• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.5A
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• pp.623-629
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• 2008

New high strength bolts are required due to the development of the high strength steel, the ultra-thick steel plates, and the long-span bridge, though high strength bolts with tensile strength of 1,000 MPa are mainly used in construction site of every country. Consequently, in this study, we estimated the fatigue strength by performing fatigue test of slip-resistant splices with slip coefficients applying the newly developed F13T high strength bolts. The fatigue test satisfied the Category B requirements with the fatigue strength of slip-resistant splices. Also we analyzed the fatigue fracture characteristics of slip-resistant splices.

• Structural Engineering and Mechanics
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• v.91 no.2
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• pp.177-195
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• 2024

This research plans to investigate the simultaneous impact of bamboo fibers (BF) and steel fibers (SF) on the mechanical and spalling characteristics of ultra-high-performance concrete (UHPC) exposed to high temperatures (HT). To this aim, 25 mixtures were made and assessed. BF was added at five contents of 0, 2.5, 5, 7.5 and 10 kg/m³. Additionally, SF was used at five weight contents: 0%, 1%, 2%, 3% and 4%. Specimens were exposed to temperatures ranging between 25℃ and 800℃. Thus, com-pressive, tensile, and flexural strengths, elastic moduli, mass loss, and permeability were measured. Experiments revealed that the simultaneous use of low BF and SF contents could totally prevent spalling of UHPC, but the use of either SF or BF alone could not prevent spalling at high levels of fibers. Besides, the synergetic positive impact of BF and SF on the spalling resistance of UHPC was by reason of the rise of BF' permeability and the bridging role of SF at HT. Moreover, it was concluded that the use of SF could moderate the adverse influence of BF on the compressive resistance of UHPC.

• Journal of Welding and Joining
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• v.4 no.2
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• pp.21-29
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• 1986

The influence of welding heat input variation(600-900J/cm) and heat-treatment condition after welding on tensile strength of butt welded joint in $175Kg/mm^2$ strength level Maraging steel(Co-free and Co-containing) sheets was investigated on the basis of hardness distribution, microstructure of weld metal and fracture surface. The obtained main results are as follows; 1. The strength of weldment (UTS, NTS), joint efficiency showed a little decreasing tendency with the increase in welding heat input, and the elongation showed a little increasing tendency with the increase in the width of weld metal. It was considered because of the plastic constraint of the high strength base metal. 2. The strength of weldment was better in the solution treatment and aging than the aging only after welding due to the disappearance of almost denverite in weld metal. 3. The hardness distribution in weldment after welding and heat-treatment was almost similar to both Co containing and Co free Maraging steel with change in welding heat input. 4. The fracture was occurred at weld metal, and the fracture surface showed a relatively shallow dimples in both Co containing and Co free Maraging steel.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.123-128
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• 2001

The creep constants which are used to the reference stress equations of creep damage were obtained to type 316LN stainless steel, and their determining methods were described in detail. Typical Kachanov and Rabotnov(K-R) creep damage model was modified into the damage equations with reference stress concepts, and the modified equations were applied practically to type 316LN stainless steel. In order to determine the reference stress value, a series of high-temperature tensile tests and creep tests were accomplished at $550^{\circ}C$ and $600^{\circ}C$. By using the experimental creep data, the creep constants used in reference stress equations could be obtained to type 316LN stainless steel, and a creep curve on rupture strain was predicted. The reference stress concept on creep damage can be utilized easily as a design tool to predict creep life because the process, which is quantified by the measurement of voids or micro cracks during creep, is omitted.

• International Journal of Naval Architecture and Ocean Engineering
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• v.6 no.4
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• pp.922-934
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• 2014

In casting steels for offshore construction, manufacturing integral casted structures to prevent fatigue cracks in the stress raisers is superior to using welded structures. Here, mold design and casting analysis were conducted for integral casting steel. The laminar flow of molten metal was analyzed and distributions of hot spots and porosities were studied. A prototype was subsequently produced, and air vents were designed to improve the surface defects caused by the release of gas. A radiographic test revealed no internal defects inside the casted steel. Evaluating the chemical and mechanical properties of specimens sampled from the product revealed that target values were quantitatively satisfied. To assess weldability in consideration of repair welding, the product was machined with grooves and welded, after which the mechanical properties of hardness as well as tensile, impact, and bending strengths were evaluated. No substantive differences were found in the mechanical properties before and after welding.

