• Journal of the Earthquake Engineering Society of Korea
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• v.16 no.1
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• pp.27-35
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• 2012

In this study, the ground motion was synthesized using the finite fault model by the stochastic green function method, and the difference in the ground motions was evaluated by using various values of the source parameters. An earthquake with a moment magnitude of 6.5 was assumed for the example fault model. The distribution of the slip in the fault plane was calculated using the statistical data of the asperity area. The source parameters considered in this study were the location of the hypocenter in the fault plane and the ratio of the rupture to the shear wave velocity, the rise time, the corner frequency of the source spectrum, and a high frequency filter. The values of the parameters related to the stochastic element source model were adjusted for different tectonic regions, and the others were selected for several possible cases. The response spectra were constructed from the synthesized ground motion time history and compared with the different parameter values. The frequency range affected by each parameter and the differences of the spectral accelerations were evaluated.

• Proceedings of the Korean Geotechical Society Conference
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• 1988.06c
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• pp.3-67
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• 1988

Model studies on the response of homgeneous earth embankment dams subjected to strike-slip fault movement have been penomed via centrifuge and finite element analysis. The centrifuge model tests have shown that crack development in earth embankment experiences two major patters: shear failure deep inside the embankment and tension failure near the surface. The shear rupture zone develops from the base level and propagates upward continuously in the transverse direction but allows no open leakage chnnel. The open tensile cracks develop near the surface of the embankment, but they disappear deep in the embankment. The functional relationship has been developed based on the results of the centrifuge model tests incorporating tile variables of amount of fault movement, embankment geometry, and crack propagation extent in earth des. This set of information can be used as a guide line to evaluate a "transient" safety of the duaged embankment subjected to strike-slip fault movement. The finite element analysis has supplemented the additional expluations on crack development behavior identified from the results of the centrifuge model tests. The bounding surface time-independent plasticity soil model was employed in the numerical analysis. Due to the assumption of continuum in the current version of the 3-D FEM code, the prediction of the soil structure response beyond the failure condition was not quantitatively accurate. However, the fundamental mechanism of crack development was qualitatively evaluated based on the stress analysis for the deformed soil elements of the damaged earth embankment. The tensile failure zone is identified when the minor principal stress of the deformed soil elements less than zero. The shear failure zone is identified when the stress state of the deformed soil elements is at the point where the critical state line intersects the bounding surface.g surface.

• Nuclear Engineering and Technology
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• v.30 no.5
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• pp.403-415
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• 1998

The CANDU 6 reactor assembly consists of an array of 380 pressure tubes, which are installed horizontally in a large cylindrical vessel, the Calandria, containing the low pressure heavy water moderator. The pressure tube is located inside the calandria tube and the annulus between these tubes, which forms a closed loop with $CO_2$ gas recirculating, is called the Annulus Gas System(AGS). It is designed to give an alarm to the operator even for a small pressure tube leak by a very sensitive dew point meter so that he can take a preventive action for the pressure tube rupture incident. To judge whether the operator action time is enough or not in the design of Wolsong 2,3 & 4, the Leak Before Break(LBB) assessment is required for the analysis of the pressure tube failure accident. In order to provide the required data for the LBB assessment of Wolsong Units 2, 3, 4, a series of leak detection capability tests was performed by injecting controlled rates of heavy water vapour. The data of increased dew point and rates of rise were measured to determine the alarm set point for the dew point rate of rise of Wolsong Unit 2. It was found that the response of the dew point depends on the moisture injection rate, $CO_2$ gas flow rate and the leak location. The test showed that CANDU 6 AGS can detect the very small leaks less than few g/hr and dew point rate of rise alarm can be the most reliable alarm signal to warn the operator. Considering the present results, the first response time of dew point to the AGS $CO_2$ flow rate is approximated.

