1. EUROPEAN CENTER OF PREVENTION AND FORECASTING OF EARTHQUAKES – ECPFE
EARTHQUAKE PLANNING AND PROTECTION ORGANIZATION – EPPO
Athens Workshop
April 12/2013
IMPLEMENTATION
OF THE EC8-P3:2005 ASSESSMENT AND INTERVENTIONS ON BUILDINGS
IN EARTHQUAKE PRONE AREAS
T.TASSIOS A.KOUTSIA Some comparisons between retrofitting provisions of EC8-P3 and other Codes for RC elements

2. Table of Contents

3. 1. Scope (a) EC8-P3 will need, as all Codes do,
to be improved and modified on a regular basis,
to intergrade:
the ongoing work,
the feedback from Code-users and
continuing developments in “repair technology”;
as well as to eliminate:
possible mistakes and
internal inconsistencies.

4. 1. Scope (b) This study attempts to make some comparisons
between retrofitting provisions
of EC8-P3 and KANEPE (GCSI)
for RC elements;
regarding:
Strengthening against shear,
Confinement action versus local ductility and
Clamping of lap-splices.

5. 2. Strengthening against shear 2.1 FRP jacketing
i. EC8-P3
2. Strengthening against shear
2.1 FRP jacketing
a. Design formulae
NOTE: γfd=1,5 is the partial factor for FRP debonding
For fully wrapped (i.e. closed) or properly anchored (in the compression zone) jackets:

6. 2. Strengthening against shear 2.1 FRP jacketing
i. EC8-P3
2. Strengthening against shear
2.1 FRP jacketing
b. Notation
θ: strut inclination angle,
β: angle between the (strong) fibre direction in the FRP sheet and the axis of the member,
wf: width of the FRP sheet measured orthogonally to the (strong) direction of the fibres (for sheets: wf=min(0,9d,hw)sin(θ+β)/sinθ),
sf: spacing of FRP sheet measured orthogonally to the (strong) fibre direction (=wf),
Le: effective bond length,
z =0,9d; internal lever arm,
ffdd: design debonding strength,
ffu,W(R): ultimate strength of the FRP sheet wrapped around the corner with a radius R and
fdd,e,W: design FRP effective debonding strength

7. U-shaped (i.e., open) jackets
ii. KANEPE
2. Strengthening against shear
2.1 FRP jacketing
Design formulae
NOTE: γRd=1,5
For beams:
For columns:
U-shaped (i.e., open) jackets
Fully wrapped (i.e., closed) or properly anchored (in the compression zone) jackets

8. NOTE: the partial factor of the FRP is taken equal to 1,1
2.1.1 Numerical example (a)
2. Strengthening against shear
2.1 FRP jacketing
Column: b=250 mm
Concrete: fc=19 MPa, c=20 mm
Reinforcement: S400, 4Φ20, Φ6/250
FRP: ffu=2900 MPa, Ef= MPa, tl=0,12 mm
Additional shear load: ΔV=70 kN
NOTE: the partial factor of the FRP is taken equal to 1,1
EC8-P3
KANEPE
for θ=π/4 in favor of safety
σj0=1757,58 MPa
and β=π/2,
z0=176 mm
4 layers of FRP with Σtf=0,48 mm account for:
tj,req=0,23 mm
2 layers of FRP with Σtj=0,24 mm are required
ffdd =467,88 MPa
<ηRffu-ffdd>=903,03 MPa>0
ffu,w=1370,91 MPa
τmax=2,73 MPa
ffdde,w=392,70 MPa
VRd,f=74,64 kN

9. 2. Strengthening against shear 2.1 FRP jacketing
2.1.1 Numerical example (b)
2. Strengthening against shear
2.1 FRP jacketing
Column: b=250 mm
Concrete: fc=19 MPa, c=20 mm
Reinforcement: S400, 4Φ20, Φ6/250
FRP: ffu=2900 MPa, Ef= MPa, tl=0,12 mm
(VRd,f=74,64 kN)

10. 2. Strengthening against shear 2.1 FRP jacketing
2.1.2 Conclusion
2. Strengthening against shear
2.1 FRP jacketing
The two documents lead in average
to the same values of required FRP thickness.
However, we confess that
we were unable to understand
why, following EC8-P3
A (5), such a simple
strengthening, in such a
small column, fails by
debonding in spite of the
equilibrium offered near the
curved corner (forces Fc).
Fully wrapped (i.e., closed) or properly anchored (in the compression zone) jackets

11. 2. Strengthening against shear 2.2 Steel jacketing
i. EC8-P3
2. Strengthening against shear
2.2 Steel jacketing
a. Design formulae
b. Notation
θ: as previously stated,
β: as previously stated,
b: width of the steel straps and
s: spacing of the steel straps
Evidently b/s=1 in case of continuous steel plates.

