• Journal of the Korean Geosynthetics Society
• /
• v.16 no.4
• /
• pp.221-230
• /
• 2017

We developed a polymer pouch using PVP that is water soluble in the precedent study. Yet melt viscosity was so low that it was not possible to produce hemispheric type which is essential for mass production, therefore we used another material to make the polymer pouch. It enabled to figure out a water-soluble transition and mechanic physical property of PEG that is newly chosen, and to blend the PEG with LLDPE and TALC followed by result. So, we could implement an evaluating property on blended proportion. It is important to find out a proper blending ratio throughout an experiment since its property is different or varied followed by each proportion as a water soluble character is conflict to a solid character. With the blending technique we were able to produce the polymer pouch enhanced for a tensile force and an impact intensity maintaining a water soluble character. We could identify a ground solidity effect of the polymer pouch as a result of a direct shear test using the product developed.

• Earthquakes and Structures
• /
• v.12 no.2
• /
• pp.237-250
• /
• 2017

There has been increasing attention in many countries on seismic retrofit of old fashioned RC structures in recent years. In such buildings, the joints lack transverse reinforcement and suffer inadequate seismic dimensional requirements and the reinforcement is plain bar. The behavior of the joints is governed by sliding of steel bars and diagonal shear failure is less influential. Different methods to retrofit beam-column joints have been proposed in the literature such as wrapping the joint by FRP sheets, enlargement of the beam-column joint, and strengthening the joint by steel sheets. In this study, an enlargement technique that uses external prestressed cross ties with steel angles is examined. The technique has already been used for substructures reinforced by deformed bars and has advantages such as efficient enhancement of seismic capacity and lack of damage to the joint. Three reference specimens and two retrofitted units are tested under increasing lateral cyclic load in combination with two levels of axial load. The reference specimens showed relatively low shear strength of 0.150${\surd}$($f_c$) and 0.30${\surd}$($f_c$) for the exterior and interior joints, respectively. In addition, relatively brittle behavior was observed and large deformations extended into the panel zone of the joints. The retrofit method has increased ductility ratio of the interior beam-column joints by 63%, and energy dissipation capacity by 77%, relative to the control specimen; For external joints, these values were 11%, and 94%. The retrofit method has successfully relocated the plastic joints far from the column face. The retrofit method has improved shear strength of the joints by less than 10%.

• Elastomers and Composites
• /
• v.33 no.4
• /
• pp.231-237
• /
• 1998

In order to investigate the physical properties of rubber blend compound, this experiment was carried out on the cure rate, loss tangent, reinforcement and abrasion properties of S-SBR (solution styrene-butadiene rubber) blends containing silane coupled silica and E-SBR (emulsion styrene-butadiene rubber) blends containing carbon black as a model compound. E-SBR blend showed the highest total bound rubber(TBR), while S-SBR blends showed constant TBR level regardless of rubber type. Rapid cure rate was achieved when the styrene and vinyl content of rubber microstructure decreased and TBR content of rubber compounds increased. The modulus as the index of rubber reinforcement showed the linear relation with TBR content. The large amount of PICO loss was observed when the styrene and vinyl content of rubber microstructure increased, while the small amount of PICO loss was observed when the ratio of bu-tadiene increased in the S-SBR blends with silane copuled silica. The high loss tangent at $0^{\circ}C$, the low loss tangent at $60^{\circ}C$, and the large difference of loss tangent were shown in the S-SBR blends with high styrene content compared to E-SBR blend.

• Structural Engineering and Mechanics
• /
• v.84 no.5
• /
• pp.619-632
• /
• 2022

