prefabricated high -strength rebar systems with high ......primary objective reduce field...
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Prefabricated High-Strength Rebar Systems with High-Performance Concrete for Accelerated Construction of Nuclear Concrete Structures
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Primary ObjectiveReduce field construction times and fabrication costs of reinforced concrete nuclear structures through:
1) High-strength reinforcing steel bars (rebar)
2) Prefabricated rebar assemblies, including headed anchorages
3) High-strength concrete
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Scope• Explore effectiveness, code conformity, and viability of
existing high-strength materials• Focus on shear walls – most common lateral load
resisting members in nuclear structures (pressure vessels not in scope)
• Aim to reduce complexities in rebar to improve construction quality and ease of inspection US-APWR Design Control Doc.
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Collaboration
Yahya C. Kurama, Ph.D., P.E. Ashley P. Thrall, Ph.D.Professor Myron and Rosemary Noble
Assistant Professor
Scott Sanborn, Ph.D.Senior Member of the Technical Staff
Matthew Van Liew, P.E.Structural Engineer
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Notre Dame Research TeamPostdoc:
Steve Barbachyn
Graduate Student:Rob Devine
Undergraduate Students:Laura BobichMax DuceyMarlena FernandezMolly PhillipsMadalyn Sowar
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Project Tasks1. Evaluation of High-Strength Materials
• Limit-benefit Analysis • Cost-benefit Analysis
2. Evaluation of Prefabricated Rebar Cages3. Optimization, Modeling, and Design
• Pre-test Analyses
4. Experimental Testing• Deep Beam (Wall Slice) Specimens• Shear Wall Specimens
5. Design/Modeling/Construction Recommendations
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1. High-Strength Materials: Scope• High-strength rebar (up to Grade 120) with high-
strength concrete (up to 15 ksi compressive strength)• Concrete strength of
5 ksi typical in current practice
• ACI 349 limits headed bars and shear reinforcementto Grade 60
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1. High-Strength MaterialsNumerical limit-benefit study to establish effects of high-strength materials on peak lateral strength of low-aspect-ratio shear walls:
• Parametric numerical investigation of 192 walls• Peak strength predicted via finite element model
Parameter Wall 1 Wall 2 Wall 3length, lw (ft) 20 60 120height, hw (ft) 40 120 120
thickness, tw (in.) 15 45 45moment to shear ratio, M/(Vlw) 0.5, 1.0 0.5, 1.0 0.5, 1.0
concrete strength, f'c (ksi) 5, 10, 15, 20 5, 10, 15, 20 5, 10, 15, 20rebar strength, fy (ksi) 60, 80, 100, 120 60, 80, 100, 120 60, 80, 100, 120
reinforcement ratio, ρs (%) 0.25, 0.50 0.60, 1.20 0.60, 1.20
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1. High-Strength MaterialsResults for Wall 2 (60 ft x 120 ft x 45 in.):
Vwm = Predicted peak lateral strength Vwm,b = Predicted peak lateral strength of “benchmark” with normal strength materials
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1. High-Strength MaterialsSummary of results of limit-benefit analysis
• Combination of high-strength rebar with high-strength concrete resulted in a higher-performing structure than with either high-strength material on its own
• Significant benefits by using concrete strength of f’c =10 ksi, with diminishing returns for higher strengths
• Greatest benefits of high-strength materials for walls with large rebar ratios, ρs
Barbachyn, SM, Devine, RD, Thrall, AP, and Kurama, YC “Effect of High-Strength Materials on Lateral Strength of Shear-Critical Reinforced Concrete Walls.” ACI Structural Journal, Submitted May 2016
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1. High-Strength MaterialsNumerical cost-benefit study of economic effectiveness of high-strength materials for low-aspect-ratio shear walls:
• Parametric numerical investigation of 2304 walls• Construction cost metric (Γ) includes rebar material cost,
rebar labor cost, and concrete material cost (𝐶𝐶𝑤𝑤), normalized by peak strength (𝑉𝑉𝑤𝑤𝑚𝑚): Γ =
