• 대한토목학회논문집
• /
• 제28권2A호
• /
• pp.243-247
• /
• 2008

본 연구에서는 수정유효탄성계수법에 근거하여 2축 휨과 축력을 동시에 받는 경우에 콘크리트의 크리프와 건조수축을 고려한 철근콘크리트 보의 효율적이고 합리적인 단면해석 방법을 제안하였다. 제안된 방법은 재령보정계수와 선형 크리프 이론을 이용하였으며, 응력의 분포를 평형조건으로부터 유도하였다. 제안된 방법을 사용하여 직사각형 단면에 대한 예제해석을 수행하였으며 직사각형 단면에서 변형도의 변화와 응력의 변화를 검토하였다.

• Structural Engineering and Mechanics
• /
• 제40권1호
• /
• pp.105-120
• /
• 2011

The strengthening and rehabilitation of reinforced concrete structures with externally bonded carbon fibre reinforced polymer (FRP) laminates has shown excellent performance and, as a result, this technology is rapidly replacing steel plate bonding techniques. This paper addresses this issue, and presents results deals with the influence of external bonded CFRP-reinforcement on the time-dependent behavior of reinforced concrete beams. A total of eight reinforced concrete beams with cracked and un-cracked section, with and without externally bonded CFRP laminates, were investigated for their creep and shrinkage behavior. All the beams considered in this paper were simply supported and subjected to a uniform sustained loading for the period of six months. The main parameters of this study are two types of sustained load and different degrees of strengthening scheme for both cracked and un-cracked sections of beams. Both analytical and experimental work has been carried out on strengthened beams to investigate the cracking and deflection performance. The applied sustained load was 56% and 38% of the ultimate static capacities of the un-strengthened beams for cracked and un-cracked section respectively. The analytical values based on effective modulus method (EMM) are compared to the experimental results and it is found that the analytical values are in general give conservative estimates of the experimental results. It was concluded that the attachment of CFRP composite laminates has a positive influence on the long term performance of strengthened beams.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 1998년도 가을 학술발표논문집(II)
• /
• pp.462-467
• /
• 1998

A rational method for prediction of long-term deflections of reinforced concrete beams under sustained loads was proposed. Strain and stress distributions of uncracked and fully cracked sections after creep and shrinkage were determined from the requirements of strain compatibility and force equilibrium of a section, and then long-term deflections were calculated from the section analysis results. In fully cracked section analysis, noncoincidence of the neutral axis of strain and the neutral axis of stress after creep and shrinkage was taken into account. The accuracy of the proposed method was verified by comparison with several experimental measurements of beam deflections. The proposed approximate procedure gave the better predictions than the existing approximate methods. At the same time, the proposed method also retained simplicity of the calculation, since maximum long-term deflection could be obtained without tedious integration of the curvatures.

• Computers and Concrete
• /
• 제8권1호
• /
• pp.43-57
• /
• 2011

Force-deformation modelling of cracked reinforced concrete is essential for a displacement-based seismic assessment of structures and can be achieved by fibre-element analysis of the cross-section of the major lateral resisting elements. The non-linear moment curvature relationship obtained from fibre-element analysis takes into account the significant effects of axial pre-compression and contributions by the longitudinal reinforcement. Whilst some specialised analysis packages possess the capability of incorporating fibre-elements into the modelling (e.g., RESPONSE 2000), implementation of the analysis on EXCEL is illustrated in this paper. The outcome of the analysis is the moment-curvature relationship of the wall cross-section, curvature at yield and at damage control limit states specified by the user. Few software platforms can compete with EXCEL in terms of its transparencies, versatility and familiarity to the computer users. The program has the capability of handling arbitrary cross-sections that are without an axis of symmetry. Application of the program is illustrated with examples of typical cross-sections of structural walls. The calculated limiting curvature for the considered cross-sections were used to construct displacement profiles up the height of the wall for comparison with the seismically induced displacement demand.

• 콘크리트학회지
• /
• 제10권6호
• /
• pp.253-260
• /
• 1998

본 논문에서는 장기지속하중을 받는 철근콘크리트 보의 처짐을 계산하는 방법을 제안하였다. 균열단면에 대하여 적합조건 및 평형조건을 적용하여 크리프에 의한 중립축의 변화를 계산하는 효율적인 알고리즘을 제시하였으며, 이 값을 이용하여 임의의 시간에서의 휨강성을 유도하였다. 그리고 유사한 방법으로 비균열단면에서의 휨강성을 계산하고 균열단면과 비균열단면에서 각각 계산된 휨강성을 사용하여 ACI규준식의 유효단면 2차모멘트를 계산하는 것과 유사한 방법으로 휨강성을 계산하여 지속하중을 받는 철근콘크리트 보의 처짐을 예측하는 방법을 제시하였다. 제안된 방법과 기존의 실험결과를 비교하여 볼 때, 제안된 방법이 장기지속하중을 받는 철근콘크리트보의 처짐을 잘 예측하였다.

