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

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26 Νοε 2013 (πριν από 3 χρόνια και 11 μήνες)

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1

1

1





Stephanos E. Dritsos

Department of Civil Engineering
,

University of Patras

Differences in the design of interventions

according 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
:


2

2

2



Interfaces

Retrofitting of Buildings


Retrofitting


between existing


new elements

Greek Code



Greek Code



Eurocode

Greek Code


Retrofitting

of existing elements

(strengthening)

by adding new elements

(of the whole structure)

3

3

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

4

4

BASIC DESIGN CONSIDERATIONS

Influence of Interface Connection

Repaired/Strengthened Element


Multi


Phased Element

Composite Element


INTERFACES

GCSI
:

5

5

5

VERIFICATION OF A SUFFICIENT CONNECTION


BETWEEN

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


6

6

6

6

6

6

F

δ

F
y,μ

F
y,ε

Monolithic Element

Strengthened Element

F
res,μ

F
res,ε

δ
y,μ

δ
y,ε

δ
u,μ

δ
u,ε

Κ
μ

Κ
ε

y,
ε
r
y,
μ
F
Κ =
F
y,
ε
δy
y,
μ
δ
Κ =
δ


ε
κ
μ
Κ
Κ =
Κ


u,
ε
δu
u,
μ
δ
Κ =
δ
INFLUENCE OF INTERFACES

CAPACITY CURVES

Deformation

Action Effect

7

7

7

MONOLITHIC BEHAVIOUR FACTORS



For
the
Stiffness
:

k
the stiffness of the strengthened element
k
the stiffness of the monolithic element



For
the

Resistance
:

r
the strength of the strengthened element
k
the strength of the monolithic element

(EI)
strength
en
ed

= k
k

(EI)
M

R
strengthened

= k
r

R
M



For
the

Displacement
:

y
the displacement at yield of the strengthened e
lement
k
the displacement at yield of the monolithic ele
ment


y
the ultimate displacement of the strengthened
element
k
the ultimate displacement of the monolithic el
ement


δ
i
,
strengthened

= k
δ
i

δ
i,M

8

8

8



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 masonries)

(
Shotcreting

reinforced


layers)

(By steel or RC elements)

Reinforced concrete walls

and jackets

STRENGHTENING THE WHOLE STRUCTURE

9

9

9

9

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
:

10

10

10

10

Strengthening of existing masonry infills


Reinforced

shotcrete

layers

applied

to

both

sides

of

the

wall




Minimum

concrete

thickness

50

mm


Minimum

reinforcement

ratio

ρ
vertical

=

ρ
horizontal

=

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 column

New wall

New column

Existing column

New wall

conversion of frames to shear walls

GCSI
:

12

12

12

Addition of New External Walls

Schematic arrangement of connections between

existing building and new wall

GCSI
:

13

13

13

Addition of a Bracing System

GCSI
:

14

14

14


OBJECTIVES

GREEK 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

Interfaces

Strengthening

of elements

Retrofitting
whole
structure

15

15

15

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.4.3.3

A.4.4.4

Clamping of lap
-
splices

by FRP wrapping


8.2.1.3

8.2.1.4

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
capacity

by concrete jackets

8.2.2.1

8.2.2.2

Interventions to increase the shear capacity

a) inadequacy of the compression struts

b) inadequacy of transverse reinforcement

A.4.3.2

A 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
capacity


by concrete jackets

Confinement action


by
FRP

wrapping

8.2.4

Interventions to increase the stiffness

A.4.2.2

Enhancement of strength,
stiffness and deformation
capacity

by concrete jackets

Interventions in Critical Regions of Linear Structural Members

16

16

16

EC 8
-
3

ANNEX A (informative)
:
REINFORCED CONCRETE STRUCTURES

CAPACITY MODELS FOR STRENGTHENING



Concrete

Jacketing



Steel

Jacketing




FRP

Plating

and

Wrapping


17

17

17



Concrete

Jacketing

Proposed to enhance the strength

stiffness and deformation capacity

Correlation with a monolithic equivalent

R
0,9V

*
R
v
*
y y
M M

*
y y y
1,05 or 1,20
   
*
u u
 
EC 8
-
3

if roughened

if not

18

18

18



Steel

Jacketing


(a)

Increase

shear

strength


(b)

Prevent

lap
-
splice

failure

Only

construction

detailing


to
:


EC8
-
3

(in

case

of

inadequate

shear

reinforcement)


19

19

19



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
)

20

20

NECESSARY AMOUNT OF CONFINEMENT


for a target curvature ductility

,t r
 

Applied

to

circular

and

rectangular

cross

sections

2
2
1,5
0,4

cu
x c
ju
f I f


(A.34)
,t ar
x
,
I

 



j
f f
f f ju f j j
c
f
4t 2t
1 1 1
f E f f
2 2 2 D f D
      
j
f
s s w
c c
f
f
2t
k 0,5 k
f D f

  
2
1,5
ju
,t r
s w
2
ave cu
1,25 k
 


 
 
 
 
 
First choice

EC
8
-
3
:

(A.34)

Confinement

pressure

s
f k f


s
k 1,0

c
s
2R
k
D

circular

rectangular


In

practice

s
k 0.2 0.35
 
21

21

Second

choice

Applied

only

to

rectangular

cross

sections

wx
0,35
v 0,225
s
um c
el
L
1
0,016 0,3 f 25
h

 
      
 

 
EC
8
-
3
:





u
u,y u
y
f f
  

        

w
wx w
(1 0,35 )
2

   
where

f,e
f
c
f
0,35
f
v 0,225
s
um c
el
L
1
0,016 0,3 f 25
h

 
      
