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ASME Conference Presenter Attendance Policy and Archival Proceedings

2013;():V008T00A001. doi:10.1115/PVP2013-NS8.
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This online compilation of papers from the ASME 2013 Pressure Vessels and Piping Conference (PVP2013) 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to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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

2013;():V008T08A001. doi:10.1115/PVP2013-97267.

In Japan, the application of seismic isolation systems using rubber bearings to industrial structure and new generation Nuclear Power Plants have been considered in order to enhance seismic safety. However, the isolation performance will decline in case of huge earthquakes, because of the nonlinearity of both horizontal and vertical restoring characteristics of the rubber bearings. The horizontal restoring force has a hardening characteristic and the vertical restoring force has a softening characteristic. In addition, the horizontal nonlinearity depends on vertical load, so the interaction between the horizontal and vertical response is important. Consequently, in this paper, the analysis of the nonlinearity of the rubber bearings and the coupling between those two directions will be carried out. Then, after comparing these two approaches, the utility of considering this dependency will be estimated.

To do so, a simulation program, based on the Runge-Kutta-Gill’s method has been developed in order to evaluate the seismic response of the isolated structure composed of rubber bearings and oil dampers. The nonlinearity of the rubber bearings is considered, and the coupling of the vertical load and the horizontal hardening has been implemented.

Topics: Rubber , Bearings
Commentary by Dr. Valentin Fuster
2013;():V008T08A002. doi:10.1115/PVP2013-97351.

The authors propose a damper that generates electrical power in order to not only suppress vibration and also get electrical energy when many traffic signal poles are oscillated by wind, traffic turbulence, and earthquake. The damper consists of a displacement magnifying mechanism by using levers, solenoid coils and rare-earth magnets. It is useful for small deformation between a beam and a column of the traffic pole. Vibration modes of the pole are analyzed by using FEM, and then a small scale model of the traffic pole is built up. The small scale model has 2.3 m high, consists of a steel column and a cantilever beam due to rescale about 1/3 of real scale one, and natural frequency is about 3.5 Hz. Trial damper is manufactured and a damping force, which is caused by the coils crossing magnetic field, is adjusted. Dynamic characteristics of the trial damper are measured by a shaking actuator. In order to confirm vibration reduction, both of seismic and harmonic vibration tests of small scale model when the trial damper is installed are carried out by using a shaking table. The experimental results of harmonic responses are compared with the calculated results by FEM, and effect of vibration suppression and efficiency of generating power are discussed experimentally and numerically.

Commentary by Dr. Valentin Fuster
2013;():V008T08A003. doi:10.1115/PVP2013-97451.

As a method for semi-active control of structural systems, the active-control-based method that emulates the control force of a targeted active control law by semi-active control devices has been studied. In the active-control-based method, the semi-active control devices are not necessarily able to generate the targeted active control force because of the dissipative nature of those devices. In such a situation, the meaning of the targeted active control law becomes unclear in the sense of the control performance achieved by the resulting semi-active control system. In this study, a new semi-active control strategy that approximates the control output (not the control force) of the targeted active control is proposed. The variable parameter of the semi-active control device is selected at every time instant so that the predicted control output of the semi-active control system becomes close to the corresponding predicted control output of the targeted active control as much as possible. Parameters of the targeted active control law are optimized in the premise of the above “output emulation” strategy so that the control performance of the semi-active control becomes good and the “error” of the achieved control performance between the targeted active control and the semi-active control becomes small.

Commentary by Dr. Valentin Fuster
2013;():V008T08A004. doi:10.1115/PVP2013-97529.

Experiences of the previous earthquakes such as Bam, Northridge etc demonstrate that lifelines have no proper performance due to Near-Fault (NF) earthquakes. Hence, this research evaluates the influence of viscous dampers on the better performance of the water pipelines subjected to NF earthquakes. For this purpose, the water pipelines network of a zone in Tehran city was selected as a case study. The pipeline network was modeled using Finite Element Analysis (FEA), and nonlinear time-history analysis was undertaken via seismic scaled records of NF earthquakes. The obtained results indicated the critical points of network which were failed due to seismic waves. As a solution, viscous dampers were employed for improving the behavior of the mentioned points. The obtained results demonstrate that the failure points were retrofitted efficiently by viscous dampers.

Commentary by Dr. Valentin Fuster
2013;():V008T08A005. doi:10.1115/PVP2013-97572.

A new methodology is being introduced to address the life-cycle cost (LCC) of base-isolated large liquefied natural gas (LNG) tanks. The relationship between LCC and seismic fortification intensity is established to evaluate how much reduction of earthquake force can minimize the LCC. Each composition of LCC is analyzed including the initial cost, the isolators cost and the excepted damage cost. The isolators cost consists of the cost of lead rubber bearings and dampers. The cost of lead rubber bearings is proposed proportional to its volume and the cost of dampers is not only related to its maximum displacement but also to its tonnage. The concept of seismic intensity is being used to estimate the expected damage cost, greatly simplifying the calculation. Moreover, a tank in a LNG receiving terminal in China is employed as an example to assess its LCC in isolated and non-isolated situation respectively. The results show that the proposed method is efficient and the expected damage cost is enormously reduced because of the application of isolators, which leads to the reduction of the LCC of the tank.

Commentary by Dr. Valentin Fuster
2013;():V008T08A006. doi:10.1115/PVP2013-97650.

The authors have developed a new aseismic device, which has a ball screw and rotational mass. It not only generates the resistive inertial force originating in the rotational mass but also dissipates the energy of vibration through a viscous damping mechanism. Furthermore, the damping capability of the device can be controlled externally with an applied magnetic field. A magneto-rheological (MR) fluid is used to change the dynamic characteristics of the device. Through comprehensive experimental testing of a prototype device, the dynamic characteristics of the device have been verified. The test results show that the force-displacement relationship varies with an applied magnetic condition. Only a few amperes of electric current is required to generate a magnetic field effective for the prototype device with a capacity of 100kN.

Commentary by Dr. Valentin Fuster
2013;():V008T08A007. doi:10.1115/PVP2013-97686.

