• Journal of Korean Society of Steel Construction
• /
• v.24 no.4
• /
• pp.435-442
• /
• 2012

Recently, high performance(strength) steels have been utilized to structural materials in buildings and bridges with the demand for high-rise and long-span of main structures. This paper is a series of basic study for the design specification of structural members using high performance steel, material properties of high performance rolled steel building structures. HSA800 was compared with the requirements of Korean Standards(KS) for HSA800. Welded square tube stub columns with variables of width-to-thickness ratios are planned in order to investigate the local buckling behaviors and check the current design limit of width-to-thickness ratio and uniaxial compressive tests are carried out. In addition, the local buckling behaviors of stub columns obtained finite element analysis were compared with those of test results.

• Journal of Korean Society of Steel Construction
• /
• v.24 no.6
• /
• pp.627-636
• /
• 2012

Recently, high performance(strength) steels have been utilized to structural materials in buildings and bridges with the demand for high-rise and long-span of main structures. This paper is a series of basic study for the design specification of structural members using high performance steel, material properties of high performance rolled steel building structures; material properties of HSA800 steel was compared with the requirements of Korean Standards(KS) for HSA800. Welded H-shape stub columns with variables of width-to-thickness ratios are planned in order to investigate the local buckling behaviors and check the current design limit of width-to-thickness ratio and uniaxial compressive tests are carried out. In addition, the buckling behaviors of stub columns obtained finite element analysis were compared with those of test results.

• Journal of Korean Society of Steel Construction
• /
• v.26 no.4
• /
• pp.299-309
• /
• 2014

HSA800 is a new high strength steel (HSS) plate for building structures developed by POSCO and RIST in 2011. It has upper and lower bounds for yield ($F_y$) and tensile ($F_u$) strength as of 650-770MPa and 800-950MPa, respectively, with yield ratio ($F_y/F_u$) limit as of 0.85 which make steel quality more reliable and enhance the seismic resistance of structures. As made by TMCP, it has a good weldability without increasing carbon percentage. The objective of this study is to provide alternative design of mega-structural members of the Lotte World Tower (555m, 123 story), a first super-tall building in Korea, using HSS considering structural safety, constructability, and cost-effectiveness. Steel outrigger trusses, belt-trusses and steel exterior columns were selected and analyzed to evaluate the structural performance between original and alternative designs using HSS. The results show that HSS can be applied to the members which do not affect lateral stiffness of a building and, in this study, approximately 1100tons of steel were saved. It implies that HSS can save overall construction costs - manufacturing, delivery, and erection costs - by reducing mega structural member size. HSA800 was very first applied to the Lotte World Tower based on the results of this study.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.16 no.2
• /
• pp.1339-1347
• /
• 2015

This study discusses a remote control torch system equipped with a GMAW double wire reel. The welding machine is 30m away from the wire feeder at the industrial site and the feeder is three to five meters away from the torch. Accordingly, the welders cannot control the current and voltage that meets the welding condition during work when they are working at a place that prevents them from seeing the control panel, such as inside a vehicle or tank or at a far work site. They also have no choice but to stop working to change the wire reel when it is burned out completely. Such work suspension resulting from frequent moves to adjust the current and voltage as well as to replace the wire and subsequent cooling causes welding defects. This study produced a remote control torch equipped with a double wire reel by simplifying and streamlining the existing GMAW functions to reduce the troubling issue. The remote control torch equipped with a double wire reel and the existing $CO_2$ /MAG welding torch were applied as a V-groove butt in the vertical position using 6mm rolled steel for a SM50A welding structure. After welding, the condition of welded surface beads underwent a visual inspection and radiographic inspection to analyze the welding quality inside the welded part. This study also evaluated the reduction of welding defects, cost saving, the replacing performance against the existing commercial welders, and the effects on possible compatibility.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.6 no.2
• /
• pp.122-128
• /
• 2005

A feasibility study on the application of self?shielded flux cored arc welding to the on-site SM520 steel bridge box fabrication for express trains and high way construction instead of gas-shield flux cored arc welding was conducted in terms of weld soundness, mechanical properties, toughness and microstructures. All welded specimens made with the self?shielded FCAW process were tested by magnetic particle and ultrasonic techniques and they were found to be sound. All multipass weld specimens made with both self-shielded and gas-shielded FCAW processes showed yield and tensile strengths of $462{\sim}549\;MPa$ and $548{\sim}640\;MPa$, respectively. The impact values of Charpy V-Notch weld specimens also met with the required value of 40J at $-20^{\circ}C$. The hardness values of the top area of weldments were higher than those of the bottom area because of higher residual stresses in the near surface. It was found that welding characteristics of SM520 steel by the on-site welding conditions with self-shielded FCAW showed almost equivalent to those by gas-shielded FCAW in terms of sound welds, mechanical properties and microstructure.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.14 no.2
• /
• pp.38-43
• /
• 2015

