• Steel and Composite Structures
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• v.19 no.1
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• pp.153-171
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• 2015

Twelve large-scale composite deck slabs were instrumented and tested in a cantilever diaphragm configuration to assess the effect of fibers and welded wire mesh (WWM) on the in-plane shear capacity of composite deck slabs. The slabs were constructed with reentrant decking profile and reinforced with different types and dosages of secondary reinforcements: Conventional welded wire mesh (A142 and A98); synthetic macro-fibers (dosages of $3kg/m^3$ and $5.3kg/m^3$); and hooked-end steel fibers with a dosage of $15kg/m^3$. The deck orientation relative to the main beam (strong and weak) was also considered in this study. Fibers and WWM were found efficient in distributing the applied load to the whole matrix, inducing multiple cracking, thereby enhancing the strength and ductility of composite deck slabs. The test results indicate that fibers increased the slab's ultimate in-plane shear capacity by up to 29% and 50% in the strong and weak directions, respectively. WWM increased the ultimate in-plane shear capacity by up to 19% in the strong direction and 9% in the weak direction. The results suggest that discrete fibers can provide comparable diaphragm behavior as that with the conventional WWM.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.725-728
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• 2008

Most of shrinkage is mainly caused by autogenous shrinkage in Ultra high strength steel-fiber reinforced cementitious composites(UHSFRC). water to binder ratio is very low, about 0.2. It occurs faster hydration and cause a large amount of autogenous shrinkage in early ages. the large autogenous shrinkage can cause harmful cracks in a structure and deteriorate the designed structural performance. therefore it is very important to predict the autogenous shrinkage accurately. The study about the autogenous shrinkage of UHSFRC was carried out in this paper. through comparing with JSCE recommendations for UHSFRC, it was found out that UHSFRC in this study showed higher autogenous shrinkage than that of JSCE. And Applicability of early proposed models by some researchers was also investigated. the analytical results let us know that Miyazawa's model showed the best agreement with the experimentally obtained autogenous shrinkage of UHSFRC.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.4
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• pp.50-58
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• 2014

Due to the cost burden of new construction, the necessity of repair and retrofitting of aged structures is sharply increasing as the domain of repair and retrofitting construction is expanding. Because of the necessity, new technologies for repair and retrofitting are continuously studied in Korea and foreign countries. Steel adhesive method, fiber reinforced plastic (FRP) surface adhesive method, and external prestressing method are used to perform the repair and retrofitting works in Korea. In order to consider a repair method using steel mesh reinforced cement mortar (SMCM), 3-point flexural member test was conducted considering repair area and layer number of SMCM. Five types of specimens including ordinary reinforced concrete (RC) specimen with dimensions of $1400{\times}500{\times}200$ (mm) were cast for testing the deflection measurement, a LVDT was installed at the top center of the specimens. Also, a steel strain gauge and a concrete strain gauge were placed at the center of the specimens. A steel strain gauge was also installed on the shear reinforcement. The 3 point flexural member test results showed that the maximum load of SMCM reinforced specimen was higher than that of basic RC specimen in all of the load-displacement curves. Also, the results showed that, when the whole lower part of the basic RC specimen was reinforced, the maximum load and strain were 1.18 and 1.37 times higher than that of the basic RC specimen, respectively. Each specimen showed a slightly different failure behavior where the difference of the results was caused by the difference in the adhesive level between SMCM and RC. Particularly, in SM-B1 specimen, SMCM spalled off during the experiment. This failure behavior showed that the adhesive performance for RC must be improved in order to utilize SMCM as repair and retrofitting material.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.1023-1030
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• 2002

From the early 1980s, the New Austrian Tunnelling Method (NATM) has been developed as a one of the standard tunneling method in Korea. Approximately 10 years ago, wet-mix shotcrete with sodium silicate accelerator (waterglass) was introduced and widely used to tunnel lining and underground support. However, this accelerator had some disadvantages due to the decrease of long-term strength compared to plain concrete (without accelerator) and low quality of the hardened shotcrete. In order to compensate for these disadvantages, recently developed alkali-free accelerator has been successfully demonstrated in numerous projects and applications as a new material to make tunnels more durable and safer. An experimental investigation was carried out in order to verify the strength behavior of wet-mix Steel Fiber Reinforced Shotcrete (SFRS) with alkali-free accelerator. Compressive strength, flexural strength and equivalent flexural strength were measured by testing specimens extracted from the shotcrete panels. From the results, wet-mix SFRS with alkali-free accelerator exhibited excellent strength improvement compared to the conventional shotcrete accelerator.

