• Structural Engineering and Mechanics
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• v.63 no.3
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• pp.371-384
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• 2017

Ultra high performance concrete (UHPC) has recently been applied as an alternative to conventional concrete in construction due to its extremely high compressive and tensile strength, and enhanced durability. However, up to date, there has been insufficient information regarding the confinement behavior of UHPC columns. Therefore, this study aims to perform an assessment of axial stress-strain model for UHPC confined by circular steel tube stub columns. The equations for calculating the confined peak stress and its corresponding strain of confined concrete in existing models suggested by Johansson (2002), Sakino et al. (2004), Han et al. (2005), Hatzigeorgiou (2008) were modified based on the regression analysis of test results in Schneider (2006) in order to increase the prediction accuracy for the case of confined UHPC. Furthermore, a new axial stress-strain model for confined UHPC was developed. To examine the suitability of the modified models and the proposed model for confined UHPC, axial stress-strain curves derived from the proposed models were compared with those obtained from previous test results. After validating the proposed model, an extensive parametric study was undertaken to investigate the effects of diameter-to-thickness ratio, steel yield strength and concrete compressive strength on the complete axial stress-strain curves, the strength and strain enhancement of UHPC confined by circular steel tube stub columns.

• Journal of the Korea Concrete Institute
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• v.27 no.5
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• pp.521-530
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• 2015

Design of fiber reinforced ultra-high strength concrete members should be verified with analytical or experimental methods for safety. Members with compressive strength larger than limitation of current design code usually be designed with analytical verification using stress-strain relation of concrete and reinforcements. For this purpose, mechanical characteristics of steel fiber reinforced ultra-high strength concrete were defined under uniaxial compression. Mix proportions of test specimens were based on reactive powder concrete and straight steel fibers were mixed with different volume fraction. Compressive strength of matrix were distributed from 80 MPa to 200 MPa. Effect of fiber inclusion were investigated : increase of compressive strength of concrete, elastic modulus and strain corresponding to peak stress. For the wide range application of investigation, previously tested test specimens were collected and used for investigation and estimation equation. Based on the investigation and evaluation of previous research results and estimation equation of mechanical characteristics of concrete, regression equations were suggested.

• Steel and Composite Structures
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• v.29 no.1
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• pp.125-138
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• 2018

The research on the confinement behavior of ultra high performance concrete without and with the use of steel fibers (UHPC and UHPFRC) has been extremely limited. In previous studies, authors experimentally investigated the axially compressive behavior of circular steel tube confined concrete (STCC) short and intermediate columns with the employment of UHPC and UHPFRC. Under loading on only the concrete core, the confinement effect induced by the steel tube was shown to significantly enhance the utimate stress and its corresponding strain of the concrete core. Therefore, this paper develops a simplified stress - strain model for circular STCC columns using UHPC and UHPFRC with compressive strength ranging between 150 MPa and 200 MPa. Based on the regression analysis of previous test results, formulae for predicting peak confined stress and its corresponding strain are proposed. These proposed formulae are subsequently compared against some previous empirical formulae available in the literature to assess their accuracy. Finally, the simplified stress - strain model is verified by comparison with the test results.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.659-664
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• 2001

Concrete has a different fracture mechanism from the other materials, with the existing of FPZ at the ahead of its cracks, and represents the softening curves at the post-peak load in the load-displacement diagrams. So, it can transmit the stress at the post-peak load. This can not be understood with the traditional concept of strength, but with the theory based energy approach. For the purpose of this study is mainly used RILEM(1990 TC89-FMT) and TPM, and the concrete fracture properties have been evaluated according to the its compressive strength. The evaluated fracture properties is $G_{F}$, $a_{c}$, $K_{IC}$ , CTODc, Q etc.c.c.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1499-1502
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• 2003

This paper describes the result of carbody and vibration test for freight car. The purpose of the test is to evaluate an safety which carbody structure shall be considered fully sufficient rigidity so as to load a freight car under maximum load and operating condition on line track. The test carbody is constructed by RS korea co., LTD. in accordance with KNR specfication. The test cases of the carbody is tested the vertical load and compressive load to verify the strength and stillness. The vibration test is tested for analysis and evaluation of vibration, to allow for the fact that mechanical vibration in railway vehicles have specific characteristics.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.45-46
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• 2005

The piezoelectric ZnO thin films were deposited onto Al/Si substrate in order to figure out the crystalline and the residual stress of deposited films. As the $Ar/O_2$ gas ratio is increased, c-axis orientation of deposited films is significantly enhanced and also the residual stresses of ZnO films are all compressive. They are decreased from -1.2 GPa to -950 MPa as the $Ar/O_2$ gas ratio is increased. A diaphragm-based piezoelectric microspeaker fabricated on ONO films shows about 14 mPa output pressure at 1 kHz with $8V_{peak-to-peak}$.

