• Journal of the Korean GEO-environmental Society
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• v.11 no.4
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• pp.19-24
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• 2010

Generally, slope behavior is analyzed by 2-dimensional creep model. Creep behavior shows the deformation variation as time goes by without stress increment. Convention 2-dimensional creep analysis does not have the term of stress variation, it means creep analysis could not figure out the relationship of shear strength variation according to the stress variation and displacement. The slope weight and shear strength is directly related and interlocked to the safety variation and displacement of slope, therefore, this phenomenon could be treated and analyzed as combining the hysteresis and creep, the iteration of this process will result in the slope safety. Furthermore, the combined analysis will be the slope analysis considering shear stress, displacement and shear strength with time variation. In real case, because the variation of shear stress and strength happen at the same time, they should be changed into safety factor which is function of them. This paper shows the 3-dimensional variation of unit weight of soil with hybrid analysis considering creep and hysteresis on the seepage and drainage of rainfall, futhermore variations of shear stress and strength which make the safety factor change.

• Journal of the Korean Institute of Gas
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• v.13 no.1
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• pp.21-27
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• 2009

This paper presents the numerical study on the strength safety of the prestressed concrete outer tank for a LNG storage tank, which is manufactured by sets of membrane panels with special corrugations. This study for a finite element analysis assumes that the membrane panel of the inner tank was fractured and the liquefied natural gas stored in the inner membrane tank was leaked to the prestressed concrete outer tank. The stress and displacement of the outer tank have been analyzed for five different loadings, which are originated by a hydrostatic pressure and a weight of a LNG, a temperature difference, a weight of the prestressed concrete and a boil-off gas pressure. The computed FEM results indicate that the PC outer tank with a storage capacity of 200,000$m^3$ has a good strength safety for a leaked LNG from the membrane inner tank, but the increased cryogenic loadings in which are originated by a leaked LNG decreases the strength safety of the PC structure. This may lead to the collapse of the outer storage tank.

• Journal of the Korean Society of Safety
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• v.34 no.2
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• pp.40-47
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• 2019

The Half-depth precast deck is a structural system that utilizes pre-cast panels pre-built at the factory as formwork at the construction stage and as a major structural member at the same time after completion. These systems have joints between segments, and the detail and performance of the joints are factors that have a very large impact on the quality, such as the constructability and durability of the bridge decks. In this study, strength performance evaluation was performed for improved joints using connecting rebar by experimental method. Static loading tests were conducted on the test specimen with improved joint, those with existing joint and those without joint. The test results of the specimens were compared to each other, and the flexural strength required by the design was compared. The flexural strength required in the design was presented by finite element analysis. It has been shown that the flexural strength of the specimens with joints were more than twice that required by the design. But the flexural strength of the specimen with existing joint was about 84% of that without joint. The flexural strength of the specimen with improved joints was a nearly similar degree of that compared to the specimen without joint. And a comparison of the moment-deflection relationship curves of the two specimens also shows a very similar flexural behavior. It is confirmed that improved joint has sufficient flexural strength. In addition to strength, the bridge decks require serviceability, such as deflection and cracking, and in particular, fatigue resistance due to repetitive live loads is an important performance factor. Therefore, further verification studies are required.

• Journal of the Korean Society of Safety
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• v.23 no.4
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• pp.67-71
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• 2008

Formwork is a temporary structure that supports its weight and that of fresh concrete as well as construction live loads. Slab formwork consists of sheathing, stringer, hanger and shore. In construction site, pipe supports are usually used as shores which are consisted of the slab formwork. In this study, compressive strength of 80 pipe supports was measured by knife edge test and plate test. Buckling load of pipe supports was analyzed by structural analysis program(MlDAS). Theoretical buckling load with/without initial deformation was got by theoretical analysis. According to these results, buckling load which was analyzed by structural analysis program(MlDAS) was larger than compressive strength of knife edge test and plate test. Theoretical buckling load without initial deformation was larger than compressive strength of knife edge test and plate test. But Theoretical buckling load with initial deformation was lower than compressive strength of knife edge test and plate test. Initial deformation equation for test method according to the pipe support length was suggested. Therefore, the present study results will be used to design the slab formwork safely.

• Journal of the Korean Society of Safety
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• v.19 no.1
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• pp.56-59
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• 2004

In this paper, we investigated the influence of gap length and tip radius on breakdown of mineral based insulation oil. Applied voltages were DC and AC voltage. Electrode system was needle-plane structure. The tip radius of needle electrode was 5, 10, 20 and 25${\mu}m$, respectively. We measured breakdown voltage for each of tip radius with increasing electrode gap, 2mm to 12mm. Electric breakdown strength at tip was calculated using Mason's equation contained geometric figure. As gap length increased, breakdown strength increased linearly. But, as tip radius of needle increased, breakdown strength decreased exponentially. It can be explained by the phenomenon that electron is easily injected, as tip radius increases, and effective work function decreases. When appling DC voltage, breakdown strength was higher when polarity of needle was negative than positive. It is because of the space charge effect in accordance with the influence of liquid motion.

