List of Titles

Dynamic cohesive crack propagation modelling using the scaled boundary finite element method

- Ooi, Ean Tat, Yang, Zhenjun, Guo, Zaoyang

Authors: Ooi, Ean Tat , Yang, Zhenjun , Guo, Zaoyang
Date: 2012
Type: Text , Journal article
Relation: Fatigue and Fracture of Engineering Materials and Structures Vol. 35, no. 8 (2012), p. 786-800
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Description: This study develops a scaled boundary finite element method (SBFEM)-based approach for modelling fast cohesive crack propagation in quasi-brittle materials subjected to transient dynamic loadings. In this approach, the elastic bulk material is modelled by SBFEM subdomains and the cracks by nonlinear cohesive interface finite elements that are automatically inserted by a remeshing procedure. The global equation system is solved using an implicit time integration algorithm. Because all the solutions (displacements, stresses, velocities, accelerations) are semi-analytical in an SBFEM subdomain, this approach offers a few advantages over other methods, such as accurate calculation of dynamic stress intensity factors and T-stress without using fine crack-tip meshes, simpler remeshing, more accurate and efficient mesh mapping, and the need of much fewer degrees of freedom for the same accuracy. The approach is validated by modelling two concrete beams under impact, subjected to mode-I and mixed-mode fracture, respectively. © 2012 Blackwell Publishing Ltd.

Experimental study on the time-dependent dynamic mechanical behaviour of C60 concrete under high-temperatures

- Li, Hong-chao, Liu, Dian-shu, Zhao, Lei, You, Greg, Liang, Shu-feng, Wang, Yu-tao

Authors: Li, Hong-chao , Liu, Dian-shu , Zhao, Lei , You, Greg , Liang, Shu-feng , Wang, Yu-tao
Date: 2015
Type: Text , Journal article
Relation: Journal of Beijing Institute of Technology (English Edition) Vol. 24, no. 3 (2015), p. 313-320
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Description: To study the dynamic mechanical behavior of C60 concrete at high temperatures, impact tests under different steady-state temperature fields (100, 200, 300, 400 and 500â„ƒ) were conducted under a variety of durations at the corresponding constant high temperature, namely 0, 30, 60, 90 and 120 min, employing split Hopkinson pressure bar (SHPB) system. In addition, the impact tests were also conducted on the specimens cooled from the high temperature to the room temperature and the specimen under room temperature. From the analysis, it is found that C60 concrete has a time-dependent behavior under high-temperature environment. Under 100, 200, 300, 400 and 500â„ƒ steady-state temperature fields respectively, as the duration at the corresponding constant high temperature increases, the dynamic compressive strength and the elastic modulus decrease but the peak strain generally ascends. After cooling to the room temperature, the dynamic compressive strength and the elastic modulus descend as well, but the peak strain increases first and then decreases slightly, when the duration increases. For specimens under and cooled from the high-temperature, as the temperature increases, the dynamic compressive strength and the peak strain raise first and then reduce gradually, and the dynamic compressive strength of specimen under high temperature is higher than that of the specimen cooled from the same high temperature. © 2015, Editorial Department of Journal of Beijing Institute of Technology. All right reserved.

The screening and morphological quantification of bacterial production of calcium carbonate

- Seifan, Mostafa, Samani, Ali Khajeh, Berenjian, Aydin, Eckersley, Joshua

Authors: Seifan, Mostafa , Samani, Ali Khajeh , Berenjian, Aydin , Eckersley, Joshua
Date: 2016
Type: Text , Conference paper
Relation: Chemeca 2016 p. 12-22
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Description: In recent years, the microbial production of calcium carbonate has emerged as a promising way to address the structural issues associated with concrete structures. Although calcium carbonate can be produced by some genera of bacteria through autotrophic and heterotrophic pathways, the significance level of nutritional and energy sources has remained a challenge to determine. In this study, a Placket-Burman design was used to screen significant factors on the production of calcium carbonate by fermentation; the experimental data was analyzed using Analysis of variance (ANOVA) to determine the significance of each factor. To find the optimum level of nutrients and operating conditions, different media were prepared by altering the concentrations of seven variable factors including inoculum volume, nutrients and calcium sources as well as three constant operating conditions (incubation time, agitation and temperature). Since calcium carbonate polymorphs (calcite, vaterite and aragonite) have different mechanical properties, a morphological quantification using X-ray diffraction (XRD) was developed. It was concluded that peptone and calcium lactate have a negative effect while, remaining variables including urea, yeast extract, and calcium chloride have a positive effect on the production of calcium carbonate by Bacillus sphaericus.