• Magazine of the Korea Concrete Institute
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• v.10 no.5
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• pp.139-149
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• 1998

동적하중하에서 강섬유보강 콘크리트(SFRC)는 유연도 및 균열억제에서 우수한 재료로서 최근에 각종 구조물에 널리 사용되었으며, 특히 내진설계를 위한 강섬유보강 콘크리트 의 재료적 감쇠에 관한 규명이 절실히 요구되고 있다. 본 연구는 강섬유보강 콘크리트(SFRC)보의 재료적 감쇠효과증진을 실험적 및 수치해석적 방법으로 규명하는 데에 목적이 있으며, 일반적으로 강섬유 보강콘크리트(SFRC)보의 감쇠거동은 인장철근비, 강섬유의 혼입량과 형태, 콘크리트의 강도 그리고 응력의 크기에 좌우된다. 강섬유보강 콘크리트보의 감쇠비는 보의 균열상태 변화에따른 동적실험결과로부터 얻을 수 있으며, 일반적으로 강섬유보강 콘크리트는 증가된 에너지감쇠능력으로 인장철근이 소성전 상태에서 철근 콘크리트보의 경우보다 향상된 감쇠거동을 갖고 있는 것으로 판명되었다. 이들 결과의수치해석적인 입증을 위하여 curvature(곡률)와 감쇠값사이의 관계를 기초로 유한요소프로그램 (TICAL)을 개발하였으며, 결론적으로 0.44%인장철근비을 갖고 있는 강섬유보강 콘크리트의 감쇠비는 하중상태에 따라 철근 콘크리트보의 경우보다 약 5%에서 35%정도 향상된 감쇠비를 갖고 있는 것으로 조사되었다.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1999.04a
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• pp.239-246
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• 1999

recently there have been many destructive seismic events in Kobe Japan in 1995 and in Northridge California USA in 1994. etc. The Korean Bridge Design Standard Specifications adopted the seismic design requirements in 1992. Comparing the earthquake magnitude in Korea with those in the west coast of the USA it may be said that the current seismic design requirements of the Korean Bridge Design Standard Specifications provides too conservation design results especially for transverse reinforcement details and amount in reinforced concrete columns. This fact usually makes construction problems in concrete casting due to transverse reinforcement congestion. And the effective stiffness Ieff depends on the axial load P(Ag{{{{ {f }_{ck } }}) and the longitudinal reinforcement ratio Ast/Ag and it is conservative to use the effective stiffness Ieff than the gross section moment Ig. Seismic design for transverse reinforcement content of concrete column is considered of extreme-fiber compression strain R-factor axial load and stiffness etc.

• Computers and Concrete
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• v.10 no.5
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• pp.435-455
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• 2012

In the recent years, rehabilitation of structures, strengthening and increasing the ductility of them under seismic loads have become so vital that many studies has been carried out on the retrofit of steel and concrete members so far. Bridge piers are very important members concerning rehabilitation, in which the plastic hinging zone is very vulnerable. Pier is usually confined by special stirrups predicted in the design procedure; moreover, fiber-reinforced polymers (FRP) jackets are used after construction to confine the pier. FRP wrapping of the piers is one of the most effective ways of increasing moment and ductility capacity of them, which has a growing application due to its relative advantages. In many earthquake-resistant bridges, reinforced concrete columns have a major defect which could be retrofitted in different ways like using FRP. After rehabilitation, it is important to check the strengthening adequacy by dynamic nonlinear analysis and precise modeling of material properties. If the plastic hinge properties are simplified for the strengthened members, as the simplified properties which FEMA 356 proposes for non-strengthened members, static nonlinear analysis could be performed more easily. Current paper involves this matter and it is intended to determine the plastic hinge properties for static nonlinear analysis of the FRP-strengthened circular columns.

