Cyclic Deformation and Buckling Behavior of Pipe With Local Metal Loss Subjected to Seismic Ground Motion

Buried pipelines may be deformed due to earthquakes and also corrode despite corrosion control measures such as protective coatings and cathodic protection. In such cases, it is necessary to ensure the integrity of the corroded pipelines against earthquakes. This study developed a method to evaluate the earthquake resistance of corroded pipelines subjected to seismic ground motions. Axial cyclic loading experiments were carried out on line pipes subjected to seismic motion to clarify the cyclic deformation behavior until buckling occurs. The test pipes were machined so that each one would have a different degree of local metal loss. As the cyclic loading progressed, displacement shifted to the compression side due to the formation of a bulge. The pipe buckled after several cycles. To evaluate the earthquake resistance of different pipelines, with varying degrees of local metal loss, a finite-element analysis method was developed that simulates the cyclic deformation behavior. A combination of kinematic and isotropic hardening components was used to model the material properties. These components were obtained from small specimen tests that consisted of a monotonic tensile test and a low cycle fatigue test under a specific strain amplitude. This method enabled the successful prediction of the cyclic deformation behavior, including the number of cycles required for the buckling of pipes with varying degrees of metal loss. In addition, the effect of each dimension (depth, longitudinal length and circumferential width) of local metal loss on the cyclic buckling was studied. Furthermore, the kinematic hardening component was investigated for the different materials by the low cycle fatigue tests. The kinematic hardening components could be regarded as the same for all the materials when using this component as the material property for the finite-element analyses simulating the cyclic deformation behavior. This indicates that the cyclic deformation behavior of various line pipes can be evaluated only based on their respective tensile properties and common kinematic hardening component.

A Load Combination Method for Seismic Design of Multiple Supported Piping Systems With Friction Characteristics: Part 1—Generally Correlated Excitations

A load combination method for seismic response calculation of piping systems with friction characteristics to multiple support excitations is presented. This method has an advantage, such that the cross-correlation among support excitations and “response reduction factor” due to friction are taken into account by use of a stationary random vibration theory approach. Using a simple analytical SDOF piping system with friction characteristics to two support excitations, This method is supplied to various correlation cases of two support excitations and friction characteristics and the maximum responses of piping is calculated. From these calculation results, it is clear that the maximum acceleration responses of nonlinear piping systems can also depend on the cross-correlation among support excitations and can be reduced due to the friction effect. Finally, the conventional equation of the response reduction factor and the maximum response calculated by the proposed method are presented for practical use.

Linear Friction Damper Consisted of Cylindrical Block and Inclined Lever (Improvement to Avoid Sprag-Slip Problem and Analytical Model to Verify Cause)

For the passive isolation systems, the ordinary friction damper of constant friction force has performance limitations. This is, because the isolation characteristic declines and the displacement remains apart from the equilibrium position after the disturbance disappears, when the friction force is large. It is known that the above drawbacks are improved when the friction force varies depending on the displacement. The authors have proposed a new type of friction damper in our previous paper. This friction damper uses an inclined lever, which contacts the cylindrical block by means of a rotational spring. The angle of inclination of the lever varies together with the displacement of the cylindrical block. Then, the normal and friction forces on the contact surface vary depending on the displacement. However, “Sprag-slip” vibration occurred in some cases in the experiments. This paper investigates the cause of the vibration and a design to prevent it. Then, an analytical model is proposed to simulate the problem and to estimate the effect of improvement.

Impact Response Analysis of a Coaxial Double-Pipe Structure by Using Spectral Element Method

A coaxial double-pipe structure is to be used in the primary and auxiliary coolant system of a high-temperature gas-cooled reactor. In order to study the vibration characteristics of the coaxial double-pipe structure, hammering experiments were performed using specimens of the structure. Because the structural responses obtained in the experiments contained high-frequency components, impact response analysis was performed by using the spectral element method, which has high accuracy in the high-frequency region. A comparison between analysis results and experiment results showed good agreement between them. We also performed parametric studies on the damping properties of the specimens. The damping properties determined from the experiment results indicated that the inner and outer pipes had different damping properties.

