• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.6
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• pp.209-217
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• 2021

This paper investigates the effect of high strength hooked-end steel fiber content and aspect ratio on the compressive and flexural performance of concrete. A total of ten mixtures were prepared and tested. Concretes with specific compressive strength of 30 MPa were reinforced with three different aspect ratios (l/d) of steel fibers 64, 67, and 80 and three different percentages of steel fibers 0.25, 0.50, and 0.75% by volume of concrete. Tensile strengths of steel fibers with l/d of 64, 67, and 80 are 2,000, 2,400, and 2,100 MPa, respectively. The compressive and flexural properties of plain and steel fiber-reinforced concrete (SFRC) mixtures were evaluated and compared. The experimental results indicated that the incorporation of high-strength hooked-end steel fibers had significant effects on the compressive and flexural performance of concrete. With the increase of steel fiber content, compressive performances, such as Poisson's ratio and toughness, of concrete were improved. The steel fibers with the least l/d of 67 resulted in a larger enhancement of compressive performances. The residual flexural strength, that is, post-cracking flexural resistance and toughness, of concrete is mainly depended on the dosage and aspect ratio of steel fibers. The residual flexural strength at serviceability (SLS) and ultimate limit state (ULS) defined in fib Model Code 2010 (MC2010) is increased as the fiber content and aspect ratio increase.

• Tunnel and Underground Space
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• v.21 no.1
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• pp.33-40
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• 2011

This study focuses on having a temperature and water pressure effects on the change of material properties of rocks. Granite and limestone specimens from Gagok Mine were thermally treated with predetermined temperatures of 200, 300, 400, 500, 600 and $700^{\circ}C$ (excepting $700^{\circ}C$ for limestone) to estimate the reduction of material properties of rocks caused by heat. Specific gravity, effective porosity, elastic wave velocity, uniaxial compressive strength, Young's modulus and Poisson's ratio for pre-heated specimens were measured. With increasing temperature, material properties of both rock specimens change sequentially. Significant changes of specific gravity, effective porosity and elastic wave porosity occur above $400^{\circ}C$ for granite and $300^{\circ}C$ for limestone. Changes of uniaxial compressive strength, Young's modulus and Poisson's ratio seem to be similar to those of physical properties. GSI of 500, 600 and $700^{\circ}C$ specimens inferred by using uniaxial compressive strength and Young's modulus of preheated granite specimens is found to be 81, 66 and 58 each. In case of pre-heated limestone specimens of 400, 500 and $600^{\circ}C$, the corresponding GSI is 76, 71 and 65 each. 500, 600 and $700^{\circ}C$ granite specimens and 400, 500 and $600^{\circ}C$ limestone specimens were pressurized to 7.5 MPa and their effective porosity, elastic wave velocity, uniaxial compressive strength and Young's modulus were measured. The average value of material properties (mentioned above) of 500, 600 and $700^{\circ}C$ granite specimens under water pressure compared with material properties of non-pressurized pre-heated specimens exhibits the reduction of 7.6, 11.3 and 14.9%, respectively. In case of 400, 500 and $600^{\circ}C$ limestone specimens under water pressure, the average value of material properties decreases by 8.2, 13.8 and 21.9%, respectively.

• Tunnel and Underground Space
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• v.26 no.4
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• pp.293-303
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• 2016

Underground $CO_2$ storage technology is one of the most effective methods to reduce atmospheric $CO_2$. In this study, $CO_2$ storage condition was simulated in the laboratory. Sandstone and shale specimens were saturated in 1M NaCl and were reacted at $45^{\circ}C$, 10 atm for 4 weeks. The physical and microstructural properties of rock specimens were measured. Variations on physical properties of shale specimens were bigger than those of sandstone specimens, such as volume, density, elastic wave velocity, Poisson's ratio and Young's modulus. Microstructure were analyzed using X-ray computed tomography. Total number of pores were decreased, and average volume, average area and average equivalent diameter of each pore were changed after $CO_2$ reaction. Swelling and leakage of clay mineral caused by $CO_2$-mineral reaction were the reason of changes. The results of this study can be applied to predict the physical and microstructural changes in underground $CO_2$ storage condition.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.5
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• pp.653-660
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• 2010

The stern tube bearing is installed to the stern tube and stern boss casting by using the method of the force pressured fitting. The adequate value of the interference between the stern tube bearing and casting should be considered owing to the slip. In this study, to review and compare the fitting force and the contact pressure, the theory of thick walled cylinder is considered to clarify the formula which received from the maker. Also the fitting force and contact pressure are calculated by using the standard value of interference, Young's modulus, Poisson's ratio and friction coefficient.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.2
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• pp.148-155
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• 2008

The aim of the study is to interpret the distribution of occlusal force by 3-dimensional finite element analysis of ISP(Implant Supported Prosthesis) supported by minimum number of implant to restore the edentulous patients. For this study, the Astra Tech implant system is used. Geometric modeling for 6 and 4 fixture ISP group is performed with respect to the bone, implant and one piece superstructure, respectively. Implants are arbitrarily placed according to the anatomical limit of lower jaw and for the favorable distribution of occlusal force, which is applied at the end of cantilever extension of ISP with 30mm. Element type is tetrahedral for finite element model and the typical mechanical properties, Young's modulus and Poisson's ratio of each material, cortical, cancellous bone and implant material are utilized for the finite element analysis. From this study, we can see the distribution of equivalent stress equal to real situation and speculate the difference in the stress distribution in the whole model and at each implant fixture, From the analysis, the area of maximum stress is distributed on distal contact area between bone and fixture in the crestal bone. The maximum stress is 53MPa at the 0.2mm area from the bone-implant interface in the maximum side for 300N load condition for 4 fixture case, which is slightly less than the stress calculated from allowable strain. This stress has not been deduced to directly cause the loss of crestal bone around implant fixture, but the stress can be much reduced as the old peoples may have lower chewing force. Thus, clinical trial may be performed with this treatment protocol to use 4 fixtured ISP for old patients.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.11 no.5
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• pp.89-100
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• 2001

