• Journal of the Earthquake Engineering Society of Korea
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• v.8 no.3
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• pp.63-76
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• 2004

This paper presents LRB-based hybrid base isolation systems employing additional active/semiactive control devices for mitigating earthquake-induced vibration of a cable-stayed 29 bridge. Hybrid base isolation systems could improve the control performance compared with the passive type-base isolation system such as LRB-installed bridge system due to multiple control devices are operating. In this paper, the additional response reduction by the two typical additional control devices, such as active type hydraulic actuators controlled by LQG algorithm and semiactive-type magnetorheological dampers controlled by clipped-optimal algorithm, have been evaluated bypreliminarily investigating the slightly modified version of the ASCE phase I benchmark cable-stayed bridge problem (i.e., the installation of LRBs to the nominal cable-stayed bridge model of the problem). It shows from the numerical simulation results that all the LRB based hybrid seismic isolation systems considered are quite effective to mitigate the structural responses. In addition, the numerical results demonstrate that the LRB based hybrid seismic isolation systems employing MR dampers have the robustness to some degree of the stiffness uncertainty of in the structure, whereas the hybrid system employing hydraulic actuators does not. Therefore, the feasibility of the hybrid base isolation systems employing semiactive additional control devices could be more appropriate in realfor full-scale civil infrastructure applications is clearly verified due to their efficacy and robustness.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.4
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• pp.243-254
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• 2021

In this study, the conservatism of the response displacement method (RDM) for the seismic response analysis of box-shaped power cable tunnels was evaluated. A total of 50 examples were used considering the cross-sections of 25 power cable tunnels and two soil conditions for each power cable tunnel. The following three methods were applied for the analysis by the RDM: (1) single cosine method, (2) double cosine method, and (3) dynamic free-field analysis method. A refined dynamic analysis method considering soil-structure interaction (SSI) was employed to compare the conservatism of the RDM. The double cosine method demonstrated the most conservative result, while the dynamic free-field analysis method yielded the least deviation. The soil stiffness reduction factor, C, for the double cosine method was recommended to be 0.9 and 0.7 for the operational performance and collapse prevention levels, respectively, to ensure a probability of at least 80% that the member force by the RDM is larger than that of dynamic SSI analysis.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.6A
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• pp.1013-1022
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• 2006

Although the cable-stayed bridges with two I-type girders inherently do not have good aerodynamic characteristics, a lot of the bridges with this type girders are constructed in Korea recently because of an economical merit. This paper investigated the aerodynamic characteristics of the cable-stayed bridges with two I-type girders. Section model tests were conducted in order to investigate the aerodynamic behaviors of this section with varying of the angles of attack, turbulence intensity and damping ratios. Two deck section configurations with different torsional stiffness were studied under construction and after completion respectively. Three types of the fairings were investigated to improve the aerodynamic characteristics of the bridges. The result of this study showed that the traditional section model test in uniform flow estimates the aerodynamic behavior rather pessimistically. The wind induced responses of the bridges were severely varied in accordance with the turbulence intensity and the structural damping ratio. The proposed fairing reduced the magnitude of the vortex-shedding vibrations and buffeting responses. It also increased the wind speed at which flutter occurs. It is expected that these investigations would provide a lot of information for the design of the cable stayed bridges with two I-type girders regarding wind resistance.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.1254-1261
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• 2011

Application of long-span bridge, which is affected by parameters such as span length, shoe boundary condition, track property and stiffness of superstructure and substructure etc., can vary. Especially, by CWR aspects of the axial force, long-span high speed railway bridges are limited at type and span length. In this study, in terms of CWR axial force, the long-span high-speed railway bridges without REJ(Rail Expansion Joint) is to propose the bridge type. Various Parameters analysis performed for the proposed type(Arch bridge, Cable-stayed bridge).

