• Journal of the Korean Society of Safety
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• v.23 no.6
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• pp.131-137
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• 2008

SCP(Sand Compaction Pile) method that forms a composite ground by driving compacted sand piles into the soft ground. This method is one of the soil improvement techniques for reinforcing and strengthening soft ground deposits. This thesis describes the investigation on the behavior of soft ground reinforced with SCP by low improvement ratio. Direct shear test and consolidation test carried out to verified behavior of composite ground reinforced with SCP. Test results were discussed with reference to the amount of consolidation settlement, variation of shear resistance with area replacement ratio and effect of the stress concentration. And, laboratory model loading test carried out to verified the effect of the location and failure mode of reinforced embankment. Residual shear strength varies with the area replacement and constrict load in the low replacement ratio. Calculated stress concentration ratio overestimate than proposed valve by experimental, theoretical and analytical method. As regards the location, improving right below of the top of the slope was more effective than below of the toe of the slope. This thesis carried out to obtain fundamental information of behavior of the composit ground. Hereafter, centrifuge test that reproduce stress state of the in-situ must be necessary through the further study about pile penetration, reinforce position and construct time.

• Advances in materials Research
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• v.6 no.3
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• pp.257-278
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• 2017

A simple closed-form solution to calculate the interfacial shear and normal stresses of retrofitted concrete beam strengthened with thin composite plate under mechanical loads including the creep and shrinkage effect has been presented in this paper. In such plated beams, tensile forces develop in the bonded plate, and these have to be transferred to the original beam via interfacial shear and normal stresses. Consequently, debonding failure may occur at the plate ends due to a combination of high shear and normal interfacial stresses. These stresses between a beam and a soffit plate, within the linear elastic range, have been addressed by numerous analytical investigations. Surprisingly, none of these investigations has examined interfacial stresses while taking the creep and shrinkage effect into account. In the present theoretical analysis for the interfacial stresses between reinforced concrete beam and a thin composite plate bonded to its soffit, the influence of creep and shrinkage effect relative to the time of the casting, and the time of the loading of the beams is taken into account. Numerical results from the present analysis are presented both to demonstrate the advantages of the present solution over existing ones and to illustrate the main characteristics of interfacial stress distributions.

• Computers and Concrete
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• v.23 no.5
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• pp.329-334
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• 2019

Traffic flow capacity of some old road bridges is insufficient due to limited deck width. In such cases bridge deck widening is a common solution. For multi-girder reinforced concrete (RC) bridges it is possible to add steel-concrete composite girders as the new outermost girders. The deck widening may be combined with bridge strengthening thanks to thickening of the existing deck slab. Joint action of the existing and the added parts of such bridge span must be ensured. It refers especially to the horizontal plane at the interface of the existing slab and the added concrete layer as well as to the vertical planes at the external surfaces of the initially outermost girders where the added girders are connected to the existing bridge span. Since the distribution of the added concrete is non-uniform in the span cross-section the structure is particularly sensitive to the added concrete shrinkage. The shrinkage induces shear forces in the aforementioned planes. Widening of a 12 m long RC multi-girder bridge span is numerically analysed to assess the influence of the added concrete shrinkage. The analysis results show that: a) in the vertical plane of the connection of the added and the existing deck slab the longitudinal shear due to the shrinkage of the added concrete is comparable with the effect of live load, b) it is necessary to provide appropriate longitudinal reinforcement in the deck slab over the added girders due to tension induced by the shrinkage of the added concrete.

• Journal of the Korea Concrete Institute
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• v.21 no.3
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• pp.337-345
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• 2009

The purpose of this study is to investigate the shear strengthening effectiveness of the beams strengthened with near surface mounted (NSM) and external bonded (EB) CFRP strips. A total of nine concrete beams were made and tested. From this study, it was found that the shear stiffness and strength of the beams strengthened with NSM and EB strips were significantly improved compared to the control beam. Failure of the beam strengthened with NSM and EB strips was initiated by shear cracks, propagated diagonally to the adjacent epoxy grooves without crossing the epoxy and finally sudden diagonal crack connecting the point of application of load and flexural crack was occurred. For the beam strengthened combined with NSM and EB CFRP strips, the tensile strains in the NSM CFRP strips were observed in the range of 0.35% to 0.45% and strains with EB strips were measured about 0.3%.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.5
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• pp.491-496
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• 2015

The headed studs used extensively for steel-composite construction are specified as SS400 in the current Korean Standard specification considering the welding condition. And the corresponding equation for the shear force calculation is limited for the use of compression strength of concrete below $300kgf/cm^2$. However, it is expected that the high strengthening and precasting of both steel and concrete due to the necessity of shear connector or other connecting material for the combination of steel and concrete. Therefore, the experimental results obtained during the development process of high strength stud for the connection of high strength concrete and the steel member are reported in this paper. Also the effectiveness of newly developed shear connector using pipe(pipe stud) to increase the stiffness of a stud is verified by comparing both the stiffness and the strength with common stud bolt through the welding ability, mechanical characteristics and experimental investigation.

