• Computers and Concrete
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• v.34 no.3
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• pp.307-328
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• 2024

The concrete damage plasticity (CDP) model is widely used to simulate concrete behaviour using either implicit or explicit analysis methods. To effectively execute the models and resolve convergence issues in implicit analysis, activating the viscosity parameter of this material model is a common practice. Despite the frequent application of implicit analysis to analyse concrete structures with the CDP model, the viscosity parameter significantly varies among available models and lacks consistency. The adjustment of the viscosity parameter at the element/structural level disregards its indirect impact on the material. Therefore, the accuracy of the numerical model is confined to the validated range and might not hold true for other values, often explored in parametric studies subsequent to validations. To address these challenges and develop a unified numerical model for varied conditions, a quasi-static analysis using the explicit solver was conducted in this study. Fifteen thick flat plates tested under load control with different geometries and different eccentric loads were considered to verify the accuracy of the model. The study first investigated various concrete material behaviours under compression and tension as well as the concrete tensile strength to identify the most reliable models from previous methodologies. The study compared the results using both implicit and explicit analysis. It was found that, in implicit analysis, the viscosity parameter should be as low as 0.0001 to avoid affecting material properties. However, at the structural level, the optimum value may need adjustment between 0.00001 to 0.0001 with changing geometries and loading type. This observation raises concerns about further parametric study if the specific value of the viscosity parameter is used. Additionally, activating the viscosity parameter in load control simulations confirmed its inability to capture the peak load. Conversely, the unified explicit model accurately simulated the behaviour of the test specimens under varying geometries, load eccentricities, and column sizes. This study recommends restricting implicit solutions to the viscosity values proposed in this research. Alternatively, for highly nonlinear problems under load control simulation, explicit analysis stands as an effective approach, ensuring unified parameters across a wide range of applications without convergence problems.

• Journal of Chest Surgery
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• v.37 no.6
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• pp.467-473
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• 2004

Background: The sinus conversion rate after the maze procedure in chronic atrial fibrillation using radiofrequency energy is lower than with either conventional 'cut and saw' technique or cryothermia. The creation of incomplete transmural lesions due to poor tissue-catheter contact is thought to be the main cause. To address this problem, the current study was aimed to evaluate the effectiveness of a specially constructed compression device designed to enhance tissue catheter contact during unipolar radiofrequency catheter ablation. Material and Method: Circum-ferential right auricular epicardial lesions were created with a linear radiofrequency catheter in 10 anesthetized pigs. A device specially designed to increase contact by compression of the catheter to the atrial wall was used in 5 pigs (study group). This device was not used in the control group (5 pigs). Conduction block across the right auricular lesion was assessed by pacing, and the transmurality of the lesions were confirmed by microscopic examination. Result: Conduction block was observed in a total of 8 pigs; 5 in study group and 3 in control group. Transmural injury was confirmed microscopically by the accumulation of acute inflammatory cells and loss of elastic fibers in the endocardium. In two pigs with failed conduction block, microscopic examination of the endocardium appeared normal. Conclusion: Failed radiofrequency ablation is strongly related to non-transmural energy delivery. The specially constructed compression device in the current study was successful in creating firm tissue-catheter contact and thereby generating transmural lesions during unipolar radiofrequency ablation.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.3
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• pp.173-179
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• 2014

This is an experimental study for recycling coal ash left over from coal use as a potential fine aggregate in concrete. Coal ash is generally divided into either fly ash or bottom ash. Fly ash has been utilized as a substitution material for cement in concrete mixes. On the other hand, bottom ash has the problem of low recycling rates, and thus it has been primarily reclaimed. This study partially substituted fine concrete aggregates with bottom ash to increase its application rate and therefore its recycling rate; its suitability for this purpose was confirmed. The concrete's workability dropped noticeably with increasing bottom ash content when a fixed water-cement ratio of concrete mix was used. Thus, concrete mixes with higher ratio levels are required. To address this problem, concrete was mixed using a polycarboxylate high-range water reducing agent. The fluidity and air entrainment immediately after mixing the concrete and 1 h after mixing were measured, thereby replicating the time concrete is placed in the field when produced either in a ready-mixed concrete or in a batch plant. As a result of this research, the workability and air entrainment were maintained 1 h after mixing for a concrete mixture with approximately 30% of its fine concrete aggregates substituted with the bottom ash. A slight drop in compression strength was seen; however, this confirmed that potential of using bottom ash as a fine aggregate in concrete.

