SC SOLUTIONS, Inc. © 2014, CONFIDENTIAL SC SOLUTIONS, Inc. © 2017
DOE NPH Meeting
Fluid-Soil-Structure Interaction Analysis of Tank for Seismic Evaluation of Nozzle Subjected to Differential Movement
October 23, 2018
LA-UR-18-29880
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Problem Statement
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• Seismically qualified critical storage tanks
• Nonlinear anchor response
• Founded on soft soil with stiffness reversals
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Problem Statement
3
DNFSB concern:
– Over-restrained pipe-tank connection
– SAM-induced stress at connection
TANK
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Previous Analysis
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Max soil displacement + allowable anchor elongation
Δdemand = Δrocking + εallow·lbolt induced on tank end of system
1% strain
Δrocking
Δdemand
Concluded nozzle significantly overloaded
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Project Scope
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Assess functionality (pressure retention) of tank and draw-off piping connection during and after DBE
Phase 1: Determine if detailed analysis can address concern
Phase 2: Perform final analysis and documentation to full code and QA requirements for support of safety basis
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Acceptance Criteria
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• No failure of tank shell at piping connection
– API 650 moment capacity
– AWWA allowable stress
• No failure of draw-off piping at connection
– ASME B31E
• No local tank failure caused by anchor behavior
– SQUG GIP 3A
– Elongation limit ~1%
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Global System Model
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Global System Model
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Soil Model
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• Equivalent linear properties
• Visco-elastic material model
• 400x400x500 ft. soil domain
• Single soil profile
• Single time history
• Lysmer damper
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Soil Verification
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Fluid-Structure Model
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• Tank shell elements (w/ beam elements)
• Fluid continuum elements
• Lagrangian fluid model
• Fluid constrained w/in tank:
• Horizontally along wall
• Vertically across base
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Nonlinear Anchor Model
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Nut
Free
Tension-only spring
Elastic-plastic anchor
Contact surface
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Nonlinear Anchor Response
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Model Verification
• Site response analysis deconvolution
• Finite element soil model site response
• Fluid model static and modal response
• Nonlinear anchor behavior
• Nozzle response due to uplift
• System behavior in sensitivity studies
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Response at Maximum Nozzle Stress
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5x magnification, with fluid
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Response at Maximum Nozzle Stress
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50x magnification, without fluid
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System Response
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Tank Dynamic Response
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Nozzle demands driven by:
• Fluid convection
• Fluid stress (impulse)
• Tank rocking and uplift
• Local tank – nozzle deformation
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Tank Dynamic Response
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Nozzle demands driven by:
• Fluid convection
• Fluid stress (impulse)
• Tank rocking and uplift
• Local tank – nozzle deformation
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Tank Dynamic Response
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Nozzle demands driven by:
• Fluid convection
• Fluid stress (impulse)
• Tank rocking and uplift
• Local tank – nozzle deformation
Uplift
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Tank Dynamic Response
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Nozzle demands driven by:
• Fluid convection
• Fluid stress (impulse)
• Tank rocking and uplift
• Local tank – nozzle deformation
X=Diff Disp.
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Tank Dynamic Response
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15 15.5 16 16.5 17 17.5 18 18.5 19
Forc
e /
Mo
men
t
Time, s
Forces at Tank Wall
Y moment, k*in
Axial force, k
Vertical force, k
Uplift-driven
Axial-driven
Uplift-driven
axial+uplift driven axial+uplift driven
Nozzle demand
Axial response
Uplift response
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Tank Dynamic Response
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1. Tank rocking and uplift contribution weaker than
anticipated
2. Local tank longitudinal differential displacement observed
3. Overall maximum stress due to combined behavior
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Sensitivity Studies
Purpose: Confirm behavior, inform Phase 2
Varied Parameters:
• Stiff anchors
• Reduced water height
• 1st pipe support removed
• Longitudinal support removed
• Time history variability
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Benefits of Detailed Analysis
• Nozzle moments roughly 1/3
• Reduced tank displacement due to SSI rocking effect
• Combined FSI-SSI-nonlinear anchor response explicitly captured
• Local tank deformation a result of combined system response vs. imposed boundary conditions
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Project Conclusion
• Functionality controlled by tank shell stress
• Anchor strain close to recommended limit
• Tank experienced minor overstress
– ~10% above yield stress, half of tensile stress
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Detailed analysis likely to address concern given acceptability of minor overstress
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Questions?
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