• The Journal of Korea Robotics Society
• /
• v.17 no.2
• /
• pp.178-182
• /
• 2022

Post-tension duct in nuclear reactor containment building is filled with grease to prevent steel strand from corroding. If grease leaks by break of duct, steel strand will corrode and cause problem in building safety. Therefore, grease leak should be checked preventatively. But currently used method is inefficient, since it has to remove grease and strand to check. And other methods for checking post-tension dust are not well-researched. In this paper, we develop screw-propelled robot that can move in grease and detect grease duct directly. Also, we make the test environment that is similar to real post-tension duct of containment building and test robot in that environment to verify that our robot is feasible in the post-tension duct. The robot can move forward and backward in grease duct by twin screw mechanism and has mount for sensors to detect grease leakage and strand corrosion.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.10 no.2
• /
• pp.102-110
• /
• 2006

This paper examines experimentally the ultimate behavior of I-type steel beam strengthened with external tendon and cylindrical anchorage and analyzes the strengthening effect on the parameters such as initial tendon force, eccentricity, number of strands, and strand areas. The experiment demonstrated that increasing the number of strands, strand areas and eccentricity is more effective than increasing initial tendon force. The proposed cylindrical anchorage system has advantages in applying these parameters. The results showed that the cylindrical anchorage system is efficient and applicable to strengthen steel beam.

• Journal of the Korean Ceramic Society
• /
• v.35 no.1
• /
• pp.33-40
• /
• 1998

A MgO-CaO-based coating material for ferrous melt refining is applied to the tundish operation for mol-ten steel having low carbon. The changes in the total oxygen content insoluble aluminum content and the content of inclusions in molten steel during tundish operation were measured at the pouring part strand of tundish and mold. On the basis of the experimental results the interfacial reaction occurring between the coating materials and the molten steel in tundish was discussed and compared with the theoretical con-sideration. It is concluded that interfacial reaction is not active at the strand part of tundish but is active at the pouring part because of the turbulent flow in the molten steel.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.24 no.6
• /
• pp.699-714
• /
• 2022

The objective of this study is to suggest a safe and economical pillar reinforcement method when very near-twin tunnels with a minimum interval of 1 m passes through a soft zone such as weathered soil or weathered rock. A standard cross-sectional view of a two-lane road tunnel was applied to suggest a pillar reinforcement method for the very near-twin tunnels. The thickness of the pillar was 1 m. The ground condition around the tunnel was weathered soil or weathered rock. There were four reinforcement methods for pillar stability evaluation. These were rock bolt reinforcement, pre-stressed steel strand reinforcement, horizontal steel pipe grouting reinforcement, horizontal steel pipe grouting + prestressed steel strand reinforcement. When the ground condition was weathered soil, only the pillar reinforced the horizontal steel pipe grouting + prestressed steel strand did not failed. When the ground condition was weathered rock, there were no failure of the pillar reinforced the horizontal steel pipe grouting or the horizontal steel pipe grouting + prestressed steel strand. It is considered that the horizontal steel pipe grouting reinforcement played a role in increasing the stability of the upper part of the pillar by supporting the upper load applied to the upper part of the pillar.

• Proceedings of the KSME Conference
• /
• 2001.06e
• /
• pp.436-443
• /
• 2001

In order to investigate the mixing of dissimilar grades during the arbitrary grade transition in bloom caster, a computational model has been developed. The model is fully transient and consists of two sub models, which account for mixing in the bloom tundish, mixing in the strand. The developed model was verified using concentration histories measured on 1 : 1 scale bloom tundish water model. The result of numerical model showed good agreement with the experimental results of water model. By using this numerical model, the mixing of dissimilar grades in bloom caster has been simulated. As that result, the characteristics of the steel mixing in the bloom tundish and strand was showed and the amount of the intermixed grade bloom was predicted.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2008.04a
• /
• pp.133-138
• /
• 2008

