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Kim D.-K.,Seoul National University | Lee C.-H.,Seoul National University | Han K.-H.,Seoul National University | Kim J.-H.,Steel Structure Research Division | And 2 more authors.
Journal of Constructional Steel Research | Year: 2014

In this study, stub columns subjected to concentric and eccentric loads were tested to check the applicability of the current local stability criteria to 800 MPa high-strength steel (HSA800) recently developed in Korea. The key test variables in the concentrically loaded tests included the plate-edge restraints and the width-to-thickness ratio. Specimens made of ordinary steel (SM490) were also tested for comparison 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 even higher than that of compact H-section counterparts. The experimental P-M interaction strength was very accurately predicted with the strain compatibility method by using the measured stress-strain curve, or by explicitly considering early strain-hardening property of high strength steel. Residual stresses were also measured by using the non-destructive indentation method to see their dependency or independency on the yield stress of steel material. The measured results of this study again indicated that the magnitude of residual stresses bears no strong relation to the yield stress of steel material, implying that the impact of residual stress on inelastic local buckling of high strength steels is less. © 2014 Elsevier Ltd. All rights reserved.


Lee C.-H.,Seoul National University | Han K.-H.,Seoul National University | Uang C.-M.,University of California at San Diego | Kim D.-K.,Seoul National University | And 2 more authors.
Journal of Structural Engineering (United States) | Year: 2013

Flexural tests on full-scale I-shaped beams, built up from high-strength steels (HSB800 and HSA800) with a nominal tensile strength of 800 MPa, were carried out to study the effect of flange slenderness on flexural strength and rotation capacity. The primary objective was to investigate the appropriateness of extrapolating current stability criteria (originally developed for ordinary steel) to high-strength steel. For comparison purposes, specimens with ordinary steel (SM490) were also tested and showed sufficient flexural strength and rotation capacity in accordance with the AISC specification. The performance of high-strength steel specimens was also very satisfactory from the strength, but not from the rotation capacity, perspective. The inferior rotation capacity of high-strength steel beams was shown to be directly attributable to the absence of a distinct yield plateau and the high yield ratio of the material. When a higher rotation capacity is required as in plastic design, the testing clearly showed that high-strength steel beams were vulnerable to brittle fracture when full-height transverse stiffeners were welded to the tension flange in the plastic hinge region. Residual stress measurements reconfirmed that the magnitude of the residual stress is almost independent of the yield stress of the base metal. © 2013 American Society of Civil Engineers.


Choung J.,Inha University | Nam W.,Inha University | Noh M.-H.,Steel Structure Research Division | Lee J.-Y.,Inha University | Shim S.,Steel Structure Research Division
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2014

This paper provides study on theoretical and experimental results to verify crashworthiness of a high strength steel FH32 for arctic marine structures against ice impact. Assuming that side shell structures of Korean arctic research vessel, ARAON with ice-notation PL10, collide with sheet ice, 1/3 scaled-down test specimens with single transverse frame are manufactured. Impact bending tests have been conducted using rigid steel striker which mimics sheet ice. Drop height is calculated by considering real ramming speed to sheet ice. Prior to impact bending tests, tensile coupon tests are conducted at various temperature levels. The impact bending tests are carried out with test specimens fully fixed by inside bottom frame of cold chamber. Velocity of the drop weight and deformation speed of the test specimen are measured using DICA (digital image correlation analysis) after high speed camera measurement. Numerical simulations are also carried out under the same conditions as the impact bending tests. The simulation results well agree with test results, but it is recognized that strain rate is a key factor to decide accuracy of numerical simulations. Copyright © 2014 by the International Society of Offshore and Polar Engineers (ISOPE).


Kim C.-E.,RandD Team | Ahn H.-Y.,SamhyunPF | Lee P.-G.,Steel Structure Research Division | Shim C.-S.,Chung - Ang University
Composite Construction in Steel and Concrete VII - Proceedings of the 2013 International Conference on Composite Construction in Steel and Concrete | Year: 2013

Concrete filled tubular structures have advantages to overcome stability of thin plates and to increase stiffness. A hybrid bridge combining common steel box girders and truss girders was suggested to increase the span length of steel-concrete composite bridges. In negative moment regions, a truss girder has lower chords of concrete filled rectangular steel box section to increase flexural stiffness. A bridge model with span length of 30m was fabricated and static tests were performed to assess the effect of composite chords on the flexural behavior of the girder. Depth of the girder varies from 2.0 m to 3.0 m. Significant reduction of stresses in lower steel chord was observed and measured deflections showed a good agreement with calculated values considering the contribution of infilled concrete. Cracking and crack width of the upper concrete slab were observed and indirect crack control by longitudinal reinforcing bars can be used for the design. © ASCE.


Shin H.-S.,Andong National University | Tuazon B.,Andong National University | Bae K.-O.,Andong National University | Lee S.H.,Andong National University | And 3 more authors.
Applied Mechanics and Materials | Year: 2014

The responses of three high strength steels under impact loading were examined, specifically on their strain rate dependence. Split Hopkinson pressure bar test was used in this study. Over a wide strain rate range, the Johnson-Cook model and modified Johnson-Cook mode were adopted to determine the strain rate hardening behavior of the materials. The group determined the material parameters for each metallic material tested. Obtained material parameters were used to predict the behavior of each steel at high strain rate region. The modified Johnson-Cook model was not able to represent well enough the plastic deformation behavior of steels, specifically the steel that exhibited strain softening behavior at high strain rate region. © (2014) Trans Tech Publications, Switzerland.