Seismic Fragility Evaluation of a Buried Auxiliary Cooling Water System Pipeline for Liquefaction-Induced Soil Settlement

Seismic fragility evaluation of the buried Auxiliary Cooling Water System (ACWS) intake pipeline of the Mu¨hleberg Nuclear Power Plant (KKM) was conducted to determine its performance when subjected to liquefaction-induced soil settlement. This evaluation utilized nonlinear analysis as a rigorous alternative to more approximate methods due to the importance of the ACWS to plant safety. The ACWS intake line is constructed of welded steel pipe with a nominal outside diameter of 23.6 in. (600 mm) and a wall thickness of 0.22 in. (5.6 mm). The line was modeled and analyzed using computer program Abaqus, considering nonlinearities of the pipe material and pipe-soil interaction. Failure of the pipe is initiated by local wrinkle-type buckling at the wall penetration followed by local ductile tearing. Failure criterion for local tearing is expressed in terms of effective plastic strain including the effects of triaxiality at the critical section. Parameters critical to the pipe settlement capacity include pipe yield and ultimate strengths, pipe effective strain capacity, and soil yield strength and displacement. The variabilities in the pipe settlement capacities were calculated considering varabilities of the critical parameters by the Separation-of-Variables Method recommended by EPRI TR-103959. The 1% non-exceedance probability (NEP) settlement capacities were determined to be well in excess of the 99% NEP settlements estimated by the geotechnical investigation. Based on this comparison, it was concluded that the probability of ACWS intake line failure due to soil liquefaction is negligible.

Finite Element Analysis of Industrial Steel Elbows Under Strong Cyclic Loading

Steel elbows are used in petrochemical facilities and power plants. In the case of an earthquake event, in addition to other service loads, they are subjected to strong repeated cyclic structural loading that may lead to failure due to cyclic accumulation of plastic strain or collapse. Furthermore, due to their flexibility, significant non-linearities occur and the elbow cross-section shape distorts as cyclic loading takes place resulting at an oval or flatten shape at the end of the loading sequence. Accumulation of plastic strains takes place at the most stressed parts of the elbow, associated with extensive bulging of the cross-section which is more pronounced in the presence of internal pressure. The present study is numerical, based on a finite element simulation of the elbow, and examines elbow behavior subjected to strong cyclic bending in the presence of internal pressure. The material constitutive model has a dominant effect on describing the elbow response, and this is shown through the employment of three different classical plasticity models.

Experimental Study of a Full Scale Building Isolated With Multiple Friction Pendulum System With Multiple Sliding Interfaces

Presented in this paper is the performance evaluation of the multiple friction pendulum system (MFPS) with multiple sliding interfaces on seismic mitigation through a series of shaking table tests of a full scale MFPS-isolated building. In the tests, a three-story steel building of 40 tons in total weight, 3m and 4.5m in two horizontal directions and 9m in height, was equipped with MFPS isolators each with 4 sliding interfaces and subjected to various types of earthquakes to examine the efficiency of the isolators in reducing seismic response of a structure. Experimental results from shaking table tests tells that the roof accelerations, base shears, column shear forces have been significantly lessened with negligible residual displacements in the isolators while compared to the responses of a fixed-base structure.

Design Criteria for a New Weir Surface Repair Method Containing Shock Absorbing Cushions

Although a weir surface layer is subjected to shocks of the floods with particles of varies sizes, they are generally repaired by covering an abrasion-resistant layer. In the past, based on the knowledge that higher strength materials have higher abrasion resistances, many reports have focused on enhancing the strength of the repair materials. However, the occurrence of brittle fracture and peeling were also significantly increased. These resulted in an awkward situation that the need of repairing becomes more urgent even if the material properties have been greatly improved. In an attempt to break through the traditional methods, the major thrust of this paper is to propose criteria for designing a weir surface containing shock absorbing cushions, and a new method accordingly.. It was then confirmed by in situ tests that such criteria have the capability to lead the above-mentioned shocks to be absorbed. Due to the limited space of this paper, all related test layout and results will be presented on another paper.

The Parameter Study of the Seismically Isolated Bridge System by Lead Rubber Bearing Based on Energy Analysis

The energy response equations of the seismically isolated bridge system are established based On the energy equilibrium theory. Bilinear analysis model of the energy response of the seismically isolated bridge is constructed by series connecting the bridge piers and the Lead rubber bearings. According to the applicable Code of Seismic Design for Railway Engineering, forty strong ground motion records are appropriately selected as the seismic input and the nonlinear time history analyses for the seismic energy responses of the bilinear SDOF seismically isolated bridge systems with different natural periods are carried out. The influences of peak ground accelerations, principal dynamic parameters of isolated bridge system on input energy and their distributions are studied.

A Simple Method to Estimate the Vibration Characteristics of a PWR Fuel Assembly

The main objective of this study is to establish a simple method making it possible to analyze the dynamic characteristics of the nuclear fuel assembly considering the geometrical configuration and the supporting condition of reactor internals etc. without any prototype test or FE models. In this study, a general frequency expression has been suggested for Bernoulli-Euler beams with generally restrained boundary conditions using Fourier series as a mode function. And using the frequency expression, the natural frequencies and mode shapes of a conventional fuel assembly for OPR1000 plants with reactor end conditions are calculated and compared with the test results in order to figure out its applicability to estimation on vibration characteristics of the fuel assembly. As a result, since the method suggested in present study gives quite a similar one with test result, present method will be useful to perform design evaluation preliminarily on the vibration characteristic of developing new fuel assembly.