• 소성∙가공
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• 제13권5호
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• pp.415-421
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• 2004

The effect of transformation temperature on microstructural features and their effects on ductility in 0.55%C steels were investigated, compared with in 0.82%C eutectoid steel. The samples were austenitized at 100$0^{\circ}C$ for 30min. followed by quenching in a salt bath in the temperature range of 500 ~ $620^{\circ}C$. It was found that reduction of area(RA) increased with increasing transformation temperature and then, decreased after reaching its maximum value in steels containing pro-eutectoid ferrite less than 6%. The thickness of lamellar cementite was found to be the main factor controlling RA. Additionally, the presence of cementite thickness for the maximum ductility in all the tested steels was observed as about 0.015${\mu}{\textrm}{m}$ for tested steels.

• 전산구조공학
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• 제10권4호
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• pp.281-290
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• 1997

현행 내진설계 규준에서 사용하고 있는 반응수정계수는 설계지진하중과 유사한 지진발생시 구조물이 비선형 거동을 하도록 탄성응답에서 요구되는 밑면전단력 값을 낮추는 계수라 할 수 있다. 따라서 반응수정계수는 하중저감계수(force reduction factor)라고 할 수 있으며, 이러한 값들은 경험적으로 결정된 것이어서 예상지진에 대하여 구조설계자가 설계한 건물이 어느정도의 비선형 거동을 할지는 예측하기가 힘들다. 본 연구에서는 목표가 되는 연성비(target ductility ratio)에 따라 요구되는 밑면전단력의 값을 구하고 이를 규준에서 요구하는 값과 비교할 것이다. 만약 요구되는 값이 규준 값 보다 크다면 이는 구조물이 가지는 부가강도(overstrength)나 잉여력(redundancy)이 담당해야 한다. 모멘트연성골조 건물을 설계한 후 이를 push-over 해석에 의하여 부가강도를 찾아 보아 요구강도와 비교할 것이다.

• Structural Engineering and Mechanics
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• 제89권6호
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• pp.579-588
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• 2024

The present paper investigates the curvature ductility of confined reinforced concrete (RC) beams with normal (NSC) and high strength concrete (HSC). For the purpose of predicting the curvature ductility factor, an analytical model was developed based on the equilibrium of internal forces of confined concrete and reinforcement. In this context, the curvatures were calculated at first yielding of tension reinforcement and at ultimate when the confined concrete strain reaches the ultimate value. To best simulate the situation of confined RC beams in flexure, a modified version of an ancient confined concrete model was adopted for this study. In order to show the accuracy of the proposed model, an experimental database was collected from the literature. The statistical comparison between experimental and predicted results showed that the proposed model has a good performance. Then, the data generated from the validated theoretical model were used to train the artificial neural network (ANN) prediction model. The R² values for theoretical and experimental results are equal to 0.98 and 0.95, respectively which proves the high performance of the ANN model. Finally, a parametric study was implemented to analyze the effect of different parameters on the curvature ductility factor using theoretical and ANN models. The results are similar to those extracted from experiments, where the concrete strength, the compression reinforcement ratio, the yield strength, and the volumetric ratio of transverse reinforcement have a positive effect. In contrast, the ratio and the yield strength of tension reinforcement have a negative effect.

• Steel and Composite Structures
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• 제18권1호
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• pp.71-90
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• 2015

Axial compression tests have been carried out on 18 rectangular concrete-filled cold-formed steel tubular (CFST) columns with the aim of investigating the axial behaviour of rectangular CFST columns under different loading methods (steel loaded-first and full-section loaded methods). The influence of different loading methods on the ultimate strength of the specimens was compared and the development of Poisson's Ratio as it responds to an increasing load was reported and analysed. Then, the relationship between the constraining factor and the strength index, and the relationship between the constraining factor and ductility index of the specimens, were both discussed. Furthermore, the test results of the full-section loaded specimens were compared with five international code predicted values, and an equation was derived to predict the axial carrying capacity for rectangular CFST columns with a steel loaded-first loading method.

• 한국구조물진단유지관리공학회 논문집
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• 제23권6호
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• pp.61-69
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• 2019

본 연구에서는 단일강섬유와 하이브리드강섬유로 보강된 UHPC의 휨강도 및 연성을 평가하기 위해 세 개의 휨파괴형 보에 대한 4점 가력 실험을 수행하였다. 실험 결과 단일섬유로 보강된 UHPC보다 하이브리드 섬유로 보강된 UHPC가 강도 및 연성 모든 측면에서 더 우수한 구조성능을 보유한 것으로 나타났다. 설계시의 안전성에 대해 평가하기 위하여, K-UHPC 구조설계지침에서 제공하는 방법에 따라 실험체의 강도와 연성을 평가해본 결과 현재의 재료모델은 강도에 대해서는 보수적으로 평가할 수 있으나 연성에 대해서는 과대평가하는 것으로 나타났다.

