ON THE SEISMIC RETROFITTING OF EXISTING ... Classification Strategies for the seismic retrofitting...

UNIVERSITÀ DEGLI STUDI DI SALERNO

Department of Civil Engineering

ON THE SEISMIC RETROFITTING OFEXISTING REINFORCED CONCRETE STRUCTURES

Dr. Eng. Carmine Lima, PhD - [email protected]

6 de Octubre 2014Universidad de Buenos Aires – Faculdad de Ingenieria

mailto:[email protected]

http://www.carminelima.eu/

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Lab of Material testing and

structures

Experimental tests

Numerical Simulation

TOPICS

1. New and existing RC,

masonry and steel

structures

2. Materials

Nonlinear response Beam-column jointsSeismic retrofitting of

existing structures

Strengthening of masonry

walls

EnCoRe project: Eco-friendly solutions

for making concrete

RECYCLED AGGREGATES, FIBER

REINFORCED CONCRETE WITH

RECYCLED AND NATURAL FIBERS

FRP confinement of columns

and joints

Introduction

Classification

Strategies for the seismic retrofitting

Increasing Stiffness/strength

Ductility enhancement

Static Strengthening of floors and beams

Increasing Stiffness

Steel bracings

RC shear walls

Ductility enhancement

Confinement with steel members

RC Jacketing

Confinement with FRP

Advenced techniques

Seismic Isolation

Dissipative towers

SUMMARY

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Introduction Strengthening offloors and beams

Increasing stiffness Ductility enhancementAdvencedtechniques

INTRODUCTION

Seismic risk in Italy

Estimated structural collapse for each year

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INTRODUCTION

Seismic damage after earthquakes

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The seismic assessment of a structure should allow to evaluate if:

The structure can be used without retrofitting interventions;

The use have to be reduced [reducing loads, changing the destination (i.e.

library to residence) or introducing limitation in the use (i.e. access permitted to

only n-persons at the same time)];

The structure is needed for retrofitting in order to repair it or increase the

structural safety under static and seismic conditions

INTRODUCTION

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Two classes can be identified:

Strategies that allow to increase the stiffness and strength of the existing structure

Strategies that allow to increase the displacement capacity (ductility enhancement) of the

structure.

INTRODUCTION –Classification and strategies for the seismic retrofitting

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INTRODUCTION –Strategies for seismic retrofitting

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INTRODUCTION –Strategies for seismic retrofitting



Strengthening of floors and beams

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Before taking into account the seismic conditions, an assessment under static gravitational

loads is needed.

Generally, structures can be modified or the use can be modified resulting in increasing

loads. Moreover, degradation can affect the structural materials (concrete, steel, etc.)

resulting in a reduction of their mechanical characteristics.

The first assessment is performed in terms of flexural and shear capacity of floors and beams,

and axial load in the columns.

STRENGTHENING OF FLOORS AND BEAMS

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Flexural strengthening


Steel plates in tension, joined

with mechanical anchors

Slab on the top (increasing of

stiffness, but also lads)

Including steel bars in tension

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Flexural strengthening


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Design of the strengthening

Taking into account the existing deformation (due to the load on the structural member at thetime of the strengthening) and the deformation of the strengthened section

hypothesis:

Plane cross section;

Optimal adherence between steel and concrete;

Concrete with zero tension strength;

Modes of crisis:

Crisis of the existing steel;

Crisis in compression of the concrete;

Crisis of the strengthening

Rupture of the steel plate

De-bonding and crisis of the connection


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Increasing Stiffness

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RC shear walls

STIFFNESS

Including new elements and sub-structures

Control the seismic demand

(reducing displacement) of the existing

structure

Steel Bracings

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RC SHEAR WALLS

- School building

- Avellino (South Italy)

- Three-story reinforced concrete structure

- Unidirectional reinforced concrete floors

- Foundation T-beam section

Case of study

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Seismic assessment of the existing structure

RC SHEAR WALLS

• First storey:

• Meccanismi duttili:mini{(θc,LS,i-θd,i)/θc,LS,i} = - 0,15

• Meccanismi fragili: mini{(VRd,i-VSd,i)/VRd,i} = - 0,16

• Second storey:

• Meccanismi duttili:mini{(θc,LS,i-θd,i)/θc,LS,i} = - 0,30

• Meccanismi fragili: mini{(VRd,i-VSd,i)/VRd,i} = - 0,14

• Third storey:

• Meccanismi duttili:mini{(θc,LS,i-θd,i)/θc,LS,i} = 0,08

• Meccanismi fragili: mini{(VRd,i-VSd,i)/VRd,i} = 0,04

, 0.0013 1 1.5 0.133

b yVc DL y y y

V c

d fL h

L f

,

3

4c LS u

0.225 0.35

100

,

max 0.01; '10.016 0.3 25 1.25

max 0.01;

ywsx

c d

f

fvc CO c

el

Lf

h

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Design

,i

i d i i

i

VH

k

,

,

ii c i i

i p i

VH

k k

,

ip i

c i i

Vk k

H

From Δp,i can be evaluated the geometrical dimensions a and b of walls:

,

, , , 1 1 1( , ) ( , )

i ip i

p i p i i i p i i i

V Vk

a b a b

23 2

1 31 1 2 1 1,1 ,1 1 2 3

1 1

1

3 3 3p p

H HH H H VHV V V

EI GA

22 32 2 31 2 2 2 2

,2 ,2 ,1 1 2 1 2 3 1 2 3 2 3

1 2 2

1 1

2 3 2p p p

H HH H H V HV V H H V H H H V V

EI EI GA

2 2 32 21 3 2 3 3 3 3

,3 ,3 ,2 1 2 1 2 3 3 1 3 2 3 2 3 3

1 2 3 3

1 1 1

2 2 3p p p

H H H H H V HV V H H H V H H V V H H V

EI EI EI GA

Required stiffness

Stiffness of one shear wall

RC SHEAR WALLS

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7 rc walls are needed, 2 in x-direction and 5 in y-direction.

RC SHEAR WALLS

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RC floors transmits the actions at columns and walls. Before the intervention the actions are almost distributed and diffused on the floor.

After the intervention the seismic action are concentrated within the walls that have a stiffness higher than columns

RC SHEAR WALLS

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Assessment of floors



1 872

10 151411 1312

3 5 6

20 25

169

19 2622 23

1817

4

21 24

27 28

30x50 30x5030x50

30x5030x50 30x5030x50 30x5030x50

30x50 30x50

20x8

0

20x8

0

50x2

650

x26

50x2

650

x26

50x2

6

50x2

6

50x2

650

x26

50x2

650

x26

30x5

0

30x5

0

30x50

30x50

rompitratta 4ø12 con staffe ø8/25

armatura di ripartizionemaglia ø8/30


























6.30

5.40

2.05

2.70 8.00 1.00 1.40 1.00 4.00 4.00 2.70

6.30

5.40

2.05

3.95 2.70 3.50 4.00 4.00 2.70 3.95

0.50

5.80

1.10

3.20

1.10

1.45

0.60

0.20

2.50 1.00 0.00

2.50 1.00 2.50 1.00 0.30 0.70 1.40 0.70 0.30 1.00 2.49 0.00

1.00 0.00

2.49 0.00

1.00 2.50 0.20

0.50

5.80

1.10

3.20

1.10

1.45

0.60

0.30 3.35 0.30 2.70 1.00 0.00

2.50 1.00 0.00

2.49 0.01

1.00 0.00

2.50 0.00

1.00 2.70 0.30 3.35 0.30

13.7

5

24.80

13.7

5

24.80

5d

1d

3d

2c

4d

6d

2d

30x50 30x50

30x8030x80

30x80 30x8030x8030x80 40x8040x80

30x100 30x100 30x100

30x100 30x100

20x11020x110

20x110 20x110

T-90/30x130/30 T-90/30x130/30

30x8030x80

30x100

30x100 30x100

30x60 30x60

paretes=30

paretes=30

paretes=30

paretes=30

paretes=20

paretes=20

paretes=30

paretes=30

paretes=30

paretes=30

paretes=30

paretes=30

paretes=30

A A

A A

A A

A

A

A

A

A

A A

1,3*755 kN 1,3*755 kNSection with base 5cm

(slab thickness)

1,3 2 755 2 680150,44 /

24,80q kN m

m

k1 k2 k2 k1

3

21 3

3

H EIdeformabilità parete

EI GA H

3

2

1

1 33

k rigidezza pareteH EI

EI GA H

K1 = 8931,81 N/mm

K2 = 11591,78 N/mm

1,3*680 kN

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RC SHEAR WALLS




Deformed shape with no rigid modellingdd = 91,0747

Deformed shape with infinitely rigid modellingdr = 90,8933

1,10 infinite stiffnessd rd d

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RC SHEAR WALLS




Strength assessment [kN-m]

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RC SHEAR WALLS





Bending and shear resistance taking into account the steel reinforcement in the

slab (section with base 5cm and height 11m)

