• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.205-208
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• 2005

A single span-to-depth ratio function is proposed for control of deflection in one-way concrete construction. The equation can be applied to one-way slabs, beams, and flat plates. Effects of cracking, time-dependent deformation, boundary conditions, applied loading, and target deflection-to-span ratio are taken into account.

• KCI Concrete Journal
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• v.11 no.3
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• pp.45-52
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• 1999

A Computer-based iterative method is provided for the calculation of minimum thickness values for one-way slabs to satisfy the maximum permissible limits given in the ACI Building Code. An algorithm includes the effects of cracking and time-dependent effects due to creep and shrinkage. Comparison of the calculated minimum thickness values with the current ACI limits is conducted to investigate limitations of the current tabulated minimum thickness. which are constant to a range of design conditions.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.1
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• pp.10-18
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• 2016

RC(Reinfored Concrete) structures exposed to carbonation in urban city have durability degradation with extended service life and cracks in concrete causes a local accelerated carbonation. In the present work, crack effect on carbonation depth is investigated and the service life of RC structure is evaluated considering cracks from early age and time-dependent cracks based on the previous field investigation. DFP(Durability Failure Probability), safety index, and the related service life are calculated considering the time to crack width reaches to maximum crack width(0.3mm). The results with time effect on crack width show lower DFP and longer service life, which seems to be reasonable compared with conservative results from crack effect from initial stage. Furthermore, crack effect is evaluated to be insignificant on DFP and service life. The technique with time-dependent crack effect on carbonation can be effectively used for RC structure containing cracking in use.

• Journal of the Korea Concrete Institute
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• v.18 no.4 s.94
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• pp.543-552
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• 2006

The current design for crack width control in concrete bridges is incomplete in analytical models. As one of the important serviceability limit states, the crack width be considered with the quantitative prediction of the initiation and propagation of corrosion and corrosion-induced cracking. A serviceability limit state of cracking can be affected by the combined effects of bond, slip, cracking, and corrosion of the reinforcing elements. Considering life span of concrete bridges, an improved prediction of crack width affected by time-dependent general corrosion has been proposed for the crack control design. The developed corrosion models and crack width prediction equation can be used for the design and the maintenance of prestressed and non-prestressed reinforcements by varying time, w/c, cover depth, and geometries of the sections. It can also be used as the rational criteria for the maintenance of existing concrete bridges and the prediction of remaining life of concrete structures.

• Computers and Concrete
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• v.14 no.4
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• pp.369-385
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• 2014

In the existing method for analyzing the liquid tightness of the outer concrete tank in an emergency LNG spillage, the temperature variation over time inside the tank, and the concrete properties dependent on temperature and internal moisture content, have not been taken into account. In this study, the analyses for a typical LNG concrete tank subjected to thermal load due to spillage were performed with three different cases: the existing method was adopted in the first case, the transient temperature variation was considered in the second, and the temperature-moisture content dependent concrete properties were taken into account as well as the transient states of temperature in the third. The analysis results for deformation, compressive zone size, cracking, and stress of reinforcements were compared, and a discussion on the difference between the results obtained from the different analysis cases was made.

• Structural Engineering and Mechanics
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• v.34 no.2
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• pp.189-211
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• 2010

The behaviour of a reinforced concrete tension member is governed by the contribution of concrete between cracks, tension stiffening effect. Under highly repeated loading, this contribution is progressively reduced and the member response approximates that given by the fully cracked member. When focusing on the unloaded state, experiments show deformations larger than those of the naked reinforcement. This has been referred to as negative tension stiffening and is due to the fact that concrete carries compressive stresses along the crack spacing, even thought the tie is subjected to an external tensile force. In this paper a cycle-dependent approach is presented to reproduce the behaviour of the axially loaded tension member, paying attention to the negative tension stiffening contribution. The interaction of cyclic bond degradation and time-dependent effects of concrete is investigated. Finally, some practical diagrams are given to account for the negative tension stiffening effect in reinforced concrete elements.

