• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.24 no.12
• /
• pp.3010-3017
• /
• 2000

For integrity evaluation of cracked or damaged structures, fracture toughness test results in ASTM are widely used. The fracture toughness values of the structures are used as an effective design criterion in nuclear plants and aircraft structures. Sometimes the difference of P-$\delta$ curve trend during the unloading /reloading cycle in the fracture toughness test using partial unloading compliance was observed. The phenomenon as a possible source of error in determining fracture toughness may be caused by the residual stress during unloading work-hardening and bucking of a specimen. Therefore, we evaluate the effect of bucking and compressive residual stress during the K-R and J-R testing using a finite element method.

• Journal of the Korea Concrete Institute
• /
• v.12 no.4
• /
• pp.69-78
• /
• 2000

Creep of concrete is the most dominating factor affecting time-dependent deformations of concrete structures. Especially, creep deformation for design and construction in prestressed concrete structures should be predicted accurately because of its close relation with the loss in prestree of prestressed concrete structures. Existing creep-prediction models for special applications contain several impractical factors such as the lack ok accuracy, the requirement of long-term test and the lack of versatility for change in material properties, ets., which should be improved. In order to improve those drawbacks, a methodology to modify the creep-prediction equation specified in current Korean concrete structures design standard (KCI-99), which underestimates creep of concrete and does not consider change of condition in mixture design, is proposed. In this study, short-term creep tests were carried out for early-age concrete within 28 days after loading and their test results on influencing factors in the equation are analysed. Then, the prediction equation was modified by using the early-age creep test results. The modified prediction equation was verified by comparing their results with results obtained from long-term creep test.

• Steel and Composite Structures
• /
• v.11 no.5
• /
• pp.391-402
• /
• 2011

It is clear from the former researches on reinforced concrete filled steel tubular (RCFT) structures that RCFT structures have higher strength and deformation capacity than concrete filled steel tubular (CFT) structures. However, in the case of actual applications to large-scaled structures, the thin-walled steel tube must be used from the view point of economic condition. Therefore, in this study, compression tests of RCFT columns which were made by thin-walled steel tube or small load-sharing ratio in cooperation with high strength concrete were carried out, meanwhile corresponding tests of CFT, reinforced concrete (RC), pure concrete and steel tube columns were done to compare with RCFT. By the a series of comparison and analysis, characteristics of RCFT columns were clarified, and following conclusions were drawn: RCFT structures can effectively avoided from brittle failure by the using of reinforcement while CFT structures are damaged due to the brittle failure; with RCFT structures, excellent bearing capacity can be achieved in plastic zone by combining the thin-walled steel tube with high strength concrete and reinforcement. The smaller load-sharing ratio can made the reinforcement play full role; Combination of thin-walled steel tube with high strength concrete and reinforcement is effective way to construct large-scaled structures.

• Journal of Welding and Joining
• /
• v.27 no.6
• /
• pp.49-54
• /
• 2009

In this study, the numerical analysis model for fatigue life prediction of welded structures are presented. In order to evaluate the structural degradation of welded structures due to fatigue loading, continuum damage mechanics approach is applied. Damage evolution equation of welded structures under arbitrary fatigue loading is constructed as a unified plasticity-damage theory. Moreover, by integration of damage evolution equation regarding to stress amplitude and number of cycles, the simplified fatigue life prediction model is derived. The proposed model is compared with fatigue test results of T-joint welded structures to obtain its validation and usefulness. It is confirmed that the predicted fatigue life of T-joint welded structures are coincided well with the fatigue test results.

• Proceedings of the KSME Conference
• /
• 2007.05a
• /
• pp.502-505
• /
• 2007

PMMA has been extensively adopted in Nano Imprint Lithography(NIL). PMMA nano-structures experience severe mechanical load and deformation during NIL process, and understanding its mechanical behavior is very important in designing and optimizing NIL process. One of the most promising techniques for characterizing the mechanical behavior of nano structures is nano pillar compression test. In this study, the mechanical behaviors of PMMA pillars during compression test are analyzed using Molecular Dynamics. Two methods for simulation of PMMA nano pillars are proposed. The stress-strain relationship of nano-scale PMMA structure is obtained based on CVFF(Covalent Valence Force Fields) potential and the dependency of the applied strain rate on the stress-strain relationship is analyzed. The obtained stress-strain relationships can be useful in simulating nano-scale PMMA structures using Finite Element Method(FEM) and understanding the experimental results obtained by compression test of PMMA nano pillars.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1998.10b
• /
• pp.894-899
• /
• 1998

