• Polymer(Korea)
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• v.26 no.1
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• pp.61-70
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• 2002

The effects of molecular weights and rheological properties of polypropylene (PP), on its foam structures in batch process were investigated. The effects of crosslinking process were also considered in this study. The rheological properties of polypropylene, such as storage modulus(G'), loss modulus(G"), zero shear viscosity($\eta_O$), and relaxation time($\lambda$), increased with the increase of molecular weights, and these increases in rheological properties directly affected the stability improvements of the PP foam. The increase of crosslinked PP's gel content stopped at the irradiation dose of 3.2 Mrad. The development of foam structures was more enhanced as the irradiation dose increased up to 3.2 Mrad. When the irradiation dose exceeded 3.2 Mrad, however, it negatively affected the structural development of the foam by diminishing gel contents of the foaming material, which resulted in instability of the foam structure.ture.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.5
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• pp.447-454
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• 2012

Considering that the weight of a hollow slab system is not increased with an incremental increase in its thickness, and that the flexural stiffness of a hollow slab is not significantly lower than that of a general slab, there has been a growing need for hollow slab system, because long span structures are in great demand. In a long span structure, the problem of vibration of floor slabs frequently occurs, and the dynamic characteristics of a hollow slab system are quite different from the conventional floor system. It is required to investigate the safety and the serviceability of hollow slab. Therefore, there exists a necessity for accurate vibration analysis. Hollow slab should be modeled by refined mesh for accurate vibration analysis. For the efficiency of the Eigenvalue Analysis, an equivalent plate slab model when can relatively precisely represent the dynamic behavior of a one-way hollow slab system is used. In conclusion, equivalent plate models relatively precisely presented the dynamic characteristics of one-way hollows.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.4
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• pp.417-425
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• 2000

This paper describes the application of discretized continuum-type optimality criteria(DCOC) and the development of optimum design program for the reinforced concrete continuous beams with rectangular cross-section. The cost of construction as objective function which includes the costs of concrete, reinforcing steel and formwork is minimized. The design constraints include limits on the maximum deflection, flexural and shear strengths, in addition to ductility requirements, and upper and lower bounds on design variables as stipulated by the design Code. Based on Kuhn-Tucker necessary conditions, the optimality criteria are explicitly derived in terms of the design variables-effective depth, and steel ratio. The self-weight of the beam is included in the equilibrium equation of the real system. An iterative procedure and computer program for updating the design variables are developed. Two numerical examples of reinforced concrete continuous beams are presented to show the applicability and efficiency of the DCOC-based technique.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.4
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• pp.335-345
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• 2008

In this study, we suggest a stochastic finite element scheme for the probabilistic analysis of the composite laminated plates, which have been applied to variety of mechanical structures due to their high strength to weight ratios. The applied concept in the formulation is the weighted integral method, which has been shown to give the most accurate results among others. We take into account the elastic modulus and in-plane shear modulus as random. For individual random parameters, independent stochastic field functions are assumed, and the effect of these random parameters on the response are estimated based on the exponentially varying auto- and cross-correlation functions. Based on example analyses, we suggest that composite plates show a less coefficient of variation than plates of isotropic and orthotropic materials. For the validation of the proposed scheme, Monte Carlo analysis is also performed, and the results are compared with each other.

• Journal of Biomedical Engineering Research
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• v.34 no.1
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• pp.14-23
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• 2013

In this study, biomechanical stability of the newly developed revision total knee arthroplasty (rTKA) was evaluated through strain and stress distribution analysis within the implanted proximal tibia using a three-dimensional finite element (FE) analysis. 2000N of compressive load (about 3 times body weight) was applied to the condyle surface on spacer, sharing by the medial (60%) and lateral (40%) condyles simulating a stance phase before toe-off. The results showed that PVMS within the revision total knee arthroplasty and the proximal tibia were less than yield strength considering safe factor 4.0 (rTKA: less than 10%, Cortical bone: less than 70%, Cancellous bone: less than 70%). The materials composed of them and the strain and stress distributions within the proximal tibia were generally well matched with those of a traditional revision total knee arthoplasty (Scorpio TS revision system, Stryker Corp., Michigan, USA) without the critical damage strain and stress, which may reduce the capacity for bone remodeling, leading to bone degeneration. This study may be useful to design parameter improvement of the revision total knee arthoplasty in biomechanical stability point of view beyond structural stability of revision total knee arthoplasty itself.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.4
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• pp.9-17
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• 2012

