• Journal of the Korean GEO-environmental Society
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• v.16 no.1
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• pp.37-43
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• 2015

Korea has four distinct seasons, showing hot and humidity in summer and cold weather lasted in winter. Domestic research on earth work has been developed according to the seasonal characteristics, and most of research topics have focused on the effect of freezing-thawing on the performance of geo-materials. However, the previous research was performed on the ground compacted at room temperature and therefore, the effect of the sub-zero temperature at the time of construction was not fully investigated. The ground characteristics compacted at freezing temperature can be different from those at room temperature and show different characteristics of strength and deformation caused by freezing and thawing. Therefore, the compaction tests on sandy materials were conducted under various temperature at $-3^{\circ}C$ and $-8^{\circ}C$ with various fine contents of 0%, 5%, 10% and 15% in weight fraction. The effectiveness of soil compaction at below-freezing temperatures were compared with the compaction at room temperature at $18^{\circ}C$ in terms of the maximum dry unit weight and optimum water contents. Based on the test results, the maximum dry unit weight tends to decrease with the freezing temperature and the relative compaction at $-8^{\circ}C$ can not be satisfied with general specification standard.

• Journal of Korean Society of Steel Construction
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• v.21 no.5
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• pp.451-459
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• 2009

The purpose of this study was to evaluate the in-plane bending moment for T-joints made of cold-formed square hollow steel sections. In the previous studies, the T-joint was shown not to have an obvious peak load, and the failure mode was the main chord flange failure at the branch-width-to-chord-width ratio ($\beta$) of below 0.71. Based on the experimental results, including the tests conducted by Zhao, the deformation limit of 1% B was proposed for ${16.7{\leq}2{\gamma}(=B/T){\leq}33}$ and ${0.34{\leq}{\beta}(=b_{1}/B){\leq}0.71}$. Then, the ultimate in-plane bending strength was shown to be Mu=1.5${\cdot}$M1% B. The existing strength formulae for the original T-joint were investigated and were determined to be the main chord flange failure for the branch-squared T-joint. The bending strength formulae of CIDECT and other researchers were compared with the test results. Finally, a reasonably good agreement with Zhao's formula was found. Therefore, the design guidelines were presented based on Zhao's strength formula for T-joints.

• International Journal of Highway Engineering
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• v.3 no.3 s.9
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• pp.119-133
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• 2001

The stiffness of chemcrete modified asphalt mixtures increase rapidly with time in the presence f oxygen and high temperature, Sometimes the asphalt pavements that have chemcrete modified asphalt mixture applied on the surface none show premature cracking because of the excessive increase in the stiffness f the asphalt mixtures. To mitigate this premature cracking, the chemcrete modified mixtures have been used as a base course material. In this study, the performance of the chemcrete modified asphalt binder and mixtures are investigated through a course of various laboratory tests including dynamic shear rheometer and bending beam rheometer tests for binders and uniaxial tensile fatigue, wheel tracking, and moisture damage tests for the mixtures. And also the resilient modulus of the conventional and chemcrete modified mixtures are compared based on the test results conducted on the specimens obtained from various in-situ test sections. It can be concluded from the tests results that the chemcrete modified mixtures show better rutting resistance than conventional mixtures. The chemcrete modified mixtures may have low temperature cracking when it is applied in the cold region. The stiffness of chemcrete modified mixtures is approximately 50 percent higher than that of conventional mixtures more than two years after the chemcrete modified mixture was applied in the base course.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.8
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• pp.857-863
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• 2012

In this study, tailor-welded blanks(TWB) were formed between high-strength steel(SABC1470) and cold rolled steels(SPFH590 and SPFC980) to improve passenger safety and reduce the weight of cars. Multi-material TWB specimens were highly strengthened through the heat treatment of SABC1470. The change in tensile strength caused by the stand-by time until water cooling after stamping and the deformation behavior of high-speed bending in a statically indeterminate condition such as in the center-pillar were evaluated. Multi-material TWB specimens that were heat-treated at the same temperature tended to show a decrease in tensile and yield strength, depending on the stand-by time until water cooling. On the other hand, Multi-material TWB specimens(SABC1470+SPFH590) that were heat treated at $850^{\circ}C$ showed good properties that were suitable for ensuring passenger safety in car accidents. From the viewpoint of passenger safety, it is best to use SABC1470 and SPFH590 in the upper and lower area of the center-pillar, respectively.

