1. Streamlined Process for Soil-Structure Interaction Analysis of Nuclear Facilities Utilizing GTSTRUDL and MTR/SASSI
Wei Li, Michael Perez,
Mansour Tabatabaie, and Basilio Sumodobila
June 23, 2011
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Introduction
Key advantages of this streamlined process
Streamlined process for SSI:
Development of structural FE model in GTSTRUDL
Conversion of structural FE model from GTSTRUDL to MTR/SASSI
Verification of model conversion
Development of SSI model and SSI analysis using MTR/SASSI
Seamless transfer of SSI analysis results to GTSTRUDL for post-processing/plotting
Sample analysis results from two category I nuclear structures
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3. Key Advantages of this Streamlined Process
GTSTRUDL and MTR/SASSI structural models are carbon copies
Single structural FE model
Stress analysis using GTSTRUDL
SSI analysis using MTR/SASSI
Same FE mesh, element numbering, node numbering, etc.
Allows efficient model development and refinement and for seamless transfer of pre- and post-processing data and results between the two programs
Simplifies transfer of results such as maximum nodal accelerations between the two programs
Large scale structural FE model
Eliminates need for separate reduced model for SSI analysis
Captures out-of-plane floor and wall dynamic responses
Allows large scale SSI models with over 100,000 nodes to be efficiently analyzed
Simplifies QA process due to identical structural FE models
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4. GTSTRUDL - MTR/SASSI Streamlined Process
Develop & QA GTSTRUDL structural model
Convert model “as is” to MTR/SASSI structural model
Perform fixed base static and dynamic analyses for verification of model conversion
Add excavated soil model & soil layers to complete SSI model
GTSTRUDL Structural FE MODEL
MTR/SASSI Structural FE MODEL
MTR/SASSI EXCAVATED SOIL FE MODEL
MTR/SASSI SOIL LAYERS
Perform SSI analysis and extract results for plotting using GTSTRUDL
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5. Development of FE model in GTSTRUDL
Construct linear-elastic structural model
Use elements available in MTR/SASSI (shells, solids, beams, etc.)
Beam elements should be discretized into desired FE mesh
Include added masses, applied loads, and load combinations
Structural FE model should satisfy passing frequency requirements for SSI analysis
Perform fixed base static analysis
Obtain dead load reactions to verify model geometry, material densities, and added masses
Obtain reactions for other load cases to verify applied loads
Refine model as needed to capture target frequencies and design iterations
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6. Model Conversion: GTSTRUDL to MTR/SASSI
Export structural model from GTSTRUDL database
Nodal coordinates
Elements – shells, solids, plates, etc
Element connectivity
Material properties
Element thickness for shell elements
Members (Beam elements)
Member connectivity
Material and section properties
Beta angles
Springs
Spring connectivity
Spring stiffness and damping constants
Other types of elements also available in MTR/SASSI
Nodal masses for added masses
Masses for elements/members included in structural FE model by MTR/SASSI
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7. Model Conversion: GTSTRUDL to MTR/SASSI
Export:
GTSTRUDL database files (*.dbx): joints, members, elements, materials, etc
GTSTRUDL model
Export/ Combine into MTR/SASSI HOUSE input file (_h.dat)
MTR/SASSI Structural FE MODEL
Import:
database files (*.dbx) files to Excel for formatting into MTR/SASSI syntax
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8. Verification of Model Conversion
Structural FE models
GTSTRUDL model
MTR/SASSI model
Fixed-base static analysis results
Compare reactions for all load cases considered
Fixed-base dynamic analysis results
Identify nodes of interest (base mat, walls, roof, etc)
Extract acceleration time histories at selected nodes
Compute and plot acceleration response spectra at selected nodes
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9. Comparison of Acceleration Response Spectra – Wall
Wall normal to X-axis (out of plane response)
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10. Comparison of Acceleration Response Spectra – Wall
Wall normal to Y-axis (out of plane response)
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11. Comparison of Acceleration Response Spectra – Intermediate Floor
Floor slab normal to Z-axis (out of plane response)
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12. Comparison of Acceleration Response Spectra – Beam
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13. SSI analysis using MTR/SASSI
Development of SSI model
Add soil layers and properties
Define interaction nodes
Define excavated soil elements
