Abstract A total of 12 flange assemblies, spanning both class 300 and 600 were instrumented with ultrasonic transducers and observed following differing assembly patterns to gain insight into the BFJ elastic interactions. Each flange assembly was additionally tested to multiple load targets to monitor the overall sensitivity of interaction to load. Analytical work following the data collection led to the development of a simplified installation method and sequencing that dramatically reduces the work effort required to effectively close a joint while being independent of fastener condition or tool selection. The range of validity for the simplified method is further extended with linear multivariate solving techniques and accelerated joint “snugging” to promote joint stiffness. Limits on the acceptable load achievement was set to < 5% error on the average load and < 10% normalized standard deviation to be considered acceptable when targeting Appendix-O calculated loads of ASME PCC-1. Validation of the proposed method was undertaken by the University of Houston at the Bechtel WATC facility with support of Carber Engineering which included full size pressure testing following joint assembly. The observations made from the 60+ full size trials then served to validate FEA work towards the analysis of the remaining sizes of class 300/600 from 4″ to 24″.

Abstract Anisotropic composite cylinders and pressure vessels have been widely employed in automotive, aerospace, chemical and other engineering areas due to high strength/stiffness-to-weight ratio, exceptional corrosion resistance, and superb thermal performance. Pipes, fuel tanks, chemical containers, rocket motor cases and aircraft and ship elements are a few examples of structural application of fiber reinforced composites (FRCs) for pressure vessels/pipes. Since the performance of composite materials replies on the tensile and compressive strengths of the fiber directions, the optimum design of composite laminates with varying fiber orientations is desired to minimize the damage of the structure. In this study, a complete mathematical 3D elasticity solution was developed, which can accurately compute stresses of a thick multilayered anisotropic fiber reinforced pressure vessel under force and pressure loadings. A rotational variable is introduced in the formalism to treat torsional loading in addition to force and pressure loadings. Then, the three-dimensional Tsai-Wu criterion is used based on the analytical solution to predict the failure. Finally, a global optimization algorithm is used to find the optimum fiber orientation and their best combination through the thickness direction.

Abstract Additional lateral load tests, with improved techniques, were conducted on M22 stainless bolts to supplement the series of metric system stainless bolt tests which were conducted previously. Using the strain gage-deflection data collected from the entire set, i.e., of different sizes and different lengths, of the bolt tests, the “rigidity coefficient”, which is used in calculating the deflection of the bolts under lateral loads, using the conventionally assumed effective shank length, is derived. Alternatively, a new analytical effective shank length, which is more accurate than the conventional assumed effective shank length, derived from the test data, is proposed.

Abstract This paper presents several modeling methods for performing a valve assembly modal analysis. It discusses the background of the methods, their strengths and limitations, and then introduces a new approach that can be used in performing valve modal analysis. An early paper presents a classical approach based on a lumped mass model and the Rayleigh energy principal to determine primary mode natural frequencies. A follow up paper reaffirms the classical method and introduces enhancements. A recent paper provides a comparative study of the classical approach, laboratory testing, and solid modeling results using the finite element analysis program ANSYS Mechanical. In this paper, a third approach is presented, which is an extension of the classical method, where 3-D beam-based geometry is defined using the ANSYS SpaceClaim program that is then ported to ANSYS Mechanical. The classical and solid modeling approaches from the previously cited papers are reviewed to highlight the modeling evolution and then the newly developed approach is presented. An example is presented that compares natural frequency results of the new method and the previous methods. The motivation for the new method is to provide better compatibility with 3-D piping system models, which are typically used to study the effect of valve mass and stiffness on system response without the complexity of a solid model or the difficulty of communicating the details of a classical model to the system modeler. Much of the process of creating a 3-D beam model is automated. It uses input from an existing classical model and employs the following ANSYS software packages: SpaceClaim, Workbench, Mechanical, and ACT. A great feature of the resulting 3-D model is that beam geometry is more realistic to scale, and therefore provides valuable user feedback for checking model validity. This approach is an improvement over the classical model where only manual data input validation is possible. Other benefits of the new method are covered in greater detail in the paper.