• Journal of the Korea Concrete Institute
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• v.27 no.4
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• pp.451-458
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• 2015

The infill-wall strengthening method has been widely used for the seismic performance enhancement of the conventional reinforced concrete (RC) frame structures with non-seismic detail, which is one of the promising techniques to secure the high resisting capacity against lateral forces induced by earthquake. During the application of the infill-wall strengthening method, however, it often restricts the use of the structure. In addition, it is difficult to cast the connection part between the wall and the frame, and also difficult to ensure the shear resistance performances along the connection. In this study, an advanced strengthening method using the externally-anchored precast wall-panel (EPCW) was proposed to overcome the disadvantages of the conventional infill-wall strengthening method. The one-third scaled four RC frame specimens were fabricated, and the cyclic loading tests were conducted to verify the EPCW strengthening method. The test results showed that the strength, lateral stiffness, energy dissipation capacity of the RC frame structures strengthened by the proposed EPCW method were significantly improved compared to the control test specimen.

• Journal of the Korea Concrete Institute
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• v.22 no.2
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• pp.149-158
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• 2010

Recently, numerous construction techniques for repairing and strengthening methods for above ground or air exposed concrete structure have been developed. However repairing and strengthening methods for underwater structural members under continuous loading, such as piers and steel piles need the further development. Therefore, this study develops an aqua epoxy, which can be used for repairing and strengthening of structural members located underwater. Moreover, using the epoxy material and strengthening fibers, a fiber reinforced composite sheet called Aqua Advanced FRP (AAF) for underwater usage is developed. To verify and to obtain properties of the material and the performance of AAF, several tests such as pull-off strength test, bond shear strength test, and chemical resistance test, were carried out. The results showed that the developed aqua epoxy does not easily dissolve in wet conditions and does not create any residual particle during hardening. In spite of underwater conditions, it showed the superior workability, because of the high viscosity over 30,000 cps and adhesion capacity over 2 MPa, which are nearly equivalent to those used in dry conditions. In case of the chemical resistance test, the developed aqua epoxy and composite showed the weight change of about 0.5~1.0%, which verifies the superior chemical resistance.

• Geomechanics and Engineering
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• v.12 no.5
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• pp.785-801
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• 2017

Biopolymer treatment of geomaterials to develop sustainable geotechnical systems is an important step towards the reduction of global warming. The cutting edge technology of biopolymer treatment is not only environment friendly but also has widespread application. This paper presents the strength and slake durability characteristics of biopolymer-treated sand sampled from Al-Sharqia Desert in Oman. The specimens were prepared by mixing sand at various proportions by weight of xanthan gum biopolymer. To make a comparison with conventional methods of ground improvement, cement treated sand specimens were also prepared. To demonstrate the effects of wetting and drying, standard slake durability tests were also conducted on the specimens. According to the results of strength tests, xanthan gum treatment increased the unconfined strength of sand, similar to the strengthening effect of mixing cement in sand. The slake durability test results indicated that the resistance of biopolymer-treated sand to disintegration upon interaction with water is stronger than that of cement treated sand. The percentage of xanthan gum to treat sand is proposed as 2-3% for optimal performance in terms of strength and durability. SEM analysis of biopolymer-treated sand specimens also confirms that the sand particles are linked through the biopolymer, which has increased shear resistance and durability. Results of this study imply xanthan gum biopolymer treatment as an eco-friendly technique to improve the mechanical properties of desert sand. However, the strengthening effect due to the biopolymer treatment of sand can be weakened upon interaction with water.

• Steel and Composite Structures
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• v.20 no.5
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• pp.999-1022
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• 2016

The use of Carbon Fiber Reinforced Polymer (CFRP) to strengthen steel structures has attracted the attention of researchers greatly. Previous studies demonstrated bonding of CFRP plates to the steel sections has been a successful method to increase the mechanical properties. However, the main limitation to popular use of steel/CFRP strengthening system is the concern on durability of bonding between steel and CFRP in various environmental conditions. The paper evaluates the performance of I-section steel beams strengthened with pultruded CFRP plate on the bottom flange after exposure to diverse conditions including natural tropical climate, wet/dry cycles, plain water, salt water and acidic solution. Four-point bending tests were performed at specific intervals and the mechanical properties were compared to the control beam. Besides, the ductility of the strengthened beams and distribution of shear stress in adhesive layer were investigated thoroughly. The study found the adhesive layer was the critical part and the performance of the system related directly to its behavior. The highest strength degradation was observed for the beams immersed in salt water around 18% after 8 months exposure. Besides, the ductility of all strengthened beams increased after exposure. A theoretical procedure was employed to model the degradation of epoxy adhesive.

• Computers and Concrete
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• v.4 no.2
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• pp.119-134
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• 2007

External bonding of steel or FRP plates to reinforced concrete (RC) structures has been a popular method for strengthening RC structures; however, unexpected premature failure often occurs due to debonding between the concrete and the epoxy. We proposed a Coulomb criterion with a constant failure surface as the debonding failure criterion for the concrete-epoxy interface. Diagonal shear bonding tests were conducted to determine the debonding properties that were related to the failure criterion, such as the angle of internal friction and the coefficient of cohesion. In addition, an interface element that utilized the Coulomb criterion was implemented in a nonlinear finite element analysis program to simulate debonding failure behavior. Experimental studies and numerical analysies on RC beams strengthened by an externally bonded steel or FRP plate were used to determine the range of the coefficient of cohesion. The results that were presented prove that premature failure loads of strengthened RC beams can be predicted with using the bonding properties and the finite element program with including the proposed Coulomb criterion.