• Structural Engineering and Mechanics
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• v.69 no.3
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• pp.243-255
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• 2019

Utilization of fiber beam-column element has gained considerable attention in recent years due mainly to its ability to model distributed plasticity over the length of the element through a number of integration points. However, the relatively high sensitivity of the method to modeling parameters as well as material behavior models can pose a significant challenge. Residual drift is one of the seismic demands which is highly sensitive to modeling parameters and material behavior models. Permanent deformations play a prominent role in the post-earthquake evaluation of serviceability of bridges affected by a near-fault ground shaking. In this research, the influence of distributed plasticity modeling parameters using both force-based and displacement-based fiber elements in the prediction of internal forces obtained from the nonlinear static analysis is studied. Having chosen suitable type and size of elements and number of integration points, the authors take the next step by investigating the influence of material behavioral model employed for the prediction of permanent deformations in the nonlinear dynamic analysis. The result shows that the choice of element type and size, number of integration points, modification of cyclic concrete behavior model and reloading strain of concrete significantly influence the fidelity of fiber element method for the prediction of permanent deformations.

• Magazine of the Korea Concrete Institute
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• v.11 no.2
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• pp.209-220
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• 1999

This paper is aimed to evaluate the effectiveness of flexural toughness of slab panel structures($60{\times}60{\times}10$) reinforced by steel fiber instead of wire mesh. Steel fiber used in this study is double hooked Dramix type fiber. And the fiber length is 60mm, diameter is 0.8mm, Various assessment methods of toughness index are used to estimate the proper effectiveness. In this experimental study, we find that Johnston, JCI-SF4 and EFNARC method are more effective to assess the flexural toughness of slab panels than the others. And the steel fiber is very effective alternative material to reinforce slab panel structures instead of wire mesh. Fiber volume fraction of 0.5~0.75% is more useful than the others in enhancing the post-peak energy absorption and toughness index by Johnston's $I_{5.5}$ assessment method. And the slab panels reinforcing with steel fiber are more resistant to crack propagation than wire mesh reinforcing slabs.

• Journal of the Korea Concrete Institute
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• v.27 no.3
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• pp.229-236
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• 2015

This paper describes the effect of aggregate size on compressive behavior of high-strength steel fiber reinforced concrete. The Specified compression strength is 60 MPa and the range of fiber volume fraction is 0~2%. The main variable is the aggregate size, which was used for the aggregate size of 8 and 20 mm. So, ten concrete mixtures were prepared and tested to evaluate the fresh and hardened properties of SFRC at curing ages (7, 14, 28, 56 and 91 days), respectively. Items estimated in this study are the fresh properties (air contents, slump), hardened properties (compressive strength, modulus of elasticity, post-peak response and compressive toughness). As a result, the aggregate size has little effect on the compressive strength and modulus of elasticity. On the other hand, the ductile behavior was shown after post peak and the compressive toughness was increasing as decreasing the aggregate size. These effects are clearly represented in the fiber volume fraction 2%, which are the point appeared fiber ball. It is considered that the decreasing the aggregate size has effect on the fiber dispersibility.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.965-970
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• 2002

The strengthening of concrete structures in situ with externally bonded carbon fiber is increasingly being used for repair and rehabilitation of existing structures. Carbon fiber is attractive for this application due to its good tensile strength, resistances to corrosion, and low weight. Generally bond strength and behavior between concrete and carbon fiber mesh(CFM) is very important, because of the enhanced bond of CFM. Therefore if bond strength is sufficient, it will be expected to enhance reinforcement effect. If insufficient, reinforcement effect can not be enhanced because of bond failure between concrete and CFM. This study is to investigate the bond strength of CFM to the concrete using direct pull-out test and tensile-shear test. The key variables of the experiment are the location of clip, number of clips and thickness of cover mortar. The general results indicate that the clip anchorage technique for increasing bond strength with CFM appear to be effective to maintain the good post-failure behavior.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.18-21
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• 2004

This paper discusses how steel cord and PVA hybrid fibers enhance the performance of high performance fiber reinforced cementitious composites (HPRFCC) in terms of elastic limit, strain hardening response and post peak of the composites. The effect of microfiber(PVA) blending ratio is presented. For this purpose flexure, direct tension and split tension tests were conducted. It was found that HFRCC specimen shows multiple cracking in the area subjected to the greatest bending tensile stress. Uniaxial tensile test confirms the range of tensile strain capacity from 0.5 to $1.5\%$ when hybrid fiber is used. The cyclic loading test results identified a unique unloading and reloading response for this ductile composite. Cyclic loading in tension appears not to affect the tensile response of the material if the uniaxial compressive strength during loading is not exceeded.