Abstract Securing adequate seismic safety margins has been important in safety reviews regarding the seismic design of equipment and piping systems in nuclear power plants, and there exists an increasing need for a more exact method for evaluating these margins. To this end, it is reasonable to take into account the reduction of seismic responses resulting from inelastic deformation. The authors studied this approach utilizing an elastic allowable limit in existing standard. The applicability of the proposed evaluation method was investigated by comparison with the conventional evaluation method. The proposed method consists of an inelastic dynamic analysis and an elastic-static analysis. The elastic-static analysis uses a load obtained from the inelastic dynamic analysis. For the investigation, the result obtained from the proposed method was compared with that obtained from the conventional elastic analysis to quantify the reduction in responses leading to seismic safety margins. For the comparison, the authors constructed three models that simulate a cantilever-type beam, four-legged tank, and core shroud and applied them to the analysis herein, and the applicability of our method was discussed for these models. In this paper, we present three topics. First, we present a scheme for developing the design approach of using inelastic analysis. Second, we report a sensitivity study of model parameters, such as yielding stress and second stiffness, done by analyzing the cantilever-type beam for the proposed method. Finally, we report the application of the method to the four-legged tank and core shroud.

Abstract Reinforced Concrete (RC) frame structures that were designed and built according to older standards can be damaged during destructive earthquakes as a result of insufficient lateral strength and/or deformation capacity. Such structures must be retrofitted to satisfy the current requirements and to survive future earthquakes. Owing to its high lateral strength and stiffness capacity of an RC wall, the post-installation of an RC wall in a non-ductile frame for retrofit is a widely used retrofitting technique. However, for frame structures with low-strength concrete, the typically used connected construction method on the interface between existing and new concrete may be not able to provide effective force transfer, and may cause unexpected brittle failure in the retrofitted structure. Such unexpected brittle failure may reduce the seismic capacity of the structure and threaten its safety. Therefore, in this experimental investigation, two retrofitting methods that use a post-installed RC wall are proposed to improve the load transfer mechanism on the interface. The first involves a wall with diagonal rebar and boundary spirals, and the second involves a wall with an additional inner frame. A typical traditional retrofitting specimen was constructed and tested for comparison. Reversed cyclic loading is used to test the seismic capacity of the specimens. Finally, post-embedded piezoceramic-based sensors were used to monitor the structural health and detect damage in one of specimens during the test. The experimental results demonstrate the effectiveness of the piezoceramic-based approach to structural health monitoring and the ability of the method to detect damage in shear governed RC structures under seismic loading.

Abstract To avoid unacceptable vibration of suction and discharge piping for reciprocating pumps and compressors, acoustic and mechanical response analyses are to be carried out. These analyses are generally provided by the suppliers of such equipment. This paper explains the fundamentals behind an acoustic and mechanical response analysis and provides a simple set of consolidated design and engineering rules. The paper encourages application of these rules while developing the equipment and piping layout as well as pipe support configuration. The aim of these rules is to minimize the chance for the ultimate supplier’s detailed acoustic & mechanical response analysis to recommend significant changes to the design in a late stage of a project. Specific emphasis is placed on how the support stiffness affects the natural frequency of the piping system and a practical methodology is provided to account for this in pipe support span calculations. This paper also describes the process information that needs to be submitted to the supplier to conduct a meaningful acoustic as well as mechanical response analysis. Acknowledging requirements for lines in pulsating service at a late stage in the project, not providing the supplier with the required process information or a piping and support configuration that is not ‘mature’ enough will most likely result in significant delay and cost.