Reinforced concrete (RC) structures may be subjected to sudden dynamic impact loads such as explosions occurring for different reasons, the collision of masses driven by rockfall, flood, landslide, and avalanche effect structural members, the crash of vehicles to the highway and seaway structures. Many analytical, numerical, and experimental studies focused on the behavior of RC structural elements such as columns, beams, and slabs under sudden dynamic impact loads. However, there is no comprehensive study on the behavior of the RC column-beam connections under the effect of sudden dynamic impact loads. For this purpose, an experimental study was performed to investigate the behavior of RC column-beam connections under the effect of low-velocity impact loads. Sixteen RC beam-column connections with a scale of 1/3 were manufactured and tested under impact load using the drop-weight test setup. The concrete compressive strength, shear reinforcement spacing in the beam, and input impact energy applied to test specimens were taken as experimental variables. The time histories of impact load acting on test specimens, accelerations, and displacements measured from the test specimens were recorded in experiments. Besides, shear and bending crack widths were measured. The effect of experimental variables on the impact behavior of RC beam-column connections has been determined and interpreted in detail. Besides, a finite element model has been established for verification and comparison of the experimental results by using ABAQUS software. It has been demonstrated that concrete strength, shear reinforcement ratio, and impact energy significantly affect the impact behavior of RC column-beam connections.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.28 no.5A
• /
• pp.719-727
• /
• 2008

The tensile and bond performance of GFRP rebar are different from those of conventional steel reinforcement. It requires some studies on concrete members reinforced with GFRP reinforcing bars to apply it to concrete structures. GFRP has some advantages such as high specific strength, low weight, non-corrosive nature, and disadvantage of larger deflection due to the lower modulus of elasticity than that of steel. Bridge deck is a preferred structure to apply FRP rebars due to the increase of flexural capacity by arching action. This paper focuses on the behavior of concrete bridge deck reinforced with newly developed GFRP rebars. A total of three real size bridge deck specimens were made and tested. Main variables are the type of reinforcing bar and reinforcement ratio. Static test was performed with the load of DB-24 level until failure. Test results were compared and analyzed with ultimate load, deflection behavior, crack pattern and width.

• Journal of the Korea Concrete Institute
• /
• v.20 no.2
• /
• pp.165-173
• /
• 2008

One of the most important requirements for reinforced concrete constructions is the bond behavior between concrete and reinforcement. For practical application, it is very important to study bond behavior of reinforcing bars in recycled aggregate concrete (RAC). Thirty six pull-out tests were carried out in order to investigate the bond behaviour between recycled coarse aggregate concrete (RCAC) and deformed bars. RCA replacement ratios (i.e., 0%, 30%, 60% and 100%) and positions of deformed bar (i.e., vertical and horizontal position) were considered as variables in this paper. Each specimen was in the form of a cube, with edges of 150 mm in length and for the pull-out tests, a deformed bar, 13 mm in diameter, was embedded in the center of each specimen. Based on the test results, the bond strength between the RCAC and deformed bars were influenced by both RCA replacement ratios and positions of deformed bars. It was found that under the equivalent mix proportion (i.e., the mix proportions are the same, except for different RCA replacement ratios), the bond strength between the RCAC and the ribbed bar has no obvious relation with the RCA replacement ratio, whereas the positions of deformed bars have a significant effect on the bond behavior between the RCAC and deformed bars. Under the condition of same RCA replacement ratio, the specimen of horizontal reinforcement at upper position (HU type) appear considerably low bond stress.

• 한국태양에너지학회:학술대회논문집
• /
• 2009.11a
• /
• pp.32-37
• /
• 2009

An energy loss through the window system occupies about 10 to 30 percent on energy consumption of the whole building. That is the reason, several elements for a building composition of window system are the weakest from the heat. Insulation performance increases for the reducing heat loss. Heat transfer through the window system that is reducing heat transfer through conduction, convection and radiation. Insulation performance reinforcement methods classify improving heat specific quality of window system and improving efficiency of whole window system. The most application method among each methods is reducing emission ratio of the window system(Low-E glass), increasing a number of glazing(multiple window) and a method of vacuuming between glazing and glazing. Therefore this study is investigated a sort of glazing and specific character, U-value calculation with changing glazing thickness and calculation of temperature distribution and U-value with a glazing charging gas kind from double glazing. For a conclusion, an aspect of U-value figure at the smallest value case of vacuum glazing with Low-E coating. That means insulation efficiency is the best advantage during a building plan selecting vacuum glazing with Low-E coating for a energy saving aspect. In this way, U-value become different the number of glazing, coating whether or not and selecting injection gas. Therefore selecting of glazing is very important after due consideration by a characteristic and use of building and consideration of strong point and weak point.

