2022/06/28 更新

写真a

リム ソーポーケム
リム ソーポーケム
所属
理工学術院 創造理工学部
職名
講師(任期付)

学位

  • Waseda University   Ph.D.

 

研究分野

  • 構造工学、地震工学   Concrete material and structural engineering

研究キーワード

  • Material engineering

  • Concrete structural engineering

  • Concrete material engineering

  • FE modeling

  • X-ray technology

  • Steel fiber reinforced concrete

  • Spatial variability in steel corrosion

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論文

  • Modelling method of fibre distribution in steel fibre reinforced concrete based on X-ray image recognition

    Yue Li, Xin Ruan, Mitsuyoshi Akiyama, Mingyang Zhang, Jiyu Xin, Sopokhem Lim

    Composites Part B: Engineering   223  2021年10月

     概要を見る

    The accurate and efficient simulation of steel fibre reinforced concrete (SFRC) is of great significance for its further application in civil engineering. Problems of existing modelling methods can be recognized as two points; (1) the integral model only simplified fibre contribution into the unified post-peak ductility in concrete element but cannot reflect the material variation caused by real fibre distribution, and (2) the separate model built the concrete matrix and fibre inclusions respectively, but the directly random fibre distributions still need to be refined based on the actual material. In this paper, based on the X-ray image recognition results from real SFRC material, a mathematical model of fibre distribution and orientation is proposed for SFRC simulation, and the detailed value distributions of geometrical parameters are optimized for convenience and accuracy of material modelling. In the geometrical extraction of near 4000 fibres from X-ray images, the whole comprehensive procedure of image processing, enhancement and recognition is presented with technologies like pixel semantic classification and Hough transform. With the proposed geometrical mathematical model, the modelling method that consists of multiple refined sampling is illustrated with mechanical applications. After the model verification by experimental comparison, the detailed contribution of steel fibre and the effect of fibre distribution refinement are discussed as well.

    DOI

  • A novel casting procedure for SFRC piles without shear reinforcement using the centrifugal forming technique to manipulate the fiber orientation and distribution

    Ramiz Ahmed Raju, Mitsuyoshi Akiyama, Sopokhem Lim, Tatsuya Kakegawa, Yuka Hosono

    Construction and Building Materials   303  2021年10月

     概要を見る

    The structural performance of steel fiber-reinforced concrete (SFRC) members primarily depends on the distribution and orientation of the fibers. Previous experimental studies revealed that the distribution and orientation of fibers are random and hardly controlled during the fabrication process. The centrifugal forming technique may improve the orientation and distribution of steel fibers in hollow circular SFRC piles and increase the shear strength of the piles. Accomplishing this task can lead to the possible replacement of shear reinforcements with steel fibers in piles, thereby improving the demanding productivity that is desired in the pile construction industry by saving considerable time and labor. This paper presents a novel experimental program to (a) develop the casting procedure for SFRC piles and (b) investigate the shear strength of SFRC piles without shear reinforcement compared to that of conventional reinforced concrete (RC) piles with shear reinforcement. With the aid of X-ray technology, different mix proportions and casting methods were investigated to determine the optimum procedure, which produced fiber distributions and orientations in SFRC piles superior to those of RC piles. The centrifugal forming method influenced the orientation of the fibers so that they were oriented in the shear stress direction (i.e., circumferential direction). The loading test demonstrated that the steel fibers effectively worked as shear reinforcement and that the shear capacity increased with the steel fiber content. Moreover, the SFRC piles exhibited stable crack propagation and improved post-cracking stiffness without severe concrete damage compared to that of the RC piles.

