ASME Conference Presenter Attendance Policy and Archival Proceedings

2014;():V008T00A001. doi:10.1115/PVP2014-NS8.

This online compilation of papers from the ASME 2014 Pressure Vessels and Piping Conference (PVP2014) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Seismic Engineering: Base Isolation and Structural Control Technology

2014;():V008T08A001. doi:10.1115/PVP2014-28014.

Laboratory experiments play a critical role in earthquake engineering research for seismic safety evaluation of civil engineering structures. Real-time hybrid simulation provides a viable alternative for shake table testing to evaluate seismic performances of structures with rate-dependent seismic devices. Servo-hydraulic actuators play a vital role in a real-time hybrid simulation to maintain the boundary condition between the analytical and experimental substructures. Compensation of actuator delay is critical to minimize synchronization error from actuator delay and to achieve a successful real-time hybrid simulation. Research on how actuator delay can affect the real-time hybrid simulation involving viscous fluid damper is presented in this study. It is demonstrated that although the viscous fluid damper can help stabilize the real-time hybrid simulation with actuator delay, the experimental results need to be interpreted appropriately to evaluate the performance of viscous fluid damper for seismic hazard mitigation.

Commentary by Dr. Valentin Fuster
2014;():V008T08A002. doi:10.1115/PVP2014-28132.

A load combination scheme for seismic response calculation of multi-degree-of-freedom (MDOF) piping systems with friction characteristics to multiple support excitations is presented. This scheme has an advantage, such that the “response reduction factor” due to friction is taken into account by use of a stationary random vibration theory approach. Using a simple and analytical 5DOF piping system with friction characteristics to two support excitations, combination law is supplied to various friction characteristics and the maximum responses of piping is calculated. From these calculation results, it is clear that the maximum acceleration responses of piping systems calculated by the proposed scheme are reasonable compared with those by the numerical simulations.

Commentary by Dr. Valentin Fuster
2014;():V008T08A003. doi:10.1115/PVP2014-28133.

A number of artificial earthquake ground motions compatible with time-frequency characteristics of recorded actual earthquake ground motions as well as the given target response spectrum are generated using wavelet transform. The coefficient of variation (C.O.V..) of maximum displacement on elasto-plastic SDOF systems excited by these artificial ground motions are numerically evaluated.

Commentary by Dr. Valentin Fuster
2014;():V008T08A004. doi:10.1115/PVP2014-28161.

Structural health monitoring of RC structures under seismic loads has recently attracted dramatic attention in the earthquake engineering research community. In this paper, a piezoceramic-based device called “smart aggregate” was used for the health monitoring of a two stories one bay RC frame structure under earthquake excitations. The RC moment frame instrumented with smart aggregates was tested using a shake table with different ground excitation intensities. The distributed piezoceramic-based smart aggregates embedded in the RC structure were used to monitor the health condition of the structure during the tests. The sensitiveness and effectiveness of the proposed piezoceramic-based approach were investigated and evaluated by analyzing the measured responses.

Commentary by Dr. Valentin Fuster
2014;():V008T08A005. doi:10.1115/PVP2014-28192.

This paper focuses on investigating the effects of soil-structure interaction (SSI), higher modes, and damping on the response of a mid-story-isolated structure founded on multiple soil layers overlying bedrock. Closed-form solutions were obtained for the entire system, which consists of a shear beam type superstructure, seismic isolator, and multiple soil layers overlying bedrock, while subjected to ground motion. The proposed formulations simplify the problem in terms of well-known frequency and mechanical impedance ratios that can take into account the effects of SSI, higher modes, and damping in the entire system, and be capable of explicitly interpreting the major dynamic behavior of a mid-story-isolated structure interacting with the multiple soil layers overlying bed rock. The SSI effects on the dynamic response of a mid-story-isolated structure as a result of multiple soil layers overlying bedrock were extensively investigated through a series of parametric studies and physically explained by virtue of derived formulations. In addition, the results of numerical exercises show that higher damping provided by the isolator may provoke higher mode response of the superstructure; that the lower structure below the isolator may have significantly larger deformations compared to those of the upper structure above the isolator; and that isolator displacements may be amplified by the SSI effects while compared to those of mid-story-isolated structures with fixed-base.

Topics: Damping , Soil
Commentary by Dr. Valentin Fuster
2014;():V008T08A006. doi:10.1115/PVP2014-28346.

According to the statistics of the World Bank between years 1970–2010, most economy losses caused by disasters in rich countries were due to floods and earthquakes. The East Asia was the most disastrous area in terms of the death toll caused by earthquakes, which proved that the earthquake is unpredictable. To cope with the crisis of the rise of the sea level, the concept of Marine Cities has been proposed. The most famous one among these concepts is the Dutch amphibious house. People living in earthquake and flood prone areas should be aware of the threat from oceans. Therefore, Ministry of Interior in Taiwan passed the rule 4 No. 2 in the chapter of the design and construction regulations to allow the use of high-raised buildings for reducing life and property loss. Furthermore, the most threatening natural hazards we are facing over a long period of time are floods and earthquakes. When are focusing on the flood resistant buildings in flood-prone areas, we should also aim at the prevention of earthquake disasters.

The purpose of this study is to simulate the seismic behavior of the high-raised structures with different water levels, which are capable of flood resistance. We also propose a new seismic isolation system for these structures and study its efficiency in protecting these types of structures from earthquake damage. It appears from experimental results that the seismic responses of high-raised houses have been significantly reduced by the proposed device. Experimental results also disclosed that the proposed concept in this study is feasible for protecting structures in lowlands from damage resulting from floods as well as earthquakes.

Commentary by Dr. Valentin Fuster
2014;():V008T08A007. doi:10.1115/PVP2014-28358.

This paper proposes the mechanism using lever and attached weight at point of action of lever, installed horizontally in the space between two floor slabs for the purpose of seismic response control of a base isolated building. This mechanism produces the dynamic mass related to the relative displacement between two slabs. The generated dynamic mass is shown to be effectiveness for the seismic response control of base isolated building from the point of view of the enlarged mass ratio of dynamic mass to mass of base isolated building.

Commentary by Dr. Valentin Fuster
2014;():V008T08A008. doi:10.1115/PVP2014-28611.

The concept of periodic materials, based on solid state physics theory, is applied to earthquake engineering. The periodic material is a material which possesses distinct characteristics that do not allow waves with certain frequencies to be transmitted through; therefore, this material can be used in structural foundations to block unwanted seismic waves with certain frequencies. The frequency band of periodic material that can filter out waves is called the band gap, and the structural foundation made of periodic material is referred to as the periodic foundation. In designing a periodic foundation, the first step is to match band gaps of the periodic foundation with the natural frequencies of the superstructure. This is an iterative process. Starting with a design of the periodic foundation, the band gaps are identified by performing finite element analyses using ABAQUS. This design process is repeated until the band gaps match natural frequencies of the superstructure, and the field tests of a scaled specimen are conducted to validate the design. This is an on-going research project. Presented in this paper are the preliminary results, which show that the three dimensional periodic foundation is a promising and effective way to mitigate structural damage caused by earthquake excitations.

