Summary
Past earthquakes, in many instances, have demonstrated poor performance of commonly used built‐in staircase configurations. Codal provisions in India pertaining to staircases present a rather ...simple approach wherein the effects of built‐in staircases on the overall dynamic properties or on the local behavior of structures are not addressed explicitly. Studies in the past have highlighted the scale of such effects, but most of them have relied completely on analytical models of buildings. This study analyzes the adequacy of the codal provisions by investigating two finite element (FE) models calibrated using ambient and forced vibration measurements. The effects of variations in building height, layout of staircase in plan, and presence of masonry infill walls in stairwells are also examined. The codal guidelines regarding empirical estimation of period and provision of enclosure walls around built‐in staircases are found to be adequate. However, for the case of built‐in staircases without enclosure walls, the force and displacement demands on landing beams are found to be considerably high. Drift‐based approaches to estimate these demands are proposed.
Seismic design and qualification of advanced reactors will rely heavily on the use of verified and validated numerical models capable of capturing the interaction of the vessel, its contained fluid, ...and the internal equipment: fluid‐structure interaction (FSI) analysis. Analytical solutions can be used for preliminary sizing and design of such vessels but their application is limited to simple geometries and boundary conditions, and small amplitude, translational (and rotational) inputs. To validate numerical models for seismic FSI analysis in finite element codes, a comprehensive set of experiments was performed on a liquid‐filled cylindrical vessel, using a 6 degree‐of‐freedom earthquake simulator. Results in terms of sloshing frequency, damping ratio in sloshing modes, and hydrodynamic responses (wave height, hydrodynamic pressure, base shear, and base moment) for multidirectional earthquake simulator inputs are reported and compared with analytical solutions for liquid‐filled vessels. The impact of seismic (base) isolation on hydrodynamic responses was studied using earthquake simulator inputs generated using a virtual isolation system. Data from the experiments are used to validate a numerical model of the fluid‐filled vessel using the Arbitrary Lagrangian Eulerian (ALE) solver in the commercial finite element program LS‐DYNA. Validation studies are presented for multidirectional seismic inputs, including rocking motions. Lagrangian modeling approaches using an elastic material formulation for the fluid are also investigated and their limitations and possible applications are identified. The results are broadly applicable to the seismic response of base supported, liquid‐filled vessels.
One Generation IV nuclear reactor, which uses a fluoride salt as a coolant, graphite reflector blocks as a moderator, and circulating buoyant TRISO pebbles as fuel is at an advanced stage of ...development. To characterize the seismic behavior of components of this reactor, validate numerical models for analysis, and develop recommendations for design, a set of earthquake‐simulator experiments on a scaled model of the reactor vessel and its internals was executed on a six‐degree‐of‐freedom earthquake simulator. The model was seismically isolated at its base using two types of spherical sliding bearings. The scaled model involved representations of the prototype reactor vessel, core barrel, reflector blocks, coolant, and spherical fuel pebbles. The material and geometric properties of different test components were selected based on a dynamic similitude scaling analysis and an approximate length scale of 0.4. Four sets of three‐component earthquake motions were used as inputs for testing. Instrumentation on the test specimen recorded the dynamic responses of the outer vessel, core barrel, and reflector‐block assembly, the hydrodynamic responses (sloshing and hydrodynamic pressure) of the liquid coolant, pebble consolidation under earthquake shaking, and the behavior of the isolation systems. This paper describes the design of the experiments and presents key results from the tests. The dynamic responses of the outer vessel, core barrel, and the reflector blocks revealed that the components responded as a unit for the intense shaking used in the experiments. The sloshing response of the fluid in a thin annulus near the perimeter of the vessel was heavily damped. The change in the packing fraction of the pebble bed under repeated, intense 3D earthquake shaking was less than 3%. Seismically isolating the vessel substantially reduced demands on its internal components.