The fundamental natural frequency that can determine the seismic response of large LNG storage tank is usually within 2Hz∼10Hz, it is in the range of predominant frequency of strong ground motion. It has been proved that the isolation control technique can be adopted to mitigate the seismic action on the liquid storage tank in the hard site, but in the soft site, if the conventional isolation design methods are still be used for seismic mitigation of the large LNG storage tank, the problems that the isolation period is too long, and the horizontal displacement of the isolation layer is too large under strong earthquake will be produced. For these problems, a combined isolation design method that is suitable for soft site is proposed in this paper. Based on the Malhotra’s simplified elastic-wall model of liquid storage tank, the simplified multi-mass mechanical model of combined isolated large LNG storage tank is established, and the seismic response of the LNG storage tank under the case of SSE (safety shutdown earthquake) is analyzed. The results show that the seismic-reduced effectiveness of the combined isolated LNG storage tank is obvious, and the horizontal displacement of isolation layer can be controlled in an acceptable range.

Commentary by Dr. Valentin Fuster
2013;():V008T08A008. doi:10.1115/PVP2013-97724.

Previously, the authors proposed an approximation formula for designing an air spring that consists of two air tanks connected by a long pipe. The analysis was based on a linear approximation, so there is no amplitude dependency in the amplitude ratio for the sinusoidal vibration of a system with an the air spring. However, according to the experiment, it was found that there is remarkable amplitude dependency in a system with this type of air spring, so the frequency response curves for the system change with the magnitude of the input amplitude. It became clear that the approximation formula is in agreement with the limit value when the input amplitude approaches zero.

We consider that the deviation between the approximation formula and the experimental results are caused by the various assumptions which used in the analysis. As we remove these assumptions one by one, we perform the numerical analysis based on the finite difference method for this air spring. As a result, it was found that the effects of the turbulent flow in the pipe and the pressure loss at the inlet and outlet of the pipe are very small. A major influence is attributed in the connector that connects the pipe to the air chamber. The flow is throttled and disturbed at the connector whose inner diameter is smaller than the inner diameter of the pipe.

Commentary by Dr. Valentin Fuster
2013;():V008T08A009. doi:10.1115/PVP2013-97775.

This paper attempts to investigate the effects of soil-structure interaction (SSI) and higher modes on the dynamic responses of base-isolated structures through closed-form solutions for a superstructure, seismic isolator, and soil system under various conditions, comprising the cases of rigid and half-space foundations. The proposed system considers continuum media for both the superstructure and soil foundation, which can take the effects of higher modes into account, along with a discontinuous layer with a governing equation that interprets the mechanical behavior of the base-isolation system. Then, the closed-form solutions in terms of well-known frequency and impedance ratios under various conditions of soil foundations were obtained through rigorous mathematical derivations and validations by collapsing the entire system to a single degree-of-freedom system in structural dynamics and well-known cases of wave propagation in elastic solids. The closed-form solutions derived in this study explicitly revealed the characteristics of the SSI and higher mode effects in influencing the seismic behavior of base-isolated structures. Furthermore, the SSI effects on the dynamic responses of the entire system were extensively evaluated. The conclusive results of this paper will be useful for understanding the SSI and higher mode effects on the dynamic responses of base-isolated structures.

Commentary by Dr. Valentin Fuster
2013;():V008T08A010. doi:10.1115/PVP2013-97776.

This paper attempts to assess the role of soil-structure interaction (SSI) and higher modes in base-isolated structures founded on a soil layer overlying a half space. Closed form solutions for a system that includes a superstructure, seismic isolator and soil stratum overlying a half space have been obtained. The derived formulations considering the effects of SSI and higher modes in terms of well-known frequency and impedance ratios can explicitly interpret the dynamic behavior of a base isolated structure founded on soil stratum overlying a half space. Furthermore, the SSI effects on dynamic responses of isolated structures founded on soil stratum overlying a half space were extensively investigated. The conclusions drawn by this study provide considerable information for comprehending the SSI and higher mode effects on the dynamic responses of isolated-structures especially for those founded on soil stratum overlying a half space.

Commentary by Dr. Valentin Fuster
2013;():V008T08A011. doi:10.1115/PVP2013-97826.

In order to investigate the bidirectional characteristic of a multiple friction pendulum system (MFPS) with multiple sliding surfaces, a series of component tests were performed by using the shaking table in the National Center for Research on Earthquake Engineering, Taipei, Taiwan. The multiple friction pendulum system with multiple sliding surfaces consists of double concave surfaces, more than one intermediate sliding plates and one articulated slider located between the concave surfaces and intermediate sliding plates. These devices can continuously change their horizontal stiffness, damping, and displacement capacities during ground shaking by virtue of the properties such as radii and friction coefficients of multiple sliding surfaces. In this study, both uni- and bidirectional component tests of a multiple friction pendulum system with three and four sliding surfaces were carried out to investigate its mechanical characteristic. Furthermore, results obtained from the shaking table tests of an isolated steel structure demonstrate that the MFPS isolation system with multiple sliding surfaces could properly change its stiffness and damping effect, and effectively reduce the excitation force during ground shaking.

Topics: Friction , Pendulums
Commentary by Dr. Valentin Fuster
2013;():V008T08A012. doi:10.1115/PVP2013-97884.

Experiences of previous earthquakes demonstrate that lifelines have no proper performance exposed to Near-Fault (NF) earthquakes. Due to considerable effects of NF earthquakes and recommendation of the related design codes such as FEMA, evaluating the effects of these earthquakes on the pipelines is so important. In this research, the optimal placement of the viscous dampers in the water pipeline network subjected to NF earthquakes has been studied using Genetic Algorithm (GA). For this purpose, the water pipeline network of a zone in Tehran city was selected as a case study and was modeled using the Finite Element Method (FEM). Then, the nonlinear time-history analysis was undertaken via seismic scaled records of NF earthquakes. The obtained results indicated the critical points of network which were failed due to applied seismic waves. However, due to economical and technical issues, the optimal damper placement at critical points is necessary; all of the mentioned points were considered for optimization procedure using GA. Then, the viscous dampers were installed in the acquired optimal points. Eventually, a statistical test demonstrated optimum performance of the water pipelines network equipped with viscous dampers under NF earthquakes.

Commentary by Dr. Valentin Fuster
2013;():V008T08A013. doi:10.1115/PVP2013-97921.