Commentary by Dr. Valentin Fuster
2014;():V008T08A009. doi:10.1115/PVP2014-28856.

In this study, a design of a regenerative damper for low-frequency applications, such as vibration suppression of long period infrastructures, tanks and pipings, and maritime and offshore structures, is presented. In this design, the low-frequency input motion to the damper is transformed to a high-frequency motion of piezoelectric cantilever oscillators by mechanical switching, so that the input work into the damper during the loading phase induces the free vibration of the oscillator. The mechanical energy of the free vibration is converted to the electric energy by a high efficiency interfacing circuit. In this paper, a conceptual model is mathematically formulated and tested to evaluate the potential performance of the proposed idea. It is shown that the combination of the mechanical switching with a circuit switching interface technique can expect the enhancement of the energy regeneration efficiency up to 30%.

Topics: Dampers
Commentary by Dr. Valentin Fuster
2014;():V008T08A010. doi:10.1115/PVP2014-28989.

The authors propose a Magneto-Rheological (MR) fluid damper that utilizes multi pole electromagnets in order to control variable damping effect such as a semiactive damper. The damper consists of a piston, a cylinder, a by-pass pipe, 8 electromagnets, and MR fluid. The electromagnets are installed octagonal around the pipe. When each electromagnet can control both of the magnetic flux density and direction, resisting force can be switched by several types of magnetic field such as artificial orifice. The test damper is manufactured. Resisting force characteristics are measured by using a shaking actuator. Finally, dynamic performance of the damper is confirmed experimentally.

Commentary by Dr. Valentin Fuster
2014;():V008T08A011. doi:10.1115/PVP2014-29000.

This paper provides a part of series of “Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities”. This part shows improvements of seismic isolator design method applied to nuclear power facilities. The proposed improvement design methods consist of the following two items.

One is an improvement of design method for axial stress in a laminated rubber bearing. Largely different natural frequency in vertical and horizontal direction of the seismic isolator may need a special consideration to combine the design seismic loads in different directions. Therefore isolator’s behavior under multiple direction earthquake is studied, and an improved design method is proposed in the axial stress in a laminated rubber bearing.

The other is a reasonable design method for seismic isolator joints. A seismic isolator joint is considered to be one of the key factors for assuring seismic integrity of the seismic isolation system for nuclear power facilities. As a series of design method of seismic isolators, evaluation method of axial force of anchor bolts, among various parts of joints, under design level seismic load is studied and improved method is proposed to confirm the structural behavior for a better performance of the system.

Commentary by Dr. Valentin Fuster
2014;():V008T08A012. doi:10.1115/PVP2014-29001.

This paper presents a part of “Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities”. Ultimate behavior and failure modes of full-scale Lead Rubber Bearings (LRBs) of 1600mm diameter were described herein based on a series of the break tests which conducted on 11 LRBs to obtain a break surface. The shear break tests were monotonically conducted on 3 full-scale LRBs under various axial stresses. Then the monotonic tensile break tests were performed on 5 full-scale LRBs with or without constant offset shear strain. In addition, 3 half-scale LRBs of 800mm diameter were also tested to study the size effect and the ultimate shear behavior in significantly high compression. In the evaluation on the test results, the ultimate strain and stress were firstly summarized to define a break surface for the real-scale LRBs. Then the LRBs broken in the testing were carefully observed to evaluate their failure modes. It was found that the full-scale LRBs exhibited good seismic performance in horizontal ductility capacity and vertical load carrying capacity. It seems that the ultimate properties and the failure modes were basically less affected by the scale of the models.

Commentary by Dr. Valentin Fuster
2014;():V008T08A013. doi:10.1115/PVP2014-29002.

This paper provides a series comprising the “Development of Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities”. Part 6 presents scaled tests for Lead Rubber Bearing (LRB) newly developed for this project.

Following tests are performed to obtain the basic characteristics of LRB,.

(1) Horizontal and Vertical Simultaneous Loading Test:

LRBs with diameter of 250mm are tested dynamically under simultaneous axial and lateral loading. The hysteresis characteristics is not changed under compressive load although it is changed under tensile load.

(2) Basic Break Test:

LRBs with a diameter of 800mm are tested statically under various combinations of axial and lateral forces. The hysteresis characteristics model of LRB is determined by this test. It is confirmed that the breaking strain of LRB under compression load exceeds 450%.

(3) Horizontal Hardening and Vertical Softening Test:

For LRBs with a diameter of 1200 mm, 75% scale of actual LRB are tested statically for horizontal hardening and vertical softening regions. It is confirmed that the hysteresis model which is developed by smaller LRBs is applicable to these large scale models.

Commentary by Dr. Valentin Fuster
2014;():V008T08A014. doi:10.1115/PVP2014-29006.

This paper provides a part of the series “Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities.” This part shows the fundamental properties of full-scale lead rubber bearings with 1600 mm diameter based on break tests. The following results are mainly obtained.

One: The deformations and the acting loads of the full-scale specimens were accurately obtained up to break by the measurement system for the break tests.

Two: The fundamental properties for the full-scale lead rubber bearings with a large-diameter lead plug were obtained by the basic property tests. The load-displacement relations were stable and similar basic properties were obtained among the specimens.

Three: The result of shear break tests showed that the hardening property of the specimens had a certain harmony with the hardening stiffness model which was used in the seismic response analysis to investigate the safety margin for severe earthquakes beyond design basis earthquakes of nuclear power facilities. The effect of axial pressure on hardening property was not specifically observed. The evaluated linear strain limit was larger than 250% for every specimen.

Four: The softening property of the specimens was obtained from the tensile break tests. The axial stress of tensile yield was approx. 1.4 MPa and the axial stress did not show any negative gradient at least up to approx. 10% axial strain after the tensile yield even with offset shear strains.

Five: The tensile force acting on the bolts which secure the specimen to the testing machine was lower than the estimated tensile force at shear break, which indicates tensile force was conservatively calculated to maintain safety in the design for foundation of lead rubber bearings.

Commentary by Dr. Valentin Fuster
2014;():V008T08A015. doi:10.1115/PVP2014-29008.

In the Great East Japan Earthquake (GEJE), the lot of seismic damage in hanging type mechanical structure with low damping occurred by a long duration earthquake. Therefore, the industrial function stopped at many facilities. Moreover, the fall from a ceiling of a mechanical structure and the falling off of some elements in a mechanical structure were connected for outbreak of the secondary damage such as a cut of an evacuation route. This study has been carried the seismic safety improvement of mechanical structure in long duration earthquake from an analytical and experimental approach. In this paper, the fundamental experimental results of falling mechanism of hanging type mechanical structure from a ceiling is shown, and analytical results using nonlinear model with hysteresis damping is described.

Commentary by Dr. Valentin Fuster
2014;():V008T08A016. doi:10.1115/PVP2014-29009.