• International Journal of Naval Architecture and Ocean Engineering
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• v.5 no.3
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• pp.376-391
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• 2013

Brackets in ships and offshore structures are added structures that can endure stress concentrations. In this study, a concurrent engineering solution was proposed, and a high strength low carbon cast steel alloy applicable to offshore structures was designed and developed. The yield strength and ultimate tensile strength of the designed steel were 480 and 600 MPa, respectively. The carbon equivalent of the steel was 0.446 with a weld crack susceptibility index of 0.219. The optimal structural design of the brackets for offshore structures was evaluated using ANSYS commercial software. The possibility of replacing an assembly of conventional built-up brackets with a single casting bulb bracket was verified. The casting process was simulated using MAGMAsoft commercial software, and a casting fabrication process was designed. For the proposed bulb bracket, it was possible to reduce the size and weight by approximately 30% and 50%, respectively, compared to the conventional type of bracket.

• Korean Journal of Metals and Materials
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• v.50 no.1
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• pp.1-7
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• 2012

The fracture resistance and tensile properties of $Y_2O_3$ oxide dispersion strengthened steel containing 9 wt% Cr(9Cr-ODS) were measured at various temperatures up to $700^{\circ}C$. The fracture characteristics were compared with those of commercial E911 ferritic/martensitic steel. The strength of 9Cr-ODS was at least 30% higher than that of E911 steel at the test temperatures below $500^{\circ}C$. The strength difference between the two materials was almost diminished at $700^{\circ}C$. 9Cr-ODS showed cleavage fracture behavior at room temperature and unstable crack growth behaviors at $300^{\circ}C$ and $500^{\circ}C$. The J-R fracture resistance of 9Cr-ODS was much lower than that of E911 steel at all temperatures. It was deduced that the coarse $Cr_2O_3$ particles that were formed during the alloying process provided the crack initiation sites of cleavage fracture in 9Cr-ODS.

• Steel and Composite Structures
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• v.48 no.2
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• pp.131-143
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• 2023

The CFRP bar was used to achieve more ductile and durable headed-stud shear connectors in composite components. Three series of push-out tests were firstly conducted, including specimens reinforced with pure steel fibers, steel and CFRP bars. The distributed stress was measured by the commercial PPP-BOTDA (Pre-Pump-Pulse Brillouin optical time domain analysis) optical fiber sensor with high spatial resolution. A series of numerical analyses using non-linear FE models were also made to study the shear force transfer mechanism and crack response based on the test results. Test results show that the CFRP bar increases the shear strength and stiffness of the large diameter headed-stud shear connection, and it has equivalent reinforcing effects on the stud shear capacity as the commonly used steel bar. The embedded CFRP bar can also largely improve the shear force transfer mechanism and decrease the tensile stress in the transverse direction. The parametric study shows that low content steel fibers could delay the crack initiation of slab around the large diameter stud, and the CFRP bar with normal elastic modulus and the standard reinforcement ratio has good resistance to splitting crack growth in headed stud shear connectors.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.6C
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• pp.295-301
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• 2009

In general the stability of soil nail-slope system, the shear resistance is neglected because the tensile resistance of nail acts mainly for slope stabilization. This is because that deformed steel is generally used for nail and it does ductile behavior. In other side when the steel pipe with high rigidity is used for nail, the shear resistance at failure surface work more than deformed steel. In order to analyze effects of shear resistance at the soil nail-slope system with high steel piped nail, a series of numerical analyses were performed. Also numerical analyses at 3 conditions - 5 nailed, 7 nailed, 9 nailed at the same slope were perfomed for investigating the trend of shear resistance effect. From these 3D numerical analyses, it was found that the maximum shear resistances at each nails were larger in case of steel piped nail and because of this, the factor of safety at the condition of the steel piped nail appears larger than that of deformed steel nail.

• Journal of the Korea Institute of Building Construction
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• v.14 no.6
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• pp.639-645
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• 2014

For the construction materials, concrete, as the most widely used material, is focused on its improvement of performance. Although concrete has many advantages of easiness of handling, economical benefits, and high compressive strength, low tensile strength, brittleness and drying shrinkage are reported as the drawbacks of concrete. Hence, to solve these drawbacks of concrete, many research has conducted especially using fiber-reinforced concrete technology. Especially, HPFRCC which has high volume of fiber reinforcement was suggested as a solution of these drawbacks of normal concrete with increased ductility while it has the possibility of workability loss with fiber clumping which can cause low performance of concrete. Therefore, in this paper, optimized fiber combination with either or both metal and organic fibers is suggested to provide better performance of HPFRCC in tensile strength and ductility. As the results of experiment, better workability was achieved with 1 % of single fiber rather than multiple fibers combinations, espeically, short steel fiber showed the best workability result. Furthermore, in the case of organic fibers which showed higher air content than steel fibers, higher compressive strength was achieved while lower tensile and flexural strength were shown.