Modal frequency responses of composite bridges under temperature and boundary condition variations
Arjun Poudel, Seungwon Kim, Jinhu Song, Janghwan Kim
IF 8.2
Developments in the Built Environment
The natural frequencies of composite bridges are affected by temperature variations and boundary conditions, presenting challenges for damage-detection methods based on these parameters. In this study, the individual and combined effects of temperature variations and boundary condition changes were investigated both numerically and experimentally. Temperature variations included uniform temperature fields and temperature gradients within the bridge section. For modal testing, a temperature-controllable composite girder with adjustable supports was developed. Numerical analysis further evaluated the influence of temperature and boundary condition changes on natural frequencies. The results demonstrated that changes in geometric stiffness due to the combined effects of temperature and boundary conditions, as well as the temperature-dependent behavior of the elastic modulus, significantly affected the natural frequencies. • This study is the first to experimentally investigate the combined effects of temperature and boundary conditions on frequency responses of a composite girder. • The Natural frequency of composite bridges decreases with temperature, mainly due to temperature-dependent elastic modulus. • Under temperature gradient, the H-R boundary shows a higher frequency reduction rate than H-H, influenced by greater convex deformation. • For uniform temperature, both boundary conditions have similar frequency reduction rates, primarily driven by elastic modulus changes. • Linear regression models accurately predict frequency responses to temperature and boundary conditions.
A new enhanced coding scheme for robust bit-stream of ATSC DTV
Jaebum Kim, Namshik Kim, Kumran Ji, Seungwon Kim, Hyuncheol Park
IF 10.9
IEEE Transactions on Consumer Electronics
In this paper a new enhanced coding scheme of ATSC DTV standard is presented. The proposed coding scheme is a modified trellis codes of enhanced 8-VSB for robust bit-stream mode. By computing the distance spectrum, we derive the theoretical upper bound on the first event error probability of the proposed trellis codes. Based on the derivation, the proposed coding scheme has slightly better performance on AWGN channel than the conventional enhanced S-VSB coding scheme at high signal-to-noise ratio (SNR). We also show that the proposed coding scheme has better performance than any existing coding schemes of ATSC DTV standard by using the Monte Carlo simulations.
Modal frequency responses of composite bridges under temperature and boundary condition variations
Arjun Poudel, Seungwon Kim, Jinhu Song, Janghwan Kim
IF 8.2
Developments in the Built Environment
The natural frequencies of composite bridges are affected by temperature variations and boundary conditions, presenting challenges for damage-detection methods based on these parameters. In this study, the individual and combined effects of temperature variations and boundary condition changes were investigated both numerically and experimentally. Temperature variations included uniform temperature fields and temperature gradients within the bridge section. For modal testing, a temperature-controllable composite girder with adjustable supports was developed. Numerical analysis further evaluated the influence of temperature and boundary condition changes on natural frequencies. The results demonstrated that changes in geometric stiffness due to the combined effects of temperature and boundary conditions, as well as the temperature-dependent behavior of the elastic modulus, significantly affected the natural frequencies. • This study is the first to experimentally investigate the combined effects of temperature and boundary conditions on frequency responses of a composite girder. • The Natural frequency of composite bridges decreases with temperature, mainly due to temperature-dependent elastic modulus. • Under temperature gradient, the H-R boundary shows a higher frequency reduction rate than H-H, influenced by greater convex deformation. • For uniform temperature, both boundary conditions have similar frequency reduction rates, primarily driven by elastic modulus changes. • Linear regression models accurately predict frequency responses to temperature and boundary conditions.
A new enhanced coding scheme for robust bit-stream of ATSC DTV
Jaebum Kim, Namshik Kim, Kumran Ji, Seungwon Kim, Hyuncheol Park
IF 10.9
IEEE Transactions on Consumer Electronics
In this paper a new enhanced coding scheme of ATSC DTV standard is presented. The proposed coding scheme is a modified trellis codes of enhanced 8-VSB for robust bit-stream mode. By computing the distance spectrum, we derive the theoretical upper bound on the first event error probability of the proposed trellis codes. Based on the derivation, the proposed coding scheme has slightly better performance on AWGN channel than the conventional enhanced S-VSB coding scheme at high signal-to-noise ratio (SNR). We also show that the proposed coding scheme has better performance than any existing coding schemes of ATSC DTV standard by using the Monte Carlo simulations.
