Papers by Author: Seung Sik Lee

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Authors: Seung Sik Lee, Soo Ha Chae, Soon Jong Yoon, Sun Kyu Cho
Abstract: The strengths of PFRP thin-walled columns are determined according to the modes of buckling which consist of local mode for short columns, global mode for long columns, and interaction mode between local and global modes for intermediate columns. Unlike the local and global buckling, the buckling strength of interaction mode is not theoretically predictable. Refined theoretical approaches which can account for different elastic properties of each plate component consisting of a PFRP thin-walled member are used. Based on both the analytical buckling loads and the experimentally measured buckling loads from literatures, the accuracies of Ylinen’s equation and modified AISC/LRFD column design equation for isotropic steel columns were compared. From the comparison, it was found that the modified AISC/LRFD column design equation is more suitable for the prediction of the buckling loads of PFRP thin-walled members than Ylinen’s equations.
Authors: Y.H. Kim, S.K. You, Jae Ho Jung, Soon Jong Yoon, Seung Sik Lee
Abstract: Concrete-steel composite members are formed by bonding a steel component, such as an I-section beam, to a concrete component, such as a reinforced concrete slab, so that the two components can act as a unit. The use of such type of composite member becomes main stream of construction technology since it provides efficient load resisting mechanism in structural system. In a composite member, bond between steel and concrete is a crucial factor for the composite action. Usually this bond behavior is achieved by installation of mechanical device so called shear connector. The composite action can be divided into two categories (i.e., full and partial) depending on the shear strength of mechanical shear connector embedded in the concrete, i.e., understanding of shear load resisting mechanism is necessary to develop a new shear connector for better, wider and more efficient application of composite action. For this purpose, the push-out tests are performed for the evaluation of several existing shear connectors including carefully designed perforated shear connector with flange head. One of the purposes of this experimental research is to define the shear resisting mechanism of the proposed new type shear connector. The experimental results show that the degree of composite action using perforated shear connector with flange head is superior to those of existing shear connectors such as a general headed stud, perfobond, etc. The experimental parameters, such as the number of perforated holes, the distance between perforated holes, and the height of shear connector, are carefully chosen for the verification of their effect on the capacity of shear resistance. From this experimental investigation it was found that the mechanical performance of proposed shear connector was efficient as a rigid shear connector.
Authors: Seung Sik Lee, Soon Jong Yoon, S.K. Cho, Jong Myen Park
Abstract: Pultruded fiber reinforced polymer (FRP) structural members have been used in various civil engineering applications. T-shapes are commonly used for chord members in trusses and for bracing members. In these cases, T-shapes are mainly subjected to axial forces, and stability of a member is one of the major concerns in the design. Due to the monosymmetry existing in the cross-section of T-shapes, T-shapes are likely to buckle in a flexural-torsional mode. An energy solution, using the Ritz method, to the buckling problem of a pulturuded T-shape under uniform compression is derived based on a composite thin-walled beam theory developed by Bauld and Tzeng. The solution accounts for the bending-twisting and bending-extension coupling effects. The derived energy solutions are compared to the experimental results of buckling tests conducted on seventeen pultruded T-shapes. It is found that the ratios of the experimental to analytical results are in the range of 1.00 to 1.32.
Authors: Seung Sik Lee, Soon Jong Yoon, Sung Yong Back
Abstract: The use of pultruded fiber reinforced polymeric (FRP) members in civil engineering applications can greatly reduce construction time and maintenance cost of structures, because pultruded members have high specific strength and excellent corrosion resistance compared to steel and concrete. Pultruded members for civil engineering application are mostly made of a polymeric resin system reinforced with E-glass fibers and, as a result, they have low elastic moduli. Therefore, stability is an important issue in the design of pultruded members. In this paper, the results of an experimental investigation into the global buckling behavior of pultruded thin-walled members subjected to axial compression are presented. The analytical solutions are validated through a comparison with the results of FE analysis as well as the experimental results.
Authors: Hyung Joong Joo, Seung Sik Lee, Soon Jong Yoon, Ju Kyung Park, Kwang Yeoul Shin
Abstract: The concrete-filled steel tubes have been widely used in buildings and civil structures. However the corrosion of the steel tubes results in the loss of load carrying capacities of the members and, therefore, there is a need for regular maintenance. To mitigate such maintenance issues and prevent the loss of load carrying capacity, FRP composite were suggested as the candidate material. A number of research works has shown that the use of FRP tubes produced by filament winding technique was very effective on the improvement of compressive strength of the concrete-filled FRP tubes (CFFT). However the filament wound FRP tubes did mot contribute to the increase of the flexural strength of a CFFT. In this paper, a new type of FRP tube which consists of several pultruded open sections assembled by filament winding technique is proposed to improve compressive strength as well as flexural strength of a CFFT. The load carrying capacity of proposed CFFT is discussed through the analytical investigation.
