• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2022.04a
• /
• pp.43-44
• /
• 2022

In this study, the optimum amount of chloride ions is used to collaborate with hybrid corrosion inhibitor for carbon steel rebar treatment in simulated pore concrete (SCP) solution is discovered. The corrosion inhibition performance of hybrid inhibitors is carried on by open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PP). The highest corrosion inhibition resistance is found in case of LP-C2 after 240 h exposure. Surface studies including scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to figure out the surface morphology of the steel rebar treated with hybrid inhibitors in order to collaborate well with electrochemical studies. Anodic type inhibition action was confirmed by potentiodynamic polarization study.

• Structural Engineering and Mechanics
• /
• v.67 no.5
• /
• pp.505-516
• /
• 2018

In this paper, the effects of particle size and model scale of concrete has been investigated on the failure mechanism of PFC2D numerical models under uniaxial compressive test. For this purpose, rectangular models with same particle sizes and different model dimensions, i.e., $3mm{\times}6mm$, $6mm{\times}12mm$, $12mm{\times}24mm$, $25mm{\times}50mm$ and $54mm{\times}108mm$, were prepared. Also rectangular models with dimension of $54mm{\times}108mm$ and different particle sizes, i.e., 0.27 mm, 0.47 mm, 0.67 mm, 0.87 mm, 1.07 mm, 1.87 mm and 2.27 mm were simulated using PFC2D and tested under uniaxial compressive test. Concurrent with uniaxial test, direct shear test was performed on the numerical models. Dimension of the models were $75{\times}100mm$. Two narrow bands of particles with dimension of $37.5mm{\times}20mm$ were removed from upper and lower of the model to supply the shear test condition. The particle sizes in the models were 0.47 mm, 0.57 mm, 0.67 mm and 0.77 mm. The result shows that failure pattern was affected by model scale and particle size. The uniaxial compressive strength and shear strength were increased by increasing the model scale and particle size.

• Smart Structures and Systems
• /
• v.22 no.5
• /
• pp.611-620
• /
• 2018

In this research the effect of bedding layer angle and bedding layer thickness on the shear failure mechanism of concrete has been investigated using PFC3D. For this purpose, firstly calibration of PFC3d was performed using Brazilian tensile strength. Secondly shear test was performed on the bedding layer. Thickness of layers were 5 mm, 10 mm and 20 mm. in each thickness layer, layer angles changes from $0^{\circ}$ to $90^{\circ}$ with increment of $25^{\circ}$. Totally 15 model were simulated and tested by loading rate of 0.016 mm/s. The results shows that when layer angle is less than $50^{\circ}$, tensile cracks initiates between the layers and propagate till coalesce with model boundary. Its trace is too high. With increasing the layer angle, less layer mobilize in failure process. Also the failure trace is very short. It's to be note that number of cracks decrease with increasing the layer thickness. The minimum shear test strength was occurred when layer angle is more than $50^{\circ}$. The maximum value occurred in $0^{\circ}$. Also, the shear test tensile strength was increased by increasing the layer thickness.

• Structural Engineering and Mechanics
• /
• v.68 no.4
• /
• pp.507-517
• /
• 2018

In this research the effect of bedding layer angle and bedding layer thickness on the shear failure mechanism of concrete has been investigated using PFC3D. For this purpose, firstly calibration of PFC3d was performed using Brazilian tensile strength. Secondly punch shear test was performed on the bedding layer. Thickness of layers were 5 mm, 10 mm and 20 mm. in each thickness layer, layer angles changes from $0^{\circ}$ to $90^{\circ}$ with increment of $25^{\circ}$. Totally 15 model were simulated and tested by loading rate of 0.016 mm/s. The results show that when layer angle is less than $50^{\circ}$, tensile cracks initiates between the layers and propagate till coalesce with model boundary. Its trace is too high. With increasing the layer angle, less layer mobilizes in failure process. Also, the failure trace is very short. It's to be note that number of cracks decrease with increasing the layer thickness. The minimum shear punch test strength was occurred when layer angle is more than $50^{\circ}$. The maximum value occurred in $0^{\circ}$. Also, the shear punch test tensile strength was increased by increasing the layer thickness.

• Journal of Environmental Science International
• /
• v.18 no.4
• /
• pp.423-434
• /
• 2009

In recent years, the urban thermal environment has become worse, such as days on which the temperature goes above $30^{\circ}C$, sultry nights and heat stroke increase, due to the changes in terrestrial cover such as concrete and asphalt and increased anthropogenic heat emission accompanied by artificial structure. The land use type is an important determinant to near-surface air temperature. Due to these reasons we need to understand and improve the urban thermal environment. In this study, the fifth-generation Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model(MMS) was applied to the metropolitan of Daegu area in order to investigate the influence of land cover changes and urban modifications increase of Albedo to the surface energy budget on the simulated near-surface air temperature and wind speed. The single urban category in existing 24-category U.S. Geological survey land cover classification used in MM5 was divided into 6 classes to account for heterogeneity of urban land cover. As a result of the numerical simulation intended for the metropolitan of Daegu assumed the increase of Albedo of roofs, buildings, or roads, the increase of Albedo (Cool scenario)can make decrease radiation effect of surface, so that it caused drops in ambient air temperature from 0.2 to 0.3 on the average during the daylight hours and smaller (or near-zero) decrease during the night. The Sensible heat flux and Wind velocity is decreased. Modeling studies suggest that increased surface albedo in urban area can reduce surface and air temperatures near the ground and affect related meteorological parameters such as winds, surface air temperature and sensible heat flux.

