Recent Revisions of SRP 3.7 and 3.8

During U.S. Nuclear Regulatory Commission (NRC) reviews of Design Certifications (DC) and Combined License (COL) applications, the NRC staff identified several technical issues related to seismic analysis and structural design of the containment and other seismic Category I structures and foundations. These technical issues resulted in a need of improved technical guidance to facilitate reviews of future DC and COL applications. NUREG-0800, “Standard Review Plan (SRP)”, Sections 3.7 and 3.8 provide guidance related to the review of seismic analysis and structural design. NUREG-0800 SRP Sections 3.7 and 3.8 have been revised recently in an effort to enhance NRC staff guidance for the review of future DC and COL applications. SRP Sections 3.7 and 3.8 have not been revised since 2007. Recent revisions of these Sections have been completed in 2013, except for SRP 3.7.1, only a “DRAFT” revision was completed in 2013. The objective of this paper is to briefly describe the important technical issues that presented technical challenges to the applicants during the NRC staff review process of DC and COL applications, and the proposed enhancements to the specific Sections of SRP 3.7 and 3.8. The paper presents complete details of the recent revisions of NUREG-0800 SRP Sections 3.7.1, 3.7.2, 3.7.3, 3.8.1, 3.8.3, 3.8.4, and 3.8.5.

Development of Target Power Spectral Density Functions Compatible With Design Response Spectra

For seismic analysis of nuclear structures, synthetic acceleration time histories are often required and are generated to envelop design response spectra following the U.S. Nuclear Regulatory Commission, Standard Review Plan (SRP) Section 3.7.1. It has been recognized that without an additional check of the power spectral density (PSD) functions, spectral matching alone may not ensure that synthetic acceleration time histories have adequate power over the frequency range of interest. The SRP Section 3.7.1 Appendix A provides a target PSD function for the Regulatory Guide 1.60 horizontal spectral shape. For other spectral shapes, additional guidance on developing the target PSD functions compatible with the design spectra is desired. This paper presents a general procedure for the development of target PSD functions for any practical design response spectral shapes, which has been incorporated into the recent SRP 3.7.1, Revision 4.

Method for Estimating Maximum Response for Seismic Design of Multiple Supported Elastic-Plastic Piping Systems

This study describes a simple method to estimate the maximum response in the seismic response analysis of multi-input nonlinear system. There are many studies on the response analysis of a system having nonlinear properties, such as elasto-plastic characteristic, but they are intended for the one input system because they cannot be applied to multi-input system. On the other hand, a simple method for estimating the multi-input response analysis can also be proposed, which is applied to a linear system, but they cannot be applied to a nonlinear system. However, the importance of seismic design in consideration of both nonlinear and multi-input problems has been increasing in recent years. Therefore, we propose a simple method for estimating the maximum response of multi-input system with elasto-plastic characteristic in the present study.

Probabilistic Assessment of Innovative Mitigating Measures for Buried Steel Pipeline–Fault Crossing

A methodology is presented on assessing the effectiveness of flexible joints in mitigating the consequences of faulting on buried steel pipelines through a comprehensive analysis that incorporates the uncertainty of fault displacement magnitude and the response of the pipeline itself. The proposed methodology is a two-step process. In the first step the probabilistic nature of the fault displacement magnitude is evaluated by applying the Probabilistic Fault Displacement Hazard Analysis, considering also all pertinent uncertainties. The second step is the “transition” from seismological data to the pipeline structural response through the fault displacement components as the adopted vector intensity measure. To mitigate the consequences of faulting on pipelines, flexible joints between pipeline parts are proposed as innovative measure for reducing the deformation of pipeline walls. Thus, the mechanical behavior of continuous pipelines and pipelines with flexible joints is numerically assessed and strains are extracted in order to develop the corresponding strain hazard curves. The latter are a useful engineering tool for pipeline – fault crossing risk assessment and for the effectiveness evaluation of flexible joints as innovative mitigating measures against the consequences of faulting on pipelines.

Performance-Based Analysis of Coupled Support Structures and Piping Systems Subject to Seismic Loading

The prevailing lack of proper and uniform seismic design guidelines for piping systems impels designers to follow standards conceived for other structures, such as buildings. The modern performance-based design approach is yet to be widely adopted for piping systems, while the allowable stress design method is still the customary practice. This paper presents a performance-based seismic analysis of petrochemical piping systems coupled with support structures through a case study. We start with a concept of performance-based analysis, followed by establishing a link between limit states and earthquake levels, exemplifying Eurocode and Italian prescriptions. A brief critical review on seismic design criteria of piping, including interactions between piping and support, is offered thereafter. Finally, to illustrate actual applications of the performance-based analysis, non-linear analyses on a realistic petrochemical piping system is performed to assess its seismic performance.

