• 한국지진공학회논문집
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• 제19권2호
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• pp.75-83
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• 2015

The purpose of this study is to improve the previous damage evaluation model for RC members which is proposed by Igarashi[1] in 2010.The previous model was not confirmed by enough data of damage such as, residual crack length, width and area for exfoliation of concrete, etc. In addition, validation of the model is still insufficient. Therefore, experiment of a real-scale RC structure and experiment of RC columns using the high-strength concrete were conducted to gather the data of damage in RC members. The investigation has been conducted gathering the data not only additional experiments data but also existing data for modification of damage evaluation model. It has been investigated on changing damage in RC due to axial force ratio, shear reinforcement and shear span ratio. As a result, several problems were founded in the previous model, such as, hinge length($l_p$), spacing of flexural crack($S_{av,f}$), total width of flexural cracks regulated by maximum width of flexural crack($n_f$) and total width of shear cracks regulated by maximum width of shear crack($n_s$). New model is proposed and evaluated the damage properly.

• 산업기술연구
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• 제24권A호
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• pp.179-184
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• 2004

Each year, new technological advancements for repair-purpose are being introduced to overlay the old deterioration of RC bridge deck at highway by latex-modified concrete. The days may come when this old problem will be successfully resolved. While the experimental works and researches are very active at both laboratory and field, only a few theoretical studies were performed on interfacial problems, especially on stress distribution and concentration of RC beam overlayed by latex-modified concrete. The repaired and strengthened structures would induce a premature failure due to the stress concentration at the adhesive layer of different material before the design expected failure. This paper investigated and proposed an analytical model for predicting interfacial shear and normal stresses of RC beam repair-purpose overlayed by latex-modified concrete. This would be used for predicting interfacial stresses and preventing premature failure at interfaces. This study modified Smith-Teng method for applying to cementitious repairing material, which was based on a direct governing equation and linear-elastic approach for interfacial normal and shear stresses. The proposed theoretical model was verified using commercial FEA program, LUSAS, in terms of interfacial stresses predicted by the proposed model and calculated by LUSAS.

• Advances in Traditional Medicine
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• 제9권1호
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• pp.58-66
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• 2009

Allergic conjunctivitis is the most common allergic disease. These diseases are severe & frequent which requires search of new treatments. The aim of the study was to investigate the effects of Tinospora cordifolia (TC), Rubia cordifolia Linn. (RC) on experimentally induced allergic conjunctivitis in rats. In this study, dried water soluble extracts of TC and RC. (250 and 500 mg/kg, p.o. for 7 days) were evaluated for their antiallergic activity in Wistar rats. They were tested for inhibition of egg albumin-induced vascular permeability, inhibition of histamine release from the rat conjunctiva as well as in histamine content in tears. TC and RC showed significant (P < 0.05) inhibition in vascular permeability, inhibition in histamine release from the rat conjunctiva which is reflected by reduced level of histamine content in tears. The activities were found to be comparable to azelastine hydrochloride. These results suggest that the inhibitory effect on egg albumin-induced experimental allergic conjunctivitis in rat may be due to the antihistaminic activity of TC and RC. Our studies provide evidence that TC and RC may be beneficial in the treatment of allergic conjunctivitis.

• Structural Engineering and Mechanics
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• 제27권4호
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• pp.439-456
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• 2007

Reinforced concrete (RC) joint shear strength models are constructed using an experimental database in conjunction with a Bayesian parameter estimation method. The experimental database consists of RC beam-column connection test subassemblies that maintained proper confinement within the joint panel. All included test subassemblies were subjected to quasi-static cyclic lateral loading and eventually experienced joint shear failure (either in conjunction with or without yielding of beam reinforcement); subassemblies with out-of-plane members and/or eccentricity between the beam(s) and the column are not included in this study. Three types of joint shear strength models are developed. The first model considers all possible influence parameters on joint shear strength. The second model contains those parameters left after a step-wise process that systematically identifies and removes the least important parameters affecting RC joint shear strength. The third model simplifies the second model for convenient application in practical design. All three models are unbiased and show similar levels of scatter. Finally, the improved performance of the simplified model for design is identified by comparison with the current ACI 352R-02 RC joint shear strength model.

• 한국강구조학회 논문집
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• 제19권1호
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• pp.53-65
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• 2007

새로운 형식의 기둥인 내부 구속 중공 콘크리트 충전 튜브 기둥(내부 구속 중공 CFT 기둥, ICH CFT column ; Internally Confined Hollow CFT Column)의 내진 성능 평가 실험을 수행하였다. 준정적 실험을 통하여 2가지 종류의 ICH CFT 기둥과 일반 중실 RC 기둥의 내진 성능을 비교 평가 하였다. 각각의 기둥 시험체에 대해 최대 하중과 변위의 관계를 측정하였으며, 이를 바탕으로 연성도, 소산에너지, 등가 감쇠비, 손상 지수가 계산되었다. 실험 결과 ICH CFT 기둥은 중실 RC 기둥에 비해 약 2배의 모멘트에 저항을 하였으며, 에너지의 흡수와 소산에서도 1.5배 정도의 성능을 보여주어, ICH CFT 기둥이 일반 중실 RC 기둥보다 더 뛰어난 성능을 가짐을 보여주었다.

