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Alternate modal combination methods in response spectrum analysis

Description: In piping analyses using the response spectrum method Square Root of the Sum of the Squares (SRSS) with clustering between closely spaced modes is the combination procedure most commonly used to combine between the modal response components. This procedure is simple to apply and normally yields conservative estimates of the time history results. The purpose of this study is to investigate alternate methods to combine between the modal response components. These methods are mathematically based to properly account for the combination between rigid and flexible modal responses as well as closely spaced modes. The methods are those advanced by Gupta, Hadjian and Lindley-Yow to address rigid response modes and the Double Sum Combination (DSC) method and the Complete Quadratic Combination (CQC) method to account for closely spaced modes. A direct comparison between these methods as well as the SRSS procedure is made by using them to predict the response of six piping systems. For two piping systems thirty-three earthquake records were considered to account for the impact of variations in the characteristics of the excitation. The results provided by each method are compared to the corresponding time history estimates of results as well as to each other. The degree of conservatism associated with each method is characterized. 7 refs., 4 figs., 2 tabs.
Date: January 1, 1989
Creator: Wang, Y.K. & Bezler, P.
Partner: UNT Libraries Government Documents Department

HDR URL confirmatory evaluations

Description: One phase of the seismic studies conducted with the decommissioned Heissdampfreaktor in Kahl, West Germany was the prediction of the response of the Recirculation Loop piping (URL) to the 5 Kg blast loading. As a follow-on study to the US effort in this area, BNL performed linear analyses of the URL piping to corroborate the linear analyses performed by an alternate NRC contractor and to verify those analyses considering distinct, independent support excitations. In this study the computer models and processed input data developed by the alternate contractor were used. The BNL effort was initiated in FY 1982 under the Mechanical Piping Benchmark Project. Specifically response predictions were made for the HDR URL system subjected to the 5 Kg blast loading considering uniform support motion with elastic supports and independent support motion with elastic supports. For the evaluations the independently developed BNL finite element piping analysis code, PSAFE2, was used. The paper includes a description of the computer model and comparisons between measured and predicted acceleration time history records for selected points in the system. Predicted results considering both uniform support excitation and independent support excitation are provided.
Date: January 1, 1983
Creator: Bezler, P.; Subudhi, M. & Wang, Y.K.
Partner: UNT Libraries Government Documents Department

Nonlinear failure analysis of a reinforced concrete containment under internal pressure

Description: A detailed nonlinear finite element model is used to investigate the failure response of the Indian Point containment building under severe accident pressures. Refined material models are used to describe the complex stress-strain behavior of the liner and rebar steels, the plain concrete and the reinforced concrete. Structural geometry of the containment is idealized by eight layers of axisymmetric finite elements through the wall thickness in order to closely model the actual placement of the rebars. Soil stiffness under the containment base mat is modeled by a series of nonlinear spring elements. Numerical results presented in the paper describe cracking and plastic deformation (in compression) of the concrete, yielding of the liner and rebar steels and eventual loss of the load carrying capacity of the containment. The results are compared with available data from the previous studies for this containment. 8 references, 9 figures.
Date: January 1, 1984
Creator: Sharma, S.; Wang, Y.K. & Reich, M.
Partner: UNT Libraries Government Documents Department

Effect of PVRC damping with independent support motion response spectrum analysis of piping systems

Description: The Technical Committee for Piping Systems of the Pressure Vessel Research Committee (PVRC) has recommended new damping values to be used in the seismic analyses of piping systems in nuclear power plants. To evaluate the effects of coupling these recommendations with the use of independent support motion analyses methods, two sets of seismic analyses have been carried out for several piping systems. One set based on the use of uniform damping as specified in Regulatory Guide 1.61, the other based on the PVRC recommendations. In each set the analyses were performed using independent support motion time history and response spectrum methods as well as the envelope spectrum method. In the independent response spectrum analyses, 14 response estimates were in fact obtained by considering different combination procedures between the support group contributions and all sequences of combinations between support groups, modes and directions. For each analysis set, the response spectrum results were compared with time history estimates of those results. Comparison tables were then prepared depicting the percentage by which the response spectrum estimates exceeded the time history estimates. By comparing the result tables between both analysis sets, the impact of PVRC damping can be observed. Preliminary results show that the degree of exceedance of the response spectrum estimates based on PVRC damping is less than that based on uniform damping for the same piping problem. Expressed differently the results obtained if ISM methods are coupled with PVRC damping are not as conservative as those obtained using uniform damping.
Date: January 1, 1986
Creator: Wang, Y.K.; Bezler, P. & Shteyngart, S.
Partner: UNT Libraries Government Documents Department