• Geomechanics and Engineering
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• v.34 no.3
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• pp.285-301
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• 2023

During the construction of E75 highway through Grdelica gorge in Serbia, a major failure occurred in the zone of reinforced rock slope. Excavation was performed in highly anisotropic Paleozoic schist rock formation. The reinforcement consisted of the two rows of micropile wall with pre-stressed anchors. Forces in anchors were monitored with load cells while benchmarks were installed for superficial displacement measurements. The aim of the study is to investigate possible causes of instability considering different probability distributions of the strength of discontinuities and anchor bond strength by applying different optimization techniques for finding the critical failure surface. Even though the deterministic safety factor value is close to unity, the probability of failure is governed by variability of shear strength of anisotropic planes and optimization method used for locating the critical sliding surface. The Cuckoo search technique produces higher failure probabilities compared to the others. Depending on the assigned statistical distribution of input parameters, various performance functions of the factor of safety are obtained. The probability of failure is insensitive to the variation of bond strength. Different sampling techniques should yield similar results considering that the sufficient number of safety factor evaluations is chosen to achieve converged solution.

• Nuclear Engineering and Technology
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• v.56 no.9
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• pp.3528-3535
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• 2024

SA508 Gr.1A low-alloy steel is being considered as a candidate material for main steam line piping in nuclear power plants. Therefore, improving its strength and toughness is essential for enhancing the leak-before-break (LBB) margin. In this study, six types of model alloys were fabricated by varying the contents of microalloying elements (C, Cu, B, Ti, and Nb) to enhance the mechanical properties of the specimens. The addition of a few ppm of B led to the formation of a fine-grained low-temperature transformation microstructure, resulting in the highest strength among the model alloys. However, the addition of Nb and Ti increased the formation of coarse ferrite, significantly decreasing the strength of the alloys. Reducing the C content while adding a small amount of B simultaneously maintained strength and enhanced toughness. Furthermore, the LBB margins of model alloys and commercial steel were evaluated to validate the influence of varying microalloying content. The model alloys exhibited a substantial increase in yield strength and fracture resistance, resulting in a more than 10% increase in the LBB margin. Notably, the LBB margin of the alloy with 15 ppm B was 1.39, approximately 25% higher than that of commercial steels.

• Journal of the Korean Society of Safety
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• v.32 no.5
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• pp.62-68
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• 2017

It is necessary to analyze on the compressive strength among material properties of concrete for confirming damages of architectures due to large explosion. A non destructive test is known as the representative methods estimating compressive strength and ultrasonic pulse velocity, rebound hardness test are widely used because of their simplicity, convenience. But combined method supplementing two types is applied at now as they are affected by the characteristics of test specimen. In this research to check damages on the members of structure before and after explosion, the characteristics of compressive strength are compared and analyzed through a real explosion test prior to full scale structures. The test results showed that the larger the TNT powder and the shorter the distance, the greater the decrease in strength before and after the explosion and that the largest displacement and moment for the explosive load and the greatest decrease in the strength at the central part. Due to the surface condition and the thickness variation of the concrete specimens, the standard deviation value is the smallest in the combining method of fusion of the ultrasonic method and rebound hardness method. Thus, the combining method can be one of appropriate methods to evaluate the strength in the reinforced concrete structures damaged by the explosion.

• Journal of the Korean Institute of Gas
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• v.11 no.2 s.35
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• pp.55-59
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• 2007

This paper presents the strength safety of a LPG cylinder, which is fabricated by a steel sheet forming and a welding technology. The strength safety of a cylinder is guaranteed by analyzing a stress distribution of a LPG cylinder structure using a finite element method. The FEM computed results indicate that the hydraulic test gas pressure of $31kg/cm^2$ generates a concentrated local stress near the upper round end plate, which exceeds the yield strength of a LPG cylinder. Thus, the current hydraulic test pressure may be rechecked and revised because this pressure increases the fatigue failure and decreases the lift of the pressure vessel. The normal operation and sealing gas pressures such as $9kg/cm^2\;and\;18.6kg/cm^2$ are relatively safe for a steel LPG cylinder.

• Journal of the Korean Institute of Gas
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• v.23 no.3
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• pp.46-50
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• 2019

In this study, the strength stability of an LPG mini tank with a storage capacity of about 250 kg was analyzed by FEM. According to the results of the FEM analysis, it is preferable that the corner radius of the LPG mini tank having a storage capacity of 250 kg is designed to be 175 to 205 mm. Generally, the larger the corner radius of the end plate of the gas storage tank, the higher the safety of the strength, but the volume or capacity of the tank is reduced. Therefore, it is important to derive the optimum design data. Further, in order to securely design the strength of the gas tank, the thickness of the tank is designed to be thick. However, when the thick steel sheet is used, the material and the transportation costs are increased. The result shows that it is preferable to select the optimum thickness of the steel sheet from 4.5 to 5.5 mm. Using the level gauge type of column on the central axis of the gas tank, the safety strength of the LPG tank can be enhanced as much as twice, compared with the tank of the existing level gauge to measure the liquid level by piercing the side wall of the tank.