01. a Summary of Essential Differences Between EC2 and BS8110 Code (2014 10 07)

1 . A s u m m a r y o f es e s s e n t i al al d if iffe fere ren n c e s b e tw e e n EC EC2 2 an d BS8110 Prof Tan Kang Hai Email: [email protected] Director of Protective Technology Technology Research Centre (PTRC) School of Civil & Environmental Engineering All the rights of of 11 11 lecture materials materials belong belong to Tan Tan Kang Hai Hai

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QUIZ • Which is the most challenging hurdle in migration from

BS8110 to EC2? • What is the highest grade of concrete in EC2? • How are notional horizontal loads represented in EC2? • What are the essential differences in shear design

between BS 8110 and EC2? • What is the main difference in column design in EC2? 2

Outline 

Similarities and differences of BS8110 and EC2

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Influence of material behaviour

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Basis of design and load combination

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Global geometric imperfections

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Nonlinear versus linear elastic analysis

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Shear design of beams and slabs

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Design of columns

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Detailing of members 3

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Design of columns

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Similarities of BS8110 and EC2

Similarities and differences of BS8110 and EC2 Influence of material behaviour Basis of design and load combination Global geometric imperfections Nonlinear versus linear elastic analysis

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Ultimate limit state and serviceability limit state Permanent actions, imposed loads and wind loads Plane strain assumption for design of beams, slabs, columns, and walls Linear elastic analysis

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Linear elastic analysis with limited distribution

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Plastic analysis

Shear design of beams and slabs Design of columns Detailing of members

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Differences between BS8110 and EC2

Similarities and differences of BS8110 and EC2 Influence of material behaviour Basis of design and load combination Global geometric imperfections Nonlinear versus linear elastic analysis Shear design of beams and slabs Design of columns Detailing of members

• • •

EC2 is phenomenon-based code unlike the BS8110 Entire code is based on reliability index Based on Model Concrete Code 1978 and 1990

1. Influence of material behaviour (Concrete grade 90/105) 2. Basis of design and load combination 3. Global geometric imperfections 4. Nonlinear versus linear elastic analysis 5. Shear design of beams and slabs 6. Design of columns 7. Detailing of members

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Outline 


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Design of columns

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Similarities and differences of BS8110 and EC2 Influence of material behaviour

EC2 stress-strain relationships of concrete under compression max stress level for idealized curve must be below the max stress of the schematic diagram for the same area under the curve

Basis of design and load combination Global geometric imperfections Nonlinear versus linear elastic analysis Shear design of beams and slabs Design of columns Detailing of members

The design value of concrete compressive strength f cd is given by:

f cd 

 cc f ck  c



0.85f ck 1.5



0.567f ck

(3.15)

Where the factor allows for the difference between the bending strength and the cylinder crushing strength of concrete, and  c  1.5 is the concrete material partial safety factor. 8


Table 3.1 Strength and deformation characteristics for concrete

Influence of material behaviour Basis of design and load combination Global geometric imperfections

Class 1

Class 2

Class 3

Nonlinear versus linear elastic analysis Shear design of beams and slabs Design of columns Detailing of members

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EC2 stress-strain relationships of reinforcing steel


k =f t/f y indicates ductility; the greater the k value, the longer is the

plateau or the plastic zone

uk.


The design value of the modulus of elastic E s is 200 GPa. In the ultimate limit state calculation, by taking a partial safety factor of  s  1.15 , design values of yield strength f yd and yield strain  y of reinforcing steel are respectively computed as:

f yd



f yk 1.15



0.87f yk

 y



f yk  s E s

3



500  10



6

1.15 200  10





0.00217 10

Similarities and differences of BS8110 and EC2 Influence of material behaviour Basis of design and load combination

Table C.1: Properties of reinforcement Product form Class Characteristic yield strength f yk or f 0.2k (MPa) Minimum value of k = (f t/f y )k

Bars and de-coiled rods A B C

Wire Fabrics A

B

C

400 to 600

≥1.05

≥1.08

≥1.15

≥1.05

Requirement or quantile value (%) 5.0

≥1.08

<1.35

≥1.15

10.0

<1.35

Global geometric imperfections Nonlinear versus linear elastic analysis Shear design of beams and slabs Design of columns Detailing of members

Characteristic strain at maximum force, (%) Bendability Shear strength Maximum deviation from nominal mass (individual bar of wire) (%)

Nominal bar size (mm)

≥2.5

≥5.0

≥7.5

≥2.5

Bend/Rebend test -

≥5.0

≥7.5

0.3 A f yk (A is area of wire)

6.0 ± 4.5 ±

10.0

Minimum

5.0

≤8

>8

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7.2.3 Tensile properties The specified values for the tensile properties are given in Table 4.

