• Computers and Concrete
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• v.1 no.2
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• pp.115-130
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• 2004

The flexural ductility of solid rectangular reinforced concrete beams has been studied quite extensively. However, many reinforced concrete beams are neither solid nor rectangular; examples include T-, ${\Gamma}$-, ${\Pi}$- and box-shaped beams. There have been few studies on the flexural ductility of non-rectangular reinforced concrete beams and as a result little is known about the possible effect of sectional shape on flexural ductility. Herein, the effect of sectional shape on the post-peak flexural behaviour of reinforced normal and high-strength concrete beams has been studied using a newly developed analysis method that employs the actual stress-strain curves of the constitutive materials and takes into account the stress-path dependence of the stress-strain curve of the steel reinforcement. It was revealed that the sectional shape could have significant effect on the flexural ductility of a concrete beam and that the flexural ductility of a T-, ${\Gamma}$-, ${\Pi}$- or box-shaped beam is generally lower than that of a solid rectangular beam with the same overall dimensions and the same amount of reinforcement provided. Based on the numerical results obtained, a simple method of ensuring the provision of a certain minimum level of flexural ductility to non-rectangular concrete beams has been developed.

• Steel and Composite Structures
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• v.48 no.5
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• pp.565-582
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• 2023

The present research reports the application of engineered cementitious composites (ECC) as an alternative to conventional concrete to improve the seismic behavior of short columns. Experimental and finite element investigation was conducted by testing five reinforced engineered cementitious composite (RECC) concrete columns (half-scale specimens) and one control reinforced concrete (RC) specimen for different shear-span and transverse reinforcement ratios under cyclic lateral loads. RECC specimens with higher shear-span and transverse reinforcement ratios demonstrated a significant effect on the column lateral load behavior by improving ductility (>5), energy dissipation capacity (1.2 to 4.1 times RC specimen), gradual strength degradation (ultimate drift >3.4%), and altering the failure mode. The self-confinement effect of ECC fibers maintained the integrity in the post-peak region and reserved the transmission of stress through fibers without noticeable degradation in strength. Finite element modeling of RECC specimens under monotonic incremental loads was carried out by adopting simplified constitutive material models. It was apprehended that the model simulated the global response (strength and stiffness) and damage crack patterns reasonably well.

• Korean Journal of Radiology
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• v.23 no.7
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• pp.752-762
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• 2022

Objective: To compare a deep learning-based reconstruction (DLR) algorithm for pediatric abdominopelvic computed tomography (CT) with filtered back projection (FBP) and iterative reconstruction (IR) algorithms. Materials and Methods: Post-contrast abdominopelvic CT scans obtained from 120 pediatric patients (mean age ± standard deviation, 8.7 ± 5.2 years; 60 males) between May 2020 and October 2020 were evaluated in this retrospective study. Images were reconstructed using FBP, a hybrid IR algorithm (ASiR-V) with blending factors of 50% and 100% (AV50 and AV100, respectively), and a DLR algorithm (TrueFidelity) with three strength levels (low, medium, and high). Noise power spectrum (NPS) and edge rise distance (ERD) were used to evaluate noise characteristics and spatial resolution, respectively. Image noise, edge definition, overall image quality, lesion detectability and conspicuity, and artifacts were qualitatively scored by two pediatric radiologists, and the scores of the two reviewers were averaged. A repeated-measures analysis of variance followed by the Bonferroni post-hoc test was used to compare NPS and ERD among the six reconstruction methods. The Friedman rank sum test followed by the Nemenyi-Wilcoxon-Wilcox all-pairs test was used to compare the results of the qualitative visual analysis among the six reconstruction methods. Results: The NPS noise magnitude of AV100 was significantly lower than that of the DLR, whereas the NPS peak of AV100 was significantly higher than that of the high- and medium-strength DLR (p < 0.001). The NPS average spatial frequencies were higher for DLR than for ASiR-V (p < 0.001). ERD was shorter with DLR than with ASiR-V and FBP (p < 0.001). Qualitative visual analysis revealed better overall image quality with high-strength DLR than with ASiR-V (p < 0.001). Conclusion: For pediatric abdominopelvic CT, the DLR algorithm may provide improved noise characteristics and better spatial resolution than the hybrid IR algorithm.