Abstract Pipe support and restraint assemblies are an integral part of engineered piping systems for power, petrochemical, refinery, and process industries. Such assemblies are specially designed and analyzed for the purpose of transferring loads from piping to building structure or supplemental steel structure. Thus, a support assembly protects the piping, or any other components, from damage that may result from startup, shutdown, shocks from valve operation, water hammer, steam hammer, wind, seismic, and other catastrophic events such as pipe rupture or explosions. It also restrains against unacceptable movements in the piping system while preserving movement due to thermal growth. The support and restraint stiffness values are utilized based on assumptions and calculations of load versus displacement. A case study of pipe support elements is performed in various static and dynamic load cases to determine the effects of assumptions of utilizing one stiffness value versus multiple stiffness values within an assembly. Additionally, the stiffness for the connected building structure opens more assumptions within industry practice. Multiple industry practices of stiffness values are integrated into this research to compare and contrast the realistic attributes of each.

Abstract The importance of fluid-elastic forces in tube bundle vibrations can hardly be over-emphasized, in view of their damaging potential. In the last decades, advanced models for representing fluid-elastic coupling have therefore been developed by the community of the domain. Those models are nowadays embedded in the methodologies that are used on a regular basis by both steam generators providers and operators, in order to prevent the risk of a tube failure with adequate safety margins. From an R&D point of view however, the need still remains for more advanced models of fluid-elastic coupling, in order to fully decipher the physics underlying the observed phenomena. As a consequence, new experimental flow-coupling coefficients are also required to specifically feed and validate those more sophisticated models. Recent experiments performed at CEA-Saclay suggest that the fluid stiffness and damping coefficients depend on further dimensionless parameters beyond the reduced velocity. In this work, the problem of data reduction is first revisited, in the light of dimensional analysis. For single-phase flows, it is underlined that the flow-coupling coefficients depend at least on two dimensionless parameters, namely the Reynolds number Re and the Stokes number Sk . Therefore, reducing the experimental data in terms of the compound dimensionless quantity V r = Re/Sk necessarily leads to impoverish results, hence the data dispersion. In a second step, experimental data are presented using the dimensionless numbers Re and Sk . We report experiments, for a 3 × 5 square tube bundle subjected to water transverse flow. The bundle is rigid, except for the central tube which is mounted on a flexible suspension allowing for translation motions in the lift direction. The evolutions of the flow-coupling coefficients with the flow velocity are determined using two different experimental procedures: (1) In the direct method, an harmonic motion of increasing frequency is imposed to the tube. (2) In the indirect method, the coefficients are obtained from the modal response of the tube (frequency, damping). The coefficient identification was performed well beyond the system instability boundary, by using active control, allowing an exploration of a significant range of flow velocity. For a given Sk , the results show that: (a) at low Re , the flow-coupling coefficients are close to zero; (b) at intermediate Re , the flow stabilizes the tube; (c) at high Re , the flow destabilizes the tube, leading to a damping-controlled instability at a critical Re . Reducing the data in terms of Re and Sk clarifies the various experimental “branches”, which are mixed when using V r . The two identification techniques lead to reasonably compatible fluid-elastic coefficients.

Abstract This paper proposed a homogenization model, and compiled a VUMAT subroutine to simulate the tension and shear of fiber-reinforced pultrusion composite (FRPC). Experiments were also performed to verify the accuracy of the homogenization model. The results show that, the simulation results agree well with the experiment data. The stiffness and strength increase with the increase of the diameter of the carbon composite part. The limit shear load and the horizontal shear strength decrease with the increase of the span. When FRPC is under shear with smaller span, the matrix tensile damage initiates first and it is the dominate failure mode, then the matrix and fiber compression damage occur at where the indenters contact. However, with the increase of the span, the delamination damage between the wound glass-fiber reinforced composite and pultrusion glass-fiber reinforced composite occurs and becomes the dominate failure mode for FRPC shear.

Ductile damage appears in ductile metallic materials when these undergo sufficient plastic deformation, and it is caused by voids and microcracks that are formed within the material due to those severe conditions. The main interest of the present research is to experimentally characterise ductile damage in different conditions of strain rate (from quasi-static to 10 3 s −1 ) and temperature (from −80°C to 180°C). Estimations of damage accumulation along the plastic regime have been taken by measuring the stiffness reduction of the material. The effects of strain localisation and necking have been accounted for by monitoring the changes in the geometry of the specimens during the test. At high speed these experiments have required the use of an in-situ shadowgraph method to monitor the sample silhouette and accurately calculate stress-strain behaviour throughout the test. The design of a novel experimental rig to perform high speed interrupted tensile tests has also been needed, in order to measure the damage accumulation in those conditions. The low and high temperature tests have been carried out inside an environmental chamber maintaining the rest of the technique unchanged. These experiments at varying strain rate and temperature have allowed to better understand the effect these conditions have on damage properties.