BS 4449:2005 +A2:2009

Table 4 – Characteristic tensile properties Basis of design and load combination Global geometric imperfections Nonlinear versus linear elastic analysis Shear design of beams and slabs Design of columns Detailing of members

B500A

Yield strength, Re MPa 500

Tensile/yield strength ratio, Rm/Re

Total elongation at maximum force, Agt %

1.05a

2.5b

B500B

500

1.08

5.0

B500C

500

≥1.15,<1.35

7.5

a R /R characteristics is 1.02 for sizes below 8mm. m e b A characteristics is 1.0% for sizes below 8mm. gt

Values of Re specified are characteristic with p = 0.95. Values of Rm/Re and Agt specified are characteristic with p = 0.90. Calculate the values of Rm and Re using the nominal cross sectional area.

The absolute maximum permissible value of yield strength is 650 MPa.

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7.2.3 Tensile properties

Influence of material behaviour Basis of design and load combination Global geometric imperfections Nonlinear versus linear elastic analysis Shear design of beams and slabs Design of columns Detailing of members

BS 8666:2005 - Scheduling, dimensioning, bending and cutting of steel reinforcement for concrete — Specification has been revised to incorporate: (i) Shape codes available under BS EN ISO 3766:2003; (ii) Revised notation in accordance with BS 4449:2005 and BS EN 10080:2005; (iii) Revisions to BS 4449:2005 (including the omission of grade 250 and grade 460 reinforcement) (iv) The provisions of BS EN 1992-1-1 (including the preclusion of wire to BS 4482:2004 for structural purpose). 13

Similar to BS specification Similarities and differences of BS8110 and EC2 Influence of material behaviour Basis of design and load combination Global geometric imperfections

BS system: notation is T


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Outline 


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Design of columns

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Load combinations according to EC0 Leading variable action and accompanying variable action:


(6.10)

Comparison of partial factors for loading Design situations With one variable action (Live load) With one variable action (Wind load) With two variable actions (leading and accompanying)

BS 8110

EC2

1.4DL + 1.6LL

1.35Gk + 1.5Qk

1.4DL + 1.6W

1.35Gk + 1.5W k

1.2DL + 1.2LL + 1.2W

1.35 Gk + 1.5 Qk + 0.75W k Or 1.35 Gk + 1.05 Qk + 1.5W k

(Wind & live loads) 0.7x1.5Qk for office or residential buildings

0.5x1.5W k 16


Load combinations To be applied together according to EC0


(6.10a)


(6.10b)


Ultimate states Eq. (6.10)

Combinations of actions 1.35 Gk + 1.5 Qk + 1.5*0.5W k

For EQU, STR, GEO Eq. (6.10a)

1.35 Gk + 1.5*0.5W k +1.5*0.7 Qk

For STR, GEO

1.35 G k + 1.5*0.5W k

Eq. (6.10b) For STR, GEO

Or 1.35 Gk + 1.05 Qk + 1.5W k

0.925*1.35Gk + 1.5W k +1.5*0.7 Qk For unfavourable Or 0.925*1.35 G k + 1.5W k permanent actions – single source principle in EC0 - Table 17 A1.2 (B) Set B


Load combinations according to EC0


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Load combinations according to EC2 Cl 5.1.3


Single source for G k

Basis of design and load combination Global geometric imperfections

1.35G k + 1.5Q k

Nonlinear versus linear elastic analysis Shear design of beams and slabs

1.35Gk + 1.5Qk

1.35Gk

1.35Gk + 1.5Qk

1.4Gk + 1.6Qk

1.0Gk

1.4Gk + 1.6Qk

Design of columns Detailing of members

1.35Gk + 1.5Qk 1.35Gk

1.35Gk

1.0Gk

1.4Gk + 1.6Qk

1.0Gk

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Outline 


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Design of columns

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When to consider geometric imperfections?


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In EC2, there is no notional horizontal load.

•

Global geometric imperfections due to out-of-plumbness of vertical elements must be modelled by equivalent loads in two design situations:



Persistent design situations: Possible extreme loading condition of wind, imposed loads.


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Accidental design situations: fire, impact. 21

When to consider geometric imperfections?


•


Imperfection loads are quantified by three considerations: 

Global analysis of building structures.



Analysis of isolated vertical members.



Analysis of floor diaphragms as horizontal elements transferring forces to bracing members.

Only imperfection loads in global analysis are similar to notional horizontal loads, although they are very different in the way to be considered. •

Imperfections need not be considered for serviceability limit states. 22

How to consider geometric imperfections?


•

Basis of design and load combination Global geometric imperfections

The structure is assumed with inclination

where: θ 0 is

θ l ,

given by:

the basic value ( θ 0 = 1/200)

•

α h is

the reduction factor for height

•

α m is

the reduction factor for number of members:


where m is the number of vertically continuous members in the storey contributing to total horizontal forces on the floor. 23


How to consider geometric imperfections?

