• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.3
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• pp.271-280
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• 2003

The purpose of the study presented in this paper is to develope the general model for capture of the linear and nonlinear response of a flexible diaphragm building in which there are significant contributions from the out-of-plane walls. Two single-story single-diaphragm half scale reinforced masonry buildings were tested by researchers at the United States Army Construction Engineering Research Laboratory (CERL). The first had a metal deck diaphragm. The second specimen had a diaphragm with a single layer of diagonal lumber sheathing, A multiple degree of freedom (MDOF) approach is adopted in this paper. The required stiffnesses and strengths of the components within this model are determined.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.6
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• pp.7-15
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• 2002

In this paper, the nonlinear parameter estimation method using the estimated hysteresis of each structural members was studied for the purpose of efficient seismic damage prediction and estimation of MDOF nonlinear structural model in the shaking table test. The hysteresis of each structural members can be obtained by the conversion of measured response histories into relative motions of each structural members and member forces. These hysteresis can be used to evaluate various kinds of damage indices of each structural members. The MDOF nonlinear structural model for further analysis(re-analysis) can be easily reconstructed using estimated nonlinear structural parameters of each structural members. To demonstrate the proposed techniques, several numerical and experimental example analyses are carried out. The results indicate that the proposed method can be very useful to assess local seismic damages of structures.

• Earthquakes and Structures
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• v.8 no.6
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• pp.1481-1497
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• 2015

Vertical earthquake ground motion may magnify vertical dynamic responses of structures, and thus cause serious damage to bridges. As main support structures, piers and bearings play an important role in vertical seismic response analysis of girder bridges. In this study, the pier and bearing are simplified as a vertical series spring system without mass. Then, based on the assumption of small displacement, the equation of motion governing the simply-supported straight girder bridge under vertical ground motion is established including effects of vertical deformation of support structures. Considering boundary conditions, the differential quadrature method (DQM) is applied to discretize the above equation of motion into a MDOF (multi-degree-of-freedom) system. Then seismic responses of this MDOF system are calculated by a step-by-step integration method. Effects of support structures on vertical dynamic responses of girder bridges are studied under different vertical strong earthquake motions. Results indicate that support structures may remarkably increase or decrease vertical seismic responses of girder bridges. So it is of great importance to consider effects of support structures in structural seismic design of girder bridges in near-fault region. Finally, optimization of support structures to resist vertical strong earthquake motions is discussed.

• Journal of Ocean Engineering and Technology
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• v.22 no.3
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• pp.41-46
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• 2008

It is a recent trend for advanced ships and submarines to incorporate composite structures with viscoelastically damping material. Much research has been done on curve-fitting techniquesto identify vibration characteristic parameters such as natural frequencies, modal damping ratios, and mode shapes of the composite structure. In this study, an advanced technique for accurately determining vibration characteristic of a circular cylindrical shell-attached viscoelastically damping material is used, based on a multi-degree of freedom (MDOF) curve-fitting method. First, an initial value is obtained by using a linear least square method. Next, using the initial value, the exact modal parameters of the composite circular cylindrical shell are obtained by using a nonlinear least square method. Results show computation time is greatly decreased and accurate results are obtained by the MDOF curve-fitting method.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.4
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• pp.377-386
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• 2003

The proposed simplified MDOF model is applied to a half-scale single-story reinforced masonry test building with a single diagonally-sheathed diaphragm. Comparisons of analytical studies to experimental tests can be valuable for understanding the seismic response of these types of buildings and for determining the qualities and limitations of the simplified models. A model calibration process is performed in this paper to determine the required structural properties based on the elastic and inelastic test responses for test building. This approach is necessary since established methods to determine the in-plane and out-of-plane stiffness, strength, and hysteresis do not exist.

• Wind and Structures
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• v.21 no.5
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• pp.523-536
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• 2015

To study the vibration frequency of super high-rise buildings in the process of vortex induced vibration (VIV), wind tunnel tests of multi-degree-of-freedom (MDOF) aero-elastic models were carried out to measure the vibration frequency of the system directly. The effects of structural damping, wind field category, mass density, reduced wind velocity ($V_r$), as well as VIV displacement on the VIV frequency were investigated systematically. It was found that the frequency drift phenomenon cannot be ignored when the building is very high and flexible. When $V_r$ is less than 8, the drift magnitude of the frequency is typically positive. When $V_r$ is close to the critical wind velocity of resonance, the frequency drift magnitude becomes negative and reaches a minimum at the critical wind velocity. When $V_r$ is larger than12, the frequency drift magnitude almost maintains a stable value that is slightly smaller than the fundamental frequency of the aero-elastic model. Furthermore, the vibration frequency does not lock in the vortex shedding frequency completely, and it can even be significantly modified by the vortex shedding frequency when the reduced wind velocity is close to 10.5.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.6
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• pp.846-855
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• 2021

Eco-friendly and renewable energy sources are actively being researched in recent times, and of shore wind power generation requires advanced design technologies in terms of increasing the capacities of wind turbines and enlarging wind turbine installation vessels (WTIVs). The WTIV ensures that the hull is situated at a height that is not affected by waves. The most important part of the WTIV is the leg structure, which must respond dynamically according to the wave, current, and wind loads. In particular, the wave load is composed of irregular waves, and it is important to know the exact dynamic response. The dynamic response analysis uses a single degree of freedom (SDOF) method, which is a simplified approach, but it is limited owing to the consideration of random waves. Therefore, in industrial practice, the time-domain analysis of random waves is based on the multi degree of freedom (MDOF) method. Although the MDOF method provides high-precision results, its data convergence is sensitive and difficult to apply owing to design complexity. Therefore, a dynamic amplification factor (DAF) estimation formula is developed in this study to express the dynamic response characteristics of random waves through time-domain analysis based on different variables. It is confirmed that the calculation time can be shortened and accuracy enhanced compared to existing MDOF methods. The developed formula will be used in the initial design of WTIVs and similar structures.

• Journal of the Korean Geotechnical Society
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• v.38 no.4
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• pp.47-58
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• 2022

Many 1g shaking table tests with an SDOF structure supported by a single pile were performed to evaluate the soil-structure interaction (SSI) effect. Since most structures supported by group piles are MDOF structures with columns, the SSI effect is simulated using a large 1g shaking table test and numerical analysis. According to the results, the movement in the piles tends to increase with input acceleration and when the input frequency is similar to the natural frequency. Furthermore, the slope of the dynamic p-y curve remains constant regardless of the variation of acceleration and input frequency. According to the results of the dynamic p-y backbone curve and the moment of group piles, a center pile with a leading pile has more soil resistance than side piles with a trailing pile, and the effect of group piles is observed above the 7D center to center pile distance.

• Steel and Composite Structures
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• v.3 no.6
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• pp.403-420
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• 2003

In the paper one investigates the benefits deriving from the introduction of SMA provisions in a structure subject to dynamic excitation and vertical loads. At this purpose one considers a multi-degree-of-freedom (mdof) shear elastic-plastic frame and designs couples of super-elastic SMA tendons to be placed at critical locations of the structure. Particular attention is focused on the reduction of $P-{\Delta}$ effects.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.700-703
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• 2004

The purpose of this study is to present the design methodology of base isolated buildings. To achieve the goal of this study, time-history analysis was performed with seismic performance level and recorded seismic data. From the analysis results of MDOF system, the maximum. displacement and base shear were evaluated as 25 cm and $4\%$ by the input level which is maximum velocity of 50 kine. By introducing hybrid isolation system, seismic energy can be concentrated consequently high seismic capacity of the total building is secured.