• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.5
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• pp.331-338
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• 2020

In this study, the characteristic of a 3-D micro-woven material, which is one of the newly developed periodic open-cell structure, is analyzed through various computational simulations. To increase the accuracy of the numerical simulations, the distance between each directional wire is parameterized using six design variables, and its model geometry is precisely discretized using tetrahedron elements. Using the improved computational model, the material properties of the mechanical, thermal, and fluidic behavior are investigated using commercial software and compared with the previous experimental results. By changing the space between the x- and y-directional wires, a parametric test is performed to determine the tendency of the change in the material properties. In addition, the correlation between two different material properties is investigated using the Ashby chart. The result can further be used in determining the optimal pattern and wire spacing in 3-D micro-woven materials.

• Journal of the Korea Concrete Institute
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• v.23 no.6
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• pp.799-808
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• 2011

In this study, a standardized test method to analyze tensile properties of multi-directional GFRP plate was proposed. Presently, tensile strength test of FRP composite reinforced with isotropic and orthotropic fiber is standardized according to ISO standard. Also, even though many studies were performed on test method to analyze the dynamic properties, the properties of tensile strength for multi-directional GFRP plate were not clearly identified. Currently, the domestic test method in accordance with ASTM, which is applicable to unidirectional FRP plate, gave tensile test results greater than actual properties. Thus, in this study, GFRP tensile test was conducted using the method found to be commonly applicable to all standards based on literature review of domestic and international references. Then, anchorage length experiments were performed using the proposed tension test method to evaluate validity of the method. Finally, optimal anchorage length was estimated from the numerical analysis to propose the standardized tensile strength method for GFRP multi-directional composite evaluation.

• Journal of the Korea Concrete Institute
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• v.22 no.5
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• pp.727-736
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• 2010

This paper describes results of an preliminary study to produce strain hardening cement-based composites (SHCCs)with consideration of sustainability for infrastructure applications. The aims of this study are to evaluate the influence of recycled materials on the mechanical characteristics of SHCCs, such as compressive, four-point bending, and direct tensile behaviors, and to give basic data for constitutive model for analyzing and designing infra structures with SHCCs. In this study, silica sand, cement, and PVA fibers, were partially replaced with recycled sand, fly-ash, and FET fibers in the mixture of SHCCs, respectively. Test results indicated that fly-ash could improve both bending and direct tensile performance of SHCCs due to increasing chemical bond strength at the interface between PVA fibers and cement matrices. However, SHCCs replaced with PET fibers showed much lower performance in bending and direct tensile tests due to originally low mechanical properties of own fibers, although compressive behavior is similar to PVA2.0 specimen. Also, it was noted that the recycled sand would increase elastic modulus of SHCCs due to larger grain size compared to silica sand. Based on pre-set target value to maintain the performance of SHCCs, it was concluded that the replacement ratio below 20% of fly-ash or below 50% of recycled sands would be desirable for creating sustainable SHCCs.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.6
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• pp.36-44
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• 2003

In this paper, an analytic solution method is proposed to overcome the numerical problems when the slewing dynamics of hybrid coordinate systems is investigated via time finite element analysis. It is shown that the dynamics of the hybrid coordinate systems is governed by the coupled dual differential equations for both slewing and structural modes. Structural modes are transformed into the time-based modal coordinates and analytic spatial propagation equations are derived for each space-dependent time mode. Slew angle history is obtained analytically by appropriate applications of the boundary conditions and structural propagation is re-calculated using the slew angle. Numerical examples are demonstrated to validate the proposed analytic method in comparison to the existing state transition matrix method.

• Magazine of the Korea Concrete Institute
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• v.2 no.3
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• pp.81-88
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• 1990

For the protectioon of radioactive leakage, the quality control of main concrete structure in nuclear power plants is very important. So, this studey is designed to analyze the influence of kind of cement and aggregate on the mechanical properties of high density concrete. Test results of this study are as follows; 1)The slump of magnetite aggregate concrete(MAC) is found half value of nat.ural aggregate concrete (NAC). 2)As the effect of cement, the compressive strength of concrete using moderate heat cement is found higher 5-19 % than that of ordinary portland cement. 3)As the effect of fine aggregate, t.he compressive strength of MAC is found higher than that. of NAC below 340kg/$cm^2$ and lower t.han NAC above 340kg/$cm^2$. 4)As the effect of coarse aggregate, the compressive strength of MAC is found higher 17-22% than that of NAC.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.3
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• pp.51-58
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• 2008

