7 Cas Perspect

8/11/2019 7 Cas Perspect

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CIVIL-706 - retrofitting methods

EPFL-ENAC-SGC 2009 -1-

Doctoral School: StructuresCIVIL-706 Advanced Earthquake Engineering

Retrofittingmethods


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Content

Strategies

Weakening

Steel bracing

Reinforced concrete shear walls

Jacketing

Masonry reinforced by composites


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Seismic retrofitting strategies

In the plane strength-ductility


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Seismic retrofitting techniques

Passive Additional new lateral bracing system

! Reinforced concrete shear walls

! Steel bracing

Seismic improvement of elements (columns orshear walls) of the existing structure

! By jacketing (concrete, steel, composites )

! By composite strips

! By additional post-tensioning

Semi-active

Seismic isolation

Additional energy dissipation devices! By friction

! By liquid mass


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Illustration: initial situation


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1st

option: additional RC shear walls

Increase in strength

Increase of seismic forces anddecrease of deformations


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2nd

option: columns jacketing

Increase in ductility and strength

Increase of damping anddisplacements


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3rd

option: bracing + beam weakening

Increase in strength and ductility

Increase of seismic forces and damping


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4th

option: isolators + dampers

Decrease in strength, increase in ductility

Decrease of seismic forces and displacements of the structure,increase of damping


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Reinforcement not always optimal

Mind the first intuition

Increase of seismic

demand(for constant ductility and

damping)


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Example: tank in Valais


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Tank: seismic isolation


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Tank in VS

Decrease ofdemand:

- decrease of frequency- increase of damping

Displacements


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Example: moment-resisting steel frame


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Beam weakening(dog bone)


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Architectural challenge !!


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Physic building at ETH Zurich


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Building in Fribourg


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Delicate intervention in the building


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Police building in Sion


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RC frame infilling

RC precast panels and post-tensioning


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RC frame infilling

RC precast panels and post-tensioning


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RC frame infilling

Static-cyclic tests


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RC frame infilling: failure mode


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Jacketing: deficient overlapping


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Jacketing: RC bridge piles


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Steel jacketing: RC bridge pile

Elliptic jacketing - rectangular pile


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Jacketing: composites

Easy to apply, light, resistant, durable


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Jacketing: composites

Failure of retrofitted RC column

Fragile failure of the jacket but

ductile behavior of the column


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Unreinforced masonry very vulnerable

Failure modes

in-plane

Pay attention for out-of-plane


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Unreinforced masonry buildings

Example in Yverdon


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Prototype building tests

5 stories, 1:1, reinforced masonry


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Masonry: conventional techniques

Reinforced plaster

Anchor 6mm

Welded mesh 4-6mm

@150 - 200 mm

Existing wall

Reinforced cement

coating

Welded mesh

4-6mm

250-400 mm

25-30 mm

250-400 mm

250-400 mm

25-30 mm


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Shotcrete


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Shotcrete: static-cyclic tests


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Bracing and confinement (RC column)

14-16 mm

.c. tie-column

Existing masonry wall

Existing masonry wall

R.c. tie-column

14 -16 mm

240

1 1

Section 1-1

240

240


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External or internal post-tensioning


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Center-core


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Composites: carbon fiber


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Retrofitting: composites

On the twoinferior stories


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Increase of ductility

Static-cyclic tests


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Dynamic tests EPFL-ETHZ


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Experimental results


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Dynamic tests: test parameters

1. Aspect Ratio (0.7, 1.4)

2. Mortar Type

3. Material Type (glass, carbon, and aramid)

4. Fiber Product (fabric, grid, and plates)

5. Upgrading Configurations

Wall parameters

Strengthening materials


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URM Long Specimen(L1-REFE)

32 kN

Upgraded Long Specimen(L1-WRAP-G-F)

65 kN


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-20

Long URM(L1-REFE)

Long Upgraded(L1-WRAP-G-F)

Horizontal Displacement mm)

F

c

a

W

a

T

k

N

-80

-60

-40

20

40

60

-20 -15 -10 -5 5 10 15 20

0

0

Hysteresis curves: before and after


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Sample Hysteretic Behavior

![mm]

-70

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

70

-20 -15 -10 -5 0 5 10 15 20

F[kN]

L2-GRID-G-F

Test Run 19

UG1R 220%


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Experimental results: lateral strength

0

0.5

1

1.5

2

2.5

3

3.5

HUpgraded/H

Reference

N=57 kN

L1-WRA

P-G-F

L2-GRID-G-F

L1-WRAP-G-X

!

