Vibration Characteristics of a Perforated Plate Immersed in Fluid

Perforated plates are used in many mechanical structures in thermal power plants, nuclear power plants, or chemical plants etc. Cylindrical structures made by the perforated plates are also found in many places. However, vibration characteristics of the structures made by perforated plates are not fully clarified, especially for the structures immersed in liquid. The stiffness of the structures becomes smaller than that of ones made by simple plates with no holes, while the mass of the structures also becomes smaller. According to the balance between the stiffness reduction and mass reduction, natural frequencies will be decided. Moreover, added mass and added damping effects are very large in liquid, and are thought to largely change due to holes. In this study, as a fundamental step, a perforated plate is treated. The vibration characteristics such as natural frequency and damping ratio are studied for various hole numbers or various opening ratios by both numerical simulations and simple test models. Vibration tests are conducted in liquid as well as in air.

Beam-Mode Buckling of Buried Pipeline Subjected to Seismic Ground Motion

During seismic events, buried pipelines are subjected to deformation by seismic ground motion. In such cases, it is important to ensure the integrity of the pipeline. Both beam-mode and shell-mode buckling may occur in the event of compressive loading induced by seismic ground motion. In this study, the beam-mode buckling of a buried pipeline that occurred after the 2007 Niigataken Chuetsu-oki earthquake in Japan is investigated. A simple formula for estimating the critical strain, which is the strain at the peak load, is derived, and the formula is validated by finite-element analysis. In the formula, the critical strain increases with the pipeline diameter and hardness of the surrounding soil. By comparing the critical strain derived in this study for beam-mode buckling with the critical strain derived in a past study for shell-mode buckling, the formula facilitates the selection of the mode to be considered for evaluating the earthquake resistance of a pipeline. In addition to the critical strain, a method to estimate the deformation caused by seismic ground motion is proposed; the method can be used to evaluate the earthquake resistance of buried pipelines. This method uses finite-element analyses, and the soil–pipe interaction is considered. This method is used to reproduce the actual beam-mode buckling observed after the Niigataken Chuetsu-oki earthquake, and the earthquake resistance of a buried pipeline with general properties is evaluated as an example.

LBB Under Beyond Design Basis Seismic Loading

The Atucha II nuclear power plant is a unique pressurized heavy water reactor (PHWR) being constructed in Argentina. The original plant design was by Kraftwerk Union (KWU) in the 1970’s using the German methodology of break preclusion. The plant construction was halted for several decades, but a recent need for power was the driver for restarting the construction. The US NRC developed leak-before-break (LBB) procedures in draft Standard Review Plan (SRP) 3.6.3 for the purpose of eliminating the need to design for dynamic effects that allowed the elimination of pipe whip restraints and jet impingement shields. This SRP was originally written in 1987 with a modest revision in 2005. The United States Nuclear Regulatory Commission (US NRC) is currently developing a draft Regulatory Guide on what is called the Transition Break Size (TBS). However, modeling crack pipe response in large complex primary piping systems under seismic loading is a difficult analysis challenge due to many factors. The initial published work on the seismic evaluations for the Atucha II plant showed that even with a seismic event with the amplitudes corresponding to the amplitudes for an event with a probability of 1e−6 per year, that a Double-Ended Guillotine Break (DEGB) was pragmatically impossible due to the incredibly high leakage rates and total loss of make-up water inventory. The critical circumferential through-wall flaw size in that case was 94-percent of the circumference. This paper discusses further efforts to show how much higher the applied accelerations would have to be to cause a DEGB for an initial circumferential through-wall crack that was 33 percent around the circumference. This flaw length would also be easily detected by leakage and loss of make-up water inventory. These analyses showed that the applied seismic peak-ground accelerations had to exceed 25 g’s for the case of this through-wall-crack to become a DEGB during a single seismic loading event. This is a factor of 80 times higher than the 1e−6 seismic event accelerations, or 240 times higher than the safe shutdown earthquake (SSE) accelerations.

Effects of Base Uplifting on the Seismic Response of Unanchored Liquid Storage Tanks

Unanchored liquid storage tanks under strong earthquake loading tend to uplift. In the present study, the effects of base uplifting on the seismic response of unanchored tanks are presented with emphasis on elephant’s foot buckling, base plate strength and shell-to-base connection capacity. Towards this purpose, base uplifting mechanics is analyzed through a detailed simulation of the tank using non-linear finite elements, and a static pushover analysis is conducted that considers the hydrodynamic pressure distribution due to seismic loading on the tank wall and the base plate. The uplifting provisions from EN 1998-4 and API 650 Appendix E standards are briefly described. Numerical results for a typical 27.8-meter-diameter steel tank are compared with the above design provisions.

