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Papers by Mansour Tabatabaie

International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1987

ASME 2010 Pressure Vessels and Piping Conference: Volume 8, 2010

The US EPR™ standard design currently under development by AREVA consists primarily of a nuclear ... more The US EPR™ standard design currently under development by AREVA consists primarily of a nuclear island (NI) and several other significant structures outside of and in close proximity to the NI. The NI structures consist of the Reactor Building (RB), Fuel Building (FB), Safeguard Building 1 (SB1), Safeguard Building 2/3 (SB2/3), Safeguard Building 4 (SB4), and Reactor Building Internal Structures (RBIS) — all of which share a common foundation basemat. The Nuclear Island is embedded approximately 11.6 m below the ground surface. Seismic soil-structure interaction (SSI) analysis of nuclear power plants is often performed in the frequency domain using a lumped-mass stick and/or coarse finite element model of the structure. These models are designed to capture the global dynamic response of the system, the results of which provide the inertia forces that are used for foundation stability assessment as well as input to a static detailed finite element model of the structure for design. The in-structure response spectra is calculated from a separate dynamic analysis of detailed structural model on fixed base excited by the base motion developed from the SSI analysis or often by including single-degree-of-freedom (SDOF) oscillators representing the local response in the stick/coarse finite element SSI models. With recent advances in computer software and hardware technologies, it is now possible to perform SSI analysis of detailed structural models in the frequency domain. This paper presents the results of the seismic SSI analysis of the US EPR™ nuclear island using both a stick and detailed finite element representation of the structure. The soil profile corresponds to a medium stiff soil case used for the standard design. Because the EPR™ nuclear island is a complex, unsymmetric structure, the stick model consists of multiple interconnected sticks developed and calibrated against a detailed finite element model of the structure on a fixed base. Both models are analyzed using SASSI [1]. The results of the detailed finite element model in terms of maximum accelerations and response spectra, as well as total interstory forces and moments, are calculated and compared with those of the lumped-mass stick model.Copyright © 2010 by ASME

Several deterministic methods are currently available for incorporating spatial incoherence of gr... more Several deterministic methods are currently available for incorporating spatial incoherence of ground motions in the SSI analysis using SASSI. The Response SRSS method is the first implementation of the incoherent ground motions in the SASSI code that was done by EPRI in the late 90’s. A decade later, this procedure was further investigated by EPRI for application to the licensing of the new reactors in the United States. From that study three other procedures -Transfer Function SRSS (TF-SRSS), Algebraic Summation (AS) and Simulation Mean (SM) have been developed and recommended for applications to the new plant designs. The EPRI AS and SM procedures are implemented at the ground motion level and TF-SRSS at the structural response level. The purpose of this paper is to present a brief overview of each of the above methodologies, and recommend two new procedures: TF-Summation and Response-Simulation implemented at the structural response level. A numerical possibility issue in the TF...

Volume 8: Seismic Engineering, 2009

Three-dimensional seismic soil-structure interaction (SSI) analysis of nuclear power plants (NPP)... more Three-dimensional seismic soil-structure interaction (SSI) analysis of nuclear power plants (NPP) is often performed in frequency domain using the computer program SASSI [1]. This enables the analyst to properly a) address the effects of wave radiation in an unbounded soil media, b) incorporate strain-compatible soil shear modulus and damping properties and c) specify input motion in the free field using de-convolution method and/or spatially variable ground motions. For large, complex structural systems with multi-million degrees of freedom (DOF) and large foundation impedance matrices associated with deeply embedded foundations, the conventional sub-structuring analysis approach employed in SASSI often results in a coefficient matrix that is too large to solve with currently available computer resources. To address this problem, the method of component mode synthesis (CMS) is employed in the SSI analysis. This involves partitioning the structure into several interconnected compone...

Dynamic soil-structure interaction (SSI) analysis of nuclear power plants is often performed in f... more Dynamic soil-structure interaction (SSI) analysis of nuclear power plants is often performed in frequency domain using programs such as SASSI In this paper we have expanded the DPFI model to incorporate nonlinearities at the soil/structure interface by introducing nonlinear shear and normal springs arranged in series between the DPFI and structure model. This combination of the linear far-field impedance (DPFI) plus nonlinear near-field soil springs allows the foundation sliding and/or uplift behavior be analyzed in time domain while maintaining the frequency-dependent stiffness and radiation damping nature of the far-field foundation impedance. To check the accuracy of this procedure, a typical NPP foundation mat supported at the surface of a layered soil system and subjected to harmonic forced vibration was first analyzed in the frequency domain using SASSI to calculate the target linear response and derive a linear, far-field DPFI model. The target linear solution was then used t...