Tungsten inert gas (TIG) welding is commonly used in industries that require airtightness, watertightness, oiltightness, and precision. It is a non-consumable welding method that is commonly used for the welding of non-ferrous metals, but it can be used to weld most metals. The methods of TIG welding can be divided into three types. The first, manual welding is done directly on the metal by a welder with a torch. The second, semi-automatic welding, gets help from a material supplying machine, but it is conducted by a welder. Lastly, automated welding is conducted fully by a machine during its process and operation. Depending on the selection of electrode, the amount of heat that is applied to the base material and the electrode rod changes and makes the shape of welded parts different. A direct-current positive electrode was used for this study. Through the change of shielding gas type on a structural steel (SS-400) that is commonly used in industry, the composition and shape changes in welded parts were detected after welding. The heat-affected area, hardness value, and tensile strength were also identified through hardness testing and tensile testing. In this study, it was found that the higher hardness value of the heat-affected is, the weaker the tensile strength becomes.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.1
• /
• pp.85-90
• /
• 2010

Friction welding is a common practice to join axially symmetrical parts for automobile industry applications. The shaft for automobile reverse idle gear is generally produced by forging steel, SF 45. This method is not so good because of high cost of material and production. In this study, in order to investigate the possibility of application of SM 45C to SF 45 dissimilar friction welding, the dissimilar friction welded joints were performed using 20 mm diameter solid bar in forging steel(SF 45) to carbon steel(SM 45C). The optimal friction welding parameters were selected to ensure reliable quality welds on the basis of visual examination, tensile test, micro-Virkers hardness surveys of the bond of area and optical microstructure investigations for welded joint parts. Finally, post weld heat treatment(PWHT) of the high-frequency induction hardening was performed for the friction welded specimens under the optimal welding conditions. And then, the mechanical properties were compared for as-welded and PWHT in SM 45C to SF 45.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.28 no.6A
• /
• pp.843-851
• /
• 2008

The conventional pile cap reinforcement systems regulated in the design specifications have some restrictions in design and construction such as requirement of shear key, disposition of reinforcing bars and insurance of anchoring length of reinforcements. This study suggests a new type of steel pipe pile cap system with perforated flat bar shear connector as an alternative to the conventional pile cap system for the improvement in structural performance and simplification of construction. And, experimental results of push-out and bending behavior are scribed for the evaluation of structural performance of the new pile cap system and it was compared to the structural behavior of conventional pile cap system.

• Journal of Korean Society of Steel Construction
• /
• v.27 no.6
• /
• pp.513-523
• /
• 2015

In steel moment frames constructed of H-shapes, strong-axis moment connections should be used for maximum structural efficiency if possible. And most of cyclic seismic testing, domestic and international, has been conducted for strong-axis moment connections and cyclic test data for weak-axis connections is quite limited. However, when perpendicular moment frames meet, weak-axis moment connections are also needed at the intersecting locations. Especially, both strong- and weak-axis moment connections have been frequently used in domestic practice. In this study, cyclic seismic performance of RBS (reduced beam section) weak-axis welded moment connections was experimentally investigated. Test specimens, designed according to the procedure proposed by Gilton and Uang (2002), performed well and developed an excellent plastic rotation capacity of 0.03 rad or higher, although a simplified sizing procedure for attaching the beam web to the shear plate in the form of C-shaped fillet weld was used. The test results of this study showed that the sharp corner of C-shaped fillet weld tends to be the origin of crack propagation due to stress concentration there and needs to be trimmed for the better weld shape. Different from strong-axis moment connections, due to the presence of weld access hole, a kind of CJP butt joint is formed between the beam flange and the horizontal continuity plate in weak-axis moment connections. When weld access hole is large, this butt joint can experience cyclic local buckling and subsequent low cycle fatigue fracture as observed in this testing program. Thus the size of web access hole at the butt joint should be minimized if possible. The recommended seismic detailing such as stickout, trimming, and thicker continuity plate for construction tolerance should be followed for design and fabrication of weak-axis welded moment connections.

• Journal of the Society of Naval Architects of Korea
• /
• v.41 no.6
• /
• pp.40-47
• /
• 2004

The influence of heat input on fracture toughness was investigated in SAW weldments, which were prepared at two different welding conditions in API 2W Gr.50 and EN10225 5420. By examining the fracture initiation point, refined areas(ICHAZ and SCHAZ) in weld metal was identified as local brittle zone, in which M-A constituents and coarsed grain size were observed. Impact values showed the most significant difference at root portion, and CTOD transition temperature was related with impact values obtained at root portion. Hardness values in refined area were less than columnar microstructure about 20 HV5.