=0.0

72%

!=0.068%

!

=0.0

28%

!

=0

.049%

S

1-LAMI-C-X

S1-WRAP-G-F

S2-WRAP-A-F

!=0.072% !=0.189%

"=?


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Different FRP products and configurations

1. Long Walls

+Fabrics of

Glass FRP

+Grids of

Glass FRP


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1. Long Walls (Cont.)

+Fabrics of Glass FRP

-Plates of Carbon FRP



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+Plates of

Carbon FRP

2. Short Walls

+Fabrics of

Glass FRP



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+Fabrics of

ARMID FRP

2. Short Walls (Cont.)



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L2-GRID-G-F L1-WRAP-G-FCompression FailureFRP Rupture

Failure Modes1.Masonry Compression &Tearing of the FRP

F il M d


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Failure Modes2.Tearing of the FRP


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Failure Modes3.Debonding and Anchorage Failure


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Failure ModesNo Failure Was Reached


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Anchorage Solutions1. Ductile Connection (Hamilton)


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Master Bkir Omrovic, EPFL 2005


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Without anchorage


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Design

Shear

2FRPhFRPhFRP )E(!0.0104)E(!0.02050.0119# +$=Triantafillou 98:

F = Fm+ FFRP

FFRP= !hEFRP #eff

Fm= EC6


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Design

Shear (part FFRPof composites)

Triantafillou andAntonopoulos

AC 125


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Comparison with tests (ElGawady)

Shear


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Design

Flexural strength (usual model)


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Design

Flexural strength (usual model)

equilibrium:

neutral axis:

strength:


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Comparison with tests (ElGawady)

Flexural strength


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Model

Analytical (doctoral thesis ElGawady, 2004)


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Masonry infill frames

Truss model (FEMA 356)


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Truss model (NZSEE 2002)


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potential column shear


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potential column shear


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short column effect


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Truss model (FEMA 356)

opening considerations

NZSEE:


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Lightly RC squat shear walls

Static-cyclic tests (doct. thesis Greifenhagen)


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Static-cyclic tests (doct. thesis Greifenhagen)

h ~ 0.003

v ~ 0.003


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Test program


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Specimen reinforcement

h=0.28%

v=0.31%


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Specimens after failure

M3


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Results (failure modes and crack pattern)

sliding shear slidingrebars failure rocking

concrete fail. crushingdiag. tension rebars fail.

wall M3 wall M4

wall M2wall M1


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Results (hysteretic curves)


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Diagonal tension failure: specimen M3

Ultim.

LS67

LS65

LS69Crack pattern M3


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Summary of test resultsShear capacity

Brittle shear failure is not observed.

Tests provide evidence for inherent shear strength of concrete.

Peak shear stress: 1.4 .. 1.9 N/mm^2

Dimensionless shear capacity:0.28 < c < 0.52

Deformation capacity Negative effect of lacking horizontal reinforcement not evidenced.

Flexural deformation dominates the plastic response.

Observed drifts: 0.90 .. 2.20%.

Low to moderate ductile behavior is observed (5.6 < %< 8.0).

Energy dissipation and stiffness

Dissipated energy nearly is equal to 70 % of introduced energy. Stiffness decreases by 80 % up to %= 1.0 and by 95% up to failure.


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Example industrial building

Plane


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Cross-section


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Model


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Proposed

measure


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Example bridge

Precast concrete bridge


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Example precast concrete bridge

Diag M- of interior piles


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Example precast concrete bridge

Transversal displacement-based evaluation

0

0.5

1

1.5

2

2.5

3

3.5

4

0 20 40 60 80 100

Sd [mm]

Sa[m/s

2]

2.0 Hz

0.50 Hz

0.75 Hz

1.0 Hz1.5 Hz

wr,d

wd

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