Ground shaking and ground deformation are the major causes of damage to waterfront improvements i... more Ground shaking and ground deformation are the major causes of damage to waterfront improvements including bridges and port facilities. Large cyclic and/or permanent ground deformations related to slope displacements are the main source of distress to the foundations and structural elements of waterfront structures. Modeling this soil structure interaction (SSI) problem analytically is difficult because it involves kinematic soil-foundation interaction during large (cyclic and permanent) ground deformations as well as inertial foundation-superstructure interaction during shaking, all of which occur while the soil and possibly structural properties rapidly degrade with time. The paper presents an example from the Port of Oakland’s Berth 37, which suffered significant damage during the 1989 Loma Prieta Earthquake. The example is a parametric study performed to calibrate geotechnical/structural properties based on the damage observed to Berth 37 from the directional ground shaking durin...

Dynamic response analysis of pile-supported structures in SASSI is relatively complex and require... more Dynamic response analysis of pile-supported structures in SASSI is relatively complex and requires proper modeling and knowledge of pile-soil-structure interaction. The original hybrid pile procedure implemented in SASSI requires a large number of interaction nodes that makes it unappealing for practical applications. The Spile methodology, developed from the point load solution of an axisymmetric pile model in SASSI, provides accurate results for a single pile analysis but cannot be easily extended to large pile groups. As a result, the current practice in SASSI is to use Beam elements to model pile groups. A recent benchmark study to evaluate the adequacy of Beam element to model pile groups in SASSI has revealed severe deficiencies in this procedure for such applications. To overcome the deficiencies of Spile and Beam elements, a new Pile element has been developed and implemented in SASSI. This paper examines the results of Spile, Beam and new Pile element procedures by comparin...

This paper presents the results of seismic structure-soil-structure interaction (SSSI) analysis o... more This paper presents the results of seismic structure-soil-structure interaction (SSSI) analysis of a deep well and adjacent bunker. The well structure consists of a deep shaft, approximately 1,200 ft in length installed below ground surface and attached at the top to a partially embedded well head building. A surface-supported bunker structure is also located adjacent to the well structure. The well is constructed with different horizontal layers of steel and cement materials encapsulated by FRP material to provide a seal and water integrity. The FRP has no structural functionality but the stresses and/or strains in this material should remain within tolerable limits to ensure acceptable performance following the postulated seismic event. The site soil response is sensitive to frequencies below 10Hz, which can significantly affect the well structure response as the spectral peak of foundation input response spectra (FIRS) is located below 10Hz. The analysis included several sensitiv...

Metocean loads typically govern the design of steel-jacket fixed offshore structures in zones of ... more Metocean loads typically govern the design of steel-jacket fixed offshore structures in zones of moderate seismicity. In contrast, the steel gravity structure (SGS) presented in this paper is heavy and stiff. The large mass results in foundation forces from seismic events that may exceed those created by extreme cyclonic storm events. When computing the earthquake response of such structures, it is essential to account for soil-structure interaction (SSI) effects incorporating nonlinear soil behavior. Seismic SSI analysis of the SGS platform was performed using an advanced version of the SASSI program. A detailed three-dimensional model of the SGS supported on horizontally layered soil was developed. Primary soil nonlinearity in the free field was accounted for through one-dimensional site response analysis. To account for soil consolidation under the self-weight of the structure and its secondary nonlinear behavior under an Abnormal Level Event (ALE) in the SSI analysis, a portion ...

Spatial incoherence of seismic waves has the effect of lowering responses of structural foundatio... more Spatial incoherence of seismic waves has the effect of lowering responses of structural foundations. The effect is more significant at higher frequencies (generally exceeding 10 Hz) and larger building footprints. The purpose of this paper is to present the results of a seismic SSI analysis of the US EPR Emergency Power Generating Building (EPGB), a surface-founded concrete structure, for a hard-rock soil case using both coherent and incoherent ground motion input. For this study both a detailed FE model of the building, and a corresponding tuned lumped-mass stick model on a rigid foundation were used. These models were subjected to horizontal and vertical components of input motion and incorporated the coherency model for hard rock. The hard rock reference motions consisted of high-frequency rock motions. The incoherent structural responses were obtained using the Response Simulation method in MTR/SASSI. The SSI results were compared against each other to evaluate the effects of gr...

