• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.10
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• pp.1567-1574
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• 2001

In order to operate an RPV safely it is necessary to keep the pressure-temperature (P-T) limit during the heatup and cooldown process. While the ASME Code provides the P-T limit curve for safe operation, this limit curve has been prepared under conservative assumptions In this paper the effects of conservative assumptions involved in the P-T limit curve specified in the ASME Code Sec. XI were investigated. Three different parameters the crack depth the cladding thickness and the cooling rate, were reviewed based on 3-D finite element analyses. Also the constraint effect on P-T limit curve generation was investigated based on J- T approach. It was shown that the crack depth and the constraint effect change the safe region in P-T limit curve significantly Therefore it is recommended to prepare a more precise P-T limit curve based on finite element analysis to obtain P-T limit for safe operation of an RPV.

• Journal of the Korean Society of Industry Convergence
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• v.25 no.5
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• pp.791-797
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• 2022

Using the fatigue limit (△σ_unsm) and residual stress (σ_r) of the UNSM smooth specimen, the harmless maximum crack depth (α_hml) according to the crack aspect ratio (As) was evaluated. α_hml evaluated the reliability in the relationship between the minimum crack depth (α_NDI1, α_NDI2) detectable by nondestructive inspection(NDI) and the crack depth (α₂₅, α₅₀) that reduces the fatigue limit by 25% and 50%. All α_hml was determined by the crack depth. The α_hml of 80N UNSM with high σ_r and high △σ_unsm was found to be large. σ_r in the depth direction had a much effect on α_hml. Since α_hml>α₅₀(As=0.6-0.1) and α_hml>α₂₅, α₂₅ and α₅₀(some range) can secure the safety and reliability. Since α_hml<α₅₀ (As=1. 0-0. 6), it cannot be made harmless by UNSM. So safety and reliability cannot be secured. α_NDI1 and α_NDI2 are larger than α₂₅, α₂₅ cannot be detected by NDI. α_NDI1 and α_NDI2 are smaller than α₅₀, α₂₅ can detected by NDI.

• Journal of the Korean Society of Safety
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• v.34 no.4
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• pp.76-84
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• 2019

The precast pannels are used as formwork in Half-depth precast deck systems. Therefore, it has many advantages, including safe and convenient construction and reduced construction period compared to cast-in-place construction method. In half-depth precast deck systems, the bonding of precast pannels to cast-in place concrete is very important. To enhance the performance of half-depth precast deck system, it is necessary to improve the composite efficiency of the interface or increase the stiffness of the precast pannel to reduce deformation or stress on the interface. In this study, a flexural test of half-depth precast deck system was performed, in which the shear connecting reinforcement was applied to increase the bonding performance at the interface, and the rib shape precast panels were applied to improve stiffness. In addition, the safety and serviceability of these systems were evaluated. Test results show that all of specimens have the required flexural strength under the ultimate strength limit design. It was also evaluated to have sufficient safety for the serviceability of deflection and crack under the serviceability limit design.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.349-356
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• 2010

In this study, a new design method of pile bent structure considering plastic hinge was proposed on the basis of the beam-column model. Based on the analysis results, it is found that the positioning of plastic hinge on the pile bent structure was influenced by nonlinear behavior of material and p-$\Delta$ effect. Moreover, concrete cracking began to occur at the joint section between the pile and column in case of pile bent structure with different cross-sections. The plastic hinge can be developed on the pile bent structure when large displacement was occurred, and pile bent structures can be maintained well only if it is developed on the column part. Therefore, in this study, the optimized cross-section ratio between column and pile was analyzed to induce the plastic hinge at the joint section between the pile and column. Based on this, the optimized diameter ratio of pile and column can be obtained below the inflection point of the bi-linear curve depending on the relations between column-pile diameter ratio($D_c/D_p$) and normalized lateral cracking load ratio($F/F_{Dc=Dp}$). And through this study, it is founded that in-depth limit($L_{As}$=0.4%) normalized by the pile length($L_P$) are proportionally decreased as the pile length($L_P/D_P$) increases up to $L_P/D_P$=17.5, and beyond that in-depth limit converges to a constant value. Finally, it is found that the proposed limit depth by taking into account the minimum concrete-steel ratio would be more economical design of the pile bent structure.

• Journal of the Korean Society of Safety
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• v.23 no.2
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• pp.72-80
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• 2008

In a case of an automobile collision, vehicle damage and injury of the driver and the passenger occur. The scale of the collision which is effected by the extent of vehicle damage and the injury of the passenger, depends on the delta-V. Based on the photograph interpretation o the actual case of accidents in the Seoul and the Incheon area, this study measured the depth of crush and calculated the delta-V. Through verifying the correlation of the depth of crush and the change of velocity, relative equation was evaluated and compared with the prior study results to prove that they are almost identical. Thus, the depth of crush can be used as an index of the degree of impact, which can be utilized as the change of velocity to evaluate the level of injury done to the passengers. However, the period of hospitalization and diagnostics claimed by the injured proves to have no correlation with the delta-V and the extent of vehicle damage, this is due to the non-objective way of diagnosis and the anamnesis of the injured. This study established the absolute limit harmlessness and the choosing limit harmlessness, allowing the appraisal for Yes or No of the injury or the harmlessness based on the prior studies. Moreover, utilizing the relative equation formed between the depth of crush and the delta-V, each case of collision was compared and evaluated in comparison to the limit harmlessness to prove that the 90.4% of the so-called 'claiming-to-be-injured' were exaggerating or fabricating.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.2
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• pp.277-287
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• 2017