This paper is a part of the series “Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities.” This part presents a break test plan and development of a test machine for a full-scale lead rubber bearing (LRB). Application of seismic base-isolation systems using LRBs of 1600 mm in diameter to reactor building has been considered for the purpose of enhancing seismic safety. It is important to obtain the ultimate properties of isolators in order to estimate the seismic safety margin of seismic base-isolated structures against a beyond design-basis earthquake events. Recent studies reveal that the scaled effect appears on the ultimate properties of seismic rubber bearings. However, because of the limitation of the loading capabilities of loading machines, the ultimate property of such a large scale LRBs has not been confirmed.

In this study, the break tests for LRBs of 1600 mm in diameter is planned on the basis of estimation that refers to previous studies on break tests for small-scale LRBs and natural rubber bearings. The world-largest class test machine is designed and constructed to conduct static break tests for the full-scale LRBs. Furthermore, the performance of the test machine is evaluated from test results including those for break tests.

Commentary by Dr. Valentin Fuster
2014;():V008T08A017. doi:10.1115/PVP2014-29040.

This paper provides a part of series of “Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities”. This part shows an evaluation of seismic isolator design established in this project where several methods are newly developed. The major four accomplishments are as follows.

One: establishment of design earthquake specially considered for seismically isolated nuclear power facilities. The design earthquakes are made to fit multiple target spectra with different damping factors considering a building, equipment and seismic isolators for more precise response analyses.

Two: design and development of a high-performance seismic isolator. Against the large design earthquakes, a seismic isolator is newly developed which has a large diameter lead plug for more damping; the isolators were actually manufactured and tested.

Three: seismic response analyses for seismically isolated nuclear power plants. Light water reactors are designed where the structural characteristics of the seismic isolation system is reflected.

Four: evaluation of thermal effects on seismic isolators by a long-duration earthquake. Considering a long-duration earthquake, the heat generation phenomenon in the lead plug is analytically evaluated to ensure the lead plug’s damping performance.

By introducing these accomplishments, the realistic design of a seismically isolated nuclear power plant is achieved.

Commentary by Dr. Valentin Fuster

Seismic Engineering: European Research on Structural Safety of Industrial Facilities

2014;():V008T08A018. doi:10.1115/PVP2014-28563.

This paper deals with the effectiveness of two isolation system for the seismic protection of elevated steel storage tanks. In particular the performance of High Damping Rubber Bearings and Friction Pendulum isolators has been analyzed. As case study an emblematic example of elevated tanks collapsed during the Koaceli Earthquake in 1999 at Habas Pharmaceutics plant in Turkey has been considered. A time-history analysis conducted using lumped mass models demonstrated the high demand in terms of base shear required to the support columns and their inevitable collapse due to the insufficient shear strength. A proper design of HDRB and FPS isolator and a complete non-linear analysis of the isolated tanks proved the high effectiveness of both isolation systems in reducing the response of the case tank. Actually, a reduced level of displacements of isolators and a reduced level of convective base shear obtained with the second isolation typology, suggested the used of FPS isolators rather than HDRB.

Commentary by Dr. Valentin Fuster
2014;():V008T08A019. doi:10.1115/PVP2014-28703.

The load bearing behavior of piping systems depends considerably on support distances and stiffness as well as cross section characteristics.

Stiffness of supports can often be defined only with difficulty by applying simplified procedures or guidelines based on assumptions. Load cases can be estimated quite well, but the safety assessment of a piping system can only be as reliable as the system model can realistically describe the present support stiffness or imperfections e.g. local wall thinning. As a consequence, the prediction of the system response may be poor. It is likely that calculated frequencies differ from natural frequencies determined experimentally. These frequency shifts lead to unrealistic predictions of stress analysis.

Examples for overestimations and underestimations of stress analysis are given regarding the load case earthquake, depending on whether the frequency shift runs into or out of the plateau of the applied floor response spectrum.

The influence of local wall thinning on modal characteristics is investigated. Conservative estimations of the influence on the load bearing behavior regarding severe local wall thinning are given. For fatigue checks the linear response of an experimental piping system is calculated and safety margins are demonstrated by comparing calculated with experimental results.

Commentary by Dr. Valentin Fuster
2014;():V008T08A020. doi:10.1115/PVP2014-28846.

The behavior of steel pipe junctions (Tees) subjected to strong loading in the presence of internal pressure is examined in the present study. The analysis is based on a set of monotonic and cyclic out-of plane bending tests under constant and increasing amplitude displacement-controlled loading schemes leading to low-cycle fatigue failure.

Rigorous finite element models are developed to support the experiments, accounting for detailed dimensional measurements and material testing results obtained prior to testing. A parametric analysis is also conducted focusing on the effect of the geometrical characteristics on the overall junction behavior. The performance of the Tee-junctions with varying geometries under out-of plane bending, in-plane bending and axial loading is also examined numerically accounting for the presence of internal pressure.

Topics: Steel , Pipes , Junctions
Commentary by Dr. Valentin Fuster
2014;():V008T08A021. doi:10.1115/PVP2014-29010.

This paper describes the SILER (Seismic-Initiated event risk mitigation in LEad-cooled Reactors) Project results obtained so far in the design of the seismic isolation system of two nuclear power plants: the ELSY configuration for the LFR (Lead-Cooled Fast Reactor) design and the MYRRHA configuration for the accelerator-driven systems (ADS).

The seismic protection of the nuclear buildings by means of seismic isolation has been chosen in order to minimize changes to the standard design of the civil works and internal components of the Nuclear Power Plant. The work led to the identification of the optimal design solution, in terms of type and location of seismic devices, to achieve compliance to the floor response acceleration spectra in horizontal and vertical direction, with levels of horizontal displacements not exceeding the maximum acceptable values for structural and non-structural elements.

The isolators studied in the project are of the type elastomeric, both High Damping Rubber Bearings and Lead Rubber Bearings; moreover the adoption of a fail-safe system to limit the horizontal isolator deformation in case of beyond design earthquakes is studied.

Topics: Design
Commentary by Dr. Valentin Fuster

Seismic Engineering: Pipe Components and Fittings Under Strong Cyclic and Seismic Loading

2014;():V008T08A022. doi:10.1115/PVP2014-28116.

Severe damages in aboveground storage tanks (AST) have been often experienced due to earthquakes in Japan and Taiwan. In this paper, earthquake damages of ASTs which occurred for the last several decades are reviewed. These are damages in the 1964 Niigata Earthquake, the 1978 Miyagi Earthquake, the 1983 Sea of Japan Earthquake, the 1995 Kobe Earthquake, the 2003 Hokkaido Earthquake and the 2011 Great East Japan Earthquake in Japan. Damages of ASTs in the 921 Earthquake in Taiwan are also included in this paper. The damages of ASTs can be classified into 3 types in accordance with the causes. These are the impulsive motion due to a high frequency earthquake, the sloshing motion due to a low frequency earthquake and the tsunami attack. In the impulsive motion, buckling of sidewall plates and uplift of sidewall-to-bottom joints occurred. In the sloshing motion, sinking of floating roofs into liquid and buckling of sidewall-to-roof joints occurred. In the tsunami attack, ASTs moved and overturned to leak oil.

Commentary by Dr. Valentin Fuster
2014;():V008T08A023. doi:10.1115/PVP2014-28234.