    DOI

  • Effect of the correlation of steel corrosion in the transverse direction between tensile rebars on the structural performance of RC beams

    Mingyang Zhang, Naoki Nishiya, Mitsuyoshi Akiyama, Sopokhem Lim, Keisuke Masuda

    Construction and Building Materials   264   120678 - 120678  2020年12月

    DOI

  • Effects of concrete flow on the distribution and orientation of fibers and flexural behavior of steel fiber-reinforced self-compacting concrete beams

    Ramiz Ahmed Raju, Sopokhem Lim, Mitsuyoshi Akiyama, Takumi Kageyama

    Construction and Building Materials   262  2020年11月  [査読有り]

     概要を見る

    © 2020 Elsevier Ltd Several parameters during the fabrication process cause segregation and poor orientation of the fibers in steel fiber-reinforced concrete (SFRC) members. With its high flowability and compactability, self-compacting fiber-reinforced concrete (SCFRC) can be used as an alternative to conventional SFRC, as it exhibits improved orientation and lesser fiber segregation. This study aims to investigate (1) the effects of concrete type (i.e., SCFRC versus SFRC), fiber content, and specimen depth on the fiber distribution and orientation and (2) the structural performance of SCFRC and SFRC beams considering their fiber distribution and orientation using X-ray images. The X-ray images showed that owing to the high-flow properties, the SCFRC beams exhibited a lower fiber segregation and better fiber alignment than the SFRC beams. The bending test results demonstrated that the SCFRC beams exhibited better flexural performance than the SFRC beams owing to the improved distribution and orientation of the fibers. Moreover, a finite element (FE) analysis was performed to evaluate the structural performance of the beams considering the varying fiber distribution properties observed in the X-ray images. The FE method could differentiate the superior structural performance of the SCFRC beam from that of the SFRC beam.

    DOI

  • LCC-based identification of geographical locations suitable for using stainless steel rebars in reinforced concrete girder bridges

    Md Abul Hasan, Kekui Yan, Sopokhem Lim, Mitsuyoshi Akiyama, Dan M. Frangopol

    Structure and Infrastructure Engineering   16 ( 9 ) 1201 - 1227  2020年09月  [査読有り]

     概要を見る

    © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group. Reinforced concrete (RC) bridges under traffic loads and a severe airborne chloride environment require more frequent and intensive maintenance activities to preserve an adequate performance level. The use of stainless steel (SS) reinforcement in lieu of carbon steel (CS) reinforcement can be a promising alternative to avoid corrosion problems and reduce the maintenance cost. As the airborne chloride intensity depends on the meteorological condition and the distance from coastline, it is essential to determine the appropriate geographical locations where the use of SS rebar provides economic benefits. The main purpose of this paper is to present a novel approach for identifying the location of RC bridge suitable for SS rebar use considering the hazard intensity associated with the airborne chloride based on the probabilistic life-cycle cost (LCC) analysis. A novel probabilistic method for LCC estimation of RC bridge girders under traffic and airborne chloride hazards is established. In an illustrative example, the suitable location and critical distance for SS rebar application in RC bridges under different coastal environments in Japan are identified based on the proposed method. Sensitivity of LCC to four key parameters including discount rate of money, corrosion rate of SS rebar, concrete cover, and water-cement ratio is performed.

    DOI

  • Reliability estimation of corroded RC structures based on spatial variability using experimental evidence, probabilistic analysis and finite element method

    Mingyang Zhang, Huijuan Song, Sopokhem Lim, Mitsuyoshi Akiyama, Dan M. Frangopol

    Engineering Structures   192   30 - 52  2019年08月  [査読有り]

     概要を見る

    © 2019 Elsevier Ltd Corrosion of steel reinforcement is spatially distributed over RC structures due to several factors such as different environmental exposure, concrete cover, and concrete quality, among others. Ignoring the effect of spatial variability is a drastic simplification for the prediction of the remaining service life of RC structures. Therefore, it is essential to identify the factors influencing the spatial steel corrosion and structural performance of corroded RC structures. In this paper, an experimental research is conducted to study the effects of main parameters (i.e. current density, concrete cover, rebar diameter, and fly ash)on the spatial variability associated with steel weight loss, corrosion crack, and structural behavior of accelerated-corrosion RC beams using X-ray radiography and digital image processing. The test results showed that low current density (Icorr ≤ 50 µA/cm2)induced highly non-uniform corrosion associated with few large pits and cracks at certain locations while higher current density produced more uniform corrosion and cracks over the beam length. Gumbel distribution parameters were derived from the steel weight loss data for modeling spatial steel corrosion. A novel approach was established to assess the reliability of RC structures using finite element (FE)analysis and probabilistic analysis considering the effects of modeled spatial variability of steel weight loss based on X-ray photographs. Using the Gumbel distribution parameters derived from the steel weight loss data associated with higher current density may underestimate the non-uniformity of corrosion distribution which can lead to an overestimation of the load capacity of corroded RC structures.