Authors: Hyung Joong Joo, Seung Sik Lee, Soon Jong Yoon, Ju Kyung Park, Seok Goo Youn
Abstract: Feasibility study on the use of newly developed FRP and concrete composite bridge deck system is conducted. To lengthen the service life of bridge deck, the steel-free bridge deck system is developed. In this deck system, shear connectors between FRP module and concrete are utilized and structural behavior of shear connectors is investigated experimentally. The result of an investigation reveals that the system is promising.
Authors: Jeong Hun Nam, Seung Sik Lee, Soon Jong Yoon, Won Sup Jang, S.K. Cho
Abstract: FRP composite materials are widely applicable in the construction industries as a load-bearing structural element or a reinforcing and/or repairing materials for the concrete. In this paper, we presented the flexural behavior of steel reinforced concrete beams reinforced with FRP re-bars manufactured by different fibers but the same vinylester resin. Experimental investigation pertaining to the load-deflection and load-strain characteristics of steel reinforced concrete beams reinforced with FRP re-bars with garnet coated surface is presented and the theoretical prediction is also conducted. In the investigation, the effects of FRP re-bar reinforcement in addition to the steel reinforcement are estimated. The experimental results are compared with theoretical predictions. Good agreements are observed.
Authors: Sang Kyoon Jeong, Seung Sik Lee, C.H. Kim, Dong Min Ok, Soon Jong Yoon
Abstract: Nowadays, the investigations relating to the FRP re-bars have been increased due to their superior physical and mechanical properties such as environmental resistance, electro-magnetic transparency, and high specific strength and stiffness. In this paper, we present the results of an experimental investigation pertaining to the flexural behavior of concrete beams reinforced with GFRP re-bar bundles for tension and CFRP grids for shear. A total of eight specimens, two pairs of four different shear reinforcement spaces, is loaded to failure under the 4-point bending test set-up. In addition to the experimental investigation, theoretical evaluation is also conducted according to the ACI Committee 440 for all beam specimens. Both experimental and theoretical results such as failure modes and load-deflection relations are compared and good agreements are observed.
Authors: Young Ho Kim, Seung Sik Lee, Jae Ho Jung, Soon Jong Yoon
Abstract: This paper presents the results of an investigation on the force transfer mechanism in an embedded column base of a composite structure. In the experimental program, eighteen push-out specimens were tested. The factors influencing the mechanism of force transfer were the amount of confining reinforcement, compressive strength of concrete, and diameter of stud connectors. The results of experiment indicated that force transfer could be characterized into two stages, and the factors governing each stage were identified. The first stage was governed by the bond strength between the steel column base and the concrete. The second stage begun after chemical debonding and was governed by the shear strength of stud connectors as well as the frictional strength between the steel and the concrete. Based on the experimental results, the equations to estimate the bond strength, the friction strength, and the shear strength of stud connectors were proposed. The load carrying capacity of an embedded steel column base could be predicted by taking the sum of the shear strength of stud connectors and the friction strength. The predicted load carrying capacity was found to agree well with the experimental results over various range of concrete stress.
Authors: Jin Woo Choi, Seung Sik Lee, Hyung Joong Joo, Young Jong Sim, Soon Jong Yoon
Abstract: As a new construction material, fiber reinforced polymeric plastic structural shapes are readily available. Therefore, construction and structure rehabilitation using FRP materials are an ever increasing trend because of FRP material’s superior chemical and mechanical properties compared with those of conventional construction materials such as steel and concrete. Among the FRP materials, pultruded fiber reinforced polymeric plastics are the most popular for civil engineering applications. However, it has relatively low modulus of elasticity and also cross-section of structural shapes is composed of plate components such as flange and web. Therefore, stability is an important issue in the design of pultruded structural shapes. For the design of pultruded structural member under compression, buckling and post-buckling strengths of plate components should be taken into account. In the structural steel design following AISC/ LRFD, this effect, in addition to the buckling strength, is incorporated with a form factor. In this research, the form factor for the design of pultruded structural shapes under compression is investigated. Based on the analytical study, the form factor for the design of pultruded structural shapes have been suggested.
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