In Japan, seismic assessments considered aging phenomena have been conducted as part of activities for aging measures of nuclear power plants. In the activities, it is found that FAC (Flow Accelerated Corrosion) of piping components made of carbon steel impact on seismic integrity because of decreasing a cross section of piping. Therefore, many destructive tests of piping have been conducted in Japan and the other countries.

At first, factors on which did not focus in the past destructive test have been extracted in this investigation. displacement controlled cyclic tests of piping components which focused on extracted factors have been conducted additionally in order to provide enough test data for past destructive test data of piping components. Moreover, fatigue curve for practical evaluation of piping components made of carbon steel has been settled after obtained test data were put in order including past destructive test data of piping components from a point of fatigue.

Commentary by Dr. Valentin Fuster
2014;():V008T08A024. doi:10.1115/PVP2014-28805.

Low-cycle fatigue experiments of short radius elbows were conducted and the recorded responses were compared with the long radius elbow responses from literature. Elbow components are widely used in piping systems in energy and chemical industries; however, the fatigue failure prediction of elbows remains a challenge. Additionally, the selection criteria between a long or short radius elbow merely considers the long radius elbow as standard, and to use short radius elbows only when spacing requirement prohibit a long radius elbow. The ASME design code provides some guidance for fatigue design of elbows but it is not known if the short radius elbow fatigue failures can be predicted. Hence, low-cycle fatigue experiments of short radius elbows were conducted and force, displacement, and strain data under cyclic loading were recorded. The recorded fatigue responses were critically analyzed for understanding the difference in fatigue lives between long and short radius elbows. These results are presented and discussed in the paper.

Commentary by Dr. Valentin Fuster
2014;():V008T08A025. doi:10.1115/PVP2014-28819.

The Transition Break Size analysis is given in Draft Regulatory Guide 1216 for assessment of ECCS requirements. There are additional analyses required for seismic considerations for beyond design basis seismic loading. The beyond design basis loading was for seismic event with a probability of occurrence of 1e−6 per year, whereas safe-shutdown earthquake loading is typically closer to a probability of 1e−4 events per year. The peak-ground accelerations for US plants are typically in the 0.1 to 0.2 g’s range for SSE loading, while the 1e−6 seismic loading may be about 3 times higher (depending on site specific seismic hazard curves).

A simplified method was created for the TBS seismic consideration analysis, which is given in Appendix A and B in the Draft Reg Guide. The technical basis is in NUREG-1903. The TBS analysis approach utilizes a simple method for scaling the seismic stresses from the SSE to 1e−6 loading, allowing for a bilinear stress correction (linear to yield of the material and an ultimate point consistent with uncracked seismic tested pipe results). A best-estimate fracture analysis is then conducted using the ASME Section XI Service Level D flaw size, but a best-estimate fracture analysis uses more realistic material properties and more accurate fracture analyses than the ASME Code.

In this paper, the TBS flaw size was calculated by the Draft Regulatory Guide approach for the Atucha II nuclear plant in Argentina that is about to start up. Additionally a full 3D FE model of the plant including the whole NSSS, containment building, and supports between the building and the NSSS components was developed. Circumferential surface cracks were put in the nonlinear time-history FE model at the highest stressed locations in the primary pipe loop to determine the depth of the flaw that would fail at the 1e−6 seismic excitation to the plant building. This was done to assess the margins in the flaw size for the TBS analysis, and also characterize the magnitude of the LOCA.

Where the TBS simplified model showed that a surface flaw of 0.709 and 0.669 of the thickness for the RPV/hot-leg and pump/cold-leg (respectively) and 270-degrees around the circumference could be tolerated, the full 3D FE analysis showed that even a surface crack of 90-percent of the thickness and 270-degrees around the circumference would not reach crack initiation for the material used in this plant with its seismic hazard curve. The information developed here may also be useful for assessing the piping integrity of a plant once it has exceeded the Service Level D limits of the ASME Code.

Topics: Design , Pipes
Commentary by Dr. Valentin Fuster
2014;():V008T08A026. doi:10.1115/PVP2014-29112.

According to the seismic risk assessment results presented in the Final Safety Analysis Report (FSAR) for a nuclear power plant in Taiwan, the failure of Residual Heat Removal (RHR) piping system occurs in both of the two accident sequences with the highest contributions for core damage. The seismic performance of RHR piping system depends on the capacity of its components, such as supports, flanged joints and reducers. For the need of seismic response-history analysis of RHR piping systems, we developed detailed numerical models of flanged joint and reducer using finite element analysis software (ABAQUS and SAP2000). The proposed finite element models were verified by the experimental results. The pure bending tests with four-point cyclic loading were conducted for sample flanged joint and reducer to investigate their mechanical behaviors. The displacement and rotation responses identified from the tests are in good agreement with the results of numerical analysis. A preliminary simplified model of flanged joints was also proposed in this study to improve the efficiency of numerical analysis for RHR piping system.

Commentary by Dr. Valentin Fuster
2014;():V008T08A027. doi:10.1115/PVP2014-29113.

The objective of this study is to build a credible numerical model using SAP2000 for fragility analysis of RHR piping system, and to establish the load pattern of a cyclic loading test to identify the seismic vulnerability of the system. The RHR piping system selected for test and numerical analysis is duplicated from a part of the RHR system in a nuclear power plant (NPP) in Taiwan, and this part is distributed between the floor of the reactor building (RB) to the wall of the reinforced concrete containment vessel (RCCV) of the sample NPP.

The numerical model for the sample RHR piping system was developed, and the nonlinear response-history analysis was conducted using input motions compatible with the floor response spectrum at the anchor points of the sample piping system subjected to Safe Shutdown Earthquake (SSE). Based on the distribution of resultant inertial forces and the responses at critical locations of the piping system under SSE, the magnitudes and locations of the equivalent concentrated static loads were determined and used in the pushover analysis to estimate the capacity of the RHR piping system. The numerical results will be verified by the aforementioned cyclic loading test. More studies are on the way including shaking table test and fragility analysis for the sample piping system to further identify the seismic performance and risk of the system.

Commentary by Dr. Valentin Fuster

Seismic Engineering: Risk Assesment of Components and Industrial Facilities

2014;():V008T08A028. doi:10.1115/PVP2014-28177.

Seismic risk assessment of industrial plants is of paramount importance to ensure adequate design against earthquake hazards. Seismic vulnerability of industrial plant components is often evaluated through a fragility analysis to conform to structural safety requirements. Fragility curves of single components are usually developed by neglecting the effect of actual boundary conditions. Thus, an incorrect evaluation of individual fragility curves can affect the overall fragility curve of a system. This may lead to “erroneous” seismic risk evaluation for a plant in comparison with its real state. Hence, it is important to study the effect of uncertainties, introduced at the boundaries when coupling effects are neglected, on the dynamic characteristics of a system.

