• Structural Engineering and Mechanics
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• v.17 no.1
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• pp.15-27
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• 2004

A rational and simple analytical model to predict the time varying cracking moment of reinforced concrete sections under sustained loading is developed. The modeling procedure is based on equilibrium and compatibility requirements and takes into account the interdependent effects of creep and shrinkage as well as the presence of axial loading. A parametric study is conducted in which particular consideration is given to the effects of reinforcement ratio, level of loading, and creep and shrinkage characteristics of concrete. It is concluded that the reduction in cracking moment is mainly attributed to shrinkage. The effect of shrinkage is more pronounced at low levels of sustained loading and at high reinforcement ratios. This effect is lessened by the compression steel and creep particularly when the applied moment is near the cracking moment.

• Journal of Korea Foundry Society
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• v.40 no.5
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• pp.129-133
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• 2020

The outcomes of solution annealing and stress corrosion cracking in cold-worked 316L austenitic stainless steel have been studied using x-ray diffraction (XRD) and the slow strain rate test (SSRT) technique. The good compatibility with a high-temperature water environment allows 316L austenitic stainless steel to be widely adopted as an internal structural material in light water reactors. However, stress corrosion cracking (SCC) has recently been highlighted in the stainless steels used in commercial pressurized water reactor (PWR) plants. In this paper, SCC and inter granular cracking (IGC) are discussed on the basis of solution annealing in a chloride environment. It was found that the martensitic contents of cold-worked 316L stainless steel decreased as the solution annealing time was increased at a high temperature. Moreover, mode of SCC was closely related to use of a chloride environment. The results here provide evidence of the vital role of a chloride environment during the SCC of cold-worked 316L.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2000.04b
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• pp.238-245
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• 2000

Separation strips are temporary joints to prevent crack due to stress induced by shrinkage. In this study, an analysis procedure considering separation strip is proposed to decide proper casting time of separation strip and cracking stresses of the example building slabs are calculated using this procedure. The result of the example high rise building shows that the percentage of cracking stress to the modulus of fracture is 43.4% when closing of separation strip are 30 days after placing the slab, so it is enough time for the separation strip in each floor to absorb the effects of shrinkage.

• Journal of the Korea Institute of Building Construction
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• v.7 no.1 s.23
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• pp.91-98
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• 2007

In this study, the property and plastic cracking pattern of concrete were compared and analyzed with the replacement ratio of fly ash 0, 5, 10, 15, 20% by cement weight. And curing conditions of concrete were given variously such as indoors(with wind speed as 0, 300, 500m/min), outdoors and chamber. The hydration temperature had a tendency to decrease as the replacement ratio of fly ash increased, and in the case of the wind speed 0m/min, it was showed that the moment that the amount of evaporation of water from surface of reference concrete was more than the volume of bleeding was 90 min since casting concrete. The time that the crack initiated had a tendency to be more quickly as the replacement ratio of fly ash increased. The number, length, width and area of crack in the indoor curing, exposed outdoor curing, enclosed outdoor curing had a tendency to decrease as the replacement ratio of fly ash increased. The crack had a tendency to decrease in sequence of exposed outdoor, enclosed outdoor curing, indoors curing. The outbreak of cracking by the change of temperature and humidity was affected by relative humidity more than temperature and the cracking had a tendency to increase as relative humidity lowered.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.265-268
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• 2004

Plastic shrinkage cracking is a major concern for concrete, especially for flat structures as highway pavement, bridge deck slabs, and bridge deck pavement. LMC(Latex Modified Concrete) be used mainly for bridge deck overlays, so occurrence possibility of plastic shrinkage cracking is very high. But LMC is form a close-packed layer of polymer particles in very early time from the time of adds the latex and water. So plastic shrinkage cracking compare with normal concrete is not occur at final setting time. Results indicates that LMC is advantage to prevent occurrence of plastic shrinkage crack and it's possible co construction for bridge deck overlay effectively.

