Demand for research on the use of hydrogen, an eco-friendly fuel, is rapidly increasing in accordance with global environmental problems and IMO environmental regulations in the shipbuilding and marine industry. In the case of hydrogen, similar to liquefied natural gas, it has a characteristic that its volume decreases hundreds of times during phase transformation from gas to liquid, so it must be stored in a tank in the form of liquefied hydrogen for transport efficiency. The material of the liquid hydrogen tank is selected in consideration of mechanical properties and hydrogen embrittlement at cryogenic temperatures. In this study, welding research was conducted on STS316L material, which was most commonly used in the space industry. In this study, flux cored arc welding was performed under 4 welding conditions to derive the optimal welding conditions for STS316L material, and then mechanical properties of the welded part were compared and analyzed.

Due to the environmental regulations of the International Maritime Organization (IMO), the number of ships using cryogenic fuel such as LNG (liquefied natural gas) is increasing rapidly, and the demand for eco-friendly ships is expected to grow further in the future. The material of the tank for storing cryogenic fuel such as LNG is limited within the IGC Code, and available materials include 9% nickel steel, Invar (36% nickel steel), Al5083-0, STS304L, and high manganese steel. Recently, 9% nickel steel has been used as a tank in LNG fuel-powered ship projects, and it has excellent thermal/mechanical properties in cryogenic LNG environmental conditions (-163°C). In this study, it is conducted an experimental study on SAW(Submerged Arc welding), which has better welding efficiency than FCAW(Flux Cored Arc Welding), which is mainly used for 9% nickel steel materials. In addition, to verify the reliability of the welded part after the welding test, cross-sectional observation of the welded part was performed and the mechanical properties such as the tensile strength and cryogenic impact strength of the welded part were evaluated.

Due to stricter environmental regulations of the International Maritime Organization(IMO), the number of ships fueled by Liquefied Natural Gas(LNG) is rapidly increasing. The International Code of the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk(IGC Code) limits the material of tanks that can store cryogenic substances such as LNG. Among the materials listed in the IGC Code, ASTM A553M-17 has been recently adopted as a material for LNG fuel tank projects because of its excellent mechanical properties at cryogenic temperatures. In shipyards, this material is being used to build tanks through Flux Cored Arc Welding (FCAW). However, there is a problem that magnetization occurs during welding and there is a big difference in welding quality depending on the welding position. In order to overcome this problem, this study intends to conduct basic research to apply laser welding to ASTM A553M-17 material. In this study, a study on penetration (HAZ depth, Penetration) and welding defects during fiber laser welding according to three types of shielding gases(nitrogen, argon, and helium) was conducted. To this end, a Bead on plate(BOP) experiment was performed under four fiber laser conditions(Power, Speed) for each shielding gas and welding defects caused by the use of the shielding gas were compared through cross-sectional observation, and the penetration depth was analyzed.

Due to the strengthening of domestic and international environmental regulations, the replacement of FRP ships with aluminum ships for small ships is continuously in progress. Domestic aluminum ships are being applied to various types of ships, mainly special ships, passenger ships and fishing ships. Gas metal arc welding(GMAW) is used as a welding method when manufacturing ships using aluminum materials for ships with a thickness of 5mm or more. However, it is carried out manually by the workers in the shipyard, and there is a limit to relying on the skills of the workers. In this study, basic research on high-efficiency tandem welding was performed as a basic study for the application of high-quality automatic welding equipment when working on aluminum ships. In this study, welding deformation according to constraint conditions was comparatively analyzed using tandem welding equipment and cross-sections of welds were evaluated for each experiment.

콘크리트가 충전된 강관 합성기둥은 화재 시 내부 콘크리트가 내력을 견딜 수 있어 높은 하중을 받는 건축물에 적용되고 있으나 높은 내화성능을 요구하는데 반해 이를 평가할 수 있는 방법은 제한되어 있다. 본 논문에서는 폭 700mm 이상인 무피복 대형합성기둥의 온도분포를 확인하기 위해서 수평가열로에서 3시간 내화실험을 수행하고 이후에 압축실험에 수행하여 잔존내력을 확인하였다. 실험 결과 3시간의 화재 노출 후에 폭 700mm 대형합성기둥은 57%의 잔존내력을 가지는 것으로 나타났으며, 재료의 화재 강도저감만을 고려한 잔존내력 예측은 내력을 낮게 평가하는 것으로 나타났다.