Along this line, this paper investigates the effects of uncertain boundary conditions on the probability distributions of the dynamic properties of a simple chain-like system with increasing number of degrees of freedom. In order to describe the uncertain boundary condition, a modified version of the well-known β distribution is proposed. Subsequently, the Analytical Moment Expansion (AME) method is employed to estimate the statistical moments of the output random variables as an alternative to more computationally-demanding Monte Carlo simulations. Finally, a preliminary extension of the proposed approach to a realistic piping system connected to a class of broad/slender tanks is discussed.

Commentary by Dr. Valentin Fuster
2014;():V008T08A029. doi:10.1115/PVP2014-28596.

Japan is one of the most advanced countries in earthquake technology. Isolation systems are widely used in large-scale structures such as hospitals and communication centers. For example, an isolated office building has been used as a hub of recovery from accident by Great East Japan Earthquake in Fukushima nuclear power plant. In the meantime, application of probabilistic risk assessment is used for structure of nuclear power plants. In 2006, Regulatory Guide for Reviewing Seismic Design was revised and according to guideline, it is necessary to consider the residual risk1. In addition, seismic isolation systems are expected to be used for nuclear power plants. Recently, the risk of isolation system’s failure needs to be assessed in case of large ground motion. This paper deals with probabilistic approach on seismic response of an isolated structure. Consequently, sensitivity analysis is carried out. Then, as nonlinear behavior in rubber bearings occurs during huge earthquake, it has to be considered in the sensitivity analysis.

Commentary by Dr. Valentin Fuster
2014;():V008T08A030. doi:10.1115/PVP2014-29116.

Seismic probabilistic risk assessment (SPRA) has been widely used to compute the frequencies of core damage and release of radiation of a nuclear power plant (NPP). In 2011, Huang et al. (2011a, 2011b) published a SPRA methodology with the following characteristics different from the widely used Zion method: (a) seismic fragility curves are defined as a function of structural response parameters, such as floor spectral acceleration and story drift; (b) nonlinear response-history analysis is used to estimate statistical distributions of seismic demands for structural and non-structural components of NPPs; (c) Monte Carlo simulation is used to determine damage states of structural and non-structural components. In the study presented in this paper, the seismic risk of a sample NPP was evaluated using the methodology of Huang et al. (2011a, 2011b). The seismic risk was quantified using the annual frequency of unacceptable performance defined by a sample accident sequence for a sample NPP. The values of seismic risk computed using the methodology of Huang et al. (2011a, 2011b) and Boolean Algebra were compared to evaluate the accuracy and efficiency of the methodology of Huang et al. (2011a, 2011b). The two procedures generate similar risk values and the methodology of Huang et al. (2011a, 2011b) is more efficient than the procedure using Boolean Algebra.

Commentary by Dr. Valentin Fuster

Seismic Engineering: Seismic Analysis and Design of Piping Systems

2014;():V008T08A031. doi:10.1115/PVP2014-28183.

Per guidelines for piping system reconciliation such as EPRI NP-6628 (NCIG-14), simplified seismic design methods have been used by nuclear piping designers to deal with small bore piping for many years. These methods are generally based on enveloping the results of rigorous dynamic or conservative static analysis.

Small bore piping is generally more flexible with larger margin in support design comparing to large bore piping. Consequently, Classes 2 & 3 piping less than 2-1/2 inch NPS that is analyzed by a conservative “cookbook method” is excluded from the as-built verification actions in IE Bulletin 79-14. The ASME code’s Subsection NF and B31.1 provide recommended pipe spans by pipe size considering only piping weight; therefore, the seismically qualified piping span must be developed for the peak acceleration of the applicable amplified or floor response spectra.

Simplified seismic analysis method being considered for the Korean nuclear power plants is based on the Load Coefficient Method provided in Appendix N-1225 of ASME Section III. However, since the simplified analysis method involves conservative and enveloping approach in an effort to comply with applicable requirements and results in an excessive number of supports and unrealistically high support loads, the successful implementation largely depends on how the issues related to the excessive conservatism are resolved when determining allowable pipe spans and support design loads of the piping system.

In this paper, simplified engineering equations are presented as a less-conservative approach based on a detailed computer analysis method, which is alternative to the various handbooks and design charts that are based on the conventional hand calculation method.

Commentary by Dr. Valentin Fuster
2014;():V008T08A032. doi:10.1115/PVP2014-28619.

In recent years, earthquakes over design condition were observed in Japan. Confirming the ultimate strength and design safety margin of mechanical components is important for the seismic integrity. This study focused on piping components, and it was one of the most important mechanical components for protecting boundary of coolant. Failure tests of thick-walled piping components for Light Water Reactors (LWRs) described previously in the literature. According to these tests, the failure mode of thick-walled piping components under seismic cyclic loading was low cycle fatigue. However, failure tests have scarcely been performed on thin-walled piping components pressurized at low levels for Fast Breeder Reactors (FBRs).

This paper presents dynamic failure tests of thin-walled piping components in FBRs. Based on the test results, the failure mode, the ultimate strength, and the elastic-plastic behavior are discussed.

Commentary by Dr. Valentin Fuster
2014;():V008T08A033. doi:10.1115/PVP2014-28675.

Piping in a nuclear power plant is usually laid across several floors of a single building or adjacent buildings, and is supported at many points. As the piping is excited by a large earthquake through multiple supporting points, seismic response analysis by multiple excitations within the range of plastic deformation of piping material is necessary to obtain the precise seismic response of the piping. The verification of the dynamic analysis method of piping under an elastic domain, which is excited by multiple seismic inputs, was performed in our study last year and the correspondence of a piping response between an analysis and an experiment have been confirmed [17][18]. However, few experiments under plastic deformation conditions have been performed to verify the validity of multiple excitation analysis under a plastic deformation range. To obtain better understanding of the behavior of piping under a large seismic input, it is important to investigate the seismic response by multiple excitations and to verify the validity of the analytical method by multiple excitation experiments.

This paper reports the validation results of the seismic elastic-plastic time history analysis of piping compared with the results of the shaking test of a 3-dimensional piping model under a plastic deformation range using triple uni-axial shake table. Three directional strains from the analysis and the experiments were compared in order to validate the analysis method. As a result, it is confirmed that the elastic-plastic analysis by time history excitation shows good agreement with the test results.

Topics: Pipes
Commentary by Dr. Valentin Fuster
2014;():V008T08A034. doi:10.1115/PVP2014-28851.

The earthquake-proof safety of piping systems with local wall thinning due to liquid droplet impingement erosion (LDI) was evaluated using a hybrid experiment which has been incorporated a numerical analysis of the whole system with a static loading test of elbow pipe model. Seismic performance effects of wall thinned elbow were clarified by comparing three cases of different thickness elbow models such as no defect, 50% defect and 75% defect. No damage was observed for in-plane and out-of-plane bending of elbows in the 75% condition under a seismic load equal to five times the design basis earthquake required to reach allowable stress level. In addition, torsion buckling occurred and through wall crack penetrated by cyclic loading under eight times large amplitude the above mentioned seismic motion.

Commentary by Dr. Valentin Fuster
2014;():V008T08A035. doi:10.1115/PVP2014-28857.

