• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.233-236
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• 2008

In the traditional way floors has been constructed there are no shear connectors between the concrete slab and timber joists. In this study, an existing floor system os improved by simply providing normal bolts or lag screw so that the composite action can be achieved. It is evident that the key elements in the composite beam are the shear connectors. The selection of these connectors was based on their shear capacity. The experimental study carried out in this research investigated the flexural behavior of composite beams. The experimental studies of composite beams showed that the ultimated load capacity of the proposed composite beam(LS-S10 specimen) is 1.29 times as high as the noncomposite one. Finally, it can be concluded that LS-S10 specimen consisting structural laminated timber beam and concrete slab can be significantly improved by providing appropriate shear connectors.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.453-456
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• 2008

Fiber composite is high anticorrosive, high strength and low weight ratio of strength(1/4 of reinforcing bar) so that strengthens concrete structures without increase of additional weight. But fiber composite has a brittle character which increases to the maximum stress point lineally and is suddenly destroyed. Hybrid fiber composite is developed to overcome weakness of fiber composite. The hybrid fiber composite is manufactured by bar type and consists of 9:1 volume ratio(glass : carbon). In this study the result indicates that it is purposed to find out reinforcing characteristics of hybrid fiber composite fixed with impact anchor.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.5
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• pp.171-178
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• 2006

It was presented that the spalling of high strength concrete exposed to high temperature could be reduced by using polypropylene fiber. However, as the concrete strength increase, the demanded quantity of PP fiber increase and this results in the loss of workability of ultra high strength concrete. The silica fume which is essentially mixed in ultra high strength concrete decrease the permeability of concrete, and this will increase the degree of spalling. In this study the effect of silica fume on the spalling of ultra high strength concrete and the fire resisting efficiency of PP fiber and poly vinyl alchol, instead of PP fiber, for the security of workability were experimentally examined.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.73-74
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• 2010

The objective of this research is to improve the flexural capacity of RC Beams. To delay prematured tension failure of concrete specimen and to improve flexural capacity of RC beam by increasing the contribution of FRP strengthening plates, a method for inserting a laminate to the interface between concrete and FRP materials. This method makes it possible to increase overall flexural performance of RC beam by FRP plate compared to normal RC beams and RC beam strengthened by bonded FRP plates. The new bonding technique is applicable to all types of reinforcement available FRP laminate, and in principle is also applicable to materials other than FRP.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.1
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• pp.81-94
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• 2010

This paper deals with the fracture simulation of UHPFRC girder with the interface type model. Based on the existing numerical simulation of quasi-brittle fracture in normal strength concrete, constitutive modeling for UHPFRC I-girder has been improved by including a tensile hardening at the failure surface. The finite element formulation is based on a triangular unit, constructed from constant strain triangles, with nodes along its sides and neither at the vertex nor the center of the unit. Fracture is simulated through a hardening/softening fracture constitutive law in tension, a softening fracture constitutive law in shear as well as in compression at the boundary nodes, with the material within the triangular unit remaining linear elastic. LCP is used to formulate the path-dependent hardening-softening behavior in non-holonomic rate form and a mathematical programming algorithm is employed to solve the LCP. The piece-wise linear inelastic yielding-failure/failure surface is modeled with two compressive caps, two Mohr-Coulomb failure surfaces, a tensile yielding surface and a tensile failure surface. The comparison between test results and numerical results indicates this method effectively simulates the deformation and failure of specimen.

