MCEER is a national center of excellence dedicated to the discovery and development of new knowle... more MCEER is a national center of excellence dedicated to the discovery and development of new knowledge, tools and technologies that equip communities to become more disaster resilient in the face of earthquakes and other extreme events. MCEER accomplishes this through a system of multidisciplinary, multi-hazard research, in tandem with complimentary education and outreach initiatives.
Seismic isolation is a viable strategy for protecting safety-related nuclear structures from the ... more Seismic isolation is a viable strategy for protecting safety-related nuclear structures from the effects of moderate to severe earthquake shaking. Although seismic isolation has been deployed in nuclear structures in France and South Africa, it has not seen widespread use because of limited new build nuclear construction in the past 30 years and a lack of guidelines, codes and standards for the analysis, design and construction of isolation systems specific to nuclear structures. The funding by the United States Nuclear Regulatory Commission of a research project to the Lawrence Berkeley National Laboratory and MCEER/University at Buffalo facilitated the writing of a soon-to-be-published NUREG on seismic isolation. Funding of MCEER by the National Science Foundation led to research products that provide the technical basis for a new section in ASCE Standard 4 on the seismic isolation of safety-related nuclear facilities. The performance expectations identified in the NUREG and ASCE 4 for seismic isolation systems, and superstructures and substructures are described in the paper. Robust numerical models capable of capturing isolator behaviors under extreme loadings, which have been verified and validated following ASME protocols, and implemented in the open source code OpenSees, are introduced.
• Response-history analysis of nuclear structures base-isolated using lead–rubber bearings is per... more • Response-history analysis of nuclear structures base-isolated using lead–rubber bearings is performed. • Advanced numerical model of lead–rubber bearing is used to capture behavior under extreme earthquake shaking. • Results of response-history analysis obtained using simplified and advanced model of lead–rubber bearings are compared. • Heating of the lead core and variation in buckling load and axial stiffness affect the response. a b s t r a c t Seismic isolation using low damping rubber and lead–rubber bearings is a viable strategy for mitigating the effects of extreme earthquake shaking on safety-related nuclear structures. The mechanical properties of these bearings are not expected to change substantially in design basis shaking. However, under shaking more intense than design basis, the properties of the lead cores in lead–rubber bearings may degrade due to heating associated with energy dissipation, some bearings in an isolation system may experience net tension, and the compression and tension stiffness may be affected by the lateral displacement of the isolation system. The effects of intra-earthquake changes in mechanical properties on the response of base-isolated nuclear power plants (NPPs) are investigated using an advanced numerical model of a lead–rubber bearing that has been verified and validated, and implemented in OpenSees. A macro-model is used for response-history analysis of base-isolated NPPs. Ground motions are selected and scaled to be consistent with response spectra for design basis and beyond design basis earthquake shaking at the site of the Diablo Canyon Nuclear Generating Station. Ten isolation systems of two periods and five characteristic strengths are analyzed. The responses obtained using simplified and advanced isolator models are compared. Strength degradation due to heating of lead cores and changes in buckling load most significantly affect the response of the base-isolated NPP.
SUMMARY The nuclear accident at Fukushima Daiichi in March 2011 has led the nuclear community to ... more SUMMARY The nuclear accident at Fukushima Daiichi in March 2011 has led the nuclear community to consider seismic isolation for new large light water and small modular reactors to withstand the effects of beyond design basis loadings, including extreme earthquakes. The United States Nuclear Regulatory Commission is sponsoring a research project that will quantify the response of low damping rubber (LDR) and lead rubber (LR) bearings under loadings associated with extreme earthquakes. Under design basis loadings, the response of an elastomeric bearing is not expected to deviate from well-established numerical models, and bearings are not expected to experience net tension. However, under extended or beyond design basis shaking, elastomer shear strains may exceed 300% in regions of high seismic hazard, bearings may experience net tension, the compression and tension stiffness will be affected by isolator lateral displacement, and the properties of the lead core in LR bearings will degrade in the short-term because of substantial energy dissipation. New mathematical models of LDR and LR bearings are presented for the analysis of base isolated structures under design and beyond design basis shaking, explicitly considering both the effects of lateral displacement and cyclic vertical and horizontal loading. These mathematical models extend the available formulations in shear and compression. Phenomenological models are presented to describe the behavior of elastomeric isolation bearings in tension, including the cavitation and post-cavitation behavior. The elastic mechanical properties make use of the two-spring model. Strength degradation of LR bearing under cyclic shear loading due to heating of lead core is incorporated. The bilinear area reduction method is used to include variation of critical buckling load capacity with lateral displacement. The numerical models are coded in OpenSees, and the results of numerical analysis are compared with test data. The effect of different parameters on the response is investigated through a series of analyses.
