• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.240-248
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• 2004

Recently, the customer's demands for automotive steel sheet have been diversified and sterned more. Therefore, as the tendency of auto industry light-weight, one among these requirements is the trend for high strength together with the thinness of automotive steel sheet. Because Mn added essentially in producing high strength steel sheet is bonded strongly with oxygen, the Fine oxidation layer was created at the welding face after the flash butt welding operated in entry section of pickling line. Thereby it was caused the crack or breakage of welding part in process of cold rolling. At this research, in order to protect the contact Mn with oxygen in atomosphere it was considered to fire oxygen with LNG and the related researches have been gone forward with the find out concrete and to apply them to operation.

• Earthquakes and Structures
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• v.20 no.4
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• pp.417-430
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• 2021

Due to functional requirements, SRC column-RC beam abnormal joints with characteristics of strong beam weak column, variable column section, unequal beam height and staggered height exist in the Steel reinforced concrete (SRC) frame-bent main building structure of thermal power plant (TPP). This paper presents the experimental results of these abnormal joints through cyclic loading tests on five specimens with scaling factor of 1/5. The staggered height and whether adding H-shaped steel in beam or not were changing parameters of specimens. The failure patterns, bearing capacity, energy dissipation and ductile performance were analyzed. In addition, the stress mechanism of the abnormal joint was discussed based on the diagonal strut model. The research results showed that the abnormal exterior joints occurred shear failure and column end hinge flexural failure; reducing beam height through adding H-shaped steel in the beam of abnormal exterior joint could improve the crack resistance and ductility; the abnormal interior joints with different staggered heights occurred column ends flexural failure; the joint with larger staggered height had the higher bearing capacity and stiffness, but lower ductility. The concrete compression strut mechanism is still applicable to the abnormal joints in TPP, but it is affected by the abnormal characteristics.

• Journal of Korean Society of Steel Construction
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• v.24 no.1
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• pp.23-34
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• 2012

In this study, stub columns subjected to concentrical and eccentrical loads were tested to check the applicability of the current local stability criteria (KBC2009, AISC2005) to 800MPa high-strength steel (HSA800). The key test variables in the concentrically loaded tests included the plate-edge restraints and the width-to-thickness ratio normalized by the yield strength of steel. Specimens made of ordinary steel (SM490) were also tested for comparative purposes. Eccentrically loaded stub column tests were conducted for a range of the P-M combinations by controlling the loading eccentricity. All the concentrically loaded specimens with non-compact and slender sections developed sufficient strengths according to the current local stability criteria. All the eccentrically loaded specimens with non-compact H sections also exhibited a sufficient P-M interaction strength that was even higher than that of compact H- section counterparts. Residual stresses were also measured by using the non-destructive indentation method to demonstrate their dependency or independency on the steel material's yield strength. The measured results of this study also indicated that the magnitude of residual stresses bears no strong relation to the yield strength of the steel material.

• Journal of Korean Society of Steel Construction
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• v.16 no.1 s.68
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• pp.113-121
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• 2004

A test program was conducted on full-scale steel moment connections constructed using a T-stiffener. In the T-stiffener connection, the beam-to-column connection was reinforced with the horizontal and vertical element of the T-stiffener to resist moment under severe cyclic loads. A total of five specimens were tested in this study together with a concrete-filled tubular(CFT) column(${\sqsubset}-500{\times}500{\times}12$) and a steel beam($H-506{\times}201{\times}11{\times}19$). For the specimens, the T-stiffener was combined with RBS (also known as "Dog-bone") detail or Horizontal Element Hole(HEH) detail constructed to enhance deformation capacity. The test program showed excellent seismic performance for specimens constructed with an RBS or an HEH. except the specimens had brittle failure of VE. The test results also showed that the connections all developed maximum moments at the face of the column. Such moments were at least 15% and as much as 36% larger than the plastic moment capacity of the beam. based on the actual yield stress of the beam steel.

• Steel and Composite Structures
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• v.38 no.2
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• pp.165-176
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• 2021

Existing research on confined concrete filled steel tubular (CCFT) columns has been mainly focused on static or cyclic loading. In this paper, square section CCFT and CFT columns were tested under both static and impact loading, using a 10,000 kN capacity compression test machine and a drop weight testing equipment. Research parameters included bonded and unbonded fiber reinforced polymer (FRP) wraps, with carbon, basalt and glass FRPs (or CFRP, BFRP, and GFRP), respectively. Time history curves for impact force and steel strain observed are discussed in detail. Experimental results show that the failure modes of specimens under impact testing were characterized by local buckling of the steel tube and cracking at the corners, for both CCFT and CFT columns, similar to those under static loading. For both static and impact loading, the FRP wraps could improve the behavior and increase the loading capacity. To analyze the dynamic behavior of the composite columns, a finite element, FE, model was established in LS-DYNA. A simplified method that is compared favorably with test results is also proposed to predict the impact load capacity of square CCFT columns.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.4
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• pp.83-91
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• 2021

