• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.4
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• pp.46-55
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• 2021

Concrete structures can cause various problems as the number of common years increases when exposed to external extreme climate conditions. Among these problems, freezing and thawing occur due to the action of extreme climate factors such as heavy rain and heavy snow, which have become the most problematic in recent years. In this study, we present a rapid freezing and thawing test method of concrete in the air, referring to KS F 2456, as Seoul exhibits very dry weather during the period of freezing and thawing. Concrete test specimens and RC beams were fabricated to perform rapid freezing and thawing of 0, 100, 200, and 300 cycles, and the performance evaluation confirmed the degradation of each subject in material and member units. The design strength of 24 MPa, which performs rapid freezing and thawing in the air up to 300 cycles, decreases by 5.24 MPa (21%), and as rapid freezing and thawing in the air increases the stress burden on reinforced concrete bending members, reducing the energy absorption (dissipation) ability of structures due to earthquakes.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.4
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• pp.116-124
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• 2011

RC frames with unreinforced masonry infiledl walls are common in worldwide. Since infilled walls are normally considered as non-structural elements, their presence is often ignored by engineers. In this study, to improve the seismic performance of masonry walls, hexagonal block was developed and the influence of masonry infilled wall on the seismic performance of reinforced concrete(RC) frames that were designed in accordance with current code provisions without the consideration of earthquake loadings are investigated. Two 1/2 scale, single story, single bay, frame specimens were tested. The parameters investigated included that the strength of infilled wallls with respect to that of the lateral load history. The experimental results indicate that infilled walls can significantly improve the lateral stiffness and strength of RC frames. The lateral loads developed by the infilled frame specimen is higher than that of the bare frame. It also indicates that infilled walls can be potentially used to improve the performance of existing nonductile frames. For this purpose. methods should be developed to avoid irreparable damage and catastrophic failure.

• Advances in concrete construction
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• v.15 no.5
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• pp.333-348
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• 2023

Fast infrastructure development boosts the demand for shotcrete. Despite sand and stone being the most common coarse and fine aggregates for shotcrete, excessive exploration of these materials challenges the ecological environment. This study utilized an industrial solid waste, high-titanium heavy slag, blended with steel fibers to form Wet Shotcrete of Steel Fiber-reinforced High-Titanium Heavy Slag (WSSFHTHS). It investigated its workability, shotcrete performance and mechanical properties under different water-to-cement ratios, fly ash content, superplasticizer dosage, and steel fiber content. The tunnel excavation and support were investigated by conducting finite element numerical simulation analysis and was used in 3 tunnel lining pipes in Zhonggouwan tailing pond. The major findings are as follows: (1) The water-to-cement ratio (w/c ratio) significantly impacted the compressive strength of WSSFHTHS. The highest 28-day compressive strength of 60 MPa was achieved when the w/c ratio was 0.38; (2) Adding fly ash improved the workability and shotcrete performance and strength development of WSSFHTHS. The best anti-permeability performance was achieved when the fly ash constituted 15%, with the lowest permeability coefficient of 4.596 × 10-11 cm/s; (3) The optimum superplasticizer dosage for WSSFHTHS is 0.8%. It provided the best workability and shotcrete performance. Excessive dosage resulted in water bleeding and poor aggregate encapsulation, while insufficient dosage decreased flowability and adversely affected shotcrete performance; (4) The dosage of steel fibers significantly impacted the flexural and tensile strength of WSSFHTHS. When the steel fiber dosage was 45 kg/m³, the 28-day flexural and tensile strengths were 8.95 MPa and 6.15 MPa, respectively; (5) By integrating existing shotcrete techniques, the optimal lining thickness was 80 mm for WSSFHTHS per simulation. The results revealed that after using WSSFHTHS, the displacement of the tunnel surrounding the rock significantly improved, with no cracks or hollows, similar to the simulation results.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.6 no.4
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• pp.53-60
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• 1986

This study is directed to propose a probability based LRFD design code, which could possibly replace the traditional USD provisions of the current code, based on the AFOSM reliability theory. The uncertainties of resistances and load effects for each R.C. structural elements are evaluated and adopted considering our practice, and a set of rational target reliability indices are selected based on the calibration with the reliability of the current R.C. design code and by considering the desired hierarchy of safety level. Then, a set of common load factors are chosen from the results of load and resistance factors which are computed by AFOSM method using the Rackwitz-Fiessler's efficient practical algorithm which is to transform the non-normal variables into the equivalent normal variables. It may be asserted that the proposed LRFD code for the R.C. building structures may have to be incorporated into the current RC. design codes as a design provision corresponding to the USD provisions of the current R.C. design code.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.3 no.3
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• pp.71-86
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• 1983

Current R.C. retaining wall design is bared on WSD, but the reliability based design method is more rational than the WSD. For this reason, this study proposes a reliability based design criteria for the cantilever retaining wall, which is most common type of retaining wall, and also proposes the theoretical bases of nominal safety factors of stability analysis by introducing the reliability theory. The limit state equations of stability analysis and design of each part of cantilever retaining wall are derived and the uncertainty measuring algorithms of each equation are also derived by MFOSM using Coulomb's coefficient of the active earth pressure and Hansen's bearing capacity formula. The levels of uncertainties corresponding to these algorithms are proposed appropriate values considering our actuality. The target reliability indices (overturning: ${\beta}_0$=4.0, sliding: ${\beta}_0$=3.5, bearing capacity: [${\beta}_0$=3.0, design for flexure: [${\beta}_0$=3.0, design for shear: ${\beta}_0$=3.2) are selected as optimal values considering our practice based on the calibration with the current R.C. retaining wall design safety provisions. Load and resistance factors are measured by using the proposed uncertainties and the selected target reliability indices. Furthermore, a set of nominal safety factors, allowable stresses, and allowable shear stresses are proposed for the current WSD design provisions. It may be asserted that the proposed LRFD reliability based design criteria for the R.C. retaining wall may have to be incorporated into the current R.C. design codes as a design provision corresponding to the USD provisions of the current R.C. design code.