The spent fuel of a nuclear power plant is generally stored in a wet storage pool. In case of a seismic event, one has to ensure the integrity of the spent fuel and structures holding them called spent fuel racks. In this study, a simple model accounting for 12 racks is proposed and compared with experimental results involving reduced scale racks. Fluid–structure interactions are modeled in terms of added coupling mass and damping, and free surface effects are accounted for. Comparison between simulations and experimental results showed good agreement. In spite of the simplicity of the model, simulations succeed to give a reasonable estimation of racks accelerations and were able to reproduce the effect of excitation amplitude and water level.

Long-distance pipelines for the transport of oil and natural gas to onshore facilities are mainly fabricated by girth welding, which has been considered as a weak location for cracking. Pipeline rupture due to crack initiation and propagation in girth welding is one of the main issues of structural integrity for a stable supply of energy resources. The crack assessment should be performed by comparing the crack driving force with fracture toughness to determine the critical point of fracture. For this reason, accurate estimation of the crack driving force for pipelines with a crack in girth weld is highly required. This paper gives the newly developed J-integral and crack-tip opening displacement (CTOD) estimation in a strain-based scheme for pipelines with an internal surface crack in girth weld under axial displacement and internal pressure. For this purpose, parametric finite element analyses have been systematically carried out for a set of pipe thicknesses, crack sizes, strain hardening, overmatch and internal pressure conditions. Using the proposed solutions, tensile strain capacities (TSCs) were quantified by performing crack assessment based on crack initiation and ductile instability and compared with TSCs from curved wide plate tests to confirm their validity.

In general, low cycle fatigue analysis of pressurized water reactor (PWR) components, requires strain-controlled fatigue test data such as using strain versus life ( ε –N) curves. Conducting strain-controlled fatigue tests under in-air conditions is not an issue. However, controlling strain in a PWR-test-loop-autoclave is a challenge, since an extensometer cannot be placed in a narrow autoclave (typically used in a high-temperature-pressure PWR-test-loop). This is due to lack of space inside an autoclave that houses the test specimen. In addition, installing a contact-type extensometer in the path of a high-pressure flow can be a challenge. These difficulties of using an extensometer inside an autoclave led us to use an outside-autoclave displacement sensor which measures the displacement of pull-rod-specimen assembly. However, in our study (based on in-air fatigue test data), we found that a pull-rod-controlled based fatigue test can lead to substantial cyclic hardening/softening resulting in substantially different cyclic strain amplitudes and their rates compared to the desired cyclic strain amplitudes and its rates. In this paper, we propose an Artificial-Intelligence and Machine-Learning based technique such as using k -means clustering technique to improve the pull-rod-control based fatigue test method, such that the gage-area strain amplitude and rates can reasonably be achieved. In support of this, we present the fatigue test results for both 316 SS base and 81/182 dissimilar-metal-weld specimens.

This study focuses on the numerical analysis of a piping structure subjected to the water-hammer event caused by a rapid valve closure that is combined with external harmonic loading representing an idealized machine excitation. The fluid-structure interaction procedure applied to solutions involves the method of characteristic for the fluid equations with the finite element method for pipe structures, which are modeled as beams. Junction coupling at the pipe elbow governs the two-way coupled fluid-structure interaction, and both the friction and Poisson couplings are incorporated as well. There is an application on a piping structure that consists of a valve, tank, and elbow that are defined as boundary conditions. The solved result quantities include pressure and bending stress responses as well as dynamic displacement modes of the piping structure. Comparisons of the results show that water hammer loading combined with the mechanical excitation load induces significantly increased displacements and higher stress peaks when frequencies of the harmonic load and the acoustic natural mode of the piping system coincide. Additionally, the resulting mode of lateral structural vibration of the piping member closely resembles an analytically solved eigenmode of the beam. The conclusion is that dynamically changing flows due to a water hammer event can solely excite natural frequencies of the piping structure causing resonance in the system.

