• 한국지반공학회논문집
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• 제27권2호
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• pp.35-42
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• 2011

현장타설말뚝의 하중전이분석 시, 말뚝에 작용하는 잔류응력은 종종 무시되어 왔다. 그러나 말뚝에 작용하는 초기 하중를 무시함에 따라서 분석된 하중전이거동이 실제 하중전이거동과 상이하게 나타나는 결과를 초래하기도 한다. 이러한 현장타설말뚝에 작용하는 잔류응력은 콘크리트의 수축/팽창 또는 지반의 특성에 영향을 받는 것으로 몇몇의 연구결과에 의하여 나타났다. 본 연구에서는 암반에 근입된 현장타설말뚝을 시험시공하여 잔류응력을 측정하고 분석 하였으며, 이에 따른 잔류응력에 미치는 요소들에 대하여 검토 분석하였다.

• 한국해양공학회지
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• 제35권3호
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• pp.203-215
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• 2021

Current industrial practices and approaches are simplified and do not describe the actual behavior of plated elements of offshore topside structures for safety design due to fires. Therefore, it is better to make up for the defective methods with integrated fire safety design methods based on fire resistance characteristics such as residual strength capacity. This study numerically investigates the residual strength of steel stiffened panels exposed to hydrocarbon jet fire. A series of nonlinear finite element analyses (FEAs) were carried out with varying probabilistic selected exposures in terms of the jet fire location, side, area, and duration. These were used to assess the effects of exposed fire on the residual strength of a steel stiffened panel on a ship-shaped offshore structure. A probabilistic approach with a feasible fire location was used to determine credible fire scenarios in association with thermal structural responses. Heat transfer analysis was performed to obtain the steel temperature, and then the residual strength was obtained for the credible fire scenarios under compressive axial loading using nonlinear FEA code. The results were used to derive closed-form expressions to predict the residual strength of steel stiffened panels with various exposure to jet fire characteristics. The results could be used to assess the sustainability of structures at risk of exposure to fire accidents in offshore installations.

• Structural Engineering and Mechanics
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• 제85권4호
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• pp.531-543
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• 2023

The existing concrete bridges are time-varying working systems, where the maintenance strategy should be planned according to the time-varying performance of the bridge. This work proposes a time-dependent residual capacity assessment procedure, which considers the non-stationary bridge load effects under growing traffic and non-stationary structural deterioration owing to material degradations. Lifetime bridge load effects under traffic growth are predicated by the non-stationary peaks-over-threshold (POT) method using time-dependent generalized Pareto distribution (GPD) models. The non-stationary structural resistance owing to material degradation is modeled by incorporating the Gamma deterioration process and field inspection data. A three-span continuous box-girder bridge is illustrated as an example to demonstrate the application of the proposed procedure, and the time-varying reliability indexes of the bridge girder are calculated. The accuracy of the proposed non-stationary POT method is verified through numerical examples, where the shape parameter of the time-varying GPD model is constant but the threshold and scale parameters are polynomial functions increasing with time. The case study illustrates that the residual flexural capacities show a degradation trend from a slow decrease to an accelerated decrease under traffic growth and material degradation. The reliability index for the mid-span cross-section reduces from 4.91 to 4.55 after being in service for 100 years, and the value is from 4.96 to 4.75 for the mid-support cross-section. The studied bridge shows no safety risk under traffic growth and structural deterioration owing to its high design safety reserve. However, applying the proposed numerical approach to analyze the degradation of residual bearing capacity for bridge structures with low safety reserves is of great significance for management and maintenance.

• Computers and Concrete
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• 제5권6호
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• pp.509-524
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• 2008

Containment structures not only are leak-tight barriers, but also may be subjected to impacts caused by tornado-generated projectiles, aircraft crashes or the fragments of missile warhead. This paper presents the results of an experimental study of the impact resistance of steel fiber-reinforced concrete against 45 g projectiles at velocity around 2500 m/s. An explosively formed projectile (EFP) was designed to generate an equivalent missile fragment. The formation and velocity of EFP are measured by flash x-ray. A switch made of double-layered thin copper sheets controlled the exposure time of each flash x-ray. The influence of the fiber volume fraction on the crater diameter of concrete slab and the residual velocity of the projectile were studied. The residual velocity of the projectile decreased as the fiber volume fractions increased. In this work, the residual velocity of the projectile was to 44% that of plain concrete when the fiber volume fraction exceeded 1.5%. Based on the present finding, steel fiber reinforced concrete with the fiber volume fraction exceeding 1.5% appear to be more efficient in protection against high velocity fragment impact.

• Nuclear Engineering and Technology
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• 제52권11호
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• pp.2552-2564
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• 2020

The crevice stress corrosion cracking (SCC) susceptibility of austenitic stainless steels was evaluated in simulated pressurized water reactor (PWR) environments. To simulate the abnormal condition in temporary clamping devices on leaking small bore pipes, crevice bent beam (CBB) tests were performed in the oxygenated as well as hydrogenated conditions. No SCC cracks were found for SS316 in both conditions. SS304 also showed good resistance in the hydrogenated condition. However, all SS304 specimens showed SCC cracks in the oxygenated condition, indicating poor crevice SCC resistance. It was found that residual ferrites were selectively dissolved because of the galvanic corrosion coupled with the neigh-bouring austenite phase, resulting in SCC initiation in SS304. Crack morphologies were mostly transgranular assisted by the damaged δ-ferrite and deformation-induced slip bands.