The response control techniques are mainly divided into two categories. One is a storey installation damper type using a damping element such as oil, elasto-plastic, viscoelastic, and so on. The other is an additional mass damper type such as a active and passive type tuned mass damper including a hybrid type. The device configuration of later damper type becomes larger into high-rise structure and long natural period structure because of increase of additional mass in the same case of mass ratio and necessary design stroke of moving mass. In generally, however, it is desired to be a compact size with a same vibration attenuation performance because of that there is a limitation of installation space for the device, and also it is important to be realize the application of the damper with low cost and with a necessary specification for damper performance. This study has been conducted to develop the passive tuned mass damper system using coil spring for long period structure considering a design indexes such as compact size, low cost and robustness. Although a coil spring has been well used by the tuned mass damper system as one way of solving a cost problem and performance stability, the problem of compact size still remains in case of the application to a long period structure. Multistage type is therefore proposed to the system in this time. Furthermore, the distributed TMD theory is applied to the system for robustness of the system. This paper summarizes from a basic theory to the application of proposed device to the real scale long period structure.

Commentary by Dr. Valentin Fuster

Seismic Engineering: European Research on Structural Safety of Industrial Facilities (INDUSE project)

2013;():V008T08A014. doi:10.1115/PVP2013-97430.

Pipes and nozzles attached to large liquid storage tanks can be susceptible to earthquake induced damages. Adequate design and detailing of shell nozzle reinforcements significantly improves their seismic performance. Damages to nozzles, often combined with elephant-foot-buckling, belong to the most frequent failure modes of large liquid storage tanks caused by earthquakes. The failure consequences depend very much on the liquid contents which may be hazardous; prevention of leakage is a crucial design and verification criteria. European and American standards provide detailed recommendations for structural dimensioning and detailing of shell nozzle reinforcements, however no reliable statements can be made to their seismic behaviour. This paper describes the results of six experimental tests on three typical types of shell nozzle reinforcements. These full scale tests were carried out in the range of ultra-low cycle fatigue for longitudinal and transverse load directions as they can be expected under seismic actions. Based on the evaluation of the test results appropriate FE-models were derived by which parametrical numerical investigations were conducted. Through these studies the influence of different parameters (e.g. thickness of shell plate, reinforcing plate, bottom plate etc.) on the seismic behaviour has been investigated. Finally recommendations for the dimensioning of nozzles reinforcements with particular attention to seismic resistance were developed.

Topics: Nozzles
Commentary by Dr. Valentin Fuster
2013;():V008T08A015. doi:10.1115/PVP2013-97435.

An adequate design of pressure vessels, also for seismic actions, is crucial in particular if due to hazardous content the consequences of failure may become very severe. While very detailed and specific seismic design rules for structural buildings are provided by several codes, such rules are missing for pressure vessels. This paper describes the results of a study on seismic performance and applicability of existing European and American codes to pressure vessels with cylindrical and spherical shapes and provides a comparison of design outcomes according to these codes. The investigations were performed for different case studies of existing pressure vessels which were selected to be representative for the current practice. The studies comprised numerical investigations as well as simplified models for the estimation of the dynamic properties of the vessel structures. The applicability of behaviour factors was discussed based on proposals made by European and American codes, so that finally recommendations for the behaviour factor of pressure vessels with different shapes and types of supports have been developed based on pushover analyses and non-linear incremental dynamic analyses.

Commentary by Dr. Valentin Fuster
2013;():V008T08A016. doi:10.1115/PVP2013-97441.

In recent years, both pseudo-dynamic and real time heterogeneous testing with dynamic substructuring — hybrid testing — have gained significant popularity for their applicability to testing several types of nonlinear structures/systems. In a hybrid test, a heterogeneous model of the emulated system is created by combining a Physical Substructure (PS) with a Numerical Substructure (NS) that describes the remainder of the system. Nevertheless, an efficient implementation of this technique requires overcoming certain problems, e. g., proper dynamic substructuring, reduction of external forces and actuator delay compensation. This paper presents a pseudo-dynamic test campaign undertaken by the University of Trento, Italy, on a typical full-scale industrial piping system subjected to earthquake loading in order to investigate its seismic performance. Some challenges faced during the implementation are shown and strategies adopted to overcome these problems are illustrated. Experimental activities will be described and performances of different components of the piping system, i.e., elbows, tee-joints, bolted flange joints and straight pipes under earthquake loading with the presence of an internal pressure of 3.2 MPa will be presented and commented.

Commentary by Dr. Valentin Fuster
2013;():V008T08A017. doi:10.1115/PVP2013-97626.

Tee pipe junctions are piping components widely used in industrial and pipeline applications. Their performance under severe loading conditions may be critical for the structural integrity of an industrial facility. When these components are subjected to repeated loading associated with cyclic plasticity, failure is possible. The present work is a combined experimental and numerical effort which examines the behavior of piping branch T-junctions subjected to strong cyclic out-of-plane bending. The first part of this paper describes the experimental investigation of the junction performance. Tests are conducted in a constant and varying amplitude displacement-controlled mode resulting to failure in the low-cycle fatigue range. The overall behavior of each specimen in terms of fatigue life, as well as the evolution and concentration of local strains are monitored throughout the testing procedure.

The experimental investigation is supported by finite element modeling, developed to simulate the experiments. Advanced cyclic plasticity material models are employed and emphasis is given on the local strains developed at the critical part of the T-junctions where first cracking occurs.

Topics: Pipes , Junctions
Commentary by Dr. Valentin Fuster
2013;():V008T08A018. doi:10.1115/PVP2013-97642.

A significant number of damages in piping systems and components during recent seismic events have been reported in literature which calls for a proper seismic design of these structures. Nevertheless, there exists an inadequacy of proper seismic analysis and design rules for a piping system and its components. Current seismic design Codes are found to be over conservative and some components, e.g., bolted flange joints, do not have guidelines for their seismic design. Along this line, this paper discusses about the main issues on the seismic analysis and design of industrial piping systems and components. Initially, seismic analysis and component design of refinery piping systems are described. A review of current design approaches suggested by European (EN13480:3) and American (ASME B31.3) Codes is performed through a Case Study on a piping system. Some limits of available Codes are identified and a number of critical aspects of the problem e.g., dynamic interaction between pipes and rack, correct definition of the response factor and strain versus stress approach, are illustrated. Finally, seismic performance of bolted flange joints based on the results of experimental investigations carried out by the University of Trento, Italy, will be discussed.