• Structural Engineering and Mechanics
• /
• 제15권2호
• /
• pp.159-180
• /
• 2003

In this paper spacing and width of flexural cracks in reinforced concrete beams are determined using two-dimensional finite element analysis. At early loading stages on the beam the primary crack spacing is based on the slip length, which is the development length required to resist the steel stress increment that occurs at a cracked section on the formation of the first flexural crack. A semi-empirical formula is presented in this paper for the determination of the slip length for a given beam. At higher load levels, the crack spacing is based on critical crack spacing, which is defined as the particular crack spacing that would produce a concrete tensile stress equal to the flexural strength of concrete. The resulting crack width is calculated as the relative difference in extensions of steel reinforcement and adjacent concrete evaluated at the cracked section. Finally a comparative study is undertaken, which indicates that the spacing and width of cracks calculated by this method agree well with values measured by other investigators.

• 한국지진공학회:학술대회논문집
• /
• 한국지진공학회 2005년도 학술발표회 논문집
• /
• pp.300-307
• /
• 2005

Steel Reinforced Concrete (SRC) composite column has several advantage such as excellent durability, rapid construction, reduction of column section. Due to these aspect, applications of SRC columns to bridge piers are continuously increasing. For the design of relatively large SRC columns for bridge piers, it is necessary to check the current design provisions which were based on small section having higher steel ratio. In this study, seven concrete encased composite columns were fabricated and static tests were performed. Embedded steel members were a H-shape rolled beam and a partially filled steel tube. Based on the test results, the ultimate strength according to section details and local behavior were estimated. For the analysis of inelastic behavior of the SRC column, the cracked section stiffness of the columns was evaluated and compared with calculations. The stiffness of the cracked section showed that 25% of the initial value and this stiffness reduction occurred at 85% of the ultimate load in the experiments.

• Steel and Composite Structures
• /
• 제33권5호
• /
• pp.629-640
• /
• 2019

This paper presents a theoretical and finite element (FE) study on the stress intensity factors of double-edged cracked steel beams strengthened with carbon fiber reinforced polymer (CFRP) plates. By simplifying the tension flange of the steel beam using a steel plate in tension, the solutions obtained for the stress intensity factors of the double-edged cracked steel plate strengthened with CFRP plates were used to evaluate those of the steel beam specimens. The correction factor α₁ was modified based on the transformed section method, and an additional correction factor φ was introduced into the expressions. Three-dimensional FE modeling was conducted to calculate the stress intensity factors. Numerous combinations of the specimen geometry, crack length, CFRP thickness and Young's modulus, adhesive thickness and shear modulus were analyzed. The numerical results were used to investigate the variations in the stress intensity factor and the additional correction factor φ. The proposed expressions are a function of applied stress, crack length, the ratio between the crack length and half the width of the tension flange, the stiffness ratio between the CFRP plate and tension flange, adhesive shear modulus and thickness. Finally, the proposed expressions were verified by comparing the theoretical and numerical results.

• Computers and Concrete
• /
• 제4권4호
• /
• pp.317-330
• /
• 2007

Steel reinforced concrete is perhaps the most versatile and widely used construction material. The versatility is attributed to mouldability of concrete to any conceivable shape. The inherent property of cracking of concrete is the reason for its low tensile strength and hence the design approach of RCC sections in flexure adopts the cracked section theory where in concrete in tension zone is ignored. Means, modes and methods of exploitation of concrete strength by conceiving shapes other than rectangular whereby ineffective concrete in tension zone is reduced and incorporated in compression zone where it is effective needs consideration. Shape optimization of beams is attempted in this analytical investigation employing Sequential Unconstrained Minimization Technique (SUMT). The results clearly show that trapezoidal beams happen to be less costlier than their rectangular counterparts, their usage needs serious reconsideration by the designers.

• Structural Engineering and Mechanics
• /
• 제17권6호
• /
• pp.863-878
• /
• 2004

Steel corrosion in reinforced concrete structures leads to concrete cover cracking, reduction of bond strength, and reduction of steel cross section. Among theses consequences mentioned, reduction of bond strength between reinforcement and concrete is of great importance to study the behaviour of RC members with corroded reinforcement. In this paper, firstly, an analytical model based on smeared cracking and average stress-strain relationship of concrete in tension is proposed to evaluate the maximum bursting pressure development in the cover concrete for noncorroded bar. Secondly, the internal pressure caused by the expansion of the corrosion products is evaluated by treating the cracked concrete as an orthotropic material. Finally, bond strength for corroded reinforcing bar is calculated and compared with test results.