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
Table of Contents
2
1. Scope…………………………………………………
3
2. Strengthening against shear……………….
5
2.1 FRP jacketing……………………………………….
5
i. EC8-P3……………………………………………….. 5
α. Design formulae……………………………………
5
b. Notation……………………………………………..6
ii. KANEPE……………………………………..…….. 7
Design formulae………………………………….7
2.1.1 Numerical example…………………………… 8
2.1.2 Conclusion……………………………………………
10
2.2 Steel jacketing……………………………………..
11
i. EC8-P3…………………………………………………..
11
α. Design formulae……………………………………..
11
b. Notation………………………………………………..
11
ii. KANEPE/TH.P.T……………………………………….
12
Design formulae……………………………………..
12
2.2.1 Numerical example……………………………13
2.2.2 Conclusion……………………………………………
15
3. Confinement versus local ductility…….
16
3.1 FRP jacketing………………………………………
16
i. EC8-P3………………………………………………..16
α. Design formulae……………………………………..
16
b. Notation……………………………………………..16
ii. KANEPE……………………………………………. 17
Design formulae…………………………………17
3.1.1 Numerical example……………………………18
3.1.2 Conclusion……………………………………………20
3.2 Steel jacketing………………………………… 21
i. EC8-P3……………………………………………….. 21
ii. EC8-P1……………………………………………….. 22
α. Design formulae……………………………………..
22
b. Notation…………………………………………….. 22
iii. KANEPE…………………………………………….. 23
Design formulae…………………………………..23
3.2.1 Numerical example…………………………… 24
3.2.2 Conclusion……………………………………………26
4. Clamping of lap-splices………………………………………
27
4.1 FRP jacketing………………………………………
27
i. EC8-P3……………………………………………….. 27
α. Design formulae……………………………………27
b. Notation…………………………………………….. 27
ii. KANEPE……………………………………………. 29
Design formulae……………………………………29
4.1.1 Numerical example…………………………… 30
4.1.2 Conclusion……………………………………………32
4.2 Steel jacketing……………………………………..
33
i. EC8-P3……………………………………………….. 33
ii. KANEPE……………………………………………. 34
Design formulae……………………………………34
4.2.1 Numerical example…………………………… 35
4.2.2 Conclusion……………………………………………37
1. Scope (a)
3
EC8-P3 will need, as all Codes do,
to be improved and modified on a regular basis,
:
 the ongoing work,
 the feedback from Code-users and
 continuing developments in “repair technology”;
as well as
:
 possible mistakes and
 internal inconsistencies.
1. Scope (b)
4
This study attempts to make some comparisons
between retrofitting provisions
of EC8-P3 and KANEPE (GCSI)
for RC elements;
:
 Strengthening against shear,
 Confinement action versus local ductility and
 Clamping of lap-splices.
2. Strengthening
against shear
2.1 FRP jacketing
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:
5
i. EC8-P3
a. Design formulae
2. Strengthening
against shear
2.1 FRP jacketing









θ:
β:
6
i. EC8-P3
b. Notation
strut inclination angle,
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
2. Strengthening
against shear
2.1 FRP jacketing
ii. KANEPE
7
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
2. Strengthening
against shear
2.1 FRP jacketing
8
2.1.1 Numerical example (a)
Column: b=250 mm
Concrete: fc=19 MPa, c=20 mm
Reinforcement: S400, 4Φ20, Φ6/250
FRP: ffu=2900 MPa, Ef=260000 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  tj,req=0,23 mm
account for: 2 layers of FRP with Σtj=0,24 mm are
 ffdd =467,88 MPa required
 <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
2. Strengthening
against shear
2.1 FRP jacketing
9
2.1.1 Numerical example (b)
Column: b=250 mm
Concrete: fc=19 MPa, c=20 mm
Reinforcement: S400, 4Φ20, Φ6/250
FRP: ffu=2900 MPa, Ef=260000 MPa, tl=0,12 mm
(VRd,f=74,64 kN)
2. Strengthening
against shear
2.1 FRP jacketing
 The
10
2.1.2 Conclusion
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.4.4.2 (5), such a simple
strengthening, in such a
small column, fails by
debonding in spite of the
Fully wrapped (i.e., closed)
equilibrium offered near the or properly anchored (in the
compression zone) jackets
curved corner (forces Fc).
2. Strengthening
against shear
2.2 Steel jacketing
b. Notation