    DOI

  • Visualization of the fibre dispersion in the steel fibre reinforced concrete using X-ray image

    Ramiz Ahmed Raju, Sopokhem Lim, Takumi Kageyama, Mitsuyoshi Akiyama

    Proceedings of the fib Symposium 2019: Concrete - Innovations in Materials, Design and Structures     351 - 357  2019年  [査読有り]

     概要を見る

    © Federation Internationale du Beton (fib) - International Federation for Structural Concrete, 2019. Uniform distribution of fibres which are orientated parallel to the direction of tensile stress is essential to improve the structural performance of steel fibre reinforced concrete (SFRC) members. However, the fibre distribution in concrete structures is hardly uniform due to the effects of many parameters during the fabrication process (vibration, placing methods, concrete moulds, etc.) which can negatively affects their structural performance. The use of self-compacting concrete (SCC) instead of normal concrete can be a good alternative where the fibres can be aligned in the direction of flow without the use of vibration. This paper presents an effort for improving the structural performance of fibre-reinforced concrete members by utilizing the high-flowability and self-placability properties of SCC to achieve better distribution and orientation of fibres. In the experiment, the self-compacting fibre reinforced concrete (SCFRC) was flown into beams and the X-ray image was taken over the whole length of each specimen to investigate the effects of flow distance from the casting point on the distribution and orientation of fibres. In addition, other specimens were also fabricated using SFRC (with normal concrete). The bending tests were performed to observe the flexural performance of SCFRC and SFRC specimens. By the comparison of their structural performance, it was found that SCFRC ones provided better performance due to the more uniform distribution of fibres which were aligned in the flow direction of SCFRC.

  • Modeling spatial variability of steel corrosion using Gumbel distribution

    Mingyang Zhang, Sopokhem Lim, Mitsuyoshi Akiyama, Dan M. Frangopol

    13th International Conference on Applications of Statistics and Probability in Civil Engineering, ICASP 2019    2019年  [査読有り]

     概要を見る

    © 13th International Conference on Applications of Statistics and Probability in Civil Engineering, ICASP 2019. All rights reserved. Performance of corrosion-affected RC structures depends on the spatial variability of steel corrosion of reinforcing bars. The effect of spatial variability of steel corrosion on the remaining service life of concrete structures is significant. In this paper, an experimental study was conducted to investigate the effect of current density on the spatial variability of steel corrosion. This variability is modeled using Gumbel distribution derived from experiments and incorporated with FE method to estimate the yield loading capacity of RC beams. The results show that using Gumbel distribution parameters derived from the specimens with high current density may lead to an overestimation of load capacity of corroded RC beams.

  • Influences of current density on the spatial steel corrosion and reliability of corrosion-affected RC beams

    Sopokhem Lim, Mingyang Zhang, Mitsuyoshi Akiyama

    Proceedings of the fib Symposium 2019: Concrete - Innovations in Materials, Design and Structures     2091 - 2097  2019年  [査読有り]

     概要を見る

    © Federation Internationale du Beton (fib) - International Federation for Structural Concrete, 2019. Ignoring the effects of spatial variability of steel corrosion can lead to an error in the long-term performance assessment of RC structures. Recent research has been focusing on modelling spatial steel corrosion using experimental data from the corroded RC members by means of the impressed current method. However, researchers have applied a wide range of current density neglecting its effects on the spatial steel corrosion and the reliability of corrosion-affected RC beams. This paper aims to study effects of current density on the spatial steel corrosion and reliability of RC structural beam using finite element analysis. Three RC beams were corroded using current density of 50, 100, and 500 μA/cm2. The spatial growth in steel weight loss in RC specimens was quantified at different corrosion levels using X-ray and image processing techniques. It was found that low current density of 50 μA/cm2 induced more non-uniform steel corrosion than higher levels of current density. Gumbel distribution parameters were derived from the experimental results and used to approximately model the spatial steel corrosion. An illustrative example was provided to study the effect of the modelled steel corrosion associated with low and high current densities on the reliability analysis of a structural RC beam. It was found that the failure probability of the RC beam estimated using the modelled spatial steel corrosion associated with small current density was higher than that associated with high current density.