This paper describes the specifications on balanced steel ratio and maximum reinforcement for the design of RC flexural members by the Korean Highway Bridge Design Code based on limit states design. The Korean Highway Bridge Design Code (Limit States Design) is not provide for the balanced steel ratio specification for the calculation of required steel area of RC flexural members design. The maximum steel area limited the depth of the neutral axis at the ultimate limit states after redistribution of the moment, and also recommended the maximum steel area should not exceed 4 percent of the cross sectional area. However, from the maximum neutral axis depth provisions should increase the cross section is calculated to be less the maximum reinforcement area, and according to the 4% of the cross sectional area of the concrete, the tensile strain of the reinforcement is calculated to be greater than double the yielding strain, so can not guarantee a ductile behavior. This study developed a balanced reinforcement ratio that is basis for the required reinforcement calculation for tension-controlled RC flexural members design in the ultimate limit states verification provisons and material properties and applied the ultimate strain of the concrete compressive strength with a simple formular to be applied to design practice induced. And assumed the minimum allowable tensile strain of reinforcement double the yielding strain, and applying correction coefficient up to the ratio of maximum neutral axis depth, proposed maximum steel ratio that can be applied irrespective of the reinforcement yield strength and concrete compressive strength.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2001.10a
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• pp.225-230
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• 2001

Small diameter drilling which take high precision in cutting work is needed more small hole and high speed working. Especially, small hole deep drilling is one of the most important machining types and its necessity and importance become more and more increasing in the whole field of industry. This paper shows the limit depths with small diameter drills using experimental analysis. The results are gained by tool dynamometer and Labview system and obtained during small diameter twist drilling system on SM45C steel for different machining conditions. The machine and tools are the CNC machining center and twist drill of diameter 1.5mm. And additionally, tool microscope show the relationship between shapes of chips and breakage shapes of small diameter drills.

• Computers and Concrete
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• v.24 no.4
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• pp.303-311
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• 2019

The depth of superstructure is the summation of the height of girders and the thickness of the deck floor. In this study, it is aim to determine the maximum span length of girders and minimum depth of the superstructure of prestressed concrete I-girder bridge. For this purpose the superstructure of the bridge with the width of 10m and the thickness of the deck floor of 0.175m, which the girders length was changed by two meter increments between 15m and 35m, was taken into account. Twelve different girders with heights of 60, 75, 90, 100, 110, 120, 130, 140, 150, 160, 170 and 180 cm, which are frequently used in Turkey, were chosen as girder type. The analyses of the superstructure of prestressed concrete I girder bridge was conducted with I-CAD software. In the analyses AASHTO LRFD (2012) conditions were taken into account a great extent. The dead loads of the structural and non-structural elements forming the bridge superstructure, prestressing force, standard truck load, equivalent lane load and pedestrian load were taken into consideration. HL93, design truck of AASHTO and also H30S24 design truck of Turkish Code were selected as vehicular live load. The allowable concrete stress limit, the number of prestressed strands, the number of debonded strands and the deflection parameters obtained from analyses were compared with the limit values found in AASHTO LRFD (2012) to determine the suitability of the girders. At the end of the study maximum span length of girders and equation using for calculation for minimum depth of the superstructure of prestressed concrete I-girder bridge were proposed.

• Journal of the Korean Society of Industry Convergence
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• v.25 no.2_2
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• pp.239-245
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• 2022

Using the fatigue limit (∆σ_unsm) and residual stress (σ_r) of the UNSM smooth specimen, the harmless maximum crack depth (a_hlm) according to the crack aspect ratio (As) was evaluated. In addition, the relationship between the minimum crack depth (a_NDI1, a_NDI2) detectable by non-destructive inspection(NDI), the crack depth (a₂₅, a₅₀) that reduces the fatigue limit by 25% and 50%, and a_hlm were evaluated. The harmless crack condition was determined by the deepest crack point (point A). Since a_hlm is larger than a₂₅ and a₅₀, a₂₅ and a₅₀ can secure the safety and reliability of steel via UNSM. Because a_NDI1 and a_NDI2 are larger than a₂₅ and a₅₀, cracks in a₂₅ and a₅₀ cannot be detected by non-destructive testing. Therefore it is necessary to apply more precise NDI.

• Transactions of Materials Processing
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• v.8 no.2
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• pp.152-159
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• 1999

This study is to investigate the effects of warm deep drawing with aluminum sheets of A1050-H16 and A5020-H32 for improving deep drawability. Experiments for producing circular cups and square cups were carried out for various working conditions, such as forming temperature and blank shapes. The limit drawing ratio(LDR) of 2.63 in warm deep drawing of circular cups in case of A5020-H32 sheet, whereas LDR of 2.25 in case of A1050-H16, could be obtained and the former was 1.4 times higher than the value at room temperature. The maximum relative drawing depth for square cups of A5020-H32 material was also about 1.92 times deeper than the depth drawn at room temperature. The effects of blank shape and forming temperature on drawability as well as thickness distribution of drawn cups were examined and discussed.