Commentary by Dr. Valentin Fuster
2013;():V008T08A019. doi:10.1115/PVP2013-97700.

Unanchored liquid storage tanks under strong seismic loading may exhibit uplifting of their bottom plate, with significant effects on the dynamic behavior and the structural integrity of the tank. In the present paper, base uplifting mechanics is examined numerically through a two-step methodology: (a) a detailed finite element shell model of the tank for incremental static analysis, capable of describing the state of stress and deformation at different levels of loading and (b) a simplified modeling of the tank as a spring-mass system for dynamic analysis, enhanced by a nonlinear spring at its base to account for the effects of uplifting. Three cylindrical liquid storage tanks of different aspect ratios are modeled and examined both as anchored and unanchored. The results are aimed at possible revisions in the relevant seismic design provisions of EN 1998-4 and API 650.

Topics: Storage tanks
Commentary by Dr. Valentin Fuster
2013;():V008T08A020. doi:10.1115/PVP2013-97894.

Temporary ground deformations produced by strong seismic activity can result in severe cyclic loading applied to piping, fittings and components such as flanges, elbows, tee joints etc. The integrity of the piping system in such condition is of critical importance for the safety of petro-chemical plants or refineries. Among various reasons of failures under earthquakes, the accumulation of plastic strains due to cyclic bending loading of pressurized piping sections containing bolted flanged joints, have to be carefully considered. This paper reports the results of the experimental full scale tests performed within the RFCS INDUSE Project [1] on PN40 and PN63 piping sections containing bolted flanged joints subjected to monotonic and cyclic bending load, in presence of internal pressure. On the basis of the experimental results, a FE model adopting Lemaitre-Chaboche nonlinear kinematic hardening rule for the pipe material has been developed, allowing to extend the results of the tests by performing a study on the main parameters affecting resistance of the joint.

Commentary by Dr. Valentin Fuster
2013;():V008T08A021. doi:10.1115/PVP2013-97903.

In this paper the low cycle fatigue behaviour of steel elbows under strong cyclic loading conditions (in-plane and out-of-plane) is examined. The investigation is conducted through advanced finite element analysis tools, supported by real-scale test data for in-plane bending. The numerical results are successfully compared with the experimental measurements. In addition, a parametric study is conducted, which is aimed at investigating the effects of the diameter-to-thickness ratio on the low-cycle fatigue of elbows, focusing on the stress and strain variations. Strain gauge measurements are compared with finite element models. Upon calculation of local strain variation at the critical location, the number of cycles to fracture can be estimated.

Commentary by Dr. Valentin Fuster
2013;():V008T08A022. doi:10.1115/PVP2013-97977.

The present work examines the behavior of pipe elbows subjected to strong cyclic in-plane bending loading in the presence of internal pressure. In the first part of this work the experimental procedure is presented in detail. The tests are conducted in a constant amplitude displacement-controlled mode resulting to failures in the low-cycle fatigue range. The overall behavior of each tested specimen, as well as the evolution and concentration of local strains are monitored throughout the testing procedure. Different internal pressure levels are used in order to examine their effect on the fatigue life of the specimens.

The above experimental investigation is supported by rigorous finite element analysis. Using detailed dimensional measurements and material testing obtained prior to specimen testing, detailed numerical models are developed to simulate the conducted experiments. An advanced cyclic plasticity material model is employed for the simulation of the tests. Emphasis is given on the local strain development at the critical part of the elbow where cracking occurs. Finally, the results of the present investigation are compared with available design provisions in terms of both ultimate capacity and low-cycle fatigue.

Topics: Pipes
Commentary by Dr. Valentin Fuster

Seismic Engineering: Seismic Analysis and Design of Piping Systems

2013;():V008T08A023. doi:10.1115/PVP2013-97117.

The steam supply piping connected to the high pressure (HP) turbine of APR1400 (Korea’s advanced power plant 1400 MW-class) is a typical example of multi-supported piping system, and it is routed from the Containment building to the Turbine building via the Main Steam Isolation Valve House in the Auxiliary building. In the seismic analysis of this piping system, using the Enveloped Response Spectrum (ERS) method, a commonly used methodology for seismic analysis of nuclear power plant piping in industry circles, generates overly conservative analysis results. Therefore, Time History Method (THM) which applies excitation characteristic of each support attached to individual building was used to eliminate unnecessary conservatism. However, it was noticed that the Time History Method requires considerable amount of labor and time in generating combined time history equivalent to the spectrum applied for each support although it is regarded as the most exact and realistic method for seismic analysis. The nuclear industry has been making lots of efforts in finding out the mathematic logicality and practical applicability to resolve this issue. This paper deals with parametric research on combination effects of responses between support groups, damping effects, and modal combination method with close modes in applying the Independent Support Motion (ISM) method to the analysis model of the steam supply piping connected to the high pressure turbine of APR1400. Quantitative assessment and comparison with the analysis results of the ERS method and THM were also carried out. As a result, it is shown that the analysis results of the ISM method together with the SRSS combination between support groups, 4% damping with ±15% spectrum peak broadening and grouping of modal combination are remarkably similar to those of THM.

Topics: Pipes , Turbines , Steam
Commentary by Dr. Valentin Fuster
2013;():V008T08A024. doi:10.1115/PVP2013-97222.

This study discussed seismic response of a piping system when the pipe support structure was deformed plastically on being subjected to a much larger seismic load than the designed one. This case is expected as one of the conditions beyond seismic design that should be analyzed. To examine the effect of elastic-plastic deformation of the pipe support structure on seismic response, the effect of various shapes and failure mode of support structures was investigated. Difference of failure modes of the pipe support structure was modeled by change of initial stiffness and secondary stiffness of the load-displacement curve in this study. Seismic response analyses were conducted by using a typical small bore piping system shaped in a three-dimensional arrangement. The investigated change of seismic response behavior generated by plastic deformation of the pipe support structure was clarified based on comparison of seismic responses by using the elastic-fully plastic model and bi-linear model with various initial stiffness and secondary stiffness values. The results showed that the secondary stiffness of the load-displacement curve of the support structure did not affect the decreasing area of the response acceleration and the amount of the decrement significantly. It was concluded that the plastic deformation behavior of the pipe support structure could be modeled by using the elastic-fully plastic model when modeling plastic deformation characteristics of the pipe support structure.

