RC Detailing to EC2

Jenny Burridge

MA CEng MICE MIStructE

Head of Structural Engineering

Eurocodes & Standards

Materials, Cover & Detailing

Cracking and minimum steel

Anchorage & Laps + Worked Example

Beams, Slabs, Columns & Walls

Detailing comparison BS8110 & EC2

Resources

R C Detailing to Eurocode 2

BS EN 1992Design of concrete structures

Part 1-1: General & buildings

Part 1-2: Fire design

Part 2: Bridges

Part 3: Liquid retaining

Standards

BS EN 13670Execution of Structures

BS 4449Reinforcing

Steels

BS EN 10080Reinforcing

SteelsBS 8500Specifying Concrete

BS EN 206-1Specifying Concrete

BS 8666Reinforcement Scheduling

National AnnexPD 6687-1 (Parts 1 & 3)

PD 6687-2 ( Part 2)

1. General2. Basis of design3. Materials4. Durability and cover to reinforcement5. Structural analysis6. Ultimate limit state7. Serviceability limit state8. Detailing of reinforcement and prestressing tendons General9. Detailing of member and particular rules10. Additional rules for precast concrete elements and structures11. Lightweight aggregated concrete structures12. Plain and lightly reinforced concrete structures

Eurocode 2 - contents

A. (Informative) Modification of partial factors for materialsB. (Informative) Creep and shrinkage strainC. (Normative) Reinforcement propertiesD. (Informative) Detailed calculation method for prestressing steel

relaxation lossesE. (Informative) Indicative Strength Classes for durabilityF. (Informative) Reinforcement expressions for in-plane stress

conditionsG. (Informative) Soil structure interactionH. (Informative) Global second order effects in structuresI. (Informative) Analysis of flat slabs and shear wallsJ. (Informative) Examples of regions with discontinuity in geometry

or action (Detailing rules for particular situations)

Eurocode 2 - Annexes

EC2 Annex J - replaced by Annex B in PD 6687

EC2 does not cover the use of plain or mild steel reinforcement

Principles and Rules are given for deformed bars, decoiled rods,

welded fabric and lattice girders.

EN 10080 provides the performance characteristics and testing methods

but does not specify the material properties. These are given in Annex

C of EC2

Reinforcement

Product form Bars and de-coiled rods Wire Fabrics

Class

A

B

C

A

B

C

Characteristic yield strength fyk or f0,2k (MPa)

400 to 600

k = (ft/fy)k

1,05

1,08

1,15

Extract BS 8666

Reinforcement

To avoid damage to bar is

Bar dia 16mm Mandrel size 4 x bar diameterBar dia > 16mm Mandrel size 7 x bar diameter

The bar should extend at least 5 diameters beyond a bend

Minimum mandrel size, m

To avoid failure of the concrete inside the bend of the bar:

m,min Fbt ((1/ab) +1/(2 )) / fcdFbt ultimate force in a bar at the start of a bend

ab for a given bar is half the centre-to-centre distance between bars.

For a bar adjacent to the face of the member, ab should be taken as

the cover plus /2

Min. Mandrel Dia. for bent barsEC2: Cl. 8.3

Bearing stress inside bends

Minimum mandrel size, m

Mandrel size need not be checked to avoid concrete failure if :

anchorage does not require more than 5 past end of bend bar is not the closest to edge face and there is a cross bar inside bend mandrel size is at least equal to the recommended minimum value

Min. Mandrel Dia. for bent barsEC2: Cl. 8.3

Stress inside bends

13

Nominal cover, cnom

Minimum cover, cmin cmin = max {cmin,dur; cmin,b ; 10 mm}

Axis distance, aFire protection

Allowance for deviation, cdev

bond durability as per BS 8500

10 mmRecommended

Tables in Section 5 of part 1-2

Nominal cover

EC2 - Cover

cdev: Allowance for deviation = 10mm

A reduction in cdev may be permitted:

for a quality assurance system, which includes measuring concrete cover, 10 mm cdev 5 mm

where very accurate measurements are taken and non conforming members are rejected (eg precast elements)