Shorter development design schedules and increasingly dense product designs create difficult challenges in predicting structural performance of a mainframe computer’s structure. To meet certain certification benchmarks such as the Telcordia Technologies Generic Requirements GR-63-CORE seismic zone 4 test profile, a physical test is conducted. This test will occur at an external location at the end of design cycle on a fully functional and loaded mainframe system. The ability to accurately predict the structural performance of a mainframe computer early in the design cycle is critical in shortening its development time. This paper discusses an improved method to verify the finite element analysis results predicting the performance of the mainframe computer’s structure long before the physical test is conducted. Sine sweep and random vibration tests were conducted on the frame structure but due to a limitation of the in-house test capability, only a lightly loaded structure can be tested. Evaluating a structure’s modal stiffness is key to achieving good correlation between a finite element (FE) model and the physical system. This is typically achieved by running an implicit modal analysis in a finite element solver and comparing it to the peak frequencies obtained during physical testing using a sine sweep input. However, a linear, implicit analysis has its limitations. Namely, the inability to assess the internal, nonlinear contact between parts. Thus, a linear implicit analysis may be a good approximation for a single body but not accurate when examining an assembly of bodies where the interaction (nonlinear contact) between the bodies is of significance. In the case of a nonlinear assembly of bodies, one cannot effectively correlate between the test and a linear, implicit finite element model. This paper explores a nonlinear, explicit analysis method of evaluating a structure’s modal stiffness by subjecting the finite element model to a vibration waveform and thereafter post processing its resultant acceleration using Fast Fourier Transformation (FFT) to derive the peak frequencies. This result, which takes into account the nonlinear internal contact between the various parts of the assembly, is in line with the way physical test values are obtained. This is an improved method of verification for comparing sine sweep test data and finite element analysis results. The final verification of the finite element model will be a successful physical seismic test. The tests involve extensive sequential, uniaxial earthquake testing in both raised floor and non-raised floor environments in all three directions. Time domain acceleration at the top of the frame structure will be recorded and compared to the finite element model. Matching the frequency content of these accelerations will be proof of the accuracy of the finite element model. Comparative analysis of the physical test and the modeling results will be used to refine the mainframe’s structural elements for improved dynamic response in the final physical certification test.

Taniguchi, et al. [1] developed an analytical method for evaluating the absolute maximum elasto-plastic displacements of multi-degree-of-freedom (MDOF) oscillators under the action of base excitation based on a modal combination. Its essence is that 1) modal frequencies, shapes and damping during yielding of any member of the MDOF oscillators are readily specified by the modal analysis with the secondary stiffness of the members being yielded, 2) assuming that a bilinear hysteresis may describe the force-displacement relationship of each mode, an equivalently linearized system consisting of a single-degree-of-freedom (SDOF) oscillator is introduced to approximate the absolute maximum elasto-plastic displacement of each mode, 3) the absolute maximum elasto-plastic displacement of the MDOF oscillator is evaluated by the Square Root of Sum of Squares rule (SRSS-rule) by combining the maximum elasto-plastic displacement of each mode approximated by the proposed equivalently linearized system. This study first provides small modification in the equivalently linearized system. Then, employing a couple of MDOF oscillators whose spring at arbitrary storey may yield and an accelerogram, the maximum elasto-plastic displacement of the MDOF oscillator is calculated by the proposed method and is compared with that computed by the time history analysis. Their comparison suggests that the proposed method can reasonably evaluate the absolute maximum elasto-plastic displacement of the MDOF oscillator subjected to earthquake excitation as the conventional SRSS-rule does that for the linear MDOF oscillators.