Commentary by Dr. Valentin Fuster
2013;():V008T08A025. doi:10.1115/PVP2013-97308.

The concerns about Fitness-For-Service (FFS) assessment technique for pressure equipments with local metal loss have been growing from some characteristic damages, for example, many examples of the corrosion under insulation (CUI) of pressure equipment, have been reported from petroleum and petrochemical industries. FFS assessment procedure for the pressure equipments for metal loss has been validated by the results of various burst tests and FEM simulations for internal pressure loads.

There has, however, been little study to validate FFS assessment for pressure equipments subjected to seismic load. This paper suggests an FFS assessment procedure for pressure equipments with local metal loss subjected to both internal pressure and seismic loading. To ensure consistency to High Pressure Gas Law in Japan, allowable stress is based on the Japanese seismic design code. Developed stress on local metal loss from both internal pressure and seismic load is evaluated in accordance with API 579/ASME FFS-1.

The authors have verified safety margin and reliability of this method to toward to practical application. In order to verify, some cyclic bending load testings and finite element analysis were implemented under the conditions of ambient temperature and 300 degree C. The results of these validations show that the safety margins against low cycle fatigue are the range of 2.6 to 4.6. In addition, the test results at 300 degree C showed higher safety margin than that in ambient temperature.

Commentary by Dr. Valentin Fuster
2013;():V008T08A026. doi:10.1115/PVP2013-97716.

Seismic behavior of the urban water pipelines has been considered due to its vital role, and also experiences of recent earthquakes which demonstrate poor seismic performance of mentioned pipelines. Previous experiences such as Bam (2003), Chile (2010) and Japan (2011) earthquakes indicated that urban water pipelines were out of service after earthquake and numerous problems were apparent on the post-disaster management. In this research, the water pipeline network of a zone in Tehran city was selected as a case study. The Hydraulic Failure Analysis (HFA) of the water pipelines in the proposed zone was carried out and failure potential points of the pipelines were determined. In addition, these points were investigated using orifice theory of leakage problem. Then, the proposed network was modeled using Finite Element Analysis (FEA). Also, nonlinear time-history analysis has been undertaken using three seismic scaled records of different earthquakes. Eventually, a statistical test demonstrated that there is a significant difference in the seismic performance of piping system before and after an earthquake.

Commentary by Dr. Valentin Fuster
2013;():V008T08A027. doi:10.1115/PVP2013-97832.

The piping in a nuclear power plant is laid across multiple floors of a single building or two buildings, which are supported at many points. As the piping is excited by multiple inputs from the supporting points during an earthquake, seismic response analysis by multiple excitations is needed to obtain the exact seismic response of the piping. However, few experiments involving such multiple excitations have been performed to verify the validity of multiple excitation analysis. Therefore, analysis of the seismic design of piping in Japan is performed by the enveloped Floor Response Spectrum (FRS), which covers all floor response spectra at all supporting points. The piping response estimated by enveloped FRS is conservative in most cases compared with the actual seismic response by multiple excitations. To perform rational seismic design and evaluation, it is important to investigate the seismic response by multiple excitations and verify the validity of the analysis method by multiple-excitation test.

This paper reports on the result of the shaking test using triple uni-axial shaking tables and a 3-dimensional piping model (89.1mm in diameter and 5.5mm thickness). The piping model was fixed to three shaking tables, meaning three. Different inputs were possible. By the shaking test, dynamic behavior under multiple excitations was confirmed, and data to verify multiple-excitation analysis was obtained.

Topics: Pipes
Commentary by Dr. Valentin Fuster
2013;():V008T08A028. doi:10.1115/PVP2013-97841.

The piping in a nuclear power plant is laid across multiple floors of a single building or two buildings, which are supported at many points. As the piping is excited by multiple-inputs from the supporting points during an earthquake, seismic response analysis by multiple excitations is needed to obtain the exact seismic response of the piping. However, few experiments involving such multiple excitation have been performed to verify the validity of multiple excitation analysis. Therefore, analysis of the seismic design of piping in Japan is performed by the enveloped Floor Response Spectrum (FRS), which covers all floor response spectra at all supporting points. The piping response estimated by enveloped FRS is conservative in most cases compared with the actual seismic response by multiple excitations. To perform rational seismic design and evaluation, it is important to investigate the seismic response by multiple excitations and to verify the validity of the analytical method by multiple excitation test.

This paper reports the validation results of the multiple-excitation analysis of piping compared with the results of the multiple excitations shaking test using triple uni-axial shaking table and a 3-dimensional piping model (89.1mm diameter and 5.5mm thickness). Three directional moments from the analysis and the shaking test were compared on the validation. As the result, it is confirmed that the analysis by multiple time history excitation corresponds with the test result.

Topics: Pipes
Commentary by Dr. Valentin Fuster
2013;():V008T08A029. doi:10.1115/PVP2013-97852.

It is well known that the seismic safety capacity of a piping system itself is considerably high compared to the design limitation from the various preceding studies. But most of the preceding studies focused on the seismic capacity of a piping system without other elements as supports, and the safety capacity may be reduced if the failure at supports, nozzles, or flange connections were precedent to the failure at the body of pipe. Therefore the shake table test on the piping system model with supports was conducted. The piping system model used in the shake table test had three supports, a tank, a valve, and flange connections. Excitations were conducted at several input acceleration intensity, and the response characteristics and the failure mode of the piping system were obtained. The failure mode of the piping system model was the broken damage at a pipe support, and after that the leakage at a flange connection occurred. Though the piping system was damaged at pipe supports, it was shown that the piping system model had a certain seismic capacity compared to the design limitation.

Commentary by Dr. Valentin Fuster
2013;():V008T08A030. doi:10.1115/PVP2013-98067.

