How_GetStarted_June05.pdf

PROOF 1 1/06/05

Design note – Diagrams and tables will be artworked when overall layout approved. They have all been

given realistic depths and areas.

Table 8 being one full page, (and ensuring Table 7 is before it and Table 9 after), plus Tables 4 and 10

needing a full page width, has dictated the layout somewhat. However, within those constraints we have tried

to keep tables and Figs as close to relevant text as possible, and also break columns / pages for sense.

How to design concrete structures using Eurocode 2:

Getting started

O Brooker BEng, CEng, MICE

Introduction

The introduction of European standards to UK

construction is a significant event. The ten design

standards, known as the Eurocodes, will affect all

design and construction activities as current British

Standards for design are due to be withdrawn in

2010.

The design process

The design process will not change as a result of using to Eurocode 2.

Conceptual designs should be similar irrespective of the Code of Practice

used; therefore, current conceptual designs may confidently be taken

through to detailed design using Eurocode 2. In the long term it is

anticipated that Eurocode 2 will lead to more economic structures.

This publication is part of the series of guides

entitled How to design concrete structures using

Eurocode 2 . Their aim is to make the transition

to Eurocode 2 as easy as possible by drawing

together in one place key information and

commentary required for the design of typical

concrete elements.

During the detailed design phase, the design information for the project

will be assembled. This will include design life, loading, material

properties, method of analysis, stability, minimum concrete cover and

maximum crack widths. This publication gives guidance on these topics

based on the Eurocodes. It should be noted that the design principles,

actions on structures and load combinations are covered in a number of

Eurocodes common to all materials. Guidance on the analysis and design

of individual members in a structure will be given in subsequent guides in

this series.

The cement and concrete industry recognised that

a substantial effort was required to ensure that

the UK design profession would be able to use

Eurocode 2: Design of concrete structures 1 quickly,

effectively, efficiently and with confidence. With

support from government, consultants and

relevant industry bodies, the Concrete Industry

Eurocode 2 Group (CIEG) was formed in 1999

and this Group has provided the guidance for a

co-ordinated and collaborative approach to the

introduction of Eurocode 2. As a result, a range

of resources is to be made available through The

Concrete Centre to help designers during the

transition period (see back cover for details).

The design process will be completed with the detailing of the

reinforcement, and guidance can be obtained from the Standard method

of detailing . 2

Design note – we have copied heading

hierachy from original Word document supplied,

(eg ‘The design process’ header is the same

size as ‘Design life’ and ‘Load cominations and

arrangements’. However this may be wrong -

please confirm.

Design life

The design life for a structure is given in the UK NA to Eurocode: Basis of

structural design 3 (see Table 1), and this should be used to determine the

durability requirements for the design of reinforced concrete structures.

Load combinations

and arrangements

PIC HERE

Design note – I would have preferred to put Table

1 on this page and started ‘Load Contamination’

on p2. However, that does not leave room for the

blue box to go directly after its relevant text, as

‘Load Contamination’ makes exactly 1 column if it

starts at the top of a page.

The term load combinations refers to the value of actions or loads to be

used when a limit state is under the influence of different actions. They

are detailed in Eurocode and the UK National Annex (NA). The term load

arrangements refers to the arranging of variable actions to give the most

onerous forces in a member or structure and are given in Eurocode 2 and

its UK NA.

The only way I can start ‘Load Contamination’ at

the top of page 2 is if the blue box can go at the

bottom of the ‘spare’ column, or some text is cut.

However maybe you will think this is OK as it

stands.

For building structures, the UK NA to Eurocode 2, Part 1–1 allows either

of the following sets of load arrangements to be used:

Table 1

Indicative design working life (from UK National Annex to Eurocode)

1. Alternate or adjacent spans loaded

The design values should be obtained from the more critical of:

Alternate spans carrying the design variable and permanent loads with

other spans loaded with only the design permanent load (see Figure 1).

The value of _G should be the same throughout.

Any two adjacent spans carrying the design variable and permanent

loads with other spans loaded with only the design permanent load

(see Figure 2). The value of _G should be the same throughout.

Figure 1

Alternative spans loaded

2. All or alternate spans loaded

The design values should be obtained from the more critical of:

All spans carrying the design variable and permanent loads (see

Figure 3).

Design note – ignore

hands, they will go!

Alternate spans carrying the design variable and permanent loads

with other spans loaded with only the design permanent load (see

Figure 1). The value of _G should be the same throughout.

3. Simplified arrangements for slabs

The load arrangements can be simplified for slabs where only the all

spans loaded needs to be checked (see Figure 3), provided the

following conditions are met:

Figure 2

Adjacent spans loaded

In a one-way spanning slab the area of each bay exceeds 30 m 2 (a

bay means a strip across the full width of a structure bounded on

the other sides by lines of support).

The ratio of the variable action ( Q k ) to the permanent action ( G k )

does not exceed 1.25

The magnitude of the variable action excluding partitions does not

exceed 5 kN/m 2 .