Numerical models capable of generating robust estimates of isolation‐system and fluid‐structure responses for multidirectional, high‐intensity shaking will be required for analysis, design, and risk ...assessment of seismically isolated advanced reactors. None of the few studies to date on base‐isolated, fluid‐filled vessels have generated datasets suitable for formal validation of numerical models. Earthquake‐simulator experiments on a fluid‐filled, cylindrical vessel, base isolated using four single concave friction pendulum bearings (SFP isolators) were performed. The dataset was used to validate a numerical model for high intensity, multidirectional seismic inputs. Fluid and isolation‐system responses obtained from analysis of the numerical model were in excellent agreement with experimental results. The numerical models and outcomes from the experiments are broadly applicable to base‐isolated, fluid‐filled vessels, regardless of industry sector.
The acoustic fluid‐structure interaction (FSI) formulation is a practical numerical approach for the seismic analysis of fluid‐filled tanks. However, there are no verification and validation studies ...reported in the literature that demonstrate the ability of an acoustic FSI numerical model to predict responses important to structural and mechanical design for intense translational and rotational earthquake inputs. Herein, an acoustic FSI formulation is implemented in the open‐source Multiphysics Object‐Oriented Simulation Environment (MOOSE), and is formally verified and validated using analytical solutions and code‐to‐code verification, and experimental data, respectively. The analytical solutions are for small amplitude, unidirectional seismic inputs. The code‐to‐code verification utilizes a previously verified and validated Arbitrary Lagrangian‐Eulerian (ALE) numerical model in the commercial finite element code LS‐DYNA. The validation studies utilize a comprehensive data set assembled from results of 3D earthquake‐simulator tests of a fluid‐filled vessel. The acoustic numerical model in MOOSE is verified and validated for hydrodynamic pressures and support reactions except for cases that involve significant convective response. For small amplitude inputs, numerically predicted wave heights match those of the analytical solutions. The numerical model is not verified and validated for wave height calculations under intense 3D seismic inputs. The run times for the acoustic FSI simulations in MOOSE are an order of magnitude, or more, shorter than for the corresponding ALE simulations in LS‐DYNA. The utility of the MOOSE acoustic FSI implementation is demonstrated by seismic analysis of a building equipped with a fluid‐filled, advanced nuclear reactor.
The 2014 Kashmir floods caused widespread damage in the valley of Kashmir, particularly in the city of Srinagar, and had a significant socioeconomic impact. Around 175,000 residential houses were ...damaged in the valley. Recent studies focusing on the flood–hazard that the Jhelum river poses have shown that a flood event with a return period of five or more years is likely to cause overflowing in the river. As such, policy decisions regarding flood safety are rather important. This paper seeks to inform such future policy decisions from a structural engineering point of view by presenting results from a survey of damaged houses in an area of Srinagar city. The surveyed houses are classified based on construction type and material, exposure level, and age for an adequate interpretation of results. A rational and easy-to-use method of quantifying damage using a damage index scale is proposed and used in this study. Damage index values evaluated using the proposed method are found to correlate well with actual damage in surveyed structures. 80% of the surveyed houses were submerged to more than half of their heights and nearly 20% were found to be completely collapsed. Houses with mud mortar, and timber as the material for beams, slabs and plinth were the found to be most damaged, while houses with cement mortar having a damp proof course and reinforced cement concrete beams and slabs were found to have performed well. It is emphasized that structural design in Kashmir has to account for seismic forces as well, and that any guideline thereof needs to take into account both hazards–floods as well as earthquakes.
•Seismic FSI numerical models of a vessel, validated using experimental data.•Dataset generated using earthquake-simulator tests.•Responses critical to advanced reactors considered: pressure, ...reactions, wave height.•The ALE and ICFD solvers in LS-DYNA for seismic FSI analysis.•Recommendations for validation of seismic FSI numerical models.
