• Journal of the Korea Concrete Institute
• /
• v.23 no.4
• /
• pp.405-411
• /
• 2011

Using combinations of carbon and glass fiber composites normally used for strengthening of concrete structures, the hybrid effect from strengthening concrete structures using the composite is studied. To produce the hybrid effects, the specimens were made with optimum proportions of carbon fibers with glass fibers. Then, direct tensile tests were conducted on the hybrid FRP (fiber reinforced polymer) specimens. Unlike the woven fiber sheet currently used in construction sites, the FRP specimens have to be directly combined with the fibers, which make the work very complicated. Therefore, direct tensile test specimens manufacturing method based on the combination of high-tension carbon fibers and E-type glass fibers was proposed and the effects of hybridization is studied through the direct tensile test. By comparing the ductility index, the modulus of elasticity, and the stress-strain curves of the specimens, the most optimum glass to carbon fiber combination ratio for the hybrid FRP was found to be 9 to 1 with ductile K-type epoxy. The study results are discussed in detail in the paper.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.37 no.2
• /
• pp.269-276
• /
• 2017

In order to study ultimate flexure behavior of FRP-concrete composite structures which can replace reinforced concrete structures, ABAQUS, a general purpose analysis program, was utilized for numerical nonlinear analysis of structural performance and behavior characteristics of FRP-concrete composite beams. Explicit nonlinear finite element analysis was conducted and the numerical results were compared with previous experiments. Concrete damaged plasticity model was adopted as material properties of concrete and Euro code was used as compressive stress state. Nonlinear analysis was performed for four different types of FRP-concrete composite beams, and ultimate load and cracking pattern was compared and analyzed. The model suggested in this research was able to simulate ultimate load and cracking pattern properly, it is expected to be utilized in study of precise structural and behavioral characteristics of various FRP-concrete composite structures.

• Journal of Korean Society of societal Security
• /
• v.2 no.2
• /
• pp.63-68
• /
• 2009

Seismic design of newly built bridges can be considered and carried out during construction process according to the revised road bridge design standard issued recently. While for the existing reinforced concrete bridge priers under service before new standard implements, their resistance capacity against lateral seismic loading is inferior. In this research, seismic reinforcing for existing bridge piers by nickel-chrome alloy bar has been analyzed. Based on the established model by MIDAS program, the behaviors of bridge piers including deformation and stress with and without nickel-chrome alloy reinforcing bars have been compared and discussed under lateral seismic loading. And the advantages of using nickel-chrome alloy bar as seismic reinforcement over other materials, such as good performance, good economy etc. have been demonstrated by comparison with other researches. Also the anti-seismic efficiency of nickel-chrome alloy reinforcing bars has been confirmed by MIDAS modeling analysis.

• Journal of Korean Society of Steel Construction
• /
• v.27 no.4
• /
• pp.399-410
• /
• 2015

Concrete filled steel tube(CFT) has outstanding deformation capacity and strength in comparison with reinforced concrete or steel tube. CFT drilled shaft, which is developed large shear force due to seismic load and soil liquefaction, is designed as large diameter. However, shear design equations of the current standards do not consider bond stress of CFT and it results in extremely conservative design. Currently, previous studies for improving shear equations scarcely exist and are impossible applied to large CFT drilled shafts since these studies focus on only small scale experimental research. In this study, eventually to propose improving shear equation of large diameter CFT, it is preliminary research to compare and investigate the previous studies and current standards.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.37 no.3
• /
• pp.521-529
• /
• 2017

In this study, analyzed the effective width of concrete unfilled composite steel grid deck which has different shear connector details from that of composite bridge. The effective width of concrete unfilled composite steel grid deck according to effective width calculation method, load size and main bearing bar spacing-span ratio was evaluated. As a result of analysis, it is analyzed that the effective width is calculated to be nearly equal to the actual effective width by idealizing the stress shape as a trapezoidal shape. In addition, shear hole penetration reinforcing bars applied to increase the shear strength is shown to increase the effective width. From the results of the analysis of the effective width according to main bearing bar spacing-span ratio, proposes the correction factor that can calculate the effective width ratio of the unfilled steel composite steel grid deck.

