• Journal of Korean Association for Spatial Structures
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• v.13 no.3
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• pp.45-55
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• 2013

The core aim of this paper is to empirically scrutinize a strength characteristic and ductility of the beam-column frame of reinforced with steel subjected to the cyclic lateral load. First and foremost, I the author embarks upon making four prototypes vis-$\grave{a}$-vis this research. Through this endeavour, the author has analysed cyclic behavior, fracture shape, ductility and energy dissipation of the normal beam-column frame and a beam-column frame of reinforced with steel. In addition, the survey has revealed the exact stress transfer path and the destructive mechanism in order to how much a beam-column frame of reinforced with steel has resistance to earthquake regarding all types of building, as well as school construction. To get the correct data, the author has compared the normal beam-column frame and three types of the beam-column frame of reinforced with steel following these works, the characteristic of cyclic behavior, destructive mechanism, ductility, and Energy dissipation of normal beam-column frame and a beam-column frame of reinforced with steel have been examined clearly.

• Computers and Concrete
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• v.21 no.1
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• pp.11-20
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• 2018

The possibilities of non-linear analysis of reinforced-concrete structures are under development. In particular, current research areas include structural analysis with the application of advanced computational and material models. The submitted article aims to evaluate the possibilities of the determination of material properties, involving the tensile strength of concrete, fracture energy and the modulus of elasticity. To evaluate the recommendations for concrete, volume computational models are employed on a comprehensive series of tests. The article particularly deals with the issue of the specific properties of fracture-plastic material models. This information is often unavailable. The determination of material properties is based on the recommendations of Model Code 1990, Model Code 2010 and specialized literature. For numerical modelling, the experiments with the so called "classic" concrete beams executed by Bresler and Scordelis were selected. It is also based on the series of experiments executed by Vecchio. The experiments involve a large number of reinforcement, cross-section and span variants, which subsequently enabled a wider verification and discussion of the usability of the non-linear analysis and constitutive concrete model selected.

• Magazine of the Korean Society of Agricultural Engineers
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• v.38 no.3
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• pp.58-69
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• 1996

In recent years, the research and development about the new material proceeds rapidly and actively. In building industry, high strength concrete is of interest as a new material. Since the building structure becomes bigger, higher and more specialized, the demand of material and member with high strength expands greatly. Therefore in this experiment, cement complex with high strength was made using the condensed silica fume, a basic experiment was performed on strength property, and optimum-mixture-state was determined for manufacturing a high-strength concrete. Shear behaviour and fracture property of concrete beams with high strength were evaluated. On the whole, in spite of many researches, it is one of the difficult problems that shear fracture of concrete beams has not yet been clearly understood theoretically, and now the shear-design-standard forms in many countries are a formula based on experiment. In this study, the variable of shear behavior experiment was shear-reinforcement-ratio. By analyzing test results and comparing with computation value by ACI code, the basic data was offered on shear design of reinforced concrete beams with high strength. The effect of epoxy repair was also investigated for the beams with cracks due to flexural and shear loading.

• Advances in concrete construction
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• v.11 no.2
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• pp.163-171
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• 2021

This paper studies the effect of using multi-scale reinforcement additives on mechanical strengths, damage performance, microstructure, and water absorption of cementitious composites. Small dosages of carbon nanotubes (CNTs) or polypropylene (PP) microfibers; 0.05%, 0.1%, and 0.2% by weight of cement; were added either separately or simultaneously into cement mortar. The experimental results show the ability of these additives to enhance the mechanical behavior of the mortar. The best improvement in compressive and flexural strengths of cement mortar reaches 28% in the case of adding a combination of 0.1% CNTs and 0.2% PP fibers for compression, and a combination of 0.2% CNTs and 0.2% PP fibers for flexure. Adding CNTs does not change the brittle mode of failure of plain mortar whereas the presence of PP fibers changes it into ductile failure and clearly enhances the fracture energy of the specimens. Scanning electron microscopic (SEM) images of the fracture surfaces highlights the role of CNTs in improving the adhesion between the PP fibers and the hydration products and thus enhance the ability of the fibers to mitigate cracks propagation and to enhance the mechanical performance of the mortar.

• Journal of the Korea Concrete Institute
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• v.26 no.2
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• pp.159-169
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• 2014

This study generalizes the lateral load-displacement relationship of reinforced concrete shear walls from the section analysis for moment-curvature response to straightforwardly evaluate the flexural capacity and ductility of such members. Moment and curvature at different selected points including the first flexural crack, yielding of tensile reinforcing bar, maximum strength, 80% of the maximum strength at descending branch, and fracture of tensile reinforcing bar are calculated based on the strain compatibility and equilibrium of internal forces. The strain at extreme compressive fiber to determine the curvature at the descending branch is formulated as a function of reduction factor of maximum stress of concrete and volumetric index of lateral reinforcement using the stress-strain model of confined concrete proposed by Razvi and Saatcioglu. The moment prediction models are simply formulated as a function of tensile reinforcement index, vertical reinforcement index, and axial load index from an extensive parametric study. Lateral displacement is calculated by using the moment area method of idealized curvature distribution along the wall height. The generalized lateral load-displacement relationship is in good agreement with test result, even at the descending branch after ultimate strength of shear walls.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.137-140
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• 2008