Seismic design, qualification, and risk assessment of nuclear safety-related vessels filled with liquid will have to consider the interaction between the vessel (tank), the contained liquid, and submerged components, if any. Seismic fluid-structure-interaction (FSI) analysis of nuclear vessels will rely on numerical models, which are required to be verified and validated. This study validates previously-verified numerical models using test data generated from earthquake-simulator experiments involving a cylindrical tank. Two solvers in LS-DYNA for FSI simulations are used for the numerical analysis: Arbitrary-Lagrangian-Eulerian (ALE) and Incompressible Computational Fluid Dynamics (ICFD). Numerical and test results are compared for responses critical to seismic design of advanced reactor vessels: hydrodynamic pressures on the tank wall, reactions at the support, and wave heights of the contained liquid. Analysis is performed for one-, two-, and three-directional seismic inputs with a range of intensity, and rocking motions. The accuracy of the numerical results and different methods for outputting wave heights are discussed. Recommendations for validation of seismic FSI numerical models of advanced reactors are provided. The validation exercise presented in this study is broadly applicable to cylindrical tanks, regardless of industry sector.
The seismic design of an advanced nuclear reactor must consider the interaction of vessel internal components with the surrounding coolant: fluid–structure interaction (FSI). Available analytical ...solutions for FSI of submerged components do not accommodate multiple-component, intense seismic inputs and complex reactor and internal geometries. Physical testing of reactor vessels and internals to inform seismic design is impractical and cost-prohibitive, leaving the use of verified and validated, robust numerical models as the only plausible option for analysis and design. Physical data that could be used for validating such numerical models for multi-component shaking are not available. This article describes an experimental program performed on a 6-degree-of-freedom earthquake simulator to generate data that could support validation of seismic FSI numerical models for submerged components in commercial finite element codes. A scaled model of a base-supported reactor vessel with simplified representations of submerged internals was tested to generate submerged-component response histories for a range of seismic inputs. The generated data were used to validate numerical models in the finite element code LS-DYNA. Numerical models were validated for calculation of hydrodynamic pressure responses on internals, in-water frequencies of internals, and acceleration responses of internals. The generated data and the analysis recommendations could aid engineering analysts designing submerged components and systems for seismic effects.
Seismic design and qualification of advanced reactors will rely heavily on the use of verified and validated numerical models capable of capturing the interaction of the vessel, its contained fluid, ...and the internal equipment: fluid-structure interaction (FSI) analysis. Analytical solutions can be used for preliminary sizing and design of such vessels but their application is limited to simple geometries and boundary conditions, and small amplitude, translational (and rotational) inputs. To validate numerical models for seismic FSI analysis in finite element codes, a comprehensive set of experiments was performed on a liquid-filled cylindrical vessel, using a 6 degree-of-freedom earthquake simulator. Results in terms of sloshing frequency, damping ratio in sloshing modes, and hydrodynamic responses (wave height, hydrodynamic pressure, base shear, and base moment) for multi-directional earthquake simulator inputs are reported and compared with analytical solutions for liquid-filled vessels. The impact of seismic (base) isolation on hydrodynamic responses was studied using earthquake simulator inputs generated using a virtual isolation system. Data from the experiments are used to validate a numerical model of the fluid-filled vessel using the Arbitrary Lagrangian Eulerian (ALE) solver in the commercial finite element program LS-DYNA. Validation studies are presented for multi-directional seismic inputs, including rocking motions. Lagrangian modeling approaches using an elastic material formulation for the fluid are also investigated and their limitations and possible applications are identified. Here, the results are broadly applicable to the seismic response of base supported, liquid-filled vessels.
A Fluoride-salt cooled High-temperature Reactor (FHR) that uses circulating solid TRISO pebbles, as a fuel and positively buoyant graphite reflector blocks as a moderator is at an advanced stage of ...development. Seismic base isolation supports a pathway for cost competitive and rapid deployment of this molten salt reactor (MSR) in regions of different seismic hazard. This paper presents recommendations for analysis and modelling of different components of a base-isolated MSR, based on results of earthquake-simulator tests on a scale model of the reactor. Recommendations are provided for evaluating the sloshing behavior of the coolant in an annular region inside the reactor and for estimating hydrodynamic loads for use in analysis of structural and mechanical components. Hydrodynamic loading on the reflector blocks is discussed and a practical approach to estimate forces in the connections between them is presented. Approaches for modelling and analysis of two 2D horizontal base-isolation systems, utilizing spherical sliding bearings, are validated using results from experiments. The recommendations apply to reactor vessels with similar fluid-structure systems.
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