• Journal of the Korean Institute of Gas
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• v.15 no.2
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• pp.69-74
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• 2011

As a way to propose a method for the establishment of practical damage-minimizing plan for chemical plants, the release scenario was established by using API-581 BRD and the effect zone was estimated by the KS-RBI program supporting the quantitative cause analysis. And the risk assessment was performed. As a result, we found that to minimize the damage of a chemical plant, it is effective to use four release hole diameters (small, medium, large and rupture) and release time estimated according to the classes of detection and isolation systems. In addition, it can be safely said that through appling the damage areas considering weighted average by failure frequency and worst-case simultaneously, industrial sites can come up with the effective emergency response plan.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 1997.04a
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• pp.34-34
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• 1997

The effect of alloying mode and porosity on the axial tension-tension fatigue behavior of a P/M steel of nominal composition Fe-4w/o Ni-1.5w/o Cu-O.5w/o Mo-O.5w/o C has been evaluated. Alloying modes utilized were elemental powder mixing, partial alloying(distaloy) and prealloying by water atomization; in each case the carbon was introduced as graphite prior to sintering. Powder compacts were sintered($1120{\circ}C$/30 min.) in 7Sv/o $H_2$/25v/o $N_2$ to densities in the range 6.77-7.2 g/$cm^3$. The dependence of fatigue limit response on alloying mode and porosity was interpreted in terms of the constituent phases and the pore and fracture morphologies associated with the three alloying modes. For the same nominal composition, the three alloying modes resulted in different sintered microstructures. In the elemental mix alloy and the distaloy, the major constituent was coarse and fine pearlite, with regions of Ni-rich ferrite, Ni-rich martensite and Ni-rich areas. In contrast, the prealloy consisted primarily of martensite by with some Ni-rich areas. From an examination of the fracture surfaces following fatigue testing it was concluded that essentially all of the fracture surfaces exhibited dimpled rupture, characteristic of tensile overload. Thus, the extent of growth of any fatigue cracks prior to overload was small. The stress amplitude for the three alloying modes at 2x$l0^6$ was used for the comparison of fatigue strengths. For load cycles <3x$l0^5$, the prealloy exhibited optimum fatigue response followed by the distaloy and elemental mix alloy, respectively. At load cycles >2x$l0^6$, similar fatigue limits were exhibited by the three alloys. It was concluded that fatigue cracks propagate primarily through pores, rather than through the constituent phases of the microstructure. A decrease in pore SIze improved the S-N behavior of the sintered steel.

• Geomechanics and Engineering
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• v.39 no.2
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• pp.157-170
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• 2024

In the present study, the acoustic emission characteristics of hard sedimentary sandstone with varying bedding dip angles were examined through uniaxial compression tests using a rock mechanics creep apparatus combined with an acoustic emission system. The deformation and failure behavior of the sandstone was analyzed by correlating acoustic emission parameters with stress over time. A damage constitutive model was developed, incorporating cumulative acoustic emission ringing counts as a key parameter, with time acting as the intermediary. The findings indicate that, despite the differences in bedding dip angles, the stress-strain curves of the samples follow a similar pattern throughout the loading process, passing through four distinct phases: compaction, elastic deformation, yielding, and post-peak failure. The fracture patterns of the sandstone are influenced by the dip angle of the bedding. Acoustic emission parameters, including the ringing count, cumulative ringing count, and energy, align with these four stages of the stress-strain curve. During the compaction and elastic deformation phases, acoustic emissions remain in a quite state, with only brief spikes at points of rapid stress change. In the unstable fracture stage, acoustic emissions become highly active, while they return to a quite state in the post-fracture stage. The RA value of the acoustic emission displays a banded pattern as time progresses, with areas of dense clustering. When the stress curve declines, RA values enter an active period, mainly associated with the generation of shear cracks. Conversely, during periods of smooth stress progression, RA values remain in a quiet state, primarily linked to the formation of tensile cracks. The time-based damage constitutive model for layered sandstone effectively captures the entire process of rock fracture development.

