Design of Water-Retaining Structures

Application of Eurocodes to Control Crack Widths

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Evolution of Eurocodes• The Commission of European Community (EC)• Action programme in the construction

industry based on Article 95 of the Treaty of Rome

• Eliminating technical obstacles to trade between member states

• Set of common technical rules for the design of buildings and civil engineering works

• Established a steering committee in 19752

Evolution of Eurocodes (continued)

• A set of first generation Eurocodes were published after 15 years

• The responsibility of producing structural Eurocodes was given in 1989

• Agreement between the European Commission; and

• European Committee for Standardization (CEN) - Comité Européen de Normalization

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Evolution of Eurocodes (continued)• European Pre-standard - EuroNorm Vornorm-

(ENV)• National Application Document (NAD)• Conversion

– National Comments on ENVs– Feedback from users on ENVs– Co-ordination conditions– Format and editorial consistency

• European standard - EuroNorm (EN)

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Eurocodes• After publication of an EN• 2 year period is allowed for national

calibration• During which National Annex is issued• There is a 3-year coexistence period• Adapt there national provisions to withdraw

conflicting national rules• At the end of the coexistence period• The former national standards will be

withdrawn (e.g. withdrawal of BS 8110 )5

National Annexes• The National Standards body of a state should

publish the parameters in a National Annex• On behalf and with the agreement of the

national competent authorities• A National Annex cannot change or modify• The contents of a EN text in anyway other

than• Where it indicates that national choices may

made by means of Nationally Determined Parameters

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Eurocodes at National Level• National Title Page

– National Title, e.g. SLS EN 1992-3:xxxx• National Forward• EN Title Page

– e.g. EN 1992-3 June 2006 Supersedes ENV1992-4:1998

• EN Text• EN Annex(es)

– Normative, and Informative• National Annex

– e.g. NA to SLS EN 1992-3:xxxx7

Maintenance of the Eurocodes

• All ENs will have a 5 year review• The primary objective of the first review• Reduce the number of Nationally Determined

Parameters• Strong wish from EC• Makes up-to-date source of information

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The Structural Eurocodes

• EN 1990 Eurocode: Basis of structural design• EN 1991 Eurocode 1: Actions on structures• EN 1992 Eurocode 2: Design of concrete

structures• EN 1993 Eurocode 3: Design of steel

structures• EN 1994 Eurocode 4: Design of composite

steel and concrete structures

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The Structural Eurocodes (continued)

• EN 1995 Eurocode 5: Design of timbre structures

• EN 1996 Eurocode 6: Design of masonry structures

• EN 1997 Eurocode 7: Geotechnical design• EN 1998 Eurocode 8: Design of structures for

earthquake resistance• EN 1999 Eurocode 9: Design of aluminium

structures

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Related Parts of Eurocodes• EN 1991-1-5 Eurocode 1, Actions on structures

– Part 1-5: General actions-Thermal actions• EN 1991-4 Eurocode 1, Actions on structures

– Part 4: Silos and tanks• EN 1992-1-1 Eurocode 2, Design of concrete

structures – Part 1.1: General rules and rules for buildings

• EN 1992-3 Eurocode 2, Design of concrete structures – Part 3: Liquid retaining and containment structures

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Related Eurocodes

• EN 206-1: Concrete: Specification, performance, production and conformity

• EN 10080: Steel for the reinforcement of concrete

• EN 10138: Prestressing steels

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Basis of Structural DesignAssumptions (EN 1990:2002 – Cl 1.3)

(1) Design which employs the Principles and Application Rules is considered to meet the requirements, provided that the assumptions given in EN 1990 to EN 1999 are satisfied

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Principles and Application Rules (EN 1990:2002 – Cl 1.4)

• The Principles comprise:– General statements and definitions for which

there are no alternatives, as well as;– Requirements and analytical models for which no

alternative is permitted unless specifically stated

• The Principles are identified by the letter P following the paragraph number

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Principles and Application Rules (EN 1990:2002 – Cl 1.4)

• The Application Rules are generally recognized rules which comply with the Principles and satisfy their requirements

• It is permissible to use design rules which are different from the Application Rules given in EN 1990 for works, provided that– It is shown that the alternative rules agree with the

relevant Principles, and– Are at least equivalent with regard to the structural safety,

serviceability and durability which would be expected when using Eurocodes

• In EN 1990, the Application Rules are identified by a number in brackets ()

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Indicative Design Working Life

Design working life category

Indicative design working life (years)

Examples

1 10 Temporary structures (1)

2 10 to 20 Replaceable structural parts, e.g. gantry girders, bearings

3 15 to 30 Agricultural and similar structures

4 50 Building structures and other common structures

5 100 Monumental building structures, bridges, and other civil engineering structures

(1) Structures or parts of structures that can be dismantled with view to being re-used should not be considered as temporary

