• Journal of the Korea Concrete Institute
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• v.21 no.1
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• pp.105-116
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• 2009

Reinforced concrete (RC) structures have been most widely used because of their good economic efficiency. However, it is very weak in tensile stresses and difficult to control deflection due to the heavy self-weight of concrete. On the other hand, it is generally known that prestressed concrete structures can be the most effective to overcome the demerits of RC structures by using various tendon lay-out and its amount. In the prestressed concrete members, the inflection points of tendons should be placed effectively for the deflection control and the moment reduction. Therefore, in this study, the equations of tendon profiles are derived in terms of polynomials that satisfy essential conditions of tendon geometries such as inflection points and natural curved shapes of tendons placed in continuous members, from which vertical components of prestressing forces can be also calculated. The derived high order polynomial expression for the distributed shape of the upward and downward forces was transformed to an simplified equivalent uniform vertical force in order to improve the applicability in the calculation of member deflection. The influences of vertical forces by tendons to deflection and moment in a continuous slab were also considered depending on the distance from column face to the location of tendons. The applicability of the proposed method was examined by an example of deflection calculation for the cases of slabs with and without tendons, and the efficiency of deflection control by tendons was also quantitatively estimated.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.3 no.4
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• pp.11-20
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• 1983

This study investigates reliability based design criteria for the spiral R.C. columns, and proposes practical algorithm which is based on Ellingwood's algorithm for the reliability analysis and the derivation of reliability based design criteria. Cornell's MFOSM theory is used for the derivation of the algorithm for the evaluation of uncertainties associated with resistances, whereas the magnitude of the uncertainties associated with load effects are chosen primarily by considering our level of practice. And thus the uncertainties so obtained are applied for the relilability analysis and the derivation of reliability based design criteria. A target reliability (${\beta}_0=3.5$) is selected as an appropriate value by comparing the values used in foreign countries and by analyzing, the reliability levels of our current USD and WSD design standards. Then, a set of load and resistance factors corresponding to the target reliability is proposed as a reliability based design provision, and furthermore a set of allowable stresses for reinforcing steel and concrete having same level of reliability with the corresponding LRFD criteria is also propared for the current WSD design provision. It may be concluded that the proposed LRFD reliability based design provisions and the corresponding allowable stresses give more rational design than the current code for spiral R.C. columns.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.3
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• pp.542-552
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• 2018

In this paper, the precast method of a concrete eco-pillar debris barrier was proposed to improve the construct ability and economic efficiency. The performance was validated by experimental and structural analysis. The steel debris barrier has a high construction cost and causes environmental damage with corrosion. The construction of a concrete eco-pillar debris barrier has been increased recently. On the other hand, there are no design standards regarding debris barriers in Korea, and debris barriers are being designed by the experience and sense of engineers. Therefore, in this study, a method to determine the design external forces was proposed and the design was performed by applying a hollow cross-section to the debris barrier. In addition, three types of connection methods of a concrete cantilever column with the maximum bending moment acts were proposed, and validation of the performance of each type was performed with a real-scale experiment. The experimental results showed that the type with loop reinforcement had the highest rigidity and the type with anchorage performance exceeded the maximum bending moment according to the ultimate load. In the manufacturing procedure of mock-up debris barriers, the type with an anchorage-bar was found to have superior construct ability.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.6
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• pp.315-329
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• 2018

Recently, RC transfer slab systems have been used widely to construct high-rise wall-type apartments for securing parking space or public space. However, it is problem that the design method and structural performance evaluation method developed for thin RC flat slab are still used in the design of the transfer slab whose thickness is very thick and therefore structural behavior is expected to be different from RC flat slab. Thus, for the rational design of the transfer slab, the ultimate shear behavior of the RC transfer slab system is required to be analyzed properly. Accordingly, in the present study, the two-way shear behavior of the transfer slab was analyzed using nonlinear FEM according to various design parameters such as thickness of the transfer slab, strength of concrete, shear span ratio, and reinforcement ratio. In addition, the two-way shear strength evaluations of RC transfer slab by the existing evaluation methods were verified by comparing those with the results of nonlinear FEM analysis.