• Structural Engineering and Mechanics
• /
• v.65 no.4
• /
• pp.491-504
• /
• 2018

Because of sandwich structures with low weight and high stiffness have much usage in various industries such as civil and aerospace engineering, in this article, buckling and free vibration analyses of coupled micro composite sandwich plates are investigated based on sinusoidal shear deformation (SSDT) and most general strain gradient theories (MGSGT). It is assumed that the sandwich structure rested on an orthotropic elastic foundation and make of four composite face sheets with temperature-dependent material properties that they reinforced by carbon and boron nitride nanotubes and two flexible transversely orthotropic cores. Mathematical formulation is presented using Hamilton's principle and governing equations of motions are derived based on energy approach and applying variation method for simply supported edges under electro-magneto-thermo-mechanical, axial buckling and pre-stresses loadings. In order to predict the effects of various parameters such as material length scale parameter, length to width ratio, length to thickness ratio, thickness of face sheets to core thickness ratio, nanotubes volume fraction, pre-stress load and orthotropic elastic medium on the natural frequencies and critical buckling load of double-bonded micro composite sandwich plates. It is found that orthotropic elastic medium has a special role on the system stability and increasing Winkler and Pasternak constants lead to enhance the natural frequency and critical buckling load of micro plates, while decrease natural frequency and critical buckling load with increasing temperature changes. Also, it is showed that pre-stresses due to help the axial buckling load causes that delay the buckling phenomenon. Moreover, it is concluded that the sandwich structures with orthotropic cores have high stiffness, but because they are not economical, thus it is necessary the sandwich plates reinforce by carbon or boron nitride nanotubes specially, because these nanotubes have important thermal and mechanical properties in comparison of the other reinforcement.

• Journal of the Korea Concrete Institute
• /
• v.18 no.6 s.96
• /
• pp.749-757
• /
• 2006

Many losses of life and extensive damage of social infrastructures have occurred due to moderate and strong earthquakes all over the world. In this research various design parameters have been evaluated to develop a rational seismic design code of rectangular reinforced concrete(RC) bridge piers. It was confirmed from this study that the axial force ratio and longitudinal steel ratio were most influencing design parameters on the seismic displacement ductility from experimental results of 54 rectangular RC bridge piers, which were tested at domestic and foregin countries. However, these important parameters are not considered in the confinement steel ratio of Korea Highway Bridge Design Specification(KHBDS). The objective of this study is to propose a rational design provision for the transverse reinforcement of rectangular RC bridge piers. New confinement steel ratio is proposed by reflecting the effect of the axial force and longitudinal steel into the current code of KHBDS. furthermore, minimum transverse confinement steel ratio is also proposed to avoid a probable buckling of longitudinal reinforcing steels of RC bridge piers with a relatively low axial force. New practical code can alleviate the rebar congestion in the plastic hinge region of RC bridge pier, which contributes to construct RC bridge piers in a simple and economic way.

• Composites Research
• /
• v.30 no.5
• /
• pp.303-309
• /
• 2017

Organo-montmorillonite (OMMT) has attracted much attention for fiber-reinforced polymer composites as a filler material due to high aspect ratio and low charge density. The present study focused on the fabrication of nanocomposites using Vinyl ester and Jute fabric as matrix and reinforcement respectively. The OMMT was uniformly dispersed in vinyl ester resin at 1, 2 and 3 wt%, loading through high speed mechanical stirrer at room temperature and further nanocomposites were manufactured through vacuum assisted resin infusion (VARI) technique. Effects of OMMT on the mechanical properties of vinyl ester/Jute composites were carefully investigated through tensile, bending and Izod impact tests, which revealed significant improvement in mechanical properties. The morphology of the nanocomposites after tensile test was investigated by SEM which affirmed that OMMT filled nanocomposites has improved interactions with the host matrix than the pure composites. Based on the nature and flame retardancy mechanism, the OMMT slightly improved the flammability property which was clearly explained by horizontal burning test.