• Journal of the Korea Concrete Institute
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• v.12 no.2
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• pp.13-20
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• 2000

In this study, the compression test of steel fiber reinforced high-strength concrete have been performed with varying strengths and volume factions of steel fiber. Three types of matrices including low strength concrete( c'=30 MPa), medium strength concrete( c'=50 MPa), and high strength concrete( c'=70 MPa) were selected. Five types of fiber fractions were studied including 0.0%, 0.5%, 0.75%, 1.0%, and 1.5% by volume. From the results of the compressive strength test, the post-peak characteristics of the stress-strain relationship were investigated, and the existing equations to predict the elastic modulus were experimentally evaluated.

• Journal of Korean Society of Steel Construction
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• v.26 no.4
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• pp.335-348
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• 2014

For high-strength steel, it is difficult to be applied to flexible structural member because it have high yield ratio and low basic material's toughness. One of the great problems when using high-strength steel connections is the brittle fracture at the end of the beam member in common with general mild steel connections. In the cases of mild steel connections, it has be developed that special moment frame connection details by reinforcing structural member or improvement of welding access hole. But, it is incomplete at yet about applicability estimation of high-strength steel connections. This study is the initial step research for the applicability estimation of beam-to-column connections being applied to developed high-strength steel, HSA800. And, it studied about structural performance of the high-strength steel connections according to the details of welding access hole through full-scale test and analytical method.

• Steel and Composite Structures
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• v.49 no.5
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• pp.533-546
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• 2023

Cost-effective solutions provided by composite construction are gaining popularity which, in turn, promotes the appearance on the market of new types of composite sections that allow not only to take advantage of the synergy of steel and concrete working together at room temperature, but also to improve their behaviour at high temperatures. When combined with high performance materials, significant load-bearing capacities can be achieved even with reduced cross-sectional dimensions. Steel-reinforced concrete-filled steel tubular (SR-CFST) columns are one of these innovative composite sections, where an open steel profile is embedded into a CFST section. Besides the renowned benefits of these typologies at room temperature, the fire protection offered by the surrounding concrete to the inner steel profile, gives them an enhanced fire performance which delays its loss of mechanical capacity in a fire scenario. The experimental evidence on the fire behaviour of SR-CFST columns is still scarce, particularly when combined with high performance materials. However, it is being much needed for the development of specific design provisions that consider the use of the inner steel profile in CFST columns. In this work, a new experimental program on the thermo-mechanical behaviour of SR-CFST columns is presented to extend the available experimental database. Ten SR-CFST stub columns, with circular and square geometries, combining high strength steel and concrete were tested. It was seen that the circular specimens reached higher failure times than the square columns, with the failure time increasing both when high strength steel was used at the embedded steel profile and high strength concrete was used as infill. Finally, different proposals for the reduction coefficients of high performance materials were assessed in the prediction of the cross-sectional fire resistance of the SR-CFST columns.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.23 no.5
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• pp.525-531
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• 2014

A cowl cross is a part of the car's instrument panel used to maintain the rigidity of the vehicle body side. The application of laser welding has the benefits of speed and thermal deformation compared to arc welding. An ultra-high strength steel sheet is used to reduce the weight of the vehicle body parts. Generally, formability of such a steel sheet is poor because its elongation is very low. For this reason, a method for cold forming of an ultra-high strength steel sheet is required. This paper describes how to improve the formability and weldability of the ultra-high strength steel sheet. Mechanical tests of this material were also performed to evaluate the welding properties of $CO_2$ (GMAW) and those of laser welding.

• Structural Engineering and Mechanics
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• v.81 no.5
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• pp.539-550
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• 2022

A detailed experimental program was conducted to investigate the flexural behavior of ultra high performance concrete (UHPC) beams reinforced with high strength steel (HSS) rebars with a specified yield strength of 600 MPa via direct tensile test and monotonic four-point bending test. First, two sets of direct tensile test specimens, with the same reinforcement ratio but different yield strength of reinforcement, were fabricated and tested. Subsequently, six simply supported beams, including two plain UHPC beams and four reinforced UHPC beams, were prepared and tested under four-point bending load. The results showed that the balanced-reinforced UHPC beams reinforced with HSS rebars could improve the ultimate load-bearing capacity, deformation capacity, ductility properties, etc. more effectively owing to interaction between high strength of HSS rebar and strain-hardening characteristic of UHPC. In addition, the UHPC with steel rebars kept strain compatibility prior to the yielding of the steel rebar, further satisfied the plane-section assumption. Most importantly, the crack pattern of the UHPC beam reinforced with HSS rebars was prone to transform from single main crack failure corresponding to the normal-strength steel, to multiple main cracks failure under the condition of balanced-reinforced failure, which validated by the conclusion of direct tensile tests cooperated with acoustic emission (AE) source locating technique as well.