Kim K.-S.,Steel Structure Research Division | Cho W.-Y.,Steel Structure Research Division | Cho K.-I.,Steel Structure Research Division | Song W.-H.,POSCO
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2014

CWPT (Curved Wide Plate Tensile) and SENT (Single Edge Notched Tensile) tests were carried out to evaluate the TSC (Tensile Strain Capacity) of girth welded X80 line pipes. Two kinds of X80 line pipes were compared, i.e., SBD (Strain-Based Design) and conventional (or non-SBD) X80 line pipes manufactured by POSCO. Round-house type strain-stress curves were obtained from full thickness tensile specimens of SBD X80, while Lüder's bands were shown in those of non-SBD X80. The overmatch ratio of weld metal to base metal tensile strength were 26% for SBD X80 pipes and 18% for non-SBD X80 pipes. The SBD X80 pipe shows 1∼2% higher tensile strain capacity compared with non-SBD X80 pipes where cracking occurred in the HAZ of specimens. Copyright © 2014 by the International Society of Offshore and Polar Engineers (ISOPE).


Chung K.-S.,Steel Structure Research Division | Kim J.-H.,Steel Structure Research Division | Yoo J.-H.,Seoul National University of Science and Technology
Steel and Composite Structures | Year: 2013

The concrete-filled steel tube (CFT) columns have several benefits of high load-bearing capacity, inherent ductility and toughness because of the confinement effect of the steel tube on concrete and the restraining effect of the concrete on local buckling of steel tube. However, the experimental research into the behavior of square CFT columns consisting of high-strength steel and high-strength concrete is limited. Six full scale CFT specimens were tested under flexural moment. The CFT columns consisted of high-strength steel tubes (fy=325MPa, 555MPa, 900MPa) and high-strength concrete (fck=80MPa and 120MPa). The ultimate capacity of high strength square CFT columns was compared with AISC-LRFD design code. Also, this study was focused on investigating the effect of high-strength materials on the structural behavior and the mathematical models of the steel tube and concrete. Nonlinear fiber element analyses were conducted based on the material model considering the cyclic bending behavior of high-strength CFT members. The results obtained from the numerical analyses were compared with the experimental results. It was found that the numerical analysis results agree well with the experimental results.


Kim J.-K.,Steel Structure Research Division | Kwak H.-G.,Korea Advanced Institute of Science and Technology | Kwak J.-H.,Korea Advanced Institute of Science and Technology
Steel and Composite Structures | Year: 2013

A hybrid double skin concrete filled (HDSCF) circular steel tube column is proposed in this study. The yield strength of the outer steel tube is larger than 690MPa and the inner tube has less strength. In order to achieve efficiency with the high strength outer tube, a feasibility study on reducing the thickness of the tube below the specified design codes for CFTs was conducted based on an experimental approach. The experiment also took variables such as thickness of the inner tube, hollow ratio, and strength of concrete into consideration to investigate the behavior of the HDSCF column. In order to estimate the applicability of design equations for CFTs to the HDSCF column, test results from CFT and HDSCF columns with design codes were compared. It was found that the axial compressive performance of the proposed HDSCF column is equivalent to that of the conventional CFT member irrespective of design variables. Furthermore, the design equation for a circular CFT given by EC4 is applicable to estimate the ultimate strength of the HDSCF circular steel tube column.


Kwak J.-H.,Steel Structure Research Division | Kwak H.-G.,Steel Structure Research Division | Kim J.-K.,Korea Advanced Institute of Science and Technology
Steel and Composite Structures | Year: 2013

The major objective of this paper is to evaluate the behavior and ultimate resisting capacity of circular CFT columns. To consider the confinement effect, proper material models with respect to the confinement pressure are selected. A fiber section approach is adopted to simulate the nonlinear stress distribution along the section depth. Material nonlinearity due to the cracking of concrete and the yielding of the surrounding steel tube, as well as geometric nonlinearity due to the P-Δ effect, are taken into account. The validity of the proposed numerical analysis model is established by comparing the analytical predictions with the results from previous experimental studies about pure bending and eccentric axial loading. Numerical predictions using an unconfined material model were also compared to investigate the confinement effects on various loading combinations. The ultimate resisting capacities predicted by the proposed numerical model and the design guidelines in Eurocode 4 are compared to evaluate the existing design recommendation.


Chung K.-S.,Steel Structure Research Division | Kim J.-H.,Steel Structure Research Division | Yoo J.-H.,Seoul National University of Science and Technology
International Journal of Steel Structures | Year: 2012

This study aimed at predicting the structural behavior of high-strength square CFT (concrete-filled steel tube) columns. First, the material models of the existing steel tube and concrete were compared, and a nonlinear fiber element analysis method was proposed. To verify the proposed fiber element analysis method, the behavior of CFT columns made from high-strength materials was investigated experimentally. CFT members consisted of high-strength steel tubes (yield strength; f y=913 MPa) and high-strength concrete (f ck=91.3 MPa). The moment-rotation relationships for hollow and concrete-filled steel tubes were compared. In addition, the P-M interaction diagrams for the experiment result and AISC-LRFD code provisions were compared. Finally, the result of the fiber element analyses was compared with the test results. © KSSC and Springer 2012.

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