This study presents the estimation of the ductility responses of inelastic SDOF structures to an earthquake motion from the velocity responses of elastic SDOF structures. Based on the energy balance equation, the ductility response and the baseline drift of the inelastic structure can reasonably be estimated from the extrema of the elastic velocity response. Then, the estimation of the maximum ductility is derived by accumulating them. Illustrative examples are presented to show the performance of the proposed ductility estimation. Because the velocity responses of the elastic SDOF structure are correlated with the time-frequency characteristics of the earthquake motion via the velocity response wavelet transform (VRWT), which was previously proposed by the authors, in which the latter are represented in the wavelet-domain using former as time-frequency building blocks, the proposed estimation method may have a potential to help to obtain an in-depth understanding of time-frequency characteristics of the earthquake motion that impacts the ductility responses of the inelastic structure.

Topics: Earthquakes , Wavelets
Commentary by Dr. Valentin Fuster

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

2013;():V008T08A031. doi:10.1115/PVP2013-97229.

A multi dynamic absorber for suppressing liquid sloshing in a floating roof tank is presented. As well known, many seismic damages on floating roof tanks by the sloshing of their contained liquid due to long periodic components of earthquake motion were reported. Since the natural period of sloshing varies according to the height of liquid surface, robustness for parameters such as natural period is required for the sloshing suppression device to obtain a good suppression performance. From this point of view, we developed a multi dynamic absorber instead of the single dynamic absorber which is sensitive to the parameter variance. A multi degree of freedom mechanical model for sloshing of the contained liquid and the presented multi dynamic absorber which sets up on the floating roof of the tank is derived to design the optimal tuning for parameters of the multi dynamic absorber and to evaluate the sloshing suppression performance. Numerical simulations for an actual size floating roof tank were conducted to examine the performance of the present device. As the result the effect of the presented multi dynamic absorber was effective to suppress the sloshing response of the floating roof and to be robust for the natural period variance.

Commentary by Dr. Valentin Fuster
2013;():V008T08A032. doi:10.1115/PVP2013-97306.

Flat-bottom cylindrical shell tanks may rock and have a crescent-like uplift part in the bottom plate at the event of a severe earthquake. Effects of the deformed tank bottom plate on the fluid pressure on the cylindrical tank have not been, however, quantified yet. Since the crescent-like uplift part appears eccentrically on the periphery of the tank bottom plate, its mathematical treatment would be troublesome. Regarding a cylindrical tank as a set of pieces of a thin rectangular tank with a deformed bottom plate that correspond radially sliced parts of the cylindrical tank with the crescent-like uplift part in the bottom plate, this paper defines the fluid pressure on the cylindrical tank by calculating that on the rectangular tank. For designer’s convenience, the fluid pressure computed are normalized and depicted in accordance with the aspect of the cylindrical tank and the uplift ratio of the tank bottom plate.

Commentary by Dr. Valentin Fuster
2013;():V008T08A033. doi:10.1115/PVP2013-97371.

A large-scale earthquake simulation experiment about the unanchored cylindrical steel liquid storage model tanks has been completed. The self-vibration characteristics of the model tanks with liquid inside were investigated based on the experimental data of the acceleration dynamic response. The seismic table test, the analysis methods are designed and conducted, and experimental results of the model tanks were carefully measured. Furthermore, ANSYS finite element software was used to simulate and calculate the low order natural frequency and fundamental frequency of the model tank systems according to the national design standard. The reasons for the existence of consistency and differences among the results obtained from experiments, numerical simulation and national design standard were discussed.

Commentary by Dr. Valentin Fuster
2013;():V008T08A034. doi:10.1115/PVP2013-97421.

Under severe seismic design conditions for LNG storage tanks in recent years, detail verification of soundness of structure including uplift behavior of bottom plate has been required. The design state is used to be analyzed statically as if the maximum dynamic pressure represents reciprocal processes during the earthquake. However, the previous studies reveals that the static analysis fails to calculate dynamic response behavior including uplift of bottom plate. In this paper, fluid-structure coupled 3-dimensional time-history FE analysis was performed for study of dynamic response including uplift of bottom plate. The time history FE analysis reveals undulating deformation at top of sidewall, which had not been observed under static conditions. This deformation is affected by stiffness of stiffener rings installed at the sidewall and effect of that on tank response was investigated. The FE analysis also proves that uplift height of bottom plate under reciprocal pressure is significantly smaller than that due to static conditions. This study makes clear the dynamical behavior of tank during earthquake and magnitude of influence of dynamic loading on that. In addition, the concept of introducing such dynamic effect to static analysis is proposed.

Commentary by Dr. Valentin Fuster

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

2013;():V008T08A035. doi:10.1115/PVP2013-97072.

In Japan, ensuring the structural integrity of cask systems during seismic events is becoming increasingly important. Cask systems, which are free-standing cylindrical structures that contain spent fuel assemblies, are considered as sliding isolation systems. Thus far, analytical studies conducted by the authors have already indicated that cask systems subjected to strong seismic motions, undergo large sliding motions, and in the worst case, may collide with one another. Therefore, reducing the sliding motions of casks to avoid mutual collisions and consequent contamination of radioactive substances is critical.

To suppress sliding motions for very heavy free-standing structures such as cask systems, the authors proposed a sliding motion suppression system that uses high-viscous liquid and coaxial circular cylinders. This system is installed at the bottom end of the structure and the annular space is filled with a high-viscous liquid. A previous study showed that high-viscous liquid in annular spaces provides added damping effects of considerable magnitude, and thus allows the sliding motion to be suppressed.

In this study, the added damping effects of the annular space liquid are clarified using a fundamental testing device for various liquid viscosities, ratios of diameters for the inner and outer cylinders, and eccentricities of the inner cylinder. Moreover, shaking table tests are conducted to confirm that the added damping effects suppress excessive displacement.

Commentary by Dr. Valentin Fuster
2013;():V008T08A036. doi:10.1115/PVP2013-97457.

This paper deals with new types of steel seismic ties, which are energy absorbing devices installed between boiler and its support structure. To enhance the aseismic reliability of the boiler and its support structure, energy absorbing capacities of the seismic ties must be increased. To increase the capacities, sectional shapes of the seismic ties have been optimally designed. Concretely, I-section seismic ties as new types have been gained by optimizing the design parameters, material (conventional carbon steel and low yield strength steel), sectional height, web thickness, flange thickness under conditions to maximize absorbing energy and to restrict the reaction force equal to or smaller than that of round-section current seismic tie. As a result of cyclic load testing using 1/3 scale model, it was verified that energy absorption of the new types of seismic ties were 16–23 % larger than that of the current seismic tie.