• 한국생물공학회:학술대회논문집
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• 2000.11a
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• pp.745-748
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• 2000

Anaerobic digester coupled with hollow fiber membrane unit. Treatment of starch waste with anaerobic digester-membrane system was studied. $0.17\;m^2$ area of hollow fiber membrane unit of known pore size was immersed into laboratory-scale anaerobic digestion system. The gas production was about $0.74\;m^3/kg$ COD treated. The COD removal efficient was about 80-95% depending on the hydraulic retention time. Crossflow ultrafiltration as Post treatment to anaerobic filter. The study conducted with different membrane pore size indicated that membrane with 1,000,000 molecular weight cut-off size gave a higher COD removal efficiency in the range of 83-87% while giving a study flux of $120-130\;L/m^2\;{\cdot}\;h$. A study was conducted to see the long term clogging effect of membrane also.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.3
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• pp.177-187
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• 2004

This investigation attempts to analyze the flexural behavior of a strengthened beam with carbon fiber sheets in three stages according to the conditions of the constituents : elastic stage, pre-yielding stage, and post-yielding stage. The proposed analytical method for strengthened beams is compared with the experimental results such as yield load, ultimate load, and flexural rigidities. The contributions of the constituents to the strengthened beam capacity are examined from the flexural analysis. The validity of using KCI strength method to estimate ultimate moment of a strengthened beam is also investigated.

• Elastomers and Composites
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• v.23 no.3
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• pp.223-229
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• 1988

The effect of triazine thiol derivative on the physical properties of silica-polychloroprene(CR) composites and glass fiber(MGF)-CR composites was investigated. Optimum cure time of the MGF composites filled with 2-dibuthylamino-4, 6-dithiol-s-triazine(DBT) was the fastest one, while maximum torque was the best in case of the silica composites filled with s-triazine-2,4,6-trithiol(TAT) on the Oscillating Disk Rheometer(ODR) test. Stress-strain curves of the composites showed that the physical properties such as 100% modulus, 300% modulus, tensile strength of the silica composites filled with DBT was very satisfactory and the silica composites filled with TAT was higher density of crosslinking than other crosslinked elastomer. In aging properties, elastomer filled DBT and TAT were progress post-curing reaction with increasing of aging time and it have been improved the tensile strength and crosslinking density.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.825-828
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• 2004

The objective of this study is to examine mechanical properties of ductile fiber-reinforced mortar designed based on micromechanics. This mortar was produced by employing raw materials commercially available in Korea. To verify property level of this material in uniaxial tension, a series of direct tensile tests were performed with varying water cement ratio. In addition to this, flexural tests as well as compressive tests were carried out. Experiments revealed that the fiber reinforced mortar exhibited high ductility represented by strain hardening behavior in uniaxial tension. Significant enhancements of ductility, in terms of strain at peak stress and post-peak behavior, were also observed during the tests in compression and in bending.

• Computers and Concrete
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• v.17 no.6
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• pp.831-848
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• 2016

This study aims to characterize the multiple cracking behavior of HTPP-ECC (High tenacity polypropylene fiber reinforced engineered cementitious composites) by Digital Image Correlation (DIC) Method. Digital images have been captured from a dogbone shaped HTPP-ECC specimen exhibiting 3.1% tensile ductility under loading. Images analyzed by VIC-2D software and ${\varepsilon}_{xx}$ strain maps have been obtained. Crack widths were computed from the ${\varepsilon}_{xx}$ strain maps and crack width distributions were determined throughout the specimen. The strain values from real LVDTs were also compared with virtual LVDTs digitally attached on digital images. Results confirmed that it is possible to accurately monitor the initiation and propagation of any single crack or multiple cracks by DIC at the whole interval of testing. Although the analysis require some post-processing operations, DIC based crack analysis methodology can be used as a promising and versatile tool for quality control of HTPP-ECC and other strain hardening composites.