• Journal of the Korea Concrete Institute
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• 제28권3호
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• pp.279-288
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• 2016

The present study simplified the moment-curvature relationship to straightforwardly determine the flexural behavior of reinforced concrete (RC) columns. For the idealized column section, moments and neutral axis depths at different stages(first flexural crack, yielding of tensile reinforcing bar, maximum strength, and 80% of the maximum strength at the descending branch) were derived on the basis of the equilibrium condition of forces and compatibility condition. Concrete strains at the extreme compression fiber beyond the maximum strength were determined using the stress-strain relationship of confined concrete, proposed by Kim et al. The lateral load-displacement curves converted from the simplified moment-curvature relationship of columns are well consistent with test results obtained from column specimens under various parameters. The moments and the corresponding neutral axis depth at different stages were formulated as a function of longitudinal reinforcement and transverse reinforcement indices and/or applied axial load index. Overall, curvature ductility of columns was significantly affected by the axial load level as well as concrete compressive strength and the amount of longitudinal and transverse reinforcing bars.

• KSCE Journal of Civil and Environmental Engineering Research
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• 제33권4호
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• pp.1349-1360
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• 2013

The post-tensioned anchorage zones of normal concrete have larger cross sections because of congested reinforcements to resist high bearing and bursting stresses. The high compressive and tensile strength of newly developed UHPC (Ultra High Performance Concrete) may reduce the cross sectional dimensions and simplify the reinforcement details, if used for post-tensioned members. The Finite Element Analysis was performed to evaluate the mechanical behavior of post-tensioned anchorage zones using UHPC without anchorage plates and confining reinforcements. The results show that the maximum bursting stresses are less than the values given in current design code without failure due to vertical cracks. The location of maximum bursting stresses were at 0.2 times of width of the models. The bursting force from FEA is less than that is obtained using simplified formular in Korean Bridge Design Code.

• Transactions of the Korean Society of Mechanical Engineers A
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• 제25권3호
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• pp.510-519
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• 2001

The tensile and fracture toughness tests have been conducted to investigate the degradations of mechanical properties induced mainly by neutron irradiations in Zr-2.5Nb CANDU pressure tube materials operated in Wolsung Unit-1. the tests were performed at room, 150, 200, 250, 300 $\^{C}$ for the irradiated and unirradiated specimens in hot cell. The specimens were directly machined from the tube retaining original curvature using specially designed electric discharge machine(EDM). From the tensile tests of the irradiated specimens, it was found that tensile strength was increased and total elongation was decreased compared to those of the unirradiated ones. The active voltages in the fracture toughness tests for the irradiated showed the discontinuous abrupt increases caused by crack jumping in lower temperature. In the crack resistance curves we found the stable crack growth in the unirradiated, whereas the unstable and three crack growth stages in the irradiated specimens due to the accumulated irradiation defects. The various fracture characteristic values in the irradiated are remarkably lower than those of the unirradiated. Through the fractography, we found in the irradiated that smaller dimple and shorter fissures than the unirradiated, and that the fractured surface had three regions that were flat, transition and slant/shear area. These can explain the difference in the crack growth characteristic values of the irradiated and the unirradiated ones.

• Transactions of the Korean Society of Mechanical Engineers A
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• 제25권4호
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• pp.592-601
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• 2001

Fiber reinforced metal laminates(FRMLs) are new types of hybrid materials. FRMLs consists of high strength metal(Al 5052-H34) and laminated fiber with structural adhesive bond. The mixture ratio effect of epoxy resin$.$curing agent$.$accelerator on the fatigue behavior of FRMLs was investigated in this study. The epoxy, diglycidylether of bisphenol A(DGEBA), was cured by methylene dianiline(MDA) with or without an accelerator(K-54). Eight different kinds of resin mixture ratios were selected for the test ; five kinds of FRMLs(1) and three others of FRMLs(2). The relationship between da/dN and ΔK with variation of resin mixture ratio was studied. FRMLs(1) and FRMLs(2) indicated approximately 2 times and 2.2 times more improved maximum bending strengths in comparison with those of Al 5052-H34. The resin mixture ratio <1:1> in case of FRMLs(1) indicated the maximum fatigue life, while the resin mixture ratio <1:1:0.2> in case of FRMLs(2) indicated the maximum fatigue life. As results, FRMLs(2) turned out to have more effective characteristics on the fatigue properties and the bending strength than those of FRMLs(1).

• Journal of the Computational Structural Engineering Institute of Korea
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• 제30권1호
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• pp.55-61
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• 2017

Recently several researches have been conducted to develop sliding track system in which friction between concrete track and bridge slab has been reduced. This paper investigated shear load carrying capacity of lateral supporting concrete block which should be implemented to resist lateral load due to train in sliding track system. In order to evaluate shear load carrying capacity of lateral supporting concrete block, analytical model has been developed considering concrete friction and rebar dowel action along construction joint. The proposed model predicted test results on the shear load carrying capacity from literature conservatively by 13~23% because effect of aggregate interlock along crack surface was neglected. Since construction joint status is ambiguous on construction site, it can be concluded that the proposed model can be used for reasonable design of lateral supporting concrete block. Based on the proposed model, design proposal for lateral supporting concrete block has been established.

