ContentCIVIL 706 - Advanced Earthquake Engineering Retrofitting methods ... Seismic retrofitting techniques Passive – Additional new lateral bracing system ! Reinforced concrete

CIVIL 706 - Retrofitting methods EDCE-EPFL-ENAC-SGC 2016 -1-

EDCE: Civil and Environmental Engineering CIVIL 706 - Advanced Earthquake Engineering

Retrofitting methods


Content

•  Strategies

•  Weakening

•  Steel bracing

•  Reinforced concrete shear walls

•  Jacketing

•  Masonry reinforced by composites


Seismic retrofitting strategies

•  In the plane strength-ductility


Seismic retrofitting techniques

Passive –  Additional new lateral bracing system

!  Reinforced concrete shear walls !  Steel bracing

–  Seismic improvement of elements (columns or shear 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



•  Illustration: initial situation



•  1st option: additional RC shear walls

Increase in strength Increase of seismic forces and

decrease of deformations



•  2nd option: columns jacketing

Increase in ductility and strength Increase of damping and

displacements


Reinforcement not always optimal

•  Mind the first intuition

Increase of seismic demand (for constant ductility and damping)



•  Seismic isolation of fireman building in Basel



•  Example: moment-resisting steel frame



•  Beam weakening (dog bone)


External steel bracing


Architectural … challenge !!


Physic building at ETH Zurich


Reinforced concrete shear walls

•  Building in Fribourg


Jacketing: deficient overlapping


Jacketing: RC bridge piles


Steel jacketing: RC bridge pile

•  Elliptic jacketing - rectangular pile


Jacketing: composites

•  Easy to apply, light, resistant, durable …


Unreinforced masonry buildings

•  Example in Yverdon


Masonry: conventional techniques

•  Reinforced plaster

Anchor Ø 6mm

Welded mesh Ø 4-6mm@150 - 200 mm

Existing wall

Reinforced cement coating

Welded mesh Ø 4-6mm

250-400 mm

25-30 mm250-400 mm

250-400 mm

25-30 mm



•  Shotcrete



•  Shotcrete: static-cyclic tests



•  External or internal post-tensioning


Composites: carbon fiber


Dynamic tests EPFL-ETHZ


Experimental results




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



URM Long Specimen (L1-REFE)

32 kN

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

65 kN


-20

Long URM (L1-REFE)

Long Upgraded (L1-WRAP-G-F)

Horizontal Displacement (mm)

Forc

e at

Wal

l Top

([k

N)

-80

-60

-40

20

40

60

-20 -15 -10 -5 5 10 15 200

0

Hysteresis curves: before and after


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 [k

N]

L2-GRID-G-FTest Run 19UG1R 220%


Different FRP products and configurations

1. Long Walls

+Fabrics of

Glass FRP

+Grids of

Glass FRP


+Plates of

Carbon FRP

2. Short Walls

+Fabrics of Glass FRP

Different FRP products and configurations


L2-GRID-G-F L1-WRAP-G-F Compression Failure FRP Rupture

Failure Modes 1.Masonry Compression &Tearing of the FRP


Failure Modes 3.Debonding and Anchorage Failure


Failure Modes No Failure Was Reached


Masonry infill frames

•  Truss model (FEMA 356)



•  Truss model (NZSEE 2002)



•  Truss model (NZSEE 2002) potential column shear



•  Truss model (NZSEE 2002) potential column shear



•  Truss model (NZSEE 2002) short column effect



•  Truss model (FEMA 356) opening considerations NZSEE:


Lightly RC squat shear walls

•  Static-cyclic tests (doct. thesis Greifenhagen)



•  Static-cyclic tests (doct. thesis Greifenhagen)

ρh ~ 0.003

ρv ~ 0.003



•  Test program



•  Specimen reinforcement

ρh=0.28%

ρv=0.31%



•  Specimens after failure

M3



•  Results (failure modes and crack pattern) sliding shear sliding rebars failure rocking concrete fail. crushing diag. tension rebars fail.

wall M3 wall M4

wall M2 wall M1



•  Results (hysteretic curves)



•  Diagonal tension failure: specimen M3

Ultim.

LS67

LS65

LS69 Crack pattern M3



•  Summary of test results Shear 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 < µΔ < 8.0). Energy dissipation and stiffness •  Dissipated energy nearly is equal to 70 % of introduced energy. •  Stiffness decreases by 80 % up to µΔ = 1.0 and by 95% up to failure.

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ContentCIVIL 706 - Advanced Earthquake Engineering Retrofitting methods ... Seismic retrofitting techniques Passive – Additional new lateral bracing system ! Reinforced concrete