Commentary by Dr. Valentin Fuster
2013;():V008T08A037. doi:10.1115/PVP2013-97504.

This paper describes the finite element modeling of a mainframe server frame. The frame consists of a server rack or frame with its add-on stiffening brackets. The frame is anchored directly to the floor with bolts at each of the four corners. The Telcordia Zone 4 earthquake test profile represents a severe dynamic load input and will be used herein to analyze the mainframe server frame. The main objective of this modeling is to validate the frame design prior to actual seismic testing, which ultimately ensures the structural integrity of a functional mainframe system during a seismic event. The server frame finite element (FE) model is derived from a three dimensional CAD model of a standard sheet metal frame weldment assembly which is then simplified and meshed with finite elements. This FE model represents the server frame, welded connections, and stiffening brackets, which are specifically designed to withstand seismic test profiles. To represent the components that populate the server frame, point masses are tied to the frame at the same attachment points that exist in the real assembly. The validation of the FE model involves the use of a horizontal shaker test to assess the server frame’s stiffness. The goal of this paper is to show a good correlation between FE model and test results using two separate FE solver technologies: implicit and explicit. For an implicit solver, linear material properties were used to obtain modal behavior that approximates the actual server frame’s behavior. Once these outputs were achieved, further response refinement was attempted by porting the model to an explicit dynamic solver. An explicit solver allowed non-linear material properties and body to body contact behavior to be included in the FE model while applying the seismic test profile to the server frame using a time domain input. The explicit dynamic model outputs used to correlate to actual test results were the modal dynamics, the displacement of the top of the server frame, and the maximum reaction force at the anchored corners. Finally, a functional system was subjected to the Telcordia Zone 4 seismic test profile. The system was functional during and after the seismic test with no significant structural damage having occurred.

Topics: Modeling
Commentary by Dr. Valentin Fuster
2013;():V008T08A038. doi:10.1115/PVP2013-97560.

In this study, the vibrational behavior of a system supporting large-scale structures that are subjected to multiple random inputs is investigated based on probabilistic vibration theory. The analytical model (FEM) of a system that is subjected to white noise is constructed first. Pipings are assumed to be supported by a nonlinear elastoplastic damper. The vibrational behavior of the structures subjected to multiple random inputs is calculated via numerical simulations. After calculating the stress, energy absorption, etc., the dynamic reliability is calculated based on random theory. Finally, the effects of the supporting location and supporting capacity on the dynamic reliability are investigated.

Topics: Vibration
Commentary by Dr. Valentin Fuster
2013;():V008T08A039. doi:10.1115/PVP2013-97651.

In great east Japan earthquake, resonances of structures which have long natural period by long period seismic wave were reported. The duration time of the long period seismic wave was more than a few minutes. Meanwhile many dampers have been proposed and applied to actual structures in order to suppress seismic response. However large stroke and energy absorption capacity are required for these conventional oil dampers against the long period seismic wave. In this paper, authors propose a viscous-friction hybrid damper as an effective vibration control device suitable for structures which have long natural period. In general, structures with long natural period resonate with long period ground motion. The hybrid damper consists of an oil damper and a friction damper in series. In our hybrid damper, the friction damper can absorb vibration energy as well, in the case of long period seismic wave. Thus energy absorption of oil damper is suppressed, and the damper retains good performance. In addition, the oil damper of the hybrid damper is effective for small earthquake. In this paper, a boiler building was selected as an example of industrial buildings. The boiler building was modeled as 2-degree-of-freedom for analysis. Seismic response analysis of the building with the hybrid damper was carried out. As a result good vibration control performance was confirmed.

Commentary by Dr. Valentin Fuster

Seismic Engineering: Structural Dynamics - Linear and Nonlinear

2013;():V008T08A040. doi:10.1115/PVP2013-97044.

A novel family of structure-dependent integration method is proposed for time integration. This family method can have the possibility of unconditional stability, second-order accuracy and the explicitness of each time step. Since it can integrate the most important advantage of an implicit method, unconditional stability, and that of an explicit method, the explicitness of each time step, a lot of computational efforts can be saved in solving an inertial type problem, where the total response is dominated by low frequency modes and high frequency responses are of no interest.

Commentary by Dr. Valentin Fuster
2013;():V008T08A041. doi:10.1115/PVP2013-97168.

For high earthquake resistance and ease of installation, free standing racks which are not anchored to the pool floor or walls has been adopted in many countries.

Under the earthquake, the response of the free standing rack is highly nonlinear and involves a complex combination of motions (sliding, rocking, twisting, and turning) and impacts between the fuel assemblies and the fuel cell walls, rack-to-rack, and the pit floor and the rack pedestals. To obtain an accurate simulation of the free standing rack, the seismic analysis requires careful considerations of these complex phenomena (sliding, rocking, twisting, and turning), fluid coupling effects and frictional effects.

The important evaluation items while applying the free standing rack to the actual nuclear plants are maximum sliding displacement of the rack, maximum rocking displacement and maximum leg load under earthquake. When the sliding displacement increases, the rack may collide against the spent fuel pool wall. In addition, the free standing rack should not exhibit tilt sufficient to cause to the rack to overturn. The vibration tests were conducted in order to predict the rack behavior under earthquake, and the analysis method was validated by comparison to tests results. Furthermore, we developed the seismic design method to obtain the margin of safety for free standing rack.

Commentary by Dr. Valentin Fuster
2013;():V008T08A042. doi:10.1115/PVP2013-97225.

A response spectrum analysis (RSA) has been widely known as one of the methods used for the purpose of an earthquake-resistant design of a structure in the nuclear industry through evaluating the structural integrity during and after seismic events. Recently, as the structures, systems, and components for the design are massive, complex, and complicate, a considerable amount of computational resources and time is required for applying the RSA. Reduced methods have been considered as important technique to resolve computational resources and time problem. For a few decades, various approximate techniques have been developed to obtain the dynamic characteristic in a reduced manner. This paper adopts the model order reduction (MOR) technique known as the one of various reduction methods. The MOR for solving the large linear system in mathematics has been studied by a number of researchers. The MOR is achieved by applying a projection from a higher-order to a lower-order space using Krylov subspaces generated by the Arnoldi algorithm. It has been extended to engineering applications such as circuit analysis, structural analysis, and multi-scale analysis. However, it has not yet been applied in RSA. The aim of this study is to evaluate applicability of the MOR into RSA. Numerical examples demonstrate that the proposed method saves computational costs effectively with maintaining accuracy. Thus, it is confirmed that the proposed method is valid and applicable in predicting seismic responses.