 

 
where

f
f,e u u
c
f f (1 0,7f )
f

 
p p
1
3 (1 0.5 )
1


 
   
 
e.g.
p
p
s
L
for 0.10 3.5 2.5
L
 
      
p
p
s
L
for 0.20 2 1
L
 
      
22

22

GREEK CODE

cu,c
sy
2,2 v


 

CFRP
:


2
2
cc
cu,c w
c
f
0,0035 0,0035(1,125 1,25a )
f
 
    
 
 
y
sy
s
f
E
 
c
N
v
bhf

Yield

strain

Normalized

axial

load

Approximate

procedure

23

23

Therefore,



w
f a

  
However,

quite

different

relationships

are

proposed

with

different

influences

from

crucial

parameters
.



w
...a

  




w
w
1 0.35
2
...25

 

 




2
w
...

  
EC8
-
3

EC8
-
3

GCSI

In all Expressions

24

24

circular

D

rectangular

b

j j j
w
2
con c c
V f f
Dt
V f ( D/4) f

  

Collars

or

stirrups

A
t
S


j
w
c
f
4t
b f
 
Assume

Φ
8
/
100

stirrups

in

a

300
x
300

mm

cross

section

or

circular

D

=

300

mm,


f
ck

=

14
-
16

MPa,

f
cm

=

20

MPa

eq
50
t 0,5mm
S 100


  
w
4 0,5 500 10
0,2
300 20 6

   
If


10/75 0,4
  
w

For

an

CFRP

jacket

t

=

1

mm

w
4 3000
2
300 20
  
j
c
f
4t
D f

j j j j
0,015 f E 200.000 0,015 3000MPa
       
Volumetric

Confinement

Ratio

ω
w

w
maxa?
 
A


collar

cross

section

area

25

0
5
10
15
20
25
30
0
0.5
1
1.5
2
2.5
ω
w
μ
φ
GCSI
EC8(1)
EC8(2)
300mm

300mm

50mm

20

cm
f MPa
4 20,500

S
1.4%

ju

3.0

L m
1.5

s
L m
0.25

v
26

500mm

500mm

50mm

20

cm
f MPa
8 20,500

S
1.4%

ju

3.0

L m
1.5

s
L m
0
5
10
15
20
25
0
0.5
1
1.5
2
2.5
ω
w
μ
φ
GCSI
EC8(1)
EC8(2)
0.25

v
27

0
5
10
15
20
25
30
0
0.5
1
1.5
2
2.5
ω
w
μ
φ
GCSI
EC8(1)
EC8(2)
300mm

300mm

50mm

20

cm
f MPa
4 20,500

S
1.4%

ju

3.0

L m
1.5

s
L m
0.50

v
28

500mm

500mm

50mm

20

cm
f MPa
8 20,500

S
1.4%

ju

3.0

L m
1.5

s
L m
0
5
10
15
20
25
0
0.5
1
1.5
2
2.5
ω
w
μ
φ
GCSI
EC8(1)
EC8(2)
0.50

v
29

0
5
10
15
20
25
30
0
0.5
1
1.5
2
2.5
ω
w
μ
φ
GCSI
EC8(1)
EC8(2)
0.75

v
300mm

300mm

50mm

20

cm
f MPa
4 20,500

S
1.4%

ju

3.0

L m
1.5

s
L m
0.75

v
30

0
5
10
15
20
25
0
0.5
1
1.5
2
2.5
ω
w
μ
φ
GCSI
EC8(1)
EC8(2)
500mm

500mm

50mm

20

cm
f MPa
8 20,500

S
1.4%

ju

3.0

L m
1.5

s
L m
0.75

v
31

31

EXPERIMENTAL DATA FOR CONCRETE JACKETING

(UNIVERSITY OF PATRAS)


32

32

-150
-100
-50
0
50
100
150
-200
-150
-100
-50
0
50
100
150
200
Δύναμη
(KN)
Οριζόντια μετακίνηση (mm)
I2
-150
-100
-50
0
50
100
150
-200
-150
-100
-50
0
50
100
150
200
Δύναμη (mm)
Οριζόντια μετακίνηση (mm)
I4
O

F2

F4

R

D

RD

NT

M

Displacement (mm)

L
ateral force

(kN)

Displacement (mm)

L
ateral force

(kN)

L
ateral force

(kN)

Displacement (mm)

Displacement (mm)

Displacement (mm)

Displacement (mm)

L
ateral force

(kN)

L
ateral force

(kN)

L
ateral force

(kN)

Displacement (mm)

Displacement (mm)

Displacement (mm)

L
ateral force

(kN)

L
ateral force

(kN)

L
ateral force

(kN)

NTP

33

33


-200
-150
-100
-50
0
50
100
150
200
-150
-100
-50
0
50
100
150
Displacement (mm)
Load (kN)
R1
R2
D1
D2
RD1
RD2
W1
W2
Mo
O
Load Against Displacement Envelope Curves for All Tested Specimens

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

34

y,GCSI y,exp
?
 
Total data (42 specimens)

,exp GCSI
y y
k?if

 
(Kappos et al, EPPO report 2012)

y
k 1.26
 
GCSI
:

y
k 1.25
 
EC8
-
3
:

y
k 1.05 or 1.20
 
35

35

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
.


36

36

CONCLUDING REMARKS



EC
8
-
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

EC
8
-
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

EC
8
-
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

EC
8
-
3

does

not

touch

while

the

GCSI

attempts

to

provide

guidance,

however

with

extremely

limited

experimental

existing

data
.