• Magazine of the Korea Concrete Institute
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• v.9 no.4
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• pp.207-214
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• 1997

This study was performed to verify the effect of axial force due to restraint on the mechanical behavior and the average crack spacing of the reinforced concrett. ilexural menlbers. For. this purpose, the flexural sttvngt.h and rigidity werc experimentally investigated undcl. axially rcstmined and unr.est.rainrd conditions. Furthermore , the average crack spacing was also checkcd for the axilly restrained contlit.ion. Thc test results showd that the flexual strength and rigidity of t,he restrained beam were higher. than those of the unrestrained beam. The major. factors affecting on the average crack spacing were steeel stress, axial force, cicumference of reinforcing bar and effective tension arm of concrete. However. the concrete compressive strength was minor effect. Including thesc factors, a prediction equation for the average crack spacing of the restrained member was proposed.

• Magazine of the Korea Concrete Institute
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• v.10 no.5
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• pp.109-115
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• 1998

철근콘크리트 구조물이 과소설계되어 있거나 과다 하중이 작용하게 되면 그 구조물의 구조성능을 파악하여 보수.보강을 시행하게 된다. 최근에 가장 맣이 사용되는 보수.보강 재료로는 특히 휨내력을 보강하는데 탄소섬유를 들 수 있다. 탄소섬유쉬트는 내열성과 내호염성에 있어서 회재가 발생할 경우 보강재료로서 충분한 성능을 가지고 있다. 그러나 이를 접착시키는데 사용되는 에폭시는 유기계 물질로서 화재시 유독가스가 발생하고 내열성능도 30$0^{\circ}C$정도에도 지탱하기 어려워 화재 발생이 가능한 구조물에 사용하기 어렵다. 이 연구에서는 무기계 폴리머 복합재료로 접착된 탄소섬유를 고온(약 800~100$0^{\circ}C$, 1시간)으로 가열한 후 가열된 섬유판의 인장, 휨 전단내력을 검토하여 내열성능을 파악하고 이 섬유쉬트로 보강한 철근콘크리트 부재의 휨 성능을 실험적으로 규명하여 화재의 위험이 있는 구조물에 구조적인 보강재료로 사용이 가능한가를 검토하였다. 연구 결과, 개발된 무기계 폴리머 복합체는 인장강도, 휨강도 및 접착강도가 유기계 접착제와 유사하게 나타났고 800~100$0^{\circ}C$ 정도로 1시간 가열한 이후에도 상온 시험체 휨내력과 전단내력의 63%, 33% 정도를 유지하여 화재의 위험이 있는 부위에도 사용이 가능한 것으로 판단되었다.

• Journal of the Korea Concrete Institute
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• v.14 no.4
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• pp.483-491
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• 2002

This paper summarizes the results of experimental studies concerning the flexural strengthening of reinforced concrete beams by the external bonding of the new reinforcement material, which is composite panel with an advanced fiber sheet bonded on light concrete precast panel. The structural behaviors of strengthened beams are compared with codes in terms of yield load and ultimate load, deflection, flexural stiffness, ductility. Thirty nine large-scale beams were tested experimentally to evaluate the strength enhancement provided by the composite panel. According to the results, it is shown that beams strengthened with composite panel are structurally efficient and that the strength of the strengthened beams are improved comparing with beams strengthened with fiber sheet.

• Journal of Korean Society of Steel Construction
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• v.19 no.3
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• pp.323-333
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• 2007

This paper presents a study that attempted to improve the site applicability of profile sheets and check the effects of bending reinforcement in composite profiled beams, and consequently, to suggest an improved modular-type CB2 and two types of bending reinforcement methods. As a result of the reinforcing and reforming modular profiled beam experiment conducted, CBIIshowed an adequate deformation capacity as well as a sufficient plastic plateau at the maximum load and thereafter. For all the specimens, an insignificant modular slip occurred while linear relations were kept constant, at up to approximately 50% of the maximum load and at constant linear relations. The experimental values were very low. Probably, due to the small-scale experiment, the area of the concrete for the concrete filling and covering might have been insufficient, which might have led to the failure to improve the strength. Comparing the results with the standard design stress, all the specimens-except for T16 and B16-indicated more than 0.9. Based on the standard design stress, the reinforced modular profiled beam was consideredto have positive applicability.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.3
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• pp.315-323
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• 2010