𝐶𝐶𝑤𝑤𝑉𝑉𝑤𝑤𝑚𝑚
Parameter Wall 1 Wall 2 Wall 3length, lw (ft) 20 60 120height, hw (ft) 40 120 120
thickness, tw (in.) 10, 15, 20 30, 45, 60 30, 45, 60moment to shear ratio, M/(Vlw) 0.5, 1.0 0.5, 1.0 0.5, 1.0
concrete strength, f'c (ksi) 5, 10, 15, 20 5, 10, 15, 20 5, 10, 15, 20rebar strength, fy (ksi) 60, 80, 100, 120 60, 80, 100, 120 60, 80, 100, 120
reinforcement ratio, ρs (%) low to high low to high low to high
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1. High-Strength MaterialsSummary of results of cost-benefit analysis:
• Combination of high-strength rebar with high-strength concrete resulted in greatest economic benefits for walls with lower M/(Vlw) ratios and large reinforcement ratios, ρs
• A concrete strength of f’c =10 ksi showed the largest incremental reduction in construction cost
• Rebar grades greater than 100 can lead to decreased economic benefits due to the increased unit cost
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2. Prefabricated Rebar• Evaluating prefab rebar
cages for:- transportability - liftability- modularity
• Using mini-scale rapid prototyping
Most Congested(current)
Least Congested(envisioned)
Multiple layers of hooked
Grade 60 bars
Fewer layers of headed high-strength bars
3D printedrebar cage
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3. Optimization, Modeling and Design
Pre-test Analyses of Deep Beam (Wall Slice) and Shear Wall Specimens in Vector2, ATENA, and ABAQUS
Vector2 ATENA ABAQUS
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4. Experimental Testing
representative slice of generic wall for deep beam tests (@ 1:6.5 scale)
• “Generic wall” dimensions determined using publicly-available design control documents
• Provides basis for future deep beam and shear wall tests
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Deep Beam Test Setupspreader
beam
foundation
beam
hydrauliccylinder
strong floor
tie-downrods
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Deep Beam Construction
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Normal-Strength Concretef’c = 6500 psislump = 8 in.
High-Strength Concretef’c = 14690 psi
slump = 8.75 in.
Deep Beam Construction
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Deep Beam Test Parameters
Specimen f’c (psi) fy (ksi) ρs (%) M/(Vlw)
DB1 6500 70 0.833 0.5
DB2 6500 133 0.833 0.5
DB3 14960 70 0.833 0.5
DB4 14960 133 0.833 0.5
Specimen f’c (psi) fy (ksi) ρs (%) M/(Vlw)
DB1 6500 70 0.833 0.5
DB2 6500 133 0.833 0.5
DB3 14960 70 0.833 0.5
DB4 14960 133 0.833 0.5
Definitions: f’c – concrete 28 day compressive strengthfy – rebar yield strength, determined by tensile tests and 0.2% offset methodρs – reinforcement ratio, symmetric for longitudinal and transverse rebar
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Deep Beam Instrumentation
Type Number
pressure transducer 2
string potentiometer 9
linearpotentiometer 8
inclinometer 4
strain gauge 42
TOTAL 65
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3D Digital Image Correlation
foundation
beamrandom pattern
field-of-view(FOV)near full-field map of max principal strains
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VecTor2 pre-test prediction
VecTor2 pre-test DB4 prediction
Specimens DB2 and DB4 Response
VecTor2 pre-test DB2 prediction
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Vertical crack initiation at cold joint 1st large diagonal crack develops and vertical slip at cold jointAdditional cracking near bottom of beamConcrete crushing at toe and beam slip along diagonal crackPropagation of 2nd large diagonal crackSlipping along 2nd diagonal crack
DB2 (f’c = 6500 psi, fy = 133 ksi)
load application point
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DB2 (f’c = 6500 psi, fy = 133 ksi)
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DB4 (f’c = 14960 psi, fy = 133 ksi)
Vertical crack initiation at cold joint Propagation of large diagonal (shear) crack from loading platePropagation of 2nd large diagonal crack towards center of plateBeam slip along cold jointAnchorage failure and beam slip along diagonal crackSignificant concrete degradation through beam depth
