• Journal of the Korea Concrete Institute
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• v.29 no.2
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• pp.131-139
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• 2017

Recently, earthquakes have frequently occurred near Korean peninsula. An experimental study is needed for developing a reinforcing method for seismic strengthening to apply to RC structures. Recently, PolyUrea (PU) as structural reinforcement materials has been receiving great interest from construction industry. The reinforcing effect of PU appeared to be excellent under blast and impact as well as earthquakes. In this study, Flexible Type PolyUrea (FTPU) developed in preceding studies was modified to develop Stiff Type PolyUrea (STPU) by varying the ratio of the components of prepolymer and hardener of FTPU. The material performance evaluation has been performed through hardening time, tensile strength and percent elongation test, pull-off test, and shore hardness test. The experimental results showed that STPU has higher tensile strength and lower elongation than FTPU. Therefore, STPU coating agent can be used for semi-permanent products. By using STPU with Fiber-Reinforced Polymer (FRP) on concrete columns, confinement effect can be enhanced to maximize seismic strength and ductility.

• Journal of the Korea Concrete Institute
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• v.24 no.4
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• pp.369-379
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• 2012

The collapse of concrete structures by extreme loads such as impact, explosion, and blast from terrorist attacks causes severe property damage and human casualties. Concrete has excellent impact resistance to such extreme loads in comparison with other construction materials. Nevertheless, existing concrete structures designed without consideration of the impact or blast load with high strain rate are endangered by those unexpected extreme loads. In this study, to improve the impact resistance, the static and impact behaviors of concrete beams caste with steel fiber reinforced concrete (SFRC) with 0~1.5% (by volume) of 30 mm long hooked steel fibers were assessed. Test results indicated that the static and impact resistances, flexural strength, ductility, etc., were significantly increased when higher steel fiber volume fraction was applied. In the case of the layered concrete (LC) beams including greater steel fiber volume fraction in the tensile zone, the higher static and impact resistances were achieved than those of the normal steel fiber reinforced concrete beam with an equivalent steel fiber volume fraction. The impact test results were also compared with the analysis results obtained from the single degree of freedom (SDOF) system anaysis considering non-linear material behaviors of steel fiber reinforced concrete. The analysis results from SDOF system showed good agreement with the experimental maximum deflections.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.2
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• pp.21-33
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• 1992

Under the intense-impulsive loading, structures are subjected to the wide range of pressures at an instantaneous time. The constitutive laws capable to describe the material behavior under the extreme pressure as well as the low pressure are necessary for the analysis of the structural behavior under the intense -impulsive loadings. In this study, two plastic models, the pressure independent Von-Mises model and the pressure dependent Drucker-Prager model, are employed for the wave propagation analysis. Governing equations of this study are conservation equations of momentum and mass in Lagrangian coordinate system which is fixed to the material. Due to the shock-front which violates the continuity assumptions inherent in the differential equations numerical artificial viscosity is used to spread the shock front over several computational zones. These equations are solved by Finite Difference Method with discretized time and space coordinates. The associate normality flow rule as a plastic theory is implemented to find the plastic strains.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.4
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• pp.231-237
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• 2018

In this study, two important requirements for the home production of a robot to detect and remove improvised explosive devices (IEDs) are presented in terms of the total cost for robot system development and the performance improvement of the mine detection technology. Firstly, cost analyses were performed in order to provide a reasonable solution following an engineering estimate method. As a result, the total cost for a mass production system without the mine detection system was estimated to be approximately 396 million won. For the case including the mine detection system, the total cost was estimated to be approximately 411 million won, in which labor costs and overhead charges were slightly increased and the material costs for the mine detection system were negligible. Secondly, a method for fabricating the carbon nanotube (CNT) based gas detection sensor was studied. The detection electrodes were formed by a photolithography process using a photosensitive CNT paste. As a result, this method was shown to be a scalable and expandable technology for producing excellent mine detection sensors. In particular, it was found that surface treatments by using adhesive taping or ion beam bombardment methods are effective for exposing the CNTs to the ambient air environment. Fowler-Nordheim (F-N) plots were obtained from the electron-emission characteristics of the surface treated CNT paste. The F-N plot suggests that sufficient electrons are available for transport between CNT surfaces and chemical molecules, which will make an effective chemiresistive sensor for the advanced IED detection system.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.9
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• pp.1133-1140
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• 2013

A computer model is a useful tool that provides solution via physical modeling instead of expensive testing. In reality, however, it often does not agree with the experimental data owing to simplifying assumption and unknown or uncertain input parameters. In this study, a Bayesian approach is proposed to calibrate the computer model in a probabilistic manner using the measured data. The elasto-plastic analysis of a pyrotechnically actuated device (PAD) is employed to demonstrate this approach, which is a component that delivers high power in remote environments by the combustion of a self-contained energy source. A simple mathematical model that quickly evaluates the performance is developed. Unknown input parameters are calibrated conditional on the experimental data using the Markov Chain Monte Carlo algorithm, which is a modern computational statistics method. Finally, the results are applied to determine the reliability of the PAD.