  • Effects of current density on the spatial variability associated with steel corrosion and flexural behaviour of corroded RC beams

    リム ソーポーケム

    Proceeding of the 9th International Conference on Bridge Maintenance, Safety and Management (IABMAS18)     1024 - 1028  2018年07月  [査読有り]

  • Structural behavior prediction of SFRC beams by a novel integrated approach of X-ray imaging and finite element method

    Sopokhem Lim, Ramiz Ahmed Raju, Mitsuhiro Matsuda, Takehiro Okamoto, Mitsuyoshi Akiyama

    Construction and Building Materials   170   347 - 365  2018年05月  [査読有り]

     概要を見る

    © 2018 Elsevier Ltd Several studies have revealed that the fiber distribution is usually not uniform since many parameters during the fabrication process cause different fiber distributions and orientations within individual steel fiber-reinforced concrete (SFRC) members. This phenomenon results in large scattering in the post-cracking flexural responses among the material characterization specimens. Consequently, when estimating the flexural behavior of SFRC beams, conflicting results are often obtained using only a single constitutive stress-crack opening laws to characterize the material behavior in tension without considering the different fiber distributions and orientations. In this paper, a novel integrated approach is established to estimate the flexural behavior of SFRC beams using both a finite element (FE) method and X-ray imaging. In the prediction approach, a parameter that can be determined using the measured fiber distribution properties from an X-ray image is proposed to consider the variability of the fiber dispersion in each SFRC member. A method is presented for deducing the constitutive stress-crack opening laws using an FE analysis and the proposed parameter from X-ray images. In the numerical FE method, the variability of the fiber dispersion of the individual SFRC beams is determined by identifying the stress-strain relation in each mesh based on the proposed parameter from the X-ray images. The FE method provides better prediction results of the loading capacity for the SFRC beams.

    DOI

  • Effect of concrete flow on the flexural behavior of fiber reinforced self-compacting concrete beams

    リム ソーポーケム

    Proceedings of the Japan Concrete Institute   40 ( 2 ) 1189 - 1194  2018年

  • Structural performance assessment of aging RC beams considering the spatial variability of steel corrosion: experimental study and probabilistic model

    リム ソーポーケム

    The Fifteenth East Asia-Pacific on Structural Engineering and Construction Conference (EASEC-15)    2017年10月  [査読有り]

  • Effect of spatial variability associated with steel corrosion on the reliability of corroded RC beams

    リム ソーポーケム

    The 8th Asia and Pacific Young Researchers and Graduates Symposium (YRGS2017)    2017年09月  [査読有り]

  • Assessment of the structural behavior of corrosion-affected rc beams: Experimental study and modeling

    S. Lim, M. Akiyama, D. M. Frangopol

    Life-Cycle of Engineering Systems: Emphasis on Sustainable Civil Infrastructure - 5th International Symposium on Life-Cycle Engineering, IALCCE 2016     379 - 384  2017年

     概要を見る

    Structural performance of deteriorated reinforced concrete (RC) members depends on the magnitude and location of steel corrosion. Finite element (FE) method has been applied to the structural performance assessment of corroded RC members; however, the difficulty in quantifying cross-sectional area of rebar embedded into the concrete has been reported as a main challenge for conducting the FE analysis precisely. The two main objectives of this paper are to: (1) experimentally investigate the effects of spatial variability associated with steel corrosion on the structural behavior of a corroded RC beam and (2) establish a FE numerical modeling to assess the structural performance of corroded RC beams. In the experimental study, the spatial variability associated with the steel weight loss over the RC beam is quantified using X-ray and digital image processing techniques. This experimental result is used as input data for the FE analysis. The proposed model provides good agreement with the test results.