The authors have developed a new pipe support, which is intended for use as an anchor of piping system in power plants. This anchor type support takes a pipe between two-tiered metal blocks and ideally restraints the pipe movement with six degrees of freedom, namely all directions of the piping movement. The four bolts adequately join the two-tiered metal block of the anchor type support with the pipe that is not subjected to unnecessary stress. The internal shape of the two-tiered metal block is designed to stabilize the pipe firmly by increasing area of contact between the pipe and the support. Developing the four-point support design for the internal shape of the blocks has also reduced the stress on the pipe. The restraint forces and restraint moments of the support have been investigated and the verification testing has been conducted for the restraining capability. The relaxation of the bolted joint over time and thermal influence on the relaxation has been also studied experimentally. Since no welding operation on the pipe is required for installation of this anchor support, reduction of time and labor is expected for both a combination of planning and construction of an anchor on piping system.

Topics: Pipes , Piping systems
Commentary by Dr. Valentin Fuster
2014;():V008T08A036. doi:10.1115/PVP2014-28999.

This paper provides a part of series of “Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities”. Paper is focused on the seismic evaluation method of the multiply supported systems, as the one of the design methodology adopted in the equipment and piping system of the seismic isolated nuclear power plant in Japan.

Many of the piping systems are multiply supported over different floor levels in the reactor building, and some of the piping systems are carried over to the adjacent building. Although Independent Support Motion (ISM) method has been widely applied in such a multiply supported seismic design of nuclear power plant, it is noted that the shortcoming of ignoring correlations between each excitations is frequently misleaded to the over-estimated design.

Application of Cross-oscillator, Cross-Floor response Spectrum (CCFS) method, proposed by A. Asfura and A. D. Kiureghian[1] shall be considered to be the excellent solution to the problems as mentioned above. So, we have introduced the algorithm of CCFS method to the FEM program.

The seismic responses of the benchmark model of multiply supported piping system are evaluated under various combination methods of ISM and CCFS, comparing to the exact solutions of Time History analysis method. As the result, it is demonstrated that the CCFS method shows excellent agreement to the responses of Time History analysis, and the CCFS method shall be one of the effective and practical design method of multiply supported systems.

Commentary by Dr. Valentin Fuster
2014;():V008T08A037. doi:10.1115/PVP2014-29011.

This paper provides a part of the series titled “Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities”. This part shows the failure behavior of crossover piping installed in a seismic isolated plant. The considered crossover piping is supported on one side by an isolated building and by a non-isolated building on the other side. During an earthquake, the piping structure is deformed due to the large relative displacements between the two buildings and at the same time excited by the different building seismic responses. Therefore, the high-pressure crossover piping structure requires both flexibility and strength.

In this study, 1/10 scaled shaking tests and FEM analyses have been performed to investigate the failure behavior of the crossover piping, where both seismic motions and excitations have been taken into account. It was confirmed that the failure occurs at the piping elbow through low cycle fatigue. Moreover, the results of the elastic-plastic response analysis, which simulates an extreme level of excitation corresponding to more than three times the design level, are in good agreement with the test results. The simulation also succeeded in predicting the experimental failure location.

Commentary by Dr. Valentin Fuster
2014;():V008T08A038. doi:10.1115/PVP2014-29012.

This paper, which is part of the series entitled “Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities”, shows the linear seismic response of crossover piping installed in a seismically isolated plant. The crossover piping, supported by both isolated and non-isolated buildings, deforms with large relative displacement between the two buildings and the seismic response of the crossover piping is caused by two different seismic excitations from the buildings. A flexible and robust structure is needed for the high-pressure crossover piping.

In this study, shaking tests on a 1/10 scale piping model and FEM analyses were performed to investigate the seismic response of the crossover piping which was excited and deformed by two different seismic motions under isolated and non-isolated conditions. Specifically, as linear response analysis of the crossover piping, modal time-history analysis and response spectrum analysis with multiple excitations were carried out and the applicability of the analyses was confirmed. Moreover, the seismic response of actual crossover piping was estimated and the feasibility was evaluated.

Commentary by Dr. Valentin Fuster
2014;():V008T08A039. doi:10.1115/PVP2014-29032.

This paper provides a part of the series of “Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities”.

It is assumed the main steam crossover piping is damaged by the ratcheting deformation based on the relative displacement and the inertia load by the earthquake between the buildings and the internal pressure.

This part shows a low cycle ratcheting fatigue test using the scaling model under the combined loadings based on the relative displacement and the inertia load by the earthquake between the buildings and analyses were performed to confirm the failure modes and the fatigue life of the pipe elbow for the fatigue damage of the long-period ground motion.

As a result, the fatigue life under combined loads was sufficiently higher than the design criteria and analyses are good match with the test results. So, it confirmed the structural integrity of the crossover piping.

Commentary by Dr. Valentin Fuster
2014;():V008T08A040. doi:10.1115/PVP2014-29035.

This paper provides a part of series of “Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities” [1]–[4]. This part describes the work schedule of this project and the summary of a seismic design for crossover piping system.

Since the Southern Hyogo Prefecture Earthquake in 1995, a seismic isolated design has been widely adopted for Japanese typical buildings. The Japanese government accepted utilizing seismic isolation technology for nuclear power facilities with the 2006 revision of the “Regulatory Guide for Reviewing Seismic Design of Nuclear Power Reactor Facilities”. Under these backgrounds, the Japan national project with the participation of all electric power companies and reactor vendors has been started from 2008 to develop seismic isolation systems of nuclear power facilities under the support of the Ministry of Economy, Trade and Industry.

In the design of seismic isolated plant, the crossover piping systems, such as Main Steam line and other lines related to the safety system have the important roles for overall plant safety. Therefore, the design of multiply supported piping systems between isolated and non-isolated buildings is one of the major key issues.

This paper focuses on the seismic response analysis of Main Steam crossover piping between seismic isolated Reactor Building and non-isolated Turbine Building. Multiple input response spectra and time history analyses of the crossover piping have been performed and the structural integrity of piping and the validity of the multiple input analysis method have been verified based on comparisons with the results obtained by conventional response spectrum analysis using enveloped floor response spectrum.

Commentary by Dr. Valentin Fuster
2014;():V008T08A041. doi:10.1115/PVP2014-29059.

This study introduces an approach by which to estimate fatigue damage in a three-dimensional piping system under seismic loadings. A hybrid piping system simulator consisting of detailed elbow/tee models and piping line elements was constructed in order to estimate fatigue damage in the piping system. A dynamic non-linear finite element analysis with modified seismic wave inputs was carried out in order to calculate the entire strain profile of the piping system. Fatigue damage due to seismic loading was calculated by Miner’s rule since seismic wave contains several amplitudes of total strain ranges. Several tests reported in previous papers were used in order to verify the validity of the proposed approach for fatigue damage estimation.

Commentary by Dr. Valentin Fuster

Seismic Engineering: Seismic Response and Design of Storage Tanks, Piping and Other Components

2014;():V008T08A042. doi:10.1115/PVP2014-28371.

