• International Journal of High-Rise Buildings
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• v.9 no.4
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• pp.307-314
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• 2020

High-rise buildings with vertical setback are widely used in practice. From the field investigation of the past earthquakes, it was found that such kind of vertically irregular high-rise building structures easily suffer severe damage during strong earthquakes. This paper presents an extensive study on the earthquake responses of moment-resisting frame structures (MFS) popularly applied in high-rise buildings with vertical setback. Four groups of MFS are designed, including three groups of structures with vertical setback and one group of structures with the lateral stiffness varying along the building height but without vertical setback. The numerical models of the structures are established, and the time history analysis of the structures under different levels of earthquakes is conducted. The earthquake responses of the structures are compared. The influence of the ratio between the horizontal setback dimension and the previous plan dimension, the eccentricity of setback, and the position where the setback occurs on the seismic performance of structures is studied. The rationality of the provisions for the structures with vertical setback specified in the current design codes is checked by the findings from this study.

• Structural Engineering and Mechanics
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• v.49 no.4
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• pp.463-477
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• 2014

In this paper, seismic performance of Kozyatagi Bridge is evaluated by employing nonlinear elasto-plastic dynamic analysis and the deformation-based performance. The time-history records of the 1999 Izmit, 1971 San Fernando and 1989 Loma Prieta earthquakes are modified by adopting a probability of exceedance of 2% in 50 years corresponding to the return period of 2475 years. The analysis is carried out for three different bearing cases which are movable bearings, restrained bearings, and movable bearings with viscous fluid dampers in the radial direction. The analysis results show that the bridge can be retrofitted with viscous fluid dampers. In this case the reinforced concrete piers need not be strengthened by any jacketing techniques in order to preserve the original architectural appearance of the bridge. The retrofitting design of the bridge with viscous fluid dampers is also presented in detail.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.943-948
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• 2003

The experimental study for oblong section was carried out by the column test in weak axis. The column specimens had 3 types of transverse steel configurations, such as interlocking spirals, interlocking circular hoop ties and rectangular ties. The oblong columns with interlocking spirals and with interlocking circular hoop ties showed better seismic performance than the rectangular columns with rectangular hoops and cross-ties. The objectives of this study were to provide experimental data on the behavior of interlocking spiral columns under cyclic loading, to compare the performance of columns with interlocking spirals to columns with various transverse steel configurations, to study the flexural detailing of interlocking spirals, interlocking circular hoops, and other transverse steel configurations as the transverse reinforcement, and to make recommendations for the design of bridge columns incorporating interlocking spirals, circular hoops as the transverse reinforcement.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.13-22
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• 2018

In this study, seismic performance of existing RC frames reinforced with steel chevron bracing systems was experimentally evaluated. For this purpose, the unreinforced base specimen and seismically reinforced specimens with steel chevron bracing systems were fabricated and tested. Both strength and stiffness of the reinforced specimens were targeted about 2-3 times larger than the base specimen. Test results showed that the stiffness, strength, and ductility of the reinforced specimens considerably improved than those of unreinforced base specimen. Therefore, the results from this study could offer the basic information on the developing design guideline for the seismic reinforcement of RC frames.

• Journal of the Earthquake Engineering Society of Korea
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• v.17 no.1
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• pp.11-19
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• 2013

This research presents that seismic performance of steel moment resisting frame building designed by past provision(UBC, Uniform Building Code) before and after retrofitted with BRB (Buckling-Restrained Brace) was evaluated using response modification factor (R-factor). In addition, the seismic performance of the retrofitted past building was compared with that specified in current provision. The past building considered two different connections: bilinear connection, which was used by structural engineer for building design, and brittle connection observed in past earthquakes. The nonlinear pushover analysis and time history analysis were performed for the analytical models considered in this study. The R-factor was calculated based on the analytical results. When comparing the R-factor of the current provision with the calculated R-factor, the results were different due to the hysteresis characteristics of the connection types. After retrofitted with BRBs, the past buildings with the bilinear connection were satisfied with the seismic performance of the current provision. However, the past buildings with the brittle connection was significantly different with the R-factor of the current provision.