• Journal of Korean Society of Steel Construction
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• v.21 no.3
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• pp.211-219
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• 2009

The purpose of the study described in this paper was to experimentally investigate branch squared T joints with cold formed hollow structural sections under the in plane moment in a Vierendeel Truss. The branch in the T joints was welded to the upper flange of the chord. The main experimental parameters were the ratio of the width to the thickness of the chord ($2{\gamma}$), with ${16.7{\leq}2{\gamma}{\leq}33.3}$, and the width ratio of the branch to the chord ($\beta$), with ${0.40{\leq}{\beta}{\leq}0.71}$. Nine specimens were tested and manufactured in joints under the in plane bending moment. Based on the results of the test, the in plane moment strength of the branch squared T joints was determined according to the bending deformation of the chord flange yielding, regardless of the ratio of the width to the thickness of the chord and the ratio of the width of the branch to the width of the chord. Also, the in plane moment strength of the branch squared T joints in the hollow structural sections can be defined as 1.5 times the moment load at M1%B the strength of the joints that governed the serviceability in the control group. Finally, the experimental results with the branch squared T joints show that the in lane moment strength of the joint increased as $2{\gamma}$ decreased and $\beta$ increased.

• Journal of the Korean GEO-environmental Society
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• v.16 no.8
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• pp.13-20
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• 2015

Due to the population growth and exhaustion of resource, the development on the harsh environment such as cold weather is emerging as an alternative for new resource development. The permafrost area covers about 14 percent of the world's land area and the global construction market for such area is rapidly expanded. Whereas the developed countries have already recognition of the need for research of coldest place and invested heavily in technology development, the domestic technology for the coldest place development is less developed and related research has rarely been performed. There is not a detailed national specification standard for the strength and deformation properties of the earthworks at sub-zero temperature but simple field directions. Therefore, the D compaction tests were conducted on the sand with fine contents of 0%, 5%, 10% and 15% at room temperature ($18^{\circ}C$), $-3^{\circ}C$ and $-8^{\circ}C$ to investigate the effect of the compaction energy on the compacted soils at sub-zero temperatures. Based on the test results, the larger compaction energy, the larger maximum dry unit weight under sub-zero temperature and D type compaction at $-3^{\circ}C$ show similar max. dry unit weights as those obtained from the compaction at the room temperature. However, compaction at $-8^{\circ}C$ showed significant performance degradation regardless of the compaction energy.

• Korean Journal of Metals and Materials
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• v.50 no.4
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• pp.316-323
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• 2012

The aim of this study is to investigate the effect of post heat treatment on bonding properties of roll cladded Ti/MS/Ti materials. First grade Ti sheets and SPCC mild steel sheets were prepared and then Ti/MS/Ti clad materials were fabricated by a cold rolling and post heat treatment process. Microstructure and point analysis of the Ti/MS interfaces were performed using the SEM and EDX Analyser. Diffusion bonding was observed at the interfaces of Ti/MS. The thickness of the diffusion layer increased with post heat treatment temperature and the diffusion layer was verified as having $({\epsilon}+{\zeta})+({\zeta}+{\beta}-Ti)$ intermetallic compounds at $700^{\circ}C$ and an $({\zeta}+{\beta}-Ti)$ intermetallic compound at $800^{\circ}C$, respectively. The micro Knoop hardness of mild steel decreased with post heat treatment temperature; however, those of Ti decreased at a range of $500{\sim}600^{\circ}C$ and showed a uniform value until $800^{\circ}C$ and then increased rapidly up to $900^{\circ}C$. The micro Knoop hardness value of the diffusion layer increased up to $700^{\circ}C$ and then saturated with post heat treatment. A T-type peel test was used to estimate the bonding forces of Ti/Mild steel interfaces. The bonding forces decreased up to $800^{\circ}C$ and then increased slightly with post heat treatment. The optimized temperature ranges for post heat treatment were $500{\sim}600^{\circ}C$ to obtain the proper formability for an additional plastic deformation process.