• Steel and Composite Structures
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• v.16 no.2
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• pp.221-231
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• 2014

The purpose of this study was to evaluate the cyclic behavior of steel column-tree moment connections used in steel moment resisting frames. These connections are composed of shop-welded stub beam-to-column connection and field bolted beam-to-beam splice. In this study, the effects of beam splice length on the seismic performance of column-tree connections were experimentally investigated. The change of the beam splice location alters the bending moment and shear force at the splice, and this may affect the seismic performance of column-tree connections. Three full-scale test specimens of column-tree connections with the splice lengths of 900 mm, 1,100 mm, and 1,300 mm were fabricated and tested. The splice lengths were roughly 1/6, 1/7, 1/8 of the beam span length of 7,500 mm, respectively. The test results showed that all the specimens successfully developed ductile behavior without brittle fracture until 5% radians story drift angle. The maximum moment resisting capacity of the specimens showed little differences. The specimen with the splice length of 1,300 mm showed better bolt slip resistance than the other specimens due to the smallest bending moment at the beam splice.

• Journal of Ocean Engineering and Technology
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• v.28 no.5
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• pp.452-465
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• 2014

The application of friction stir welding (FSW) technology has been extended to all industries, including shipbuilding. A heat transfer analysis evaluates the weldability of a welded work piece, and elasto-plastic analysis predicts the residual stress and deformation after welding. A thermal elasto-plastic analysis based on the heat transfer analysis results is most frequently used today. However, its application to large objects such as offshore structures and hulls is impractical owing to its long computational time. This paper proposes a new method, namely an equivalent strain method using the inherent strain, to overcome the disadvantages of the extended analysis time. In the present study, a residual stress analysis of FSW was performed using this equivalent strain method. Additionally, in order to reflect the external constraints in FSW, the reaction force was predicted using a neural network, Finally, the approach was verified by comparing the experimental results and thermal elasto-plastic analysis results for the calculated residual stress distribution.

• Steel and Composite Structures
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• v.34 no.3
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• pp.377-391
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• 2020

A concrete filled steel tube (CFT) column with stiffeners has preferable behavior subjected to axial loading condition due to delay local buckling of the steel wall than traditional CFT columns without stiffeners. Welding lines in welded built-up steel box columns is expected to behave as longitudinal stiffeners. This study has presented a numerical investigation into the behavior of built-up concrete filled steel tube columns under axial pressure. At first stage, a finite element model (FE) has been built to simulate the behavior of built-up CFT columns. Comparing the results of FE and test has shown that numerical model passes the desired conditions and could accurately predict the axial performance of CFT column. Also, by the raise of steel tube thickness, the load bearing capacity of columns has been increased due to higher confinement effect. Also, the raise of concrete strength with greater cross section is led to a higher load bearing capacity compared to the steel tube thickness increment. In CFT columns with greater cross section, concrete strength has a higher influence on load bearing capacity which is noticeable in columns with more welding lines.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.7
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• pp.551-558
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• 2016

Reduction of welding residual stress is very important in the railway industry, but calculating its distribution in structures is difficult because welding residual stress formation is influenced by various parameters. In this study, we developed a finite element model for simulating the repair welding process to recover a surface damaged rail, and conducted a series of parametric studies while varying the cooling rate and the duration of post weld heat treatment (PWHT) to find the best conditions for reducing welding residual stress level. This paper presents a three-dimensional model of the repair welding process considering the phase transformation effect implemented by the ABAQUS user subroutine, and the results of parametric studies with various cooling rates and PWHT durations. We found that heat treatment significantly reduced the residual stress on the upper rail by about 170 MPa.