• Journal of the Korean Institute of Gas
• /
• v.13 no.2
• /
• pp.30-35
• /
• 2009

The result of this research explains an interactive behavior of buried steel pipe located below hume pipe using concept of effective depth and effective length against their intersection angle and burial distance. The cover depth of upper rigid (hume) pipe is 1.0m and depth range of flexible (steel) pipe is 0.5m to 5m from beneath bottom of hume pipe. And one more variable is their intersection angle in this study, it was considered from $0^{\circ}$ to $90^{\circ}$. From the results of this study, the effective depth is proportionally increasing with its intersection angle and decreasing with distance increment between two pipes. Finally, the relationship between effective length and summation of occurred bending stress is defined.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.1 no.3
• /
• pp.59-68
• /
• 1997

The necessity of a high-rise building in big cities gave a new problem to structural engineers. The shortening effect of vertical members needs special considerstion in the desigh and construction of high-rise buildings. The shortening of each column transfers load to nonstructural members such as partitions, cladding, and M/E systems which are not designed to carry gravity loads. Also, the slabs and beams will tilt due to the cumulative differential shortening of adjacent vertical members. The main purpose of estimating the total shortening of vertical structural members is to compensate the differential shortening between adjacent members. This paper presents the structural effect of differential shortening between in main structural members. Lateral earthquake load is applied to the 52 story concrete structure which has an initial vertical displacement due to the gravity load. Shortening amount for each vertical member was estimated using the computerized column shortening software. Comparison of stresses between the shortening corrected structure and the uncorrecated structure due to earthquake load was discussed.

• Computational Structural Engineering
• /
• v.8 no.4
• /
• pp.75-85
• /
• 1995

The purpose of the present study is to develop a computer program which can be used to analyze prestressed concrete structures containing either bonded or unbonded tendons. To accomplish this, first, the concrete, nonprestressed, and prestressed steels are modeled with cyclic constitutive laws to take into account the various loading effects. Then, the hybrid-type element method is derived to improve the computations capability of stresses and strains, especially for the unbonded tendon. Since it allows one to determine the cross-sectional deformations in an element without any assumptions for its deformed shape, the element length can be much longer than that of the conventional finite element method. In order to achieve such a long element, various integral schemes are examined to implement them into the program. Then, the computational method for prestressing effects is developed consistently with the analytical method for the structure. Finally, analytical studies for actual tests were carried out to verify the program developed in this study.

• Journal of the Korea Concrete Institute
• /
• v.21 no.1
• /
• pp.65-74
• /
• 2009

Glass fiber reinforced polymer (GFRP) bars are sometimes used when corrosion of conventional reinforcing steel bar is of concern. In this study, a total of 36 beams and one-way slabs reinforced using GFRP bars were tested in flexure. Four different GFRP bars of 13 mm diameter were used in the test program. In most test specimens, the GFRP bars were lap spliced at center. All beams and slabs were tested under 4-point loads so that the spliced region be subject to constant moment. Test variables were splice lengths, cover thicknesses, and bar spacings. No stirrups were used in the spliced region so that the tests result in conservative bond strengths. Average bond stresses that develop between GFRP bars and concrete were determined through nonlinear analysis of the cross-sections. An average bond stress prediction equation was derived utilizing two-variable linear regression. A splice length equation based on 5% fractile concept was then developed. As a result of this study, a rational equation with which design splice lengths of the GFRP bars can be determined, was proposed.

• Journal of the Korea Concrete Institute
• /
• v.21 no.1
• /
• pp.47-53
• /
• 2009

12 concrete blocks, on which hybrid fibrous sheets (carbon fiber and glass fiber) had been bonded, were subjected to tensile load in order to estimate properties of the bonded interface. the sheet length was varied by 100mm, 200mm and 400mm. It was found that more than 150mm bond length is required to achieve the maximum bearing capacity of the interface. In this study, maximum bond stress $\tau_{F,max}$, ultimate slip $S_{FU}$ of the interface were estimated $\tau_{F,max}$=3.0MPa and $S_{FU}$= 0.175mm, respectively.