• KSCE Journal of Civil and Environmental Engineering Research
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• v.43 no.3
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• pp.277-285
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• 2023

Recently, as the magnitude and frequency of earthquakes increases, research is needed to increase the ductility of the columns in order to prevent the collapse of structures. In this study, to evaluate the performance of columns reinforced with continuous transverse reinforcing bars, the FE model for the dynamic analysis of structures reinforced with continuous transverse reinforcing bars for circular and rectangular columns is to be verified using the results of uniaxial compression experiments in the previous study. As a result, the experimental value of the column reinforced with continuous transverse reinforcement and the result value related to the dynamic analysis showed similar behavior, and the reliability was high. As a result of the analysis, the usability of the rectangular column reinforced with continuous lateral reinforcing bars was confirmed because the dissipated energy performance of the columns reinforced with spiral reinforcing bars was higher than that of the columns reinforced with band reinforcing bars.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.2A
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• pp.169-176
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• 2010

Generally, poly-urea is widely used as waterproof coating material due to its superior adhesiveness, elongation capacity, and permeability resistance. In addition, it can be quickly and easily applied on structure surfaces using spray application. Since it hardens in about 30 seconds after application, its construction efficiency is very high and its usage as a special functional material is also excellent. However, currently, poly-urea is mostly used as waterproof coating material and the researches on its usage as a retrofitting material is lacking at best. Therefore, basic studies on the use of poly-urea as a general structural retrofitting material are needed urgently. The objective of this study is to develop most optimum poly-urea composition for structure retrofitting purpose. Moreover, the structural strengthening capacity of the developed poly-urea is evaluated through flexural capacity experiments on RC beams and RC slabs. From the results of the flexural test of poly-urea strengthened RC beam and slab specimens, the poly-urea and concrete specimen showed monolithic behavior where ductility and ultimate strength of the poly-urea strengthened specimen showed slight increase. However, the doubly reinforced specimens with FRP sheet and poly-urea showed lower capacity than that of the specimen reinforced only with FRP sheet.

• Korean Journal of Materials Research
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• v.10 no.8
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• pp.569-574
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• 2000

To improve the ductility of $Al_3Hf$ and $Al_3Ta$ intermetallic compounds, which are the potential temperature structural materials, the mechanical alloying behaviour and the effect of ternary additions on the $Ll_2$ phase formation were investigated. During the mechanical alloying by the SPEX mill, the $Ll_2$ $Al_3Hf$ intermetallic compound was formed after 6 hours of milling in AL-25%Hf system. In AL-25%Ta system, however, only the $D0_{22}$ $Al_3Ta$ intermetallic compound was formed until 30 hours of milling and the $Ll_2$ phase was not observed. In AL-12.5%M-25%Ta(M=Cu, Zn, Mn, Fe, Ni) systems, the additions of Cu and Zn had no effect on the $D0_{22}$ structure of the binary $Al_3Hf$ and the additions of Mn, Fe and Ni produced the amorphous phase. Therefore it was considered that these ternary additions could not overcome the energy difference between $Ll_2$ and $D0_{22}$ structures in the $Al_3Hf$ intermetallic compound. In AL-12.5%M-25%Hf(M=Cu, Zn, Mn, Fe, Ni)systems, the additions of Cu and Zn did not affect the $Ll_2$ structure of the binary $Al_3Hf$ but the additions of oMn, Fe and Ni produced the amorphous phase as they did in AL-12.5%M-25%Ta systems. Therefore, it was considered that the Ni, Mn and Fe additions promote the formation of amorphous phase in $Al_3X$ intermetallic compounds.

• Journal of Korean Society of Steel Construction
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• v.23 no.4
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• pp.417-428
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• 2011

Depending on the plastic deformation capacity required, structural steel design under the current codes can be classified into three categories: elastic, plastic, and seismic design. Most of the current steel codes explicitly forbid the use of a steel material with a yield strength higher than 450 MPa in the plastic design because of the concerns about its low plastic deformation capacity as well as the lack of test data on local and lateral torsional buckling behavior. In this study, flexural tests on full-scale H-shape members built with SM490A (ordinary steel or benchmark material) and HSB800 (high-strength steel) were carried out. The primary objective was to investigate the appropriateness of extrapolating the local buckling criterion of the current codes, which was originally developed for normal-strength steel, to the case of high-strength steel. All the SM490A specimens performed consistently with the current code criteria and exhibited sufficient strength and ductility. The performance of the HSB800 specimens was also very satisfactory from the strength perspective; even the specimens with a noncompact and slender flange developed the plastic moment capacity. The HSB800 specimens, however, showed an inferior plastic rotation capacity due to the premature tensile fracture of the beam bottom flange beneath the vertical stiffener at the loading point. The plastic rotation capacity that was achieved was less than 3 (or the minimum level required for a plastic design). Although the test results in this study indicate that the extrapolation of the current flange local-buckling criterion to the case of high-strength steel is conservative from the elastic design perspective, further testing together with an associated analytical study is required to identify the causes of the tensile fracture and to establish a flange slenderness criterion that is more appropriate for high-strength steel.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.1
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• pp.73-80
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• 2022

In this study, details of NRC beam-column connections were developed in which beam and columns pre-assembled in factories using steel angles were bolted on site. The developed joint details are NRC-J type and NRC-JD type. NRC-J type is a method of tensile joining with TS bolts to the side and lower surfaces of the side plate of the NRC column and the end plate of the NRC beam. NRC-JD type has a rigid joint with high-strength bolts between the NRC beam and the side of the NRC column for shear, and with lap splices of reinforcing bar penetrating the joint and the beam main reinforcement for bending. For the seismic performance evaluation of the joint, three specimens were tested: an NRC-J specimen and NRC-JD specimen with NRC beam-column joint details, and an RC-J specimen with RC beam-column joint detail. As a result of the repeated lateral load test, the final failure mode of all specimens was the bending fracture of the beam at the beam-column interface. Compared to the RC-J specimen, the maximum strength of the specimen by the positive force was 10.1% and 29.6% higher in the NRC-J specimen and the NRC-JD specimen, respectively. Both NRC joint details were evaluated to secure ductility of 0.03 rad or more, the minimum total inter-story displacement angle required for the composite intermediate moment frame according to the KDS standard (KDS 41 31 00). At the slope by relative storey displacemet of 5.7%, the NRC-J specimen and the NRC-JD specimen had about 34.8% and 61.1% greater cumulative energy dissipation capacity than the RC specimen. The experimental strength of the NRC beam-column connection was evaluated to be 30% to 53% greater than the theoretical strength according to the KDS standard formula, and the standard formula evaluated the joint performance as a safety side.