• Journal of the Korean Institute of Gas
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• v.26 no.3
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• pp.38-44
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• 2022

As the supply of hydrogen charging stations for hydrogen supply accelerates due to the hydrogen economy revitalization policy, the risk of accidents is also increasing. Since most hydrogen explosion accidents lead to major accidents, it is very important to secure safety when using hydrogen energy. In order to utilize hydrogen energy, it is essential to secure the safety of hydrogen storage containers used for production, storage, and transportation of liquid hydrogen. In this paper, in order to evaluate the structural safety of a hydrogen-filled pressure vessel, the behavioral characteristics of gas pressure were analyzed by finite element analysis. SA-372 Grade J / Class 70 was used for the material of the pressure vessel, and a hexahedral mesh was applied in the analysis model considering only the 1/4 shape because the pressure vessel is axisymmetric. A finite element analysis was performed at the maximum pressure using a hydrogen gas pressure vessel, and the von Mises stress, deformation, and strain energy density of the vessel were observed.

• Journal of the Korean Institute of Gas
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• v.24 no.4
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• pp.18-24
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• 2020

The purpose of this study is to validate thermal hinderance effects, i.e., feasibilities, of fire-proof structure for LPG tank exposed to fire from adjacent burning building. The panel materials suggested for the fire-proof structure are (1) 10 mm-thick wood, (2) wood with fireproof coating, (3) 75 mm-thick Expanded Polystyrene, (4) 75 mm-thick glass wool filled sandwich panel, and (5) 75 mm-thick autoclaved lightweight concrete. The square planar fire source of 1 ㎡, a matrix of nozzles releasing 120-140 g/s of LPG, is used to heat up the wall and the tank beyond, mimicking heat transfer from burning exterior wall finishes. The feasibility is tested by inspecting structural integrity after test, and then by examining temperatures at both sides of panels and tank's front surface as well as heat fluxes. As a result, it can be concluded that, among the suggested sample materials, fire-proof wall with ALC panel only showed the feasibility for explosion prevention with the proven evidences of structural integrity and least increase in temperature of tank.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.745-748
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• 2008

The past structures were just required bearing capacity to service load, serviceability, and resistance to corrosion. However this point of view has changed after 9.11 terrorism, capacities which can bear impact loading by explosion, and heat by fire happening at the same time, become to be important as a basic condition. The blast resistance capacity of structures is very important part against all over the world is intimidated by terrorism everyday in current point of time. The target of this research is a development of segmented composites and layered structures with high blast resistance using cementitious composites, concrete and FRP composites, which has high tensile strength and ductility, to apply in not only existing facilities but also new ones. Through the improvement of blast resistance, casualties and economic loss can be minimized, and it is possible to diminish the structure collapse and delay the time of structure collapse by thermal effect, impact loading, dynamic loading and high strain.

• Tunnel and Underground Space
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• v.21 no.4
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• pp.320-327
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• 2011

In this study, for stemming effect in blast of the mortar block body, the crushed granite sand as fine aggregate, which is waste rock obtained at the ○○ limestone mine, was investigated to compare with stemming materials such as sea sand, river sand, clayed soil and water can be acquired easily at the field. The mortar block body was manufactured with the dimensions of 50 cm width, 50 cm length and 70 cm height. The direct shear and sieve separator test were performed, and the properties of friction resistance were analyzed by the extrusion test for five stemming materials. Axial strain of steel bar and ejection velocity of stemming materials due to the explosive shock pressure in blasthole with the stemming length of 10 cm and 20 cm in the mortar blast test were measured by the dynamic data acquisition system. Among stemming materials, axial strain showed the largest value at the crushed granite sand as fine aggregate, and the ejection velocity was the smallest value at the stemming of water. The results has shown correlate with harden unit weight in blasthole, particle size distribution, shear resistance, and extrusion strength of stemming materials. The ejection velocity of stemming material at the mouth of blasthole and the axial strain of steel bar in the inside of blasthole tend to be inversely proportional to each other, represent exponentially.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.6
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• pp.699-705
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• 2011

High-maneuver missile is a projectile which demands a strong momentum at short time. To produce a necessary thrust for the flight, the gas of high temperature and pressure is generated through explosive combustion of solid propellant, and a great thrust can be obtained by expanding this high temperature and pressure gas. Although the operating time of a rocket motor is less than a few seconds, a failure of part or ablation near the throat of nozzle may take place during the expansion of high temperature and pressure gas for great thrust. In other words, for the precise control of a missile an exact stress analysis considering both, the thermal stress caused by the heat transfer between combustion gas and wall, and the mechanical stress caused by the pressure change in the flow, should be considered first. In this connection, this study investigated the safety, as a point of view of stress and melting point of the material, of the pre-designed thrust generating structure which is subjected to high temperature and pressure as a function of motor operating time.