The study discusses remote control torch system that is equipped with CO2 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 completely burned out. Such work suspension resulting from frequent moves to adjust current and voltage as well as replace the wire and subsequent cooling causes welding defects. The study produced a remote control torch equipped with double wire reel by simplifying and streamlining the existing CO2 functions to reduce the troubling issue. The remote control torch equipped with double wire reel and the existing CO2 /MAG welding torch were applied as V-groove butt in the vertical position using 9mm rolled steel for SM50A welding structure. After completion of welding, the condition of welded surface beads went through visual inspection as well as radiographic inspection to analyze the welding quality inside the welded part. The study also evaluated reduction of welding defects, cost saving, the replacing performance against the existing commercial welders and the effect on possible compatibility

In GMAW welding used mostly at the scene of a welding industry, welders can not see control panels in internal welds of vehicles and tanks, and can not adjust the current and voltage properly during the welding, which is caused by distance from the working area. Therefore, welders have to move to control the current and voltage by stopping welding. This, however, can result in the welding defects by momentary cooling. In this research related to the existing GMAW welding methods and the manners with the remote control torch their performances were evaluated by comparing and analyzing the welds of V-type butt using SM50A 6 mm and welding structural rolled steels. As the result of conducting the visual inspection and bending test one by one against the V-type butt welds, the amount of spatter by the remote control torch method showed reducing effects about five times lower and it had a performance that did not affect the weld defects by displaying suitable effects on the bending test of welds. Consequently, the experimental study on the possibility of replacement and compatibility with the existing commercial welder for the remote control torch was performed.

This study presents an experimental study of the structural behavior for steel plate-concrete column-to-steel girder connections. Experiments were carried out to investigate the moment-rotation characteristics, failure behavior and ultimate moment capacity of these connections. The results of this experimental study involving three welded moment-resisting connections subjected to cyclic loading are presented. The specimens were fabricated at full scale to evaluate their hysteretic behavior. A description of the test specimens, the details of the joint, the test system and the testing methods are described. The test results showed that the structural behavior of these composite connections was influenced by the connection details.

Stainless steel sheets are widely used as the structure material for the railroad cars and the commercial vehicles. These kinds structures used stainless steel sheets are commonly fabricated by using the gas welding. For fatigue design of gas welded joints such as fillet and plug and ring type joint, it is important to obtain optimum design parameter information on gas welded joints. In this paper, analysis approach for fatigue test using experimental design are evaluated optimum factor in gas welded joint type and geometrical parameters of materials. Using these results, that factors applied to fundamental information for fatigue design.

Recently the construction of residential building faces many difficulties due to the shortage of building materials and works. Simplifying the stage of processing and assembling reinforcing rods and increasing the efficiency of them in reinforced concrete construction can be used to settle the difficulties. In the respect, structural wire-fabric is utilized. The purpose of this study, instead of deformed steel bars, to examine the utilization of slab joint, which is accompanied with a large deformation in the structure subjected to seismic loads, to suggest reinforcing method which is efficient, easily constructible and structurally safe. The results are as follows ; 1. The ductility capacity of slab reinforced by welded wire fabric was less than with deformed bar in discontinuous slab joint. To enhance the ductility capacity, deformed bar should be used with welded wire fabric for the longitudinal reinforcement. 2. It is avoid to use loop welded wire fabric as the longitudinal reinforcement in wall, because the strength and ductility capacity showed lower value than that with deformed bar. 3. Using welded wire fabric in wall structures, it need deformed bar reinforcement with sufficient anchorage length.

Recently the construction of residential building faces many difficulties due to the shortage of building materials and works. Simplifying the stage of processing and assembling reinforcing rods and increasing the efficiency of them in reinforced concrete construction can be used to settle the difficulties. In the respect, structural wire-fabric is utilized. The purpose of this study, instead of deformed steel bars, to examine the utilization of slab joint, which is accompanied with a large deformation in the structure subjected to seismic loads, to suggest reinforcing method which is efficient, easily constructible and structurally safe. The results are as follows ; 1. The ductility capacity of continuous slab joints reinforced by welded wire fabric is less than that with deformed bar. But continuous slab joint is reinforced by deformed bar for the longitudinal reinforcement, it is increase strength and ductility capacity. 2. It is recommended that simple cut jointing of welded wire fabric should be avoided in wall-wall joints.