10 mm cdev 0 mm

Allowance in Design for Deviation

Tolerances (in BS8666)

Control of Cracking

In Eurocode 2 cracking is controlled in the following ways:

Minimum areas of reinforcement cl 7.3.2 & Equ 7.1

As,mins = kckfct,effAct this is the same as

Crack width limits (Cl. 7.3.1 and National Annex). These

limits can be met by either:

direct calculation (Cl. 7.3.4) crack width is Wk Used for liquid retaining structures

deemed to satisfy rules (Cl. 7.3.3)

Note: slabs 200mm depth are OK if As,min is provided.

EC2: Cl. 7.3

Minimum Reinforcement Area

The minimum area of reinforcement for slabs (and beams) is given by:

db0013.0f

dbf26.0A t

yk

tctm

min,s

EC2: Cl. 9.2.1.1, Eq 9.1N

Crack Control Without Direct Calculation

Provide minimum reinforcement.

Crack control may be achieved in two ways:

limiting the maximum bar diameter using Table 7.2N

limiting the maximum bar spacing using Table 7.3N

EC2: Cl. 7.3.3

Note: For cracking due to restraint use only max bar size

Clear horizontal and vertical distance , (dg +5mm) or 20mm

For separate horizontal layers the bars in each layer should be

located vertically above each other. There should be room to allow

access for vibrators and good compaction of concrete.

Minimum spacing of barsEC2: Cl. 8.2

The design value of the ultimate bond stress, fbd = 2.25 12fctdwhere fctd should be limited to C60/75

1 =1 for good and 0.7 for poor bond conditions2 = 1 for 32, otherwise (132- )/100

a) 45 90 c) h > 250 mm

h

Direction of concreting

300h

Direction of concreting

b) h 250 mm d) h > 600 mmunhatched zone good bond conditions

hatched zone - poor bond conditions

Direction of concreting

250

Direction of concreting

Ultimate bond stress

EC2: Cl. 8.4.2

lb,rqd = ( / 4) (sd / fbd)

where sd is the design stress of the bar at the position from where the anchorage is measured.

Basic required anchorage length

EC2: Cl. 8.4.3

For bent bars lb,rqd should be measured along the centreline of the bar

lbd = 1 2 3 4 5 lb,rqd lb,min

However:

(2 3 5) 0.7

lb,min > max(0.3lb,rqd ; 10, 100mm)

Design Anchorage Length, lbd

EC2: Cl. 8.4.4

Alpha values

EC2: Table 8.2

Cover (see fig 8.3)

Confinement (see fig 8.4)

(Ast-Ast,min)/As

Pressure

Table 8.2 - Cd & K factors

EC2: Figure 8.3

EC2: Figure 8.4

Anchorage of links EC2: Cl. 8.5

l0 = 1 2 3 5 6 lb,rqd l0,min

6 = (1/25)0,5 but between 1.0 and 1.5 where 1 is the % of reinforcement lapped within 0.65l0 from the centre of the lap

Percentage of lapped bars

relative to the total cross-

section area

< 25% 33% 50% >50%

6 1 1.15 1.4 1.5

Note: Intermediate values may be determined by interpolation.

