111

� Stephanos E. Dritsos

Department of Civil Engineering, University of Patras

Differences in the design of interventionsaccording to EC8 part 3 and the Greek CSI

COUNCIL OF EUROPE/EUROPEAN CENTRE ON PREVENTION AND FORECASTING OF EARTHQUAKES (ECPFE)EARTHQUAKE PLANNING AND PROTECTION ORGANIZATION (EPPO)

ATHENS, APRIL 12/2013

Implementation of EC8 part 3:2005. Assessment and interventions on buildings in earthquake prone regions

WORKSHOP:

222

� Interfaces

Retrofitting of Buildings

�Retrofitting

between existing – new elements

Greek CodeGreek Code

�� Greek CodeGreek Code�� EurocodeEurocode

Greek CodeGreek Code

�Retrofitting

of existing elements(strengthening)

by adding new elements(of the whole structure)

33

CONTEXT STRUCTURE (CONCEPT)

EUROCODE

GREEK CODE

Types of strengthening offered (in flexure, shear, ductility)

Specific techniques are adopted

Alternative and appropriate techniques are proposed

Specific deficiencies are diagnosed and purpose of intervention is decided

Moreover, Greek Code a much more detailed document 44

BASIC DESIGN CONSIDERATIONS BASIC DESIGN CONSIDERATIONS

Influence of Interface ConnectionInfluence of Interface Connection

Repaired/Strengthened ElementRepaired/Strengthened Element

Multi Multi –– Phased ElementPhased Element

Composite ElementComposite Element

INTERFACES INTERFACES GCSI:

S. E. D R I T S O S S. E. D R I T S O S

555

VERIFICATION OF A SUFFICIENT CONNECTIONBETWEEN CONTACT SURFACES

≤d d

S R

V V≤d d

interface interface

S R

≤Interface Shear Force Interface Shear Resistance

Under specific construction conditions (measures), verification may not be necessary

666666

F

δ

Fy,µ

Fy,ε

Monolithic Element

Strengthened Element

Fres,µ

Fres,ε

δy,µδy,ε δu,µδu,ε

Κµ

Κε

y,y,y,y,εεεεrrrr

y,y,y,y,μμμμ

FFFFΚ =Κ =Κ =Κ =FFFF

y , εδ y

y , μ

δΚ =

δε

κμ

ΚΚ =Κ

u , εδ u

u , μ

δΚ =

δ

INFLUENCE OF INTERFACES CAPACITY CURVES

Deformation

Action E

ffect

777

MONOLITHIC BEHAVIOUR FACTORS

� For the Stiffness:

k

the stiffness of the strengthened elementk

the stiffness of the monolithic element=

� For the Resistance:

r

the strength of the strengthened elementk

the strength of the monolithic element=

(EI)strengthened = kk (EI)MRstrengthened = kr RM

� For the Displacement:

y

the displacement at yield of the strengthened elementk

the displacement at yield of the monolithic elementδ =

y

the ultimate displacement of the strengthened elementk

the ultimate displacement of the monolithic elementδ =

δi,strengthened = kδi δi,M888

� Infilling Frames

• Addition of simple “infills”

• Conversion of frames to shear walls

• Strengthening of existing masonry infills

• Addition of bracing. Conversion of frames

to vertical trusses

� Construction of new lateral shear walls

GREEK CSI:

(Reinforced or unreinforced concrete walls,(Reinforced or unreinforced concrete walls,

reinforced or unreinforced masonries)reinforced or unreinforced masonries)

((ShotcretingShotcreting reinforcedreinforced

layers)layers)

(By steel or RC elements)(By steel or RC elements)

Reinforced concrete wallsReinforced concrete wallsand jacketsand jackets

STRENGHTENING THE WHOLE STRUCTURE

S. E. D R I T S O S S. E. D R I T S O S

9999

Adding Simple Infills

� Addition of walls from: a) Unreinforced or reinforced concrete

(cast in situ or prefabricated)

b) Unreinforced or reinforced masonry

� No specific requirement to connect infill to the existing frame

� Modelling of infills by diagonal strut

� Low ductility of infill. Recommended m ≤ 1,5

WARNING

Additional shear forces are induced in the columns and beams of the frame

GCSI:

