Seismic Retrofit

Case StudyBuilding Strengthening using CFRP

December 10th 2019

Avi Cohen

Yaron Offir Engineers / Exyte

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Content

1. Case study: Seismic Retrofit of an

office building into a high-tech

manufacturing facility

2. Near-surface-mounted CFRP rod

design

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Case Study:Seismic Retrofit of an office building into a high-

tech manufacturing facility

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Case Study

SEISMIC EVALUATION

ASCE/SEI 41-17

Seismic Evaluation and Retrofit of

Existing Buildings, ASCE/SEI-41-17

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Higher

Performance

(LESS Loss)

Lower

Performance

(MORE Loss)

Operational (1-A)Immediate

Occupancy (1-B)Life Safety (3-C)Collapse Prevention (5-E)

IO for a

Design

Earthquake

CP for the

Maximum

Considered

Earthquake

LS for a Design

Earthquake

Case Study

SEISMIC PERFORMANCE OBJECTIVE

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– Enhancement of Existing Concrete Shear Walls

– New Pile Foundation for the Shear Walls

– Collector reinforcements

– Structural Joint Connection

– Nonstructural Elements

Case Study

REINFORCEMENTS

– Slab Flexural Capacity

Enhancement

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– Installation of horizontal CFRP strips

– Increase in ductility, confinement and shear capacity

– Adequate plastic hinge development

– Control of energy dissipation during an earthquake prevent damage in undesired elements

Case Study

CONCRETE SHEAR WALL ENHANCEMENT

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– Installation of horizontal CFRP strips

– Increase in ductility, confinement and shear capacity

– Adequate plastic hinge development

– Control of energy dissipation during an earthquake prevent damage in undesired elements

Case Study

COLLECTOR REINFORCEMENT

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– Installation of horizontal CFRP strips

– Increase in ductility, confinement and shear capacity

– Adequate plastic hinge development

– Control of energy dissipation during an earthquake prevent damage in undesired elements

Case Study

SLAB FLEXURAL CAPACITY ENHANCEMENT

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Provide strength and ductility without adding stiffness or changing the period.

Addition of new piles to provide tensile capacity directly to the pile foundation.

Allow for controlled plastic hinge formation and energy dissipation in flexure of

existing concrete walls.

Increase the performance of existing walls (Level 1).

Ensure adequate load path transfer to walls – collector retrofit.

IO and CP criteria requirement are met for current retrofit

Case Study

OBJECTIVES

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• Displacement Demand (Performance Point):

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

0.0 2.0 4.0 6.0 8.0 10.0

Ba

se

Sh

ea

r (k

N)

Roof displacement (cm)

Pushover Curve in the Transverse Direction

First Yielding of Pile Rebar (T pier)

First Yielding of Pile Rebar (C pier)

Yield of Existing RC wall - L1 (T pier)

First SH of Pile Rebar (T pier)

First Failure of Pile Rebar (T pier)

First Rupture of Pile Rebar (T pier)

Deformation at Performance Point

Case Study

ANALYSIS RESULTS – EXISTING BUILDING

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0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

160,000

180,000

200,000

0.0 2.0 4.0 6.0 8.0 10.0

Ba

se

Sh

ea

r (k

N)

Roof displacement (cm)

Pushover Curve in the Transverse Direction

• Failure Mechanism

Yield of Existing RC wall - L1 (C pier)

Yield of Existing RC wall - L2 (T pier)

Yield of Existing RC wall - L1 (T pier)

Yield of Existing RC wall - L2 (C pier)

First Yielding of Pile Rebar

First IO limit of Pile Rebar

Deformation at Performance Point

First SH of Pile Rebar (C pier)

First Failure of Pile Rebar (T pier)

Case Study

ANALYSIS RESULTS – RETROFITTED BUILDING

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Case Study

INSTALLATION WORKS

SHEAR ENHANCEMENT OF RC WALLS

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Case Study

SITE INSTALLATION

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SITE INSTALLATION

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SITE INSTALLATION

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SITE INSTALLATION

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INSTALLATION WORKS

RC SLAB FLEXURAL REINFORCEMENT

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SITE INSTALLATION

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SITE INSTALLATION

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SITE INSTALLATION

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SITE INSTALLATION

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INSTALLATION WORKS

SHEAR ENHANCEMENT OF DIAPHRAGMS

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SITE INSTALLATION

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SITE INSTALLATION

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SITE INSTALLATION

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SITE INSTALLATION

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Near Surface Mounted CFRP Rod

Reinforcement Design

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NSM-CFRP Design

• Alternative collector

reinforcement using

NSM-CFRP Rods

Technical Article Flexural strengthening with NSM reinforcement - SIKA

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NSM-CFRP Design

BENEFITS

• Construction benefits:

Reduced installation time (compared to SIKAWRAP equivalent)

Reduced disturbance area

Can be installed in slightly undulating surfaces

• Technical benefits:

Reduced risk of buckling due to confinement of CFRP.