• Journal of the Korea Concrete Institute
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• v.26 no.2
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• pp.211-218
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• 2014

In the design of reinforced rectangular concrete beam structure, the minimum amount of flexural reinforcement is required to avoid brittle failure. KCI code is based on concept of ultimate strength and usually used as a model code. But bridge design code enacted by Ministry of land, transportation and maritime affairs in 2012 is based on concept of limit state and similar to Euro code EN 1992-2. This means that the minimum reinforcement presented in both design codes has different origination and safety margin. When rectangular concrete beams with minimum reinforcement are designed according to EN and KCI codes, the amount of minimum reinforcement specified in EN code is only 76% of that in KCI code. This makes the design engineers to be confused. In this study, flexural tests were conducted on nine beams with the two different minimum reinforcement specified in KCI and EN design codes. In results, the measured ratios of nominal strength to crack strength from the test were about 25% greater than those evaluated from the equations presented in KCI and EN codes. The EN beams having only 76% of the minimum reinforcement for the KCI beams were fractured by rupture of steel reinforcement but in ductile manner. It is confirmed that the minimum reinforcement concrete beams designed according to both codes have enough safety margin in flexural capacity and moreover in ductility.

• Magazine of the Korea Concrete Institute
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• v.10 no.6
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• pp.269-280
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• 1998

Recently, application of composite materials such as fiber reinforced concretes(FRCs) and fiber reinforced plastics(FRPs) in conjunction with conventional structural components has become one of the main research areas. A proper use of advanced composite materials requires understanding their resistance mechanism and failure mode when they are applied to structures or their components. Particular considerations are given in this research to develop an analytical model which can predict the nonlinear flexural responses of bonded and unbonded prestressed concrete beams possibly having layers of different cementitious composite matrices in a section and/or FRP tendons. The block concept is used, which can be regarded as an intermediate modeling method between the couple method with one block and the layered method with multiply sliced layers in a section. In order to find a particular deflection point of a beam under load, solutions to the 2N-variables are found numerically by using approximate N-force equilibrium equations and N-moment equilibirum equations. The model is shown to successfully predict the flexual behavior of variously reinforced bonded and unbonded prestressed concrete beams. The model is also successful in simulating a gradually increasing load after sudden drop inload resistance due to fracture of one or more FRP tendons. This feature is useful in tracing the overall load-deflection response of a beam prestressed with brittle FRP tendons.

• The Journal of Engineering Geology
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• v.9 no.3
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• pp.243-251
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• 1999

Granitic rock, by its nature, contains numerous micro-discontinuities including grain boundary, microcracks, microcavities and mineral cleavages. The brittle fracture of rock is a progressive procedure in which the failure occurs with prior microcracking. In this paper, initiation, propagation and interaction of microcracks are considered to be the dominant, controlling micromechanisms of macroscopic failure. The authors show a few patterns of microcrack initiation and propagation by using sequential photographs of water-saturated granite taken under triaxial compressive state. The failure process was observed directly and continuously by a newly developed triaxial compressive test system.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.255-258
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• 2010

최근 초고층 구조물은 다양한 형태에 따른 건축 계획 및 설계에 대한 요구되어지며 이를 충족시키기 위해 다양한 구조시스템이 개발되어지고 있다. 특히 경사기둥은 구조물의 높이가 증가할수록 구조물의 면적이 점차적으로 감소하는 Tapered 형태의 비정형 초고층 구조물의 중요한 설계 및 구조요소이다. 본 논문에서는 경사기둥의 축하중에 의해 발생하는 수평력으로 인한 접합부의 영향 및 보 플랜지의 취성파괴에 대한 저항성능을 평가하기 위하여 강구조물 경사기둥 접합부에 대한 유한요소해석을 수행하였다.

• Explosives and Blasting
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• v.37 no.1
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• pp.14-23
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• 2019

It has been an always issue for the blasting or the impact analysis to consider the strength characteristics of the rock materials associate with loading rate dependency. Due to the nature of transient loading, the dynamic rock test requires a careful technique to achieve the stress equilibrium state of the specimen. In this study, to investigate the relationship between the rock dynamic strength and the stress equilibrium state, a series of dynamic uniaxial compression tests for Pocheon granite were performed. As a result, the unbalanced stress state on the specimen can lead to the premature failure on the specimen and the less estimation of dynamic strength characteristic as well as the overestimation of strain rate. Consequently, a careful consideration of rock fracture process to achieve the dynamic force balance on the specimen should be required to make an reasonable evaluation of rock dynamic strength.