This paper presents a numerical model to simulate the initial stress stiffening effect, induced by radial pressure and/or axial load on the dynamic behavior of axisymmetric shells. This effect is particularly important for thin shells since their bending stiffness is very small compared to membrane stiffness. The theoretical formulation is based on a combination of the finite element method and classical shell theory. For a perfect geometrical consistency, two semi-analytical finite elements, conical and cylindrical, are used to model axisymmetric shells. The displacement functions are derived from exact solutions of Sanders' shell equilibrium equations. The results obtained using this approach are remarkably accurate. The potential energy is calculated to estimate the initial stiffening effect using direct membrane forces per unit width and rotations about the orthogonal axes. The final stiffness matrix of each finite element is composed of the regular stiffness matrix and the added stiffness matrix generated by membrane loads. The frequencies of vibration are compared with those obtained in other experimental and theoretical research works and very good agreement is observed.

This paper presents the steady-state thermoelasticity solution for a circular solid plate is made of an undrained porous piezoelectric hexagonal material symmetry of class 6 mm. The porosities of the plate vary through the thickness; thus, material properties, except Poisson's ratio, are assumed as exponential functions of axial variable z in cylindrical coordinates. Having axisymmetric general form, external thermal and electrical loads are acted on the plate and the piezothermoelastic behavior of the plate is investigated. Using a full analytical method based on Bessel Fourier's series and separation of variables, the governing partial differential equations are derived. A formulation is given for the displacements, electric potential, thermal stresses, and electric displacements resulting from prescribed the general form of thermal, mechanical, and electric boundary conditions. Finally, the application of the derived formulas is illustrated by an example for a cadmium selenide solid, the results of which are presented graphically. Also, the effects of material property indexes, the porosity, and Skempton coefficients are discussed on the displacements, thermal stresses, electrical potential function, and electric displacements.

Support and excavation methods have a great effect on the supporting role of the foundation pit. To investigate the effect of foundation pit with different support and excavation methods on adjacent buried hydrogen pipe, a pipe–soil coupling model was established. Deformation, strain, and stress of the pipe near the foundation pit with different support and excavation methods were analyzed. The results show that stress concentration appears on the upper and lower surfaces of the middle part of the pipe after the foundation pit excavation. The high stress areas on the upper and lower surfaces are distributed symmetrically about the pipe center. Upper surface of the pipe's middle section is pressed and the lower surface is pulled, but the strain distribution of the pipe at the pit edge is opposite. Vertical displacement of the pipe is bigger than its horizontal displacement. The underground continuous wall as the most common support structure can effectively reduce the pipe deformation. Supporting methods have different effects on buried pipe's mechanical behavior. Lateral reinforcement, inner support, and bolt support can effectively reduce the pipe deformation, but the mitigating effect of lateral reinforcement is less than inner support and bolt support. The pipe is also affected by time and space of the foundation pit excavation. The slope excavation can greatly reduce the pipe deformation, but the effects of island excavation and basin excavation are not obvious. Those results can provide references for pipe safety assessment and protection.

A 1:4 scale seismic simulation shaking table experiment was designed and performed to study the sloshing wave height response of a storage tank under displacement due to seismic excitation, wherein a 1000 m 3 vertical storage tank was used to compare the sloshing wave height for different tanks with different foundations. Under different foundation forms, the tank motion includes sway and roll. Meanwhile, the design code and finite element method were used to compare with the experiment for mutual verification. The results show that the peak value of the sloshing wave height is at its minimum at the center, and the maximum is near the tank wall when the model tank was excited to the ground motion with the predominant frequency range from 0.29 and 0.32 Hz, and the floating roof can significantly reduce the sloshing wave height. For different input conditions with equivalent seismic magnitude, the wave heights were notably different, so the design should use multiple seismic waves as inputs. The acceleration values were different when different foundations were used, but there was little effect on the sloshing wave height. Besides, the sloshing wave heights measured in the experiment were close to those calculated using standard equations and finite element results, which proves that the three can verify each other.