• Journal of Fisheries and Marine Sciences Education
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• 제9권2호
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• pp.198-208
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• 1997

Recently, with rapid increase of gas demand, there occurs much interest their security of safety in the gas storage tanks and pressure vessels etc. In order to solve the problems, the occurrence of corrosion fatigue crack and the propagation behavior must be investigated. Especially the occurrence of corrosion fatigue crack and the propagation behavior in the part which has concentrated stress or defects, must be studied more carefully. In this paper, the high-tensile steel of SPV 50 which is much used for building the LPG storage tanks was tested by the use of a plane bending corrosion fatigue tester under the various marine environment and in the air. These experiments were carried out to investigate the surface crack propagation behavior, the value of experimental constant for Paris' rule(da/dN=$C(K)^m$), the crack depth propagation rate and the accelerative factor of the surface crack propagation rate. The main results obtained are as follows ; 1) As the specific resistances of marine environment decreases, the exponential value of slope m of Paris' rule(da/dN=$C(K)^m$) decreases and the value of intercept C increases. 2) The surface crack propagation rate and the crack depth propagation rate are delayed, as the specific resistances of marine environment is increased. 3) The accelerative factor of the surface crack propagation rate by corrosion fatigue is higher, according as the stress intensity factor range ${\Delta}K_A$ is small.

• Journal of the Korean Society for Nondestructive Testing
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• 제7권2호
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• pp.42-47
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• 1988

The off-axis tensile strength of the unidirectional carbon fiber reinforced plastic and the residual strength of impact damaged CFRP were measured and compared with the stress wave factor (SWF) of the specimens. The SWF values were measured to be decreased with the strength reduction in both cases and found to be useful for the nondestructive strength evaluation of unidirectional CFRP. The failure behaviour of the unidirectional CFRP during off-axis tensile testing was also monitored by acoustic emission(AE) method. The AE energy release showed the characteristic feature depending on the off-axis angle and this result was analyzed to be caused by the difference of the expected failure mode depending on the off-axis angle. The failure mode of CFRP was found to be analyzed by investigation of the peak amplitude distribution of AE.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• 제40권4호
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• pp.344-350
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• 2004

This is the study on dry sliding wear behavior of unidirectional carbon fiber reinforced epoxy matrix composite at ambient temperature. The wear rates and friction coefficients against the stainless steel counterpart specularly processed were experimentally determined and the resulting wear mechanisms were microscopically observed. Three principal sliding directions relative to the dominant fiber orientation in the composite wear selected. When sliding took place against smooth and hard counterpart, the highest were resistance and the lowest friction coefficient were observed in the antiparallel direction. When the velocity between the composite and the counterpart went up, the wear rate increased. The fiber destruction and cracking caused fiber bending on the contact surface, which was discovered to be dominant wear mechanism.

• Fire Science and Engineering
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• 제18권3호
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• pp.51-56
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• 2004

A fire outbreak in a reinforcement concrete structure looses the organism by the different contraction and expansion of hardened cement pastes and aggregate, and causes cracks by thermal stress, leading to the deterioration of the durability. So concrete reinforcement structure is damaged partial or whole structure system. Therefore diagnosis of deterioration is needed based on mechanism of fire deterioration in general concrete structures. Fundamental information and data on the properties of concrete exposed to high temperature are necessary for accurate diagnosis of deterioration. In this study, it was presented data for the accurate diagnosis and selection of repair and reinforcement system for the deteriorated concrete heated highly, various concrete such as standard design compressive strength, fine aggregate and admixture were exposed to a high temperature environment. And fundamental data were measured engineering properties such as explosive spatting, ultrasonic pulse velocity and compressive strength.

• Magazine of the Korea Concrete Institute
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• 제9권1호
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• pp.105-113
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• 1997

The reduction phenomena of concrete compressive strength with the size of cylinders have been very interested in, but till now the adequate. analysis technique is not fixed. Based on the existing research results. the bigger the member size is, the smaller the strengt.h is. However. the real test ~.csults reveal that the wduction rate becomes blunt and there are considerable differences between size offrct law and real results. The punposc. ofthis paper is to propose tho model equat.ion which covers the compressive strength of' cylinder specimens in case of general hight/dialnetcr ratio in terms of the size effect. he effect of maximum aggregate size on the microcrack zone was also studied, and the model equation was proposed by considering the concept of'the characteristic length. These results will also be used to predict the cornprcssivt. stxngth of various sized concrete cores sampled from existing structures.