Combination of the primary and secondary stress components for piping systems. [PWR; BWR]

Description: The present study considers several typical piping models subjected to distinct support motions. The independent time history analysis yields both primary stresses due to inertia and secondary stresses due to relative support motions. In addition, this analysis predicts the total response due to both effects. These results presumably are the best estimate of the actual response of a piping system subjected to a real earthquake because the analysis involves solving the system equations at every time step and the phasing during the process of solution is not lost. The piping models were then analyzed using the response spectrum method to obtain the maximum primary stresses. The secondary stresses were next calculated by performing a set of static analysis which result in the most unfavorable combination. These two results are combined by both SRSS and absolute sum methods and the results are compared with the time history solutions.
Date: January 1, 1983
Creator: Subudhi, M.; Wang, Y.K. & Bezler, P.
Partner: UNT Libraries Government Documents Department

Comparison study of time history and response spectrum responses for multiply supported piping systems. [PWR; BWR]

Description: In the past decade, several investigators have studied the problem of independent support excitation of a multiply supported piping system to identify the real need for such an analysis. This approach offers an increase in accuracy at a small increase in computational costs. To assess the method, studies based on the response spectrum approach using independent support motions for each group of commonly connected supports were performed. The results obtained from this approach were compared with the conventional envelope spectrum and time history solutions. The present study includes a mathematical formulation of the independent support motion analysis method suitable for implementation into an existing all purpose piping code PSAFE2 and a comparison of the solutions for some typical piping system using both Time History and Response Spectrum Methods. The results obtained from the Response Spectrum Methods represent the upper bound solution at most points in the piping system. Similarly, the Seismic Anchor Movement analysis based on the SRP method over predicts the responses near the support points and under predicts at points away from the supports.
Date: January 1, 1983
Creator: Wang, Y.K.; Subudhi, M. & Bezler, P.
Partner: UNT Libraries Government Documents Department

BNL piping research

Description: Brookhaven National Laboratory (BNL) has assisted in the development of methods to evaluate the analysis methods used by industry to qualify nuclear power piping. Through FY 1985 these efforts were conducted under the Mechanical Piping Benchmarks project while current and future efforts will be performed under the Combination Procedures for piping project. Under these projects BNL has developed analytical benchmark problems for piping systems evaluated using uniform or independent support motion response spectrum methods, investigated the adequacy and limitations of linear piping analysis methods by comparison to test results and evaluated and developed criteria for new and alternate methods of analysis. A summary description of the status of these efforts is provided.
Date: January 1, 1985
Creator: Bezler, P.; Subudhi, M.; Wang, Y.K. & Shteyngart, S.
Partner: UNT Libraries Government Documents Department

Seismic analysis of fuel and target assemblies at a production reactor

Description: This paper describes the unique modeling and analysis considerations used to assess the seismic adequacy of the fuel and target assemblies in a production reactor at Savannah River Site. This confirmatory analysis was necessary to provide assurance that the reactor can operate safely during a seismic event and be brought to a safe shutdown condition. The plant which was originally designed in the 1950's required to be assessed to more current seismic criteria. The design of the reactor internals and the magnitude of the structural responses enabled the use of a linear elastic dynamic analysis. A seismic analysis was performed using a finite element model consisting of the fuel and target assemblies, reactor tank, and a portion of the concrete structure supporting the reactor tank. The effects of submergence of the fuel and target assemblies in the water contained within the reactor tank can have a significant effect on their seismic response. Thus, the model included hydrodynamic fluid coupling effects between the assemblies and the reactor tank. Fluid coupling mass terms were based on formulations for solid bodies immersed in incompressible and frictionless fluids. The potential effects of gap conditions were also assessed in this evaluation. 5 refs., 6 figs., 1 tab.
Date: January 1, 1991
Creator: Braverman, J.I. & Wang, Y.K.
Partner: UNT Libraries Government Documents Department

Piping benchmark problems for the Westinghouse AP600 Standardized Plant

Description: To satisfy the need for verification of the computer programs and modeling techniques that will be used to perform the final piping analyses for the Westinghouse AP600 Standardized Plant, three benchmark problems were developed. The problems are representative piping systems subjected to representative dynamic loads with solutions developed using the methods being proposed for analysis for the AP600 standard design. It will be required that the combined license licensees demonstrate that their solutions to these problems are in agreement with the benchmark problem set.
Date: January 1997
Creator: Bezler, P.; DeGrassi, G.; Braverman, J. & Wang, Y. K.
Partner: UNT Libraries Government Documents Department