• Wind and Structures
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• v.21 no.1
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• pp.105-117
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• 2015

This paper presents a numerical characterization of real railway overhead cables based on computational fluid dynamics (CFD). Complete analysis of the aerodynamic coefficients of this type of cross section yields a more accurate modelling of pressure loads acting on moving cables than provided by current approaches used in design. Thus, the characterization of certain selected commercial cables is carried out in this work for different wind speeds and angles of attack. The aerodynamic lift and drag coefficients are herein determined for two different types of grooved cables, which establish a relevant data set for the railway industry. Finally, the influence of this characterization on the fluid-structure interaction (FSI) is proved, the static behavior of a catenary system is studied by means of the finite element method (FEM) in order to analyze the effect of different wind angles of attack on the stiffness distribution.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2004.10a
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• pp.171-178
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• 2004

The purpose of optimum design for structures is to minimize the cost and to obtain the reasonable structural systems. This design algorithm have many objective functions including discrete variables as sections, weight, stiffness and shapes. Simulated annealing, Genetic algorithm and TABU algorithm are used search for these optimum values in the structural design. TABU algorithm is applied to many types structures to search for section and distribution optimization and compared with the results of Genetic algorithm for evaluating the efficiency of this algorithm. In this paper, the plane truss of 10 elements and the space truss of 25 element having 10 nodes, star dome and cable dome are analyzed as analytical models.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2000.10a
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• pp.51-58
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• 2000

Dynamic relaxation method is a shape finding analysis method for flexible structures by introducing the dynamic equilibrium equation. However, it is difficult for shape finding to estimate the most appropriate values for the mass and damping on each shape because the values are random one. In this study, the unit mass, the unit damping and the principal direction stiffness are utilized to avoid the random values, and the Newmarks assumption is introduced during the dynamic analysis. By introducing variant time increment method presented, the convergence time is reduced, that is, it can be reduced the total times for analysis.

• Structural Engineering and Mechanics
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• v.5 no.6
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• pp.775-784
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• 1997

A unified theory is presented for the shape analysis of curved surface with a single layer structure composed by frame, membrane or shell. The shapes produced by the theory have no shear stress in elements, and the stress states in the whole shape are as uniform as possible under an ordinary load. The theory starts from defining an element potential function expressed by the measurement of the element length or the element area. Therefore, the shape analysis can produce various forms according to the definition of the potential function, and each of those form or the cable net form with the potential function of the second power of element length is simply gotten by the linear analysis. The form in tensile stress is mechanically equal to an isotropic tension form.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.18 no.3
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• pp.227-243
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• 2005

This paper presents a hybrid control system combining lead rubber bearings and hydraulic actuators for seismic response control of a cable stayed bridge. Because multiple control devices are operating, a hybrid control system could improve the control performances. However, the overall system robustness may be impacted negatively by additional active control devices. Therefore, a secondary on-off type controller according to the responses of lead rubber bearings is combined with LQG algorithm to improve the controller robustness. Numerical simulation results show that control performances of the hybrid system controlled by an on off type LQG algorithm are improved compared to those of the passive and active control systems and are similar to those of performance oriented hybrid system controlled by a LQG algorithm with the similar peak and normed control forces. Furthermore, it is verified that the hybrid system with an on-off type LQG controller is more robust for stiffness matrix perturbation than conventional hybrid control of system, and there are no signs of instability in the overall system. The proposed control system also maintains the control performance under not only the design earthquakes but also the other earthquakes. Therefore, the hybrid control system using on-off type LQG algorithm could be proposed as an improved control strategy for seismically excited cable-stayed bridges containing many uncertainties.

• Structural Engineering and Mechanics
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• v.62 no.6
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• pp.749-758
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• 2017

In structural mechanics, traditional analyses methods usually employ matrix operations for obtaining displacement and internal forces of the structure under the external effects, such as distributed loads, earthquake or wind excitations, and temperature changing inter alia. These matrices are derived from the well-known principle of mechanics called minimum potential energy. According to this principle, a system can be in the equilibrium state only in case when the total potential energy of system is minimum. A close examination of the expression of the well-known equilibrium condition for linear problems, $P=K{\Delta}$, where P is the load vector, K is the stiffness matrix and ${\Delta}$ is the displacement vector, it is seen that, basically this principle searches the displacement set (or deformed shape) for a system that minimizes the total potential energy of it. Instead of using mathematical operations used in the conventional methods, with a different formulation, meta-heuristic algorithms can also be used for solving this minimization problem by defining total potential energy as objective function and displacements as design variables. Based on this idea the technique called Total Potential Optimization using Meta-heuristic Algorithms (TPO/MA) is proposed. The method has been successfully applied for linear and non-linear analyses of trusses and truss-like structures, and the results have shown that the approach is much more successful than conventional methods, especially for analyses of non-linear systems. In this study, the application of TPO/MA, with Harmony Search as the selected meta-heuristic algorithm, to cables net system is presented. The results have shown that the method is robust, powerful and accurate.