• Steel and Composite Structures
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• v.33 no.6
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• pp.849-864
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• 2019

One way to achieve sustainable construction is to reduce concrete consumption by use of more sustainable and higher strength concrete. Modern building codes do not cover the use of ultra-high strength concrete (UHSC) in the design of composite structures. Against such background, this paper investigates experimentally the mechanical properties of steel fibre-reinforced UHSC and then the structural behaviors of UHSC encased steel (CES) members under both concentric and eccentric compressions as well as pure bending. The effects of steel-fibre dosage and spacing of stirrups were studied, and the applicability of Eurocode 4 design approach was checked. The test results revealed that the strength of steel stirrups could not be fully utilized to provide confinement to the UHSC. The bond strength between UHSC and steel section was improved by adding the steel fibres into the UHSC. Reducing the spacing of stirrups or increasing the dosage of steel fibres was beneficial to prevent premature spalling of the concrete cover thus mobilize the steel section strength to achieve higher compressive capacity. Closer spacing of stirrups and adding 0.5% steel fibres in UHSC enhanced the post-peak ductility of CES columns. It is concluded that the code-specified reduction factors applied to the concrete strength and moment resistance can account for the loss of load capacity due to the premature spalling of concrete cover and partial yielding of the encased steel section.

• Steel and Composite Structures
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• v.31 no.1
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• pp.69-83
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• 2019

This paper investigates the structural behavior of very high strength concrete encased steel composite columns via combined experimental and analytical study. The experimental programme examines stub composite columns under pure compression and eccentric compression. The experimental results show that the high strength encased concrete composite column exhibits brittle post peak behavior and low ductility but has acceptable compressive resistance. The high strength concrete encased composite column subjected to early spalling and initial flexural cracking due to its brittle nature that may degrade the stiffness and ultimate resistance. The analytical study compares the current code methods (ACI 318, Eurocode 4, AISC 360 and Chinese JGJ 138) in predicting the compressive resistance of the high strength concrete encased composite columns to verify the accuracy. The plastic design resistance may not be fully achieved. A database including the concrete encased composite column under concentered and eccentric compression is established to verify the predictions using the proposed elastic, elastoplastic and plastic methods. Image-oriented intelligent recognition tool-based fiber element method is programmed to predict the load resistances. It is found that the plastic method can give an accurate prediction of the load resistance for the encased composite column using normal strength concrete (20-60 MPa) while the elastoplastic method provides reasonably conservative predictions for the encased composite column using high strength concrete (60-120 MPa).

• Computers and Concrete
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• v.22 no.4
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• pp.395-405
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• 2018

In this paper, the performance of post-installed adhesive bonded anchor embedded in concrete is assessed using numerical simulations. This study aims at studying the influence of parameters on the performance of a chemically bonded anchorage system. Non-linear finite element modelling and simulations are carried out by properly using the material properties and phenomenon. Materials parameters such as characteristic length, fracture energy, damage criteria, tension retention and crack width of concrete and interface characteristics are carefully assigned so as to obtain a most realistic behaviour of the chemical anchor system. The peak strength of two different anchor systems obtained from present numerical studies is validated against experimental results. Furthermore, validated numerical models are used to study the load transferring mechanism and damage progression characteristics of various anchors systems where strength of concrete, strength of epoxy, and geometry and disposition of anchors are the parameters. The process of development of strain in concrete adjacent to the anchor and energy dissipated during the course of damage progression are analysed. Results show that the performance of the considered anchorage system is, though a combined effect of material and geometric parameters, but a clear distinction could be made on the parameters to achieve a desired performance based on strength, slip, strain development or dissipated energy. Inspite the increase in anchor capacity with increase in concrete strength, it brings some undesirable performance as well. Furthermore, the pullout capacity of the chemical anchor system increases with a decrease in disparity among the strength of concrete and epoxy.