In the previous research, allowable compressive stress was analyzed based on strength theory, in which primary effect factors on the allowable compressive stress, such as eccentricity ratio, section type, section size, prestress and self-weight moment, were considered. As its results, allowable compressive stress equations were proposed. As a series of the previous research, this paper presents an experimental study on the prestress at transfer of pre-tensioned members with different eccentricity ratios. The results shows that ACI318-08 and EC2-02 are unconservative for the members under low eccentricity ratios, and they are conservative for the members under high eccentricity ratios. Compared to the code provisions, the results indicates that the proposed equation reasonably well evaluates the allowable compressive stresses for those with different eccentricity ratios.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.3
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• pp.1-10
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• 2012

In spite of high resistant to corrosion and its strength, over the last two decades, concerns still remain about the durability of FRP materials under severe environmental and thermal exposures. In this paper, authors experimentally examine the combined degradation by thermal and chemical attacks in heterogeneous FRP rebar be made up with various fibers and resins. Five types of Carbon, Glass and Hybrid FRP rebars had manufactured by different process and surface patterns are adopted for the experiments such as weight change, interlaminar shear strength, SEM and FT-IR analysis. FRP specimens were immersed in alkaline or distilled solution up to 150 days and then thermal exposed on 60, 100, 150 and $300^{\circ}C$ for 30 minutes. From the test results, the degradation of FRP bars are influnced by the resin type and manufacturing process as well as the fiber, and ILSS of exposed FRP bar in solutions is slightly increased in initial stage and then decresed with the passing of immersed time. But, in this test, it is observed that the discrepancy of ILSS between degraded by alkaline solution and distilled water is negligible value.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.4
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• pp.57-66
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• 2015

This paper is a preliminary study to apply the lightweight concrete slabs reinforced with GFRP (glass fiber reinforced polymer) bars to the bridge deck slabs or some other concrete structures. So, some different behaviors between the conventional steel reinforced concrete slab and the lightweight concrete slab reinforced with GFRP bars were investigated. For this purpose, a number of slabs were constructed and then the three point bending test and numerical analysis for these slabs were performed. The flexural test results showed that the lightweight concrete slabs reinforced with GFRP bars were failed by the shear failure due to the over-reinforced design. The weight and failure load of the GFRP bar reinforced lightweight concrete slabs were 72% and 58% of the steel reinforced concrete slab with the same dimensions, respectively. Results of the numerical analysis for these slabs using a commercial program, midas FEA, showed that the load-deflection curve could be simulated well until the shear failure of the slabs, but the applied loads and the deflections continuously increased even beyond the shear failure loads.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.6
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• pp.63-71
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• 2015

The objective of the present study is to investigate how elevated temperature ranging from $100^{\circ}C$ to $800^{\circ}C$ as well as room temperature affects the variation of mechanical properties of high strength concrete ($over\;f_{ck}=60MPa\;grade$). In this experiment, specimens were exposed for a period of $2^{\circ}C/min$ to temperatures of $20^{\circ}C$, $100^{\circ}C$, $200^{\circ}C$, $300^{\circ}C$ $400^{\circ}C$, $500^{\circ}C$, $600^{\circ}C$, $700^{\circ}C$ and $800^{\circ}C$, respectively. Accordingly, the study investigated the fire resistance performance of high strength concrete mixed with composite fibers which composed with hybrid fibers and steel fibers. After cooling down to ambient temperature, the following basic mechanical properties were then evaluated and compared with reference values obtained prior to thermal exposure: (i) compressive strength in room temperature; (ii) residual compressive strength; (iii) Poisson's ratio; (iv) weight change; (v) SEM analysis & XRD analysis In addition, XRD and SEM Images analyses were performed to investigate chemical and physical characteristics of high strength concrete with composite fibers according to high temperature.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.4
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• pp.81-90
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• 2020

A textile and capillary tube composite panel(TCP) was developed to simultaneously retrofit the seismic performance and the energy efficiency (e.g. heating or insulation performance) of existing unreinforced masonry (URM) buildings. TCP is a light-weight mortar panel in which carbon textile reinforcements and capillary tubes are embedded. Textile reinforcements plays a role of seismic retrofit and capillary tubes that hot water circulates contribute to the energy retrofit. In this paper, the static cyclic loading tests were performed on the masonry walls with/without TCP to understand the seismic retrofit effect of TCP retrofit and the results were summarized. The results of the test showed that the TCP contributed to increase the capacity of the Shear strength and ductility of the URM walls. In addition, the deformation of the wall after cracking was substantially controlled by the carbon textile.