The Ritz method Is applied In a three-dimensional (3-D) analysis to obtain accurate frequencies for thick. linearly tapered. annular plates. The method is formulated for annular plates haying any combination of free or fixed boundaries at both Inner and outer edges. Admissible functions for the three displacement components are chosen as trigonometric functions in the circumferential co-ordinate. and a1gebraic polynomials in the radial and thickness co-ordinates. Upper bound convergence of the non-dimensional frequencies to the exact values within at least four significant figures is demonstrated. Comparisons of results for annular plates with linearly varying thickness are made with ones obtained by others using 2-D classical thin place theory. Extensive and accurate ( four significant figures ) frequencies are presented 7or completely free. thick, linearly tapered annular plates haying ratios of average place thickness to difference between outer radius (a) and inner radius (b) radios (h$_{m}$/L) of 0.1 and 0.2 for b/L=0.2 and 0.5. All 3-D modes are included in the analyses : e.g., flexural, thickness-shear. In-plane stretching, and torsional. Because frequency data liven is exact 7o a\ulcorner least four digits. It is benchmark data against which the results from other methods (e.g.. 2-D 7hick plate theory, finite element methods. finite difference methods) and may be compared. Throughout this work, Poisson\`s ratio $\upsilon$ is fixed at 0.3 for numerical calculations.s.

• Composites Research
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• v.31 no.5
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• pp.276-281
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• 2018

In this paper, elastic behavior of woven fabric composites with various fiber yarn structure were predicted through a theoretical calculation model. A representative volume elements (RVE) that can represent the mechanical properties of the woven composites were selected and crimp angle of the weave yarn was defined by several sinusoidal functions. The effective material properties of the woven composite such as young's modulus, shear modulus and poisson's ratio was predicted by classical laminate theory (CLT). The fiber volume fractions were calculated according to the shape and pattern (plain, twill weave) of the fiber yarn, and the elastic behavior of each woven composite was obtained through a theoretical calculation model. Also, to verify the theoretical predictions, woven composite specimens of plain and twill weave were fabricated by vacuum assisted resin transfer molding (VARTM) process and then mechanical test was conducted. As a results, a good correlation between theoretical and experimental results for the elastic behavior of woven composites could be achieved.

• 한국터널공학회:학술대회논문집
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• 2005.04a
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• pp.348-358
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• 2005

Although the evaluation of the mechanical properties and behavior of discontinuous rock masses is very important for the design of underground openings, it has always been considered the most difficult problem. One of the difficulties in describing the rock mass behavior is assigning the appropriate constitutive model. This limitation may be overcome with the progress in discrete element software such as PFC, which does not need the user to prescribe a constitutive model for rock mass. Instead, the micro-scale properties of the intact rock and joints are defined and the macro-scale response results from those properties and the geometry of the problem. In this paper, a $30m{\times}30m{\times}30m$ jointed rock mass of road tunnel site was analyzed. A discrete fracture network was developed from the joint geometry obtained from core logging and surface survey. Using the discontinuities geometry from the DFN model, PFC simulations were carried out, starting with the intact rock and systematically adding the joints and the stress-strain response was recorded for each case. With the stress-strain response curves, the mechanical properties of discontinuous rock masses were determined and compared to the results of empirical methods such as RMR, Q and GSI. The values of Young's modulus, Poisson's ratio and peak strength are almost similar from PFC model and Empirical methods. As expected, the presence of joints had a pronounced effect on mechanical properties of the rock mass. More importantly, the mechanical response of the PFC model was not determined by a user specified constitutive model.

• Magazine of the Korea Concrete Institute
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• v.6 no.3
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• pp.131-141
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• 1994

This study was carried out to develop a procedural method to produce high strength polymer concrete using unsaturated polyt.ster resin and to examine its mechanical properties. Various mechanical properties were analyzed with respect to materials and additives. A method to produce high strength polymer concrete was successfully developed. Comperssive strength of $1,291~1,445 kg/cm^2$, splitting tensile strength of $106~145 kg/cm^2$ and flexural strength of $182~235 kg/cm^2$, at age of 7days wer-e achieved from the cylinderical ;md beam specimen prepared with the method. Modulus of elasticity. Poisson's rntio and the ultirnate corn pressive strain of cylinderical specimen were $2.8~3.8{\times}10^5\;kg/cm^2$. 0.21~0.32, and 0.005~0. 0065, respectively. Modulus of elasticity of the polymer concrete was smaller than that of hlgh strength cement concrete while the maximum compressive strain was very larger than that of high strength cement concrete.

• Magazine of the Korea Concrete Institute
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• v.9 no.1
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• pp.173-181
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• 1997

The objective of this study is to obtain the mechanical characteristics of prefoarmed lightweight foamed concrete using the polymer ham agent which has high lightness. flowability and strength. For this purpose, the prefoarmed lightweight foamed concrete which was developed to have flow value over 180mm. unit weight between 0.38t/$m^3$ and 0.64t/$m^3$, and compressive strength about 30kg/$cm^2$ was used. This paper presents extensive test data on Young's modulus. Poisson's ratio, stress-strain curve, the characteristics of strength of the foamed concrete and also presents the mechanical characteristics of the foamed concrete with different foam sizes. It is expected that this study provides an importance guide to design and manufacture lightweight foam concrete, so that it helps to expand its structural use.