To absorb the deformation of live load, thermal gradient, shrinkage and creep in bridge structures and general structures, expansion joint has to be established. Especially expansion joint for high-speed railway bridge has to accomodate the static and dynamic forces and it not only has the durability of itself but also maintain the durability of structure by preventing the leakage of water. The actual used product of expansion joint for high-speed railway bridge is only ones made in France, Germany and Japan. In this study, the development process and test results of developed expansion joint are introduced which has the functional operation and durability enough to apply to high-speed railway bridges, roadway bridges and general structures. The tests consist of fatigue-durability test of 3 million times by high-speed rail load, leakage test and jack-up test for verifying the possibility of exchanging it. The performance of developed expansion joint satisfy the specification of Korea High Speed Rail Construction authority.

• Steel and Composite Structures
• /
• v.1 no.2
• /
• pp.231-244
• /
• 2001

The strengthening of reinforced concrete structures using externally bonded steel or advanced fibre reinforced plastic (FRP) composites is becoming increasingly common. A key factor affecting the behaviour and reliability of such strengthened structures is the bond strength between the steel or FRP plate and the concrete substrate. Several different experimental set-ups have previously been used to determine bond strength. This paper presents a careful finite element analysis of the stress distributions in these test set-ups. Results show that stress distributions can be significantly different for different set-ups, for similar materials and geometry.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.5 no.4
• /
• pp.197-203
• /
• 2001

This study presents the results of shaking table test of scaled model structures with added viscoelastic dampers, which are considered to be one of the most efficient means of upgrading existing structures against seismic loads. The experimental results were compared with those from analysis based on the linear modeling of viscoelastic dampers. The parameters obtained from free vibration test were utilized in the analysis. According to the results the added viscoelastic dampers turned out to be effective in reducing the responses of the model structures. It was also found that the analysis with linear modeling of viscoelastic dampers could simulate the test results accurately.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.26 no.3
• /
• pp.117-125
• /
• 2022

In this study, centrifuge model tests were performed to evaluate the seismic response of multi-DOF structures with shallow foundations. Also, elastic time history analysis on the fixed-base model was performed and compared with the experimental results. As a result of the centrifuge model test, earthquake amplification at the fundamental vibration frequency of the soil (= 2.44 Hz) affected the third vibration mode frequency (= 2.50 Hz) of the long-period structure and the first vibration mode (= 2.27 Hz) of the short-period structure. The shallow foundation lengthened the periods of the structures by 14-20% compared to the fixed base condition. The response spectrum of acceleration measured at the shallow foundation was smaller than that of free-field motion due to the foundation damping effect. The ultimate moment capacity of the soil-foundation system limited the dynamic responses of the multi-DOF structures. Therefore, the considerations on period lengthening, foundation damping, and ultimate moment capacity of the soil-foundation system might improve the seismic design of the multi-DOF building structures.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.04a
• /
• pp.429-432
• /
• 2008

Large area members such as foundation concrete of underground structures in power plants have an effect on structural stability and durability of the structure due to danger of crack occurrence and shrinkage crack that occur owing to the difference of temperature by heat of hydration between inside and outside of the members at initial age. And a construction for waterproofness is performed additionally to protect marine structures from osmosis of seawater because the structures adjoin below the surface of sea. So, if a rise of the heat of hydration, crack, and corrosion of bars are controled effectively using a composite such as fluosilicate salt in concrete production process of a initial construction, expenses are cut down and construction hours are reduced by securing durability through improvement of watertightness. The property tests of adiabatic temperature by hydration are carried out at initial age about standard concrete and test concrete using a fluosilicate salt composite to evaluate an effect on improvement of watertightness for concrete structures in this study. And the experiments such as a permeability test of hardened concrete, a water absorption test, a compression strength test and a elongation test are carried out and the results from these are described.