• Nuclear Engineering and Technology
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• v.54 no.6
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• pp.2156-2172
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• 2022

This paper investigates the optimum fiber reinforcement for prestressed concrete containment vessels (PCCVs) under internal pressure. To achieve this aim, steel fiber, which is the most widely used fiber type in current engineering applications, is adopted to constitute steel fiber-reinforced concrete (SFRC) to substitute the conventional concrete in the PCCV. The effects of characteristic parameters, 𝜆_sf, of the steel fiber affecting significantly the mechanical behavior of the concrete are first taken into account. Partial or complete concrete regions of the PCCV are also considered to be replaced by SFRC to balance the economy and safety. By adopting the ABAQUS software, the ultimate bearing capacity and performance for the fiber-reinforced PCCV are scientifically studied and quantified, and the recommendations for the optimum way of fiber reinforcement are presented.

• Journal of the Korean Geotechnical Society
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• v.32 no.8
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• pp.47-59
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• 2016

Rocking behavior of shallow foundation reduces the superstructure load during earthquake. However, because of deficiency of understanding of rocking mechanism and soil permanent deformation, it has not been applied to real construction. In this study, slow cyclic tests were conducted for embedded shallow foundations with various slenderness ratio via centrifuge tests. From the variation of earth pressure 'soil rounding surface' phenomenon which makes maximum overturning moment equal to ultimate moment capacity was observed. Rocking and sliding behavior mechanism was evaluated. Also, nonlinear behavior and energy dissipation increase as rotation angle increases. And ultimate moment capacity of embedded foundation is larger than that of surface foundation. Finally, adequate ultimate moment capacity can be suggested for seismic design through this study.

• Journal of the Korean GEO-environmental Society
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• v.12 no.10
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• pp.63-72
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• 2011

The high capacity bi-directional pile load test is an optimum pile load test method for high-rised buildings. Especially, a high pressure and double-acting bi-directional pile load testing, a special type of the high capacity bi-directional pile load test, is the most practical way to overcome limitations of loading capacities and constraints of field conditions, which was judged to be a very useful test method for requiring high loading capacities. Total of 2 high capacity bi-directional pile load tests(P-1 and P-2) were conducted in high-rised building sites in Korea. Based on the field load test results, the sufficiency ratio of loading capacities to design loads for P-1 and P-2 were 3.3 and 2.1, respectively. For P-2, the load test could not verify the design load if 1-directional loads applied slightly smaller than the actual applied load. Also, high capacity bi-directional pile load tests were difficult to determine an ultimate state of ground or piles, although the loads were applied until their maximum loads. Hence, finite element analyses were conducted to determine their ultimate states by calibrating and extrapolate with test results.

• Geomechanics and Engineering
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• v.35 no.1
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• pp.29-39
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• 2023

As the intensity of urban underground space development increases, more and more tunnels are planned and constructed, and sometimes it is inevitable to encounter situations where tunnels have to underpass the river embankments. Most previous studies involved tunnels passing river embankments perpendicularly or with large intersection angle. In this study, a project case where two EPB shield tunnels with 8.82 m diameter run parallelly underneath a river embankment was reported. The parallel length is 380 m and tunnel were mainly buried in the moderate / slightly weathered clastic rock layer. The field monitoring result was presented and discussed. Three-dimensional back-analysis were then carried out to gain a better understanding the interaction mechanisms between shield tunnel and embankment and further to predict the ultimate settlement of embankment due to twin-tunnel excavation. Parametrical studies considering effect of tunnel face pressure, tail grouting pressure and volume loss were also conducted. The measured embankment settlement after the single tunnel excavation was 4.53 mm ~ 7.43 mm. Neither new crack on the pavement or cavity under the roadbed was observed. It is found that the more degree of weathering of the rock around the tunnel, the greater the embankment settlement and wider the settlement trough. Besides, the latter tunnel excavation might cause larger deformation than the former tunnel excavation if the mobilized plastic zone overlapped. With given geometry and stratigraphic condition in this study, the safety or serviceability of the river embankment would hardly be affected since the ultimate settlement of the embankment after the twin-tunnel excavation is within the allowable limit. Reasonable tunnel face pressure and tail grouting pressure can to some extent suppress the settlement of the embankment. The recommended tunnel face pressure and tail grouting pressure are 300 kPa and 550 kPa in this study, respectively. However, the volume loss plays the crucial role in the tunnel-embankment interaction. Controlling and compensating the tunneling induced volume loss is the most effective measure for river embankment protection. Additionally, reinforcing the embankment with cement mixing pile in advance is an alternative option in case the predicted settlement exceeds allowable limit.

