• Journal of Korean Tunnelling and Underground Space Association
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• v.14 no.3
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• pp.247-260
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• 2012

In order to reduce the amount of steel reinforcements in TBM tunnel segments, the use of Steel Fiber Reinforced Concrete(SFRC) is being tried. The steel fibers with higher aspect ratio than that used in tunnel shotcrete are preferred to compensate the deficiency in tensile strength of the segments. In this study, the tensile properties of SFRC with aspect ratio of steel fibers equal to 80 were evaluated through flexural test and Double Punch Test. In the results of flexural test, flexural strengths of the SFRC were increased about 30%~150% thanks to bond of steel fibers used to concrete and could be properly predicted by the equation proposed by Oh(2008). There was a great difference in the estimated direct tensile strengths of the SFRC by the equations presented in ACI and RILEM. It was found that the Double Punch Test could be suitable methodology to estimate the direct tensile strength presented in RILEM of the SFRC.

• Earthquakes and Structures
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• v.20 no.3
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• pp.325-335
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• 2021

The majority of Turkey's geography is at risk of earthquakes. Within the borders of Turkey, including the two major active faults contain the North-Eastern and Eastern Anatolia, earthquake, threatening the safety of life and property. On January 24, 2020, an earthquake of magnitude 6.8 occurred at 8:55 p.m. local time. According to the data obtained from the stations in the region, peak ground acceleration in the east-west direction was measured as 0.292 g from the 2308 coded station in Sivrice. It is thought that the earthquake with a magnitude of Mw 6.8 was developed on the Sivrice-Puturge segment of the Eastern Anatolian Fault, which is a left lateral strike slip fault, and the tear developed in an area of 50-55 km. Aftershocks ranging from 0.8 to 5.1 Mw occurred following the main shock on the Eastern Anatolian Fault. The earthquake caused severe structural damages in Elazığ and neighboring provinces. As a result of the field investigations carried out in this study, significant damage levels were observed in the buildings since it did not meet the criteria in the earthquake codes. Within the study's scope, the structural damage cases in reinforced concrete and masonry structures were investigated. Many structural deficiencies and mistakes such as non-ductile details, poor concrete quality, short columns, strong beams-weak columns mechanism, large and heavy overhangs, masonry building damages and inadequate reinforcement arrangements were observed. Requirements of seismic codes are discussed and compared with observed earthquake damage.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.2
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• pp.100-107
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• 2018

The material and geometrical nonlinear finite elment analysis of UHPFRC 50M composite box girder was carried out. Constitute law in tension and compressive region of UHPFRC and HPC were modeled based on specimen test. The accuracy of nonlinear FEM analysis was verified by the experimental result of UHPFRC 50M composite girder. The UHPFRC 50M segmental composite box girder which has 1.5% steel fiber of volume fraction, 135MPa compressive strength and 18MPa tensile strength was tested. The post-tensioned UHPFRC composite girder consisted of three segment UHPFRC U-girder and High Strength Concrete reinforced slab. The parts of UHPFRC girder were modeled by 8nodes hexahedron elements and reinforcement bars and tendons were built by 2nodes linear elements by Midas FEA software. The constitutive laws of concrete materials were selected Multi-linear model both of tension and compression function under total strain crack model, which was included in classifying of smeared crack model. The nonlinearity of reinforcement elements and tendon was simulated by Von Mises criteria. The nonlinear static analysis was applied by incremental-iteration method with convergence criteria of Newton-Raphson. The validation of numerical analysis was verified by comparison with experimental result and numerical analysis result of load-deflection response, neutral axis coordinate change, and cracking pattern of girder. The load-deflection response was fitted very well with comparison to the experimental result. The finite element analysis is seen to satisfactorily predict flexural behavioral responses of post-tensioned, reinforced UHPFRC composite box girder.

• Steel and Composite Structures
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• v.20 no.4
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• pp.813-832
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• 2016

This research deals with the behavior of Composite Box Girder Bridges (CBGBs) subjected to environmental effects such as solar radiation, atmospheric temperature, and wind speed. It is based on temperature and thermal stress results, which were recorded hourly from a full-scale experimental CBGB segment and Finite Element (FE) thermal analysis. The Hemi-cube method was adopted to achieve the accuracy in temperature distributions and variations in a composition system during the daily environmental variations. Analytical findings were compared with the experimental measurements, and a good agreement was found. On the other hand, parametric investigations are carried out to investigate the effect of the cross-section geometry and orientation of the longitudinal axis of CBGB on the thermal response and stress distributions. Based upon individual parametric investigations, some remarks related to the thermal loading parameters were submitted. Additionally, some observations about the CBGB configurations were identified, which must be taken into account in the design process. Finally, this research indicates that the design temperature distribution with a uniform differential between the concrete slab and the steel girder is inappropriate for describing the thermal impacts in design objective.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.5
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• pp.1-11
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• 1993

Precast/Prestressed concrete segmental bridges with moderate range of span length normally have a constant section height for economic segment manufacturing. Inside sectional dimension is often controlled for design of non-prismatic section between supports when variable stiffness is required. It is usual, in the preliminary design stage, to adopt trial bridge sections by past experience or by approximately estimated member forces. Three bridge models of different member stiffness have been selected to investigate flexural stiffness effects on member forces for preliminary design stage. The selected bridge stiffness has been determined by the flexibility index from review of the practically usable sections.