In this study, to improve the connection performance between the existing reinforced concrete (R/C) frame and the strengthening member, we proposed a new H-section steel frame with elastic pad (HSFEP) system for seismic rehabilitation of existing medium-to-low-rise reinforced concrete (R/C) buildings. This HSFEP strengthening system exhibits an excellent connection performance because an elastic pad is installed between the existing structure and reinforcing frame. The method shows a strength design approach implemented via retrofitting, to easily increase the ultimate lateral load capacity of R/C buildings lacking seismic data, which exhibit shear failure mechanism. Two full-size two-story R/C frame specimens were designed based on an existing R/C building in Korea lacking seismic data, and then strengthened using the HSFEP system; thus, one control specimen and one specimen strengthened with the HSFEP system were used. Pseudodynamic tests were conducted to verify the effects of seismic retrofitting, and the earthquake response behavior with use of the proposed method, in terms of the maximum response strength, response displacement, and degree of earthquake damage compared with the control R/C frame. Test results revealed that the proposed HSFEP strengthening method, internally applied to the R/C frame, effectively increased the lateral ultimate strength, resulting in reduced response displacement of R/C structures under large scale earthquake conditions.

• Journal of Korean Society of Steel Construction
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• v.30 no.1
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• pp.13-23
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• 2018

The use of a built-up H-beam (BH) that can easily manufacture a section is increasing. This is a basic study on standardization of BH. It confirmed the material properties of SM490 and SM520 steel such as yield strength, tensile strength, elongation, charpy absorbed energy, and else. The six BH specimens were manufactured with single-SAW or tandem-SAW. The welding performance was confirmed by collecting the macroscopic specimen and T-bar tensile specimen form the BH. As a result of the material property test, the properties of SM490 and SM520 which are made in Korea both satisfied the KS. As a result of the welding performance experiment, it is determined that the weld zone of BH has sufficient welding performance. Therefore, they are determined that the SM490 and SM520 steel are a proper material of BH, and the single-SAW and the tandem-SAW show a sufficient welding performance.

• Fire Science and Engineering
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• v.30 no.5
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• pp.54-59
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• 2016

Steel is a structural material that is inherently noncombustible. On the other hand, it has high thermal conductivity and the strength and stiffness of the material are reduced significantly when exposed to fire or high temperatures. Because the yield strength and modulus of elasticity of steel are reduced by 70% at $350^{\circ}C$ and less than 50% at $600^{\circ}C$, the load-carrying capacity of steel structure at high temperature rapidly lose. To be accepted as a fire-resisting construction, the fire test should be performed at the certificate authority. On the other hand, the fire test on a full-scale structure is limited by time, space, and high-cost. The analytical method was verified by a comparison with the fire test of H-section columns under compression and thermal analysis based on a finite element method using the ABAQUS program, and the numerical analysis method reported in this study was suggested as a complement of an actual fire test.

• Journal of Welding and Joining
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• v.1 no.2
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• pp.45-52
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• 1983

Many pressure vessels for the hot H$\sub$2//H$\sub$2/S service are made of 2+1/4Cr-1Mo steel with austenitic stainless steel overlay to combat agressive corrosion due to hydrogen sulfide. Hydrogen dissolves in to materials during operation, and sometimes gives rise to unfore-seeable damages. Appropriate precautions must, therefore, be taken to avoid the hydrogen induced damages in the design, fabrication and operation stage of such reactor vessels. Recently, hydrogeninduced cracking (or Disbonding) was found at the interface between base metal and stainless weld overlay of a desulfurizing reactor. Since the stainless steel overlay weld metal is subjected to thermal and internal-pressure loads in reactor operation, it is desirable for the overlay weld metal to have high strength and ductility from the stand point of structural safety. In section III of ASME Boiler and Pressure Vessel Code, Post-Weld Heat Treatment(PWHT) of more than one hour per inch at over 1100.deg. F(593.deg. C) is required for the weld joints of low alloy pressure vessel steels. This heat treatment to relieve stresses in the welded joint during construction of the pressure vessel is considered to cause sensitization of the overlay weld metal. The present study was carried out to make clear the diffusion of carbon migration by PWHT in dissimilar metal welded joint. The main conclusion reached from this study are as follows: 1) The theoretical analysis for diffusion of carbon in stainless steel overlay weld metal does not agree with Fick's 2nd law but the general law of molecular diffusion phenomenon by thermodynamic chemical potential. 2) In the stainless steel overlay welded joint, the PWHT at 720.deg. C for 10 hours causes a diffusion of carbon atoms from ferritic steel into austenitic steel according to the theoretical analysis for carbon migration and its experiment. 3) In case of PWHT at 720.deg. C for 10 hours, the micro-hardness of stainless steel weld metal in bonded zone increase very highly in the carburized layer with remarkable hardening than that of weld metal.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.1
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• pp.83-88
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• 2013

Progressive collapse is a chain reaction of failures propagating throughout a portion of a structure that is disproportionate to the original local failure. When column members are subjected to unexpected load (compression load), they will buckle if the applied load is greater than the critical load that induces buckling. The post-buckling strength of the columns will decrease rapidly, but if there is enough residual strength, the members will absorb the potential energy generated by the impact load to prevent progressive collapse. Thus, it is necessary to identify the relationship of the load-deformation of a column member in the progressive collapse of a structure up to final collapse. In this study, we carried out nonlinear FEM analysis and based on deflection theory, we investigated the load-deformation relationship of H-section steel columns when both ends were fixed.