Dynamic Testing of High Density Polyethylene Vent and Drain Configurations

For corroded piping in low temperature systems, such as service water systems in nuclear power plants, replacement of carbon steel pipe with high density polyethylene (HDPE) pipe is a cost-effective solution. HDPE pipe can be installed at much lower labor costs than carbon steel pipe, and HDPE pipe has a much greater resistance to corrosion. This paper presents the results of the seismic testing of selected vent and drain configurations. This testing was conducted to provide proof of the conceptual design of HDPE vent and drain valve configurations. A total of eight representative models of HDPE vent and drain assemblies were designed. The models were subjected to seismic SQURTS spectral acceleration up to maximum shake table limits. The test configurations were then checked for leakage and operability of the valves. The results for these tests, along with the test configurations, are presented. Also presented are the acceleration data observed at various points on the test specimens.

Application of a Large-Scale Database System for the Analysis and Design of the US EPR™ Standard Nuclear Power Plant

Due to the increased size and complexity of large-scale commercial and industrial structures, it is increasingly challenging to manage key engineering data including analysis and design results of these structures. This paper presents a novel approach of using large-scale database systems as a means to gather, organize and manage key analysis and design results of a large-scale structure. Specifically, this paper describes in detail the development process of the backend database management system (DBMS) for the U.S. EPR™ Standard Nuclear Power Plant (NPP) Nuclear Island (NI) structures. The database system consists of three parent database tables to represent three representative groups of load combinations applicable to the U.S. EPR™ Standard NPP. Inheriting all characteristics of an applicable parent table, a primary child table in the database system represents a particular U.S. EPR™ NI Safety-Related structure in its entirety while a secondary child table a group of slabs or walls of the structure. Each secondary table is comprised of database fields that are representative of various structural demands, section capacities, reinforcing ratios, and demand-to-capacity ratios for three reinforced concrete design conditions (i.e., combined axial force and bending design, in-plane shear design, and out-of-plane shear design). The complete database system with fully populated tables is a central repository where all analysis and design results for the U.S. EPR™ NI Common Basemat structures are stored and sorted. To facilitate data queries from the developed backend database system, this paper introduces a user-friendly frontend interface program developed using Visual Basic Application (VBA) with Excel. Potential benefits of the developed database system are demonstrated with simple application examples involving simple data queries only followed by complex engineering tasks that require a more advanced form of data queries.

An Approximate Formula to Calculate the Restoring and Damping Forces of an Air Spring With a Small Tube

This paper proposes a simple expression for calculating the restoring and damping forces of an air spring equipped with a small tube. Air springs are commonly used in railway vehicles, automobiles, and various vibration isolators. The air spring used in this study consists of two tanks connected by a long tube. Using a tube instead of an orifice enables flexibility in the arrangement of the two tanks. In addition, this makes it possible to manufacture a thin air spring. The oscillating system, which consists of a single mass supported by this type of air spring, is a single-degree-of-freedom (SDOF) system. However, it has two resonance points for a reason that had been unknown for a long period of time. In this paper, we explain why the SDOF system has two resonance points. After that, assuming that the vibration is small and the flow through the tube is laminar, we derive the spring constant and damping coefficient of an air spring subjected to a simple harmonic motion. Then, we calculate the frequency response curves for the system and compare the calculated results with the experimental values. According to the experiment, there is a remarkable amplitude dependency in this type of air spring, so the frequency response curves for the system change with the magnitude of the input amplitude. It becomes clear that the calculation results are in agreement with the limit value when the input amplitude approaches zero.

Non-Iterative Reinforced Concrete Design Methodology for Combined Axial Force and Bending Moment

This paper presents a non-iterative reinforced concrete design methodology that can be used to design structural components such as beam-columns, walls and slabs of reinforced concrete structures subjected to combined axial force and bending moment. The paper demonstrates that the required reinforcing area of a demand point (paired axial force and bending moment) on the interaction diagram can be accurately computed by 1) constructing two non-dimensionalized capacity curves approximated by a combination of polygon segments that are expected to bound all possible design cases including the demand point, 2) dividing the area enclosed by the lower- and upper-bound capacity segments into several four-sided capacity polygons, 3) locating a capacity polygon where the demand point is located and identifying associated lower- and upper-bound capacity segments, 4) identifying a capacity segment that passes through the demand point by linear interpolation from the given two bounding segments, and finally 5) determining the required reinforcing area for the demand point by linear interpolation between the minimum and maximum reinforcing ratios associated with the pre-defined lower- and upper-bound capacity segments, respectively. This essentially eliminates a cumbersome need to perform iterative trial and error solutions to obtain the required reinforcing area for the combined axial force and moment concrete design. Illustrative design examples per ACI 349 and ACI 359 are presented within the paper.

Seismic Capacity of Threaded, Brazed and Grooved Fire Protection Pipe Joints

A series of static and shake table tests were conducted on pressurized threaded, brazed and mechanical, i.e., grooved pipe joints, commonly used in fire protection systems. The objective of the tests was to understand the behavior and failure modes of these common types of joints under seismic and static lateral loads. The paper presents the measured loads and deflections of the joints up to the point of failure. It also describes the joints’ static and dynamic failure modes. While this information may be limited it can be used to model the joint flexibility under large lateral loads, determine their capacity, and help understand the leak and rupture characteristics of threaded, brazed and clamped joints.