  • 鋼繊維のX線撮影結果を用いたSFRCはりの曲げ挙動解析に関する基礎的研究

    松田充弘, 岡本健弘, Lim Sopokhem, 秋山充良

    構造工学論文集   63A   847 - 858  2017年  [査読有り]

  • Flexural behavior prediction of SFRC beams using finite element method and X-ray image

    リム ソーポーケム

    Proceedings of the Japan Concrete Institute   39 ( 2 ) 1099 - 1104  2017年  [査読有り]

  • Experimental investigation of the spatial variability of the steel weight loss and corrosion cracking of reinforced concrete members: novel X-ray and digital image processing techniques

    Sopokhem Lim, Mitsuyoshi Akiyama, Dan M. Frangopol, Haitao Jiang

    STRUCTURE AND INFRASTRUCTURE ENGINEERING   13 ( 1 ) 118 - 134  2017年  [査読有り]

     概要を見る

    The material properties of concrete structures and their structural dimensions are known to be random due to the spatial variability associated with workmanship and various other factors. This randomness produces spatially variable corrosion damages, such as steel weight loss and corrosion cracks. The structural capacity of reinforced concrete (RC) members strongly depends on the local conditions of their reinforcements. Modelling the spatial variability of steel corrosion is important, but steel corrosion in RC members can only be observed after severely damaging the concrete members. To understand the steel corrosion growth process and the change in the spatial variability of steel corrosion with time, continuous monitoring is necessary. In this study, X-ray photography is applied to observe steel corrosion in RC beams. The steel weight loss is estimated by the digital image processing of the X-ray photograms. The non-uniform distribution of steel weight loss along rebars inside RC beams determined using X-ray radiography and its correlation with longitudinal crack widths are experimentally investigated.

    DOI

  • Assessment of the structural performance of corrosion-affected RC members based on experimental study and probabilistic modeling

    Sopokhem Lim, Mitsuyoshi Akiyama, Dan M. Frangopol

    ENGINEERING STRUCTURES   127   189 - 205  2016年11月  [査読有り]

     概要を見る

    The severity of damage due to corrosion on reinforced concrete (RC) structures primarily depends on the magnitude and location of the steel corrosion. A finite element (FE) method has been used to evaluate the structural performance of RC members subjected to reinforcement corrosion. However, the difficulty in quantifying the residual rebar cross-sections in the concrete has been reported as the primary challenge in providing important parameters for modeling the corrosion damages on the steel reinforcement and concrete. The three primary objectives of this paper are to (a) experimentally investigate the effects of the spatial variability in the steel corrosion on the structural behaviors of five corroded RC beams, (b) establish a FE method to assess their deteriorated structural performances, and (c) develop Gumbel distribution parameters to estimate the spatial variability of corrosion for the rebars. In the experimental study, the spatial variability in the steel weight loss along the corroded rebars in the concrete medium was quantified using X-ray and digital image processing techniques. For the FE analysis, the experimental steel weight loss data was used for modeling the residual steel cross-sections, reduced concrete strength, and deteriorated bond interface. The flexural capacity obtained from the simulated beams is in agreement with experimental results. (C) 2016 Elsevier Ltd. All rights reserved.

    DOI

  • Investigation of the spatial variability of steel weight loss and corrosion cracking: A novel X-ray technique

    リム ソーポーケム

    Sopokhem Lim, Haitao Jiang, and Mitsuyoshi Akiyama     265 - 269  2016年06月  [査読有り]

    DOI

  • Flexural behavior prediction of SFRC beams using X-ray photograms

    リム ソーポーケム

    The Fourteenth East Asia-Pacific on Structural Engineering and Construction Conference (EASEC-14)     1254 - 1257  2016年01月  [査読有り]

  • Experimental investigation on the relationship between the spatial variation of steel weight loss and the cracking width of RC members using X-ray photograms

    S. Lim, H. Jiang, M. Akiyama, D. M. Frangopol

    LIFE-CYCLE OF STRUCTURAL SYSTEMS: DESIGN, ASSESSMENT, MAINTENANCE AND MANAGEMENT     429 - 436  2015年  [査読有り]

     概要を見る

    Deterioration of RC members due to chloride-induced corrosion of reinforcing bars is a common problem in marine environment. After surface crack initiates, RC structures are prone to the occurrence of longitudinal surface cracks and concrete spalling. These deterioration mechanisms adversely cause significant reduction of the service life and performance of RC members. Therefore, it is important to create models to reliably predict the long-term performance of deteriorated RC structures. However, the very limited amount of experimental data on spatial variation of steel weight loss in relation to propagation of surface cracking widths has been reported to create difficulty in improving the degree of accuracy associated with the prediction models. This paper is aimed to experimentally investigate the non-uniform distribution of steel weight loss along reinforcing bars inside RC means by means of X-ray radiography and its correlation with longitudinal crack widths.