A Code Case in the framework of JSME Nuclear Codes and Standards is being developed to incorporate a seismic design evaluation methodology for piping by means of advanced elastic-plastic response analysis methods and strain-based fatigue criteria. The Code Case as an alternative seismic design rule over the current rule will provide a more rational seismic design evaluation than the current criteria. This paper demonstrates an application result of the JSME Seismic Code Case to an actual complex piping system. The secondary coolant piping system of Japanese Fast Breeder Reactor, Monju, was selected as a representative of the complex piping systems. The elastic-plastic time history analysis for the piping system was performed and the piping system has been evaluated according to the JSME Seismic Code Case. The evaluation by the Code Case provides a reasonable result in terms of the piping fatigue evaluation that governs seismic integrity of piping systems. Moreover, it is found that the supporting forces and the response accelerations of the piping system obtained by the elastic-plastic response analysis also become more rational results than those with the current elastic response analysis. The contradiction of two requirements in piping design, flexibility for thermal expansion and rigidity for seismic response, can be effectively relaxed by use of the Code Case being developed.

Seismic responses from linear and nonlinear dynamic analyses of reinforced concrete (RC) shear walls are compared to see how the damping ratio and cracking behavior affect the dynamic response of the RC structures used in the nuclear power plant. The nonlinear dynamic analyses are conducted based on the numerical model which is developed to simulate the nonlinear hysteretic behavior of RC structures subjected to in-plane shear. Through comparison of the obtained numerical results with experimental data such as load-displacement relationships and response time-histories, the developed numerical model is validated. The acceleration response spectra from the nonlinear dynamic analysis results of selected RC shear wall and those from linear dynamic analysis with combinations of the damping ratio and concrete stiffness considerations according to the level of earthquake loads and the resultant stresses are addressed.

The concept of primary/secondary categorization is first reviewed and generalized for its application to a non-linear oscillator subjected to a seismic load. Categorizing the seismic load requires calculating the input level associated with the oscillator ultimate capacity and comparing it to the level associated with the plastic yield. To resolve this problem, it is assumed that the non-linear oscillator behaves like a linear equivalent oscillator, with an effective stiffness (or frequency) and an effective damping. However, as it is not a priori possible to predict the equivalent stiffness and damping, a wide range of possibilities is systematically considered. The input motion is represented by its conventional response spectrum. It turns out that key parameters for categorization are i) the “effective stiffness factor” (varying from 0 for perfect damage behaviour to 1 for elastic-perfectly plastic) and the slope of the response spectrum in the vicinity of the natural frequency of the oscillator. Effective damping and spectrum sensitivity to damping play a second order role. A formula is presented that enables the calculation of the primary part of a seismically induced stress as a function of both the oscillator and input spectrum features. The formula is also presented in the form of a diagram. This paper follows-up on a similar paper presented by the author at the PVP 2017 Conference [1]. The new development introduced here is that the oscillator exhibits hardening capacity, while no hardening was assumed in [1]. It appears that the conclusions are slightly modified but the trend is very similar to the non-hardening case. Regarding piping systems, it appears that even when experiencing large plastic strains under beyond design input motions, their observed effective frequency is very close to their natural frequency, decreasing only by a few percents (experimental data from USA, Japan and India are processed). These observations lead to the conclusion that the seismic load, or the seismically induced inertial seismic strains, should basically be regarded as secondary.