• Explosives and Blasting
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• v.37 no.1
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• pp.34-47
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• 2019

This case study is concerned with the project of the explosive demolition for the DCRE Incheon plant located in Hakik district in Incheon city. The building was severely aging due to the high temperature and sea winds of hundreds of degrees emitted by chimney-shaped steel structures inside the building. Due to this, the concrete of the column and the beam fell off and rusted rebar were exposed, and some of the slabs were severely damaged, making it difficult for workers to access the structure. Therefore, it is not possible to apply a mechanical demolition method in which heavy equipment enters the interior of the building, and an explosive demolition method was applied to allow the building to be demolished without dismantling the internal facilities of the building. The order of blasting proceeded in the order of (1) building ${\rightarrow}$ (2) chimney 2 ${\rightarrow}$ (3) chimney 1. A total of 406 electronic detonators (Unitronic 600) was used to sequentially initiate the explosives installed at appropriate in building and chimneys.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.5
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• pp.143-150
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• 2022

This paper presents an experimental study on the flexural performance of concrete members strengthened with external steel plates for the purpose of improving seismic performance. In order to strengthen the structure, a strengthening method was applied that wraps the walls and columns with steel members. The partial section of the wall with the longest span in the structure was manufactured in real size and the strengthening effect was confirmed by performing a static load test. As a result of the experiment, it was confirmed that the strengthened section exhibited sufficient flexural performance satisfied to the seismic requirements, but the behavior until failure was not obtained because of actuator capacity. It was confirmed that the strengthened member resists the out-of-plane moment with a composite behavior. It was verified that the stiffness and load carrying capacity of the strengthened member were improved compared to the non-strengthened member by displacement and strain measurements.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.1
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• pp.97-105
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• 2009

This paper studied the cause of the deterioration of the four 3-Arch tunnels built in mid-1990. The common deteriorations of the four 3-Arch tunnels were longitudinal cracks, leakage and efflorescence at the same parts of lining concrete. Three fourths of 3-Arch tunnels, there was high percentage longitudinal cracks and a quarter was low frequency about longitudinal cracks. So the material reviewed to find out the differences between two groups in construction process and analysis was conducted such as non-destructive testing, precise visual survey and safety evaluation of one tunnel which had bad ground condition As the result, the tunnels were safety condition and the primary deterioration occurred during the construction process, namely, problems arrangement of rebar and the effects of the blast at middle tunnel.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.10
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• pp.490-498
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• 2020

In this study, the seismic performance of low-rise piloti buildings with eccentric core (shear wall) positions was analyzed and reviewed. A prototype was selected among constructed low-rise piloti buildings with eccentric cores designed based on KBC2005. The seismic performance of the building showed plastic behavior in the X-direction and elastic behavior in the Y-direction. The inter-story drift is larger than that of a concentric core case and has the maximum allowed drift ratio. The displacement ratio of the first story is much larger than that of upper stories, and the frame structure in the first story is vulnerable to lateral force. Therefore, low-rise piloti buildings with eccentric cores need to have less lateral displacement, as well as reinforcement of the lateral resistance capacity in seismic design and seismic retrofit.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.4
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• pp.347-355
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• 2021

During the earthquake, for multi-story structure, if the first floor is soft, the deformation will concentrate on that floor causing a serious damage to the column members which might leads to the collapse of the whole structure like Piloti structure during the Pohang earthquake in Korea. According to the 2016 National Disaster Management Research Institute's "Investigation of Seismic Reinforcement and Cost Analysis of Domestic Non-seismic Buildings", the rate of seismic resistance of private reinforced concrete buildings was 38.3 %. Among them, it was reported that the seismic-resistance ratio of the two to five-story structures was less than 50 %. Accordingly, the government is trying to improve the seismic rate through support projects, but the conventional seismic reinforcement methods are still expensive, and emergency construction is difficult. Therefore, in this study, the field applicability was evaluated by improving the reinforcement method using Velcro, which was developed through the research project of the Ministry of Land, Transport and Maritime Affairs in 2014. In order to improve the performance of the Velcro reinforcement method, introducing the initial tension of Velcro using high foaming rigid urethane filling between the Velcro and concrete of the columns was applied. Additionally, an experiment was conducted to evaluate the ductility of Velcro specimen from the concrete confinement effect. As a result, the ductility of the Velcro specimen was improved compare to Normal specimen. However, the energy dissipation capacity of VELCRO2 is better than VELCRO1, yet the maximum ductility of those two specimens did not show a significant difference. Therefore, the improvement of the internal filler material is still needed to have a better maximum ductility.