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Basic Requirements (EN 1990:2002 – Cl 2.1)

• A structure shall be designed and executed • In such a way that it will during its intended

life• With appropriate degrees of reliability; and in

an economical way• Sustain all actions and influences likely to

occur during execution and use, and• Remain fit for the use for which it is required

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Route to Meet of Basic Requirements

• The basic requirements should be met:– By the choice of suitable materials– By appropriate design and detailing, and– By specifying control procedures for design,

production, and useto the relevant particular project

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Terminology• “Action” means a load or an imposed

deformation• “Effects of actions” or “Action effects” mean

internal moments and forces and deformations caused by actions

• “Strength” is a mechanical property of a material in units of stress

• “Resistance” is a mechanical property of a cross-section of a member, or a member or structure

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Actions

• Permanent action, G• Variable action, Q• Accidental action, A• Seismic action, AE

• Geotechnical action

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Classification of Actions (EN 1990:2002 – Cl 4.1.1)• Actions shall be classified by their variation in

time as follows:– Permanent actions (G), e.g. self-weight of

structures, fixed equipment, and indirect actions caused by shrinkage and uneven settlements, prestressing force (P)

– Variable actions(Q), e.g. imposed loads on building floors, beams and roofs, wind actions or snow loads

– Accidental actions (A), e.g. explosions, or impact from vehicles

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Classification of Actions (continued)

• Certain actions such as seismic actions and snow loads, may be considered as either accidental and/or variable actions, depending on the site location

• Actions caused by water may be considered as permanent and/ or variable actions depending on the variation of their magnitude with time

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Characteristic Values of Actions (EN 1990:2002 – Cl4.1.2)

• The characteristic value Fk of an action is its main representative value and shall be specified:– As a mean value, and upper or lower value, or a

nominal value (which does not refer to a known statistical distribution)

– The characteristic value of a permanent action shall be assessed as follows:

if the variability of G can be considered as small, one single value of Gk may be usedIf the variability cannot be considered small, two values shall be used: an upper value Gk, sup and a lower value Gk, inf

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Other Representative Values of Variable Actions(EN 1990:2002 – Cl 4.1.3)

• The combination value, represented as a product ψ0Qk, used (ψ0 − factor for combination value of a variable action )

• For the verification of ultimate limit states and irreversible serviceability limit states

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Other Representative Values of Variable Actions(EN 1990:2002 – Cl 4.1.3) (continued)

• The frequent value, represented as a product ψ1Qk used (ψ1 − factor for frequent value of a variable action )

• For the verification of ultimate limit states involving accidental actions and

• For verifications of reversible serviceability limit states

• For buildings, for example, the frequent value is chosen so that the time it is exceeded is 0.01 of the reference period

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Other Representative Values of Variable Actions(EN 1990:2002 – Cl 4.1.3) (continued)

• The quasi-permanent value, represented as a product ψ2Qk, used (ψ2 − factor for quasi-permanent value of a variable action )

• For the verification of ultimate limit states involving accidental actions; and

• For the verification of reversible serviceability limit states. Quasi-permanent values are also used for the calculation of long-term effects

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• For example, loads on building floors, the quasi-permanent value is usually chosen so that the proportion of time it is exceeded is 0.50 of the reference period

• The quasi-permanent value can alternatively be determined as the value averaged over a chosen period of time

• In the case of wind actions, the quasi-permanent load is generally taken as zero

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Variable action

Time

Inst

anta

neou

s ac

tion,

Q

Characteristic value, Qk

Frequent value, ψ1Qk

Quasi-permanent value, ψ2Qk

Combination value, ψ0Qk

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Number formats

• Word of warning• “,” is used in place of “.”

– e.g. 2,9 means 2.9– 1,000 means 1.000 NOT one thousand– Be vigilant on using expressions with constants

• “‰” stands for per mil ( one thousandth)– e.g. 3,5 ‰ means 0.0035

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Compressive Strength of Concrete• Expressed in terms of strength class• Example notation: C 25/30• This means – normal weight or heavy weight

concrete having characteristic cylinder strength of 25 N/mm2 and cube strength of 30 N/mm2

• In all expressions of Eurocodes, characteristic compressive strength denoted by fck refers to cylinder strength

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Tensile Strength of Concrete• Tensile strength of concrete, fct ,is represented

by the direct tensile strength• Direct tensile strength is related to splitting

tensile strength by fct = 0.9 fct, sp

• Mean tensile strength is denoted by fctm

• Characteristic tensile strength ( 5% fractile) is denoted by fctk,0.05

• Characteristic tensile strength ( 95% fractile) is denoted by fctk,0.95

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Limits on crack width

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Scope of Part 3 of EN 1992

“(101)P Part 3 of EN 1992 covers additional rules to those in Part 1 for the design of structures constructed from plan or lightly reinforced concrete, reinforced concrete or prestressed concrete for the containment of liquids or granular solids”

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“(102)P Principles and Application rules are given in this part for the design of those elements of structure which directly support the stored liquids and materials (i.e. the directly loaded walls of tanks, reservoirs or silos). Other elements which support these primary elements, the tower structure which supports the tank in a water tower) should be designed according to the provisions of Part 1-1.”