Mechanical properties of bio self-healing concrete containing immobilized bacteria with iron oxide nanoparticles

- Seifan, Mostafa, Sarmah, Ajit, Samani, Ali Khajeh, Ebrahiminezhad, Alireza, Ghasemi, Younes, Berenjian, Aydin

Authors: Seifan, Mostafa , Sarmah, Ajit , Samani, Ali Khajeh , Ebrahiminezhad, Alireza , Ghasemi, Younes , Berenjian, Aydin
Date: 2018
Type: Text , Journal article
Relation: Applied Microbiology and Biotechnology Vol. 102, no. 10 (2018), p. 4489-4498
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Description: Concrete is arguably one of the most important and widely used materials in the world, responsible for the majority of the industrial revolution due to its unique properties. However, it is susceptible to cracking under internal and external stresses. The generated cracks result in a significant reduction in the concrete lifespan and an increase in maintenance and repair costs. In recent years, the implementation of bacterial-based healing agent in the concrete matrix has emerged as one of the most promising approaches to address the concrete cracking issue. However, the bacterial cells need to be protected from the high pH content of concrete as well as the exerted shear forces during preparation and hardening stages. To address these issues, we propose the magnetic immobilization of bacteria with iron oxide nanoparticles (IONs). In the present study, the effect of the designed bio-agent on mechanical properties of concrete (compressive strength and drying shrinkage) is investigated. The results indicate that the addition of immobilized Bacillus species with IONs in concrete matrix contributes to increasing the compressive strength. Moreover, the precipitates in the bio-concrete specimen were characterized using scanning electron microscope (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDS). The characterization studies confirm that the precipitated crystals in bio-concrete specimen were CaCO3, while no precipitation was observed in the control sample.

Bio-reinforced self-healing concrete using magnetic iron oxide nanoparticles

- Seifan, Mostafa, Sarmah, Ajit, Ebrahiminezhad, Alireza, Ghasemi, Younes, Samani, Ali Khajeh, Berenjian, Aydin

Authors: Seifan, Mostafa , Sarmah, Ajit , Ebrahiminezhad, Alireza , Ghasemi, Younes , Samani, Ali Khajeh , Berenjian, Aydin
Date: 2018
Type: Text , Journal article
Relation: Applied Microbiology and Biotechnology Vol. 102, no. 5 (2018), p. 2167-2178
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Description: Immobilization has been reported as an efficient technique to address the bacterial vulnerability for application in bio self-healing concrete. In this study, for the first time, magnetic iron oxide nanoparticles (IONs) are being practically employed as the protective vehicle for bacteria to evaluate the self-healing performance in concrete environment. Magnetic IONs were successfully synthesized and characterized using different techniques. The scanning electron microscope (SEM) images show the efficient adsorption of nanoparticles to the Bacillus cells. Microscopic observation illustrates that the incorporation of the immobilized bacteria in the concrete matrix resulted in a significant crack healing behavior, while the control specimen had no healing characteristics. Analysis of bio-precipitates revealed that the induced minerals in the cracks were calcium carbonate. The effect of magnetic immobilized cells on the concrete water absorption showed that the concrete specimens supplemented with decorated bacteria with IONs had a higher resistance to water penetration. The initial and secondary water absorption rates in bio-concrete specimens were 26% and 22% lower than the control specimens. Due to the compatible behavior of IONs with the concrete compositions, the results of this study proved the potential application of IONs for developing a new generation of bio self-healing concrete.

3D Finite element modeling of circular reinforced concrete columns confined with FRP using a plasticity based formulation

- Piscesa, Bambang, Attard, Mario, Samani, Ali Khajeh

Authors: Piscesa, Bambang , Attard, Mario , Samani, Ali Khajeh
Date: 2018
Type: Text , Journal article
Relation: Composite Structures Vol. 194, no. (2018), p. 478-493
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Description: Strengthening reinforced concrete (RC) columns with external confining devices such as FRP wraps or steel tube is widely used in construction. By using external confining devices, both the strength and ductility of RC columns are significantly improved. However, numerical modeling to predict the capacity of strengthened RC columns is limited and often oversimplified. One of the biggest challenges in numerical modeling is to deal with unequal dilation between the concrete inner core (enclosed by both transverse steel and FRP wraps) and the concrete outer core (between the transverse steel and FRP wraps). Inaccurate modeling on the concrete dilatant behavior can lead to incorrect strength prediction. Sophisticated constitutive models which are able to model concrete dilation and robust modeling techniques are required. In this paper, three-dimensional non-linear finite element analysis (3D-NLFEA) of circular RC columns confined with conventional steel stirrups and FRP wraps is presented. In the FEA, the initial stiffness method with Process Modification (acceleration technique) is used to solve the equilibrium forces in the global solution. The constitutive model is based on the plasticity formulation proposed by the authors, which can capture the effective lateral modulus (EL) of the confining devices. This lateral modulus is obtained by observing the principal incremental stresses and strains at each element gauss point. It was found that, the lateral modulus is greatly affected by the boundary condition, dilatant behavior of the constitutive model and the Poisson's ratio of the external confining device. To validate the performance of the proposed model, several comparisons of the proposed model, using 3D-NLFEA, with experimental results is presented. The comparisons show that the predicted response using 3D-NLFEA and the experimental results of RC columns confined with FRP are in a good agreement.