• Advances in concrete construction
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• v.17 no.5
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• pp.257-271
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• 2024

During any construction involving mass concrete, it is crucial to control cracking during the placement and curing process. This study develops an intelligent cooling control system that regulates water temperature and flow based on concrete hydration heat, effectively preventing cracking in bridge construction. The system consists of hardware, a neural network-based control algorithm, and an information management system. An optimal cooling control strategy is proposed to dynamically regulate water flow and temperature, preventing cracking by utilizing real-time temperature data, target control curves, neural network algorithms, and cloud-based computing. The intelligent cooling control system has been successfully implemented in controlling cracking risks during bridge construction. It not only mitigates the risk but also provides a convenient management strategy for bridge construction projects. The optimal cooling control strategy ensures high accuracy and stability under unsupervised learning conditions. This intelligent cooling control system can be applied to similar constructions such as bridge, dam, and building that involve the use of mass concrete.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.1 s.173
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• pp.156-162
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• 2000

Sensitized STS 304 stainless steel crack growth rate(CGR) in high temperature water was investigated under trapezoidal wave loading test using fracture mechanics techniques. The CGR, due to stress corrosion cracking(SCC), were systematically measured as a function of the stress intensity factor and stress. holding time under trapezoidal wave loading. In high temperature water, CGR was enhanced by a synergistic effects in combination with an aggressive environment and mechanical damage. The CGR, $(da/dN)_{env}$ was basically described as a summation of the environmentally assisted crack growth rate $(da/dN)_{SCC}$, $(da/dN)_{CF}$ and fatigue crack growth rate in air $(da/dN)air,. The CGR, $(da/dN)_{env}$, increased linearly with increasing stress holding time. The CGR, $(da/dN)_{SCC}$ decreased linearly with increasing stress holding time. Fracture surface mode varied from trans-granular cracking to inter-granular cracking with increasing stress holding time.

• Corrosion Science and Technology
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• v.15 no.5
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• pp.203-208
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• 2016

DC potential drop technique was employed during the slow strain rate tests to study the hot salt stress corrosion crack (HSSCC) initiation at 300 and $400^{\circ}C$. Threshold stresses for HSSCC initiation were found to about 88 % of the yield strength at both temperatures, but the time from crack initiation to final failure (${\Delta}t_{scc}$) decreased significantly with temperature, which reflects larger tendency for brittle fracture and secondary cracking. The brittle fracture features consisted of transgranular cracking through the primary ${\alpha}$ grain and discontinuous faceted cracking through the transformed ${\beta}$ grains.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.657-662
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• 2003

In this study. a micro-corrosion model of steel in RC structure is established for micro-structure development in view to micro-mechanics and the model is composed of chloride penetration model and oxygen diffusion model to evaluate for corrosion rate and accumulated corrosion amounts. Also the model is composed of corrosion-cracking model for prediction of corrosion-cracking. The time and space dependent induced corrosion-cracking of RC structures including changes of corrosion rates and concentrations of chloride ion are simulated using the finite element analysis adopted the proposed model Then, results of the analysis are compared with test results for verification.

• Journal of Welding and Joining
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• v.32 no.2
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• pp.18-21
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• 2014

Cold cracking of weldment is one of the most serious welding problems. A sufficient quantity of diffusible hydrogen, a residual stress, and a sensitive microstructure are the causes of cold cracking. Removal of any one of these factors can be used to prevent cold cracking. Application of flux cored arc welding process is increasing due to high productivity and easiness of welding. In addition, to prevent cold cracking in the HAZ or weldment, preheat temperature and interpass temperature have to be controlled. In this study, the effect of preheat temperature on the levels of diffusible hydrogen in the weld metal deposited using flux cored wire was examined. The levels of preheat temperature of base metal specimen were ambient temperature, 50, 100 and $150^{\circ}C$ respectively. The result showed that the increase of preheat temperature was a linear relationship with reduction of diffusible hydrogen content in weldment.