• Journal of the Earthquake Engineering Society of Korea
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• v.22 no.2
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• pp.87-94
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• 2018

In this study, seismic performance of bushings and their connection parts was analyzed by performing shaking table tests for various types of bushings widely used as auxiliary equipment of main transformers in domestic substations. As a result of the seismic tests of five types of 154 kV bushings according to the manufacturers, all the bushings secured the structural integrity even at the acceleration of 1.4 g and it was found that leakage of insulating oil didn't occur. Also, the average acceleration amplification rate at the upper part of the bushings was about 2.5 to 3.0 times higher than the lower one. On the other hand, when a representative 345 kV bushing was subjected to the seismic test, the structural integrity was secured even at 1.0 g acceleration similar to the design earthquake load level, but in this test, leakage of insulating oil occurred. However, when a stiffener restricting the connection of the bushing is installed in the same 345 kV bushing, the displacement of the bushing connection is controlled and the stiffener prevent the oil from leaking even at the acceleration of the designed seismic level.

• Earthquakes and Structures
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• v.8 no.6
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• pp.1349-1362
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• 2015

This paper presents an analytical study aimed at evaluating the effectiveness of using buckling-restrained braces (BRBs) in mitigating the seismic response of a case study 6 storey reinforced concrete (RC) building. In the design of the BRBs with non-prismatic cross-sections, twelve combinations of ${\alpha}$ and ${\beta}$ design parameters that influence the strength and stiffness of the BRBs, respectively, were considered. The response of the structure with and without BRBs under earthquake ground accelerations were evaluated through nonlinear dynamic analysis. Two sets of ground motions representative of the design earthquake with 10% and 50% exceedance probability in fifty years were taken into account. By comparing the structural performance of the original and buckling restrained braced structures, it was observed that the use of the BRBs were very effective in mitigating the seismic response as a retrofit scheme. However, the selection of the strength and stiffness parameters of the BRBs had considerable effect on the response characteristics of RC structures. For instance, by increasing the value of ${\alpha}$ and by decreasing the value of ${\beta}$ of the buckling-restrained braces, the maximum deformation demand of the structures increased.

• International journal of steel structures
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• v.18 no.5
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• pp.1598-1606
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• 2018

An integrated optimal structural design method for a diagrid structure and control device was developed. A multi-objective genetic algorithm was used and a 60-story diagrid building structure was developed as an example structure. Artificial wind and earthquake loads were generated to assess the wind-induced and seismic responses. A smart tuned mass damper (TMD) was used as a structural control system and an MR (magnetorheological) damper was employed to develop a smart TMD (STMD). The multi-objective genetic algorithm used five objectives including a reduction of the dynamic responses, additional stiffness and damping, mass of STMD, capacity of the MR damper for the integrated optimization of a diagrid structure and a STMD. From the proposed method, integrated optimal designs for the diagrid structure and STMD were obtained. The numerical simulation also showed that the STMD provided good control performance for reducing the wind-induced and seismic responses of a tall diagrid building structure.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.5
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• pp.41-51
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• 2010

For safe seismic evaluation and design, it is necessary to predict the plastic deformation demands of members. In the present study, a quick and reasonable method for the evaluation of member plastic deformations of dual systems was developed on the basis of results of elastic analysis, without using nonlinear analysis. Plastic deformations of beams, columns, and walls are functions of member stiffness, story drift ratio, and moment redistribution determined from elastic analysis. For dual systems with rigid connections between walls and beams, an increase in the plastic deformations of beams due to the rocking effect was considered. The proposed method was applied to 8-story dual systems and the predicted plastic deformations were compared with the results of nonlinear analysis. The results showed that the proposed method accurately predicted the member plastic deformations with simple calculations, but that for the accurate evaluation of member plastic deformations, the inelastic story drift ratio must also be predicted with accuracy. The proposed method can be applied to both the performance-based seismic design of new structures and the seismic evaluation of existing structures.

• Journal of Korean Society of Steel Construction
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• v.25 no.2
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• pp.179-186
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• 2013

Steel braced frames are commonly used because braced frames are one of the most economical and efficient seismic resisting systems. However, research into the behavior of multi-story X-braced frame systems with mid-span gusset plates, as used in practice, is limited. As a result, their seismic performance and the influence of connection design on this performance are not well understood. Detailed nonlinear computer analyses of the frame were performed prior to building the test specimens and were used to aid the design and to predict the system performance. These analyses suggested significantly different behavior for the midspan gusset plate than that noted for the corner gusset plate connections. This paper summarizes the results of a full scale, 2-story braced frame analysis and test on concentrically braced frames.