• Journal of Mechanical Science and Technology
• /
• v.17 no.1
• /
• pp.1-10
• /
• 2003

This paper summarizes the results of the fatigue test of four composite bridge decks in extreme temperatures (-30$^{\circ}C$ and 50$^{\circ}C$ ). The work was performed as part of a research program to evaluate and install multiple FRP bridge deck systems in Dayton, Ohio. A two-span continuous concrete deck was also built on three steel girders for the benchmark tests. Simulated wheel loads were applied simultaneously at two points by two servo-controlled hydraulic actuators specially designed and fabricated to perform under extreme temperatures. Each deck was initially subjected to one million wheel load cycles at low temperature and another one million cycles at high temperature. The results presented in this paper correspond to the fatigue response of each deck for four million load cycles at low temperature and another four million cycles at high temperature. Thus, the deck was subjected to a total of ten million cycles. Quasi-static load-deflection and load-strain responses were determined at predetermined fatigue cycle levels. Except for the progressive reduction in stiffness, no significant distress was observed in any of the composite deck prototypes during ten million load cycles. The effects of extreme temperatures and accumulated load cycles on the load-deflection and load-strain response of FRP composite and FRP-concrete hybrid bridge decks are discussed based on the experimental results.

• Computers and Concrete
• /
• v.19 no.1
• /
• pp.99-110
• /
• 2017

In this paper, the effect of normal load on the failure mechanism of echelon joint has been studied using PFC2D. In the first step, calibration of PFC was undertaken with respect to the data obtained from experimental laboratory tests. Then, six different models consisting various echelon joint were prepared and tested under two low and high normal loads. Furthermore, validation of the simulated models were cross checked with the results of direct shear tests performed on non-persistent jointed physical models. The simulations demonstrated that failure patterns were mostly influenced by normal loading, while the shear strength was linked to failure mechanism. When ligament angle is less than $90^{\circ}$, the stable crack growth length is increased by increasing the normal loading. In this condition, fish eyes failure pattern occur in rock bridge. With higher ligament angles, the rock bridge was broken under high normal loading. Applying higher normal loading increases the number of fracture sets while dilation angle and mean orientations of fracture sets with respect to ligament direction will be decreased.

• Computers and Concrete
• /
• v.19 no.2
• /
• pp.171-177
• /
• 2017

Water pressure test operation is used before the grouting to determine the rate of penetrability, the necessity and estimations related to grouting, by the penetration of water into the borehole. One of the parameters which have the highest effect is pressure of water penetration since the application of excessive pressure causes the hydraulic fracture to occur in the rock mass, and on the other hand, it must not be so small that prevents from seeing mechanical weaknesses and the rate of permeability. Mathematical modeling is used for the first time in this study to determine the optimum pressure. Thus, the joints that exist in the rock mass are simulated using cylindrical shell model. The joint surroundings are also modeled through Pasternak environment. To obtain equations governing the joints and the surroundings, energy method is used accompanied by Hamilton principle and an analytical solution method is used to obtain the maximum pressure. In order to validate the modeling, the pressure values obtained by the model were used in the sites of Seymareh and Aghbolagh dams and the relative error rates were measured considering the differences between calculated and actual pressures. Modeling in the sections of Seymareh dam showed 4.75, 3.93, 4.8 percent error rates and in the sections of Aghbolagh dam it rendered the values of 22.43, 5.22, 2.6 percent. The results indicate that this modeling can be used to estimate the amount of pressure for hydraulic fracture in water pressure test, to predict it and to prevent it.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.22 no.4
• /
• pp.419-434
• /
• 2020

In this study, the damage parameters of Mazars model for KURT (KAERI Underground Research Tunnel) granite are measured form uniaxial compressive and Brazilian tests under the simulated coupled condition of a deep geological disposal. The tests are conducted in three different temperatures (15℃, 45℃, and 75℃) and dry/saturated conditions. Major model parameters such as maximum effective tensile strain (𝜖_d0), A_t, B_t, A_c, and B_c differ from the typical reference values of concrete specimens. This is likely due to the difference in elastic modulus between rock and concrete. It is found that the saturation of specimens causes an increase in value of B_t and B_c while, the rise in temperature increases 𝜖_d0 and B_t and decreases B_c. The damage model obtained from this study will be used as the primary input parameters in the development of coupled Thermo-Hydro-Mechanical Damage numerical model in KAERI.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.15 no.9
• /
• pp.1847-1853
• /
• 2011

Analysis of an indoor propagation channel has conventionally used the ray-tracing method. But, in this paper, we had modelling the channel for three dimensional indoor structure by the finite difference time domain method for three dimensional full wave analysis. An excitation signal of the FDTD method used plane wave. The plane wave was excited using the total field/scattered field method. And absorbing boundary condition used the perfectly matched layer method with 7 layers. An living room for the simulation of indoor channel modeling is surrounded the wall that be composed of the wood, the conductor, the glass and concrete. When there are furniture in the living room or not, it were simulated, respectively. As simulation results, we could identify the fading effect of multipath at indoor propagation environment, calculated mean excess delay and rms delay spread for the receiver design.