• Journal of Korean Association for Spatial Structures
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• v.23 no.2
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• pp.37-44
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• 2023

In the case of a school building, even though it is a regular structure in terms of plan shape, if the masonry infill wall acts as a lateral load resisting element, it can be determined as a torsionally irregular building. As a result, the strength and ductility of the structure are reduced, which may cause additional earthquake damage to the structure. Therefore, in this study, a structure similar to a school building with torsional irregularity was selected as an example structure and the damping performance of the PC-BRB was analyzed by adjusting the eccentricity according to the amount of masonry infilled wall. As a result of nonlinear dynamic analysis after seismic reinforcement, the torsional irregularity of each floor was reduced compared to before reinforcement, and the beams and column members of the collapse level satisfied the performance level due to the reduction of shear force and the reinforcement of stiffness. The energy dissipation of PC-BRB was similar in the REC-10 ~ REC-20 analytical models with an eccentricity of 20% or less. REC-25 with an eccentricity of 25% was the largest, and it is judged that it is effective to combine and apply PC-BRB when it has an eccentricity of 25% or more to control the torsional behavior.

• Journal of the Korean Geotechnical Society
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• v.24 no.1
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• pp.61-70
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• 2008

The control and prediction of surface settlement, gradient and ground displacement are the main factors in shallow tunnel design and construction in urban area. For deformation analysis of shallow tunnel due to excavation it is important to identify possible deformation mechanism of shear bands developing from tunnel shoulder to the ground surface. This paper investigaties quantitatively the deformation behavior of shallow tunneling by model tunnel test and strain softening analysis Incorporating the reduction of shear stiffness and strength parameters. The comparison of model tunnel test result and numerical simulation using strain softening analysis showed good agreement in crown settlement, normalized subsidence settlement and developing shear bands above tunnel shoulder. In this study, it is blown that the strain softening modeling is applicable to the nonlinear deformation analysis of shallow tunnel.

• Structural Engineering and Mechanics
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• v.87 no.3
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• pp.255-272
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• 2023

Spatial cable systems can provide more transverse stiffness and torsional stiffness without sacrificing the vertical bearing capacity compared with conventional vertical cable systems, which is quite lucrative for long-span earth-anchored suspension bridges' development. Higher economy highlights the importance of refined form-finding analysis. Meanwhile, the internal connection between the lateral and vertical sags has not yet been specified. Given this, an analytic algorithm of form-finding for the earth-anchored suspension bridge with spatial cables is proposed in this paper. Through the geometric compatibility condition and mechanical equilibrium condition, the expressions for cable segment, the recurrence relationship between catenary parameters and control equations of spatial cable are established. Additionally, the nonlinear general reduced gradient method is introduced into fast and high-precision numerical analysis. Furthermore, the analytic expression of the lateral and vertical sags is deduced and discussed. This is very significant for the space design above the bridge deck and the optimization of the sag-to-span ratio in the preliminary design stage of the bridge. Finally, the proposed method is verified with the aid of two examples, one being an operational self-anchored suspension bridge (with spatial cables and a 260 m main span), and the other being an earth-anchored suspension bridge under design (with spatial cables and a 500 m main span). The necessity of an iterative calculation for hanger tensions on earth-anchored suspension bridges is confirmed. It is further concluded that the main cable and their connected hangers are in very close inclined planes.

• Journal of the Korea Institute of Building Construction
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• v.23 no.6
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• pp.673-682
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• 2023

This study investigates the delay in setting characteristics of mortar influenced by variations in super retarding agent(SRA) content, curing temperature, and strength levels. Utilizing a settimeter, the research introduces an objective approach to accurately determine the setting time of concrete with SRA under diverse environmental and material mixing conditions at construction sites. The findings indicate that the settimeter, in conjunction with a nonlinear regression model, can effectively estimate the setting time of super retarding mortar. Optimal management of the initial setting is recommended at approximately 45ST and the final setting around 80ST. This methodology enables more effective quality control in the setting times of super retarding concrete.

• Journal of Advanced Navigation Technology
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• v.28 no.1
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• pp.123-128
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• 2024

When mid-span spectral inversion (MSSI), which inverts the propagated wave into phase-conjugated wave in the middle of the entire transmission distance, is combined with dispersion-managed link, it is very effective in compensating for the wavelength division multiplexed (WDM) signal distortion due to chromatic dispersion and nonlinear effects. In this MSSI combined dispersion-managed link, the shape of the dispersion map, channel data rate, channel wavelength and wavelength spacing, etc. affect the compensation and, consequently, determine the transmission distance and capacity of the WDM signal. In this paper, the compensation according to the extinction ratio of the return-to-zero (RZ) pulse that constitutes the WDM signal in the MSSI combined distributed control link was numerically analyzed. As a result of the simulation, it was conformed that the extinction ratio to obtain the best compensation should be determined depending on the shape of the dispersion map and the size of the residual dispersion per span, which determines the specific shape of the dispersion map. These results show a significant difference from the results in a general optical transmission system, where as the extinction ratio increases, the power difference between the '1' and '0' signals increases, thereby improving reception performance.