load application point
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DB4 (f’c = 14960 psi, fy = 133 ksi)
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DB4 (f’c = 14960 psi, fy = 133 ksi)longitudinal bars
transverse bars
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DB4 (f’c = 14960 psi, fy = 133 ksi)longitudinal bars
transverse bars
Initial flexural cracking, bottom three longitudinal layers active in tension
initial flexural crack
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DB4 (f’c = 14960 psi, fy = 133 ksi)longitudinal bars
transverse bars
Bottom three longitudinal layers and closest transverse layer to foundation strain to arrest diagonal crack
initial diagonal crack
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DB4 (f’c = 14960 psi, fy = 133 ksi)longitudinal bars
transverse bars
Two transverse bar layers and two longitudinal bar layers above the bottom experience strain increase
second diagonal crack
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DB4 (f’c = 14960 psi, fy = 133 ksi)longitudinal bars
transverse bars
Initiation of longitudinal reinforcement yielding
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DB4 (f’c = 14960 psi, fy = 133 ksi)longitudinal bars
transverse bars
Slip at foundation interfaceExtensive yielding of longitudinal reinforcement
slip
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DB4 (f’c = 14960 psi, fy = 133 ksi)longitudinal bars
transverse bars
Anchorage failure of first transverse bar after yielding to arrest diagonal cracks
anchorage failure
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DB4 (f’c = 14960 psi, fy = 133 ksi)longitudinal bars
transverse bars
Extensive concrete degradation
first diagonal crack
initial cracking
second diagonal crack
slip along cold joint
long. steel yields
slip along diagonal crack
anchorage failure
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DB2 and DB4 Strain Comparisons
High-strength concrete able to better take advantage of higher yield strengths of reinforcement
DB2 f’c = 6500 psi fy = 133 ksi DB4 f’c = 14960psi fy = 133 ksi
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Summary of Deep Beam Tests• 17.6% increase in peak shear strength when
increasing f’c from 6500 psi to 14960 psi• Significant increase in ductility due to increase in f’c• Pre-test analyses provided reasonable predictions for
peak strength
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Future Reduced-Scale Shear Wall Tests
• 1:6.5 scale of “generic wall”• M/(Vlw) = 0.50• Tested under cyclic and accidental thermal loads• High-strength steel and concrete
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Conclusions to Date• High-strength steel more effective when combined
with high-strength concrete- Numerically demonstrated (economics and peak strength)- Measured experimentally
• Greatest benefit for walls with low moment-to-shear ratios and large reinforcement ratios; typical of nuclear concrete shear walls
• Largest economic and structural benefits when using Grade 100 rebar together with 10 ksi concrete
• Project tasks on schedule
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Research Products• Journal Paper (submitted):
- “Effect of High-Strength Materials on Lateral Strength of Shear-Critical Reinforced Concrete Walls,” ACI Structural Journal.
• Presentations:- Presentation, 2015 Fall ACI Convention, Denver, CO.- Poster, 2015 Energy Week, Center for Sustainable
Energy, University of Notre Dame, Notre Dame, IN.- Presentation, 2016 Fall ACI Convention, Philadelphia, PA. - Presentation, 2016 American Nuclear Society Winter
Meeting and Nuclear Technology Expo, Las Vegas, NV.
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Acknowledgements• Department of Energy Award No. DE-NE0008432• Federal Point of Contact: Alison Hahn• Technical Point of Contact: Jack Lance• Integrated University Program Fellowship supporting
graduate student Rob Devine• Material/Fabrication Donations:
- MMFX Steel- Dayton Superior Corp.- HRC, Inc.- Sika Corp. U.S.
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Questions?
http://phsrc-nuclearwalls.nd.edu