• Structural Engineering and Mechanics
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• v.44 no.2
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• pp.239-255
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• 2012

This work presents a contribution to understand the inverted trussed beams behavior. The system has a main beam and struts with rectangular cross section associated to a wire rope enlaced to the main beam. It is an unpublished system with the advantage of easy positioning of the wire rope, once it is a continuous and connected by turnbuckles. It is a system that can be used as support for concrete formworks or for rehabilitation wooden beams proposal. The enlacement of the cable demands a small notch at the top of the cross section and a cross pin at the bottom. Six inverted trussed beams were tested, with spans of 180 cm with cables diameter of 1/4". Additionally, four simple beams without any external steel cable were also tested with material from the same lot of wood, allowing a comparison in rupture. The results showed capacity gain of around 60% compared to a simple beam. Once the wire rope characteristics and anchoring are very important for structure response, some improvement suggestions for the efficiency of the cables are also presented.

• Journal of the Korean Society for Precision Engineering
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• v.30 no.8
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• pp.809-814
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• 2013

The relationship between the small-punch creep test and the conventional creep test was investigated experimentally using a method similar to that of the Monkman-Grant relationship. Uniaxial and small-punch creep rupture tests were carried out on 9Cr-2W ferritic steel (Commercial Grade 92 steel: X10CrWMoVNb 9-2) at elevated temperatures. From the relation derived in the same manner as the Monkman-Grant relation, a correlation between the displacement rate in response to the small-punch creep test and the strain rate in the uniaxial creep test was found, and the creep life was calculated using this relation. Furthermore, the failure modes of the small punch creep test specimens were investigated to show that the fracture was caused by creep.

• Steel and Composite Structures
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• v.28 no.3
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• pp.349-362
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• 2018

This paper presents a semi-analytical solution for the creep analysis and life assessment of 304L austenitic stainless steel thick truncated conical shells using multilayered method based on the first order shear deformation theory (FSDT). The cone is subjected to the non-uniform internal pressure and temperature gradient. Damages are obtained in thick truncated conical shell using Robinson's linear life fraction damage rule, and time to rupture and remaining life assessment is determined by Larson-Miller Parameter (LMP). The creep response of the material is described by Norton's law. In the multilayer method, the truncated cone is divided into n homogeneous disks, and n sets of differential equations with constant coefficients. This set of equations is solved analytically by applying boundary and continuity conditions between the layers. The results obtained analytically have been compared with the numerical results of the finite element method. The results show that the multilayered method based on FSDT has an acceptable amount of accuracy when one wants to obtain radial displacement, radial, circumferential and shear stresses. It is shown that non-uniform pressure has significant influences on the creep damages and remaining life of the truncated cone.

• Advances in concrete construction
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• v.5 no.6
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• pp.587-611
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• 2017

This study focused on the influences regarding the use of polyepoxide-based polymer and silica fume (SF) on the fresh and hardened state properties of self-compacting lightweight concrete (SCLC) along with their impacts on electrical resistance and ultrasonic pulse velocity (UPV). To do so, two series of compositions each of which consists of twelve mixes, with water to binder (W/B) ratios of 0.35 and 0.4 were cast. Three different silica fume/binder ratios of 0, 5%, and 10% were considered along with four different polymer/binder ratios of 0, 5%, 10%, and 15%. Afterwards, the rupture modulus, tensile strength, 14-day, 28-day, and 90-day compressive strength, the UPV and the electrical resistance of the mixes were tested. The results indicated that although the use of polymer could enhance the passing and filling abilities, it could lead to a decrease of segregation resistance. In addition, the interaction of the SF and the polymeric contents enhanced the workability. However, the impacts regarding the use of polymeric contents on fresh state properties of SCLC were more prevalent than those regarding the use of SF. Besides the fresh state properties, the durability and mechanical properties of the mixes were affected due to the use of polymeric and SF contents. In other words, the use of the SF and the polymer enhanced the durability and mechanical properties of SCLC specimens.