Seismic Soil-Structure Interaction Analysis: A Walk Through Time Past, Present, and Future OECD/NEA IAGE / IAEA ISSC Workshop on Soil Structure Interaction (SSI) Knowledge and Effect on the Seismic Assessment of NPPs Structures and Components Ottawa, Canada, 6-8 October 2010 Sponsored by: OECD Nuclear Energy Agency International Atomic Energy Agency/ International Seismic Safety Centre (ISSC) Presentation by: Dr. James J. Johnson James J. Johnson and Associates 1
The SSI Problem Given the free-field motion at the site, determine the dynamic response of soil, structures, and components 2
Topics of Presentation Historical Perspective Elements of SSI Present State of Practice Anticipated Future Developments 3
SSI Analysis Methodologies: Historical Perspective Vintage 1960s to 1970s Rigid disk founded on the surface of a uniform half-space machine vibration methods applied to the earthquake problem inertial interaction (impedances) Simple lumped mass, spring, dashpot representations of the behavior of the foundation/soil (soil spring method) Treatment of composite damping of soil/structure Time domain solutions using standard analysis tools Linear and localized nonlinear analyses (uplift, ) No spatial variation of free-field ground motion assumed Active research on all fronts (numerical methods and finite element methods) US regulatory requirements limitation on composite damping values (20%) 4
SSI Analysis Methodologies: Historical Perspective Vintage 1970s/early 1980s Research UC Berkeley (Seed/Lysmer Group) UCSD/USC (Luco/Wong) MIT (Roesset/Kausel/Christian) NRC SSMRP (LLNL) NUREG/CR-1780 Soil Structure Interaction: The Status of Current Analysis Methods and Research (1980) Nonlinear soil material models (cap model, multi-surface plasticity models, ) Simplified soil spring methods Direct finite element methods (frequency domain) LUSH, ALUSH 2D and axisymmetric representations PLAXLY FLUSH pseudo-3d representations 5
SSI Analysis Methodologies: Historical Perspective Vintage 1970s/early 1980s Substructure methods CLASSI (1980) SASSI (1981) Controversial US regulatory requirements perform SSI analyses by the soil spring approach and the finite element method and envelope the results 6
SSI Analysis Methodologies: Historical Perspective Vintage 1980s to 1990s Soil-structure interaction tests (Lotung and Hualien, Taiwan) Established the validity of different methods when applied to the same model Frequency domain solutions Surface-founded Embedded foundations - additional data on the spatial variation of motion depth in the soil Responses compared within engineering accuracy US regulatory requirements - relaxed the requirement to perform SSI analyses with multiple approaches and envelope the results 7
SSI Analysis Methodologies (Modeling and Parameters): Historical Perspective Vintage 1990s to Present Substructure Approaches Relies on superposition (linear assumption) SASSI, CLASSI, SUPELM, others Three dimensional Earthquake acceleration time histories define control motion (3 components) Arbitrary wave fields Linear or equivalent linear material behavior Frequency domain solutions Simpler methods for standard designs 8
SSI Analysis Methodologies: Present Perspective Design of New Nuclear Power Plants Evaluation for Beyond Design Basis Earthquake Motion Seismic PRA (PSA) required for New Plants in US - Probabilistic response analyses defining seismic demand (Nakaki et al.) Evaluation of Nuclear Power Plants Experiencing Significant Earthquake Ground Motion at the Site (Forensic engineering) Japan NPPs Well instrumented in free-field and in-structure Experience significant earthquake ground motion Other countries Design vs. Analysis of a Facility experiencing earthquake ground motion 9
SSI Analysis Methodologies: Present Perspective Standard Designs - World-Wide Vendors and Sites broad-banded design basis ground motion to envelope high percentage of NPP sites Certified Standard Designs (US) Certified Seismic Design Response Spectra (CSDRS) Standard Designs (EPR- Europe) Site Dependent Response Spectra (EURH, EURM,EURS) ACR Standard Designs (Canada) 10
Spectral Acceleration (g) Standard Design: Broad-Banded Design Basis Ground Response Spectra Horizontal Spectra 5% Damping 1.0 0.9 0.8 RG 1.60 US EPR, EUR Hard US EPR, EUR Medium US EPR, EUR Soft AP1000 RG 1.60 ACR, CSA Soil ACR, CSA Rock 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0.1 1 10 100 Frequency (Hz) 11