• Journal of the Korean Geotechnical Society
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• v.24 no.11
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• pp.71-77
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• 2008

In this study, CPT-based methodology for estimating the ultimate lateral resistance, $p_u$, is proposed and verified for lateral loaded piles in sandy soil. Preexistent methods estimating the ultimate lateral resistance, $p_u$, and the ultimate lateral capacity, $H_u$, of pile have been based on the vertical effective stress, relative density, and the coefficient of lateral earth pressure. Similarly, cone resistance $q_c$ in pure sandy soil is expressed by those essential factors. As correlation between $p_u$ and $q_c$ are normalized with average effective stress ${\sigma}_m$, estimation methodology for the lateral loaded pile of $p_u$ in sandy soil is proposed. The method is verified by calibration chamber test results in pure sand. The standard derivation of estimated $p_u$ is 0.279, and COV (Coefficient Of Variation) of estimated $p_u$ is 0.272. These results showed that the estimated pus by the method are analogous with the measured $p_us$ in calibration chamber test.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.320-324
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• 2000

Nonlinear stress analysis of nuclear containment building is carried out using microscopic concrete material model. The present study mainly focuses on the evaluation of the ultimate pressure capacity of idealized containment building in nuclear power plant. For this purpose, an eight-node degenerated shell element it adopted and an imaginary opening in the apex of containment building is allowed in FE model. From numerical analysis, the adopted concrete material model performs well and has a good agreement with the result obtained by using ABAQUS. Finally, we propose the present study as a benchmark test for nonlinear analysis of containment building.

• Journal of Power System Engineering
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• v.13 no.4
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• pp.11-17
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• 2009

This paper deals with the effects of pulsating flow on volumetric efficiency, which may be generated during the gas exchange procedure, due to piston motion, valve event on intake and exhaust stroke and unsteady flow of turbocharger of a three-cylinder four stroke turbo-charged diesel engine. Consequently, volumetric efficiency affects significantly the engine performance; torque characteristics, fuel economy and further to emission and noise level. As the expansion ratio became larger the engine speed varies and torque increases, the pressure pulsation in an exhaust gas pipe acts as an increasing factor of intake air charging capacity totally. The phase and amplitude of pressure pulsation in the intake system only affects volumetric efficiency favorably, if it is well matched and tuned effectively to the engine. Thus, to verify the exact phase and amplitude of the pressure variation is the ultimate solution for the air-flow ratio assessment in the intake stroke. Some experimental results of pressure diagrams in the intake pipe and gas-flow of turbine in-outlet are presented, under various kinds of operating condition.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.12
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• pp.1393-1400
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• 2009

The objective of this study is to validate local failure criteria, which were proposed based on the notched-bar specimen tests combining with finite element (FE) simulations, using the results of real-scale pipe failure tests. This study conducted burst test using wall-thinned pipe specimens, which were made of 4 inch Sch.80 ASTM A106 Gr.B carbon steel pipe, under simple internal pressure at ambient temperature and performed associated FE simulations. Failure pressures were estimated by applying the failure criteria to the results of FE simulations and were compared with experimental failure pressures. It showed that the local stress based criterion, given as true ultimate tensile stress of material, accurately estimated the failure pressure of wall-thinned pipe specimens. However, the local strain based criterion, which is fracture strain of material as a function of stress tri-axiality, could not predict the failure pressure. It was confirmed that the local stress based criterion is reliably applicable to estimation of failure pressure of local wall-thinned piping components.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.93-98
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• 2000

Unpredictable failures can occur due to the DHC (delayed hydride cracking) or the degradation of fracture toughness by hydride embrittlement in CANDU pressure tube which can result from the absorption of hydrogen or deuterium in the high temperature coolant. To investigate the hydride embrittlement of CANDU Zr-2.5Nb pressure tube, the transverse tensile test and the fracture toughness test were performed from room temperature to $300^{\circ}C$ using three different specimens which have an AR (As Received), 100, and 200 ppm hydrogen. As the amount of absorbed hydrogen was increased, the transverse yield strength and the ultimate tensile strength were also increased. In addition, as the test temperature became higher they were decreased linearly. While, at room temperature, the hydrogenbsorbed specimens represented the embrittlement which resulted in sudden decreasing of fracture toughness, the fracture characteristics became ductile such as AR specimen at high temperatures. Through the observation of fracture surface using SEM, it was found that the stress state of mixed mode could be related to the fissure which was believed to decrease the global fracture toughness.

• Applied Chemistry for Engineering
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• v.8 no.1
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• pp.1-7
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• 1997

We show that the usage of the cyclic pressure function in the freeze drying is more effective than the drying rate of the constant pressure process. The ultimate object of this process is to reduce energy costs by shortening the drying time. In this work, the concept of cyclic pressure function to decrease the drying time and the effects of the following factors on drying rate are considered ; pulse type, size in amplitude of pressure, size of intermediate time. Temperature for drying has always been maintained constantly at $20^{\circ}C$ and the pulse type could have found to give useful results than the constant pressure by altering chamber pressure from low pressure to high pressure Also, when the amplitude of the pulse is 0.4 torr and the intermediate time is six hour the drying rate was increased considerably.