Analytical approaches for cylindrical shell are mostly based on expansion of all variables in Fourier series in circumferential direction. This leads to eighth-order differential equation with respect to axial coordinate. Here it is approximately treated as a sum of two fourth-order biquadratic equations. First one assumes that all variables change more quickly in circumferential direction than in axial one (long solution), while the second (short) one is based on opposite assumption. The accuracy and applicability of this approach were demonstrated (Orynyak, I., and Oryniak, A., 2018, “Efficient Solution for Cylindrical Shell Based on Short and Long (Enhanced Vlasov's) Solutions on Example of Concentrated Radial Force,” ASME Paper No. PVP2018-85032) on example of action of one or two concentrated radial forces and compared with finite element method results. This paper is an improvement of our previous work (Orynyak, I., and Oryniak, A., 2018, “Efficient Solution for Cylindrical Shell Based on Short and Long (Enhanced Vlasov's) Solutions on Example of Concentrated Radial Force,” ASME Paper No. PVP2018-85032). Two amendments are made. The first is insignificant one and use slightly modified expressions for bending strains, while the second one relates to the short solution. Here we do not consider any more that circumferential displacement is negligible as compared with radial one. Eventually this improves the accuracy of results, as compared with previous work. For example, for cylinder with radius, R, to wall thickness, h, ratio equal to 20, the maximal inaccuracy for radial displacement in point of force application decreases from 5% to 3%. For thinner cylinder with R/h = 100, this inaccuracy decreases from 2.5% to 1.25%. These inaccuracies are related to larger terms in Fourier expansion, the significance of which decrease when length or area of outer loading becomes greater. The last conclusion is demonstrated for the case of distributed concentrated force acting along short segment on axial line.

This work investigates the response of industrial steel pipe elbows subjected to severe cyclic loading (e.g., seismic or shutdown/startup conditions), associated with the development of significant inelastic strain amplitudes of alternate sign, which may lead to low-cycle fatigue. To model this response, three cyclic-plasticity hardening models are employed for the numerical analysis of large-scale experiments on elbows reported elsewhere. The constitutive relations of the material model follow the context of von Mises cyclic elasto-plasticity, and the hardening models are implemented in a user subroutine, developed by the authors, which employs a robust numerical integration scheme, and is inserted in a general-purpose finite element software. The three hardening models are evaluated in terms of their ability to predict the strain range at critical locations, and in particular, strain accumulation over the load cycles, a phenomenon called “ratcheting.” The overall good comparison between numerical and experimental results demonstrates that the proposed numerical methodology can be used for simulating accurately the mechanical response of pipe elbows under severe inelastic repeated loading. Finally, this paper highlights some limitations of conventional hardening rules in simulating multi-axial material ratcheting.

Pipe systems have been widely used in industrial plants such as power stations. In these systems, the displacement and stress distributions often need to be predicted. Analytical and numerical methods, such as the finite element method (FEM), boundary element method (BEM), and frame structure method (FSM), are typically adopted to predict these distributions. The analytical methods, which can only be applied to problems with simple geometries and boundary conditions, are based on the Timoshenko beam theory. Both FEM and BEM can be applied to more complex problems, although this usually requires a stiffness matrix with a large number of degrees-of-freedom. In FSM, although the structure is modeled by a beam element, the stiffness matrix still becomes large; furthermore, the matrix size needed in FEM and BEM is also large. In this study, the transfer matrix method, which is simply referred to as TMM, is studied to effectively solve complex problems, such as a pipe structure under a small size stiffness matrix. The fundamental formula is extended to a static elastic-plastic problem. The efficiency and simplicity of this method in solving a space-curved pipe system that involves an elbow are demonstrated. The results are compared with those obtained by FEM to verify the performance of the method.

The thermomechanical modeling of a sleeve rehabilitation system for pressure pipes is studied including temperature effect on system behavior. The rehabilitation system consists of a multicylinder axisymmetric layer system, with an intermediate layer of epoxy resins and two outer steel covers that are longitudinally welded forming a sleeve. The analysis is conducted over several stages; initially, the incidence of temperature on the rigidity of three types of resins currently available on the market is experimentally evaluated. Then, nonlinear relationships between rigidity and temperature are established from the evaluation of the resins, which are typical of an inhomogeneous material. The resins exhibit a significant loss of rigidity with temperature, generating a risk of delamination that could drastically reduce the effectiveness of the rehabilitation system in the event of possible temperature rises. An analytical model was developed to calculate contact pressures between the resin layer and the external sleeve, internal pipeline displacements, stresses, and deformations. Finally, contour plots were developed for different temperature, pressure levels, and pipe thickness as a graphics tool to predict pipeline failure due to plastic deformation or rupture.