The importance of safety evaluation for beyond design conditions has come to be required since the accident at the Fukushima Daiichi Nuclear Power Plant as a consequence of the Great East Japan Earthquake. Real simulations of seismic response for the plant structures and components enhance establishment of reasonable design margins and safety evaluation criteria in a situation beyond design-basis accidents. For piping systems, nonlinear seismic response analysis considering plastic deformation of pipe support structures can lead to a safety evaluation based on more rational input values.

This study discussed seismic response of a piping system and its appropriate analysis method when a plastically deformable pipe support structure was subjected to a much larger seismic load than the designed one. Seismic response analyses of the piping system including a plastically deformable pipe support structure were conducted for various input acceleration levels. The vibration characteristics, response acceleration, and moment of piping were compared in relation to the amount of plastic deformation of the pipe support structure. As a result of the comparisons, a support model with the elastic fully plastic property was proposed as a simple and proper method to calculate the seismic response of the piping system considering the plastic deformation of the pipe support structure.

Commentary by Dr. Valentin Fuster
2014;():V008T08A043. doi:10.1115/PVP2014-28634.

Accurate and easy calculation of the mass of fluid contributing to the rocking motion of cylindrical tanks with partial uplift of bottom plate, which is the effective mass of fluid for rocking motion, that for rocking-bulging interaction, effective moment inertia of fluid for rocking motion and their centroid, is proposed. Asymmetric deformation of the tank bottom plate due to crescent-like uplift is used to put quantification of the masses away from rigorous treatments. This study considers the cylindrical tank as a set of thin rectangular tanks, so-called a slice model, and puts them perpendicular to the rotational axis of the tank rock motion. Then solve a boundary-value problem of each slice model specified by uplift of the tank bottom plate and its location, the mass of fluid contributing to rocking of cylindrical tanks is quantified as the sum of that of each slice model. Values of the effective mass of fluid for rocking motion, that for rocking-bulging interaction, effective moment inertia of fluid for rocking motion and their centroid are tabulated and depicted as a function of the aspect of tanks for different values of the ratio of the uplift width of the tank bottom plate to the diameter of tank.

Topics: Fluids
Commentary by Dr. Valentin Fuster
2014;():V008T08A044. doi:10.1115/PVP2014-28635.

Based on mechanical analogy between rocking motion of cylindrical tanks and that of two degree of freedom (2DOF) system, equations of motion for cylindrical tanks allowed to rock, that naturally includes effects of rocking-bulging interaction, are derived. Employing that the tank bulging motion is specified by a value of response acceleration spectrum in the absence of uplift and ordering terms, the simplified analysis for evaluating the angular acceleration of the tank rock motion, absolute maximum response acceleration of the tank bulging motion, base shear and reaction is derived. Assuming two percent of the ratio of the uplift width of the tank bottom plate to the diameter of tank, all physical quantities used for the simplified analysis are determined, tank responses are calculated and compared with corresponding responses computed by the Explicit Finite Element Analysis (EFEA). Comparison suggests that the proposed simplified analysis conservatively estimates all responses besides the angular acceleration.

Topics: Rocks
Commentary by Dr. Valentin Fuster
2014;():V008T08A045. doi:10.1115/PVP2014-28780.

This paper describes an analytical and numerical study performed to benchmark LS-DYNA computer analysis of the response of a stacked spent fuel cask system to seismic base excitation. The LS-DYNA solution of the rocking block problem and stability of the block under the action of a base acceleration pulse are compared to the inverted pendulum solution first published by George W. Housner in 1963. Housner’s work has been cited by a number of subsequent investigations exploring the physics behind the rocking block problem, including Yim and Chopra [2]. The analytical formulation of the rocking block problem is derived in 2D in this paper. As is the case in many of the previous formulations, the solutions are provided after linearization of the governing equations.

The stability of the unanchored block subjected to an acceleration pulse is solved using the energy method. The solution displays key differences relative to Housner’s minimum acceleration required to overturn. An alternate equation for effective viscous damping is also presented, which differs from the formulation given in Appendix A of ASCE 43-05 [9]. Simulation of the rocking block problem using LS-DYNA is shown to faithfully reproduce the classical solution, albeit at lower levels of energy loss. Effective damping and minimum acceleration to overturn from the LS-DYNA benchmark agree with predictions of the classical solution even after linearization.

Commentary by Dr. Valentin Fuster

Seismic Engineering: Seismic Response Mitigation for Mechanical Structures and Energy Facilities

2014;():V008T08A046. doi:10.1115/PVP2014-28121.

In various industrial plants such as thermal power plants, nuclear power plants, and chemical plants, many cable trays are generally used to support cables for control signals. Cable trays are very long, and thus are supported from ceilings or walls by many supporting structures. When the cable trays are subjected to strong seismic excitations, the trays or the supporting structures vibrate with large amplitudes. In the worst cases, they can collapse, and plants can lose control of systems, which can lead to severe accidents. Therefore, it is very important to maintain the structural integrity of cable trays during seismic events including recent severe earthquakes such as the East Japan Earthquake in 2011.

Cable trays are generally made of thin steel plates with sides folded in the vertical direction, and with cables simply placed on the tray. Thus, cables can slide when the inertia force on the cables exceeds the friction force between the tray and cables. The mass of the cables is relatively large compared to that of a tray, thus the natural frequency of the tray will change significantly due to the cable sliding motion. Consequently, seismic responses of cable tray will also depend on the sliding motion of cables. Therefore, cable trays are seen as highly nonlinear structural systems.

In this study, seismic responses of cable trays are investigated analytically considering cable sliding motions. A cable tray is modeled by a two-degree-of-freedom system. Response acceleration, and the displacements of the tray and the cable are evaluated for both sinusoidal and seismic inputs by varying the cable mass or friction coefficient between the tray and cables. It is confirmed that the sliding motion of the cable has a very large influences on the seismic responses of the cable-tray system.

Topics: Cables
Commentary by Dr. Valentin Fuster
2014;():V008T08A047. doi:10.1115/PVP2014-28283.

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 sinusoidal input was derived, including nonlinear characteristics of the elasto-plastic dampers and gap supports. Next, a numerical simulation was performed to verify the effect of the gap support on the piping system. The effect of the input characteristics on the response behavior of the piping system was investigated.

Commentary by Dr. Valentin Fuster
2014;():V008T08A048. doi:10.1115/PVP2014-28351.

Seismic ties are steel energy absorbing devices installed between the boiler and its support structure. This paper deals with the relationship between the energy absorption of a new type of seismic tie (made of low yield strength steel and with an optimized I-sectional shape) and its reduction effect on the resultant shear force of the support structure. To quantify the relationship between the energy absorption and the reduction effect on the resultant shear force, time-history analyses using a lumped mass vibration model that simulates the boiler structure, were performed for three representative design seismic waves (The largest class (level 2) waves of Taft, El Centro and Hachinohe earthquakes). The time-history analysis results demonstrated that the energy absorption increasing rates of the new seismic ties were correlated quantitatively with the shear force reduction rates of the support structure for the three design seismic waves.

Topics: Stress , Boilers , Earthquakes
Commentary by Dr. Valentin Fuster

Seismic Engineering: Seismic Safety Margin Studies of Operating Plants (International Topics)

2014;():V008T08A049. doi:10.1115/PVP2014-28250.