SSI Analysis Methodologies: Present Perspective Site Specific Seismic Hazard PSHA Typical Procedure Generate hard rock ground motion (US Vs 9,200 fps rock) Perform probabilistic site response analyses (Simulations time/frequency domain, RVT) Ground motion on soil surface or at foundation depth Issue Relationship between large family of site profiles probabilistically determined (60 or more) and limited number of profiles to be used in SSI analyses (3 or more) FIRS 12
SSI Analysis Methodologies: Present Perspective Site Specific Seismic Hazard Empirical based Input to PSHA, DSHA Fault Modeling Numerical simulation of fault mechanism and transmission of waves from source to site Japan required approach US significant effort over last decade or more (3 or more) FIRS 13
Spectral Acceleration (g) EPR EURH, EURM, EURS, UHS CEUS Rock Sites Horizontal Spectra 5% Damping 1.2 1.0 0.8 0.6 0.4 UHS-Rock-1 UHS-Rock-2 UHS-Rock-3 UHS-Rock-4 UHS-Rock-5 UHS-Rock-6 UHS-Rock-7 UHS-Rock-8 UHS-Rock-9 UHS-Rock-10 UHS-Rock-11 UHS-Rock-12 5% Damp EUR Hard 0.25g 5% Damp EUR Medium 0.25g 5% Damp EUR Soft 0.25g 0.2 0.0 0.1 1 10 100 Frequency (Hz) 14
Elements of the SSI Analysis Chain Free-Field Ground Motion Defining the Soil Profile Low Strain Earthquake Strain Compatible Properties Soil-Structure Interaction Modeling and Parameters Structure Model SSI Analysis 15
Free-Field Ground Motion or Seismic Input: General Requirements Control Motion (Amplitude and Frequency Characteristics) Response Spectra (site independent, site dependent) Site Specific Response Spectra (PSHA GMRS, performance-based DRS) Time Histories (recorded motion, simulations, deaggregated scenario earthquakes) Control Point Spatial Variation of Motion Over the depth and width of the foundation and the embedded portion of the structure 16
Design Basis Earthquake: Historical PerspectiveVintage 1960s to 1970s Control Motion Housner Average Response Spectra Recorded Acceleration Time Histories (Golden Gate, El Centro,) Standard Response Spectra NUREG/CR-0098 Newmark-Hall (median, 84%NEP) (rock, soil) US NRC Regulatory Guide 1.60 (1973) Control Point At foundation Spatial Variation of Motion No consideration 17
Design Basis Earthquake: Historical Perspective Vintage 1970s to early 1980s Control Motion Standard Response Spectra NUREG/CR-0098 Newmark-Hall (median, 84%NEP) (rock, soil) US NRC Regulatory Guide 1.60 (1973) Japan (Ohsaki) Probabilistic Seismic Hazard Analysis Initiated by US NRC (LLNL) and EPRI Control Point Foundation level in free-field Spatial Variation of Motion Wave propagation from foundation level to surface 18
Standard Design: Broad-Banded Design Basis Ground Response Spectra 19
Design Basis Earthquake: Historical Perspective Vintage 1980s to 1990s Control Motion Standard Response Spectra US NRC Regulatory Guide 1.60 Probabilistic Seismic Hazard Analysis (PSHA) EPRI and US NRC (LLNL) US NRC Regulatory Guide 1.165 Control Point On a Free Surface of Soil or Rock actual or hypothetical outcrop on the upper most in-situ competent material Spatial Variation of Motion Wave propagation mechanisms from control point to other points in the free field 20
Issues PSHA Typical Procedure Relationship between large family of site profiles probabilistically determined (60 or more) and limited number of profiles to be used in SSI analyses (3 or more) FIRS High frequency ground motion for rock sites Filter during hazard study (e.g., CAV) Account for incoherence of ground motion in SSI analyses Vertical ground motion corresponding to horizontal PSHA and DSHA V/H ratios Fault modeling - numerical simulations of source and source to site transmission 21
Modeling the Soil Profile Soil Configuration Layering and stratigraphy Soil Material Behavior Equivalent linear viscoelastic material (earthquake level dependent) Nonlinear material models Field Exploration Borings In-situ tests Laboratory Tests Correlation of Field and Laboratory Data 22
Issues Defining soil profile heterogeneity (number and location of bore holes) Material models other than visco-elastic equivalent linear, e.g., nonlinear Functional form Parameters of model 23
SSI Modeling and Parameters: State of Practice Methodologies Substructure approach (programs, characteristics) Other Foundation Models Structure Models 24
