• 한국구조물진단유지관리공학회 논문집
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• 제20권1호
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• pp.18-24
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• 2016

본 논문은 강섬유의 일부를 철근집합체로 대체하여 초고강도 섬유보강 철근 콘크리트 I 형보의 연성거동을 유도하는 것을 목적으로 한다. 강섬유와 철근집합체의 조합을 가진 초고강도 콘크리트 I 형보 대한 휨거동 실험을 수행하였다. 강섬유의 혼입률은 0%, 0.7%, 1%, 1.5%, 2%이다. 철근집합체와 PS강연선 집합체가 압축구역에서 콘크리트를 구속하기 위해 사용되었다. 철근집합체와 강연선 집합체의 길이도 실험요소 중 하나이다. 이러한 실험요소를 조합하여 9개의 초고강도 철근 콘크리트 I 형보를 제작하였다. 강섬유 뿐만 아니라 종방향의 철근 집합체도 초고강도 철근 콘크리트 I형 보의 연성거동을 유도하는데 효과를 가지고 있다. 강섬유 혼입률 0.7% 또는 1%와 철근집합체를 사용한 조합이 I형 보의 효과적인 연성 거동을 보여주고 있다. 하중과 처짐관계 및 균열양상 등이 좁은 간격을 가진 작은 직경의 종방향 철근 집합체의 유용성을 나타내고 있다.

• Computers and Concrete
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• 제22권6호
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• pp.527-538
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• 2018

Buckling of longitudinal bars is a brittle failure mechanism, often recorded in reinforced concrete (RC) structures after an earthquake. Studies in the literature highlights that it often occurs when steel is in the post elastic range, by inducing a modification of the engineered stress-strain law of steel in compression. A proper evaluation of this effect is of fundamental importance for correctly evaluating capacity and ductility of structures. Significant errors can be obtained in terms of ultimate bending moment and curvature ductility of an RC section if these effects are not accounted, as well as incorrect evaluations are achieved by non-linear static analyses. This paper presents a numerical investigation aiming to evaluate the engineered stress-strain law of reinforcing steel in compression, including second order effects. Non-linear FE analyses are performed under the assumption of local buckling. A role of key parameters is evaluated, making difference between steel with strain hardening or with perfectly plastic behaviour. Comparisons with experimental data available in the literature confirm the accuracy of the achieved results and make it possible to formulate recommendations for design purposes. Finally, comparisons are made with analytical formulations available in the literature and based on obtained results, a modification of the stress-strain law model of Dhakal and Maekawa (2002) is proposed for fitting the numerical predictions.

• Computers and Concrete
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• 제24권4호
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• pp.313-327
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• 2019

The purpose of the present study is to present a new approach to designing and selecting the details of multidimensional continuous RC beam by applying all strength, serviceability, ductility and other constraints based on ACI318-14 using Teaching Learning Based Optimization (TLBO) algorithm. The optimum reinforcement detailing of longitudinal bars is done in two steps. in the first stage, only the dimensions of the beam in each span are considered as the variables of the optimization algorithm. in the second stage, the optimal design of the longitudinal bars of the beam is made according to the first step inputs. In the optimum shear reinforcement, using gradient-based methods, the most optimal possible mode is selected based on the existing assumptions. The objective function in this study is a cost function that includes the cost of concrete, formwork and reinforcing steel bars. The steel used in the objective function is the sum of longitudinal and shear bars. The use of a catalog list consisting of all existing patterns of longitudinal bars based on the minimum rules of the regulation in the second stage, leads to a sharp reduction in the volume of calculations and the achievement of the best solution. Three example with varying degrees of complexity, have been selected in order to investigate the optimal design of the longitudinal and shear reinforcement of continuous beam.

• Structural Engineering and Mechanics
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• 제37권6호
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• pp.649-669
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• 2011

In this paper an analytical model is presented that addresses the compressive response of short-fiber reinforced concrete members (FRC) with hooked steel fibers. This model is applicable to a wide range of concrete strengths and accounts for the interaction between the cover spalling and the concrete core confinement induced by transverse steel stirrups and also for buckling of longitudinal reinforcing bars. The load-shortening curves generated here analytically fit existing experimental data well.