If the flexural member of concrete is designed using the FRP rebar, suddenly brittleness destruction resulted from the fracture of FRP rebar is generated in the extreme situation because of brittleness characteristics of FRP rebar and concrete when designed to be less than balanced reinforcement ratio, so it is recommended to design the flexural member of concrete to be more than balanced reinforcement ratio. In ACI 440.1R-06 proposes the different bending strength decrease coefficient according to destructive form of concrete flexural member using the FRP rebar. However, ACI 440.1R-06 applies the same strength decrease coeffient to all FRP rebars made of diverse materials. If the same strength decrease coefficient is applied to all FRP rebars, effect of increasing the reinforcement ratio and selection of FRP rebar will be considerably limited. In this regard, we are to propose the formula to calculate the bending strength decrease coefficient in consideration of change in characteristics of FRP rebar and L/D through the reliability analysis in this paper.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.4
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• pp.285-291
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• 2011

In this study the mechanical performance of the new wave dissipating block is evaluated through experiment and numerical analysis. Also, by selecting adequate reinforcement, the improvement of the structural performance is examined. The reinforcement is designed by predicting the amount of tensile force and the location where the tensile stress develops in the new wave dissipating block through numerical analysis. The new wave dissipating block is reinforced with the ordinary steel bars and the fiber reinforced plastic(FRP) bars which have advantages in ocean environment in terms of corrosion and fatigue. The test result shows that the fracture resistance of the un-reinforced concrete block is 350 kN which is about 6.2 times that of the weight of the block. All the test blocks which are reinforced by either steel of FRP bars show strength capacity of over 900 kN which is the maximum load of the test equipment. Although the single reinforcement with larger-diameter bars has advantage in terms of construction convenience, it is recommended to use multiple number of smaller-diameter bars in order to reduce the crack width.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.3
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• pp.170-174
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• 2015

Composite ceramics of alumina-TZP(3Y) have good mechanical and electrical properties. So, They have been used as high strength refractory materials and thick film substrates, etc. In this study, Composite ceramics of alumina-TZP(3Y) were fabricated by uniaxial pressing and sintering at 1,400, 1,500, and $1,600^{\circ}C$, and their microstructures and mechanical properties were investigated. As the TZP(3Y) content in composite ceramics increases from 20 wt.% to 80 wt.%, the fracture toughness increases monotonically, which seems to be related to the higher relative density and/or toughening mechanism by means of stabilized tetragonal zirconia phase at room temperature. In contrast to the fracture toughness, Vickers hardness of the composite ceramics shows maximum value (1,938 Hv) at a 40 wt.% of TZP(3Y). The result of Vickers hardness is likely to be due to more dense sintered microstructure of composite ceramics than pure alumina and reinforcement of composite ceramics with TZP(3Y), considering that Vickers hardness of pure $Al_2O_3$ is greater than that of TZP(3Y). It is also shown that the $ZrO_2$ particles are $l^{\circ}Cated$ between $Al_2O_3$ grains and suppress grain growth each other.

• Elastomers and Composites
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• v.46 no.3
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• pp.223-230
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• 2011

Considering of utilizing renewable resources and recycled plastics, green composites consisted of recycled polyethylene (PE) as matrix and eco-friendly natural fibers as reinforcement were processed and characterized in the present study. First, the wood flour/recycled polyethylene pellets with different wood flour contents were prepared by twin-screw extrusion processing. Using the pellets, wood flour/recycled polyethylene green composites were fabricated and the effects of wood flour loading on their flexural, tensile, impact properties, heat deflection temperature and fracture behavior were investigated. It was concluded that the flexural strength, flexural modulus, tensile modulus and heat deflection temperature of wood flour/recycled polyethylene green composites were increased with wood flour, whereas the tensile strength and impact strength were decreased. The fracture behavior observed by means of scanning electron microscopy supported qualitatively the tendency of the impact strength with wood flour loading, compared with the ductile fracture pattern of recycled polyethylene.

• Smart Structures and Systems
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• v.17 no.1
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• pp.91-105
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• 2016

One of the most commonly used techniques to strengthen steel reinforced concrete structures is the application of externally bonded patches in the form of carbon fiber reinforced polymers (CFRP) or recently, textile reinforced cements (TRC). These external patches undertake the tensile stress of bending constraining concrete cracking. Development of full-field inspection methodologies for fracture monitoring are important since the reinforcing layers are not transparent, hindering visual observation of the material condition underneath. In the present study acoustic emission (AE) and digital image correlation (DIC) are applied during four-point bending tests of large beams to follow the damage accumulation. AE helps to determine the onset of fracture as well as the different damage mechanisms through the registered shifts in AE rate, location of active sources and change in waveform parameters. The effect of wave propagation distance, which in large components and in-situ can well mask the original information as emitted by the fracture incidents is also discussed. Simultaneously, crucial information is supplied by DIC concerning the moments of stress release of the patches due to debonding, benchmarking the trends monitored by AE. From the point of view of mechanics, conclusions on the reinforcing contribution of the different repair methodologies are also drawn.