• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.17 no.2
• /
• pp.220-226
• /
• 2016

Because MS(Multi-Strand) cables consist of many strands, a jacking force is applied to each strand one by one for cable construction. All strands should have an equal tensile force when the last one is wedged. This is the core technology for MS iso-tensioning. In this study, a new MS cable iso-tensioning system was developed for controlling and jacking the high-strength strands, with an ultimate tensile strength of 2,200MPa, for a stay cable of extra-dosed/cable-stayed bridges. The newly developed iso-tensioning system consists of electrical resistance load cells, hydraulic jacking devices, hydraulic pumps, and integrated controllers. Moreover, it is embedded with an algorithm that can control and predict the variations in tensile forces of the Master and Slave strands in real time. Actual experiments were carried out to verify the function and performance of the newly developed system. This system was applied successfully to the stay cable construction of 2nd Tae-in extra-dosed bridge in Gwangyang.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.31 no.6A
• /
• pp.435-447
• /
• 2011

This paper discusses the problems in application of a parallel wire strand with high performance steel wires, which have the tensile strength of 1960 MPa grade, as a major component of the main cables in suspension bridges. Construction methods of main cables in suspension bridges are briefly reviewed by comparing the pros and cons of available methods. Required items for performance and quality of parallel wire strands are described based on the established references. Ultimate tensile strength tests are carried out for seven specimens in order to analyze the behavior of high-performance parallel wire strands. The test results demonstrate that the properties of test specimens are satisfied with performance indexes specified in this paper. The high-performance parallel wire strands are acceptable for application in main cables of suspension bridges.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.17 no.6
• /
• pp.1351-1360
• /
• 1993

The fatigue behavior of GFRP composites is affected by environmental parameters. Therefore, we have to study on effect of sea water on fatigue behavior of GFRP composites as to maintain the safety and confidence in design of ocean structure of GFRP. In this paper, we investigated the fatigue properties of chopped strand glass mat/polyester composite in synthetic sea water. (pH 8.2) In case of the glass fiber (CSM type) reinforced polyester composite materials, the fatigue crack in the both dry and wet specimens tested in air or synthetic sea water occurred at the initial of cycle. Thereafter, it was divided with two regions that one decreased with the crack extension and the other increased with the crack extension. The transition point occurred during the crack propagation shifted to high ${\Delta}K$ value as load increase but its point is not changed regardless of immersion or test environment under a constant load. The synthetic sea water degrades the bond strength between fiber and matrix, thereby the tendency of rapid deceleration and acceleration of the crack growth was appeared.

• Structural Engineering and Mechanics
• /
• v.69 no.4
• /
• pp.371-381
• /
• 2019

A hybrid prestressed segmental concrete (HPSC) girder utilizing low carbon materials was developed in this paper. This paper introduces the hybrid prestressing concept of pre-tensioning the center segment and assembling all segments by post-tensioning, as well as the development process of the low carbon HPSC girder. First, an optimized mix proportion of 60 MPa high strength concrete containing high volume blast furnace slag was developed, then its mechanical properties and durability characteristics were evaluated. Second, the mechanical properties of 2,400 MPa high strength prestressing strands and the transfer length characteristics in pre-tensioned prestressed concrete beams were evaluated. Third, using those low carbon materials and the hybrid prestressing concept, the HPSC girders were manufactured, and their structural performance was evaluated. A 30-m long HPSC girder for highway bridges and a 35-m long HPSC girder for railway bridges were designed, manufactured, and structurally confirmed as having sufficient strength and safety. Finally, five 35-m long HPSC girders were successfully applied to an actual railway bridge for the first time.

• Journal of the Korean Wood Science and Technology
• /
• v.22 no.3
• /
• pp.17-25
• /
• 1994

This study was carried out to compare the properties of Com-Ply Boards with those of OSBs. These two kinds of boards were made of same flakes. Com-Ply Boards were covered with three different thickness veneers, such as 4mm, 3mm, and 2.5mm. All manufactured Com-Ply Boards and OSBs were 12mm thick. In MOR, all Com-Ply Boards were higher than OSB, and especially 3mm-veneer and 2.5mm-veneer Com-Ply Board were highest. But OSB showed 420kg/$cm^2$. 3mm-veneer Com-Ply Board showed the highest internal bonding 7.0kg/$cm^2$ and then 2.5mm-veneer showed 6.8kg/$cm^2$, and OSB showed 6.6kg/$cm^2$. Screw holding strength showed the high value 23.9kg/$cm^2$, 25.5kg/$cm^2$, and 29.3kg/$cm^2$ respectively at 3mm-veneer, 2.5mm-veneer Com-Ply Board and OSB. Thickness swelling of Com-Ply Boards was lower than that of OSB, but Water absorption of OSB was lower. Finally it was very encouraging that all properties of OSB without veneer, whose cost is higher than flake and whose properties is better, were not worse than those of Com-Ply Board with veneer. It seems That more researches on OSB will be required.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.19 no.1
• /
• pp.100-106
• /
• 2006