• 한국환경복원기술학회지
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• 제5권3호
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• pp.15-22
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• 2002

To analysis of the embanked slope stability using a jointed reinforcement, the internal stability and the external stability have to be satisfied, respectively. But, because the lengths of ready-made steel-grid were limited, the reinforcements must be connecting themselves to the reinforcing. In this study, the mechanical test was carried out to investigate the tensile failure and the pullout failure at the joint parts of them, which was based on the analysis of reinforced slope in field. Through the tensile tests in mid-air for the jointed steel-grid, the deformation behavior was seriously observed as follows : deformation of longitudinal member, plastic deformation of longitudinal member and of crank part. Those effects were due to the confining pressure and overburden pressure of the surrounding ground. The bearing resistance at jointed part of jointed steel-grid was due to the latter only. The maximum tensile forces were higher about 20kN~27kN than ultimate pullout resistance, but, the results of those was almost the same in mid-soil. The failures of steel-grid occurred at welded point both of longitudinal members and transverse members and of jointed parts. The strength of jointed parts itself got pullout force about 20kN, which was about 65% for ultimate pullout force of the longitudinal members N=2. To the stability analysis of reinforced structure including the reinforced slope, the studying of connection effects at jointed part of reinforcement members must be considered. Through the results of them, the stability of reinforced structures should be satisfied.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.81-84
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• 2008

The purposes of this study are to verify a reasonable model of material characteristic and to propose a rational model of reinforcement characteristic considering monotonic and cyclic loading about manufactured reinforcing steel in Korea. Longitudinal reinforcements of the plastic hinge region were behaved tensile deformation and compressional deformation by direction of lateral loading. However Confinement steels were behaved only tensile deformation by lateral loading. Transverse steels were laid the state of tension in the lateral loading of time, and they were laid state that stress is zero when it was removed lateral load. The tests for cyclic tension loading were performed for test variable as yield strength and reinforcement bar sizes. It was estimated that the total strain energy per unit volume was 74 $MJ/m^3$. The modified ultimate concrete compression strain model was proposed based on experimental study of cyclic tension test for manufactured reinforcing steel in Korea.

• 한국지반공학회논문집
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• 제20권9호
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• pp.133-144
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• 2004

NATM터널 시공 중 강관이나 FRP관을 이용하여 터널 막장을 선행보강하는 방법은 RPUM이나 UAM 등으로 알려져 있으며, 얕은 터널 및 연약지반내 터널 굴착 시 굴진면의 안정성을 확보해주거나 지반 침하를 감소시켜주는 역할을 한다. 특히 굴진지반이 연약하여 자립이 어려운 경우 최근에는 굴진면 천단뿐 아니라 굴진면 수평보강을 실시하여 굴착에 따른 터널안정을 확보하게 된다. 일반적으로 터널굴착이 진행됨에 따라 굴진면 전후에는 종방향 아칭현상이 발생하며 이는 NATM 터널 지보재 작용원리의 근간이 된다. 따라서 터널 천단과 굴진면 수평보강을 실시하는 경우도 굴진에 따른 종방향 아칭의 관점에서 해석되어야 하나 이에 대한 연구는 현재까지 거의 없는 실정이다. 본 연구에서는 토사터널 굴진면에 RPUM(천단보강)이나 굴진면 수평보강이 실시된 경우, 종방향 아칭특성을 2차원 실내시험을 통해 살펴보았다. 실험결과, 연직토압의 변화를 토대로 한 종방향아칭 영향범위는 무보강의 경우 굴진면 전${\cdot}$후방으로 각각 2.5D와 1.5D(D는 터널직경), 천단보강 및 수평보강의 경우 2.0D와 1.5D, 천단과 수평보강이 동시에 적용된 경우는 2.0D와 1.0D까지로 측정되어 굴진면 보강에 따라 아칭의 영향범위가 감소함을 알 수 있었다. 반면 연직토압의 변화량은 굴진면 보강에 따라 증가하는 것으로 나타나 역학적으로 천단 및 수평보강재가 터널의 안정에 중요한 역할을 하고 있는 것으로 판단된다.

