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 postprocessing/plotting
• Sample analysis results from two category I nuclear structures
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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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GTSTRUDL - MTR/SASSI Streamlined Process
GTSTRUDL
Structural FE
MODEL
MTR/
SASSI
Perform fixed base
static and dynamic
analyses for
verification of model
conversion
Structural FE
MODEL
Develop & QA
GTSTRUDL structural
model
Convert model “as is” to
MTR/SASSI structural
model
Add excavated soil model &
soil layers to complete SSI
model
MTR/
SASSI
Structural FE
MODEL
MTR/
SASSI
EXCAVATED SOIL
FE MODEL
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MTR/
Perform SSI
analysis and
extract results
for plotting
using
GTSTRUDL
SASSI SOIL LAYERS
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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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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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Model Conversion: GTSTRUDL to MTR/SASSI
Export:
GTSTRUDL database
files (*.dbx): joints,
members, elements,
materials, etc
GTSTRUDL model
Import:
database files
(*.dbx) files to
Excel for
formatting into
MTR/SASSI syntax
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Export/
Combine
into
MTR/SASSI
HOUSE
input file
(_h.dat)
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MTR/
SASSI
Structural FE
MODEL
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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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Comparison of Acceleration Response Spectra – Wall
• Wall normal to X-axis (out of plane response)
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Comparison of Acceleration Response Spectra – Wall
• Wall normal to Y-axis (out of plane response)
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Comparison of Acceleration Response Spectra – Intermediate Floor
• Floor slab normal to Z-axis (out of plane response)
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Comparison of Acceleration Response Spectra – Beam
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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
Interaction nodes
MTR/
SASSI
EXCAVATED SOIL
FE MODEL
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MTR/
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SASSI SOIL LAYERS
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Seamless Transfer of MTR/SASSI Analysis Results to GTSTRUDL
MTR/SASSI
SSI analysis results
1. Nodal forces and
moments
2. Nodal disps, velocities,
and accelerations
(results extracted at
each time step and
maximum results)
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GTSTRUDL
1. Results plotting
2. Additional postprocessing
3. 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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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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Example 1
• Near surface category I nuclear structure with shear keys
MTR/SASSI Excavated
Soil Model
GTSTRUDL/MTR/SASSI Structural Model
Structural model: 14420 nodes
SSI model: 17887 nodes
GTSTRUDL/MTR/SASSI shear Key Model
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Example 2
• Deeply-embedded category I nuclear structure
GTSTRUDL/ MTR/SASSI Structural Model
GTSTRUDL/ MTR/SASSI Longitudinal Cut View
Structural model: 15275 nodes
SSI model: 32133 nodes
MTR/SASSI Excavated
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Soil Model
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Maximum Accelerations
• Table of maximum accelerations at key locations
• Near surface structure
Building Location
Elevation (ft)
Node No.
Basemat SW Corner
Basemat NE Corner
Basemat Center
-6.00
Basemat Equipment
˝
Fan Room at Elevation
of 51.5 feet
+50.50
1001
1501
5757
1172
1395
3056
3396
3380
3040
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˝
˝
Maximum Absolute Accelerations
X-Dir.
Y-Dir.
Z-Dir.
0.422
0.376
0.464
0.409
0.367
0.481
0.421
0.370
0.489
0.421
0.375
0.472
0.415
0.379
0.436
0.574
0.507
0.567
0.579
0.486
0.464
0.604
0.476
0.504
0.586
0.498
0.480
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Plot of Maximum Accelerations (X-direction)
Near surface
structure
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Plot of Maximum Accelerations (Y-direction)
Deeply-embedded
structure
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Plot of Maximum Accelerations (Z-direction)
Deeply-embedded
structure
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In-Structure Spectral Acceleration Response: Base-mat
2.0
In-Structure
In-Structure
Reference Outcrop Motion
Reference Outcrop Motion
Y-Spectral Acceleration (g's)
X-Spectral Acceleration (g's)
2.0
1.5
1.0
Damping = 5%
0.5
1.5
1.0
Damping = 5%
0.5
0.0
0.0
0.1
1
10
100
0.1
1
Frequency (Hz)
10
100
Frequency (Hz)
2.0
In-Structure
Z-Spectral Acceleration (g's)
Reference Outcrop Motion
1.5
• Near surface structure
• Envelope accelerations
1.0
Damping = 5%
0.5
0.0
0.1
1
10
100
Frequency (Hz)
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In-Structure Spectral Acceleration Response: Wall Platform Supports
4.0
In-Structure
In-Structure
Reference Outcrop Motion
Reference Outcrop Motion
Y-Spectral Acceleration (g's)
X-Spectral Acceleration (g's)
4.0
3.0
2.0
Damping = 5%
1.0
3.0
2.0
Damping = 5%
1.0
0.0
0.0
0.1
1
10
100
0.1
1
Frequency (Hz)
10
100
Frequency (Hz)
2.5
Z-Spectral Acceleration (g's)
In-Structure
Reference Outcrop Motion
2.0
1.5
1.0
• Deeply-embedded structure
• Envelope accelerations
Damping = 5%
0.5
0.0
0.1
1
10
100
Frequency (Hz)
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Maximum Absolute Total Inter-story
Dynamic X-Shear Force and YY-Overturning Moment Diagram
My
80
80
70
70
60
60
50
50
40
40
Elevation (ft)
Elevation (ft)
Vx
30
30
20
20
10
10
0
0
-10
-10
-20
-20
0
10,000
20,000
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0
500,000
1,000,000
My (K-ft)
Vx (Kips)
Total
30,000
Net
Total
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Net
1,500,000
Near surface
structure
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Maximum Absolute Total Inter-story
Dynamic Y-Shear Force and XX-Overturning Moment Diagram
Mx
80
80
70
70
60
60
50
50
40
40
Elevation (ft)
Elevation (ft)
Vy
30
30
20
20
10
10
0
0
-10
-10
-20
-20
0
5,000
10,000
15,000
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0
200,000
400,000
600,000
Mx (K-ft)
Vy (Kips)
Total
20,000
Net
Total
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Net
800,000
Near surface
structure
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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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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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