12. U-shaped (i.e., open) jackets
ii. KANEPE/TH.P.T.
2. Strengthening against shear
2.2 Steel jacketing
Design formulae
NOTE: γRd=1,5
For beams:
For columns:
U-shaped (i.e., open) jackets
Fully wrapped (i.e., closed) or properly anchored (in the compression zone) jackets

13. NOTE: the partial factor of the steel plate is taken equal to 1,15
2.2.1 Numerical example (a)
2. Strengthening against shear
2.2 Steel jacketing
Column: b=250 mm
Concrete: fc=19 MPa, c=20 mm
Reinforcement: S400, 4Φ20, Φ6/250
Steel plate: f 'sy=275 MPa
Additional shear load: ΔV=70 kN
NOTE: the partial factor of the steel plate is taken equal to 1,15
EC8-P3
KANEPE
for θ=π/4 in favor of safety
σj0=159,42 Mpa
and β=π/2,
z0=176 mm
tj,req=1,17 mm
tj,req=2,50 mm

14. 2. Strengthening against shear 2.2 Steel jacketing
2.2.1 Numerical example (b)
2. Strengthening against shear
2.2 Steel jacketing
Column: b=250 mm
Concrete: fc=19 MPa, c=20 mm
Reinforcement: S400, 4Φ20, Φ6/250
Steel plate: f 'sy=275 MPa

15. 2. Strengthening against shear 2.2 Steel jacketing
2.2.2 Conclusion
2. Strengthening against shear
2.2 Steel jacketing
EC8-P3 leads to much lower values of required steel-plate thickness because:
it considers zo~h and
it does not leave stress-margins (~ 30%) for possible local overstress along the diagonal crack.

16. Effectively confined area in an FRP-wrapped section
i. EC8-P3
3. Confinement action versus local ductility
3.1 FRP jacketing
a. Design formulae
b. Notation
bw: larger section width,
εcu =0,0035,
εju =ffu/Ef; adopted FRP jacket ultimate strain, lower than the ultimate strain εfu=0,015 for CFRP and
f’1: confinement pressure f1 applied by the FRP sheet after its corners have been rounded to allow wrapping around them
Effectively confined area in an FRP-wrapped section

17. 3. Confinement action versus local ductility
ii. KANEPE
3. Confinement action versus local ductility
3.1 FRP jacketing
Design formulae
NOTE: If the number of required FRP layers k is higher than 3,
the effectiveness of the additional FRP layers is reduced;

18. 3. Confinement action versus local ductility
3.1.1 Numerical example (a)
3. Confinement action versus local ductility
3.1 FRP jacketing
Column: b=250 mm, μφ,av=1,00
Concrete: fc=19 MPa, c=20 mm
Reinforcement: S400, 4Φ20, Φ6/250
FRP: ffu=2900 MPa, Ef= MPa
Additional axial load: N=800 kN
In order to achieve μφ,tar=9,00:
NOTE: the partial factor of the FRP is taken equal to 1,1
EC8-P3
KANEPE
Ix=9,000
fjd=2636,36 MPa
εju=0,0112
v=0,674
f’1=6,40 MPa
εsy=0,0020
ks=0,400
ano=0,333
f1=16,00 MPa
an=0,733
tf,req=0,69 mm
tj,req=0,81 mm
for k=7>3, ψ=0,615
f’jd=ψfjd=1620,81 MPa
t’j,req=1,32 mm