1 2 3 5 are as defined for anchorage length

l0,min max{0.3 6 lb,rqd; 15; 200}

Design Lap Length, l0 (8.7.3)

EC2: Cl. 8.7.3

Worked example

Anchorage and lap lengths

Anchorage Worked Example

Calculate the tension anchorage for an H16 bar in the

bottom of a slab (assuming fully stressed):

a) Straight bars

b) Other shape bars (Fig 8.1 b, c and d)

Concrete strength class is C25/30

Nominal cover is 25mm

Bond stress, fbdfbd = 2.25 1 2 fctd EC2 Equ. 8.2

1 = 1.0 Good bond conditions

2 = 1.0 bar size 32

fctd = ct fctk,0,05/c EC2 cl 3.1.6(2), Equ 3.16

ct = 1.0 c = 1.5

fctk,0,05 = 0.7 x 0.3 fck2/3 EC2 Table 3.1

= 0.21 x 252/3

= 1.8 MPa

fctd = ct fctk,0,05/c = 1.8/1.5 = 1.2

fbd = 2.25 x 1.2 = 2.7 MPa

Basic anchorage length, lb,req

lb.req = (/4) ( sd/fbd) EC2 Equ 8.3

Max stress in the bar, sd = fyk/s = 500/1.15

= 435MPa.

lb.req = (/4) ( 435/2.7)

= 40.3

For concrete class C25/30

Design anchorage length, lbd

lbd = 1 2 3 4 5 lb.req lb,min

lbd = 1 2 3 4 5 (40.3) For concrete class C25/30

Alpha valuesEC2: Table 8.2 Concise: 11.4.2

Table 8.2 - Cd & K factorsConcise: Figure 11.3EC2: Figure 8.3

EC2: Figure 8.4

Design anchorage length, lbdlbd = 1 2 3 4 5 lb.req lb,min

lbd = 1 2 3 4 5 (40.3) For concrete class C25/30

a) Tension anchorage straight bar

1 = 1.0

3 = 1.0 conservative value with K= 0

4 = 1.0 N/A

5 = 1.0 conservative value

2 = 1.0 0.15 (cd )/

2 = 1.0 0.15 (25 16)/16 = 0.916

lbd = 0.916 x 40.3 = 36.9 = 590mm

Design anchorage length, lbd

lbd = 1 2 3 4 5 lb.req lb,min

lbd = 1 2 3 4 5 (40.3) For concrete class C25/30

b) Tension anchorage Other shape bars

1 = 1.0 cd = 25 is 3 = 3 x 16 = 48

3 = 1.0 conservative value with K= 0

4 = 1.0 N/A

5 = 1.0 conservative value

2 = 1.0 0.15 (cd 3)/ 1.0

2 = 1.0 0.15 (25 48)/16 = 1.25 1.0

lbd = 1.0 x 40.3 = 40.3 = 645mm

Worked example - summary

H16 Bars Concrete class C25/30 25 Nominal cover

Tension anchorage straight bar lbd = 36.9 = 590mm

Tension anchorage Other shape bars lbd = 40.3 = 645mm

lbd is measured along the centreline of the bar

Compression anchorage (1 = 2 = 3 = 4 = 5 = 1.0)

lbd = 40.3 = 645mm

Anchorage for Poor bond conditions = Good/0.7

Lap length = anchorage length x 6

(number of bars lapped at section)

How to design concrete structures using Eurocode 2

Anchorage & lap lengths

Laps between bars should normally be staggered and not located in regions

of high stress, the arrangement of lapped bars should comply with the

following:

The clear distance between lapped bars should not be greater than 4 or

50 mm otherwise the lap length should be increased by a length equal to

the clear space where it exceeds 4 or 50 mm

1. The longitudinal distance between two adjacent laps should not be

less than 0,3 times the lap length, l0;

2. In case of adjacent laps, the clear distance between adjacent bars

should not be less than 2 or 20 mm.

When the provisions comply with the above, the permissible percentage of

lapped bars in tension may be 100% where the bars are all in one layer.

Where the bars are in several layers the percentage should be reduced to

50%.

All bars in compression and secondary (distribution) reinforcement may be

lapped in one section.