2179,06

822,54

8 / 25 25

Sd

Sd

M kNm

V kN

rete x

2179,06

1 823

Rd

Rd

M kNm

V ctg kN

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RC SHEAR WALLS




1 872

10 151411 1312

3 5 6

20 25

169

19 2622 23

1817

4

21 24

27 28

30x50 30x5030x50

30x5030x50 30x5030x50 30x5030x50

30x50 30x50

20x8

0

20x8

0

50x2

650

x26

50x2

650

x26

50x2

6

50x2

6

50x2

650

x26

50x2

650

x26

30x5

0

30x5

0

30x50

30x50




























6.30

5.40

2.05

2.70 8.00 1.00 1.40 1.00 4.00 4.00 2.70

6.30

5.40

2.05

3.95 2.70 3.50 4.00 4.00 2.70 3.95

0.50

5.80

1.10

3.20

1.10

1.45

0.60

0.20

2.50 1.00 0.00

2.50 1.00 2.50 1.00 0.30 0.70 1.40 0.70 0.30 1.00 2.49 0.00

1.00 0.00

2.49 0.00

1.00 2.50 0.20

0.50

5.80

1.10

3.20

1.10

1.45

0.60

0.30 3.35 0.30 2.70 1.00 0.00

2.50 1.00 0.00

2.49 0.01

1.00 0.00

2.50 0.00

1.00 2.70 0.30 3.35 0.30

13.7

5

24.80

13.7

5

24.80

5d

1d

3d

2c

4d

6d

2d

30x50 30x50

30x8030x80

30x80 30x8030x8030x80 40x8040x80

30x100 30x100 30x100

30x100 30x100

20x11020x110

20x110 20x110

T-90/30x130/30 T-90/30x130/30

30x8030x80

30x100

30x100 30x100

30x60 30x60

paretes=30

paretes=30

paretes=30

paretes=30

paretes=20

paretes=20

paretes=30

paretes=30

paretes=30

paretes=30

paretes=30

paretes=30

paretes=30

A A

A A

A A

A

A

A

A

A

A A

Strength assessment[kN-m]

Strut-and-tie mechanism

Steel tie

Concrete strut

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RC SHEAR WALLS


Width = 2/3 of the wall width

lp

2/3 lp

Strut width =L/10;The maximum stress in the concrete should be verified




FEM modellign: shells

1 872

10 151411 1312

3 5 6

20 25

169

19 2622 23

1817

4

21 24

27 28

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30x5030x50 30x5030x50 30x5030x50

30x50 30x50

20x8

0

20x8

0

50x2

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x26

50x2

650

x26

50x2

6

50x2

6

50x2

650

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50x2

650

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30x5

0

30x5

0

30x50

30x50




























6.30

5.40

2.05

2.70 8.00 1.00 1.40 1.00 4.00 4.00 2.70

6.30

5.40

2.05

3.95 2.70 3.50 4.00 4.00 2.70 3.95

0.50

5.80

1.10

3.20

1.10

1.45

0.60

0.20

2.50 1.00 0.00

2.50 1.00 2.50 1.00 0.30 0.70 1.40 0.70 0.30 1.00 2.49 0.00

1.00 0.00

2.49 0.00

1.00 2.50 0.20

0.50

5.80

1.10

3.20

1.10

1.45

0.60

0.30 3.35 0.30 2.70 1.00 0.00

2.50 1.00 0.00

2.49 0.01

1.00 0.00

2.50 0.00

1.00 2.70 0.30 3.35 0.30

13.7

5

24.80

13.7

5

24.80

5d

1d

3d

2c

4d

6d

2d

30x50 30x50

30x8030x80

30x80 30x8030x8030x80 40x8040x80

30x100 30x100 30x100

30x100 30x100

20x11020x110

20x110 20x110

T-90/30x130/30 T-90/30x130/30

30x8030x80

30x100

30x100 30x100

30x60 30x60

paretes=30

paretes=30

paretes=30

paretes=30

paretes=20

paretes=20

paretes=30

paretes=30

paretes=30

paretes=30

paretes=30

paretes=30

paretes=30

A A

A A

A A

A

A

A

A

A

A A

s11

s22

ON

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RC SHEAR WALLS




Strengthening of the foundation

RC SHEAR WALLS

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Application

RC SHEAR WALLS

ON

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Steel bracings

ON

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Case-of-study

STEEL BRACINGS

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STEEL BRACINGS

ON

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Results of the seismic assessment

• The structures is verified in respect toseismic actions related to earthquakeswith low and medium intensity

• Vulnerability is achieved in respect to highseismic intensity. Flexural and shearcollapse is expected for columns

