• Journal of the Korea institute for structural maintenance and inspection
• /
• v.20 no.5
• /
• pp.109-115
• /
• 2016

A demand of high bearing capacity of piles to resist heavy static loads has been increased. For this reason, the utilization of large diameter PHC piles including a range from 700 mm to 1,200 mm have been increased and applied to the construction sites in Korea recently. In this study, in order to increase the flexural strength capacity of the PHC pile, the large diameter composite PHC pile reinforced by in-filled concrete and reinforcement was developed and manufactured. All the specimens were tested under four-point bending setup and displacement control. From the strain behavior of transverse bar, it was found that the presence of transverse bar was effective against crack propagation and controlling crack width as well as prevented the web shear cracks. The flexural strength and mid-span deflection of LICPT specimens were increased by a maximum of 1.08 times and 1.19 times compared to the LICP specimens. This results indicated that the installed transverse bar is in an advantageous ductility performance of the PHC piles. A conventional layered sectional analysis for the pile specimens was performed to investigate the flexural strength according to the each used material. The calculated bending moment of conventional PHC pile and composite PHC pile, which was determined by P-M interaction curve, showed a safety factor 1.13 and 1.16 compared to the test results.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.18 no.2
• /
• pp.108-116
• /
• 2014

The proper stress history measurement should be conducted in order to examine the accurate cause of fatigue cracks or the fatigue safety in the steel bridge. Only one strain gauge is generally installed in the field for the stress history examination because of the field circumstances, economic feasibility, workability, and so on. However, this method may not consider the actual size of the specific structure, the gauge length, and the affect of stress concentration in the welded joint. In addition, it is difficult to apply for the stress analysis. Therefore, this study suggests improvements that are a great number of gauge installations, the gauge location adjustment, and the use of the minimum length gauge. It is drived the correlative equation of strain for the distance between the welding toe and the strain gauge installation, and compare correlative equation with equation of IIW. Also, this study could estimate the remaining life and fatigue damage of bridge in service by selecting the suitable stress category. In conclusion, it is possible to understand the member which is high in the fatigue cracks, and the quantitative relations between the welding toe and the strain gauge installation distances. The proposed approach in this study can make an more accurate fatigue damage and a remaining life prediction so that the improved method should be applied in measuring the strain of bridges from now on.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.22 no.1
• /
• pp.40-47
• /
• 2018

Porous walkway blocks are constructed for the purpose already, but reserved water is easily consumed due to the bigger permeability than necessary. Furthermore, porous structure reduces the strength of blocks, which resulting cracking and settlements in walkways. In this study, we suggested a solution for given problems by determination for the location of minimum principal stress in walkway blocks against moving foot loads in order to design and verifying the determined location of minimum principal stress. An optimum design with a verification example for determined location of minimum principal stress have been presented in a two dimensional Block member on elastic foundation for pedestrian walkway for reserving water inside. The minimum value for sum of shear forces is found when ${\times}1$ is 58.58 mm(30% of total span, 200mm), while the minimum deformation is located at ${\times}2=80mm$(70% of total span, 200 mm). In a modified model, When moving boundary condition(walkway foot loads) is located at ${\times}1$(=0 mm), the location of minimum principal stresses is found at 168 mm( 84% of span, 200 mm), in which the stress concentration due to the foot load is modeled as two layers of distributed loads(reactions of foundation modeled as springs). Consequently, zero deformed reservoirs for rainwater on the neutral axis (${\times}2=167mm$) has been determined in the modified model with three dimensional FEM analysis verifications.

• Journal of Korean Society for Geospatial Information Science
• /
• v.16 no.1
• /
• pp.83-93
• /
• 2008

The topographic effect is one of the most important component in the solution of the geodetic boundary value problem (geodetic BVP). Therefore, topographic effect should be considered properly for developing the precise geoid model, especially for the area where contains many mountains like Korea. The selection of gravity reduction method in the context of the precise geoid determination depends on the magnitude of its indirect effect, the smoothness and magnitude of the reduced gravity anomalies, and their related geophysical interpretation. In this study, Korean digital elevation model with 100m resolution was constructed and topographic effect was calculated by three reduction methods as like Helmert condensation method and RTM method and Airy-isostatic reduction method. Through the analysis of computation results, we can find that RTM reduction method is the best optimal method and the results shows that gravity anomaly and indirect effect of geoidal height are $0.660{\pm}13.009mGal$, $-0.004{\pm}0.131m$ respectively and it is the most gentle slow of the three methods. Through this study, it was found that the RTM method is better suitable for calculating topographic effect precisely in context of precise geoid determination in Korea than other reduction methods.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.22 no.4
• /
• pp.100-107
• /
• 2018

