• Journal of the Korea Concrete Institute
• /
• v.21 no.5
• /
• pp.629-638
• /
• 2009

In this paper, the existing formulas of the step-by-step method were generalized for effective estimation of responses of complicated composite sections due to long-term deformation of concrete. The initial transformed section properties of the composite section were derived from material and section properties of concrete section and sections which confine the longterm deformation of concrete. The transformed section properties at each step were derived from the effective modulus of elasticity considered the creep coefficient variation. Improved formulas of the step-by-step method for generalized responses were derived by introducing 5 generalized parameters. The formulas can be more simplified by applying constant increment of creep coefficient at each step. The constant increment of creep coefficient at each step can also reduce computing time and make equal computing error of each step. The generalized responses for axial elastic strain of concrete section were most sensitive to the area rate of concrete section, and the ratio of the second moment of the confining section area was more sensitive than that of the concrete section. Those for elastic curvature of concrete section were most sensitive to the ratio of the second moment of concrete section area.

• Journal of Korean Society of Steel Construction
• /
• v.16 no.6 s.73
• /
• pp.807-818
• /
• 2004

Experimental tests and theoretical methods of the analysis of the concrete shrinkage behaviors of steel-concrete composite girders are described herein. Steel-concrete composite test specimens were fabricated in the laboratory, and long-term behaviors such as deflections, curvatures, and strains were measured for one year. Test results were compared to the analytical results obtained by using the age-adjusted effective modulus method (AEMM). In addition, composite girders have been analyzed to investigate the effects of several parameters on the concrete shrinkage behaviors. From the long-term test results, it could be used to validate AEMM for the evaluation of the shrinkage behavior of composite girders. Because the shrinkage of the reinforced concrete slab in composite girders may lead to large tensile stresses in the concrete section, the transverse cracking of the slab could occur both in the positive and negative regions. Therefore, if the cracking of concrete would be ignored,it might lead to an overestimation of the stresses of the steel section of composite girders. Based on this research, it is proposed that the effect of transverse concrete cracking on the shrinkage behavior of steel-concrete composite bridges be considered.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.14 no.3
• /
• pp.267-276
• /
• 2001

On the basis of structural analysis of the radial gate(that is, Tainter gate), this paper focuses on the optimization of the moment distribution according to the location of the arm of the radial gate. In spite of its importance from economical view point, we could hardly find the study on the optimum design of radial gate. Accordingly, the present study identifies the optimum section modulus for a radial arm along with the optimum position for 2 of 3 radial arms with a convex cylindrical skin plate relative to a given radius of the skin plate curvature, pivot point, water depth, ice pressure, etc. These optimum measurements are then compared with previously constructed radial gates. The results indicate that the optimum section modulus vague for a radial arm was appreciably smaller than the previously constructed examples.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.30 no.3
• /
• pp.255-263
• /
• 2017

This paper presents a beam element capable of conducting material and geometric nonlinear analysis for applications requiring the ultimate behavioral analysis of structures with composite cross-sections. The element formulation is based on co-rotational kinematics to simulate geometrically nonlinear behaviors, and it uses the fiber section method to calculate the stiffness and internal forces of the element. The proposed element was implemented using an in-house numerical program in which an arc-length method was adopted to trace severe nonlinear responses(such as snap-through or snapback), as well as ductile behavior after the peak load. To verify the proposed method of element formulation and the accuracy of the program that was used to employ the element, several numerical studies were conducted and the results from these numerical models were compared with those of three-dimensional continuum models and previous studies, to demonstrate the accuracy and computational efficiency of the element. Additionally, by evaluating an example case of a frame structure with a composite member, the effects of differences between composite material properties such as the elastic modulus ratio and strength ratio were analyzed. It was found that increasing the elastic modulus of the external layer of a composite cross-section caused quasi-brittle behavior, while similar responses of the composite structure to those of homogeneous and linear materials were shown to increase the yield strength of the external layer.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.37 no.5
• /
• pp.442-449
• /
• 2009

A two-dimensional cross-section analysis program based on the finite element method has been developed for composite blades with solid, thin-walled and compound cross-sections. The weighted-modulus method is introduced to determine the laminated composite material properties. The shear center and the torsion constant for any given section are calculated according to the Trefftz' definition and the St. Venant torsion theory, respectively. The singular value problem of cross-section stiffness properties faced during the section analysis has been solved by performing an eigenvalue analysis to remove the rigid body mode. Numerical results showing the accuracy of the program obtained for stiffness, offset and inertia properties are compared in this analysis. The current analysis results are validated with those obtained by commercial software and published data available in the literature and a good correlation has generally been achieved through a series of validation study.