Seismic soil-structure interaction (SSI) analysis of nuclear power plants (NPPs) is often perform... more Seismic soil-structure interaction (SSI) analysis of nuclear power plants (NPPs) is often performed in the frequency domain using a lumped-mass stick and/or coarse finite element (FE) model of the structure. These models are designed to capture the global dynamic response of the system. The results provide the inertia forces for foundation stability assessment, which also serve as input to a static detailed FE model of the structure for design. The in-structure response spectra is calculated from a separate dynamic analysis of a detailed structural model with fixed base, excited by either the base motion developed from SSI analysis or, more often, the inclusion of single-degree-of-freedom (SDOF) oscillators representing the local response in the stick/coarse FE SSI models. With the recent advances in computer software and hardware technology, it is now possible to perform SSI analysis of detailed structural models in the frequency domain. This paper presents the results of the seism...

The successful operation of facilities that incorporate long electron-positron beams necessitates... more The successful operation of facilities that incorporate long electron-positron beams necessitates a very low vibration environment at the beam supports. Mitigation of the ground motion and imported vibration from the numerous vibrations sources is the main engineering challenge for these projects. Computer program SASSI was selected as an analysis tool for calculating the vibrations in underground tunnels resulting from near field sources due to equipment operation as well as far-field sources for a new generation of linear colliders. The program capabilities were validated by comparing calculated vibration results with field obtained measurements performed at the Los Angeles County Metropolitan Authority (MTA) Metro Red Line tunnels which consist of twin circular parallel tunnels that run through Miocene sandstone and shale. A 3D SSI model of a representative segment of the tunnels was developed. Analyses for three loading cases were performed simulating three tests that were done ...

The results of seismic pile-soil-structure interaction (SSI) analysis of a large diameter tank su... more The results of seismic pile-soil-structure interaction (SSI) analysis of a large diameter tank supported on piles driven to a firm stratum are presented. The piles penetrate a sand layer susceptible to liquefaction. The layer was improved by driving steel inclusions into the ground. The liquefiable layer extended outside the footprint of the tank. SSI analyses were performed to demonstrate that liquefaction treatment was not required beyond the tank foundation footprint. Site response analysis was performed using SHAKE91 and the SSI analysis was performed using MTR/SASSI. Soil nonlinearities were accounted for using an equivalent linear model. The tank and fluid content were modeled using a lumped-mass stick model. The concrete base slab and insulation space between the steel and concrete base slabs were modeled using flat shell (plate) and spring elements, respectively. The piles were modeled using linear beam finite elements connected to soil at all pile nodes. The improved soil a...

International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1987

ASME 2010 Pressure Vessels and Piping Conference: Volume 8, 2010

The US EPR™ standard design currently under development by AREVA consists primarily of a nuclear ... more The US EPR™ standard design currently under development by AREVA consists primarily of a nuclear island (NI) and several other significant structures outside of and in close proximity to the NI. The NI structures consist of the Reactor Building (RB), Fuel Building (FB), Safeguard Building 1 (SB1), Safeguard Building 2/3 (SB2/3), Safeguard Building 4 (SB4), and Reactor Building Internal Structures (RBIS) — all of which share a common foundation basemat. The Nuclear Island is embedded approximately 11.6 m below the ground surface. Seismic soil-structure interaction (SSI) analysis of nuclear power plants is often performed in the frequency domain using a lumped-mass stick and/or coarse finite element model of the structure. These models are designed to capture the global dynamic response of the system, the results of which provide the inertia forces that are used for foundation stability assessment as well as input to a static detailed finite element model of the structure for design. The in-structure response spectra is calculated from a separate dynamic analysis of detailed structural model on fixed base excited by the base motion developed from the SSI analysis or often by including single-degree-of-freedom (SDOF) oscillators representing the local response in the stick/coarse finite element SSI models. With recent advances in computer software and hardware technologies, it is now possible to perform SSI analysis of detailed structural models in the frequency domain. This paper presents the results of the seismic SSI analysis of the US EPR™ nuclear island using both a stick and detailed finite element representation of the structure. The soil profile corresponds to a medium stiff soil case used for the standard design. Because the EPR™ nuclear island is a complex, unsymmetric structure, the stick model consists of multiple interconnected sticks developed and calibrated against a detailed finite element model of the structure on a fixed base. Both models are analyzed using SASSI [1]. The results of the detailed finite element model in terms of maximum accelerations and response spectra, as well as total interstory forces and moments, are calculated and compared with those of the lumped-mass stick model.Copyright © 2010 by ASME

Several deterministic methods are currently available for incorporating spatial incoherence of gr... more Several deterministic methods are currently available for incorporating spatial incoherence of ground motions in the SSI analysis using SASSI. The Response SRSS method is the first implementation of the incoherent ground motions in the SASSI code that was done by EPRI in the late 90’s. A decade later, this procedure was further investigated by EPRI for application to the licensing of the new reactors in the United States. From that study three other procedures -Transfer Function SRSS (TF-SRSS), Algebraic Summation (AS) and Simulation Mean (SM) have been developed and recommended for applications to the new plant designs. The EPRI AS and SM procedures are implemented at the ground motion level and TF-SRSS at the structural response level. The purpose of this paper is to present a brief overview of each of the above methodologies, and recommend two new procedures: TF-Summation and Response-Simulation implemented at the structural response level. A numerical possibility issue in the TF...