The objective of this study is to assess the strengthening effects of fiber reinforced polymer(FRP) sheets such as Carbon fiber, Glass fiber, and PET(polyethylene terephthalate) on reinforced concrete flexural members. Variables of theoretical analysis are types of strengthening materials, material properties and amount of strengthening materials. A virtual flexural member without FRP sheets was created as a control specimen to understand the structural behavior of the non-strengthened specimen in terms of elastic and ultimate cross section. In total, 11 specimens including one non-strengthened and ten strengthened specimens were investigated. Various variables such as types of strengthening, strengthening properties, and amount of strengthening were studied to compare the behavior of the control specimen with those of strengthened specimens with regard to moment-curvature relationship. Results of theoretical analysis showed that the moment capacity of strengthened specimens was superior to that of the control specimen. However, the control specimen indicated the best ductility among all the specimens. As the amount of strengthening increased, flexural performance was improved. Furthermore, the results indicated that the ductile effect of members was affected by the ultimate strain of FRP sheets. The strengthening effect on the damaged member was similar to that on the non-damaged one since there was less than 10% difference in terms of flexural strength and ductility. Therefore, even if a damaged member is treated as non-damaged for analysis there is probably no noticeable difference.

• KSBB Journal
• /
• v.24 no.3
• /
• pp.303-311
• /
• 2009

A scaling up study for the exopolysaccharide (EPS) production by submerged culture of Ganoderma lucidum was carried out in jar fermenter systems (2.6, 20 and 75 L) under bi-staged pH process. Profiles of dissolved oxygen (DO) and volumetric coefficient of oxygen transfer ($k_La$) as a function of operating variables (agitation speed and aeration rate) was investigated, and a correlation between $k_La$ and operating variables was analysed statistically. Under bi-staged pH process, no limitation of DO was observed at agitation speeds tested in the range of 200 and 600 rpm, and the highest EPS production was obtained at the level of DO of $40{\sim}80%$. From the regression analysis, the relation between $k_La$, gas velocity (Vs), stirrer speed (N) and impeller diameter (Di) could be expressed as : $$k_La=0.555{\times}Vs^{0.42}{\times}(N^3{\times}Di^2)^{0.33}\;(R^2=0.925,\;p<0.05)$$ It was found that under 2.6 L jar fermenter, the optimum agitation speed and aeration rate was 400 rpm and 1 vvm, respectively, obtaining the EPS production of 15.43 g/L. Under the submerged cultivation of G. lucidum in jar fermenters of $2.6{\sim}75\;L$, the similar EPS yields at each fermenter were achieved during scaling up based on $k_La$, and $k_La$ value for maximum EPS production was $85.4{\pm}26.70\;h^{-1}$.

• Progress in Medical Physics
• /
• v.13 no.4
• /
• pp.195-201
• /
• 2002

Several investigators have presented the effects of external magnetic fields on the dose distributions for clinical electron and photon beams. We focus the low energy electron beam with more lateral scatter In this study we calculated the beam profiles for an clinical electron beam of 6 MeV with longitudinal magnetic fields of 0.5 T-3.0 T using a Monte Carlo code. The principle of dose enhancements in the penumbra region is to deflect the laterally scattered electrons from its initial direction by the skewness of the laterally scattered electrons along the direction of magnetic field lines due to Lorentz force under longitudinal magnetic field. To discuss the dose enhancement effect on the penumbra area from the calculated results, we introduced the simple term of penumbra reduction ratio (PRR), which is defined as the percentage difference between the penumbra with and without magnetic field at the same depth. We found that the average PRR are 33%, and 49% over the depths of 1.5 cm, 2.0 cm, and 2.4 cm for the magnetic fields of 2.0 T and 3.0 T respectively. For the case of 0.5 T and 1.0 T the effects of magnetic filed were not observed significantly. In order to obtain the dose enhancement effects by the external magnetic field, we think that its strength should be more than 2 T approximately. We expect that the PRR would be saturated to 50-60% with magnetic fields of 3 T-5 T As a result of these calculations we found that the penumbra widths can be reduced with increased magnetic fields. This Penumbra reduction is explained as a result of electron lateral spread outside the geometrical edges of the beam in a longitudinal magnetic field. This means that the electron therapy benefits from the external magnetic fields.