• Tunnel and Underground Space
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• v.17 no.5
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• pp.411-427
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• 2007

Reliability in tunnel analysis is necessary to accomplish technically sound design and economical construction. For this, a thorough understanding of the construction procedure including the ground-support interaction has to be obtained. This paper describes a proper modelling technique to simulate the behavior of the steel fiber reinforced shotcrete (SFRS) which maintain the supporting capability in post-failure regime. The additional supporting effect of the steel support was also verified by 3-D analyses and a new load distribution factor were proposed. The use of the plastic moment limit (PML) alone can eliminate the occurrence of the awkwardly high tensile stress in the shotcrete and can successfully model the post-peak ductile behavior of the SFRS. But with this method, moment is limited whenever the stress caused by moment reaches tensile strength of the shotcrete irrespective of the stress by axial force. Therefore, it was necessary to find a more comprehensive method which can reflect the influence of the moment and axial force. This can be accomplished by the proper use of "liner element" which is the built-in model in FLAC. In this model, the peak and residual strength as well as the uniaxial compressive strength of the SFRS can be specified. Analyses were conducted with these two models on the 2-lane road tunnels excavated in class IV and V rock mass and results were compared with the conventional elastic beam model. Results showed that both models can reflect the fracture toughness of the SFRS which could not be accomplished by the elastic beam model.

• Journal of the Korean Geosynthetics Society
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• v.2 no.1
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• pp.57-68
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• 2003

Strain-softening model is developed to characterize the interface behavior of geomembrane with geotextile and geosynthetic clay liner(GCL). The model proposed in this research is calibrated by using data from direct shear tests conducted on smooth and textured geomembrane. The research is divided into two regions, pre-peak and post-peak, to take into account of strain-softening effect. Although slight difference between measured and back calculated data is observed under high normal stress, good agreements, in general, are found from back calculations. Especially, good consistency is observed in the case of low normal stress. Based on the results, it can be concluded that the proposed model can be a reasonable constitutive law to figure out the behavior of strain-softening between interfaces of geomembrane. In addition, DSC(Disturbed State Concept) model is also presented for further application in geosynthetic interfaces.

• Nuclear Engineering and Technology
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• v.56 no.1
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• pp.114-122
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• 2024

Irradiation-induced defects and the precipitates in the wrapper material of the Indian Fast Breeder Test Reactor (FBTR), SS 316 are analyzed using the synchrotron source-based Angle Dispersive X-Ray Diffraction (ADXRD) technique with X-rays of energy 17.185 keV (wavelength ~0.72146 Å). The differences and similarities in the high displacement damage samples as a function of dpa (displacement per atom) and dpa rate in the range of 2.9 × 10^-7- 9 × 10^-7 dpa/s are studied. Ferrite and M₂₃C₆ are commonly observed in the present set of high displacement damage 40-74 dpa SS 316 samples irradiated at temperatures in the range of 400-483 ℃. Also, the dislocation density has increased as a function of the irradiation dose. The X-ray diffraction peak profile parameters quantified such as peak shift and asymmetry show that the irradiation-induced defects are sensitive to the dpa rate-irradiation temperature combinations. The increase in yield strength as a function of displacement damage is also correlated to the dislocation density.

• Earthquakes and Structures
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• v.10 no.5
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• pp.1049-1066
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• 2016

An approximate analysis is presented for multi-story setback buildings subjected to ground motions. Setback buildings with mass and stiffness discontinuities are common in modern architecture and quite often they are asymmetric in plan. The proposed analysis provides basic dynamic data (frequencies and peak values of base resultant forces) and furthermore an overview of the building response during a ground excitation. The method is based on the concept of the equivalent single story system, which has been introduced by the author in earlier papers for assessing the response of uniform in height buildings. As basic quantities of the dynamic response of elastic setback buildings can be derived by analyzing simple systems, a structural layout of minimum elastic rotational response can be easily constructed. The behavior of such structural configurations, which is basically translational into the elastic phase, is also examined into the post elastic phase when the strength assignment of the various bents is based on a planar static analysis under a set of lateral forces simulating an equivalent 'seismic loading'. It is demonstrated that the almost concurrent yielding of all resisting elements preserves the translational response, attained at the end of the elastic phase, to the post elastic one.