• 한국방재학회:학술대회논문집
• /
• 2011.02a
• /
• pp.35-35
• /
• 2011

CFT가 갖는 다양한 구조적 이점으로 인해, 축력이 지배적인 기둥 구조물에만 주로 적용되던 CFT 요소가 점차 거더에 적용되어 가고 있다. 그러나, 현재 CFT 요소에 대한 설계 기준은 축력이 지배적인 보-기둥 구조물에 대한 것으로 제한되어 있으며, 휨이 지배적인 보 구조물에 대한 현행 설계 기준의 적용성을 검토해야 할 필요가 있다. 현행 설계기준에서 제시하고 있는 CFT 요소의 극한 강도 평가방법은 소성응력분배법 및 변형률적합법으로 구분되어지며, 각 방법을 이용한 극한 강도의 평가결과를 기존 연구자들의 CFT 요소 휨 실험결과와 비교 분석하였다. 휨 강성 평가에 대한 타당성을 검증하기 위해 AISC에서 제시하는 휨 강성 평가식을 기존 실험 연구와 비교 검토하였으며, 아울러 압축력에 따라 휨 강성을 보정할 수 있도록 수정된 Roeder et al.의 제안식을 함께 검토하였다. 검토 결과, 강도 평가에 있어서는 설계 기준에서 제안하는 두 방법 모두 CFT 거더의 휨 강도를 적절히 평가할 수 있었으며, 강성 평가에 있어서는 설계 기준의 제안식이 휨 초기 강성을 적절히 평가하는 반면 사용 단계에서의 휨 강성은 Roeder et al.의 수정된 강성 평가식에 의해 적절히 평가할 수 있음을 확인하였다.

• 한국방재학회:학술대회논문집
• /
• 2010.02a
• /
• pp.83.1-83.1
• /
• 2010

본 연구는 고강도 강재를 적용한 연속교 형식의 강교량에 대하여 연구를 수행하였다. 교량에 사용되는 주구조의 고강도화에 따로 연속교의 교각 부근 부모멘트부에는 정모멘트부에 비하여 큰 모멘트가 작용하게 된다. 또한 정모멘트 구간과 달리 상부플랜지에 인장력이 작용하게 되어 완공 후에도 극한 하중 상태에서 콘크리트 데크가 응력을 부담할 수 없게 된다. 이에 따라 하부 플랜지에 불안정 파괴가 발생할 가능성이 있으며 비합성 단면과 같은 방법으로 설계하게 된다. 또한 모멘트 재분배를 고려한 설계를 하기 위해서는 부모멘트부에 충분한 휨 연성이 필요하다. 고강도 강재를 적용한 교량은 일반강재를 적용한 교량에 비하여 휨연성이 감소하게 되므로 휨연성 확보를 위한 보강방안이 필요하다. 본 연구는 부모멘트부의 휨연성 향상을 휘하여 가로보의 부등 배치를 제안하였으며, 유한요소해석 결과 휨연성이 향상되었다.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.28 no.4A
• /
• pp.537-548
• /
• 2008

Recently, the prestressed unbonded concrete structures are increasingly being built. The mechanical behavior of prestressed concrete beams with unbonded tendon is different from that of normal bonded PSC beams in that the increment of tendon stress was derived by whole member behavior. The purpose of the present paper is therefore to evaluate the flexural behavior and to propose the equation of ultimate tendon stress by performing static flexural test according to span/depth, concrete compression strength, reinforcement ratio and the effect of existing bonded tendon. From experimental results, for cracking, yielding and ultimate load, the effect of reinforcement ratio was more effective than concrete compression strength, and the beams having high strength concrete had a good performance than having low concrete, but there was no difference between high strength and low strength. And as L/dp was larger, test beams had a long region of ductility. This means that unbonded tendon has a large contribution after reinforcement yielding. Especially, the equation of ACI-318 was not match with test results and had no correlations. After analysis of test results, the equation of ultimate unbonded tendon stress without slip was proposed, and the proposed equation was well matched with test results. So the proposed equation in this paper will be a effective basis for the evaluation of unbonded tendons without slip, analysis and design.

• Journal of the Korean Geotechnical Society
• /
• v.35 no.12
• /
• pp.91-100
• /
• 2019

Hollow prestressed concrete-filled steel tube (HCFT) piles, which combines PHC piles inside thin-wall steel tubes, were developed to increase the flexural strength of the pile with respect to the lateral load. Since P-M curves are needed for evaluating the structural safety of piles when applying HCFT piles to fields, equations for plotting P-M curves of HCFT piles in limit states were proposed. When the yield strength is applied to the steel tube and PC steel bar of HCFT piles, the proposed equations significantly underestimated the flexural strength of HCFT piles. Unlike the flexural strength test results, the proposed equations also provide greater flexural strengths for 12 mm thick steel pipe piles with the same diameter than for HCFT piles. However, when the ultimate strengths are used instead of the yield strengths for the steel tube and PC steel bar, the proposed equations provide the flexural strengths very close to the flexural strength test results.

• Journal of Korean Society of Steel Construction
• /
• v.27 no.1
• /
• pp.109-118
• /
• 2015

Ultimate flexural buckling strength of cylindrical steel shells for the wind turbine tower structure was investigated by applying the geometrically and materially nonlinear finite element method. The effects of initial imperfection, radius to thickness ratio, and type of steel on the ultimate flexural strength of cylindrical shell were analyzed. The flexural strengths of cylindrical shells obtained by FEA were compared with design flexural strengths specified in Eurocode 3 and AISI. The shell buckling modes recommended in DNV-RP-C202 and the out-of-roundness tolerance and welding induced imperfections specified in Eurocode 3 were used in the nonlinear FE analysis as initial geometrical imperfections. The radius to thickness ratios of cylindrical shell in the range of 60 to 210 were considered and shells are assumed to be made of SM520 or HSB800 steel.