Reduced required anchorage length.

Enhanced adhesion between CFRP (increased contact area)

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NSM-CFRP Design

MODES OF FAILURE

Technical Article Flexural strengthening with NSM reinforcement - SIKA

Adhesive

SplittingConcrete

Splitting

CFRP

Rupture

Concrete

Cover

Separation

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NSM-CFRP Design

Design Guidelines

ACI 440

Design guidance for strengthening

concrete structures using fibre

composite materials, reported by the

Concrete Society.

Technical Report No.55

Guide for the Design and Construction

of Externally Bonded FRP Systems for

Strengthening Concrete Structures

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NSM-CFRP Design

Type of Rods - SIKA

PRODUCT DATA SHEET Sika® CarboDur® Rods

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NSM-CFRP Design

Retrofit Design

ACI 440 TR-55

Design rupture strain:

Debonding strain:

Effective strength:

Design strain:

Design E-modulus: strain:

Effective strength:

DETERMINATION OF THE EFFECTIVE STRAIN

𝑓𝑓𝑒 = ε𝑓𝑑𝐸𝑓𝑑

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ACI 440 TR-55

NSM-CFRP Design

Retrofit Design

Technical Article Flexural strengthening with NSM reinforcement - SIKA

DETERMINATION OF THE EFFECTIVE STRAIN

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TR-55

Anchorage force

Anchorage length

NSM-CFRP Design

Retrofit Design

Technical Article Flexural strengthening with NSM reinforcement - SIKA

FAILURE MODE CHECK: CONCRETE SPLITTING

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TR-55

Actual Anchorage force

NSM-CFRP Design

Retrofit Design

Technical Article Flexural strengthening with NSM reinforcement - SIKA

FAILURE MODE CHECK: CONCRETE SPLITTING (cont)

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TR-55

Avoid concrete cover separation:

NSM-CFRP Design

Retrofit Design

Technical Article Flexural strengthening with NSM reinforcement - SIKA

FAILURE MODE CHECK: CONCRETE COVER SEPARATION

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TR-55

Mechanical capacity of adhesive at anchorage:

NSM-CFRP Design

Retrofit Design

Technical Article Flexural strengthening with NSM reinforcement - SIKA

FAILURE MODE CHECK: ADHESIVE LAYER AT ANCHORAGE

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TR-55

Separation due to the longitudinal shear stress

in the yield zone:

Shear stress limit:

NSM-CFRP Design

Retrofit Design

Technical Article Flexural strengthening with NSM reinforcement - SIKA

FAILURE MODE CHECK: ADHESIVE FAILURE

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TR-55

Separation due to the longitudinal shear stress

in the yield zone:

Shear stress limit:

NSM-CFRP Design

Retrofit Design

Technical Article Flexural strengthening with NSM reinforcement - SIKA

FAILURE MODE CHECK: CONCRETE FAILURE

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ACI 440

Sustained plus cyclic stress limit:

Concrete stress limit:

Steel stress limit:

NSM-CFRP Design

Retrofit Design

From: ACI440.2R-17

SERVICEABILITY LIMITS

𝑓𝑓𝑠 = 0.55𝑓𝑓𝑢

𝑓𝑐𝑠 = 0.60𝑓𝑐𝑒′

𝑓𝑓𝑠 = 0.80𝑓𝑦𝑒

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FRP solutions provided effective concrete capacity enhancement.

Increased shear strength without sacrificing ductility.

Numerous construction benefits.

Further research for NSM FRP rods in shear applications is still required.

Straightforward design.

Flexibility in on-site repair solutions.

FINAL REMARKS

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Comments / Questions

Avi Cohen

Structural Engineer M.Sc.

avi@yoe.co.il

THANK YOU!