Today, restricted energy sources, environmental considerations and the high cost of transporting fuel have limited the number and location of available power plant sites. The pressures resulting from these conditions have tended to require the construction of long, high-capacity, high-voltage power lines. it's used to adapt to STACIR/AW(Super Thermal-resistant Aluminum alloy Conductors, aluminum-clad Invar-Reinforced) conductor for coping with these situations. STACIR/AW conductor was formed by the combination of INVAR/AW as the core for low sag and super thermal-resistant aluminum alloy conductor for current capacity increase. increase of temperature by current capacity and long span lines make the susceptible to the deterioration of thermo-mechanical properties(conductivity, tensile strength, E-modulus and twist property et al). In the present work, changes of thermo-mechanical properties with aging have been studied in STACIR/AW $410 mm^2$ conductor with forms of single wire and strand wire.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.19 no.1
• /
• pp.91-99
• /
• 2006

Fatigue properties of INVAR/AW wires have been investigated under the heat exposure in order to ensure stable operation and to estimate life span of their power line. In the case of heat exposure for 10000 hr, fatigue life and limit increased. For further heat exposure, fatigue limit decreased due to the decrease in yield strength. The variation fatigue of strand wire was strongly dependent on its amplitude. Also, cracks in wires of 7 strands were caused by stress concentration at the outer surface and fretting between each wire during vibration.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.28 no.6
• /
• pp.707-714
• /
• 2015

In this paper, an experimental program has been conducted to investigate transfer length in high strength concrete members pretensioned through a seven-wire strand with FBG sensors. To measure transfer length, five members were fabricated, which had a length of 3 m and a cross-section of $150{\times}150mm$. It was measured that the concrete compressive strength was 58MPa at pretensioning. Test results indicated that more precise and reliable measurement on the transfer length was attained with FBG sensors than conventional gauges attached on concrete surface. Through comparing the measured transfer length and predictions, applicability of several transfer length models in literature was investigated. This paper can be useful for relevant research field such as investigation on the bond mechanism of a seven-wire strand in concrete members.

• Journal of the Korea Concrete Institute
• /
• v.22 no.6
• /
• pp.753-760
• /
• 2010

Ultra high performance concrete (UHPC), is characterized by its high compressive strength and advanced tensile behavior that is much superior to those of conventional concrete. In order to apply this new material in practice, the bond characteristics of UHPC were evaluated in this study. Pull-out tests between UHPC and deformed steel rebar were carried out according to the modified RILEM test method, and were verified by finite element analysis. From the test results showed that UHPC presents 5 to 10 times higher bond strength compared to normal strength concrete, this study suggested remarkably reduced development length and concrete cover comparing to existing specifications. The test results of 700 MPa high strength steel rebar demonstrated the applicability of high strength steel to UHPC. In addition, the transfer length measurements of seven-wire strand in UHPC specimens indicated that the transfer length limit set by the current design code is very conservative for UHPC.

• Korea-Australia Rheology Journal
• /
• v.12 no.3_4
• /
• pp.181-186
• /
• 2000

Rheological Properties of polypropylenes having different molecular structures (linear polypropylene (PPL) and branched one (PPB)) were studied. Both the extensional flow and oscillatory shear flow properties were checked. Especially, the melt strength of polypropylenes having various shear history were investigated by using in-house-made Rheometer (called SMER). Compared to linear polypropylene, the branched polypropylene shows enhanced melt strength during extensional flow due to the retarded relaxation of molecules. When the slope of melt tension was plotted against take up speed of melt strand, the characteristic peak was observed in case of branched polypropylene, while the linear polypropylene shows only monotonously decreasing pattern. This entanglement was partially disrupted by physical forces such as shear during melt extrusion. However, the melt strength of PPB after multiple extrusion is still higher than PPL, implying the loss of elasticity during multiple extrusion is not so comprehensive. On dynamic experiments, PPB shows typical shear thinning behavior and the tangent delta of PPB is lower than PPL, reflecting high elasticity of PPB.