Generally, option two will require three load arrangements to be

considered, while option one will often require more than three

arrangements to be assessed.

The numerical values of the partial factors for the ULS combination can

be obtained by referring to Eurocode: Basis of structural design or How

to design concrete structures to Eurocode 2: Introduction to Eurocodes 4 .

Figure 3

All spans loaded

Generally for members supporting one variable action the

combination

1.25 G k + 1.5 Q k (derived from Exp 6.10b, Eurocode)

can be used provided the permanent actions are not greater

than 4.5 times the variable actions (except for storage loads).

Actions on structures

Table 2

Selected bulk density of materials (from Eurocode 1, Part 1–1)

Eurocode 1: Actions on structures 5 contains 10 parts giving details of a

wide variety of actions. Further information on the individual codes can

be found in the first guide in this series, How to design concrete

structures using Eurocode 2: Introduction to Eurocodes . Eurocode 1, Part

1–1: General actions – Densities, self-weight, imposed loads for buildings 4

gives the densities and self-weights of building materials (see Table 2).

Design note – Is this correct strapline? Or should ‘Getting started’ be deleted? If not, should

previous leaflet’s strap be amended to match? (ie add ‘: Introduction to Eucrocodes’ to it)

How to design concrete structures using Eurocode 2: Getting started

The key change to current practice is that the bulk density of

reinforced concrete has been increased to 25 kN/m 3 . The draft

National Annex to this Code gives the imposed loads for UK buildings

and a selection is reproduced in Table 3. It should be noted that there

is no advice given for plant rooms.

Concrete up to class C90/105 can be designed using Eurocode 2. For

classes above C50/60, however, there are additional rules and

variations. For this reason, the design of these higher classes is not

considered in this series of guides.

Currently not all the parts of Eurocode 1 and their National Annexes

are available, in which case it is advised that the loads recommended

in the current British Standards are used.

It should be noted that designated concretes (e.g. RC30) still refer to

the cube strength.

Reinforcing steel

Eurocode 2 can be used with reinforcement of characteristic

strengths ranging from 400 to 600 MPa. The properties of steel

reinforcement in the UK for use with Eurocode 2 are given in BS

4449 Specification for carbon steel bars for the reinforcement of

concrete 8 and are summarised in Table 5. A characteristic yield

strength of 500 MPa has been adopted by BS 4449. There are three

classes of reinforcement, A, B and C, which provide increasing

ductility. Class A is not suitable where redistribution of 20% and

above has been assumed in the design. There is no provision for the

use of plain bar or mild steel reinforcement.

Material properties

Concrete

In Eurocode 2 the design of reinforced concrete is based on the characteristic

cylinder strength, rather the cube strength and should be specified according

to BS 8500: Concrete – complementary British Standard to EN 206-1 7 (e.g. for

class C28/35 concrete the cylinder strength is 28 MPa, whereas the cube

strength is 35 MPa). Typical concrete properties are given in Table 4.

Table 3

Selected imposed loads for buildings (from draft UK National Annex to Eurocode 1, Part 1–1)

Table 4

Selected concrete properties based on Table 3.1 of Eurocode 2, Part 1–1

Design note – Table 4 needs to be full page width which determoned overall layout of page

Table 5

Characteristic tensile properties of reinforcement

Structural analysis

The primary purpose of structural analysis in building structures is to

establish the distribution of internal forces and moments over the

whole or part of a structure and to identify the critical design

conditions at all sections. The geometry is commonly idealised by

considering the structure to be made up of linear elements and plane

two-dimensional elements.

The type of analysis should be appropriate to the problem being

considered. The following are commonly used: linear elastic analysis,

linear elastic analysis with limited redistribution and plastic analysis.

Linear elastic analysis may be carried out assuming cross sections are

uncracked (i.e. gross section properties); using linear stress-strain

relationships; and assuming mean values of elastic modulus.

Table 6

Bending moment and shear co-efficients for beams

For the ultimate limit state, the moments derived from elastic analysis

may be redistributed (up to a maximum of 30%) provided that the

resulting distribution of moments remains in equilibrium with the

applied loads and subject to certain limits and design criteria (e.g.

limitations of depth to neutral axis).

Regardless of the method of analysis used, the following principles apply:

Where a beam or slab is monolithic with its supports, the critical

design hogging moment may be taken as that at the face of the

support, and should not be taken as less than 0.65 times the full

fixed end moment.

Table 7

Exposure Classes

Where a beam or slab is continuous over a support that may be

considered not to provide rotational restraint, the moment

calculated at the centre line of the support may be reduced by

( F Ed,sup t /8), where F Ed,sup is the support reaction and t is the breadth

of the support.

Bending moment and shear force co-efficients for beams are given in

Table 6.

Stability and imperfections

As well as considering the wind loads, ULS stability calculations must

take into account the unfavourable effects of imperfections in a

structure. These effects should be considered in combination, not as

alternative load cases.

For the global analysis, the following procedure may be used.