A Review on the Performance of Fibers on Restrained Plastic Shrinkage Cracks
Abidemi Bashiru Folorunsho, Seungwon Kim, Cheolwoo Park
IF 3.1
Buildings
Multiple studies have investigated the use of steel, synthetic fibers, and natural fibers to reduce plastic shrinkage cracks in concrete, which are mostly caused by water evaporation from the surface of the material. This review used original published research articles from the Web of Science and Scopus database to evaluate the performance and relationship between the fiber volume, aspect ratio, compressive strength, and plastic shrinkage cracking. This review also discussed the most widely used technique for evaluating plastic shrinkage cracking, the ASTM C 1579, with two bottom restraints and a central stress riser to induce cracking, and its modified version with additional reinforcement for further restraining the ASTM C 1579 mold. Longer fibers function better than shorter fibers because of their larger surface area, which allows them to bridge fissures. It was also observed that crack initiation time is delayed when fibers are added to concrete. In addition, as the volume proportion of the fibers increased, the plastic shrinkage cracks decreased, but the compressive strength declined. Furthermore, the volume fraction of the fibers had a greater effect on reducing cracking than the aspect ratio. It was also concluded that a fiber volume inclusion below 1% is best.
Temperature Effects on the Natural Frequencies of Composite Girders
Arjun Poudel, Seungwon Kim, Byoung Hooi Cho, Janghwan Kim
IF 2.5
Applied Sciences
Composite bridges are typically exposed to temperature variations due to heat radiation, conduction, and convection. Temperature affects the modal parameters of bridges, hindering the application of damage detection methods based on the dynamic properties of bridges. In this study, the effects of temperature on the natural frequencies of composite bridges were investigated experimentally and numerically to derive a basis for separating temperature effects from the natural frequencies. A temperature-controllable girder specimen was developed for modal testing. Additionally, finite element (FE) analysis was conducted to analyze the effects of temperature. The FE analysis results were validated by comparing them to the static response results of the test specimen. The results of the experiments and FE simulations verified that temperature variation can affect the material properties, particularly the modulus of elasticity, of a composite girder, consequently influencing its natural frequency. Based on the tests and simulations, a linear relationship between the temperature and the natural frequency was proposed to remove the temperature effects from the natural frequency.
Bond Properties of Glass-Fiber-Reinforced Polymer Hybrid Rebar in Reinforced Concrete with Respect to Bond Length
Seungwon Kim, Janghwan Kim, Cheolwoo Park
IF 2.5
Applied Sciences
Preventing rebar corrosion in reinforced concrete (RC) structures has been actively researched worldwide. One of the most powerful solutions is the use of fiber-reinforced polymer (FRP) rebars. However, there are limitations in the mechanical design and construction of FRP rebars because their tensile characteristics are extremely different from those of conventional rebars and they have a different modulus of elasticity. FRP rebars are relatively cost-efficient when fabricated with glass fibers, but they are still costly compared to conventional rebars. Therefore, hybrid rebars fabricated by covering conventional rebars with glass FRP (GFRP) materials were developed in this study. GFRP hybrid rebars have increased durability in marine environments while maintaining the same mechanical properties as conventional rebars. As the difference in rebar diameter of the bonded area decreased, the tensile strength of the concrete increased. As a result, pull-out failure or tensile failure caused by the yielding of the rebars occurred in small-diameter rebars. The experimental results showed that the maximum load for the D13 deformed steel bar was 52.2 kN at a bond length of 50 mm and 76.1 kN at 100 mm, while for the D19 deformed steel bar, it was 65.3 kN at 50 mm and 103.7 kN at 100 mm. The bond properties of hybrid GFRB rebars were found to be lower than those of deformed steel bars. These properties were improved greatly by increasing the thickness of the GFRP materials on the surface of the deformed steel bars, highlighting a path toward high-performance, corrosion-resistant concrete.
