feq

=

the earthquake action calculated in accordance with Appendix A of AS 3600

Flp

=

the liquid pressure load

Fsh

=

the loads, or their related moments and forces, resulting from shrinkage

Fsw

=

the loads, or their related moments and forces, resulting from swelling

fcp

=

the compressive strength of concrete at transfer

fs

=

the tensile stress in non-tensioned reinforcing steel

fso

=

the nominal limiting tensile stress in reinforcing steel

fsy

=

the yield strength of the reinforcing steel

f ′c

=

the characteristic compressive cylinder strength of concrete at 28 days

f ′ s max.

=

the effective limiting tensile stress in reinforcing steel

fct.3

=

the direct tensile strength of the concrete at 3 days

G

=

the dead load

P

=

the force in the tendons; or

=

the maximum force in the anchorage

p

=

a reinforcement ratio

Q

=

the live load (including impact, if any)

T

=

temperature; or

=

the load due to temperature variation

W

=

the wind load calculated, in accordance with AS 1170.2, from a wind velocity with the appropriate return period

Y 1, Y 2, Y 3

=

exposure coefficients

∆σs

=

increase in tendon stress once decompression occurs in a partially prestressed member

εsh

=

a shrinkage strain

εsw

=

a swelling strain

1.5 USE OF ALTERNATIVE MATERIALS OR METHODS 1.5.1 General Provided that the requirements of AS 3600 are met, this Standard shall not be interpreted so as to prevent the use of materials or methods of design or construction not specifically referred to herein.

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AS 3735—2001

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1.5.2 Existing structures Where the strength or serviceability of an existing structure is to be evaluated, the principles of this Standard and AS 3600 may be applied. 1.5.3 Ferrocement 1.5.3.1 General Ferrocement shall be thin-walled, reinforced cement mortar construction in which the reinforcement comprises closely spaced layers of straight wire mesh from 1 mm to 6 mm diameter and in which the cement mortar is pneumatically placed or plastered in layers. NOTE: Other arrangements of ferrocement are not covered by this Standard.

1.5.3.2 Material The material requirements for ferrocement shall be as specified in NZS 3106. 1.6 DRAWINGS AND SPECIFICATIONS

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1.6.1 Design data The following design data shall be shown in the drawings: (a)

Reference number and date of issue of applicable design Standards.

(b)

Live loads used in design.

(c)

Exposure classification for durability.

(d)

Fire resistance level, if applicable.

(e)

Class and, where appropriate, grade designation of concrete.

(f)

Grade and type of reinforcement and tendons.

1.6.2 Design details The drawings or specification for concrete members and structures should include, as appropriate, the following: (a)

The shape and size of each member.

(b)

The finish and method of control for unformed surfaces.

(c)

Class of formwork for the surface finish specified in accordance with AS 3610.

(d)

The size, quantity and location of all reinforcement, tendons and structural fixings and the minimum cover to each.

(e)

The requirements for concrete (see Clause 4.3).

(f)

The curing procedure and duration.

(g)

The force required in each tendon, the maximum jacking force to be applied and the order in which tendons are to be stressed.

(h)

The location and details of planned construction or movement joints, connections and splices, and the method to be used for their protection.

(i)

The minimum period of time before stripping of forms and removal of shores.

(j)

Any constraint on construction assumed in the design.

(k)

Any special protective coatings.

(l)

Other design requirements.

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AS 3735—2001

8

S E CT I ON 2 LOADS AND COMBI N AT I ONS

L O AD

2.1 GENERAL The design of structures and members for stability, strength and serviceability shall take account of the load and load combinations for strength in accordance with AS 3600 and of the action effects directly arising from the loads and other actions included in this Section. 2.2 LOADS AND OTHER ACTIONS 2.2.1 Temperature The walls and roofs of tanks shall be designed for the action effect arising from differential temperature gradients through the member.