19. 3. Confinement action versus local ductility
3.1.1 Numerical example (b)
3. Confinement action versus local ductility
3.1 FRP jacketing
Column: b=250 mm, μφ,av=1,00
Concrete: fc=19 MPa, c=20 mm
Reinforcement: S400, 4Φ20, Φ6/250
FRP: ffu=2900 MPa, Ef= MPa
Additional axial load: N=800 kN

20. 3. Confinement action versus local ductility
3.1.2 Conclusion
3. Confinement action versus local ductility
3.1 FRP jacketing
A question may be raised here about the first approach of EC8-P3 (A.34) on confinement action versus local ductility; the cross sectional effectiveness factor a is not included in the design formulae – as opposed to the second EC8-P3 approach A (6) - which was examined by Prof. Dritsos in the previous presentation - and KANEPE provisions.
It is also noted that EC8-P3, as opposed to KANEPE provisions, does not consider the reduced effectiveness of additional FRP layers after a certain number (say 5).
As a result, it is rather a numerical coincidence that the values of required FRP thickness for this first approach (A.34) are quite similar in the case of EC8-P3 and KANEPE provisions for targeted local ductility values around 10,00 – as opposed for the case of lower (<9) and higher (>11) μ1/r -values when EC8-P3 values become disproportionally low and high respectively.

21. i. EC8-P3
3. Confinement action versus local ductility
3.2 Steel jacketing

22. 3. Confinement action versus local ductility
ii. EC8-P1
3. Confinement action versus local ductility
3.2 Steel jacketing
a. Design formulae
b. Notation
bc: gross cross-sectional
width and
bo: width of confined core
Evidently bc/bo=1 in case of
continuous steel plates.
NOTE: According to Table 5.1 and assuming au/a1=1,0,
qo,DCM=3,0 and qo,DCH=4,5.
Furthermore, assuming Tc=2T1 in accordance with Equation 5.5
μφ=1+2(qo-1)Tc/T1, μφ,DCM=9 and μφ,DCH=15.

23. 3. Confinement action versus local ductility
iii. KANEPE
3. Confinement action versus local ductility
3.2 Steel jacketing
Design formulae

24. In order to achieve μφ,tar=9,00:
3.2.1 Numerical example (a)
3. Confinement action versus local ductility
3.2 Steel jacketing
Column: b=250 mm, μφ,av=1,00
Concrete: fc=19 MPa, c=20 mm
Reinforcement: S400, 4Φ20, Φ6/250
Steel plate: f 'sy=275 MPa
Additional design axial load: Nd=800 kN
In order to achieve μφ,tar=9,00:
NOTE: the partial factor of the steel plate is taken equal to 1,15,
while the reduced partial factors of concrete and reinforcing steel
are taken equal to 1,3 and 1,05 respectively
EC8-P1 KANEPE
vd=0,876
εsyd=0,0019
an=0,333
as=1,000
a=0,333
ωwd,min=1,246 tj,req=3,38 mm
tj,req=4,76 mm

25. 3. Confinement action versus local ductility
3.2.1 Numerical example (b)
3. Confinement action versus local ductility
3.2 Steel jacketing
Column: b=250 mm, μφ,av=1,00
Concrete: fc=19 MPa, c=20 mm
Reinforcement: S400, 4Φ20, Φ6/250
Steel plate: f 'sy=275 MPa
Additional design axial load: Nd=800 kN

26. 3. Confinement action versus local ductility
3.2.2 Conclusion
3. Confinement action versus local ductility
3.2 Steel jacketing
EC8-P3 does not offer any quantitative guidance regarding the use of external steel confinement in the form of steel jacketing as a strengthening method for increasing the local ductility of a member.
Following EC8-P1 on this subject, however, with the appropriate modifications regarding the partial factors of existing materials, the values of required steel-plate thickness are relatively high for higher targeted local ductility values compared to the values resulting from KANEPE provisions.