The buckling restrained brace (BRB) that has been worldwide adopted as a structural control device possesses excellent energy dissipation mechanism and can overcome the disadvantages of the traditional brace. However, the traditional BRB is a fully close design, it is therefore impossible to inspect the condition of the internal components during manufacturing and after earthquakes. This study proposed an all-steel buckling restrained brace with windowed lateral support elements that allow inspecting the internal condition of the BRB. We also studied the optimization in selecting the sizes and positions of the windows in the internal components without affecting its strength to provide an economically feasible all-steel BRB that is convenient for manufacturing and installation and meets the rigorous testing protocols. The all-steel BRB consists of the steel core, lateral support and constraining elements. In this study, scaled all-steel BRBs were tested under cyclic loadings by using an MTS 250 kN test machine. Test results showed that the mechanical behavior of the BRB with windows on the sides of lateral support elements is stable and that damage always occurred at the energy dissipation sections after low cycle fatigue tests. The difference between tensile and compressive forces was small under identical strain, and the accumulated inelastic deformation exceeded the requirement of test protocols. These test results confirm that the windows opened on the proposed BRB have insignificant effects on the strength of the device and that the proposed device meets the design requirement and is thus considered as a stable energy dissipative apparatus.

Commentary by Dr. Valentin Fuster
2014;():V008T08A050. doi:10.1115/PVP2014-28644.

Structural strengths of the piping and components in NPPs have been designed with seismic margin. They are classified seismically S, B and C class in terms of the influence rate to nuclear safety. For the highest seismic class (Class S) equipment, it is clarified that they have enough seismic margins against design seismic conditions by shaking table tests or numerical simulations. However, for the lower seismic class (Class B and C) equipment, their seismic margins have not been clarified quantitatively.

In this paper, in order to evaluate seismic robustness of the lower seismic class equipment with no clarification of seismic margin, seismic influences of the lower seismic class equipment in NPPs damaged by actual large earthquakes have been surveyed and sorted as a database, and the integrity of the lower class equipment have been discussed.

Seismic effects on 24 plants damaged by the recent large 6-earthquakes are surveyed, sorted as a database, and investigated. As a result, a total of 29 cases of function deterioration or loss were observed. Considering the total number of components and piping, the frequency of those cases in class B and C components and piping was low. And also, as it is found there are a few cases of degradation or loss of function in the equipment installed on the bedrock or in the buildings.

Commentary by Dr. Valentin Fuster
2014;():V008T08A051. doi:10.1115/PVP2014-28937.

The region of the Czech Republic is mostly composed of the Bohemian Massif which is considered as a geological unit with low seismic activity. Nevertheless, all critical objects as the nuclear power plants, big dams etc. are built as aseismic structures. The nuclear installations have to satisfy the IAEA safety standards and requirements. One of important phenomena that have to be involved in the PSHA process is the diffuse seismicity.

In 2010 International Atomic Energy Agency issued a specific safety guide SSG-9 Seismic Hazards in Site Evaluation for Nuclear Installations. The key chapters are focused on general recommendations, necessary information and investigations (database), construction of a regional seismotectonic model, evaluation of the ground motion hazard, probabilistic seismic hazards analysis (PSHA), deterministic seismic hazards analysis, potential for fault displacement at the site, design basis ground motion, fault displacement and other hazards, evaluation of seismic hazards for nuclear installations other than NPPs.

In the paper a numerical example of seismic hazard assessment will be presented with emphasis on problems and particularities related to PSHA in countries with low seismic activity.

Commentary by Dr. Valentin Fuster
2014;():V008T08A052. doi:10.1115/PVP2014-29080.

The recent natural calamities, especially earthquakes, are making engineering design requirements stringent. The Process Plant Piping is no exception to it. Analyzing the seismic effect by ‘Static Equivalent Method’ is a common practice compared to performing ‘Dynamic Analysis’. This paper starts with the basic reason of earthquake and its effect on the above ground piping system. Further it compares between the results opted based on computer based ‘Spectrum Analysis (Dynamic Analysis) Method’ and ‘Static Equivalent Method’ as per the requirements of ASCE 7. One of the assumptions in Static or Dynamic seismic analysis is — ‘Pipe supports are rigid’. However, in reality the supports, especially structural supports, show elastic behavior based on their material and geometric properties. At the end, this paper compares between the results of seismic analysis performed by considering ‘Supports as rigid’ and ‘Supports as elastic’ and comments on it along with minimum requirements for safe design.

Commentary by Dr. Valentin Fuster

Seismic Engineering: Structural Dynamics - Linear and Nonlinear

2014;():V008T08A053. doi:10.1115/PVP2014-28672.

The purpose of this study is to develop a seismic analysis model of a group of fuel assemblies in a boiling water reactor and to confirm the validity of the developed model. Each fuel assembly was modeled as a beam on the basis of the finite element method. The mass matrix of the model includes an added mass matrix, which represents the coupled inertia effect caused by the coolant water, in order to simulate the coupled vibration of fuel assemblies. The added mass matrix was obtained by calculating the coefficient matrix of the acceleration vector and fluid force vector under the condition that each fuel assembly moves at unit acceleration. The validity of the model was confirmed by comparing the calculated results with experimental ones. The compared specimens for the experiments were full-scale mock-ups. The vibration characteristics of fuel assemblies in each case of 4 bodies and 368 bodies were compared. As a result of the comparison, the calculations of the frequency response were in agreement with the experimental results. Particularly, the calculation results on the resonance frequency were in good agreement, with an error of less than 2 percent, with the experimental ones. Furthermore, the calculated vibration characteristics of 368 fuel assemblies in the case of an earthquake, such as the excited vibration mode and phase characteristics, were in agreement with the experimental ones. We concluded that the developed model of fuel assemblies was applicable to seismic analysis of a boiling water core.

Commentary by Dr. Valentin Fuster
2014;():V008T08A054. doi:10.1115/PVP2014-29114.

Based on the immediate needs of emergency medical services provided by hospitals after strong earthquakes, this paper is to introduce a research program on assessment and improvement strategies for typical configuration of sprinkler piping systems in hospitals. The study involved component tests and subsystem tests. Cyclic loading tests were conducted to investigate inelastic behavior of components including concrete anchorage, screwed fittings of small bore piping and mechanical couplings. Parts of horizontal piping systems of the aforementioned seismic damaged sprinkler piping system were tested using shaking table tests. Furthermore, the horizontal piping subsystems with seismic resistant devices such as braces, flexible pipes and mechanical couplings were tested.

The test results show that the main cause of the damaged case is the poor shear capacity of the screwed fitting of the small-bore tee branch. The optimum improvement strategy to achieve higher nonstructural performance level for the horizontal piping subsystem is to strengthen the main pipe with braces and to decrease shear demands on the tee branch by flexible pipes. The hysteresis loops and failure modes of components were further discussed and will be used to conduct numerical analysis of sprinkler piping systems in future studies.

Commentary by Dr. Valentin Fuster

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