• Advances in concrete construction
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• v.8 no.2
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• pp.145-154
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• 2019

The present experimental study addresses the structural response of reinforced concrete (RC) beams strengthened in shear. Thirteen RC beams were divided into four different sets to investigate the effect of transverse and longitudinal steel reinforcement ratios, concrete compressive strength change and orientation for installing carbon fiber-reinforced polymer (CFRP) laminates. Then, we employed a shear strengthening solution through externally bonded reinforcement in grooves (EBRIG) and externally bonded reinforcement (EBR) techniques. In this regard, rectangular beams of $200{\times}300{\times}2000mm$ dimensions were subjected to the 4-point static loading condition and their load-displacement curves, load-carrying capacity and ductility changes were compared. The results revealed that using EBRIG method, the gain percentage augmented with the increase in the longitudinal reinforcement ratio. Also, in the RC beams with stirrups, the gain in shear strength decreased as transverse reinforcement ratio increased. The results also revealed that the shear resistance obtained by the experimental tests were in acceptable agreement with the design equations. Besides, the results of this research indicated that using the EBRIG system through vertical grooves in RC beams with and without stirrups caused the energy absorption to increase about 85% and 97%, respectively, relative to the control.

• Computers and Concrete
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• v.27 no.5
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• pp.437-445
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• 2021

Retrofitting of structures has gained importance over the recent years. Particularly, Reinforced Cement Concrete (RCC) column strengthening has become a challenge to the structural engineers, owing to the risks and complexities involved in it. There are several methods of RCC column strengthening viz. RCC jacketing, steel jacketing and Fiber Reinforced Polymer (FRP) wrapping etc., FRP wrapping is the most promising alternative when compared to the others. The large research database shows FRP wrapping, through lateral confinement, improves the axial load carrying capacity of the columns under concentric loading. However, its confining efficiency reduces under eccentric loading. Hence a relative newer technique called Near Surface Mounting (NSM), in which Carbon FRP (CFRP) strips are epoxy grouted to the precut grooves in the cover concrete of the columns, has been thrust domain of research. NSM technique strengthens the column nominally under concentric load case while significantly under eccentric case. A novel configuration of NSM in which the vertical NSM (VNSM) strips are being connected by horizontal NSM (HNSM) strips was numerically investigated under both concentric and eccentric loading. It was found that the configuration with 6 HNSM strips performed better under eccentric loading than under concentric loading, while the configuration with 3 HNSM strips performed better under concentric loading than under eccentric loading. Hence an optimum of 4 HNSM strips is recommended as strengthening measure for the given column specifications. It was also found that Aluminum alloy cannot be used instead of CFRP in NSM applications owing to its lower mechanical properties.

• Steel and Composite Structures
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• v.45 no.4
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• pp.591-603
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• 2022

The flexural strengthening of reinforced concrete beams by external bonding of composite materials has proved to be an efficient and practical technique. This paper presents a study on the flexural performance of reinforced concrete continuous beams with three spans (one span and two cantilevered) strengthened by bonding carbon fiber fabric (CFRP). The model is based on equilibrium and deformations compatibility requirements in and all parts of the strengthened continuous beam, i.e., the continuous concrete beam, the FRP plate and the adhesive layer. The adherend shear deformations have been included in the present theoretical analyses by assuming a linear shear stress through the thickness of the adherends. Remarkable effect of shear deformations of adherends has been noted in the results. The theoretical predictions are compared with other existing solutions that shows good agreement, and It shows the effectiveness of CFRP strips in enhancing shear capacity of continuous beam. It is shown that both the normal and shear stresses at the interface are influenced by the material and geometry parameters of the composite beam.