Development of a new design guide which is based on empirical-mechanistic concept for pavement design is in action. It is called AASHTO 2002 Design Guide in USA and the KPRP(Korean Pavement Research Project) in Korea. The material characteristic of hot mix asphalt is a key role in the design guide. Therefore it is urgent to get a proper materials database, especially the dynamic modulus of hot mix asphalt. In this research, dynamic modulus test, which is based on aged asphalt binder, has been carried out and proposed the predicted equation of dynamic modulus. Nine different hot mix asphalt with three different asphalt binder have been used for the dynamic modulus test. Short-term aging, which is covers the time for the production of asphalt plant, transportation, lay-down, and compaction, can be simulated at $135^{\circ}C$ with 2 hour curing. Long-term aging has been carried out for a performance period of asphalt pavement. The dynamic modulus of asphalt pavement increases with aging time. As the nominal aggregate size increases, the change of dynamic modulus is not big.

• Journal of Biomedical Engineering Research
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• v.22 no.5
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• pp.393-402
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• 2001

A computational model representative of cardiovascular circulation was built using 12 standard lumped compartments. Especially, both the baroreceptor reflex and the cardiopulmonary reflex control model were implemented to explain the auto-regulation of cardiovascular system. Another important aspect of this model is to utilize the impulse-response curve of the nerve system in transferring the impulse error signals to autonomous nerve system. For the verification of this model, we have computed the normal hemodynamic conditions and compared those with the clinical data. Then. hemodynamic shock of 20% hemorrhage to cardiovascular system was simulated to test the effects of the control system model. The results of these two simulations were well matched with the experimental ones. The steady state LBNP simulation was also performed. The transient changes of hemodynamic variables due to ramp increase of bias pressure of LBNP showed good agreement with the physiological experiments. Numerical solution using only the baroreflex model showed relatively a larger deviation from the experimental data. compared with the one using the control model haying both the baroreflex and the cardiopulmonary reflex systems, which shows an important role of the cardiopulmonary reflex system for the simulation of the hemodynamic behavior of the cardiovascular system .

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.2
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• pp.287-295
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• 1987

The general equation of equilibrium is presented for a stiffened plate on which the stiffeners having rectangular cross-sections are attached by one or both sides with arbitrarily angles. The principle of minimum potential energy is applied using the concept of adjusted-centroid to derive the equilibrium equation for the stiffened plate. Equivalent rigidities in the present theory are in good agreement with the experiments by the vibration method.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.3
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• pp.25-37
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• 1992

A nonlinear finite element formulation which has the capability of handling very large geometrical changes is presented. The formulation is based on an updated material reference frame and hence true stress-strain test can be directly applied to properly characterize properties of materials which are subjected to very large deformation. For the large deformation, a consistent formulation based on the continuum mechanics approach is derived. The kinematics is referred to an updated material frame. Body equilibrium is also established in an updated geometry and the second Piola-Kirchhoff stress and the updated Lagrangian strain tensor are used in the formulation. Numerical examples for very large deformation of framed structures and plane solids are analyzed for verification purposes. The numerical solutions are obtained by an incremental numerical procedure. The importance of handing material properties properly is also demonstrated.

• Journal of the Korea Concrete Institute
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• v.29 no.4
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• pp.379-387
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• 2017

The objective of this study is to develop sustainable PVA fiber-reinforced cementitious composites (FRCCs) that could exhibit comparable strength level to normal PVA FRCCs with no recycled materials. To evaluate mechanical properties of the FRCCs, compressive, flexural and direct tensile tests were conducted. In addition to the test, to calculate amount of carbon dioxide ($CO_2$) emission at the stage of manufacturing the FRCCs, life cycle inventory data base (LCI DB) were referenced from domestic and Japan. From the test results, the mechanical properties such as compressive, flexural and direct tensile strengths were decreased as the replacement ratio of recycled materials increased. And it was determined that the amount of $CO_2$ emission was reduced for the specimens with higher water-binder ratio (W/B) and replacement ratios. It was also found that binder intensity ($B_i$) value was higher as replacement ratio of fly ash (FA) increased. This result means that larger amount of FA is need to deliver one unit of a given performance indicator (1 MPa of strength) of FRCCs compared to that of ordinary portland cement (OPC). As a result, it could be concluded that FRCCs with W/B 45% replaced by FA 25% and recycled sand (RS) 25% is desirable for both target performance and $CO_2$ emission.