STEEL BRACINGS

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Shear collapse of the 1st

column

Displacement to reach without any collapse in order to have the structural safety

collapse of other columns

Displacement capacity = 7 mm

Displacement demand = 62 mm



Design of the retrofitting intervention

Displacement capacity increased = 20 mm

Confinement of Columns

STEEL BRACINGS

ON

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Displacement demand should be reduced to 20 mm by increasing stiffness



STEEL BRACINGS

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Design of the retrofitting interventionColumns confined with steel

Increasing capacity displacement



STEEL BRACINGS

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Buckling restrained bracings (BRB)

Working in tension and compression



STEEL BRACINGS

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Displacement demand = 23 mm

Displacement capacity = 29 mm

RETROFITTED STRUCTURE



Design

STEEL BRACINGS

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CORPO 2 - CONTROVENTO CAMPATE 6-5 e 5-4



Traditional steel bracings

STEEL BRACINGS

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STEEL BRACINGS

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Influence of the structural shape

+ 0.00 RC walls

Brad 46/40

Brad 39/40

Brace (d=219mm; t=5mm)

Brad 46/40

+ 0.00 RC walls

Brad 39/40

Caso 1

Caso 2

STEEL BRACINGS

ON

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Caso 1

Caso 2

STEEL BRACINGS

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Influence of the structural shape



Caso 1 Caso 2

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,70

0,00 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08

V*/m

* [

g]

* [m]

SDOF

Fx(+) Prop.ModoFx(-) Prop.ModoFy(+) Prop.ModoFy(-) Prop.ModoFx(+) Prop.MassaFx(-) Prop.MassaFy(+) Prop.MassaFy(-) Prop.Massa

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,70

0,00 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08

V*

/m*

[g

]* [m]

SDOF

Fx(+) Prop.ModoFx(-) Prop.ModoFy(+) Prop.ModoFy(-) Prop.ModoFx(+) Prop.MassaFx(-) Prop.MassaFy(+) Prop.MassaFy(-) Prop.Massa

STEEL BRACINGS

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Influence of the structural shape – Base shear



Confinement with steel members

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CONFINEMENT WITH STEEL MEMBERS

Steel members

Continuum plates

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Effects of the confinement0.86

0.51 3.7

n s s y

cc c

c

ff f

f

Confinement efficiency factors

2 2

2 21

3n

b R h R

bh

1 12 2

s ss

s h s h

b h

0.50.004 0.5

n s s y

cu

cc

f

f


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Confinement effects– horizontal confinement

2 22 2

13

n

b R h R

bh

R = raggio arrotondamento degli spigoli della sezione,

b e h = dimensioni della sezione

2

1

2 ' 1' '

3 4 6

bA b b

2

2

2 ' 1' '

3 4 6

dA d d

2 2

2 2

1 2

' '1 12 2 ' '

3 3 3e

d bA A A A bd b d bd

2 2' '

13

en

d bA

A bd

The confinement effect are negligible in sections in which b/d>2

This case can be overcomes introducing a steel bar for the connection (a perforation of the column is needed)

2

16

ien

bA

A bd

2

6

i

e i

bA A A A


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1 12 2

s ss

s h s h

b h

hs = altezza delle bande,

s = passo delle bande,

(se la camicia è continua si pone hs = s)

' '

2 2

f fe

p pA b h

' ' 1 ' '1 1

2 2 2 2

e f f f fs

A p p p pb h

A bh b h


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Confinement effects– vertical confinement



Effects of the vertical steel members

Increasing strength (composite section):

Existing concrete

Existing bars

New steel members

, ,y ang ang y barre barref A f A ,

,

ang y ang

barre

y barre

A fA

f

Esempio numerico

fy,ang = 275 MPa; fy,barre = 450 Mpa; Aang = 6.31 cm2

,

20

,

2756311.05 4.22 3 16

4501.15

y angang

Mbarre

y barre

s

fA

A cmf


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Effects of horizontal steel members

Increasing shear strength (they are equivalent to stirrups)

In which:

tj = thickness of horizontal steel members;

b = width of the horizontal steel members;

s = spacing (b/s=1 if continuum plate);

fyw = yielding strength of steel;

t = inclination of the shear cracks (generally 45°).