101010

10

Strengthening of existing masonry infills

� Reinforced shotcrete layers applied to both sides of the wall

Minimum concrete thickness 50 mm

Minimum reinforcement ratio ρvertical = ρhorizontal = 0,005

Essential to connect both sides by bolting through the wall

No need to connect to the existing frame as it is an infill

All new construction must be suitably connected to the existing foundation

GCSI:

11

Reinforced walls are constructed from one column to another enclosing the frame (including the beam) with jackets placed around the columns. Note, all new construction must be suitably connected to the existing foundation

Frame Encasement

New column

Existing columnNew wall

New column

Existing columnNew wall

conversion of frames to shear wallsGCSI:

121212

Addition of New External Walls

Schematic arrangement of connections between existing building and new wall

GCSI:

S. E. D R I T S O S S. E. D R I T S O S

131313

Addition of a Bracing SystemGCSI:

141414

OBJECTIVESGREEK CODE (2012)

DESIGN OF INTERVENTIONS

EC 8-PART 3 (2005) CAPACITY MODELS FOR

STRENGTHENING

1 Verification of the interface connection Yes No

2 Interventions in critical regions of linear structural members

Yes Yes

3 Interventions to frame joints Yes No

4 Interventions on shear walls Yes No

5 Interventions on foundation elements Yes No

6 Frame encasement Yes No

7 Construction of external new shear walls

Yes No

Int

erf

ace

sStr

eng

thening

of e

lement

s

Retr

ofitting

whole

stru

ctur

e

151515

GREEK CSI (2012) EC 8 PART 3 (2005)

8.2.1.1 Local repair of a damaged member region - -

8.2.1.2 Restoration of insufficient lap splice length of the reinforcement

A.4.3.3A.4.4.4

Clamping of lap-splicesby FRP wrapping

8.2.1.38.2.1.4

Interventions to strengthen the tension or compression zone against flexure with axial force

- -

8.2.1.5 Column jackets with the objective of simultaneous strengthening in the tension and compression zone

A.4.2.2 Enhancement of strength, stiffness and deformation capacityby concrete jackets

8.2.2.18.2.2.2

Interventions to increase the shear capacity a) inadequacy of the compression struts b) inadequacy of transverse reinforcement

A.4.3.2A 4.4.2

Enhancement of shear strength (inadequacy of transverse reinforcement)by steel or FRP wrapping

8.2.3 Interventions to increase local ductility A.4.2.2

A.4.4.3

Enhancement of strength, stiffness and deformation capacityby concrete jackets

Confinement actionby FRP wrapping

8.2.4 Interventions to increase the stiffness A.4.2.2 Enhancement of strength, stiffness and deformation capacityby concrete jackets

Interventions in Critical Regions of Linear Structural Members

161616

EC 8-3

ANNEX A (informative): REINFORCED CONCRETE STRUCTURES

CAPACITY MODELS FOR STRENGTHENING

� Concrete Jacketing

� Steel Jacketing

� FRP Plating and Wrapping

S. E. D R I T S O S S. E. D R I T S O S

171717

� Concrete Jacketing

Proposed to enhance the strength stiffness and deformation capacity

Correlation with a monolithic equivalent

R0,9 V=*Rv*

y yM M=

*

y y y1,05 or 1, 20θ = θ θ *

u uθ =θ

EC 8-3

if roughened if not

181818

� Steel Jacketing

(a) Increase shear strength

(b) Prevent lap-splice failureOnly construction detailing

to:

EC8-3

(in case of inadequate shear reinforcement)

191919

� FRP Plating and Wrapping

(a) Increase shear strength

(b) Increase ductility of critical regions

(c) Prevent lap-splice failure

to:

EC8-3

(more extended part - 6 pages out of 9)

2020

NECESSARY AMOUNT OF CONFINEMENTfor a target curvature ductility

, t rφ αµ

Applied to circular and rectangular cross sections

22

1,50,4=

l

cux c

ju

f I fεε

(A.34) ,t ar

x

,

Iφ

φ ο

µ=µ

jf ff f ju f j j

c

f4t 2 t1 1 1f E f f

2 2 2 D f D= ρ ε = ρ = =

l

jfs s w

c c

ff 2 tk 0,5 k

f D f

′= = ωl

2 1,5

ju,t r

s w2

ave cu

1,25 kφ α εµ

= ω µ ε

First choiceEC8-3:

(A.34)

Confinement pressure

sf k f′ =l l

sk 1,0=

cs

2Rk

D=

circular

rectangular

In practice sk 0.2 0.35= −

S. E. D R I T S O S S. E. D R I T S O S

2121

Second choice

Applied only to rectangular cross sections

wx

0,35

v 0,225 s

um c

el

L10,016 0,3 f 25

h

αω θ = × × × × × γ

EC8-3:

( ) ( )u

u, y u

y

f fθ φ θ

θθ θ →µ = →µ = µ = θ

θ

w

wx w(1 0,35 )

2

αωαω = − ωwhere

f ,ef

c

f0,35

fv 0,225 s

um c

el

L10,016 0,3 f 25

h

αρ θ = × × × × × γ

wheref

f ,e u u

c

f f (1 0,7 f )f

ρ= −

p p

13 (1 0.5 )

1

θ

φ

µ −= λ − λ

µ − l l

e.g.p

p

s

Lfor 0.10 3.5 2.5

Lφ θλ = ≈ →µ = µ −l

l

p

p

s

Lfor 0.20 2 1

Lφ θλ = ≈ →µ ≈ µ −l

l2222

GREEK CODE

cu ,c

sy2, 2 vφ

εµ =

ε

CFRP:

2

2cccu ,c w

c

f0, 0035 0, 0035 (1,125 1, 25 a )

f

ε = = + ω

y

sy

s

f

Eε =

c

Nv

b h f=

Yield strain

Normalized axial load

Approximate procedure

2323

Therefore, ( )wf aφµ = ω

However, quite different relationships are proposed with different influences from crucial parameters.

( ) w... aφµ = ω

( )( )w

w1 0.352... 25

αω− ω

φµ =

( )( )2

w...φµ = κ + λ αω

EC8-3

EC8-3

GCSI

In all Expressions

2424

circular D

rectangular b

j j j

w 2

con c c

V f fD t

V f ( D / 4) f

πω = =

π

Collars or stirrupsA

tS

κ =j

w

c

f4t

b fω =

Assume Φ8/100 stirrups in a 300x300 mm cross section or circular D = 300 mm,fck = 14-16 MPa, fcm = 20 MPa

eq

50t 0,5mm

S 100

κΑ = = =w

4 0,5 500 100, 2

300 20 6

×ω = = ≅

If 10 / 75 0, 4Φ → ≅wω

For an CFRP jacket t = 1 mm

w

4 30002

300 20ω = =

j

c

f4t

D f=

j j j j0,015 f E 200.000 0,015 3000MPaε = → = ε = × =

Volumetric Confinement Ratio ωw

wmax a ?ω =

Aκ =collar cross section area

S. E. D R I T S O S S. E. D R I T S O S

25

0

5

10

15

20

25

30

0 0.5 1 1.5 2 2.5ωw

µφ

GCSI

EC8(1)

EC8(2)

300mm

300m

m

50mm

20=cm

f MPa

4 20, 500Φ S

1.4%=juε

3.0=L m

1.5=s

L m

0.25=v

26

500mm

500m

m

50mm

20=cmf MPa

8 20, 500Φ S

1.4%=juε

3.0=L m

1.5=s

L m

0

5

10

15

20

25

0 0.5 1 1.5 2 2.5ωw

µφ

GCSI

EC8(1)

EC8(2)

0.25=v

27

0

5

10

15

20

25

30

0 0.5 1 1.5 2 2.5ωw

µφ

GCSI

EC8(1)

EC8(2)

300mm

300m

m

50mm

20=cmf MPa

4 20, 500Φ S

1.4%=juε

3.0=L m

1.5=sL m

0.50=v

28

500mm

500m

m

50mm

20=cm

f MPa

8 20, 500Φ S

1.4%=juε

3.0=L m

1.5=s

L m

0

5

10

15

20

25

0 0.5 1 1.5 2 2.5 ωw

µφ

GCSI

EC8(1)

EC8(2)

0.50=v

S. E. D R I T S O S S. E. D R I T S O S

29

0

5

10

15

20

25

30

0 0.5 1 1.5 2 2.5 ωw

µφ

GCSI

EC8(1)

EC8(2)