• Geomechanics and Engineering
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• v.16 no.6
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• pp.627-634
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• 2018

Soil stabilization is an essential engineering process to enhance the geotechnical properties of soils that are not suitable for construction purposes. This study focuses on using coconut coir, a natural fibre to enhance the soil properties. Lime, an activator is added to the reinforced soil to augment its shear strength and durability. An experimental investigation was conducted to demonstrate the effect of coconut coir fibers and lime on the consistency limits, compaction characteristics, unconfined compressive strength, stress-strain behaviour, subgrade strength and durability of the treated soil. The results of the study illustrate that lime stabilization and coir reinforcement improves the unconfined compressive strength, post peak failure strength, controls crack propagation and boosts the tensile strength of the soil. Coir reinforcement provides addition contact surface, improving the soil-fibre interaction and increasing the interlocking between fibre and soil and thereby improve strength. Optimum performance of soil is observed at 1.25% coir fibre inclusion. Coir being a natural product is prone to degradation and to increase the durability of the coir reinforced soil, lime is used. Lime stabilization favourably amends the geotechnical properties of the coir fibre reinforced soil.

• Journal of the Korea Institute of Building Construction
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• v.12 no.2
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• pp.183-193
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• 2012

Compressive property of high strength concrete with amorphous metal fibers subject to high temperature has been investigated. The measure of this investigation includes explosive spalling, weight loss, residual compressive strength, strain at peak stress, elastic modulus, and residual energy absorption capacity after exposure to $400^{\circ}C$, $600^{\circ}C$and $800^{\circ}C$. In addition to the amorphous metal fiber, two other types of fibers (polypropylene fiber and hooked-end steel fiber) were also included in this investigation for comparison. The experimental program was conducted with high strength concrete using several combinations of the fiber types. The testing result shows that the concrete with amorphous metal fibers plus polypropylene fibers shows a superior behavior than those using other combination or single fiber type ingredient.

• Structural Engineering and Mechanics
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• v.22 no.3
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• pp.311-330
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• 2006

Standard compression tests of steel fiber reinforced concrete (SFRC) cylinders are conducted to formulate compressive stress versus compressive strain relationship of SFRC. Axial pullout tests of SFRC specimens are also conducted to explore its tensile stress strain relationship. Cover concrete spalling and reinforcement buckling models developed originally for normal reinforced concrete are modified to extend their application to SFRC. Thus obtained monotonic material models of concrete and reinforcing bars in SFRC members are combined with unloading/reloading loops used in the cyclic models of concrete and reinforcing bars in normal reinforced concrete. The resulting path-dependent cyclic material models are then incorporated in a finite-element based fiber analysis program. The applicability of these models at member level is verified by simulating cyclic lateral loading tests of SFRC columns under constant axial compression. The analysis using the proposed SFRC models yield results that are much closer to the experimental results than the analytical results obtained using the normal reinforced concrete models are.

• 한국기계연구소 소보
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• s.15
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• pp.91-103
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• 1985

In this paper, temperature distribution and thermal stress are investigated considering engine peak pressure and the time average temperature distribution in the piston under running conditions for the diesel engine. The induced stress are calculated by the Finite Element Method(FEM). The results obtained are summerized as follows. 1) The results calculated by the FEM present good agreement with other numerical solution in literature. 2) It is confirmed that maximum compressive stress are induced in the part of outside wall between the piston crown and the pin bush. 3) In the axial direction, the hoop stresses are changed its sigh at the portion of crown near the inner wall side 4)Large gradient of temperature is shown in the piston crown near the side wall in the axial direction, in the part between the piton crown and the pin bush in radical direction 5)in case of stress distribution of piston wall surface in the axial direction, the hoop stress is a little greater than axial stress, and the latter is greater than the radial stress