Imperfections may be represented by an inclination q i of the whole

structure.

q i = (1/200) a h a m

where

How to design concrete structures using Eurocode 2: Getting started

Table 8

Selected 1 recommendations for normal-weight reinforced concrete quality for combined exposure classes

and cover to reinforcement for at least a 50-year intended working life and 20 mm maximum aggregate size

Exposure conditions

Cement/

combination

designations 2

Strength class 3 , maximum w/c ratio, minimum cement or combination

content (kg/m 3 ), and equivalent designated concrete (where applicable)

Typical Example

Primary Secondary

Nominal cover to reinforcement 4

15 +

c dev 20 +

c dev 25 +

c dev 30 +

c dev 35 +

c dev 40 +

c dev 45 +

c dev 50 +

c dev

Internal mass

concrete

Internal elements

(except humid

locations)

Buried concrete

in AC-1 ground

conditions 5

Vertical surface

protected from

direct rainfall

All

Recommended that this exposure is not applied to reinforced concrete

XC1

All

C20/25,

0.70, 240

or RC25

<<<

XC2

AC-1

All

___

C25/30,

0.65, 260

or RC30

C32/40,

0.55, 300

or RC40

C32/40,

0.55, 300

or RC40

<<<

All except IVB

___

C40/50,

0.45, 340

or RC50

C40/50,

0.45, 340

or RC50

C40/50,

0.45, 340 6

or RC50XF 6

C28/35,

0.60, 280

or RC35

C28/35,

0.60, 280

or RC35

C25/30,

0.65, 260

or RC30

<<<

Exposed vertical

surfaces

XF1

All except IVB

___

<<<

XC3

XC4

XF3

All except IVB

___

<<<

Exposed horizontal

surfaces

___

C32/40,

0.55, 300

plus air 6,7

C28/35,

0.60, 280

plus air 6,7

or PAV2

C25/30,

0.60, 280

plus air 6,7,8

or PAV1

XF3 (air

entrained)

All except IVB

<<<

Car park elements

subject to airborne

chlorides only

XD1

XC3/4

All except IVB

___

C40/50,

0.45, 360

C32/40,

0.55, 320

C28/35,

0.60, 300

<<<

IIB-V, IIIA

___

C35/45,

0.40, 380

C45/55,

0.35, 380

C32/40,

0.45, 360

C40/50,

0.40, 380

C28/35,

0.50, 340

C35/45,

0.45, 360

Car park decks and

areas subject to

de-icing spray

XC3/4

CEM I, IIA,

IIB-S, SRPC

___

IIIB

___

C32/40,

0.40, 380

C28/35,

0.45, 360

C25/30,

0.50, 340

IIB-V, IIIA

___

C35/45,

0.40, 380

C32/40,

0.45, 360

C32/40,

0.50, 340

Vertical elements

subject to de-icing

spray and freezing

XD3

XC3/4

+XF2

CEM I, IIA,

IIB-S, SRPC

___

C45/55,

0.35 ,380

C32/40,

0.40, 380

C45/55,

0.35, 380 6

C40/50,

0.40, 380

C32/40

0.45, 360

C40/50,

0.40, 380 6

C28/35

0.45,

360 6,7

C35/45,

0.45, 360

C32/40,

0.50, 340

IIIB

___

Car park decks

ramps and external

areas subject to

freezing and

de-icing salts

XC3/4

+XF4

XC3/4

+XF4 (air

entrained)

CEM I, IIA,

IIB-S, SRPC

___

<<<

IIIB

___

C28/35,

0.50,

340 6,7

IIB-V, IIIA

___

C45/55,

0.35, 380

C50/60,

0.35, 380

C35/45,

0.40, 380

C50/60,

0.35, 380 6

C35/45,

0.45, 360

C40/50,

0.45, 360

C32/40,

0.50, 340

C40/50,

0.45, 360 6

C32/40,

0.50, 340

C35/45,

0.50, 340

C32/40,

0.55, 320

<<<

Exposed vertical

surfaces near coast

XC3/4

+XF2

CEM I, IIA,

IIB-S, SRPC

___

<<<

XS1

___

IIIB

<<<

Exposed horizontal

surfaces near coast

XC3/4

+XF4

CEM I, IIA,

IIB-S, SRPC

___

<<<

1 This table comprises a selection of common exposure class combinations.

Requirements for other sets of exposure classes eg XD2, XS2 and XS3

should be derived from BS 8500-1: 2002, Annex A.

2 See BS 8500-2, Table 1. (CEM I is Portland cement, IIA to IVB are cement

combinations.)

3 For prestressed concrete the minimum strength class should be C28/35.

4 ∆ c dev is an allowance for deviations.

5 For sections less than 140 mm thick refer to BS 8500.

6 Freeze/thaw resisting aggregates should be specified.

7 Air entrained concrete is required.

8 This option may not be suitable for areas subject to severe abrasion.sections

KEY

___

Not recommended

<<<

Indicates that concrete

quality in cell to the left

should not be reduced

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