SSI Modeling and Parameters: Methodologies Methodologies Substructure approaches Relies on superposition (linear assumption) SASSI, CLASSI, SUPELM, others Three dimensional Earthquake acceleration time histories define control motion (3 components) Arbitrary wave fields Linear or equivalent linear material behavior Frequency domain solutions 25
SASSI SSI Calculational Steps: Schematically 26
Elements of the Substructure SSI Analysis as Implemented in CLASSI Programs Free-Field Motion Foundation Input Motion Kinematic Interaction M F Soil Profile Site Response Analysis Impedances SSI Structural Model 27
Modeling the Foundation Embedment Stiffness Geometry 28
Structure Models: General Detail and sophistication of the structure model is determined by it s purpose Overall dynamic response characteristics First step in a multi-step process More detailed dynamic and/or static models used to calculate responses for design and qualification (force and moment quantities, ISRS, ) input are responses from SSI model Detailed in-structure responses for design and qualification of structures, systems, and components Combination 29
Structure Models: BWR Reactor Building and Internals 30
Structure Models: Detailed EPR NI Model 31
Issues Effect of Nonlinear Behavior on Soil/Structure Response Design levels, beyond design levels Forensic engineering (recorded earthquake ground motion and structure response) Validation Complex SSI Models (approaches include validation of individual elements or analysis, sensitivity studies encompassing fixed-base to SSI, soil property variations, Peer Review, others) Complex Structure Models Foundation/soil interface nonlinear effects (separation, sliding, uplift, ) 32
Future Developments Further Define and Validate Performance-Based Design Criteria Forensic Evaluations of NPP Site and Structure Response Subjected to Actual Earthquake Motions (Continued) Integrated Models and Analyses Fully probabilistic from source to structure response Validate design-based approaches (simpler user friendly analyses) 33
Future Developments Integrated Models and Analyses Source mechanism simulations (Japan, US, ) Source to site transmission of motion In the large (wave propagation mechanisms, ) In the small (site response analyses including nonlinear soil behavior, scattering, ) Nonlinear behavior in the neighborhood Nonlinear soil material behavior Nonlinear geometric effects (sliding, separation, ) Structure response for structure design and capacity determination Structure response for input to systems, equipment, components 34
Site Response and SSI as a Learning Process Kashiwazaki-Kariwa Nuclear Power Plant Response to the NCOE and aftershocks Site response not as simple to model as one might surmise even with 5 downhole recordings of aftershocks Significant influence of embedment all reactor buildings deeply embedded Seismic margin in demand is significant IAEA/ISSC KARISMA benchmark on-going investigation Incoherency of ground motion, i.e., high freaquency ground motion effects on structure response 35
Site Response and SSI as a Learning Process Incoherency of ground motion, i.e., high frequency ground motion effects on structure response Revised thinking on definition of rock for SSI purposes Vs = 6,000 fps vs. 3,500 fps Effect of accounting for SSI effects for coherent ground motion is significant incoherency effects are in addition 36
Acceleration (m/s2) Envelope ISRS: HR (+19.5m), Horizontal 60.0 Envelope Spectra, CLASSI Fixed Base and SSI with Coherent & Incoherent Scattering vs. AREVA Soil Springs, 4% damping, Reactor Building HR, Level +19.50m, Horizontal 50.0 Fixed Base, HR +1950 Horizontal Envelope Coherent SSI, HR +1950 Horizontal Envelope Incoherent SSI, HR +1950 Horizontal Envelope AREVA Soil Spring, HR +1950 Horizontal Envelope AREVA Fixed Base, HR +1950 Horizontal Envelope 40.0 30.0 20.0 10.0 0.0 1 10 100 Frequency (Hz) 37
Acceleration (m/s2) Envelope ISRS: HR (+19.5m), Vertical 30.0 Envelope Spectra, CLASSI Fixed Base and SSI with Coherent & Incoherent Scattering vs. AREVA Soil Springs, 4% damping, Reactor Building HR, Level +19.50m, Vertical 25.0 Fixed Base, HR +1950 Vertical Envelope Coherent SSI, HR +1950 Vertical Envelope Incoherent SSI, HR +1950 Vertical Envelope AREVA Soil Spring, HR +1950 Vertical Envelope AREVA Fixed Base, HR +1950 Vertical Envelope 20.0 15.0 10.0 5.0 0.0 1 10 100 Frequency (Hz) 38
Thank you IAEA/ISSC (Ovidiu Coman et al.) OECD/NEA IAGE, IAEA/ISSC, and CNSC for organizing and sponsoring the Workshop 39