• Computers and Concrete
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• v.22 no.3
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• pp.337-353
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• 2018

The present study focuses on examining the structural behaviour of steel-fibre-reinforced concrete (SFRC) beams under high rates of loading largely associated with impact problems. Fibres are added to the concrete mix to enhance ductility and energy absorption, which is important for impact-resistant design. A simple, yet practical non-linear finite-element analysis (NLFEA) model was used in the present study. Experimental static and impact tests were also carried out on beams spanning 1.3 meter with weights dropped from heights of 1.5 m and 2.5 m, respectively. The numerical model realistically describes the fully-brittle tensile behaviour of plain concrete as well as the contribution of steel fibres to the post-cracking response (the latter was allowed for by conveniently adjusting the constitutive relations for plain concrete, mainly in uniaxial tension). Suitable material relations (describing compression, tension and shear) were selected for SFRC and incorporated into ABAQUS software Brittle Cracking concrete model. A more complex model (i.e., the Damaged Plasticity concrete model in ABAQUS) was also considered and it was found that the seemingly simple (but fundamental) Brittle Cracking model yielded reliable results. Published data obtained from drop-weight experimental tests on RC and SFRC beams indicates that there is an increase in the maximum load recorded (compared to the corresponding static one) and a reduction in the portion of the beam span reacting to the impact load. However, there is considerable scatter and the specimens were often tested to complete destruction and thus yielding post-failure characteristics of little design value and making it difficult to pinpoint the actual load-carrying capacity and identify the associated true ultimate limit state (ULS). To address this, dynamic NLFEA was employed and the impact load applied was reduced gradually and applied in pulses to pinpoint the actual failure point. Different case studies were considered covering impact loading responses at both the material and structural levels as well as comparisons between RC and SFRC specimens. Steel fibres were found to increase the load-carrying capacity and deformability by offering better control over the cracking process concrete undergoes and allowing the impact energy to be absorbed more effectively compared to conventional RC members. This is useful for impact-resistant design of SFRC beams.

• Journal of Broadcast Engineering
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• v.25 no.3
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• pp.346-352
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• 2020

Versatile Video Coding (VVC), a next-generation video coding standard that is in the final stage of standardization, has adopted various techniques to achieve more than twice the compression performance of HEVC (High-Efficiency Video Coding). VVC adopted Bi-prediction with CU-level Weight (BCW), which generates the final prediction signal with the weighted combination of bi-predictions with various weights, to enhance the performance of the bi-predictive inter prediction. The syntax element of the BCW index is adaptively coded according to the value of NoBackwardPredFlag which indicates if there is no future picture in the display order among the reference pictures. Such syntax structure for signaling the BCW index could violate the flexibility of video codec and cause the dependency issue at the stage of bitstream parsing. To address these issues, this paper proposes an efficient BCW weight signaling method which enables all weights and parsing without any condition check. The performance of the proposed method was evaluated with various weight searching methods in the encoder. The experimental results show that the proposed method gives negligible BD-rate losses and minor gains for 3 weights searching and 5 weights searching, respectively, while resolving the issues.

• Journal of the Korean Geosynthetics Society
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• v.17 no.4
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• pp.1-10
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• 2018

Although the soil nailing method is generally used as a gravity grouting, the development and application of pressurized grouting method has recently increased to address the problem of joint generation and filling due to grouting. Pressurized grouting of the soil nailing method is generally used in combination with ordinary portland cement and water. In the field, the cement is mixed with the rapid setting cement to reduce curing time because ordinary portland cement takes more than 10 days to satisfy the required strength. In this study, uniaxial compression tests and laboratory tests were carried out to confirm the efficiency of the grouting material according to the mixing ratio of rapid setting cement. The mixing ratio of 30% grouting satisfies the required strength within 7 days and satisfies the optimum gel time. As a result of the laboratory test with granite weathered soil, the reinforcing effect was confirmed to be 1.5 times as compared with the gravity type at an injection time of 10 seconds and a strain of 15%. The friction resistance increases linearly with the increase of the injection time, but it is confirmed that the friction resistance decreases due to the hydraulic fracturing effect at the injection time exceeding the limit injection pressure. Numerical analysis was performed to compare the stability of slopes not reinforced with slopes reinforced with gravity and pressurized soil nailing.