A polyethylene pipe reinforced by winding steel wires (PSP) has been widely used in the petroleum, chemical, and water supply industries. The PSP has outstanding mechanical properties due to its unique composite structure. However, interfacial debonding between steel wire and adhesive sometimes occurs when the temperature and inner pressure increases to some extent in the application. In this study, the interfacial behavior between steel wire and adhesive was investigated and the interfacial failure process was analyzed. First, to acquire test data of interfacial failure, pull-out tests were conducted using specimens consisted of steel wire and adhesive. Specimens were prepared per the PSP manufacturing process, and a temperature change occurred in the specimens' preparation. Second, as the details of failure process could not be observed directly, finite element models were established to represent the mechanical behavior of the steel-polymer interface in-order to reproduce the debonding failure process. The thermal preload was taken into account in the model, and its influence on interfacial behavior was discussed. Contact surface with cohesive behavior was utilized to characterize the interfacial property. Finally, the interfacial failure process including stick–slip interaction and frictional sliding interaction was modeled in the simulation. The simulation result agreed well with the experimental data. Based on the finite element model, the cause and the distribution of thermal residual stress in pull-out specimen were illuminated. Further, it is discussed that how the stress distribution changes along the adhesive interface.

This study designed a specimen that simulates the deformation and failure behaviors of the piping components in nuclear power plants (NPPs) under excessive seismic loads beyond the design basis, and conducted ultimate-strength tests using this specimen at room temperature (RT) and 316 °C. SA312 TP316 stainless steel (SS) and SA508 Gr.3 Cl.1 low-alloy steel (LAS) were used in the experiments. Displacement-controlled cyclic loads with constant and random amplitudes of load-line displacement (LLD) were applied as input loads. A set of input cyclic loads consisted of 20 cycles, and the LLD amplitudes of the cyclic load were determined to induce the maximum membrane plus bending stress intensity of 6–42 S m on the specimen, where S m is the allowable design stress intensity. Multiple sets of input cyclic loads, with increasing amplitude of LLD, were applied to the specimen until cracking initiated. The results demonstrate that the simulated specimen adequately showed the ratcheting deformation and fatigue-induced cracking of piping components under displacement-controlled excessive seismic loads. In addition, samples of both materials failed under displacement-controlled cyclic load levels that were several times higher than those of the design basis earthquake (DBE). The SA316 TP316 SS had greater resistance to failure under large-amplitude cyclic loads than did SA508 Gr.3 Cl.1 LAS. For both materials, resistance to failure was lower at 316 °C than at RT. This study confirmed that the evaluation procedure of the ASME design code predicted the fatigue failure of specimens very conservatively under large-amplitude cyclic loads simulating displacement-controlled excessive seismic loads.

Engineering solutions for crack-tip opening displacement (CTOD) and J-integral estimations for pipelines with a surface crack are proposed based on parametric finite element (FE) analyses for various geometries, material properties, and internal pressure conditions. Two kinds of CTOD definitions are considered in relation to strain-based estimation solutions for dealing with confusion regarding the definition of CTOD and to extend the applicability of tensile strain capacity (TSC) assessment. Moreover, influence functions of internal pressure are also suggested to take account of the effect of internal pressure on TSC. Using the proposed solutions, TSCs for cracked X65 and X70 pipes were assessed based on initiation and ductile instability. Curved wide plate tests were performed to obtain experimental TSCs, which were compared with those from the proposed solutions. Moreover, TSCs from the proposed solutions were also compared with those from other TSC-predicted models in order to assess their validity.