The main pipes of reactor coolant systems (RCS) are usually long flexible structures that are connected to multiple key equipment and components of the nuclear system (e.g., reactor pressure vessel, steam generator, main pump, etc.). Mechanical analysis of pipe responses at key elbows and weld seams under static and dynamical load conditions is an essential step to ensure safety and reliability of the whole RCS. Common practice to keep the structural integrity of RCS piping under dynamical load (seismic or shock load) is to impose supporting devices at various locations so that the stiffness at weak spots can be improved. Nevertheless, the introduction of supporting devices, especially the mechanical stops, may cause significant increase of thermal stress due to the block of thermal expansion path of the piping. Hence, cooperative design and optimization of RCS piping supports by jointly considering the piping responses under static and dynamical load cases becomes quite a necessity. In this paper, such an optimal design task is formulated as a multi-objective optimization problem (MOP) with the stress level at key elbows and weld seams of the main pipes as objectives; and various parameters of each supporting device as design variables. The key feature of such MOP is that the number of design variables is unknown in prior. A single support sampling strategy is first proposed to observe the influence of one supporting device. Clustering algorithms are then applied to discover patterns from the single support sampling pool. A 3-snubber-3-stop main pipe support layout is determined via unsupervised clustering algorithms. We perform the surrogatemodel based parameter optimization once the optimization framework is fixed. Simulation results of the optimal piping support design show good satisfactions of stress level according to ASME boiler and pressure vessel code (BPVC) under both static and dynamical load cases. The data-driven design and optimization procedures presented in this paper suit the optimal design with conflicting objectives and unclear number of design variables.

We present an iterative method to solve static piping analysis including Coulomb friction between pipes and supports. It is known that the most stable method to find the solution of this problem is to look for the correct stiffness to add in the plane orthogonal to the direction of the restraints for the resulting forces to be of correct intensity. The naivest way to pick the stiffnesses at each step is to choose the ones that would give the correct forces intensities if the displacements were correct. It is very effective in term of precision, but sometimes slow in term of execution. The penalty comes from the fact that the stiffness matrix is different at each iteration and thus that it must be factorized again. In this article we propose a way to increase the speed of convergence: selecting a subset of supports among the ones where convergence is the worst, and introducing sub-iterations focusing only on those supports can reduce the number of main iterations. Those sub-iterations can be calculated at a much lesser cost than the main ones by using the generalized Sherman-Morrison formula. This algorithm was successfully implemented into the piping analysis software PIPESTRESS version 3.9.1 developed by DST Computer Services SA (the version number is temporary, the release date is Q3/Q4 of 2018).

The loads on the equipment nozzles are generally generated by the piping stress engineer by doing the stress analysis of entire closed loop systems. Subsequently the nozzle loads are passed on to the engineers of the pressure vessel equipment. The value of the loads which have been worked out for the nozzle mostly depends upon the methods/concept by which the piping stress engineer has evaluated the piping loop. Nozzle flexibility/stiffness is the important parameter in evaluation of various components of nozzle loads. The objective of this paper is to explain the effect/influence of flexibility/stiffness generated from three different methods (Anchor, WRC and Finite element method) on nozzle load evaluation and shell/nozzle junction stresses. WRC297 bulletin [6] gives the reference to nozzle flexibility in the appendix A, example no.3. The work presented in this paper is an attempt to compare the nozzle loads calculated by evaluating the flexibilities/stiffness in various methods. Further an attempt has been made to consolidate the results of junction local stresses obtained by the various methods of stiffness/flexibilities which would result in realistic results and overall code acceptable stresses without the results being either overly conservative or unconservative.

High pressure hydrogen storage tank is a key component in hydrogen supply systems of the fuel cell vehicles. Composite hydrogen storage tanks own some advantages such as high stiffness, density and strength, and the composite tanks for storage of 70 MPa hydrogen is the hotspot of research. However, composite hydrogen storage tanks have the potential leakage and explosion hazards in the process of using due to the flammable and explosive storage medium. hydrogen cycle test is an important means to detect the macroscopic strength, safety margin, structure design rationality and reliability of composite hydrogen storage tanks. The relevant standard of 70MPa composite hydrogen storage tanks is not yet introduced in China. At present, the european union, Japan and the international standardization organization have formulated the composite hydrogen storage tanks standard or code, which have an important reference for the formulation of the relevant standards in china. In this study, foreign standards related hydrogen cycling test content such as (EU) 406-2010, ANSI HGV 2-2014, ISO CD 19881-2015, SAE J2579-2013 and ECE/TRANS/180-2013 are systematically studied, which could be helpful for the establishment of relevant standards in China and the development of hydrogen cycle test equipment.