• Structural Engineering and Mechanics
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• v.70 no.3
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• pp.257-267
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• 2019

Expressions for the calculation of ductility index for concrete girders with different ratios of prestressed and classical reinforcement were proposed using load-displacement, load-strain and load-curvature relation. The results of previous experimental static tests of several large-scale concrete girders with different ratio of prestressed and classical reinforcement are briefly presented. Using the proposed expressions, various ductility index of tested girders were calculated and discussed. It was concluded that the ductility of girders decreases approximately linearly by increasing the degree of prestressing. The study presents an expression for the calculation of the average ductility index of classical and prestressed reinforced concrete girders, which are similar to the analysed experimental test girders.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.202-207
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• 2004

An elastic-plastic finite element analysis of fatigue crack closure is performed for plane strain conditions. The stabilization behavior of crack opening level and the effect of mesh size on the crack opening stress are investigated. In order to obtain a stabilized crack opening level for plane strain conditions, the crack must be advanced through approximately four times the initial monotonic plastic zone. The crack opening load tends to increase with the decrease of mesh size. The mesh size nearly equal to the theoretical plane strain cyclic plastic zone size may provide reasonable numerical results comparable with experimental crack opening data. The crack opening behavior is influenced by the crack growth increment and discontinuous opening behavior is observed. A procedure to predict the most appropriate mesh size for different stress ratio is suggested. Crack opening loads predicted by the FE analysis based on the procedure suggested resulted in good agreement with experimental ones within the error of 5 %. Effect of the distance behind the crack tip on the crack opening load determined by the ASTM compliance offset method based on the load-displacement relation and by the rotational offset method based on the load-differential displacement relation is investigated. Optimal gage location and method to determine the crack opening load is suggested.

• Journal of Korean Society of Steel Construction
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• v.22 no.4
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• pp.365-375
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• 2010

Concrete-filled steel tube columns are expected to have confined effects of the steel on the concrete and reinforced local buckling effects of the concrete. After comparing the results of existing studies with the experimental results from this study, the stress-strain relations were modified by evaluating the load-displacement with consideration of the confined effects. The effects of the parameters on the load-displacement and moment-curvature relationship according to the sectional and material properties were analyzed.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.739-744
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• 2001

The concrete bridge deck is quitely required to be replaced or strengthened due to decreasing load carrying capacity. In this study, to increase load capacity of the reinforced concrete slab, bridge deck is reinforced with the glass fiber sheets. they are examined on the strengthen effect and the static behavior, This paper considers relation of load-displacement and strain-distance. The static behavior of the slab strengthened is represented to maximum load. Owing to that, they are examined on increasing load carrying capacity of reinforced bridge deck and strengthen effect about on the crack.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.308-313
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• 2004

SP test has been confirmed the availability, however the application of SP test is hampered because the relation of stress-strain and load-displacement is not determined definitely. This study suggested an evaluation technique of plastic flow characteristic for X20CrMoV121 steel weldment through inverse analysis using SP test and finite element analysis(FEA). From the result, good agreement was found in load-displacement curves obtained from SP test and FEA. Also, The behavior of load-displacement curve from FEA show a rule that load is increase with increasing K(strength coefficient) and displacement is increase with increasing n(work hardening index). From the inverse analysis, true stress-strain curve could be obtained for each local structure of weldment. And the CGHAZ and WM, which showed lower load- displacement behavior, have smaller work hardening index, while FGHAZ have the largest index.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.3A
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• pp.265-275
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• 2010

Concrete filled steel tube and concrete encased steel tube columns are expected to have confined effects of concrete by steel and reinforced effects of local buckling by concrete. On the basis of confined state concrete models of previous researches, stress-strain and load-displacement relations of RC, CFT and CET columns are analyzed by steel ratio. After comparing analysis results with experimental results, Modified stress-strain relations are derived through evaluation the influence upon confined effects of concrete in each cases. Also, the modified stress-strain models are carried out to be compared with specified strength of various countries.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.727-732
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• 1999

In this research, we made an experiment on the 10 specimen beams that we made. The specimen beams consist of 4 steel plate strengthening beams and 5 carbon fiber sheet strengthening beams. We applied the methods of notch, rounding off a edge, anchor bolt and side shear strengening to the steel plate and for the case of carbon fiber sheet, we applied the methods of anchor bolt, line anchor and shear strengthening. After all the cases were applied, the beams was measured and analyzed about the behavior property of strengthened beams, th ability of strengthening method, the relation between load and the shape of failure, the crack load, the yield load, the shape of crack pattern, the increasing rate from yield load and maximum load and the strain of rebar. All the strengthening methods resulted in almost same value until the yield load, and it wasn't quite different from the theoretical value. In comparison with existing method, the SER, SEAS for the steel plate and the CEA, CESS, CCESS for carbon fiber sheet showed the increasement of ductility with big displacement.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.611-616
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• 2002

The concrete beam is quickly required to be replaced or strengthened due to decreasing load carrying capacity. Flexural tests on 3.1m long reinforced concrete beams with carbon-fiber rod are reported. The selected experimental variable is the method of the anchoring beam. The effects of this variable in overall behavior are discussed. This paper considered relation of load-displacement and load-strain. The maximum load was increased to the static behavior of the R/C beam strengthened with CFR rod. The results indicated generally that the flexural strength of strengthening beam was increased. It was required a proper anchorage system and can be led the ductility of beams of a carbon-fiber rod.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.6
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• pp.1-9
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• 2009

An analysis program to predict the behavior of a concrete filled steel tube column (CFT) was developed. It considered confining effect, material nonlinearity, strain hardening of steel, and initial axial load. With the developed program, axial load-bending moment interaction analyses, moment-lateral displacement relation analyses, and lateral load-lateral displacement relation analyses were performed. For the verification of the developed program, analysis results were compared with the test results from the other researches. The verified results showed that the developed program predicted the behavior of the CFT column with agreeable accuracy. And they showed that it is necessary to consider the confining effect for the reasonable analysis of the CFT column. A simple parametric study was performed and it chose the strength of unconfined concrete and the thickness of a steel tube as the major parameters affecting the behavior of the CFT column. The parametric analysis results showed that the CFT column had higher strength and smaller ductility by increasing the strength of concrete. But the CFT column showed higher strength and larger ductility by increasing the thickness of the steel tube.

• International Journal of Concrete Structures and Materials
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• v.18 no.3E
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• pp.213-219
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• 2006

Modified singular fracture process zone(S-FPZ) model is proposed in this paper to determine a fracture criterion for continuous crack propagation in concrete. The investigated fracture properties of the proposed fracture model are strain energy release rate at a micro-crack tip and the relationship between crack closure stress(CCS) and crack opening displacement(COD) in the FPZ. The proposed model can simulate the actual fracture energy of experimental results fairly well. The results of the experimental data analysis show that specimen geometry and loading condition did not affect the CCS-COD relation. However, the strain energy release rate is a function of not only specimen geometry but also crack extension. The strain energy release rate remained constantly at the minimum value up to the crack extension of 25 mm, and then it increased linearly to the maximum value. The maximum fracture criterion occurred at the peak load for specimens of large size. The fracture criterion remained at the maximum value after the peak load. The variation of the fracture criterion is caused by micro-cracking and micro-crack localization. The fracture criterion of strain energy release rate can simply be the size effect of concrete fracture, and it can be used to quantify the micro-cracking and micro-crack localizing behavior of concrete.