Design standards for seismic isolation of nuclear power plants in USA will consider the effects o... more Design standards for seismic isolation of nuclear power plants in USA will consider the effects of beyond design basis loadings, including extreme earthquakes. Seismic isolation is being considered for new build nuclear power plant construction and design of isolation systems will have to consider these extreme loadings, which includes the possibility of net tensile force in bearings under beyond design basis shaking. A series of experiments were conducted at University at Buffalo to characterize the behavior of elastomeric bearings in tension. Sixteen low damping rubber bearings from two manufacturers, with similar geometric properties but different shear moduli, were tested under various loading conditions to determine factors that affect cavitation in an elastomeric bearing. The effect of cavitation on the shear and axial properties of elastomeric bearings was investigated by performing post-cavitation tests. The test data were used to validate a phenomenological model of an elastomeric bearing in tension, which is implemented in OpenSees, ABAQUS and LS-DYNA.
MCEER is a national center of excellence dedicated to the discovery and development of new knowle... more MCEER is a national center of excellence dedicated to the discovery and development of new knowledge, tools and technologies that equip communities to become more disaster resilient in the face of earthquakes and other extreme events. MCEER accomplishes this through a system of multidisciplinary, multi-hazard research, in tandem with complimentary education and outreach initiatives.
Seismic isolation is a viable strategy for protecting safety-related nuclear structures from the ... more Seismic isolation is a viable strategy for protecting safety-related nuclear structures from the effects of moderate to severe earthquake shaking. Although seismic isolation has been deployed in nuclear structures in France and South Africa, it has not seen widespread use because of limited new build nuclear construction in the past 30 years and a lack of guidelines, codes and standards for the analysis, design and construction of isolation systems specific to nuclear structures. The funding by the United States Nuclear Regulatory Commission of a research project to the Lawrence Berkeley National Laboratory and MCEER/University at Buffalo facilitated the writing of a soon-to-be-published NUREG on seismic isolation. Funding of MCEER by the National Science Foundation led to research products that provide the technical basis for a new section in ASCE Standard 4 on the seismic isolation of safety-related nuclear facilities. The performance expectations identified in the NUREG and ASCE 4 for seismic isolation systems, and superstructures and substructures are described in the paper. Robust numerical models capable of capturing isolator behaviors under extreme loadings, which have been verified and validated following ASME protocols, and implemented in the open source code OpenSees, are introduced.
• Response-history analysis of nuclear structures base-isolated using lead–rubber bearings is per... more • Response-history analysis of nuclear structures base-isolated using lead–rubber bearings is performed. • Advanced numerical model of lead–rubber bearing is used to capture behavior under extreme earthquake shaking. • Results of response-history analysis obtained using simplified and advanced model of lead–rubber bearings are compared. • Heating of the lead core and variation in buckling load and axial stiffness affect the response. a b s t r a c t Seismic isolation using low damping rubber and lead–rubber bearings is a viable strategy for mitigating the effects of extreme earthquake shaking on safety-related nuclear structures. The mechanical properties of these bearings are not expected to change substantially in design basis shaking. However, under shaking more intense than design basis, the properties of the lead cores in lead–rubber bearings may degrade due to heating associated with energy dissipation, some bearings in an isolation system may experience net tension, and the compression and tension stiffness may be affected by the lateral displacement of the isolation system. The effects of intra-earthquake changes in mechanical properties on the response of base-isolated nuclear power plants (NPPs) are investigated using an advanced numerical model of a lead–rubber bearing that has been verified and validated, and implemented in OpenSees. A macro-model is used for response-history analysis of base-isolated NPPs. Ground motions are selected and scaled to be consistent with response spectra for design basis and beyond design basis earthquake shaking at the site of the Diablo Canyon Nuclear Generating Station. Ten isolation systems of two periods and five characteristic strengths are analyzed. The responses obtained using simplified and advanced isolator models are compared. Strength degradation due to heating of lead cores and changes in buckling load most significantly affect the response of the base-isolated NPP.