Commentary by Dr. Valentin Fuster
2013;():V008T08A043. doi:10.1115/PVP2013-97488.

Generally, mechanical members are required to be highly safe to withstand a lot of earthquakes. Specially, seismic evaluation and design techniques for mechanical members have been required in earthquake-prone countries. According to studies on failure of pipes, the critical load due to earthquake is a cyclic loading. Therefore, the design techniques that are able to evaluate cumulative damages is needed. Recently, relationship between failure and energy has been examined by paying attention to the Energy Balance equation which is said to be effective as an earthquake response analysis technique. This study carries out failure experiments using simple mass point models having various cross section based on Energy Balance Method. Although the target model in our earlier study was a simple single degree of freedom model of hundreds of gram order, in order to perform detailed earthquake-proof evaluation for actual mechanical members, examination by large mass type models is needed. The consideration of the influence of the section modulus or the moment of inertia area on the energy required to failure is examined by using the model on the order of tens of kg, by focusing on the local response for the strain at the point of failure.

Commentary by Dr. Valentin Fuster
2013;():V008T08A044. doi:10.1115/PVP2013-97571.

A simplified method for incorporating gravitational effects into the analysis of structural vibrations, and for determining the relative importance of those effects, has been developed. The nonlinear effect has been simplified by incorporating only the first-order gravitational effects into the structural stiffness formulation, and demonstrating through both analysis and experiment that the first-order stiffness additions are sufficient to accurately characterize the gravitational effects in most cases. The simplified formulation also provides a convenient method for determining the conditions under which the effects of gravity should be considered.

Commentary by Dr. Valentin Fuster
2013;():V008T08A045. doi:10.1115/PVP2013-97584.

The rocking motion of tanks due to earthquakes causes the large uplift deformation of the tank bottom plate that has been considered to contribute to the various damages of the tanks. For analyzing the uplift displacement of the tank bottom plate statically and precisely, this paper develops a shell element, ring element and spring element partially attached to the ring element. These elements are defined as a semi-analytical finite element. Fourier series give its circumferential displacement function, while the polynomial gives its radial displacement function. In addition, the ring element can deal with effects of the large deformation, while the spring element enables to express the partial contact between the tank bottom plate and foundation. On the other hand, the loads considered are dead load, hydro-pressure and inertia force due to earthquakes acceleration as well as dynamic pressure of fluid induced by bulging and rocking motion of the tank. The numerical analyses model of the LNG Storage Tank was created using the semi-analytical finite elements shown here, and the uplift displacement of the tank bottom plate accompanying the tank rocking motion was calculated with the static analyses. For evaluating analytical accuracy of the proposed method, numerical results of the proposed method are compared with that of the explicit FE Analysis.

Commentary by Dr. Valentin Fuster
2013;():V008T08A046. doi:10.1115/PVP2013-97668.

The assessment of the seismic scrammability, which means the control rod insertability during a seismic event, is one of the most important design tasks for ensuring the seismic safety of nuclear power plants in Japan. This paper discusses the dynamic modeling of the control rod insertion behavior of a boiling water reactor (BWR) during an earthquake. A dynamic model of a control rod insertion system for BWR was developed based on multi-body dynamics. The coupled vibration behavior of the fuel assemblies in the fluid was modeled as an inertial coupling system. The effect of the interaction force between the control rod and the fuel assemblies was considered in a three-dimensional contact analysis. The hydraulic control unit and the control rod drive, which provide the control rod with drive force, were modeled in the concentrated parameter system. The model parameters, such as the friction coefficient between the control rod and the fuel assembly and the discharge coefficient of the scram piping, were obtained by conducting experiments. The validity of the model was confirmed by comparing the analytical results with the experimental ones. First, the validity of the fuel assembly model was verified through a comparison with the vibration testing in an underwater condition. It was confirmed that the calculation results for the frequency response of the fuel assembly were in good agreement with the experimental ones. Second, the validity of the modeling method of the drive system consisting of the hydraulic control unit and the control rod drive was verified through a comparison with the scram testing under non-vibration condition. The calculation results for the time history of the control rod insertion, the accumulator pressure, and the flow through the scram piping were in good agreement with the experimental ones. Finally, the validity of the modeling method of the whole system consisting of the fuel assemblies, the control rod, and the drive system was verified through a comparison with the scram testing under vibration condition. The calculation results for the time history of the control rod insertion stroke and the time delay of the insertion motion during an earthquake were in good agreement with the experimental ones. The results of these comparisons show that the developed analysis model can simulate the control rod insertion behavior during an earthquake.

Commentary by Dr. Valentin Fuster
2013;():V008T08A047. doi:10.1115/PVP2013-97850.

In this paper, we propose a method for analyzing the vibration properties of contact wires (trolley wires) using the transfer matrix method (TMM), by treating them as a periodic structure. When the speed of the train increases, self-excitation vibration of the wires may occur. When the trolley wires repeatedly contact and separate from the pantograph, the pantograph is worn by the sparks. Therefore, the vibration of the trolley wires must be kept as small as possible. For such problems, many researchers have proposed vibration analysis of the wires. However, these methods are not suitable for the vibration analysis of wires because of the very complicated wave propagation phenomenon. The TMM proposed in this study is an easy technique for studying wave propagation since the vibration properties can be simplified greatly by handling the smallest unit of repetition of the structure. Using this method, we can identify the frequencies of the vibration-attenuating domain (stop-band) and the vibration-amplifying domain (pass-band). If we can bring the excitation frequency of the wire to the stop-band domain, wear of the pantograph can be reduced. Here, we introduce three cell models; two of them do not take into account the elasticity of the trolley wire, and the other does. Then, we discuss how the stop-band appears in these models.

Commentary by Dr. Valentin Fuster

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