Arrangement of LapsEC2: Cl. 8.7.2

Arrangement of LapsEC2: Cl. 8.7.2, Fig 8.7

If more than one layer a maximum of 50% can be lapped

Arrangement of LapsEC2: Cl. 8.7.3, Fig 8.8

Anchorage of bars

F

Transverse Reinforcement

There is transverse tension reinforcement required

F/2 F/2

F tan

F tanF F

Lapping of bars

Transverse Reinforcement

There is transverse tension reinforcement required

Where the diameter, , of the lapped bars 20 mm, the transverse reinforcement should have a total area, Ast 1,0As of one spliced bar. It should be placed perpendicular to the direction of the lapped

reinforcement and between that and the surface of the concrete.

If more than 50% of the reinforcement is lapped at one point and the

distance between adjacent laps at a section is 10 transverse bars should be formed by links or U bars anchored into the body of the section.

The transverse reinforcement provided as above should be positioned at

the outer sections of the lap as shown below.

l /30A /2stA /2st

l /30FsFs

150 mm

l0

Transverse Reinforcement at LapsBars in tensionEC2: Cl. 8.7.4, Fig 8.9 only if bar 20mm or laps > 25%

As,min = 0,26 (fctm/fyk)btd but 0,0013btd

As,max = 0,04 Ac

Section at supports should be designed for a

hogging moment 0,25 max. span moment

Any design compression reinforcement () should be held by transverse reinforcement with spacing 15

BeamsEC2: Cl. 9.2

Tension reinforcement in a flanged beam at

supports should be spread over the effective width

(see 5.3.2.1)

BeamsEC2: Cl. 9.2

Shear reinforcement

Minimum shear reinforcement, w,min = (0,08fck)/fyk

Maximum longitudinal spacing, sl,max = 0,75d (1 + cot)

Maximum transverse spacing, st,max = 0,75d 600 mm

EC2: Cl. 9.2.2

For vertical links sl,max = 0,75d

Shear Design

d

V

z

x

d

x

V

z

s

EC2: Cl. 6.2.3

For members without shear reinforcement this is satisfied with al = d

a lFtd

a l

Envelope of (MEd /z +NEd) Acting tensile force

Resisting tensile force

lbdlbd

lbd

lbd

lbd lbdlbd

lbdFtd

Shift rule

Curtailment of reinforcement

EC2: Cl. 9.2.1.3, Fig 9.2

For members with shear reinforcement: al = 0.5 z Cot But it is always conservative to use al = 1.125d

h /31

h /21

B

A

h /32 h /22

supporting beam with height h1

supported beam with height h2 (h1 h2)

The supporting reinforcement is in

addition to that required for other

reasons

A

B

The supporting links may be placed in a zone beyond

the intersection of beams

Supporting Reinforcement at Indirect Supports

Plan view

EC2: Cl. 9.2.5

Simplified Detailing Rules for Beams

Curtailment as beams except for the Shift rule al = d

may be used

Flexural Reinforcement min and max areas as beam

Secondary transverse steel not less than 20% main

reinforcement

Reinforcement at Free Edges

Solid slabsEC2: Cl. 9.3

Where partial fixity exists, not taken into account in design: Internal

supports: As,top 0,25As for Mmax in adjacent spanEnd supports: As,top 0,15As for Mmax in adjacent span

This top reinforcement should extend 0,2 adjacent span

Solid slabsEC2: Cl. 9.3

Distribution of moments

EC2: Table I.1

Particular rules for flat slabs

Arrangement of reinforcement should reflect behaviour under working conditions.

At internal columns 0.5At should be placed in a width = 0.25 panel width.

At least two bottom bars should pass through internal columns in each orthogonal directions.

Particular rules for flat slabs

EC2: Cl. 9.4

h 4b

min 12 As,min = 0,10NEd/fyd but 0,002 Ac

As,max = 0.04 Ac (0,08Ac at laps)

Minimum number of bars in a circular column is 4.

Where direction of longitudinal bars changes more than

1:12 the spacing of transverse reinforcement should be

calculated.