• Research in Mathematical Education
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• v.5 no.2
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• pp.107-118
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• 2001

Mathematics subject of the seventh national curriculum in Korea, which has been effective since 2000, strongly encourages the use of calculators and computers to help children gain a better understanding of basic mathematical concepts and develop creative thinking and problem-solving skills without spending too much time and effort on making mechanical computations. Despite the recommendation by the national curriculum, however, only a small segment of elementary school teachers have been using calculators because of the fear that children\\`s dependence on calculators might bring about negative consequences. As a result, little research has been conducted in this area as well. This study has been conducted on the assumption that calculators have the potential for being a useful instructional tool in certain areas of elementary school mathematics education. To investigate the usefulness of calculators, a review was made of the scanty literature in the area. The literature review indicated that calculators are effective when they are used for the following purposes: understanding concepts and properties in numbers and operations, deducing mathematical rules, and solving problems. In view of the available research finding, we will give some concrete learning and teaching models of such uses of calculators. The teaching-learning models are organized around three categories: concept formation, discovery of principles and rules, and problem solving. Such organization is intended to help teachers use the models with ease.

• Journal of the Korean Society of Safety
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• v.29 no.2
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• pp.38-44
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• 2014

When a cable-stayed bridge is under construction, the cable tension that changes according to the construction phase is the index indicating the proper construction management. In this study, the vibration method using the least-square estimation has been implemented to monitor changing tensions of two multi-strand cables of a cable-stayed bridge under construction. The test bridge is Hwamyung Bridge in Korea with a prestressed concrete box girder. The field tests are executed during the second tensioning stage just after the installation of the key segment. The tensions of two cables are measured before and after the tensioning and 5 days later (i.e., after finishing the tensioning of all cables). The accuracy of the estimated tensions by the vibration method has been improved by employing proper effective lengths of the cables. The measured tensions are compared with the result of the lift-off tests and design tensions. The vibration method shows very good performance in monitoring the changing tensions according to the construction phase with minimal error.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.6
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• pp.103-112
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• 2007

The purpose of this study is to evaluate the characteristics of the structural behavior in precast segmental prestressed concrete girders, which consist of five precast segments. These girders were developed to save labor and cost in construction field reducing a term of work. Therefore, four different types of specimens of 25m in length were built, and they were tested and analyzed for observing flexural behavior. The analysis included the investigation of the flexural behaviors in varying tendon amount and at joints using the relationship between moment and deflection. Moreover, nonlinear finite element analysis was utilized to verify the experimental result.

• Nuclear Engineering and Technology
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• v.7 no.4
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• pp.277-284
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• 1975

A result of measurement for the relative dose distribution of neutron gamma mixed radiation field in the biological irradiation facility installed at TRIGA Mark-III reactor is described. The relative dose distributions of neutron-gamma mixed radiation field in the biological exposure room have been experimentally determined using a thermoluminescent dosimeter. Presented herein in graphical forms are the experimental results obtained. It as observed that the region commonly having the characteristics of rather homogeneous horizontal and lateral dose distributions is confined to the area bounded by the two planes horizontally parallel to the beam direction with heights of about 40 cm and 130 cm, respectively, at distances beyond 100 cm from the segmentary surface of the aluminum pool liner projected into the the exposure room, while other areas show a steeper gradient in dosage, especially the places adjacent to the segment of the aluminum pool liner and near the inner po${\gamma}$lion of the concrete walls of the exposure room.

• Earthquakes and Structures
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• v.25 no.1
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• pp.57-67
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• 2023

The buckling of longitudinal reinforcements under seismic loading accelerates the degradation of the bearing capacity of reinforced concrete columns. The traditional hysteretic constitutive model of reinforcement, which does not consider buckling, usually overestimates the seismic performance of pier columns. Subsequent researchers have also proposed many models including the buckling effects. However, the accuracy of these hysteretic constitutive models proposed for simulating the buckling behavior is inadequate. In this study, based on their works, the influence of historical events on buckling is considered, the path of the re-tensioning phase is corrected by adjusting the boundary lines, and the positions of the onset buckling point and compressive buckling path during each buckling deformation are corrected by introducing correction parameters and a boundary line. A modified hysteretic constitutive model is obtained, that can more accurately reflect the buckling behavior of reinforcements. Finally, a series of hysteresis tests of reinforcements with different slenderness ratios were then conducted. The experimental results verify the effectiveness of the proposed modified model. Indicating that the modified model can more accurately simulate the equivalent stress-strain relationship of the buckling reinforcement segment.