0.75=v

300mm

300m

m

50mm

20=cm

f MPa

4 20, 500Φ S

1.4%=juε

3.0=L m

1.5=sL m

0.75=v

30

0

5

10

15

20

25

0 0.5 1 1.5 2 2.5ωw

µφ

GCSI

EC8(1)

EC8(2)

500mm

500m

m

50mm

20=cm

f MPa

8 20, 500Φ S

1.4%=juε

3.0=L m

1.5=sL m

0.75=v

3131

EXPERIMENTAL DATA FOR CONCRETE JACKETINGEXPERIMENTAL DATA FOR CONCRETE JACKETING(UNIVERSITY OF PATRAS)(UNIVERSITY OF PATRAS)

3232

-150 -100 -50 0 50 100 150

-200

-150

-100

-50

0

50

100

150

200

∆ύναµη

(K

N)

Οριζόντια µετακίνηση (mm)

I2

-150 -100 -50 0 50 100 150

-200

-150

-100

-50

0

50

100

150

200

∆ύναµη

(m

m)

Οριζόντια µετακίνηση (mm)

I4

OO F2F2 F4F4

RR DD RDRD

NTNT MM

Displacement (mm)

Late

ralfo

rce

(kN)

Displacement (mm)

Late

ralfo

rce

(kN)

Late

ralfo

rce

(kN)

Displacement (mm)

Displacement (mm)

Displacement (mm)

Displacement (mm)

Late

ralfo

rce

(kN)

Late

ralfo

rce

(kN)

Late

ralfo

rce

(kN)

Displacement (mm)Displacement (mm)

Displacement (mm)

Late

ralfo

rce

(kN)

Late

ralfo

rce

(kN)

Late

ralfo

rce

(kN)NTPNTP

S. E. D R I T S O S S. E. D R I T S O S

3333

-200

-150

-100

-50

0

50

100

150

200

-150 -100 -50 0 50 100 150

Displacement (mm)

Loa

d (

kN

)

R1

R2

D1

D2

RD1

RD2

W1

W2

Mo

O

Load Against Displacement Envelope Curves for All Tested SpecimeLoad Against Displacement Envelope Curves for All Tested Specimensns

(Bousias et al. 2004, Vandoros and Dritsos, 2006b, Vandoros and Dritsos, 2006c)

34

y,GCSI y,exp?θ θTotal data (42 specimens)

,exp GCSIy yk ? ifθ= θ =θ

(Kappos et al, EPPO report 2012)

yk 1.26θ =

GCSI: yk 1.25θ =

EC8-3: yk 1.05 or 1.20θ =

3535

RECENT PROJECTS FUNDED BY EPPO

On the specific subject of Ch. 8 of GCSI: Design of Interventions (Budget 150.000

Euro)

1. Investigation of the behaviour of old type RC columns strengthened by

concrete jackets. (Aristotle University of Thessaloniki).

2. Investigation of the behaviour of RC columns after restoring insufficient

reinforcement lap splice lengths. (Aristotle University of Thessaloniki).

3. Experimental investigation of shear strengthening of beams in their support

areas, under seismic actions. (Aristotle University of Thessaloniki).

4. Experimental investigation of the behaviour or RC frames strengthened by

infilling with new concrete walls. (Thessali University)

5. Experimental investigation of 4-floor RC frames strengthened by infilling with

new concrete walls. (University of Patras)

Also, 5 more projects funded (Budget 150.000 Euro) on the topic of

strengthening RC buildings with one or more soft storeys. 3636

CONCLUDING REMARKS

� EC8-3 and the GCSI deal with the crucial issue of the seismic risk of existing buildings and try to give guidance for assessment and retrofitting

� However, when specifically looking at the design of interventions, two crucial differences can be identified

� Concept� Detail and topics covered

- From the three main parts of the Greek Code: a) verification of force transfer at interfaces, b) strengthening of elements, c) strengthening of the whole structure, only b is considered by EC8-3.

- Even when common objectives, different analytical expressions are provided leading to different outcomes.

- In the specific objective of “interventions to increase local ductility”, the GCSI is found to be more conservative in comparison to EC8-3 and is drastically influenced by the normalized axial load.

- More research is needed not only in the objectives where the two Codes are contradictory but also in the areas that EC8-3 does not touch while the GCSI attempts to provide guidance, however with extremely limited experimental existing data.

S. E. D R I T S O S S. E. D R I T S O S