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For tanks containing liquids at ambient temperature and subject to direct solar radiation, the design temperature gradients considered shall include the following cases: (a)

(b)

For roofs— (i)

a ±20°C variation from the mean temperature; and

(ii)

the temperature criteria given in Table 2.1.

For walls— (i)

when the tank is filled with liquid, by a +30, −20°C variation; and

(ii)

when the tank is empty, by a +20, −12°C variation; from the internal wall temperature as shown in Figure 2.1.

NOTE: Temperature effects for liquids at other than ambient temperatures are not specified in this Standard.

FIGURE 2.1 TEMPERATURE DISTRIBUTIONS IN TANK WALLS © Standards Australia

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AS 3735—2001

9

TABLE 2.1 ROOF—TEMPERATURE CRITERIA Linear temperature gradient, degrees Celsius per 100 mm of roof thickness

Region Snow (outside colder than inside)

10

Other (outside hotter than inside)

5

2.2.2 Moisture variation

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In the absence of a rational analysis of moisture variation, appropriate to the expected construction/loading history for the structure, the minimum effects due to moisture variation, either shrinkage or swelling, for both roofs and walls, shall be determined for the strains as given in Table 2.2.

TABLE 2.2 MOISTURE VARIATION—SHRINKAGE AND SWELLING STRAINS Mean shrinkage and swelling strain (creep adjusted) + 10–6 Wall thickness mm

Shrinkage (εεsh) Precast

Cast in situ

Swelling (εεsw) Precast

Cast in situ

100

70

120

300

250

150

50

85

205

170

200

45

70

160

135

250

35

60

135

110

2.2.3 Earthquake Loads due to earthquakes shall be determined in accordance with AS 1170.4. NOTE: NZS 3106 includes details for analysis of loads due to earthquakes.

2.2.4 Other actions Any action that may significantly affect the stability, strength and serviceability of structures and members, including but not limited to the following, shall be taken into account: (a)

Backfill.

(b)

Fatigue.

(c)

Progressive failure.

(d)

Ground movements.

(e)

Construction loads.

(f)

Liquid load.

(g)

Wind.

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AS 3735—2001

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2.3 STABILITY DESIGN In addition to the mass of the empty structure, the design resistance against uplift may take account of— (a)

anchoring systems;

(b)

drainage systems;

(c)

pressure relief valves; or

(d)

any combination of Items (a), (b) and (c).

The minimum safety factor against uplift shall be determined in accordance with AS 1170.1. The designer shall assess the effectiveness of the devices in Items (a) to (d). 2.4 LOAD COMBINATIONS FOR SERVICEABILITY The design load for serviceability design shall be the appropriate combinations of factored loads for long-term effects, Group A, and short-term effects, Group B, given below:

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(a)

(b)

Long-term effects (Group A): (i)

Roof—

(ii)

Wall—

G + P + Fsh

(A)

Tank full: G + Flp + Fep + P + 0.5 Fsw

(B)

Tank empty: G + Fep + P + (Fsh or 0.5 Fsw)

Short-term effects (Group B): (i)

(ii)

Roof— (A)

G+Q+P+T

(B)

0.8G + W + P

(C)

G + P + T + (0.7Fsh or 0.7Fsw)

(D)

0.8G + 0.8Feq

Wall— (A)

Tank full: G + Flp + Fep + P + 0.8Feq + 0.5Fsw

(B)

Tank full: G + Flp + Fep + P + 0.7 Fsw + T

(C)

Tank empty: G + Fep + P + T + (0.7 Fsh or 0.35 Fsw)

In Items (a) and (b) above, the dead load (G) shall be taken as the mass of structural members plus superimposed dead loads. If a worse effect is obtained by the omission of one or more of the transient loads in Item (a) or Item (b) above then such effect shall be taken into account.