θ:
β:
b:

s:


as previously stated,
as previously stated,
width of the steel straps
and
spacing of the steel straps
Evidently b/s=1 in case of
continuous steel plates.
11
i. EC8-P3
a. Design formulae
2. Strengthening
against shear
2.2 Steel jacketing
ii. KANEPE/TH.P.T.
12
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
2. Strengthening
against shear
2.2 Steel jacketing
13
2.2.1 Numerical example (a)
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
2. Strengthening
against shear
2.2 Steel jacketing
14
2.2.1 Numerical example (b)
Column: b=250 mm
Concrete: fc=19 MPa, c=20 mm
Reinforcement: S400, 4Φ20, Φ6/250
Steel plate: f 'sy=275 MPa
2. Strengthening
against shear
2.2 Steel jacketing
15
2.2.2 Conclusion
EC8-P3 leads to much lower values of required steelplate thickness because:
 it
 it
considers zo~h and
does not leave stress-margins (~ 30%) for possible
local overstress along the diagonal crack.
3. Confinement
action versus local
ductility
3.1 FRP jacketing
16
i. EC8-P3
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 FRPwrapped section
3. Confinement
action versus local
ductility
3.1 FRP jacketing
17
ii. KANEPE
Design formulae
NOTE: If the number of required FRP layers k is higher than 3,
the effectiveness of the additional FRP layers is reduced;
3. Confinement
action versus local
ductility
3.1 FRP jacketing
18
3.1.1 Numerical example (a)
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=260000 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

3. Confinement
action versus local
ductility
3.1 FRP jacketing
19
3.1.1 Numerical example (b)
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=260000 MPa
Additional axial load: N=800 kN
3. Confinement
action versus local
ductility
3.1 FRP jacketing
20
3.1.2 Conclusion

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.4.4.3 (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.
3. Confinement
action versus local
ductility
3.2 Steel jacketing
21
i. EC8-P3
3. Confinement
action versus local
ductility
3.2 Steel jacketing
22
ii. EC8-P1
a. Design formulae
b. Notation

bc:

bo:
gross cross-sectional
width and
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.
3. Confinement
action versus local
ductility
3.2 Steel jacketing
23
iii. KANEPE
Design formulae
3. Confinement
action versus local
ductility
3.2 Steel jacketing
24
3.2.1 Numerical example (a)
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
3. Confinement
action versus local
ductility
3.2 Steel jacketing
25
3.2.1 Numerical example (b)
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
3. Confinement
action versus local
ductility
3.2 Steel jacketing
 EC8-P3
3.2.2 Conclusion
26
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.
4. Clamping of lapsplices
4.1 FRP jacketing
27
a. Design formulae
b. Notation






i. EC8-P3 (a)
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 lapsplice length Ls and
σ’1: active pressure from the grouting
between the FRP and the
column at a strain of 0,001
NOTE: CFKL3 = 1,00 is
the confidence factor
for full knowledge
i. EC8-P3 (b)
4. Clamping of lap“For members of rectangular section with
splices
longitudinal bars lapped over a length Ls starting
the end section of the member, an
4.1 FRP jacketing from
alternative to the previous for the calculation of
28
the effect of FRP wrapping over a length
exceeding by no less than 25% the length of the
lapping, is:”
4. Clamping of lapsplices
4.1 FRP jacketing
29
ii. KANEPE
Design formulae
4. Clamping of lapsplices
4.1 FRP jacketing
30
4.1.1 Numerical example (a)
Column: b=250 mm
Concrete: fc=19 MPa, c=20 mm
Reinforcement: S400, 4Φ20, Φ6/250
FRP: ffu=2900 MPa, Ef=260000 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


4. Clamping of lapsplices
4.1 FRP jacketing
31
4.1.1 Numerical example (b)
Column: b=250 mm
Concrete: fc=19 MPa, c=20 mm
Reinforcement: S400, 4Φ20, Φ6/250
FRP: ffu=2900 MPa, Ef=260000 MPa
4. Clamping of lapsplices
4.1 FRP jacketing
 Several
4.1.2 Conclusion
32
opinions exist about the meaning of the
symbol εf,u being used in the alternative second
approach A.4.4.4 (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.
4. Clamping of lapsplices
4.2 Steel jacketing
33
i. EC8-P3
4. Clamping of lapsplices
4.2 Steel jacketing
34
ii. KANEPE
Design formulae
4. Clamping of lapsplices
4.2 Steel jacketing
35
4.2.1 Numerical example (a)
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
4. Clamping of lapsplices
4.2 Steel jacketing
36
4.2.1 Numerical example (b)
Column: b=250 mm
Concrete: fc=19 MPa, c=20 mm
Reinforcement: S400, 4Φ20, Φ6/250
Steel plate: f 'sy=275 Mpa
4. Clamping of lapsplices
4.2 Steel jacketing
4.2.2 Conclusion
37
It is hoped that in the near future
EC8-P3 will also offer
regarding the use of external steel confinement
in the form of steel jacketing
as a strengthening method of inadequate splices.
Thank you!