• 한국자동차공학회논문집
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• 제14권3호
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• pp.88-94
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• 2006

The compressive residual stress, which is induced by shot peening process, has the effect of increasing the intrinsic fatigue strength of surface and therefore would be beneficial in reducing the probability of fatigue damage. However, the effect of shot peening in corrosion environment was not known. In this study, investigated is the effect of shot peening on corrosion fatigue crack growth of SAE 5155 steel immersed in 6% $FeCl_3$ solution and corrosion characteristics with considering fracture mechanics. The results of the experimental study corrosion fatigue characteristics of SAE 5155 are as follows; the fatigue crack growth rate of the shot peening material was lower than that of the non-peening material. And fatigue life shows more improvement in the shot peening material than in non-peening material. This is due to the compressive residual stress of surface increases resistance of corrosion fatigue crack propagation. It is assumed that the shot peening process improve corrosive resistance and mechanical property.

• 대한조선학회지
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• 제9권2호
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• pp.21-32
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• 1972

The problems of thermal stress and residual stress in resistance spot welding are studied from two standpoint namely, effect of temperature distributions and effect of the radius of free boundary. The radius of the region where the temperature distributions are occured is taken as a function of time after welding and as a finite size, 6 times of heated zone. The region of the radial stress distribution is treated as a function of time under Saint-Venant's principle and 6 or 12 times of originally heated zone. Thermal stresses and strains are obtained by analytic solution under constant mechanical properties and by the finite difference method for varing properties under temperature variation. From the computed results following conclusions are derived (1) For the engineering purpose, the region of temperature distribution and stress distribution can be treated as a finite region, $R=r_o=6r_e$ (2) If the maximum temperature of the aluminum alloy plate is less than $500^{\circ}F$, thermal stresses and strains can be obtained with constant mechanical properties. (3) The residual stresses and strains will be remained in welds and its vicinity.

• 한국표면공학회지
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• 제38권3호
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• pp.89-94
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• 2005

We investigate the reaction stability of cobalt and nickel with side-wall materials of $SiO_2\;and\;Si_3N_4$. We deposited 15nm-Co and 15nm-Ni on $SiO_2(200nm)/p-type$ Si(100) and $Si_3N_4(70 nm)/p-type$ Si(100). The samples were annealed at the temperatures of $700\~1100^{\circ}C$ for 40 seconds with a rapid thermal annealer. The sheet resistance, shape, and composition of the residual materials were investigated with a 4-points probe, a field emission scanning electron microscopy, and an AES depth profiling, respectively. Samples of annealed above $1000^{\circ}C$ showed the agglomeration of residual metals with maze shape and revealed extremely high sheet resistance. The Auger depth profiling showed that the $SiO_2$ substrates had no residual metallic scums after $H_2SO_4$ cleaning while $Si_3N_4$ substrates showed some metallic residuals. Therefore, the $SiO_2$ spacer may be appropriate than $Si_3N_4$ for newly proposed Co/Ni composite salicide process.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2006년도 춘계학술대회
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• pp.96-98
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• 2006

Proper water management is vital to achieve high performance and durability of PEFC (Polymer Electrolyte Fuel Cell). The effects of the residual water from PEFC after purge in shut-down processes on GDL/MEAs were investigated with freeze/thaw cycles Freeze/thaw cycle tests were conducted with single cells which were designed from transparent acryl plates. Single cells which contain several amount of residual water were cycles from $80^{\circ}C$ to $-28^{\circ}C$. The resistance changes of the single cells which have various amount of residual water were evaluated by ac-impedance analysis with 24 times of freeze/thaw cycles. Also, after the freeze/thaw cycles, the property changes were characterized by visual methods such as SEM, EPMA. Though it was difficult to observe noticeable property changes in the visual characterizations, the resistance of cells dramatically increased with the amount of remained water.

• Steel and Composite Structures
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• 제32권2호
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• pp.265-279
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• 2019

The self-centering capacity and energy dissipation performance have been recognized critically for increasing the seismic performance of structures. This paper presents an innovative steel moment frame with self-centering steel reinforced concrete (SRC) wall panel incorporating replaceable energy dissipation devices (SF-SCWD). The self-centering mechanism and energy dissipation mechanism of the structure were validated by cyclic tests. The earthquake resilience of wall panel has the ability to limit structural damage and residual drift, while the energy dissipation devices located at wall toes are used to dissipate energy and reduce the seismic response. The oriented post-tensioned strands provide additional overturning force resistance and help to reduce residual drift. The main parameters were studied by numerical analysis to understand the complex structural behavior of this new system, such as initial stress of post-tensioning strands, yield strength of damper plates and height-width ratio of the wall panel. The static push-over analysis was conducted to investigate the failure process of the SF-SCWD. Moreover, nonlinear time history analysis of the 6-story frame was carried out, which confirmed the availability of the proposed structures in permanent drift mitigation.