Volume 8: Seismic Engineering, 2009

Three-dimensional seismic soil-structure interaction (SSI) analysis of nuclear power plants (NPP)... more Three-dimensional seismic soil-structure interaction (SSI) analysis of nuclear power plants (NPP) is often performed in frequency domain using the computer program SASSI [1]. This enables the analyst to properly a) address the effects of wave radiation in an unbounded soil media, b) incorporate strain-compatible soil shear modulus and damping properties and c) specify input motion in the free field using de-convolution method and/or spatially variable ground motions. For large, complex structural systems with multi-million degrees of freedom (DOF) and large foundation impedance matrices associated with deeply embedded foundations, the conventional sub-structuring analysis approach employed in SASSI often results in a coefficient matrix that is too large to solve with currently available computer resources. To address this problem, the method of component mode synthesis (CMS) is employed in the SSI analysis. This involves partitioning the structure into several interconnected compone...

Dynamic soil-structure interaction (SSI) analysis of nuclear power plants is often performed in f... more Dynamic soil-structure interaction (SSI) analysis of nuclear power plants is often performed in frequency domain using programs such as SASSI In this paper we have expanded the DPFI model to incorporate nonlinearities at the soil/structure interface by introducing nonlinear shear and normal springs arranged in series between the DPFI and structure model. This combination of the linear far-field impedance (DPFI) plus nonlinear near-field soil springs allows the foundation sliding and/or uplift behavior be analyzed in time domain while maintaining the frequency-dependent stiffness and radiation damping nature of the far-field foundation impedance. To check the accuracy of this procedure, a typical NPP foundation mat supported at the surface of a layered soil system and subjected to harmonic forced vibration was first analyzed in the frequency domain using SASSI to calculate the target linear response and derive a linear, far-field DPFI model. The target linear solution was then used t...

Ground shaking and ground deformation are the major causes of damage to waterfront improvements i... more Ground shaking and ground deformation are the major causes of damage to waterfront improvements including bridges and port facilities. Large cyclic and/or permanent ground deformations related to slope displacements are the main source of distress to the foundations and structural elements of waterfront structures. Modeling this soil structure interaction (SSI) problem analytically is difficult because it involves kinematic soil-foundation interaction during large (cyclic and permanent) ground deformations as well as inertial foundation-superstructure interaction during shaking, all of which occur while the soil and possibly structural properties rapidly degrade with time. The paper presents an example from the Port of Oakland’s Berth 37, which suffered significant damage during the 1989 Loma Prieta Earthquake. The example is a parametric study performed to calibrate geotechnical/structural properties based on the damage observed to Berth 37 from the directional ground shaking durin...

Dynamic response analysis of pile-supported structures in SASSI is relatively complex and require... more Dynamic response analysis of pile-supported structures in SASSI is relatively complex and requires proper modeling and knowledge of pile-soil-structure interaction. The original hybrid pile procedure implemented in SASSI requires a large number of interaction nodes that makes it unappealing for practical applications. The Spile methodology, developed from the point load solution of an axisymmetric pile model in SASSI, provides accurate results for a single pile analysis but cannot be easily extended to large pile groups. As a result, the current practice in SASSI is to use Beam elements to model pile groups. A recent benchmark study to evaluate the adequacy of Beam element to model pile groups in SASSI has revealed severe deficiencies in this procedure for such applications. To overcome the deficiencies of Spile and Beam elements, a new Pile element has been developed and implemented in SASSI. This paper examines the results of Spile, Beam and new Pile element procedures by comparin...

This paper presents the results of seismic structure-soil-structure interaction (SSSI) analysis o... more This paper presents the results of seismic structure-soil-structure interaction (SSSI) analysis of a deep well and adjacent bunker. The well structure consists of a deep shaft, approximately 1,200 ft in length installed below ground surface and attached at the top to a partially embedded well head building. A surface-supported bunker structure is also located adjacent to the well structure. The well is constructed with different horizontal layers of steel and cement materials encapsulated by FRP material to provide a seal and water integrity. The FRP has no structural functionality but the stresses and/or strains in this material should remain within tolerable limits to ensure acceptable performance following the postulated seismic event. The site soil response is sensitive to frequencies below 10Hz, which can significantly affect the well structure response as the spectral peak of foundation input response spectra (FIRS) is located below 10Hz. The analysis included several sensitiv...