2 10.5

cos

j

j yw

t

t bV f

s


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RC Jacketing

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RC JACKETING

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Types

Pa

rtia

l ja

cke

tin

gF

ull

jack

eti

ng

RC JACKETING

ON

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Design

RC JACKETING

ON

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Numerical example

Existing Column 45x45

Confined column 70x70 cm

RC JACKETING

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Confinement with FRP

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ON

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CONFINEMENT WITH FRP

FRP = Fiber-Reinforced Polymers

GFRP = Glass Fiber-reinforced polymers

CFRP = Carbon Fiber-reinforced polymers

AFRP = Aramid Fiber-reinforced polymers

In a lot of cases FRP can be a valid and economic alternative to traditional materials in many engineering applications

New structures Existing structures



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Confinement with FPR can enhances the mechanical properties of concrete

• Increasing the ultimate strength and the ultimate strain (ductility) for elements with axial load and small eccentricity

• Increasing ductility in members with high bending moment



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Increasing compressive strength and ultimate strain depends on the pressure of confinement related to:

• Stiffness of the FRP material;

• Shape of the cross section



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Confinement can be provided as continuum or not continuum



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Increasing strength: Dominium M-N

High eccentricity

low eccentricity

Axial load

Increasing strength is negligible

Good ductility enhancement

Good Increasing strength

Good ductility enhancement

Advanced techniques

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ON

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SEISMIC ISOLATION

• Why use of seismic isolation systems may be beneficial

• Types of seismic isolation systems available



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SEISMIC ISOLATION



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SEISMIC ISOLATION



Objectives of Seismic Isolation Systems

• Enhance performance of structures at all

hazard levels by:

o Minimizing interruption of use of facility

(e.g., Immediate Occupancy

Performance Level)

o Reducing damaging deformations in

structural and nonstructural

components

o Reducing acceleration response to

minimize contents related damage

Characteristics of Well-Designed Seismic Isolation Systems

• Flexibility to increase period of vibration and thus reduce force response

• Energy dissipation to control the isolation system displacement

• Rigidity under low load levels such as wind and minor earthquakes

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SEISMIC ISOLATION



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SEISMIC ISOLATION



Applicability of Base Isolation Systems

MOST EFFECTIVE

• Structure on Stiff Soil• Structure with Low Fundamental Period (Low-Rise Building)

LEAST EFFECTIVE

• Structure on Soft Soil• Structure with High Fundamental Period (High-Rise Building)

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SEISMIC ISOLATION

Application of Seismic Isolation to Retrofit Projects

Motivating Factors:

• Historical Building Preservation (minimize modification/destruction of building)

• Maintain Functionality (building remains operational after earthquake)

• Investment Protection (long-term economic loss reduced)

• Content Protection (Value of contents may be greater than structure)

Disavantages

• Expensive intervention

• Interaction with non-structural elements and systems

• Structures on soft soils or with low gravitational loads

• Displacement after earthquakes (re-centering)



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SEISMIC ISOLATION



Types of Seismic Isolation Bearings

Elastomeric Bearings

• Low-Damping Natural or Synthetic Rubber Bearing

• High-Damping Natural Rubber Bearing

• Lead-Rubber Bearing (Low damping natural rubber with lead core)

Sliding Bearings

• Flat Sliding Bearing

• Spherical Sliding Bearing

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SEISMIC ISOLATION



High damping

Lowdamping

Leadcore

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SEISMIC ISOLATION



The response of the dispositive depends on the axial load W, which changes during earthquakes

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Dissipative tower



New system patented in Italy bywww.torridissipative.com

http://www.torridissipative.com/

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INNOVATIVE TECHNIQUES

Design of external tower for the seismic protection, equipped withdamping systems for the energy dissipation.



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Damping system at the base of the tower

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Advantages

• Economic solution (reduction of the interventions within the existing structure)

• The tower can be used as a new buildings (stairs, elevators, etc.)

• The damping system is easily accessible for maintenance

• Completely reversible intervention.



Effects: increasing damping decreasing accelerations and displacement of the existing structure

1. DPC-ReLUIS 2010-2013 Research Project (Task 1.1.2).

2. ReLuis: Emargenza terremoto Abruzzo/Report:http://www.reluis.it/index.php?option=com_content&view=article&id=73&lang=it&Itemid=108

3. Michael D. Symans, PhD, Rensselaer Polytechnic Institute –

4. Seitec s.r.l. – Spin off Università Politecnica delle Marche (Italy): “Un sistemainnovativo per la protezione sismica di scuole e ospedali: “le torri dissipative” –www.torridissipative.com

Thank you for your kindly attention

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Acknowledgments and references

e.mail: [email protected]: www.carminelima.eu

http://www.reluis.it/index.php?option=com_content&view=article&id=73&lang=it&Itemid=108

http://www.torridissipative.com/

mailto:[email protected]

http://www.carminelima.eu/

ON THE SEISMIC RETROFITTING OF EXISTING ... Classification Strategies for the seismic retrofitting...

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Transcript of ON THE SEISMIC RETROFITTING OF EXISTING ... Classification Strategies for the seismic retrofitting...