최근에 용접 수평헌치로 보강된 내진 철골 모멘트 적합부의 응력 전달모형 및 설계법이 Lee-Uang에 의해 새로이 제안된 바가 있다. 본 연구에서는 반복재하 실물대 실험을 통하여 이 설계방안의 타당성을 실험적으로 확인하고 응력집중에서 기인하는 헌치단부의 균열을 방지할 수 있는 효과적인 상세도 제안하고자 하였다. Lee-Uang의 방안에 의해 설계된 3개의 시험체는 모두 설계의도에 부합되게, 헌치단부의 외측에서 형성된 소성힌지에서 0.04 radian에 달하는 뛰어난 소성회전능력을 발휘하였다. 도한 헌치단부에 구배를 주고 처공하거나 또는 보 웨브 스티프너를 헌치의 웨브로 부분적으로 또는 완전히 연장하는 상세에 의해 헌치단부의 균열발생을 효과적으로 방지할 수 있음을 실험적으로 입증하였다. 아울러 해석적으로 예견되었던 헌치 웨브의 스트럿 거동도 스트레인 계측을 통하여 실험적으로 입증하였다.

대부분의 선체 및 해양구조물은 용접을 통해서 만들어지며 이러한 구조물들은 항상 변화되는 하중에 노출된다. 본 논문에서는 T형 용접이음부의 응력집중과 피로특성규명을 위하여 수치해석적 방법을 통한 연구결과를 실험결과와 비교 검토하였다. 특히 필렛용접, 완전 용입용접, 부분 용입용접부의 특성을 응력집중과 피로강도면에서 연구하여ㅛ으며 이를 위한 파라메터로는 불 용입부의 길이, 각장의 크기 및 형태, 삽입판의 각도등을 채택하였다. 최적의 용접을 위하여 각 파라메터의 선정을 효과적으로 할 수 있도록 응력 및 피로수명분표, S-N선도를 정리하엿으며 필렛용접이 용입용접을 대신하여 사용될 수 있는 근거를 제시하였다. 본 연구결과는 실제 현장에서 구조의 용접이음부 형태 선정에 지침이 될 수 있다.

The purpose of this study is to investigate the ultimate strength of carbon steel (SS400) fillet-welded connections with weld metal fracture through monotonic tensile test. Specimens of CTFW series (transverse fillet weld against loading direction), CLFW series (longitudinal fillet weld against loading direction) and CFW series (a combination of transverse weld and longitudinal weld) failed by tensile fracture, shear fracture and block shear fracture, respectively. Test strengths were compared according to welding direction and weld length

오스테나이트계 스테인리스강은 우수한 내식성, 내구성 및 내화성을 지닌다. 특히, 오스테나이트계 스테인리스강중의 대표인 STS304에 비해 저탄소를 함유하고 있는 STS304L은 현장용접 후 별도의 열처리 없이 높은 내입계부식성능을 지니고 있어 용접후 내입계 부식이 우려되는 부재접합에 적용할 수 있다. 본 연구에서는 티그(TIG)용접으로 필릿 용접된 STS304L 용접접합부의 용접재(용착금속부) 내력과 파단 메카니즘을 조사하고자 한다. 주요변수인 하중방향에 대한 용접선의 배치에 따라 TFW(하중직각방향 용접), LFW(하중방향용접), FW (하중방향용접과 하중직각방향 용접조합)시리즈의 실험체를 제작하여 인장실험을 실시하였고, 각각 인장파단,전단파단, 블록전단파단(인장 파단과 전단파단의 조합)이 발생하였다. 동일 용접길이에 대해 TFW 시리즈의 접합부가 가장 높은 내력을 나타났으며, 현행기준식( KBC2016/AISC2010)과 기존 연구자의 식에 의한 예측내력과 비교한 결과, TFW와 LFW접합부는 과소평가되었고 FW실험체는 과대평가되었다 .실제 파단 위험단면과 블록전단파단 메카니즘을 고려한 내력식을 제안하였다.

The non-welded building hardware method can reduce accidents caused by welding, and can be constructed by bolt assembly, which can reduce labor costs and shorten the construction period. The purpose of this study is to evaluate the behavior of joints of non-welded and welded of building hardware frame

In this paper, block shear fracture behavior in base metal of fillet-welded connection fabricated with duplex stainless steel (STS329FLD) were investigated through experimental procedures. Main variables are weld lengths in the longitudinal and the transverse directions of applied force. As a result, test specimens failed by typical block shear facture (the combination of tensile fracture and shear-out fracture) in base metal not weld metal. Ultimate strength of the specimens tended to get higher with the increase of the weld lengths.