• Textile Coloration and Finishing
• /
• v.29 no.4
• /
• pp.239-246
• /
• 2017

Recently fiber-reinforced thermoplastic composites have attracted great interest from industry and study because they offer unique properties such as high strength, modulus, impact resistance, corrosion resistance, and damping reduction which are difficult to obtain in single-component materials. The demand for plastics is steadily increasing not only in household goods, packaging materials, but also in high-performance engineering plastic and recycling. As a result, the technology of recycling plastic is also attracting attention. In particular, many paper have studied recycling systems based on recycled thermoplastics. In this paper, properties of Glass Fiber Reinforced Thermoplastic(GFRTP) materials were evaluated using recycled PET for injection molding bicycle frame. The effect on thermal and mechanical properties of recycled PET reinforced glass chop fiber according to fiber cross section and fiber content ratio were studied. And it was compared void volume and torque energy by glass fiber cross section, which is round section and flat section. Mechanical characteristics of resulting in GF/rPET has been increased by increasing fiber contents, than above a certain level did not longer increased. And mechanical properties of flat glass fiber reinforced rPET with low void volume were most excellent.

• Fibers and Polymers
• /
• v.7 no.4
• /
• pp.372-379
• /
• 2006

The surface topography, tensile properties, and thermal properties of ramie fibers were investigated as reinforcement for fully biodegradable and environmental-friendly 'green' composites. SEM micrographs of a longitudinal and cross sectional view of a single ramie fiber showed a fibrillar structure and rough surface with irregular cross-section, which is considered to provide good interfacial adhesion with polymer resin in composites. An average tensile strength, Young's modulus, and fracture strain of ramie fibers were measured to be 627 MPa, 31.8 GPa, and 2.7 %, respectively. The specific tensile properties of the ramie fiber calculated per unit density were found to be comparable to those of E-glass fibers. Ramie fibers exhibited good thermal stability after aging up to $160^{\circ}C$ with no decrease in tensile strength or Young's modulus. However, at temperatures higher than $160^{\circ}C$ the tensile strength decreased significantly and its fracture behavior was also affected. The moisture content of the ramie fiber was 9.9 %. These properties make ramie fibers suitable as reinforcement for 'green' composites. Also, the green composites can be fabricated at temperatures up to $160^{\circ}C$ without reducing the fiber properties.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.21 no.4
• /
• pp.619-624
• /
• 2012

In this study, MMT/fiber/polymer composites were fabricated by impregnating chopped strand glass mat into a vinylester resin mixed with clay. Tensile tests has been performed by using a universal testing machine to determine the effect of MMT addition on the tensile properties of MMT/chopped strand glass fiber/vinylester composites. And some pictures which are magnified cross section of breaking parts are has been taken by using a FE-SEM to confirm the behavior at breaking. The contents ratio of MMT applied in the composites were 0.5, 1.0, 1.5, and 2.0 wt% respectively. It has been found that the tensile strength and elastic modulus of MMT/chopped strand glass fiber/vinylester composites were improved at a proper content of MMT. Tensile strength and elastic modulus were maximized at a content of 1.0 wt% due to most effective dispersion of MMT. On the contrary, the failure strain was increased as MMT content was increased.

• Structural Engineering and Mechanics
• /
• v.47 no.3
• /
• pp.443-454
• /
• 2013

A leaf spring, especially the longitudinal type is liable and persistent element in automotive suspension system. In the present scenario the composite materials are widely used in the automobile industries has shown a great interest in the replacement of steel spring due to high strength by weight ratio. Previous investigations focused on stresses and displacement analysis of single leaf spring for different materials. The present work aims to design and analysis of leaf spring for two different cases by considering the Young's modulus to yield strength ratio. In the first case the analysis deals with the design and analysis of a single cantilever solid triangle beam which is an equivalent beam of a spring with three leaves having uniform strength. In the second case a 3-beams of rectangular cross section has been considered which is equivalent to a spring with three leaves. The analysis was carried out based on contact mechanics approach. The results were compared, that the fiberglass composite leaf spring is suitable for high loading capacity, reliability and efficiency.

• Steel and Composite Structures
• /
• v.30 no.2
• /
• pp.171-183
• /
• 2019

As China's infrastructure continues to grow, concrete filled steel tubular (CFST) structures are attracting increasing interest for use in engineering applications in earthquake prone regions owing to their high section modulus, high strength, and good seismic performance. However, in a corrosive environment, the seismic resistance of the CFST columns may be affected to a certain extent. This study attempts to investigate the mechanical behaviours of square CFST members under both a cyclic load and an acid rain attack. First, the tensile mechanical properties of steel plates with various corrosion rates were tested. Second, a total of 12 columns with different corrosion rates were subjected to a reversed cyclic load and tested. Third, comparisons between the test results and the predicted ultimate strength by using four existing codes were carried out. It was found that the corrosion leads to an evident decrease in yield strength, elastic modulus, and tensile strain capacity of steel plates, and also to a noticeable deterioration in the ultimate strength, ductility, and energy dissipation of the CFST members. A larger axial force ratio leads to a more significant resulting deterioration of the seismic behaviour of the columns. In addition, the losses of both thickness and yield strength of an outer steel tube caused by corrosion should be taken into account when predicting the ultimate strength of corroded CFST columns.