SUMMARY The nuclear accident at Fukushima Daiichi in March 2011 has led the nuclear community to ... more SUMMARY The nuclear accident at Fukushima Daiichi in March 2011 has led the nuclear community to consider seismic isolation for new large light water and small modular reactors to withstand the effects of beyond design basis loadings, including extreme earthquakes. The United States Nuclear Regulatory Commission is sponsoring a research project that will quantify the response of low damping rubber (LDR) and lead rubber (LR) bearings under loadings associated with extreme earthquakes. Under design basis loadings, the response of an elastomeric bearing is not expected to deviate from well-established numerical models, and bearings are not expected to experience net tension. However, under extended or beyond design basis shaking, elastomer shear strains may exceed 300% in regions of high seismic hazard, bearings may experience net tension, the compression and tension stiffness will be affected by isolator lateral displacement, and the properties of the lead core in LR bearings will degrade in the short-term because of substantial energy dissipation. New mathematical models of LDR and LR bearings are presented for the analysis of base isolated structures under design and beyond design basis shaking, explicitly considering both the effects of lateral displacement and cyclic vertical and horizontal loading. These mathematical models extend the available formulations in shear and compression. Phenomenological models are presented to describe the behavior of elastomeric isolation bearings in tension, including the cavitation and post-cavitation behavior. The elastic mechanical properties make use of the two-spring model. Strength degradation of LR bearing under cyclic shear loading due to heating of lead core is incorporated. The bilinear area reduction method is used to include variation of critical buckling load capacity with lateral displacement. The numerical models are coded in OpenSees, and the results of numerical analysis are compared with test data. The effect of different parameters on the response is investigated through a series of analyses.
Design standards for seismic isolation of nuclear power plants in USA will consider the effects o... more Design standards for seismic isolation of nuclear power plants in USA will consider the effects of beyond design basis loadings, including extreme earthquakes. Seismic isolation is being considered for new build nuclear power plant construction and design of isolation systems will have to consider these extreme loadings, which includes the possibility of net tensile force in bearings under beyond design basis shaking. A series of experiments were conducted at University at Buffalo to characterize the behavior of elastomeric bearings in tension. Sixteen low damping rubber bearings from two manufacturers, with similar geometric properties but different shear moduli, were tested under various loading conditions to determine factors that affect cavitation in an elastomeric bearing. The effect of cavitation on the shear and axial properties of elastomeric bearings was investigated by performing post-cavitation tests. The test data were used to validate a phenomenological model of an elastomeric bearing in tension, which is implemented in OpenSees, ABAQUS and LS-DYNA.
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to severe earthquake shaking. Although seismic isolation has been deployed in nuclear structures in France and South
Africa, it has not seen widespread use because of limited new build nuclear construction in the past 30 years and a lack of
guidelines, codes and standards for the analysis, design and construction of isolation systems specific to nuclear structures.
The funding by the United States Nuclear Regulatory Commission of a research project to the Lawrence Berkeley
National Laboratory and MCEER/University at Buffalo facilitated the writing of a soon-to-be-published NUREG on
seismic isolation. Funding of MCEER by the National Science Foundation led to research products that provide the
technical basis for a new section in ASCE Standard 4 on the seismic isolation of safety-related nuclear facilities. The
performance expectations identified in the NUREG and ASCE 4 for seismic isolation systems, and superstructures and
substructures are described in the paper. Robust numerical models capable of capturing isolator behaviors under extreme
loadings, which have been verified and validated following ASME protocols, and implemented in the open source code
OpenSees, are introduced.
to severe earthquake shaking. Although seismic isolation has been deployed in nuclear structures in France and South
Africa, it has not seen widespread use because of limited new build nuclear construction in the past 30 years and a lack of
guidelines, codes and standards for the analysis, design and construction of isolation systems specific to nuclear structures.
The funding by the United States Nuclear Regulatory Commission of a research project to the Lawrence Berkeley
National Laboratory and MCEER/University at Buffalo facilitated the writing of a soon-to-be-published NUREG on
seismic isolation. Funding of MCEER by the National Science Foundation led to research products that provide the
technical basis for a new section in ASCE Standard 4 on the seismic isolation of safety-related nuclear facilities. The
performance expectations identified in the NUREG and ASCE 4 for seismic isolation systems, and superstructures and
substructures are described in the paper. Robust numerical models capable of capturing isolator behaviors under extreme
loadings, which have been verified and validated following ASME protocols, and implemented in the open source code
OpenSees, are introduced.