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Durability and Leakage of liquids

“(107) In clauses relating to leakage and durability, this code mainly covers aqueous liquids. Where other liquids are stored in direct contact with structural concrete, reference should be made to specialist literature.”

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Classification of Tightness(Table 7.105)

Tightness Class

Requirements for leakage

0 Some degree of leakage acceptable, or leakage of liquids irrelevant.

1 Leakage to be limited to a small amount. Some surface staining or damp patches.

2 Leakage to be minimal. Appearance not to be impaired by staining.

3 No leakage permitted

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Design Provisions (111)• Tightness Class 0

– the provisions in 7.3.1 of EN 1992-1-1 may be adopted.

• Tightness class 1– cracks which can be expected to pass through the

full thickness of the section should be limited to wk1. (Provided self-healing of cracks is assumed)

– provisions in 7.3.1 of EN 1992-1-1 apply• where the full thickness of the section is not cracked,

and• where the conditions in (112) and (113) are fulfilled.

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Design Provisions (continued)

• Tightness Class 2– cracks which may be expected to pass through the full

thickness should generally be avoided– unless appropriate measures (e.g. liners or water bars)

have been incorporated

• Tightness Class 3– generally, special measures (e.g. liners or prestress)

will be required to ensure watertightness

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Design Provisions (continued)• Provisions in 7.3.1 of EN 1992-1-1

– Tightness Class 0– Tightness Class 1, 2, and 3 where full thickness is

not cracked

• Provisions in 7.3.1 (111) of EN 1992-3– Tightness Class 1 where full thickness is cracked

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Cracks do Not Passing Through Full Thickness

Exposure Class Reinforced members and prestressed members with

unbonded tendons

Prestressed members with bonded tendons

Quasi-permanent load combination

Frequent load combination

X0, XC1 0.41 0.2

XC2, XC3, XC40.3

0.22

XD1, XD2, XS1XS2, XS3

Decompression

Note 1: For X0, XC1 exposure classes, crack width has no influence on durability and this limit is set to guarantee acceptable appearance. In the absence of appearance conditions this limit may be relaxed.Note 2: For these exposure classes, in addition, decompression should be checked under the quasi-permanent combination of loads.

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Cracks Passing Through Full Thickness wk1

• EN 1992-3 Note to (111) of 7.3.1• May be found in the National Annex• However, the recommended values• For hD/h ≤ 5, wk1= 0.2 mm• For hD/h ≥ 35, wk1= 0.05 mm• For intermediate values, linearly interpolate

hD- hydrostatic pressureh- wall thickness of the structure

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Cracks – Tightness Class 2 and 3• To assure that cracks do not pass through the

full thickness• The design value of the depth of compression

zone• Calculated for quasi-permanent combination

of actions• Liner elastic material behavior and sectional

properties neglecting concrete in tension• Xmin is the lesser of 50 mm or 0.2h• Where h is the member thickness

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Cracks – Tightness Class 2 and 3

• If a section is subjected to alternate actions• Cracks should be considered to pass through

the full thickness• Unless it can be shown that some part of the

section will always remain in compression

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Control of Cracking

• Provision of minimum reinforcement• Verification of crack widths

- without direct calculation of crack widths- with direct calculation of crack widths

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Control Without Direct Calculation• Cl 7.3.3 EN 1992-1-1 • Crack widths are unlikely to be excessive.• For cracking caused dominantly by restraint• The bar sizes given in Table 7.2N are not

exceeded.• For cracks caused mainly by loading, either the

provisions of Table 7.2N or the provisions of Table 7.3N are complied with.

• The steel stress should be calculated on the basis of a cracked section under the relevant combination of actions.

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Control Without Direct Calculation• Cl 7.3.3 EN 1992-3 • Crack widths are unlikely to be excessive.• For cracking caused dominantly by restraint• The bar sizes given in Figure 7.103N are not

exceeded where the steel stress is the value obtained immediately after cracking.

• For cracks caused mainly by loading, either the provisions of Figure 7.103N or the provisions of Figure 7.104N are complied with.

• The steel stress should be calculated on the basis of a cracked section under the relevant combination of actions.

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Control With Direct Calculation

• Cl 7.3.4 of EN 1992-1-1• Eqs. 7.8, 7.9, 7.10 and 7.11• C is the cover to longitudinal reinforcement• Ac,eff is the effective area of concrete in

tension surrounding the reinforcement or prestressing tendons

• hc,eff is the lesser of 2.5 (h-d), (h-x)/3 or h/2 (see Figure 7.1)

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Tutorial

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