Metocean loads typically govern the design of steel-jacket fixed offshore structures in zones of ... more Metocean loads typically govern the design of steel-jacket fixed offshore structures in zones of moderate seismicity. In contrast, the steel gravity structure (SGS) presented in this paper is heavy and stiff. The large mass results in foundation forces from seismic events that may exceed those created by extreme cyclonic storm events. When computing the earthquake response of such structures, it is essential to account for soil-structure interaction (SSI) effects incorporating nonlinear soil behavior. Seismic SSI analysis of the SGS platform was performed using an advanced version of the SASSI program. A detailed three-dimensional model of the SGS supported on horizontally layered soil was developed. Primary soil nonlinearity in the free field was accounted for through one-dimensional site response analysis. To account for soil consolidation under the self-weight of the structure and its secondary nonlinear behavior under an Abnormal Level Event (ALE) in the SSI analysis, a portion ...

Spatial incoherence of seismic waves has the effect of lowering responses of structural foundatio... more Spatial incoherence of seismic waves has the effect of lowering responses of structural foundations. The effect is more significant at higher frequencies (generally exceeding 10 Hz) and larger building footprints. The purpose of this paper is to present the results of a seismic SSI analysis of the US EPR Emergency Power Generating Building (EPGB), a surface-founded concrete structure, for a hard-rock soil case using both coherent and incoherent ground motion input. For this study both a detailed FE model of the building, and a corresponding tuned lumped-mass stick model on a rigid foundation were used. These models were subjected to horizontal and vertical components of input motion and incorporated the coherency model for hard rock. The hard rock reference motions consisted of high-frequency rock motions. The incoherent structural responses were obtained using the Response Simulation method in MTR/SASSI. The SSI results were compared against each other to evaluate the effects of gr...

Seismic soil-structure interaction (SSI) analysis of nuclear power plants (NPPs) is often perform... more Seismic soil-structure interaction (SSI) analysis of nuclear power plants (NPPs) is often performed in the frequency domain using a lumped-mass stick and/or coarse finite element (FE) model of the structure. These models are designed to capture the global dynamic response of the system. The results provide the inertia forces for foundation stability assessment, which also serve as input to a static detailed FE model of the structure for design. The in-structure response spectra is calculated from a separate dynamic analysis of a detailed structural model with fixed base, excited by either the base motion developed from SSI analysis or, more often, the inclusion of single-degree-of-freedom (SDOF) oscillators representing the local response in the stick/coarse FE SSI models. With the recent advances in computer software and hardware technology, it is now possible to perform SSI analysis of detailed structural models in the frequency domain. This paper presents the results of the seism...

The successful operation of facilities that incorporate long electron-positron beams necessitates... more The successful operation of facilities that incorporate long electron-positron beams necessitates a very low vibration environment at the beam supports. Mitigation of the ground motion and imported vibration from the numerous vibrations sources is the main engineering challenge for these projects. Computer program SASSI was selected as an analysis tool for calculating the vibrations in underground tunnels resulting from near field sources due to equipment operation as well as far-field sources for a new generation of linear colliders. The program capabilities were validated by comparing calculated vibration results with field obtained measurements performed at the Los Angeles County Metropolitan Authority (MTA) Metro Red Line tunnels which consist of twin circular parallel tunnels that run through Miocene sandstone and shale. A 3D SSI model of a representative segment of the tunnels was developed. Analyses for three loading cases were performed simulating three tests that were done ...

The results of seismic pile-soil-structure interaction (SSI) analysis of a large diameter tank su... more The results of seismic pile-soil-structure interaction (SSI) analysis of a large diameter tank supported on piles driven to a firm stratum are presented. The piles penetrate a sand layer susceptible to liquefaction. The layer was improved by driving steel inclusions into the ground. The liquefiable layer extended outside the footprint of the tank. SSI analyses were performed to demonstrate that liquefaction treatment was not required beyond the tank foundation footprint. Site response analysis was performed using SHAKE91 and the SSI analysis was performed using MTR/SASSI. Soil nonlinearities were accounted for using an equivalent linear model. The tank and fluid content were modeled using a lumped-mass stick model. The concrete base slab and insulation space between the steel and concrete base slabs were modeled using flat shell (plate) and spring elements, respectively. The piles were modeled using linear beam finite elements connected to soil at all pile nodes. The improved soil a...