This study proposes a novel method for in-service evaluation of force in an external prestressing 7-wire tendon which is employed for retrofitting bridge superstructure. For this propose, a smart strand 7.0m long whose king wire is replaced by a steel tube and the FBG sensor, is developed. Performance of the strand is demonstrated through loading-unloading tests for a RC T-shaped beam 6.4m long. Finally, a couple of test results are presented to discuss effect of temperature change in the FBG sensor.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.28 no.6
• /
• pp.699-706
• /
• 2015

This paper presents results of one-year monitoring on prestressing force of a 7-wire steel post-tensioning strand which is installed in a UHPC(ultra high performance concrete) bridge with 11.0 m long, 5.0 m wide, and 0.6 m high by using a FBG-encapsulated 7-wire steel strand. The initial prestressing forces and the prestress changes during a vehicle load test were measured using the FBG-encapsulated strand. The results show that the FBG-encapsulated 7-wire strand is very effective for monitoring the prestress forces even the change in the tension force is very small. Additionally, it was indicated that selection of the thermal expansion coefficient which is used for the temperature correction shall be carefully carried out.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.42 no.3
• /
• pp.323-331
• /
• 2022

An experimental study was conducted to investigate the effect of applied tensile force and temperature on the permeability of magnetic flux in prestressing steel. The permeability of magnetic flux is the ratio at which the magnetic flux between two points passes. The prestressing steel used in these experiments included a 7-mm PS wire mainly used for cable-stayed bridges and a 12.7-mm PS strand for prestressed concrete bridges. The experiments to extract the permeability of the magnetic flux of steel wire and strand were conducted under various tensile levels and temperature conditions. From the experimental results, it was observed that the permeability of magnetic flux of the PS tension material was linearly proportional to the applied tensile stress level, and inversely proportional to the temperature. If the experimental relationship among the magnetic permeability, temperature, and prestressing ratio of a PS tension material is known in advance, the current tension stress level on PS members can be evaluated by measuring solely the magnetic permeability and temperature.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.21 no.3
• /
• pp.287-294
• /
• 2008

This study proposes a novel method for in service evaluation of tension force of a prestressed 7-wire strand which is frequently employed for retrofitting bridge superstructure. The smart strand is made by replacing the straight king wire of the strand with an instrumented steel tube in which the FBG sensor is embedded. Since the strain of the smart strand can easily be measured using the sensor, it is possible to monitor tension force of the strand during the service. For the sake of demonstrating effectiveness of the proposed strand, we came up with a 7.0m long prototype with 2 FBG sensors, and it is applied as an external tendon to a 6.4m long and 0.6 high RC T-shaped beam. A loading-unloading test has been carried out, and estimated tension forces using the smart strand are compared with measured forces by load cell. The comparison showed that the proposed smart tendon is useful and accurate for monitering tension force of the prestressed tendon.

• International Journal of Concrete Structures and Materials
• /
• v.9 no.4
• /
• pp.401-413
• /
• 2015

In this study the progressive collapse resisting capacity of a RC beam-column subassemblage with and without strengthening was investigated. Total of five specimens were tested; two unreinforced specimens, the one designed as gravity load-resisting system and the other as seismic load-resisting system, and three specimens reinforced with: (i) bonded strand, (ii) unbonded strand, and (iii) side steel plates with stud bolts. The two-span subassemblages were designed as part of an eight-story RC building. Monotonically increasing load was applied at the middle column of the specimens and the force-displacement relationships were plotted. It was observed that the gravity load-resisting specimen failed by fractures of re-bars in the beams. In the other specimens no failure was observed until the maximum displacement capacity of the actuator was reached. Highest strength was observed in the structure with unbonded strand. The test result of the specimen with side steel plates in beam-column joints showed that the force-displacement curve increased without fracture of re-bars. Based on the test results it was concluded that the progressive collapse resisting capacity of a RC frame could be significantly enhanced using unbonded strands or side plates with stud bolts.