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S E CT I ON

3

AS 3735—2001

DES I GN FOR S E RVI CE ABI LIT Y AND S T RE NGT H

3.1 GENERAL Although design for serviceability will generally dominate, design for strength shall be considered to ensure that the load capacity and slenderness ratios for members of the structure are within acceptable limits. 3.2 REINFORCED CONCRETE 3.2.1 General The reinforcement ratio shall be calculated using the following equation:

p = As / Ac,eff

. . .3.2.1

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NOTE: a 2 = 0.5D but not greater than 250 mm, except for the surface of a slab that is in contact with the ground then not greater than 100 mm

FIGURE 3.1 EFFECTIVE CONCRETE AREA

3.2.2 Minimum reinforcement ratio A minimum reinforcement ratio shall be provided to limit cracking. This quantity is dependent on the degree of restraint afforded, as follows: (a)

Unrestrained concrete The minimum reinforcement ratio for unrestrained concrete shall be determined from the following equation: p min. =

f ct.3 f sy

. . . 3.2.2

where

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pmin.

=

the minimum reinforcement ratio

fct.3

=

the principal tensile strength of concrete at three days

fsy

=

the yield strength of the reinforcement © Standards Australia

AS 3735—2001

(b)

12

Restrained concrete The minimum reinforcement ratio for fully restrained concrete shall be as defined in Table 3.1.

Values given in Table 3.1 may be reduced in proportion to the degree of restraint. The values may be reduced by 25% if— (i)

movement joints are provided at maximum 15 m spacing; or

(ii)

partial movement joints are provided at maximum 7.5 m spacing.

TABLE 3.1

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DEFORMED BARS—PERCENTAGE FOR FULLY RESTRAINED CONCRETE db , mm

8-12

16

20

24

28

32

pmin. %

0.48

0.64

0.80

0.96

1.12

1.28

3.2.3 Limiting steel stresses for serviceability The extent of cracking should be controlled by limiting the tensile stresses in the reinforcing steel, under the most severe combination of service loads. The value of such stress shall be calculated from the following equation: f s′max. = Y1 Y2 Y3 f so

. . . 3.2.3

The values of fso, Y 1 Y 2and Y 3 are as given in Tables 3.2, 3.3, 3.4 and 3.5. When welded wire fabric is used, welded intersections shall not be further apart than 200 mm. For members less than 225 mm thick, the face remote from the liquid shall be considered as though it was in contact with the liquid

TABLE 3.2 NOMINAL LIMITING STRESSES IN STEEL REINFORCEMENT db , mm

8-12

16

20

24

28-32

f so , MPa

150

140

130

120

110

TABLE 3.3 COEFFICIENT FOR BAR TYPE Y1 Type of reinforcement Exposure coefficient

Y1

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Plain bar

Deformed bar and welded wire fabric

0.85

1.00

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AS 3735—2001

13

TABLE 3.4 LOAD COMBINATION COEFFICIENT, Y2 Load combination

Y2

Long term effects (Group A)

1.0

Short term effects (Group B)

1.25

TABLE 3.5 COEFFICIENT FOR STRESS STATE AND TYPE OF EXPOSURE Y3 Type of exposure

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Exposure coefficient

Predominant stress state

Y3

Continuously submerged

Tension

1.00

Flexure

1.25

Intermittent wetting and drying 1.00

3.2.4. Limiting concrete thickness In the hoop direction of a circular tank, the concrete is assumed to be fully cracked and the reinforcement is designed to take the full hoop force with no contribution from the concrete so that the concrete thickness is limited by the requirements for the placement of reinforcement and concrete. Where other forces are involved, the concrete thickness is limited by the moment and shear capacity of the section. 3.3 PRESTRESSED CONCRETE 3.3.1 General All prestressing tendons shall be bonded. 3.3.2 Analysis In addition to the requirements of Section 2, the analysis shall take account of the full effects of prestressing including secondary effects and time-dependent creep effects. Analysis shall be carried out for the following load conditions and combinations: (a)

Conditions at any stage of prestress.

(b)

Group A load combination that comprises predominantly long-term loads.