27. 4. Clamping of lap-splices 4.1 FRP jacketing
i. EC8-P3 (a)
4. Clamping of lap-splices
4.1 FRP jacketing
a. Design formulae
NOTE: CFKL3 = 1,00 is
the confidence factor
for full knowledge
b. Notation
bw: as previously stated,
p: perimeter line in the column cross-section along the inside of longitudinal steel,
n: number of spliced bars along p,
fyL =fy/CFKL3; yield strength of longitudinal steel reinforcement;
σ1: clamping stress over the lap- splice length Ls and
σ’1: active pressure from the grouting
between the FRP and the column at a strain of 0,001

28. 4. Clamping of lap-splices 4.1 FRP jacketing
i. EC8-P3 (b)
4. Clamping of lap-splices
4.1 FRP jacketing
“For members of rectangular section with longitudinal bars lapped over a length Ls starting from the end section of the member, an alternative to the previous for the calculation of the effect of FRP wrapping over a length exceeding by no less than 25% the length of the lapping, is:”

29. 4. Clamping of lap-splices 4.1 FRP jacketing
ii. KANEPE
4. Clamping of lap-splices
4.1 FRP jacketing
Design formulae

30. NOTE: the partial factor of the FRP is taken equal to 1,1
4.1.1 Numerical example (a)
4. Clamping of lap-splices
4.1 FRP jacketing
Column: b=250 mm
Concrete: fc=19 MPa, c=20 mm
Reinforcement: S400, 4Φ20, Φ6/250
FRP: ffu=2900 MPa, Ef= MPa
Assuming ls/db=25:
NOTE: the partial factor of the FRP is taken equal to 1,1
EC8-P3 (a)
KANEPE
σ1=1,52 MPa
su=2,0 mm
ks=0,4
sd=0,4 mm
σ’1=0,61 MPa
wd=0,33 mm
tf,req=0,29 mm
tj,req=0,36 mm
EC8-P3 (b)
a=al,f=0,760
ρf=0,0022
ff,e=2081,21 Mpa
tf,req=0,27 mm

31. 4. Clamping of lap-splices 4.1 FRP jacketing
4.1.1 Numerical example (b)
4. Clamping of lap-splices
4.1 FRP jacketing
Column: b=250 mm
Concrete: fc=19 MPa, c=20 mm
Reinforcement: S400, 4Φ20, Φ6/250
FRP: ffu=2900 MPa, Ef= MPa

32. 4. Clamping of lap-splices 4.1 FRP jacketing
4.1.2 Conclusion
4. Clamping of lap-splices
4.1 FRP jacketing
Several opinions exist about the meaning of the symbol εf,u being used in the alternative second approach A (3) of EC8-P3 regarding the clamping of lap-splices along with FRP jacketing.
Our application is literally in accordance with the provisions of the text of the Code putting εf,u equal to the actual ultimate elongation of the FRP that however should not be taken higher than 0,015.
On the other hand, if εf,u were the real strain of the FRP under the given conditions, the resulting values of required FRP thickness would then be approximately 100% higher than the previous ones.

33. i. EC8-P3
4. Clamping of lap-splices
4.2 Steel jacketing

34. 4. Clamping of lap-splices 4.2 Steel jacketing
ii. KANEPE
4. Clamping of lap-splices
4.2 Steel jacketing
Design formulae

35. 4. Clamping of lap-splices 4.2 Steel jacketing
4.2.1 Numerical example (a)
4. Clamping of lap-splices
4.2 Steel jacketing
Column: b=250 mm
Concrete: fc=19 MPa, c=20 mm
Reinforcement: S400, 4Φ20, Φ6/250
Steel plate: f 'sy=275 Mpa
Assuming ls/db=25:
NOTE: the partial factor of the steel plate is taken equal to 1,15
KANEPE
su=2,0 mm
sd=0,4 mm
(AB)=99 mm
provided that: wy=0,13 mm<wd=0,33 mm
tj,req=2,32 mm

36. 4. Clamping of lap-splices 4.2 Steel jacketing
4.2.1 Numerical example (b)
4. Clamping of lap-splices
4.2 Steel jacketing
Column: b=250 mm
Concrete: fc=19 MPa, c=20 mm
Reinforcement: S400, 4Φ20, Φ6/250
Steel plate: f 'sy=275 Mpa

37. 4. Clamping of lap-splices 4.2 Steel jacketing
4.2.2 Conclusion
4. Clamping of lap-splices
4.2 Steel jacketing
It is hoped that in the near future EC8-P3 will also offer quantitative guidance regarding the use of external steel confinement in the form of steel jacketing as a strengthening method of inadequate splices.

38. Thank you!