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A quadtree-polygon-based scaled boundary finite element method for image-based mesoscale fracture modelling in concrete

- Guo, H., Ooi, Ean Tat, Saputra, Albert, Yang, Zhenjun, Natarajan, Sundararajan, Ooi, Ean Hin, Song, Chongmin

Authors: Guo, H. , Ooi, Ean Tat , Saputra, Albert , Yang, Zhenjun , Natarajan, Sundararajan , Ooi, Ean Hin , Song, Chongmin
Date: 2019
Type: Text , Journal article , acceptedVersion
Relation: Engineering Fracture Mechanics Vol. 211, no. (2019), p. 420-441
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Description: A quadtree-polygon scaled boundary finite element-based approach for image-based modelling of concrete fracture at the mesoscale is developed. Digital images representing the two-phase mesostructure of concrete, which comprises of coarse aggregates and mortar are either generated using a take-and-place algorithm with a user-defined aggregate volume ratio or obtained from X-ray computed tomography as an input. The digital images are automatically discretised for analysis by applying a balanced quadtree decomposition in combination with a smoothing operation. The scaled boundary finite element method is applied to model the constituents in the concrete mesostructure. A quadtree formulation within the framework of the scaled boundary finite element method is advantageous in that the displacement compatibility between the cells are automatically preserved even in the presence of hanging nodes. Moreover, the geometric flexibility of the scaled boundary finite element method facilitates the use of arbitrary sided polygons, allowing better representation of the aggregate boundaries. The computational burden is significantly reduced as there are only finite number of cell types in a balanced quadtree mesh. The cells in the mesh are connected to each other using cohesive interface elements with appropriate softening laws to model the fracture of the mesostructure. Parametric studies are carried out on concrete specimens subjected to uniaxial tension to investigate the effects of various parameters e.g. aggregate size distribution, porosity and aggregate volume ratio on the fracture of concrete at the meso-scale. Mesoscale fracture of concrete specimens obtained from X-ray computed tomography scans are carried out to demonstrate its feasibility.

Crack propagation modelling in concrete using the scaled boundary finite element method with hybrid polygon-quadtree meshes

- Ooi, Ean Tat, Natarajan, Sundararajan, Song, Chongmin, Ooi, Ean Hin

Authors: Ooi, Ean Tat , Natarajan, Sundararajan , Song, Chongmin , Ooi, Ean Hin
Date: 2017
Type: Text , Journal article
Relation: International Journal of Fracture Vol. 203, no. 1-2 (2017), p. 135-157
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Description: This manuscript presents an extension of the recently-developed hybrid polygon-quadtree-based scaled boundary finite element method to model crack propagation in concrete. This hybrid approach combines the use of quadtree cells with arbitrary sided polygons for domain discretization. The scaled boundary finite element formulation does not distinguish between quadtree cells and arbitrary sided polygons in the mesh. A single formulation is applicable to all types of cells and polygons in the mesh. This eliminates the need to develop transitional elements to bridge the cells belonging to different levels in the quadtree hierarchy. Further to this, the use of arbitrary sided polygons facilitate the accurate discretization of curved boundaries that may result during crack propagation. The fracture process zone that is characteristic in concrete fracture is modelled using zero-thickness interface elements that are coupled to the scaled boundary finite element method using a shadow domain procedure. The scaled boundary finite element method can accurately model the asymptotic stress field in the vicinity of the crack tip with cohesive tractions. This leads to the accurate computation of the stress intensity factors, which is used to determine the condition for crack propagation and the resulting direction. Crack growth can be efficiently resolved using an efficient remeshing algorithm that employs a combination of quadtree decomposition functions and simple Booleans operations. The flexibility of the scaled boundary finite element method to be formulated on arbitrary sided polygons also result in a flexible remeshing algorithm for modelling crack propagation. The developed method is validated using three laboratory experiments of notched concrete beams subjected to different loading conditions.

Efficient prediction of deterministic size effects using the scaled boundary finite element method

- Ooi, Ean Tat, Yang, Zhenjun

Authors: Ooi, Ean Tat , Yang, Zhenjun
Date: 2010
Type: Text , Journal article
Relation: Engineering Fracture Mechanics Vol. 77, no. 6 (2010), p. 985-1000
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Description: This paper develops an efficient numerical approach to predict deterministic size effects in structures made of quasi-brittle materials using the scaled boundary finite element method (SBFEM). Depending on the structure's size, two different SBFEM-based crack propagation modelling methodologies are used for fracture analyses. When the length of the fracture process zone (FPZ) in a structure is of the order of its characteristic dimension, nonlinear fracture analyses are carried out using the finite element-SBFEM coupled method. In large-sized structures, a linear elastic fracture mechanics (LEFM)-based SBFEM is used to reduce computing time due to small crack propagation length required to represent the FPZ in an equivalent nonlinear analysis. Remeshing is used in both methods to model crack propagation with crack paths unknown a priori. The resulting peak loads are used to establish the size effect laws. Three concrete structures were modelled to validate the approach. The predicted size effect is in good agreement with experimental data. The developed approach was found more efficient than the finite element method, at least in modelling LEFM problems and is thus an attractive tool for predicting size effect. © 2010 Elsevier Ltd.

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