(c)

Group B load combination that includes the short-term transient loads.

3.3.3 Limiting concrete stresses for serviceability Except as permitted by Clause 3.3.5, stresses shall be calculated on the basis of uncracked sections, and shall remain within the limits specified in Table 3.6. 3.3.4 Non-tensioned reinforcement Non-tensioned reinforcement shall be provided in prestressed elements in— (a)

end anchorage zones; and

(b)

between end anchorages, where prestress is calculated to be inadequate to sustain applied forces.

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AS 3735—2001

14

TABLE 3.6 LIMITING STRESSES IN PRESTRESSED CONCRETE Load combination, MPa Type of stress Transfer

Group A (long-term loads)

Group B (short-term loads)

0.50f cp

0.40f ′ c

0.55f ′ c

(b) Minimum compression at tendon location

—

0.70

0 (Note 1)

(c) Minimum compression at construction joints

—

0.70

0 (Note 2)

0.70

0.5

f ′c

(a) Maximum compression

(d) Maximum extreme fibre tension in monolithic concrete—

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(i) at water-retaining face

0.17

f cp

(ii) at non-water-retaining face (Note 3)

0.17

f cp

0.25

f ′c

0.5

f ′c

(e) Maximum principal tension resulting from shear

0.17

f cp

0.30

f ′c

0.5

f ′c

NOTES: f ′c is permissible.

1

Where earthquake forces have been considered, a maximum tension of 0.5

2

Cracking is permitted in joints under Group B combinations when non-tensioned reinforcement is provided to carry the entire tension force across the joint. The force shall be calculated on the basis of an uncracked section and reinforcement stresses shall comply with the limits specified in Clause 3.2.3.

3

For members less than 225 mm thick, the face remote from the liquid shall be considered as though it was in contact with the liquid.

3.3.5 Partial prestressing A partially prestressed design approach, permitting cracking of concrete, may be used provided the tensile stress in the non-tensioned reinforcement (fs), and the increase in tendon stress once decompression occurs (∆σs), taking full account of shrinkage and creep effects, satisfy the following requirements: (a)

fs ≤ f ′ s max.; and

(b)

∆σs ≤ 100 MPa, for group A load combinations; or ∆σs ≤ 125 MPa, for group B load combinations.

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AS 3735—2001

15

S E CT I ON

4

DES I GN

FOR

DURABI LI T Y

4.1 GENERAL Durability shall be allowed for in design by determining the exposure classification specified in Clause 4.2 and, for that exposure classification, complying with the appropriate requirements for the following: (a)

Concrete, in accordance with Clause 4.3.

(b)

Cover, in accordance with Clause 4.4.

The exposure classification shall take into account suitable means of isolating the concrete from the exposure environment.

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4.2 EXPOSURE CLASSIFICATION The exposure classification for the surface of a member shall be determined from Table 4.1 and from AS 3600 for the most severe environment or use to which the concrete will be subjected to during its operational life. TABLE 4.1 EXPOSURE CLASSIFICATIONS Exposure classification Characteristic of liquid in contact with concrete surface

Item

1

2

3

4

Freshwater:

Predominantly submerged Generally quiescent

Agitated or flowing

Alternate wet and dry (condensation splashing or washing)

(Notes 1, 2, 3)

(a)

I positive of pH >7.5

B1

B1

B1

(b)

I negative & pH 6.5 to 7.5

B1

B2

B1

(c)

I negative & pH 5.5 to 6.5

B2

C

B2

Sewage and waste water:

(Note 4)

(a)

resh—low risk of H 2S corrosion

B1

B1

B2

(b)

tale—high risk of H 2 S corrosion (Note 8)

B2

B2

D

(c)

naerobic sludge

B1

B1

B1

B1(7)

B2(7)

C

C

C

C

Sea water:

(Notes 5, 6)

(a)

eneral immersion and pH ≥7.5

(b)

etaining or excluding situations or pH