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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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