• Earthquakes and Structures
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• 제7권5호
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• pp.667-689
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• 2014

Structural walls (also known as shear walls) are one of the common lateral load resisting elements in reinforced concrete (RC) buildings in seismic regions. The performance of RC structural walls in recent earthquakes has exposed some problems with the existing design of RC structural walls. The main issues lie around the buckling of bars, out-of plane deformation of the wall (especially the zone deteriorated in compression), reinforcement getting snapped beneath a solitary thin crack etc. This study compares performance of a typical wall designed by different standards. For this purpose, a case study RC shear wall is taken from the Hotel Grand Chancellor in Christchurch which was designed according to the 1982 version of the New Zealand concrete structures standard (NZS3101:1982). The wall is redesigned in this study to comply with the detailing requirements of three standards; ACI-318-11, NZS3101:2006 and Eurocode 8 in such a way that they provide the same flexural and shear capacity. Based on section analysis and pushover analysis, nonlinear responses of the walls are compared in terms of their lateral load capacity and curvature as well as displacement ductilities, and the effect of the code limitations on nonlinear responses of the different walls are evaluated. A parametric study is also carried out to further investigate the effect of confinement length and axial load ratio on the lateral response of shear walls.

• Computers and Concrete
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• 제15권4호
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• pp.607-642
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• 2015

The stress-strain relationship of concrete in flexure is one of the essential parameters in assessing the flexural strength and ductility of reinforced concrete (RC) columns. An overview of previous research studies revealed that the presence of strain gradient would affect the maximum concrete stress developed in flexure. However, no quantitative model was available to evaluate the strain gradient effect on concrete under flexure. Previously, the authors have conducted experimental studies to investigate the strain gradient effect on maximum concrete stress and respective strain and developed two strain-gradient-dependent factors k3 and ko for modifying the flexural concrete stress-strain curve. As a continued study, the authors herein will extend the investigation of strain gradient effects on flexural strength and ductility of RC columns to concrete strength up to 100 MPa by employing the strain-gradient-dependent concrete stress-strain curve using nonlinear moment-curvature analysis. It was evident from the results that both the flexural strength and ductility of RC columns are improved under strain gradient effect. Lastly, for practical engineering design purpose, a new equivalent rectangular concrete stress block incorporating the combined effects of strain gradient and concrete strength was proposed and validated. Design formulas and charts have also been presented for flexural strength and ductility of RC columns.

• Structural Engineering and Mechanics
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• 제88권5호
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• pp.419-437
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• 2023

The use of reinforced concrete (RC) shear walls (SW) as an efficient lateral load-carrying system has gained recent attention. However, creating openings in RC shear walls is unavoidable due to architectural requirements. This reduces the walls' strength and stiffness, resulting in the development of wall piers. In this study, the cyclic behavior of RC shear walls with openings, reinforced with carbon fiber reinforced polymer (CFRP) sheets in various patterns, was numerically investigated. Finite element analysis (FEA) using ABAQUS software was employed. Additionally, the retrofitting of sub-standard buildings (5, 10, and 15-story structures) designed based on the old and new versions of the Iranian Code of Practice for Seismic-Resistant Structures was evaluated. Nonlinear static analyses, specifically pushover analyses, were conducted on the structures. The best pattern of CFRP wrapping was determined and utilized for retrofitting the sub-standard structures. Various structural parameters, such as load-carrying capacity, ductility, stress contours, and tension damage contours, were compared to assess the efficiency of the retrofit solution. The results indicated that the load-carrying capacity of the sub-standard structures was lower than that of standard ones by 57%, 69%, and 67% for 5, 10, and 15-story buildings, respectively. However, the retrofit solution utilizing CFRP showed promising results, enhancing the capacity by 10-25%. The retrofitted structures demonstrated increased yield strength, ultimate strength, and ductility through CFRP wrapping and effectively prevented wall slipping.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.204-209
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• 2003

The purpose of this study is to develop new seismic design concept based on ductility demand for reinforced concrete bridge columns in areas of low to moderate seismicity. In developing the ductility based design approach, relationship between ductility demand and transverse reinforcement demand should be quantitatively developed. To evaluate ductility capacity of reinforced concrete columns, analytical models and a non-linear analysis program, NARCC have been developed. Based on analytical and experimental results, an equation for relationship between curvature ductility and displacement ductility, an equation for designing the transverse confinement reinforcement for ductility demand, and a new seismic design concept of RC bridge columns are presented.

• Structural Engineering and Mechanics
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• 제11권1호
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• pp.17-34
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• 2001

An improved method has been developed for the computation of the section forces and stiffness in nonlinear finite element analysis of RC plane frames. The need for a new approach arises because the conventional technique may have a questionable level of efficiency if a large number of layers is specified and a questionable level of accuracy if a smaller number is used. The proposed technique is based on automatically dividing the section into zones of similar state of stress and tangent modulus and then numerically integrating within each zone to evaluate the sectional stiffness parameters and forces. In the new system, the size, number and location of the layers vary with the state of the strains in the cross section. The proposed method shows a significant improvement in time requirement and accuracy in comparison with the conventional layered approach. The computer program based on the new technique has been used successfully to predict the experimental load-deflection response of a RC frame and good agreement with test and other numerical results have been obtained.