Optimal Placement of Viscous Dampers in the Water Pipeline Networks Subjected to Near-Fault Earthquakes Using Genetic Algorithm

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.

Dynamic Experimental Investigation on the Self-Vibration Characteristics of Liquid Storage Tanks Under Seismic Excitations

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.

Research and Development of Distributed Multistage TMD for Long Period Structure Using Coil Spring

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.

A Study of Applicability of Finite Displacement Analyses With Semi-Analytical Finite Elements for Analyzing Uplift Displacement of Flat-Bottom Cylindrical Shell Tanks Statically

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.

Development of High Energy Absorbing Seismic Tie With I-Sectional Shape for Thermal Power Boiler Structure

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.

Semi-Active Control of Structural Systems Aiming to Approximate the Performance of the Targeted Active Control Law: Output Emulation Approach

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.

Main Issues on the Seismic Design of Industrial Piping Systems and Components

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.

Investigation of Soil-Structure Interaction and Higher-Mode Effects on Dynamic Response of Base-Isolated Structure Founded on Half Space

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.

Low Cycle Fatigue Tests and Simulations on Steel Elbows

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.

A Parametric Study of Independent Support Motion Method for the Steam Supply Piping Connected to the HP Turbine of APR 1400

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.