Perform time history SSI analysis and extract results
Add excavated soil model & soil layers to complete SSI model
MTR/SASSI Structural FE MODEL
MTR/SASSI EXCAVATED SOIL FE MODEL
MTR/SASSI SOIL LAYERS
Interaction nodes
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14. Seamless Transfer of MTR/SASSI Analysis Results to GTSTRUDL
Nodal forces and moments
Nodal disps, velocities, and accelerations
(results extracted at
each time step and maximum results)
GTSTRUDL
Results plotting
Additional post-processing
Input for pseudo-static stress analysis
(Can be read directly by GTSTRUDL with proper GTSTRUDL commands since node numbers and models are identical)
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15. Typical SSI analysis results
Results plotting
Maximum nodal acceleration and dynamic soil pressure contours
In-structure time histories (ISTH) of accelerations, velocities, displacements, and dynamic soil pressures
Additional post-processing
In-structure response spectra (ISRS)
Sliding and overturning stability analysis results
Base shears and moments
Inter-story forces and moments
Input for stress analysis
Inertia forces from MTR/SASSI analysis can be imported to GTSTRUDL for pseudo-static analysis to calculate member/element forces and stresses for structural design
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Streamlined procedure used to evaluate two category I nuclear structures
Seismic SSI analysis of 2 category I structures in a nuclear power plant currently undergoing certification
Linear-elastic structural FE models constructed using:
PLATE elements and SPACE FRAME members in GTSTRUDL
PLATE/SHELL and 3D BEAM elements in MTR/SASSI
Live and dead loads including equipment weight
Added hydrodynamic masses
SSI analysis performed for combination of ground motions and soil conditions
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17. Example 1 Near surface category I nuclear structure with shear keys
GTSTRUDL/MTR/SASSI Structural Model
GTSTRUDL/MTR/SASSI shear Key Model
MTR/SASSI Excavated Soil Model
Structural model: nodes
SSI model: nodes
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18. Example 2 Deeply-embedded category I nuclear structure
MTR/SASSI Excavated Soil Model
GTSTRUDL/ MTR/SASSI Longitudinal Cut View
GTSTRUDL/ MTR/SASSI Structural Model
Structural model: nodes
SSI model: nodes
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19. Maximum Accelerations
Table of maximum accelerations at key locations
Near surface structure
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20. Plot of Maximum Accelerations (X-direction)
Near surface
structure
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21. Plot of Maximum Accelerations (Y-direction)
Deeply-embedded
structure
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22. Plot of Maximum Accelerations (Z-direction)
Deeply-embedded
structure
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23. In-Structure Spectral Acceleration Response: Base-mat
Near surface structure
Envelope accelerations
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24. In-Structure Spectral Acceleration Response: Wall Platform Supports
Deeply-embedded structure
Envelope accelerations
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Maximum Absolute Total Inter-story Dynamic X-Shear Force and YY-Overturning Moment Diagram
Near surface
structure
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Maximum Absolute Total Inter-story Dynamic Y-Shear Force and XX-Overturning Moment Diagram
Near surface
structure
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27. Sliding Stability Analysis
Near surface structure
D/C ratios and Factors of Safety
Maximum values
Values at each time step
Computes min base friction coefficient to meet F.S. = 1.1
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28. Overturning Stability Analysis
Deeply-embedded structure
D/C ratios and Factors of Safety
Maximum values
Values at each time step
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Summary
GTSTRUDL and MTR/SASSI structural models are carbon copies
Single structural FE model
Stress analysis using GTSTRUDL
SSI analysis using MTR/SASSI
Same FE mesh, element numbering, node numbering, etc.
Allows efficient model development and refinement and for seamless transfer of pre- and post-processing data and results between the two programs
Simplifies transfer of results such as maximum nodal accelerations between the two programs
Large scale structural FE model
Eliminates need for separate reduced model for SSI analysis
Captures out-of-plane floor and wall dynamic responses
Allows large scale SSI models with over 100,000 nodes to be efficiently analyzed
Simplifies QA process due to identical structural FE models
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Questions?
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