Five concrete compressive stress-strain models have been analyzed to check the validity of the strength method for determining the nominal moment of strengthened members using commercially available computer language. The results show that the concrete stress-strain models do not influence on the flexural analysis. The moment of a strengthened member obtained from the flexural analysis at concrete compressive strain reaching 0.003 is well agreed with nominal moment using the strength method. The flexural analysis results show that when the steel reinforcement, FRP ratio, FRP failure strain, and concrete failure compressive strain are relatively lower, the strength method overestimates the flexural capacity of the strengthened members.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.6
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• pp.44-51
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• 2017

Recently, the parking in downtown area has caused severe problem due to the dramatic increase of possessing automobile in the country. A parking structure has been on the spotlight to solve the parking problem in downtown area. However, the overall height of parking structure is stipulated less than 8 m. Therefore, in this research, 'wide composite beam', which is possible for reducing story height and having long span, is developed and the flexural capacity of the wide composite beam is evaluated. Based on the result of the flexural test, the flexural strength of wide composite beam increased by 20% as the thickness of steel beam increased by 3 mm ($6mm{\rightarrow}9mm$) The shapes of rebar (whether it is triangle or rectangular shape) in the wide composite beam did not affect its flexural strength. The flexural strength of wide composite beam without rebar decreased by 10% compared to that of wide composite beam with rebar. In addition, the neutral axis moved upward as a load increased, but the neutral axis moved downward, when the load exceeded a certain level of load.

• Journal of Korean Tunnelling and Underground Space Association
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• v.14 no.3
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• pp.215-230
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• 2012

An experimental research on the possibility of using high-strength concrete with the design strength of 60 MPa and high-tension rebar with the yielding strength of 600 MPa instead of conventional reinforced concrete segment to reduce its production cost was performed. Full-scale bending tests on both conventional and high-strength reinforced concrete segments were carried out to compare their mechanical and structural behaviors of the segments under flexural action. From the experiments, it was shown that the failure load of high-strength reinforced concrete segment was approximately 30% higher than that of the conventional segment even though reinforcements in high-strength segment were reduced by 26%. The test result showed that the bearing capacity of high-strength segment highly increased by high-strength concrete and high-tension rebar. It also verified the high possibility of high-strength reinforced concrete segment as a technical alternative to reduce the production cost of segments in a shield tunnel.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.685-688
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• 2008

Concrete is strong on the compressive property, but weak on the tensile and flexural properties. To improve these problems, the reinforcing bar is used in concrete. But porous concrete with steel fiber has a weak point when exposed to air, because porous concrete has the vast continuous void on its inside and steel fiber is easily rusted by air. For these reasons, this study investigated the void ratio, compressive strength, bending strength and bending toughness as steel fiber mixing ratio and target void ratio. From test results, actual void ratio and strength properties increased as the mixing ratio of steel fiber increase. In case the mixing ratio of steel fiber over the fixed ratio, strength is decreased. And from the toughness evaluation, compared to the porous concrete which isn't mixed with steel fiber, the deflection variation efficiency is remarkably improved. Consequently we can confirm the possibility of porous concrete with steel fiber for the secondary product and pavement material to improve strength and bending resistance efficiency.

• Journal of Korean Society of Steel Construction
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• v.29 no.5
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• pp.353-359
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• 2017

The purpose of this study is to evaluate the strength and behavior of the composite member in case of concrete filled steel tube embedded in concrete for application concrete filled steel tube to steel rib support in tunnel. A total of six beam specimens were prepared for steel tube in-filled with plain concrete and aerated concrete, and static bending tests were performed. As a result, the member of concrete steel tube embedded with plain concrete showed higher strength than those with aerated concrete. However, it was found that the flexural strength of member with reinforcing bar around the steel tube is more influenced by the amount of the reinforcing bar than the type of the filled concrete.

• Journal of Korean Society of Steel Construction
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• v.17 no.2 s.75
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• pp.195-206
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• 2005

Experimental research was performed on the 6m-6m two-span, continuous composite beams. Background research for the crack width control of continuous composite bridges in the Eurocode-4 is reviewed and equationsfor the calculation of crack width considering tension stiffening are presented. The behavior of the continuous composite beams was investigated using the initial and stabilized cracking process of the concrete slab in tension. Test results showed that the current requirement of minimum reinforcement for ductility in Korea Highway Bridge Design Codes could be reduced. The flexural stiffness of cracked continuous composite beams can be evaluated by the uncracked section analysis until the stabilized cracking stage. An empirical equation for the relationship between the stress of tensile reinforcements and crack width was obtained from the test results.