• Structural Engineering and Mechanics
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• v.90 no.4
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• pp.371-390
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• 2024

Investigating the impact of openings on the structural behavior of ferrocement I-beams with two distinct types of reinforcing metallic and non-metallic meshes is the primary goal of the current study. Up until failure, eight 250x200x2200 mm reinforced concrete I-beams were tested under flexural loadings. Depending on the kind of meshes used for reinforcement, the beams are split into two series. A control I-beam with no openings and three beams with one, two, and three openings, respectively, are found in each series. The two series are reinforced with three layers of welded steel meshes and two layers of tensar meshes, respectively, in order to maintain a constant reinforcement ratio. Structural parameters of investigated beams, including first crack, ultimate load, deflection, ductility index, energy absorption, strain characteristics, crack pattern, and failure mode were reported. The number of mesh layers, the volume fraction of reinforcement, and the kind of reinforcing materials are the primary factors that vary. This article presents the outcomes of a study that examined the experimental and numerical performance of ferrocement reinforced concrete I-beams with and without openings reinforced with welded steel mesh and tensar mesh separately. Utilizing ANSYS-16.0 software, nonlinear finite element analysis (NLFEA) was applied to illustrate how composite RC I-beams with openings behaved. In addition, a parametric study is conducted to explore the variables that can most significantly impact the mechanical behavior of the proposed model, such as the number of openings. The FE simulations produced an acceptable degree of experimental value estimation, as demonstrated by the obtained experimental and numerical results. It is also noteworthy to demonstrate that the strength gained by specimens without openings reinforced with tensar meshes was, on average, 22% less than that of specimens reinforced with welded steel meshes. For specimens with openings, this value is become on average 10%.

• Steel and Composite Structures
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• v.50 no.6
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• pp.627-641
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• 2024

This paper presents an experimental and numerical study to investigate the behavior of the precast segmental concrete beams (PSCBs) utilizing high-strength concrete (HSC) connected in the zone of the maximum bending moment using steel extended endplate connections (EECs). The experimental study consisted of five beams as follows: The first beam was the control beam for comparison, which was an unconnected one-piece beam made of HSC. The other four other beams consisted of two identical pieces of precast concrete. An important point to be noted is that at the end of each piece, a steel plate was used with a thickness of 10 mm. Moreover, this steel plate was welded to the lower and upper reinforcing bars of the beam. Furthermore, the steel plate was made to connect the two pieces using the technique of EECs. Several variables were taken in these four beams, whether from the shape of the connection or enhancing the behavior of the connection using the post-tensioning technique. EECs without stiffeners were used for some of the tested beams. The behavior of these connections was improved using stiffeners and shear bolts. To get accurate results, a comparison was made between the behaviors of the five beams. Another important point to be noted is that Abaqus and SAP2000 programs were used to investigate the behavior of PSCBs and to ensure the accuracy of the modeling process which showed a good agreement with the experimental results. Additionally, the simplified modeling using SAP2000 was able to model the nonlinear behavior of PSCBs connected using steel EECs. It was found that the steel pre-tensioned bolted EECs, reinforced with steel stiffeners and shear anchors, could be used to connect the precast HSC segmental beams via the internal pre-stressing technique.

• Korean Chemical Engineering Research
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• v.52 no.5
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• pp.574-580
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• 2014

Storage tanks of Carbon dioxide ($CO_2$) carriers utilized for the purpose of carbon capture and storage (CCS) into subsea strata have to undergo a pre-cooling session before beginning to load cryogenic liquid cargos in order to prevent physical and thermal deterioration of tanks which may result from cryogenic $CO_2$ contacting tank walls directly. In this study we propose dynamic model to calculate the tank inflow of $CO_2$ gas injected for precooling process and its dynamic simulation results under proportional-integral control algorithm. We selected two cases in which each of them had one controlled variable (CV) as either the tank pressure or the tank temperature and discussed the results of that decision-making on the pre-cooling process. As a result we demonstrated that the controlling instability arising from nonlinearity and singularity of the mathematical model could be avoided by choosing tank pressure as CV instead of tank temperature.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.2
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• pp.145-152
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• 2015

In the study, the effects of damping devices on damping ratio increase and wind-load reduction were investigated based on the computational platform, which is one of the parametric modeling methods. The computational platform helps the designers or engineers to evaluate the efficacy of the numerous alternative structural systems for irregular Super-Tall building, which is crucial in determining the capacity and the number of the supplemental damping devices for adding the required damping ratios to the building. The inherent damping ratio was estimated based on the related domestic and foreign researches conducted by using real wind-load records. Two types of damping devices were considered: One is inter-story installation type passive control devices and the other is mass type active control devices. The supplemental damping ratio due to the damping devices was calculated by means of equivalent static analysis using an equation suggested by FEMA. The optimal design of the damping devices was conducted by using the computational platform. The structural element quantity reduction effect resulting from the installation of the damping devices could be simply assessed by proposing a wind-load reduction factor, and the effectiveness of the proposed method was verified by a numerical example of a 455m high-rise building. The comparison between roof displacement and the story shear forces by the nonlinear time history analysis and the proposed method indicated that the proposed method could simply but approximately estimate the effects of the supplemental damping devices on the roof displacement and the member force reduction.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.3
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• pp.200-209
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• 2013

In this paper, the types of B-dot controller and the review results of B-dot controller stability are summarized. Also, it is confirmed that B-dot controller is very useful and essential tool when a dawn-dusk low earth orbit(LEO) large satellite has especially to capture the Sun for a required power supply in a reliable way after anomaly and that its algorithm is very simple for on-board implementation. New physical interpretation of B-dot controller is presented as a result of extensive theoretical investigation introducing the concept of transient control torque and steady state control torque. Also, the failure effect analysis results of magnetic torquers as well as a simulation verification are included. And the design recommendation for optimal design is provided to cope with the failure of magnetic torquer. Nonlinear simulation results are included to justify its capability as well as its performance for an application to a dawn-dusk LEO large satellite.