• Steel and Composite Structures
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• v.33 no.6
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• pp.849-864
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• 2019

One way to achieve sustainable construction is to reduce concrete consumption by use of more sustainable and higher strength concrete. Modern building codes do not cover the use of ultra-high strength concrete (UHSC) in the design of composite structures. Against such background, this paper investigates experimentally the mechanical properties of steel fibre-reinforced UHSC and then the structural behaviors of UHSC encased steel (CES) members under both concentric and eccentric compressions as well as pure bending. The effects of steel-fibre dosage and spacing of stirrups were studied, and the applicability of Eurocode 4 design approach was checked. The test results revealed that the strength of steel stirrups could not be fully utilized to provide confinement to the UHSC. The bond strength between UHSC and steel section was improved by adding the steel fibres into the UHSC. Reducing the spacing of stirrups or increasing the dosage of steel fibres was beneficial to prevent premature spalling of the concrete cover thus mobilize the steel section strength to achieve higher compressive capacity. Closer spacing of stirrups and adding 0.5% steel fibres in UHSC enhanced the post-peak ductility of CES columns. It is concluded that the code-specified reduction factors applied to the concrete strength and moment resistance can account for the loss of load capacity due to the premature spalling of concrete cover and partial yielding of the encased steel section.

• International Journal of Concrete Structures and Materials
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• v.18 no.2E
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• pp.133-142
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• 2006

An experimental study was conducted to investigate the effectiveness of transverse steel in reinforced concrete tied columns subjected to monotonically increasing axial compression. Eighteen large-scale columns($260{\times}260{\times}1,200mm$) were tested. Effects of such main variables as concrete compressive strength, configurations of transverse steel, transverse reinforcement ratio, spacing of transverse steel, and spalling of concrete cover were investigated. High-strength concrete columns under concentric axial loads show extremely brittle behavior unless the columns are confined with transverse steel that can provide sufficiently high lateral confinement pressure. A consistent decrease in the deformability of the column test specimens was observed with increasing concrete strength. Test results of this study were compared with existing confinement models of modified Kent-Park, Sheikh-Uzumeri, Mander, and Saatcioglu-Razvi. The comparison indicates many existing models to predict the behavior of confined concrete overestimate or underestimate the ductility of confined concrete.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.3
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• pp.447-456
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• 2021

Methods for predicting the ultimate/buckling strength of ship structures have been extensively improved in terms of design formulas and analytical solutions. In recent years, the design strategy of ships and offshore structures has tended to emphasize lighter builds and improve operational safety. Therefore, the corresponding geometrical changes in design necessitate the use of high-tensile steel and thin plates. However, the existing design formulas were mainly developed for thick plates and mild steels. Therefore, the calculation methods require appropriate modification for new designs beased on high-tensile steel and thin plates. In this study, a modified formula was developed to predict the ultimate strength of thin steel plates subjected to compressive and shear loads. Based on the numerical results, the effects of the yield stress, slenderness ratio, and loading condition on the buckling/ultimate strength of steel plates were examined, and a newly modified double-beta parameter formula was developed. The results were used to derive and modify existing closed-form expressions and empirical formulas to predict the ultimate strength of thin-walled steel structures.

• Journal of Korean Society of Steel Construction
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• v.24 no.6
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• pp.711-723
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• 2012

Structural tests were performed to investigate the structural performance of concrete-filled steel tube column using different strength steels in their flange and web with high-strength steel HSA800 and mild steel SM490, respectively. The test parameters included the strength of column flange and infill concrete, and effect of concrete infill. Connection between different grade steels were welded using the electrode appropriate for mild steel and verified its performance. To evaluate the behavior of test specimens, eccentric loading tests were performed and the results were compared with the prediction by current design codes. Axial load and moment carrying capacity of test specimens increased with the yield strength of compression flange and weld fracture occurred after the specimen shows full strength. The prediction result for axial load-bending moment relationship and effective flexural stiffness gave good agreement with the test result.

• Journal of the Korea Concrete Institute
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• v.11 no.4
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• pp.137-145
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• 1999

The use of steel fiber reinforced to improve the strength and flexural toughness of concrete is well known, but reinforcement of polymer concrete with steel fibers has been hardly reported till now. Polymer concrete has high strength, durability and freeze-thaw resistance than that of cement concrete, but it has disadvantage such as low flexural toughness. In this paper, the strength characteristics and flexural toughness of steel fiber reinforced polymer concrete are investigated experimentally with various steel fiber aspect ratios($\ell$/d), and contents(vol.%). As the result, the flexural and splitting tensile strengths and flexural toughness were increased aspect ratio, and reach the maximums at a aspect ratio of 50. The relationship between the compressive, flexural and splitting tensile strength were high. And the relationship between flexural strength and strain energy was approximately linear.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.40.1-40.1
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• 2010

