• Steel and Composite Structures
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• v.3 no.2
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• pp.75-95
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• 2003

A numerical model is presented to simulate the mechanical behaviour of composite steel and concrete columns taking into account the interaction between the hollow steel section and the concrete core. The model, based on displacement finite element methods with an Updated Lagrangian formulation, allows for geometrical and material non linearities combined with heating over all or a part of the section and column length. Comparisons of numerical calculations made using the model with 33 fire resistance tests show that the model is able to predict the fire resistance, expressed in minutes of fire exposure, of composite columns with a good accuracy.

• Steel and Composite Structures
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• v.3 no.4
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• pp.231-242
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• 2003

This paper deals with the formulation and development of fracture criteria for high-strength structural members containing surface damage in the form of notches (i.e., blunt defects). The important role of the yield strength of the material and its strain hardening capacity (evaluated by means of the constitutive law or stress-strain curve) is analysed in depth by considering the fracture performance of notched samples taken from high-strength steels with different levels of cold drawing (the most heavily drawn steel being commercial prestressing steel used in prestressed concrete). The final aim of the paper is to establish fracture-based design criteria for structural members made of steels with distinct yield strength and containing very different kinds of notch-shape surface damage.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.4 s.247
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• pp.428-434
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• 2006

Pulse laser welding of AISI 304 stainless steel plate was simulated to find optimal welding conditions by using commercial finite element code MARC. Due to geometric symmetry, a half model of AISI 304 stainless steel plate was considered and user subroutines were applied to boundary condition for the heat transfer. Material properties such as conductivity, specific heat, mass density and latent heat were given as a function of temperature. A moving heat source was designed on the basis of experimental data. As a result, Nd:YAG laser welding for AISI 304 stainless steel was successfully simulated and it should be useful to determine optimal welding condition.

• Journal of the Korea Safety Management & Science
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• v.11 no.4
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• pp.7-14
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• 2009

Steel and iron works have place many hazard or risk factor as a high temperature material, a high place, and so on. Accordingly, steel and iron works need system for risk assessment. In this paper, we development of risk assessment system for steel and iron works. In case study applied at the steel enterprise. The resultant, we can discovery that an human factor is an important question form risk assessment.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.833-838
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• 2001

The objectives of this study are to investigate effective stiffness of circular reinforced bridge columns and to provide reasonable effective stiffness equations for seismic design to the current Korean Bridge Design Standard. The material nonlinear analysis was conducted for 5184 columns of which variables were the concrete compressive stress, the steel yielding stress, the longitudinal steel location parameter, the longitudinal steel ratio, the axial load level, and the diameter of section. The current Korean Bridge Design Standard generally used the gross section stiffness because of unclear provision, it may be non-conservative because of being evaluated greater design seismic force and less design displacement than those of the abroad provision. Therefore, the proposed effective stiffness equations include three variables such as : the longitudinal steel location parameter, the longitudinal steel ratio, and the axial load ratio. Two equations of effective stiffness are proposed which may be used for earthquake force estimation and for earthquake displacement estimation, respectively.

• Bulletin of the Korean Chemical Society
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• v.23 no.11
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• pp.1541-1544
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• 2002

The concentration of B in steels is important due to its influence on mechanical properties of steel such as hardenability, hot workability, and creep resistance. An analytical method has been developed to determine B in steel samples by high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS). National Institute of Standard and Technology Standard Reference Material (NIST SRM) 348a was analyzed to validate the analytical method. The steel sample was digested in a centrifuge bottle with addition of aqua regia and $^{10}B$ spike isotope. Sample pH was then adjusted to higher than 10 to precipitate most matrix elements such as Fe, Cr, and Ni. After centrifugation, the supernatant solution was passed through a cation exchange column to enhance the matrix separation efficiency. B recovery efficiency was about 37%, while matrix removal efficiency was higher than 99.9% for major matrix elements. The isotope dilution method was used for quantification and the determined B concentration was in good agreement with the certified value.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.291-296
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• 2004

Cast austenitic stainless steel piping pump, valve casings, and elbows are susceptible to reductions in toughness and ductility because of long term exposure at the operating temperatures in LWR(light water reactor). In this paper, we have measured the material properties of long term aged CF-8A cast stainless steel, accelerated aging at $400^{\circ}C$. These studies have been carried out using Indentation tests(automated ball indentation and nano-indentation) and EDS(energy dispersive spectroscopy). The fracture toughness of CF-8A cast stainless steel was also determined by using standard fracture toughness and Automated Ball Indentation.

• Journal of the Korean Society for Heat Treatment
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• v.6 no.2
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• pp.98-106
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• 1993

Ultra high carbon steel (Fe-1.4%C) was prepared by means of a high frequency induction furnace. The preferred nucleation site of martensite was observed. The changes of hardness and impact thoughness due to tempering temperatures, and the spheroidization of cementite by controlled -rolling were also studied for the steel. The preferred nucleation site of martensite in the ultra high carbon steel is prior austenite grain boundary. The hardness of the steel is slightly increased up to about $300^{\circ}C$, and then decreased with further tempering temperature. However, the impact energy keeps a almost constant value, independent of the tempering temperature. The spheroidization of cementite is accelerated as the reduction in thickness per rolling pass is increased and the number of the rolling passes becomes greater.

• Proceedings of the KWS Conference
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• v.43
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• pp.153-155
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• 2004

Vibration occurs due to the wind and vehicles, etc., in the field welded joints of steel bridges. However, the effect of vibration on the fatigue strength of field welded joints in steel bridge are not yet clearly understood. In this paper, the effect of vibration on the fatigue strength of welded joints was elucidated in order to improve reliability in the field welded joints of steel bridge. The base material used in this investigation was SM 490A steel of weldable grade. Flux Cored Arc Welding(FCAW) process was used to fabricate the doubte 'V' butt joints. Welding was performed on the steel under the mechanical vibration of given frequency. The applied frequency was resonant frequency. Also, weldments formed under no vibration were fabricated. Fatigue tests were conducted using a servo hydraulic controlled 50ton1 capacity UTM with a frequency of 5Hz under constant amplitude loading.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.457-464
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• 2010

Ever since the introduction of high strength steel pipe strut(POSTRUT) in 2008, there has been over 50 applications domestically. The merits of construction period reduction and cost savings have been well reported abroad in countries such as America, Europe and China but ever in domestic projects or ground condidtions. 25 actual construction projects were investigated and statistically analyzed to evaluate the quantitative effects of POSTRUT. Also the construction projects along with the cautions that should be taken and the structural behavior differences between POSTRUT and H-section struts are briefly described in this paper.