Rcs1-chapter4-durability

Marwan SADEK 1

Reinforced Concrete

Structures 1 - Eurocodes

RCS 1

Professor Marwan SADEKhttps://www.researchgate.net/profile/Marwan_Sadek

https://fr.slideshare.net/marwansadek00

Email : [email protected]

If you detect any mistakes, please let me know at : [email protected]

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PLAN – RCS1

M. SADEK

Ch 1 : Generalities – Reinforced concrete in practice

Ch 2 : Evolution of the standards – Limit states

Ch 3 : Mechanical Characteristics of materials – Constitutive relations

Ch 4 : Durability and Cover

Ch 5 : Beam under simple bending – Ultimate limit state ULS

Ch 6 : Beam under simple bending – serviceability limit state SLS

Ch 7 : Section subjected to pure tension

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Selected ReferencesFrench BAEL Code (91, 99)

Règles BAEL 91 modifiées 99, Règles techniques de conception et de calcul des ouvrages et constructions en béton armé, Eyrolles, 2000. J. Perchat (2000), Maîtrise du BAEL 91 et des DTU associés, Eyrolles, 2000. J.P. Mougin (2000), BAEL 91 modifié 99 et DTU associés, Eyrolles, 2000.….

EUROCODES H. Thonier (2013), Le projet de béton armé, 7ème édition, SEBTP, 2013. Jean-Armand Calgaro, Paolo Formichi ( 2013) Calcul des actions sur lesbâtiments selon l'Eurocode 1 , Le moniteur, 2013. J. M. Paillé (2009), Calcul des structures en béton, Eyrolles- AFNOR, 2009. Jean Perchat (2013), Traité de béton armé Selon l'Eurocode 2, Le moniteur,2013 (2ème édition) Manual for the design of concrete building structures to Eurocode 2, TheInstitution of Structural Engineers, BCA, 2006. A. J. Bond (2006), How to Design Concrete Structures using Eurocode 2, Theconcrete centre, BCA, 2006.https://usingeurocodes.com/

M. SADEK

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In addition to Eurocodes, the references that are mainly used to prepare this course material are : Thonier 2013

Perchat 2013

Paillé 2009

Some figures and formulas are taken from

Cours de S. Multon - BETON ARME Eurocode 2 (available on internet)

Cours béton armé de Christian Albouy

M. SADEK

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Chapter IV

Durability and Cover

M. SADEK

1. Exposure Classes

2. Structural Classes

3. Cover

4. Detailing of Members / Reinforcement

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1.Exposure Classes 2. Structural Classes 3. Cover 4. Detailing for members

Introduction : Optimization of durability

The cover is the distance between the surface of thereinforcement closest to the nearest concrete surface.It should be sufficient in order to guarantee :

the protection of the steel against corrosion;

the safe transmission of bond forces;

an adequate fire resistance.

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The cover of steel and the characteristics of the surrounding

concrete are principal parameters that permit to control the

longevity of the structures.

Introduction : Optimization of durability


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Exposure CLASSES

18 classes - EC2


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Exposure classes related to environmental conditions in accordance with EN 206-1


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DIFFERENCE between the classifications of NF EN 206-1 & EC 2 (PAILLÉ 2009)

We should make the distinction between the classification relative to the concrete

(NFEN206-1) and that relative to the steel cover (EC2) function of the exposure condition.

The criterion is not always the same.


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DIFFERENCE between the classifications of NF EN 206-1 & EC 2 (PAILLÉ 2009)


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Indicative strength classes for durability

(NF EN 206-1)


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Design working life

Design workinglife category

Indicative design

working life (years)

F NA Examples

1 10 10 Temporary structures

2 10-25 25Replaceable structural parts, e.g. gantry girders,bearings

3 15-30 25Agriculture and similar structures

4 50 50 BUILDING STRUCTURES AND OTHER COMMON STRUCTURES

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


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Structural classes (6 Classes S1S6)

Classe S4 : The recommended Structural Class (design

working life of 50 years) is S4, for buildings and common civil

engineering structures

The bridges are classified in the the class S6 (4+2), for a design

working life of 100 years (Increase class by +2)