• Solar Energy
• /
• v.11 no.2
• /
• pp.51-62
• /
• 1991

Heat transfer characteristics for heat retrieving processes in a paraffin-filled horizontal circular cylinder was studied. Theoretical and experimental analyses were carried out. In the theoretical analysis, solid and liquid phases were treated separately. Namely, convection for liquid and conduction for solid phase were investigated respectively. The retrieved heat was calculated from the experimentally determined solidified mass. Furthermore, the effects of initial temperature of the liquid and cooling temperature on the heat discharge rate were also studied. In the heat retrieving process, the governing factor for the solidifying rate is the cooling temperature, because most of the liquid sensible heat is rapidly discharged in the initial stage of solidification. Hence heat transfer mechanism during heat retrieving process can be safely considered as conduction. In the cut of frozen paraffin, there showed an empty space in the upper region. It is caused by the temperature drop in the liquid paraffin. While volume shrinkage caused by phase transition was indiscernible. Irrespective of cooling temperature and initial liquid temperature, solidified mass was well-correlated with the product of Fourier number and Stefan number in the solid phase.

• The Journal of the Petrological Society of Korea
• /
• v.24 no.3
• /
• pp.193-207
• /
• 2015

This study analyzed ancient documents and established petrological database through extensive field investigation of provenance sites to presume stone source areas of the Seoul City Wall. By summarizing the ancient documents, the rampart stone was mostly supplied from a stony mountain adjacent to the City Wall in the early Joseon period, whereas the stone was provided from fixed quarry outside the City Wall in the late Joseon period. As a result of the petrological investigation based on quarries recorded in the ancient documents, pinkish granite and leucogranite were distributed as a whole, and the granitoid rocks are similar in mineralogical compositions and geochemical behavior characteristics. However, the pinkish granite with magnetic-series show that the magnetic susceptibility increased from the north slope of Namsan Mountain to Bulamsan Mountain. The leucogranite with ilmenite-series mainly occurred along the boundary between granite and gneiss from Yongmasan Mountain to Inwangsan Mountain. Consequently, the important petrological indicators for presumption of stone source areas are the rock color and the magnetic susceptibility. In addition to the petrological features, the reliability for provenance interpretation should improve considering stone quantities in the quarries, transportation distance and technical skills.

• The Journal of the Petrological Society of Korea
• /
• v.20 no.2
• /
• pp.115-135
• /
• 2011

Fe-Ti ore bodies and mafic granulite occur in the Sancheong anorthosites, south Korea. In order to determine their petrogenetic relationship and to classify the Fe-Ti ore bodies, we have synthetically analyzed characteristics in the field, such as distribution and occurrence, and petrologic features through detailed outcrop sketches. The ore bodies are divided into the regular vein dike- and irregular veinlet swarm types, according to their characteristics of contact with the anorthosites and internal structures. The former shows the tabularly intrusive contact and the pervasively ductile-sheared interior, while the latter, the irregularly tortuous contact and the almost intact interior. Most of the ore bodies are cross-cutting the foliation of the anorthosites and possess abundant anorthositic xenoliths, indicating their intrusion after the formation of foliation in the anorthosites. The mafic granulite, also bearing abundant anorthositic xenoliths, shows interior foliations nearly parallel to intrusion contact, and has abundant ilmenites approximately the same as those of the Fe-Ti ore bodies in chemical composition. And its intrusion into adjacent anorthosites is observed and the intrusion is finally changed into an irregular veinlet swarm type ore body. It is, thus, interpreted that the granulite in the study area was the host material of Fe-Ti ore bodies.