Recently high strength steel sheets with high formability for automotive parts have been being developed to meet the demands for passenger safety and weight reduction of car body. Among these high strength steels, dual-phase steels are regarded as one of the attractive steels due to their excellent mechanical properties including high strength and ductility. However, to be successfully applied to automotive parts they should be corrosion resistant enough to satisfy the required quality of car maker. This also requires their feasibility for galvannealed production including hot dip galvanizability. In this study has been placed on understanding the effects of heat-treatment(austenizing and isothermal treatment) on the microstructures and mechanical properties of a 0.06C-0.03Si-2.0Mn high strength steel for cold forming. The microstructure and phase distribution were examined with eth aids of SEM, EBSD, TEM etc.. Through the study the production of 590MPa grade DP GA steels with good formability and galvaniability were shown to be possible.

• Structural Engineering and Mechanics
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• v.57 no.4
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• pp.681-701
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• 2016

This paper presents an experimental study of six steel reinforced high strength concrete T-shaped short-limb shear walls configured with T-shaped steel truss under low cyclic reversed loading. Considering different categories of ratios of wall limb height to thickness, shear/span ratios, axial compression ratios and stirrup reinforcement ratios were selected to investigate the seismic behavior (strength, stiffness, energy dissipation capacity, ductility and deformation characteristics) of all the specimens. Two different failure modes were observed during the tests, including the flexural-shear failure for specimens with large shear/span ratio and the shear-diagonal compressive failure for specimens with small shear/span ratio. On the basis of requirement of Chinese seismic code, the deformation performance for all the specimens could not meet the level of 'three' fortification goals. Recommendations for improving the structural deformation capacity of T-shaped steel reinforced high strength concrete short-limb shear wall were proposed. Based on the experimental observations, the mechanical analysis models for concrete cracking strength and shear strength were derived using the equivalence principle and superposition theory, respectively. As a result, the proposed method in this paper was verified by the test results, and the experimental results agreed well with the proposed model.

• Computers and Concrete
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• v.9 no.2
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• pp.133-151
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• 2012

This paper presents an analytical procedure for the analysis of high strength steel fiber reinforced concrete members considering the cracking effect in the serviceability loading range. Modifications to a previously proposed formula for the effective moment of inertia are presented. Shear deformation effect is also taken into account in the analysis, and the variation of shear stiffness in the cracked regions of members has been considered by reduced shear stiffness model. The effect of steel fibers on the behavior of reinforced concrete members have been investigated by the developed computer program based on the aforementioned procedure. The inclusion of steel fibers into high strength concrete beams and columns enhances the effective moment of inertia and consequently reduces the deflection reinforced concrete members. The contribution of the shear deformation to the total vertical deflection of the beams is found to be lower for beams with fibers than that of beams with no fibers. Verification of the proposed procedure has been confirmed from series of reinforced concrete beam and column tests available in the literature. The analytical procedure can provide an accurate and efficient prediction of deflections of high strength steel fiber reinforced concrete members due to cracking under service loads. This procedure also forms the basis for the three dimensional analysis of frames with steel fiber reinforced concrete members.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.288-291
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• 2004

In this paper, to make ultra-high strength SFRCC with the range of compressive strength 180MPa, it was investigated the constitute factors of ultra-high strength SFRCC influenced on the compressive strength. The experimental variables were water-cementitious ratio, replacement of silica fume, size and proportion of sand, type and replacement of filling powder, and using of steel fiber in ultra-high strength SFRCC. As a result, in water-binder ratio 0.18, we could make ultra-high strength SFRCC with compressive strength 180MPa through using of silica fume, quartz sand with below 0.5mm, filling powder and steel fiber.

• KSTLE International Journal
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• v.9 no.1_2
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• pp.31-35
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• 2008

DLC (Diamond Like Carbon) films have predominant tribological properties like a high hardness, low friction and high chemical resistance; therefore, DLC films are applied in a wide range of industrial fields. This paper evaluated the characteristics of DLC films deposited on bearing steel with different hardness by RF-PECVD (Radio Frequency - Plasma Enhanced Chemical Vapor Deposition) method. Si-interlayer was deposited on bearing steel to improve adhesion strength by RF-Sputtering method. The DLC film structures were analyzed with Raman spectra and Gaussian function. Adhesion strength of DLC films was measured with a scratch tester. Friction and wear test were carried out with a ball-on -disc type to investigate the tribological characteristics. Experimental results showed that DLC films deposited on bearing steel under same deposition condition have typical structure DLC films regardless of hardness of bearing steel. Adhesion strength of DLC film is increased with a hardness of bearing steel. Friction coefficient of DLC film showed lower at the high hardness of bearing steel.