The class may be reduced function of design working

life, the strength class, and the binder type

(Table 4.3.NF, NA)


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Criterion Exposure Class

XO XC1 XC2, XC3 XC4 XD1 / XS1 / XA1

XD2 / XS2 / XA3

XD3 / XS3 / XA3

Design working life

100 years, Increase class by 2

25 years and less, Reduce class by 1

Strength Class

C 30/37 C 30/37 C 30/37 C 35/45 C 40/50 C 40/50 C 45/55

If the strength is greater, Reduce class by 1

C 50/60 C 50/60 C 55/67 C 60/75 C 60/75 C 60/75 C 70/85

If the strength is greater, Reduce class by 2

Binder type

- C 35/45 C35/45 C 40/50 - - -

-

Concrete with CEM Iwith fly ashes

- - -Reduce class by 1

CompactCover

Reduce class by 1

Obtaining compactness in the cover zone concerns for example :

Steel form work, precast elements ..


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Nominal cover cnom

cnom : nominal cover

cmin : minimum cover

cdev : allowance in design for deviation (Recommended value FNA = 10 mm)

(Recommended value FNA = 0)

Note : the Calculation should be conducted for longitudinal and transverse steel


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Nominal cover cnom

cmin,b : minimum cover due to bond requirement

(if dg>32)

1 bar

Bundle of nb barres

cmin,b =


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Nominal cover cnom

cmin,dur : minimum cover due to environmental conditions

requirements with regard to durability for reinforcement steel in accordance

with EN 10080 (Table 4.4 N - NF EN 1992-1-1)


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Nominal cover cnom

Raft foundation

The cover of a reinforced concrete raft cast directly against soil, the cover should be at least 75 mm (65 mm FNA).

This value could be reduced to 40 mm (30 mm ANF) concrete cast against

prepared ground (including blinding)


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Some detailing requirements

(Constructional details)


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Overlapping and anchorage of reinforcement (SBA2)

Transverse Steel

Bad practice very common in lebanon !!


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Minimum permissible mandrel diameter for bent bars avoid damage

to reinforcement

Other criterion : Avoid concrete damage (SBA2),

For this second condition we can reach quickly a value > 10 ( The obtained value with EC2 are higher than those obtained with the previous French code BAEL)

x 2mnomc

mandrin de cintrage

mdiamètre:

t

sdbt

5y

point de départ de l'ancrage

45°

nomct t

2/c tnom

For civil engineering constructions and in case of a good bond condition,

when the tensile force (at the origin of the bar bent) is lower than 75% of the

maximum design force (bt0.75fyd), the mandrel diameter could be taken

m=10 .


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Horizontal and Vertical spacing between bars (EC2, 8.2)(the concrete can be placed and compacted satisfactorily for the development of

adequate bond)

(dg=2.5 cm in general)

The bars should be placed symmetrically

to avoid any additional excentricity


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Reinforcing bars are in tension and therefore should never be bent around an

inside corner beams. They can pull straight !!


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Expansion joint

o Lmax = 25 à 30 m for Lebanon

o Top of the foundation

Construction joint

o in case of high differential settlement

Lmax

Lmax


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EXAMPLE Developed length for stirrups:

o m=5 (6 16)

o with straight length : max(10 ; 70 mm) (90°)

Carefull : When using other value of m, we obtain different values of developed length


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Bundle of bars

the bars should be of the same characteristics (type and grade).

Bars of different sizes may be bundled provided that the ratio of diameters

does not exceed 1,7.

Where two touching bars are positioned one above the other, and where

the bond conditions are good, such bars need not be treated as a bundle

[EC2 - 8.9.1(4)]


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Bundle of bars

In design, the bundle is replaced by a notional bar having the same

sectional area and the same centre of gravity as the bundle.

o nb ≤ 4 for vertical bars in compression and for bars in a

lapped joint

o nb ≤ 3 for all other cases. (tension)


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Determination of cover for longitudinal and transverse steel

Steel ratio including longitudinal and transversal steel (column , beam section)

Exercises

Rcs1-chapter4-durability

Education

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