• Journal of Korean Society of Steel Construction
• /
• v.22 no.5
• /
• pp.465-475
• /
• 2010

In the horizontally curved bridges, girders are subjected to the combined action of vertical bending and torsion due to their curvatures without any eccentric loads. As subjected to bending and torsion, the ultimate strength of steel/concrete composite box girders are limited by the diagonal tensile stress in the deck concrete induced by the St. Venant torsion. To determine the ultimate strength of composite box girders in bending and torsion and their interactions, this study conducted a 3-dimensional FEA and classical strength of materials investigation. Using ABAQUS, the FEA fully utilized advanced nonlinear analysis techniques simulating material/geometrical nonlinearity and post-cracking behaviors. The ultimate strength from numerical data were compared with theoretically derived values. Concurrent compressive stresses in the concrete deck improve the shear-resisting capacity of concrete, thereby resulting in an increased torsional resistance of the composite box girder in positive bending. The proposed interaction equation is very simple yet it provides a rational lower bound in determining the ultimate strength of concrete/steel composite box girders.

• Journal of the Korea Concrete Institute
• /
• v.14 no.5
• /
• pp.645-652
• /
• 2002

This paper presents the flexural behavior and strengthening effect of reinforced concrete beams bonded with carbon FRP plate. Parameters involved in this experimental study were plate bond length and sheet web anchorage length. Test beams were strengthened with FRP plate on the soffit and anchored with FRP sheet on the web. In general, strengthened beams with no web anchorage were failed by concrete cover failure along the longitudinal reinforcement. On the other hand, strengthened beams with web anchorage were finally failed by delamination shear failure within concrete after breaking of CFRP sheet wrapping around web. The ultimate load and deflection of strengthened beams increased with an increased bond length of FRP plate. Also, the ultimate load and deflection increased with an increased anchorage length of FRP sheet. Particularly, the strengthened beams with web anchorage maintained high ultimate load resisting capacity until very large deflection. The shape of strain distribution of CFRP plate along beam was very similar to that of bending moment diagram. Therefore, an assumption of constant shear stress in shear span could be possible in the analysis of delamination shear stress of concrete. In the case of full bond length, the ultimate resisting shear stress provided by concrete and FRP sheet Increased with an increase of web anchorage length. In the resisting shear force, a portion of the shear force was provided by FRP anchorage sheet.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.10 no.3 s.49
• /
• pp.113-123
• /
• 2006

An experimental investigation on the behavior of reinforced concrete coupling beams is presented. The test variables are the span-to-depth ratio, the ratio of flexural reinforcements and the ratio of shear rebars. The distribution of arch action and truss action which compose the mechanism of shear resistance is discussed. The increase of plastic deformation after yielding transforms the shear transfer by arch action into by truss action. This study proposes the deformation model for reinforced concrete coupling beams considering the bond slip of flexural reinforcement. The strain distribution model of shear reinforcements and flexural reinforcements based on test results is presented. The yielding of flexural reinforcements determines yielding states and the ultimate states of reinforced concrete coupling beam are defined as the ultimate compressive strain of struts and the degradation of compressive strength due to principal tensile strain of struts. The flexural-shear failure mechanism determines the ultimate state of RC coupling beams. It is expected that this model can be applied to displacement-based design methods.

• 한국방재학회:학술대회논문집
• /
• 2010.02a
• /
• pp.84.1-84.1
• /
• 2010

국내에서는 플레이트거더의 휨 강도 및 전단 강도를 허용응력설계법에 기반한 도로교설계기준(2005)에 근거하여 규정하고 있으며, 국외의 경우 하중저항계수설계법에 근간을 둔 AISC(2005) 등의 규정을 통해 산정하고 있다. 최근에는 인장강도 800MPa 급의 강재가 생산되고 있으나 국내 설계기준에서는 아직까지 상기 인장강도를 갖는 고강도강에 대한 설계기준은 마련되지 않고 있다. 본 연구에서는 휨과 전단이 동시에 작용하는 고강도강 적용 플레이트거더의 극한거동 해석을 통해 국내기준의 적용성을 판단하고, 국외기준인 AISC(2005)와 비교하여 나타내어 허용응력설계법에 근거한 국내기준의 강도산정법의 한계점에 대해 고찰하였다.

• Journal of the Society of Disaster Information
• /
• v.16 no.4
• /
• pp.796-805
• /
• 2020

Purpose: A static loading test was performed to evaluate the ultimate flexural strength of a girder in which 80MPa high-strength concrete was synthesized on the compressive flange of the I-shape steel girder. Method: This test is designed and fabricated two types of specimens with different shear-connection specifications, and evaluated their ultimate flexural behavior until reaching the extreme event limit states. In addition, the ultimate strength was evaluated by comparing the test results and the results of the strain compatibility method. Result: By confirming the displacement within 0.02mm as a result of the relative slip measurement, it was verified that the two specimens secured perfect bonding. Therefore, the difference in the shear specification does not have a great effect on the stiffness, and if the specimens are completely synthesized, there is no difference in the behavior until it reaches the extreme-event limit states. Conclusion: The girder to be tested has a working load within the elastic range and meets the usability requirements for allowable deflection. Therefore, even if a part of the casing is subjected to the tensile force at the level of cracking, the deck will first reach the compression failure due to the role of the reinforcing bar.