applicaiton of the computer program sassi for seismic ssi ... of the...application of the computer...
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![Page 1: Applicaiton of the Computer Program SASSI for Seismic SSI ... of the...Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman](https://reader033.vdocuments.us/reader033/viewer/2022043005/5f8bfdfb112fb577154c2543/html5/thumbnails/1.jpg)
Application of the Computer Program SASSI for Seismic SSI Analysis of WTP Facilities
Farhang Ostadan (BNI) &
Raman Venkata (DOE-WTP-WED)
Presented by Lisa Anderson (BNI)
US DOE NPH Workshop
October 25, 2011
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-2
Background
•SASSI computer code was developed in the early 1980’s to solve Soil-Structure-Interaction (SSI) problems
• Original version of SASSI was based on the direct solution method for embedded structures
• Requires that each soil node in the excavated soil volume be an interaction node
• Subtraction solution method was introduced in 1998
• Requires that only perimeter nodes in the excavated soil volume be considered interaction nodes
• Significantly reduces computational effort
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-3
Background
•RPP-WTP facility includes two SC I (PC3) structures
• Pretreatment Facility
• Surface structure
• High-Level Waste Structure (HLW)
• Shallowly embedded structure
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-4
Background
•SSI analysis has been previously completed using the following:
• Extensive Finite Element Model
• Simplified Stick Model
•Correlation of dynamic properties has been demonstrated between the models
• Both models have been described in RPP-WTP structural summary report and reviewed by PRT and DFNSB
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-5
Background
North
86'
57'
0'
-21'
5
A
Elev.
20 T.5
Finite Element Model of
HLW Core Structure
21’ Embedment Depth
Footprint: 438’ x 236’
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-6
Background
Y
NORTH-SOUTH
Y
ZX
EAST-WEST
EL. 86'
EL. 57'
EL. 36'
EL. 13'
EL. 0'
EL.-21'
20'
ELEVATION ELEVATION
Stick Model of
HLW Core Structure
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-7
Objective
•Compare results of HLW SSI analysis using two methods
• SASSI Direct Method
• SASSI Subtraction Method
•Confirm adequacy of the SASSI Subtraction Method analysis of the HLW structure using the SASSI Direct Method as a benchmark
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-8
Methodology
•A Hybrid Finite Element Model and Stick Model representing the HLW Structure Core Structure is created
•Dynamic characteristics of all three models are correlated
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-9
SSI Model
X
Y
Z
Elev.
0
-21
North
5
20
A
1
Hybrid Finite Element Model and Stick Model of
HLW Core Structure
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-10
Element Size in Excavated Soil
X
Z
5 20
A
T.5
North
1 8 15
B
T
Y
X-Dir: (EW) 7 15
Min (ft) Max (ft)
Y-Dir: (NS) 7 17
Z-Dir: (Vert) 10.50
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-11
WTP Ground Motion
RGM
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-12
Soil Profile at HLW Site
0
10
20
30
40
50
60
0 500 1000 1500 2000 2500
Shear Wave Velocity (ft/sec)
Dep
th f
rom
Gra
de (
ft)
RGM LB Soil
RGM M Soil
RGM UB Soil
HLW Basemat
Elevation
Consider the
Upper Bound
Site-Specific
soil case
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-13
Mesh Limiting & Cut-off Frequencies
Using the maximum element size and 1/5 ls criteria:
Critical Shear Mesh Limiting Cut-Off Wave Velocity Freq (Hz) Freq (Hz)
LB: 775 fps 9.1 10.5
M: 1269 fps 14.9 17.5
UB: 1613 fps 19.0 22.0
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-14
Comparison of SSI Results
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-15
Comparison of SSI Results
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-16
Comparison of SSI Results
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-17
Comparison of SSI Results
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-18
Comparison of SSI Results
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-19
Comparison of SSI Results
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-20
Comparison of SSI Results
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-21
Comparison of SSI Results
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-22
Observations
•Horizontal response:
• Subtraction method results are essentially the same as those of direct method
•Vertical response:
• Subtraction method results are slightly higher than those of direct method in the higher frequency range
• Results in a slightly higher ISRS
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-23
Conclusions
•Use of subtraction method for SSI Analysis of the RPP-WTP HLW (a shallowly embedded structure) is considered to be adequate and slightly conservative
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-24
Conclusions
•SASSI is a complex program
• Before use in any critical facility, the user must develop experience in modeling, analysis, and interpretation of results
• It is our observation that lack of experience and knowledge, as well as, overconfidence have caused issues with respect to use of SASSI
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-25
Conclusions
•Verification is critical
• It is very important that SASSI program, as installed on the production computer, is fully verified particularly for the options utilized
• BNI SASSI verification examples include many solutions that compare the results with reliable published papers, several SSI-related doctoral dissertations, as well as experimental data
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-26
Conclusions
•Verification is critical
• Some users modify the program SASSI and develop additional features
• Any developments must be carefully reviewed by the expert to ensure compatibility with SASSI formulations and methodology and proper verification before use in design
• Simple verification examples may not be sufficient when the new features are used for complex modeling conditions
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Application of the Computer Program SASSI for Seismic SSI Analysis for WTP Facilities, Farhang Ostadan & Raman Venkata, October 25, 2011, Page-27
Conclusions
•Independent checking is recommended
• When in doubt, perform SSI analysis by other simple methods (soil spring, dashpot) and verify the overall global responses obtained from SASSI