Instantaneous Phase Detection for Performance Verification of Tuned Mass Dampers

Vibration control using tuned mass damper (TMD) for civil structures has been widely accepted and used in buildings and bridges. However, the TMD provides a frequency-dependent damping for the primary structure. The control effectiveness of TMD will vary with the frequency content of the excitation. A method to verify the control performance of TMD is lack in the literatures. In this study, two simple indicators were developed to judge the TMD control performance based on the theoretical derivation, which indicates the maximum power flow is occurred when the TMD stroke lags the structural displacement by ninety degree. The proposed indicators were verified by numerical simulation. The results show the proposed indicators can judge the effective of TMD correctly. In addition, the waveform of the instantaneous phase is helpful to adjust the TMD stiffness to the right value.

An Experimental Study on Basic Characteristics of a Magneto-Rheological Grease Damper

As one of the semi-active vibration control devices for mechanical or civil structures, magneto-rheological fluid dampers have been enthusiastically studied and developed since the 1990s. A new magneto-rheological material for such dampers has been developed to provide a practical solution to the significant common drawback of sedimentation of ferromagnetic fine particles in the fluid. Industrial grease is used as the dispersion medium in this material. The thickener to be added in the grease to control the rheological properties seems to prevent separation of the particles from the dispersion medium. Several performance tests were carried out with a proto-type of the damper with the newly developed magneto-rheological grease, namely, the magneto-rheological grease damper. Based on the test results, the energy dissipation capabilities of the damper and the basic characteristics of the magneto-rheological grease were verified to provide semi-active vibration control. Moreover, the analytically-derived design formulae for the damper were improved on the basis of the test results.

Effects of Soil-Structure Interaction on the Response of a Structure With Tuned Mass Dampers

This paper aims at examining the effects of soil-structure interaction (SSI) on the response of a structure which is equipped with multiple tuned mass dampers (MTMD) and founded on multiple soil layers overlying bedrock. Closed-form solutions have been obtained for the entire system, which consists of a shear beam type superstructure, multiple tuned mass dampers, and multiple soil layers overlying bedrock, while subjected to ground motion. The proposed formulations simplify the problem in terms of well-known frequency ratios, mechanical impedance and mass ratio, which can take into account the effects of SSI, mass ratio of the MTMD at each excitation frequency and damping ratio in the entire system. These formulations are capable of explicitly interpreting the major dynamic behavior of a structure equipped with multiple tuned mass dampers and interacting with the multiple soil layers overlying bed rock. The SSI effects on the dynamic response of a tuned-mass-damped structure as a result of multiple soil layers overlying bedrock were extensively investigated through a series of parametric studies.

Basic Study on Dynamic Reliability of Machinery and Piping System Supported by Elasto-Plastic Supports With Gaps

In this study, the vibrational behavior of piping systems supported by elasto-plastic dampers with gap supports was considered. First, an analytical model of L-type piping systems subjected to white noise was derived, including the nonlinear characteristics of the elasto-plastic dampers and gap supports. After the stress, energy absorption, and other parameters were calculated for many inputs, the dynamic reliability was calculated based on random theory. Optimization of the support locations was investigated. Finally, the effects of a gap support on the dynamic reliability were investigated.

Semi-Active Control of Structural Systems With an Output Emulation Method Based on a Quadratic Error Function

A semi-active control method based on a controlled output of a targeted active control law is proposed in the study. As a conventional method, a semi-active control law based on the targeted active control input, e.g., a clipped optimal control and its related methods, is widely used for the vibration control of structural systems. In the present study, on the other hand, the controlled output of the targeted active control law is used as the reference of the semi-active control. The semi-active control strategy is referred to as “output emulation approach” and the authors showed a method based on the output emulation approach based on the predicted controlled output by assuming the targeted active control as the LQ optimal control law in the previous study. In this paper, a new output emulation semi-active control method with a quadratic error function between the controlled output signal of the semi-active control system and that of the targeted active control system. The semi-active control law minimizing the quadratic error function is obtained as a bang-bang type switching of the variable damping coefficient of the semi-active control device. The targeted active control law is defined as a state-space control with a constraint on the closed-loop pole placement. Design parameters to determine the region of the pole placement of the targeted active control system are adjusted so that the semi-active control based on the proposed output emulation approach is optimized. The effectiveness of the proposed approach is shown with a simulation example.