  • Visualization of corroded steel bars in RC beams using digital image processing of X-ray photograms

    リム ソーポーケム

    Proceedings of the Japan Concrete Institute   37 ( 2 ) 1327 - 1332  2015年  [査読有り]

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特定課題研究

  • Effects of casting methods and flow-properties of self-compacting concrete on tflexural behavior of fiber reinforced concrete beams using X-ray images

    2019年   Ramiz Ahmed Raju, Takumi Kageyama, Syunsuke Amano, Mitsuyoshi Akiyama

     概要を見る

    The effect of concrete casting methods and concretemixes having different fiber contents (i.e., 20 kg/m3 and 40 kg/m3)on the fiber distribution and orientation as well as the structural performanceof self-compacting concrete fiber reinforced concrete (SCFRC) beams were experimentally investigated. In the experimental program, twocasting methods were designed for pouring the concrete into the same beam molds:case 1, concrete cast from a large 35-degree-slope chute into the entire mold atonce, and case 2, concrete cast from a long pipe. It was found that, with thesame casting method, SCFRC beams with fibercontent of 40 kg/m3 showed lower segregation of fibers but fibersare less aligned to the concrete flow than other beams with fiber content of 20 kg/m3.On the other hand, the casting method of case 1 inducedthe larger velocity of concrete flow than that of case 2. Fibers distribute andorientate better in direction of tensile stress in beams in case 1 due to the larger flowvelocity than that in case 2. Therefore, the structural performance of SCFRCbeam with casting method of case 1 is found to be moderately better than thatof case 2.

  • 22020構造工学および地震工学関連

    2018年   Mingyang Zhang, Mitsuyoshi Akiyama, Dan M. Frangopol

     概要を見る

    This research aims to study effects of currentdensity on the spatial steel corrosion and to assess the residualloading capacity of corroded RC beams using finite element (FE) analysis. TwoRC beams were corroded using current density levels of 50 and 500 μA/cm2.The spatial growth in steel weight loss in RC specimens was quantified atdifferent corrosion levels using X-ray and image processing techniques. Theexperimental result shows that low current density (50 μA/cm2) induced more non-uniformsteel corrosion than the high current density (500 μA/cm2). Gumbel distributionparameters were derived from the experimental results to approximately modelthe spatial variability of steel weight loss which is used as the input into FEmodel of corroded RC beams. The FEanalysis result of the RC beam that has rebar samples generated by the Gumbel distributionparameters associated with lower current density provides a more scattering andlower yielding load capacity, compared with that from a specimen with higher currentdensity.

  • Effects of fiber distribution and orientation on the flexural performance of steel fiber reinforced normal and self-compacting concrete beams

    2018年   Ramiz Ahmed Raju, Sopokhem Lim, Takumi Kageyama, Mitsuyoshi Akiyama

     概要を見る

    This experimental research presents an effort toimprove the structural performance of fiber reinforced concrete members byutilizing the high-flowability and self-placability properties of self-compactingconcrete to achieve better distribution and orientation of fibers. In the experiment, self-compactingfiber reinforced concrete (SCFRC) was flown into beam molds while steel fiberreinforced concrete (SFRC) with normal concrete was cast into other same-size beammolds. X-ray images were taken over the length of each beam to investigateeffects of flow and normal casting method on the distribution and orientationof fibers. The bending tests were performed to study the flexural performanceof SCFRC and SFRC beams. It wasconfirmed the distribution and orientation of fibers in SCFRCbeams were better than those in SFRC ones since most fibers werealigned to the high flow. As a result, the flexural performance of SCFRCbeams was superior to those of SFRC ones. However, it is challenging to attaina uniform distribution of fibers over the entire beam length. Furtherresearch is needed to find an optimum combination of concrete flow, fiberamount, and casting method by which a uniform distribution of fibers can beachieved over the entire beam length.

 

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