Influence of material behaviour Basis of design and load combination Global geometric imperfections Nonlinear versus linear elastic analysis Shear design of beams and slabs

To design for slab (member transferring forces to bracing elements)


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The imperfection on each floor may be represented by a force acting on the floor where N a and N b are the factored axial forces a b o v e and b e l o w the floor considered. (see 24 EC3 Figure 5.3)

Similarities and differences of BS8110 and EC2 Influence of material behaviour Basis of design and load combination Global geometric imperfections

How to consider geometric imperfections? Lateral load case: in BS 8110: H design = Max(H N , 1.2W k ) However, in EC 2: H design = 1.0 H i +  FW k where H i is horizontal loads for geometric imperfection


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Outline 


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Design of columns

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Similarities and differences of BS8110 and EC2 Influence of material behaviour Basis of design and load combination Global geometric imperfections

Different types of analysis 

F i r s t o r d e r e la s t i c a n a l y s i s : represents conditions at

normal service loads very well (Section 5.4) 

F i r s t o r d e r el as t i c a n a l y s i s w i t h l i m i t e d r e d i s t r i b u t i o n :

excluded nonlinearity, represents conditions at normal service loads very well (Section 5.5)







First order inelastic analysis : Plastic analysis with no

geometrical nonlinearity (Section 5.6) : Effects of finite S ec o n d o r d e r e l as t i c a n a l y s i s

Design of columns

deformation considered. Good representation of P-  effect (Section 5.7)

Detailing of members



S ec o n d o r d e r i n e l as t i c a n a l y s i s : Both geometrical and

material nonlinearities are considered. Model can faithfully reflect the behavior of structures up to ultimate limit state 27


Different types of analysis

Influence of material behaviour Basis of design and load combination



e


Source: Fig. 8.1 of Matrix Structural Analysis, Second Edition, William McGuire, Richard H. Gallagher and Ronald D. Ziemian, John Wiley & Sons, Inc, 2000, ISBN 0-471-12918-6 28

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Design of columns

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Methodology

Similarities and differences of BS8110 and EC2 Influence of material behaviour Basis of design and load combination

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EC2 uses The Variable Strut Inclination Method for shear design. BS 8110 uses Truss Analogy with truss angle  = 45 0 DC : the concrete acts as the diagonal struts;


V T : the stirrups act as the vertical ties;


BT : the tension reinforcement forms the bottom chord;


T C : the compression steel/concrete forms the top chord.


(a) Beam and reinforcement (b) Analogous truss

 = 21.80 ÷ 450 (strut angle) (EC2 6.2.3(2)) 30

Similarities and differences of BS8110 and EC2 Influence of material behaviour Basis of design and load combination Global geometric imperfections Nonlinear versus linear elastic analysis Shear design of beams and slabs Design of columns Detailing of members

Comparison of shear design EC2

• BS 8110

•

1.  = 45o

1.  = 21.8o ÷ 45o

2. BS 8110 compares shear 2. stresses. 3. 3. The maximum shear stress is limited to 5 N/mm2 or 0.8f cu, 4. whichever is the lesser. 4. The design shear force must be less than the sum of the shear resistance of concrete plus shear links.

EC 2 compares shear forces. The maximum shear capacity of concrete V Rd,max cannot be exceeded.

Where the applied shear exceeds the min shear resistance of concrete V R d,c, the shear reinforcement should be capable of resisting all the shear forces.

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Punching shear design of slabs Control perimeters Basic control perimeter u1:


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Design of columns

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Differences in symbols


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Differences in symbols


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Differences in design


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Differences in design


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Outline 


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Design of columns

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Detailing of members DESIGN ANCHORAGE LENGTH

For the effect of the form of the bars assuming adequate cover 1=0.7~1.0 (in comp. is 1.0) For the effect of concrete minimum cover 2=0.7~1.0 (in comp. is 1.0) For the effect of confinement by tied transverse bars along the design anc. length 3=0.7~1.0 (in comp. is 1.0) For the effect of confinement by welded transverse bars along the design anc. length 4=0.7 For the effect of confinement by transverse pressure along the design anc. length 5=0.7

Basic anchorage length Design stress of the bar: Design ultimate stress: For the quality of bond condition 1=0.7 (poor) - 1=1.0 (good) For the bar diameter 2=1.0 for ≤32mm 2=(132-)/100 for  >32mm The design concrete tensile strength (
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Detailing of members DESIGN ANCHORAGE LENGTH

l bd

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SUMMARY on Differences between BS and EC •

Complex load combinations due to leading and accompanying variable load cases;

•

In EC0 - Eq 6.10 compared with Eq 6.10(a) and Eq 6.10(b).

•

Definition of member types and the choice of suitable elements;

•

Represent global geometrical imperfection load by horizontal loads and consider in all ULS;

•

Need to consider global second order effect unless structure satisfies Clause 5.8.3.3;

•

Calculation model should reflect realistic global and local behaviour of the designed RC structure

•

High strength concrete is permitted (above 50 MPa till 90 MPa);

•

Mild steel 250 MPa is no longer allowed. 41

QUIZ • Which is the most challenging hurdle in migration from

BS8110 to EC2? • What is the highest grade of concrete in EC2? • How are notional horizontal loads represented in EC2? • What are the essential differences in shear design

between BS 8110 and EC2? • What is the main difference in column design in EC2? 42

01. a Summary of Essential Differences Between EC2 and BS8110 Code (2014 10 07)

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