• Structural Engineering and Mechanics
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• v.36 no.4
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• pp.513-527
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• 2010

This paper presents a three-dimensional finite element method based structural analysis model for structural analysis of reinforced concrete high-rise buildings during construction. The model considered the time-dependency of the structural configuration and material properties as well as the effect of the construction rate and shoring stiffness. Uniaxial compression tests of young concrete within 28 days of age were conducted to establish the time-dependent compressive stress-strain relationship of concrete, which was then used as input parameters to the structural analysis model. In-situ tests of a RC high-rise building were conducted, the results of which were used for model verification. Good agreement between the test results and model predictions was achieved. At the end, a parametric study was conducted using the verified model. The results indicated that the floor position and construction rate had significant effect on the shore load, whereas the influence of the shore removal timing and shore stiffness have much smaller. It was also found that the floors are more prone to cracking during construction than is ultimate bending failure.

• Magazine of the Korea Concrete Institute
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• v.5 no.2
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• pp.181-188
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• 1993

In this study, a numerical method for the material nonlinear analysis of reinforced concrete shell structures including the time dependent effects due to creep and shrinkage is developed. Degenerate shell elements with the layered approach are used. The perfect or strain hardening plasticity model in compression and the linearly elastic model in tension until cracking for concrete are employed. The reinforcing bars are considered as a steel layer of equivalent thickness. Each :steel layer has an uniaxial behaviour resisting only the axial force in the bar direction. A bilinear idealization is adopted to model elasto-plastic stress-strain relationships. For the nonlinear anaysis, incremental load method combined with unbalanced load iterations for each load increment is used. To include time dependent effects of concrete, time domain is divided into several time steps which may have different length. Some numerical examples are presented to study the validity and applicability of the present method. The results are compared with experimental and numerical results obtained by other investigator.

• Journal of the Korea Concrete Institute
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• v.17 no.5 s.89
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• pp.857-868
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• 2005

This paper deals with the accumulated damage in concrete structures due to the cyclic freeze-thaw as an environmental load. The cyclic ice body nucleation and growth processes in porous systems are affected by the thermo-physical and mass transport properties, and gradients of temperature and chemical potentials. Furthermore, the diffusivity of deicing chemicals shows significantly higher value under cyclic freeze-thaw conditions. Consequently, the disintegration of concrete structures is aggravated at marine environments, higher altitudes, and northern areas. However, the properties of cyclic freeze-thaw with crack growth and diffusion of chloride ion effects are hard to be identified in tests, and there has been no analytic model for the combined degradations. The main objective is to determine the driving force and evaluate the reduced strength and stiffness by freeze-thaw. For the development of computational model of those coupled deterioration, micro-pore structure characterization, pore pressure based on the thermodynamic equilibrium, time and temperature dependent super-cooling with or without deicing salts, nonlinear-fracture constitutive relation for the evaluation of internal damage, and the effect of entrained air pores (EA) has been modeled numerically. As a result, the amount of ice volume with temperature dependent surface tensions, freezing pressure and resulting deformations, and cycle and temperature dependent pore volume has been calculated and compared with available test results. The developed computational program can be combined with DuCOM, which can calculate the early aged strength, heat of hydration, micro-pore volume, shrinkage, transportation of free water in concrete. Therefore, the developed model can be applied to evaluate those various practical degradation cases as well.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.9
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• pp.1452-1461
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• 1997

The hot press apparatus to obtain the solidified rocks with 60mm of diameter against rock waste was developed, and the optimum conditions for solidification were founded out, of which were 300.deg. C of temperature and 1hr of holding time. The solidified rocks reinforced with the fibers (carbon, steel) were made by means of a hydrothermal hot press method. Fracture toughness of those was obtained using the round compact tension(RCT) specimens. Load and displacement behaviours of the solidified rocks reinforced with the fibers were dependent upon the fiber volume fraction and kind of the fibers. Strength and fracture energy of the solidified rocks with steel were much larger than those of the solidified ones with carbon because of the Bridge's effect, multiple cracking and crack branching phenomena.