• Journal of Korean Society of Steel Construction
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• v.25 no.1
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• pp.71-80
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• 2013

Fire-resistant (FR) test data for a square concrete-filled steel tube (CFT) columns consisting of high-strength steel (fy>650MPa) and high strength concrete (fck>100MPa) under axial loads are insufficient. The FR behavior of square high-strength CFT members was investigated experimentally for two specimens having ${\Box}-400{\times}400{\times}15{\times}3,000mm$ with two axial load cases (5,000kN and 2,500kN). The results show that the FR performance of the high-strength CFT was rapidly decreased at earlier time (much earlier at high axial load) than expected due to high strength concrete spalling and cracks. In addition, a fiber element analysis (FEA) model was proposed and used to simulate the fiber behaviour of the columns. For steel and concrete, the mechanical and thermal properties recommended in EN 1994-1-2 are adopted. Test results were compared to those of numerical analyses considering a combination of temperature and axial compression. The numerical model can reasonably predict the time-axial deformation relationship.

• Transactions of the Korean Society of Automotive Engineers
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• v.23 no.3
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• pp.279-286
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• 2015

To achieve lightweight design, research & development of various lightweighting technologies such as hydroforming are underway worldwide. In the case of hydroforming, application of ultra high strength steel is essential for weight reduction of the car. However, considering common high-strength carbon steel, it is not suitable to the actual hydroformed parts since the lack of formability. DP steel offers an outstanding combination of strength and formability as a result of their microstructure. DP steel has high strength and good formability but it's difficult to secure stable quality of welding section because of softening of weld section and chemical composition. Therefore, most of companies use LASER welding when making high strength tube. Electric resistance welding is excellent production method for steel tube manufacturing considering the productivity. Optimum electric resistance welding technology is needed to be developed for application of high strength hydroformed parts using DP steel. This study is comprehensive research & development from electric resistance welding to actual formabililty evaluation.

• Journal of Welding and Joining
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• v.34 no.1
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• pp.7-20
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• 2016

A brief overview is given of the development of various structural steels and their welding application technology. Firstly, the general characteristics and welding performance of structural steels used in architecture and bridge are introduced. For safety against earthquakes or strong wind, and for highly efficient welding in high-rise building constructions, ultra high strength steel with tensile strength over 800 MPa or high HAZ toughness steel plates under high heat input welding have been developed. In particular, efficient welding technology ensuring high resistance to cold and hot cracking of ultra high strength steel is reviewed in the present paper. Secondly, various coated steels used mainly for outer part in construction are briefly discussed. Moreover, a major drawback of coated steel during welding operation, and several solutions to overcome such technical problem are proposed. It is hoped that this review paper can lead to significant academic contributions and provide readers interested in the structural steels with useful welding technology.

• Journal of the Korean Society for Advanced Composite Structures
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• v.4 no.3
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• pp.22-29
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• 2013

In recent years, the construction of high-rise buildings are promoted. According to these, there are many needs about new technologies to strengthen the building performance and high-strength steel is regarded as one of these for promoting building performance. In Korea, high-strength steels which stress are over 600MPa are on market and in aborad, super high-strength steels over 1000MPa are developing and they expected to promote the building performance. But there are still doubts about applying high-strength steel members because of size effect and worry of brittle fracture. In this reports, we propose results of performance and analysis tests for use with general steel. We propose the characteristic of high-strength steels first and next the results of performance test to show they satisfy the performance that designers expect. And last, we compare the results of test and analysis for acquire the alanysis reliability in non-linear analysis with high-strength steels.

• Computers and Concrete
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• v.8 no.4
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• pp.445-463
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• 2011

In the design of reinforced concrete (RC) beams, apart from providing adequate strength, it is also necessary to provide a minimum deformability even for beams not located in seismic regions. In most RC design codes, this is achieved by restricting the maximum tension steel ratio or neutral axis depth. However, this empirical deemed-to-satisfy method, which was developed based on beams made of normal-strength concrete (NSC) and normal-strength steel (NSS), would not provide a consistent deformability to beams made of high-strength concrete (HSC) and/or high-strength steel (HSS). More critically, HSC beams would have much lower deformability than that provided previously to NSC beams. To ensure that a consistent deformability is provided to all RC beams, it is proposed herein to set an absolute minimum rotation capacity to all RC beams in the design. Based on this requirement, the respective maximum limits of tension steel ratio and neutral axis depth for different concrete and steel yield strengths are derived based on a formula developed by the authors. Finally for incorporation into design codes, simplified guidelines for designing RC beams having the proposed minimum deformability are developed.