• Journal of Welding and Joining
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• v.9 no.1
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• pp.40-47
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• 1991

The most fatigue tests carried out under the either stress or strain control, but machines and structures had taken variable stress. This variable stress was treated as statistics based on p-type distributions. In this paper, the cumulative fatigue damage of SM45C round bar specimens having a center hole resulting from block loading with p-distributions in rotating bending conditions, is presented. The value of p was changed in the range from 0.25 to 1; 0.25, 0.5, 0.75, 1. The following conclusions were obtained through the constant stress amplitude experiments and the block loading experiments. (1) In constant loading test, fatigue life was affected by cyclic rate. From experimental data, N$_{f}$ (100cpm)/N$_{f}$(3000cpm)equal to 0.56. (2) In case of the cyclic rate 100cpm and 3000cpm, at the high stress amplitude level the crack propagation life N$_{*}$f is longer than the low stress amplitude level. (3) Miner's hypothesis may be valid for p=0.75 and prediction of fatigue life by Haibach's method agree with experimental data well for the case p=0.5, while the modified Miner's method agree with experimental data well for the case p=0.25.5.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.4
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• pp.532-540
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• 2012

In this study, some considerations have been suggested in developing on-site techniques to evaluate the sensitization of stainless steels. Electrochemical potentiokinetic reactivation (EPR) technique is known to be a candidate tool for field applications since it enables quantitative assessment in reasonable test time, compared to oxalic etching (ditch) technique. The on-site application of the test method imposes additional restrictions on the selection of the test method (for example, minimum surface preparation requirement, insensitivity to testing temperature, etc.). The EPR and etching techniques have been compared in order to sensitization of stainless steel structures. It has been widely reported that the maximum sensitivity in the welded structure of stainless steel is shown at heat-affected zone (HAZ) than weldments with cast structure. In this work, sectioned weldments and external surfaces were investigated to reveal the degree of sensitization by the etching and the results were compared with those of EPR test. The EPR test showed little sensitivity to surface roughness and test temperature.

• Journal of Korean Society of Steel Construction
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• v.11 no.4 s.41
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• pp.409-416
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• 1999

The fatigue crack growth analysis based on the fracture mechanics is useful to the estimation of the fatigue life on welded structures under cyclic loading. The analysis procedure in fatigue crack growth under uniform axial loading is applicable to bending fatigue problem as well. The intent of the present study is to show the procedure for calculating the fatigue crack propagation lifetimes of deckplates under bending stress and to explain the crack growth rates for the two dimensional crack problems. It is shown that the fatigue crack grows at a decreasing rate and the fatigue life depends on the initial crack length and the crack shape. The numerically predicted crack growth agree with the experimental data.

• Computational Structural Engineering
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• v.5 no.3
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• pp.97-103
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• 1992

Since many design problems in the railroad, aerospace and machine structures involve considerations of the effect of cyclic loading, manufacturing and quality control processes much fully account for fatigue of critical components. Due to the sensitivity of the Paris law, it is very important to calculate .DELTA.K numerically to minimize the error of predicted fatigue life in cycles. However, it is shown that the p-version of FEM based on LEFM analysis is far better suited for computing the stress intensity factors than the conventional h-version. To demonstrate the proficiency of the proposed scheme, the welded T-joint with crack problems of box car body bolster assembly and a crack problem emanating from a circular hole in finite strip have been solved.

• Journal of Korean Society of Steel Construction
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• v.15 no.1
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• pp.9-15
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• 2003

As building structures become higher and longer-spanned these days, welding fabrication may become more and more difficult as the thickness of the plate increases. The use of high-strength steel is one of the solutions to reduce membrane thickness. Using high-strength steel would reduce the size of the column, which is under high axial load. Performance tests of high-strength box-type and H-shaped welded columns subjected to the combined bending and axial compressive load were carried out with variable axial load and slenderness ratio. Beam-column test results showed that the ultimate strength satisfied both ASD and LRFD codes

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.1
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• pp.126-137
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• 2003

Many research works have been performed on the J-T approach for elastic-plastic crack-tip stress fields in a variety of plane strain specimens. To generalize the validity of J-T method, further investigations are however needed fur more practical 3D structures than the idealized plane strain specimens. The present study deals mainly with 3D finite element (FE) modeling of welded plate and straight pipe, and accompanying elastic, elastic-plastic FE analyses. Manual 3D modeling is almost prohibitive, since the models contain semi-elliptical interfacial cracks which require singular elements. To overcome this kind of barrier, we develop a program generating the meshes fur semi-elliptical interfacial cracks. We then compare the detailed 3D FE stress fields to those predicted with J-T two parameters. The validity of J-T approach is thereby extended to 3D yield-strength-mismatched weld joints, and useful information is inferred fur the design or assessment of pipe welds.