Implementation of Seismic Stops in Piping Systems

Description: Commonwealth Edison has submitted a request to NRC to replace the snubbers in the Reactor Coolant Bypass Line of Byron Station-Unit 2 with gapped pipe supports. The specific supports intended for use are commercial units designated ''Seismic Stops'' manufactured by Robert L. Cloud Associates, Inc. (RLCA). These devices have the physical appearance of snubbers and are essentially spring supports incorporating clearance gaps sized for the Byron Station application. Although the devices have a nonlinear stiffness characteristic, their design adequacy is demonstrated through the use of a proprietary linear elastic piping analysis code ''GAPPIPE'' developed by RLCA. The code essentially has all the capabilities of a conventional piping analysis code while including an equivalent linearization technique to process the nonlinear spring elements. Brookhaven National Laboratory (BNL) has assisted the NRC staff in its evaluation of the RLCA implementation of the equivalent Linearization technique and the GAPPIPE code. Towards this end, BNL performed a detailed review of the theoretical basis for the method, an independent evaluation of the Byron piping using the nonlinear time history capability of the ANSYS computer code and by result comparisons to the RLCA developed results, an assessment of the adequacy of the response estimates developed with GAPPIPE. Associated studies included efforts to verify the ANSYS analysis results and the development of bounding calculations for the Byron Piping using linear response spectrum methods.
Date: February 1, 1993
Creator: Bezler, P.; Simos, N. & Wang, Y.K.
Partner: UNT Libraries Government Documents Department

Independent seismic evaluation of the Diablo Canyon Unit 1 containment annulus structure and selected piping systems

Description: An independent review and development of the vertical floor spectra for the Unit 1 containment annulus structure of the Diablo Canyon Power Plant was carried out using a detailed three-dimensional model. The developed floor spectra were then utilized for confirmatory evaluations of two selected piping systems. The latter were evaluated by the envelope response spectrum method, and by the independent support motion response spectrum method. ASME class 2 evaluations of the two systems were also performed. Finally, a confirmatory evaluation was carried out for the model utilized by URS/Blume for the development of the vertical floor response spectra. Sections 1.1 and 1.2 of the report summarize the work scope and the results of the study. Details pertaining to the specific areas of the work are given in sections 2 to 8.
Date: August 1, 1982
Creator: Philippacopoulos, A.J.; Reich, M.; Bezler, P.; Miller, C.; Wang, Y.K.; Subudhi, M. et al.
Partner: UNT Libraries Government Documents Department

Alternate modal combination methods in response spectrum analysis

Description: In piping analyses using the response spectrum method Square Root of the Sum of the Squares (SRSS) with clustering between closely spaced modes is the combination procedure most commonly used to combine between the modal response components. This procedure is simple to apply and normally yields conservative estimates of the time history results. The purpose of this study is to investigate alternate methods to combine between the modal response components. These methods are mathematically based to properly account for the combination between rigid and flexible modal responses as well as closely spaced modes. The methods are those advanced by Gupta, Hadjian and Lindely-Yow to address rigid response modes and the Double Sum Combination (DSC) method and the Complete Quadratic Combination (CQC) method to account for closely spaced modes. A direct comparison between these methods as well as the SRSS procedure is made by using them to predict the response of six piping systems. The results provided by each method are compared to the corresponding time history estimates of results as well as to each other. The degree of conservatism associated with each method is characterized. 19 refs., 16 figs., 10 tabs.
Date: October 1, 1990
Creator: Bezler, P.; Curreri, J.R.; Wang, Y.K. & Gupta, A.K. (Brookhaven National Lab., Upton, NY (USA))
Partner: UNT Libraries Government Documents Department

A report on the seismic capacity of the General Laboratory and Administration Building at Los Alamos National Laboratory

Description: A seismic analysis of the General Laboratory and Administration Building at Los Alamos National Laboratory is performed. The analyses are performed in detail for one portion of the building and then qualitatively extrapolated to other portions of the building. Seismic capacities are evaluated based on two sets of acceptance criteria. The first is based on Code-type criteria and is associated with a low probability of failure. This capacity is found to be in the 0.04--0.06 G ZPA range (the free field seismic motion is defined with a NUREG 0098 response spectrum). The second capacity is based on much less conservative criteria such as might be associated with a high probability of failure. This capacity is found to be about 0.15 G. Finally structural modifications are proposed that would increase the low probability of failure capacity to 0.15 G ZPA. These modifications consist of steel double angle braces or concrete shear walls placed at some of the frames in the building.
Date: January 1, 1995
Creator: Miller, C.A.; Costantino, C.J.; Zhu, Y.; Wang, Y.K.; Shteyngart, S.; Xu, J. et al.
Partner: UNT Libraries Government Documents Department