• Steel and Composite Structures
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• 제20권5호
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• pp.1067-1085
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• 2016

Recent research on steel moment-resisting connection between steel beams and concrete filled steel tubes has shown that there are considerable advantages to be obtained by anchoring the connection to the concrete infill within the tube using anchors in blind bolts. In the research reported here, extensive experimental tests and numerical analyses have been performed to study the anchorage behaviour of cogged deformed reinforcing bars within concrete filled circular steel tubes. This data in essential knowledge for the design of the steel connections that use anchored blind bolts, both for strength and stiffness. A series of pull-out tests were conducted using steel tubes with different diameter to thickness ratios under monotonic and cyclic loading. Both hoop strains and longitudinal strains in the tubes were measured together with applied load and slip. Various lead-in lengths before the bend and length of tailed extension after the bend were examined. These dimensions were limited by the dimensions of the steel tube and did not meet the requirements for "standard" cogs as specified in concrete standards such as AS 3600 and ACI 318. Nevertheless, all of the tested specimens failed by bar fracture outside the steel tubes. A comprehensive 3D Finite Element model was developed to simulate the pull-out tests. The FE model took into account material nonlinearities, deformations in reinforcing bars and interactions between different surfaces. The FE results were found to be in good agreement with experimental results. This model was then used to conduct parametric studies to investigate the influence of the confinement provided by the steel tube on the infilled concrete.

• 콘크리트학회논문집
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• 제26권2호
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• pp.109-116
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• 2014

압축강도 160MPa과 길이 15.4 m를 가진 초고강도 섬유보강 콘크리트 분절박스 거더의 휨거동 실험을 수행하였다. 초고강도 섬유보강 콘크리트 분절 박스에 연성거동 특성을 보강하기 위한 강섬유와 종방향철근의 조합 효과를 두종류의 강섬유 혼입률로 제작된 초고강도 분절형 박스거더의 휨거동을 비교함으로써 평가하였다. 강섬유 혼입률이 1%이고 전단철근과 상부플랜지와 복부에 종방향철근으로 보강한 초고강도 콘크리트 박스거더 BF2의 거동은 탄성응력대에서 전단철근 없이 강섬유 혼입률 2%인 초고강도 섬유보강 콘크리트 박스거더와 유사한 연성거동을 보여준다. 그러나 비선형응력대에서는 BF1의 강성이 약간 더 크고 안정적인 연성거동 형태를 보여주고 있다. 초고강도 섬유보강 콘크리트 박스거더의 분절면은 휨파괴 시까지 균열이나 슬립이 발생하지 않았다.

• 콘크리트학회논문집
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• 제17권5호
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• pp.775-784
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• 2005

본 연구에서는 합리적인 내진설계기준의 정립을 위하여 철근콘크리트 교각의 내진성능에 영향을 미치는 주요 인자에 대하여 분석하였다. 기존 연구 결과에 따르면 한반도와 같은 중약진 지역에서의 철근콘크리트 교각의 심부구속철근비가 과다하게 사용되어 왔다는 결론을 내렸다. 따라서, 본 연구에서는 기존의 실험 결과들을 분석하여 합리적인 심부구속철근비를 제안하였다. 본 연구에서 제안된 심부구속철근비는 축하중비와 주철근비를 고려하였으며 낮은 축하중비에서 주철근 좌굴 방지를 위한 최소 규정을 도입하였다. 제안된 식은 일반적인 도로교상의 축하중비를 고려하면 기존 내진규정에 비해 매우 완화된 심부구속철근비를 갖게 된다. 따라서 문제로 나타나고 있는 시공성과 경제성이 상당히 향상될 수 있으리라 판단된다.