Streamlined Process for Soil-Structure Interaction Analysis of Nuclear Facilities Utilizing GTSTRUDL and MTR/ SASSI Wei Li, Michael Perez, Mansour Tabatabaie,

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

GTSTRUDL Users Group Meeting 2011 SC SOLUTIONSCopyright © 2011 SC Solutions, Inc, All Rights Reserved

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

GTSTRUDL Users Group Meeting 2011

Copyright © 2011 SC Solutions, Inc, All Rights Reserved SC SOLUTIONS

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

GTSTRUDL Users Group Meeting 2011

Copyright © 2011 SC Solutions, Inc, All Rights Reserved SC SOLUTIONS

GTSTRUDL - MTR/SASSI Streamlined Process

GTSTRUDL Users Group Meeting 2011 SC SOLUTIONS

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


MODEL

MTR/SASSI EXCAVATED SOIL

FE MODEL

MTR/SASSI SOIL LAYERS

Perform SSI analysis and extract results for plotting using GTSTRUDL

Copyright © 2011 SC Solutions, Inc, All Rights Reserved

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


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


Model Conversion: GTSTRUDL to MTR/SASSI


GTSTRUDL model

Export: GTSTRUDL database files (*.dbx): joints,

members, elements, materials, etc

Import: database files (*.dbx) files to

Excel for formatting into

MTR/SASSI syntax

Export/ Combine

into MTR/SASSI

HOUSE input file (_h.dat)


MODEL


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


Comparison of Acceleration Response Spectra – Wall

• Wall normal to X-axis (out of plane response)


Comparison of Acceleration Response Spectra – Wall

• Wall normal to Y-axis (out of plane response)


Comparison of Acceleration Response Spectra – Intermediate Floor

• Floor slab normal to Z-axis (out of plane response)


Comparison of Acceleration Response Spectra – Beam


• 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


MODEL

MTR/SASSI EXCAVATED SOIL

FE MODEL

MTR/SASSI SOIL LAYERS

SSI analysis using MTR/SASSI


Interaction nodes


Seamless Transfer of MTR/SASSI Analysis Results to GTSTRUDL


MTR/SASSI SSI analysis results

1.Nodal forces and moments2.Nodal disps, velocities, and accelerations

(results extracted at each time step and maximum results)

GTSTRUDL1.Results plotting2.Additional post-processing3.Input for pseudo-static stress analysis

(Can be read directly by GTSTRUDL with proper GTSTRUDL commands since node numbers and models are identical)


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


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


• Near surface category I nuclear structure with shear keys

Example 1


GTSTRUDL/MTR/SASSI Structural Model

GTSTRUDL/MTR/SASSI shear Key Model

MTR/SASSI Excavated Soil Model


Structural model: 14420 nodesSSI model: 17887 nodes

Example 2

• Deeply-embedded category I nuclear structure


MTR/SASSI Excavated Soil Model

GTSTRUDL/ MTR/SASSI Longitudinal Cut ViewGTSTRUDL/ MTR/SASSI Structural Model


Structural model: 15275 nodesSSI model: 32133 nodes

Maximum Accelerations

• Table of maximum accelerations at key locations• Near surface structure


Building Location Elevation (ft) Node No. Maximum Absolute Accelerations

X-Dir. Y-Dir. Z-Dir.

Basemat SW Corner -6.00 1001 0.422 0.376 0.464

Basemat NE Corner ˝ 1501 0.409 0.367 0.481

Basemat Center ˝ 5757 0.421 0.370 0.489

Basemat Equipment ˝ 1172 0.421 0.375 0.472 1395 0.415 0.379 0.436

Fan Room at Elevation of 51.5 feet

+50.50

3056 0.574 0.507 0.567 3396 0.579 0.486 0.464 3380 0.604 0.476 0.504 3040 0.586 0.498 0.480


Plot of Maximum Accelerations (X-direction)


Near surface structure


Plot of Maximum Accelerations (Y-direction)


Deeply-embedded structure


Plot of Maximum Accelerations (Z-direction)


Deeply-embedded structure


In-Structure Spectral Acceleration Response: Base-mat


0.0

0.5

1.0

1.5

2.0

0.1 1 10 100

Frequency (Hz)

X-S

pe

ctr

al A

cc

ele

rati

on

(g

's)

In-Structure

Reference Outcrop Motion

Damping = 5%

0.0

0.5

1.0

1.5

2.0

0.1 1 10 100

Frequency (Hz)

Y-S

pe

ctr

al A

cc

ele

rati

on

(g

's)

In-Structure


Damping = 5%

0.0

0.5

1.0

1.5

2.0

0.1 1 10 100

Frequency (Hz)

Z-S

pe

ctr

al A

cc

ele

rati

on

(g

's)

In-Structure


Damping = 5%• Near surface structure• Envelope accelerations


In-Structure Spectral Acceleration Response: Wall Platform Supports


0.0

1.0

2.0

3.0

4.0

0.1 1 10 100

Frequency (Hz)

X-S

pe

ctr

al A

cc

ele

rati

on

(g

's)

In-Structure


Damping = 5%

0.0

1.0

2.0

3.0

4.0

0.1 1 10 100

Frequency (Hz)

Y-S

pe

ctr

al A

cc

ele

rati

on

(g

's)

In-Structure


Damping = 5%

0.0

0.5

1.0

1.5

2.0

2.5

0.1 1 10 100

Frequency (Hz)

Z-S

pe

ctr

al A

cc

ele

rati

on

(g

's)

In-Structure


Damping = 5% • Deeply-embedded structure• Envelope accelerations


Maximum Absolute Total Inter-story Dynamic X-Shear Force and YY-Overturning Moment Diagram


-20

-10

0

10

20

30

40

50

60

70

80

0 10,000 20,000 30,000

Ele

vati

on

(ft

)

Vx (Kips)

Vx

Total Net

-20

-10

0

10

20

30

40

50

60

70

80

0 500,000 1,000,000 1,500,000

Ele

vati

on

(ft

)

My (K-ft)

My

Total Net



Maximum Absolute Total Inter-story Dynamic Y-Shear Force and XX-Overturning Moment Diagram


-20

-10

0

10

20

30

40

50

60

70

80

0 5,000 10,000 15,000 20,000

Ele

vati

on

(ft

)

Vy (Kips)

Vy

Total Net

-20

-10

0

10

20

30

40

50

60

70

80

0 200,000 400,000 600,000 800,000

Ele

vati

on

(ft

)

Mx (K-ft)

Mx

Total Net



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


Overturning Stability Analysis


• Deeply-embedded structure• D/C ratios and Factors of Safety

• Maximum values• Values at each time step


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


Questions?


Documents

Streamlined Process for Soil-Structure Interaction Analysis of Nuclear Facilities Utilizing GTSTRUDL and MTR/ SASSI Wei Li, Michael Perez, Mansour Tabatabaie,