Columns

EC2: Cl. 9.5.2

scl,tmax = min {20 min; b ; 400mm}

150mm

150mm

scl,tmax

scl,tmax should be reduced by a factor 0,6:

in sections within h above or below a beam

or slab

near lapped joints where > 14. A min of 3 bars is required in lap length

scl,tmax = min {12 min; 0.6b ; 240mm}

Columns

EC2: Cl. 9.5.3

Walls

As,vmin = 0,002 Ac (half located at each face) As,vmax = 0.04 Ac (0,08Ac at laps) svmax = 3 wall thickness or 400mm

Vertical Reinforcement

Horizontal Reinforcement As,hmin = 0,25 Vert. Rein. or 0,001Ac shmax = 400mmTransverse Reinforcement

Where total vert. rein. exceeds 0,02 Ac links required as for columns

Where main rein. placed closest to face of wall links are required (at least 4No. m2). [Not required for welded mesh or bars 16mm with cover at least 2.]

Detailing Comparisons

Beams EC2 BS 8110

Main Bars in Tension Clause / Values Values

As,min 9.2.1.1 (1): 0.26 fctm/fykbd 0.0013 bd

0.0013 bh

As,max 9.2.1.1 (3): 0.04 bd 0.04 bh

Main Bars in Compression

As,min -- 0.002 bh

As,max 9.2.1.1 (3): 0.04 bd 0.04 bh

Spacing of Main Bars

smin 8.2 (2): dg + 5 mm or or 20mm dg + 5 mm or Smax Table 7.3N Table 3.28

Links

Asw,min 9.2.2 (5): (0.08 b s fck)/fyk 0.4 b s/0.87 fyvsl,max 9.2.2 (6): 0.75 d 0.75d

st,max 9.2.2 (8): 0.75 d 600 mm

9.2.1.2 (3) or 15 from main bard or 150 mm from main bar

Detailing Comparisons

Slabs EC2 BS 8110

Main Bars in Tension Clause / Values Values

As,min 9.2.1.1 (1): 0.26 fctm/fykbd 0.0013 bd

0.0013 bh

As,max 0.04 bd 0.04 bh

Secondary Transverse Bars

As,min 9.3.1.1 (2): 0.2As for single way

slabs

0.002 bh

As,max 9.2.1.1 (3): 0.04 bd 0.04 bh

Spacing of Bars

smin 8.2 (2): dg + 5 mm or or 20mm9.3.1.1 (3): main 3h 400 mm

dg + 5 mm or

Smax secondary: 3.5h 450 mm 3d or 750 mm

places of maximum moment:

main: 2h 250 mm

secondary: 3h 400 mm

Detailing Comparisons

Punching Shear EC2 BS 8110

Links Clause / Values Values

Asw,min 9.4.3 (2): Link leg = 0.053 sr st (fck)/fyk

Total = 0.4ud/0.87fyv

Spacing of Links

Sr 9.4.3 (1): 0.75d 0.75d

St 9.4.3 (1):

within 1st control perim.: 1.5d

outside 1st control perim.: 2d

1.5d

Columns

Main Bars in Compression

As,min 9.5.2 (2): 0.10NEd/fyk 0.002bh 0.004 bh

As,max 9.5.2 (3): 0.04 bh 0.06 bh

Links

Min size 9.5.3 (1) 0.25 or 6 mm 0.25 or 6 mmScl,tmax 9.5.3 (3): min (12min; 0.6 b;240 mm) 12

9.5.3 (6): 150 mm from main bar 150 mm from main bar

Concrete Society

Concrete Society

The Concrete Centre

How toCompendium

The Concrete Centre

Detailing

1 Scope2 Bibliography3 Definitions4 Execution Management5 Falsework and Formwork6 Reinforcement7 Prestressed Concrete8 In-situ Concrete - Finishes9 Precast Concrete10 Geometric Tolerances

Specification NSCS, v4

Keep up to date

Download:

Column charts

Derivations

Worked examples

How to guides

& more

www.eurocode2.info

www.concretecentre.com