In this paper, mechanical buckling analysis of a functionally graded (FG) elliptical plate, which is made up of saturated porous materials and is resting on two parameters elastic foundation, is investigated. The plate is subjected to in-plane force and mechanical properties of the plate assumed to be varied through the thickness of it according to three different functions, which are called porosity distributions. Since it is assumed that the plate to be thick, the higher order shear deformation theory (HSDT) is employed to analyze the plate. Using the total potential energy function and using the Ritz method, the critical buckling load of the plate is obtained and the results are verified with the simpler states in the literature. The effect of different parameters, such as different models of porosity distribution, porosity variations, pores compressibility variations, boundary conditions, and aspect ratio of the plate, is considered and has been discussed in details. It is seen that increasing the porosity coefficient decreases the stiffness of the plate and consequently the critical buckling load will be reduced. Also, by increasing the pores' compressibility, the critical buckling load will be increased. Adding the elastic foundation to the structure will increase the critical buckling load. The results of this study can be used to design more efficient structures in the future.

From linear elastic fracture mechanics (LEFM), it is well accepted that only the singular stress near the crack tip contributes to the fracture event through the crack tip stress intensity factor K. In the biaxial loading, the stress component that adds to the T-stress at the crack tip, affects only the second term in the Williams' series solution around the crack tip. Therefore, it is generally believed that biaxial load does not change the apparent fracture toughness or the critical stress intensity factor (K c ). This paper revisited several specimen geometries under biaxial loading with finite element method. The sources of discrepancy between the theory and the test data were identified. It was found that the ideal biaxial loading would not be achieved for typical fracture specimens with finite geometry. Comparison to available test data shows that, while the biaxial load could affect the apparent fracture toughness, the contribution is relatively small.

To investigate the behavior of components and piping systems subjected to seismic loadings, the maximum restoring forces and maximum deformations of inelastic single-degree-of-freedom (SDOF) systems due to harmonic excitations and seismic floor motions are calculated and presented as diagrams. These systems have restoring forces characterized by a bilinear skeleton curve of a kinematic hardening rule. The diagrams show two types of characteristics, based upon which sinusoidal loadings can be categorized into force- and displacement-controlled loadings, and seismic loadings can be categorized into force- and displacement-dominant loadings, which are newly proposed herein. The characteristics of force- and displacement-dominant loadings are almost equal to those of force- and displacement-controlled loadings, respectively.

The purpose of this paper is to show the electro-elastic static behavior of cylindrical sandwich pressure vessels integrated with piezoelectric layers. The core is made of functionally graded carbon nanotube-reinforced composite (FG-CNTRC). The cylinder is embedded between two piezoelectric layers made of PZT-4. The effective material properties of reinforced core with carbon nanotubes (CNTs) are calculated based on rule of mixture. The constitutive relations are developed in cylindrical coordinate system based on a higher-order shear deformation theory for both core and piezoelectric layers. The employed higher-order theory is based on third-order variation of deformations along the thickness direction to improve the accuracy of numerical results. The method of eigenvalue–eigenvector is used for solution of system of governing equations along the longitudinal direction. The numerical results are provided along the longitudinal and radial directions in terms of significant parameters such as various patterns of CNTs, various volume fractions of CNTs, various elastic foundation coefficients, and various applied electrical potentials.

Buried pipelines are faced with and vulnerable to extreme hazards such as earthquakes, different types of faulting, and landslides. Generally, a buried pipeline is modeled as a beam on a series of springs, which represent the surrounding soil. To determine the specifications of these springs, the equations proposed by ASCE Guideline are usually used. Its accuracy was doubted by some recent studies. In this study, two full-scale tests simulating the effect of strike-slip faulting were initially carried out on 4 and 8-in. diameter steel pipes buried in compacted sandy soil. The displacement of the pipe was recorded directly at any moment, along its length. Then through optimization-based simulations, the specifications of the equivalent springs of the soil were calculated so that the deformation of the pipe along its length would be consistent with the experimental results. Then, based upon verified finite element models, a database of different parameters of buried pipes subjected to strike-slip faulting including the diameters and different burial depths was created. The results showed that the ASCE equations need modification at the condition of strike-slip faulting and so, based on the created database, a new form of the equations of lateral interaction between dense sandy soil and steel pipe in the presence of strike-slip fault was proposed.