• 콘크리트학회논문집
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• 제11권3호
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• pp.131-140
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• 1999

This paper presents a study on the flexural ductility of reinforced concrete beams, 16beams with different concrete strength, reinforcement ratio, reinfo- rcement strength. For the purpose of inducing flexural failure, the reinforce ratio ($\rho$-$\rho$') was made not to be more than $0.75\rho$b in accordance with ACi code 318-89. From the test results, it is found that in case of a concrete strength increased from 240 to 650kg/$\textrm{cm}^2$, the displacement and curvature ductility factore are increased by about 31-231 percents. And also increased in case of increased from 650 to 900kg/$\textrm{cm}^2$, but the increasing ratio is gradually decreasing accoding to a concrete strength increases. And also found that as the Double Re-bar Ratio (($\rho$-$\rho$')/$\rho$b) increases, so the displacement and curvature ductility ratio would decrease, but in case of increased from 650 to /$900kg\textrm{cm}^2$ the decreasing ration is bigger than in case of increased from 240 to $650kg/\textrm{cm}^2$.

• Earthquakes and Structures
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• 제13권4호
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• pp.337-351
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• 2017

In the present study a capacity spectrum method based on constant ductility inelastic spectra to estimate the seismic performance of structures equipped with elastic viscous dampers is presented. As the definition of the structures' effective damping, due to the damping system, is necessary, an alternative method to specify the effective damping ratio ${\xi}eff$ is presented. Moreover, damping reduction factors (B) are introduced to generate high damping elastic demand spectra. Given the elastic spectra for damping ratio ${\xi}eff$, the performance point of the structure can be obtained by relationships that relate the strength demand reduction factor (R) with the ductility demand factor (${\mu}$). As such expressions that link the above quantities, known as R - ${\mu}$ - Τ relationships, for different damping levels are presented. Moreover, corrective factors (Bv) for the pseudo-velocity spectra calculation are reported for different levels of damping and ductility in order to calculate with accuracy the values of the viscous dampers velocities. Finally, to evaluate the results of the proposed method, the whole process is applied to a four-storey reinforced concrete frame structure and to a six-storey steel structure, both equipped with elastic viscous dampers.

• 한국지진공학회논문집
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• 제10권3호
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• pp.57-64
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• 2006

현행 약진지역의 내진설계기준은 주로 강진지역에서의 연구결과에 근거하고 있다. 하지만, 약진지역의 경우 지진하중보다는 중력하중이나 풍하중에 의해 구조설계가 지배되므로 구조물의 초과강도가 강진지역의 경우보다 증가하게 된다. 따라서 약진지역에 적합한 내진설계기준을 마련하기 위해서는 강진지역에 적용되는 반응수정계수를 약진지역에 그대로 적용할 수 있는지에 대한 검증이 필요하다. 본 연구에서는 건축구조물에 대한 소성해석을 통해 그 연성도와 초과강도를 산정하고 이에 근거하여 현행 반응수정계수의 적절성 여부를 검토하였다. 강진, 중진, 약진지역 등에서의 초과강도와 연성요구도를 비교하기 위하여 UBC-97에 근거하여 설계된 예제구조물을 선정하여 해석을 수행하였다. 해석결과에 의하면 약진지역의 초과강도가 강진지역보다 크기 때문에 동일한 반응수정계수에 대한 약진지역의 연성요구도는 강진지역에서보다 적게 된다. 따라서 동일한 반응수정계수를 이용하여 설계된 약진지역 구조물의 경우 접합부에서의 소성회전각 요구량을 강진지역의 경우에 비하여 상대적으로 저감시킬 수 있을 것이다.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 춘계 학술발표회 논문집 Proceedings of EESK Conference-Spring
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• pp.259-266
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• 2000

This study was conducted to investigate the seismic behavior assessment of circular reinforcement concrete bridge piers particularly with regard to assessing the displacement ductility curvature ductility response modification factor(R) and plastic hinge region etc, The experimental variables of bridge piers test consisted of transverse steel details amount and spacing different axial load levels etc. The test results indicated that reinforcement concrete bridge piers with confinement steel by the code specification exhibited suffcient ductile behavior and seismic performance. Also it is found that current seismic design code specification of confinement steel requirements may be revised.

• Structural Engineering and Mechanics
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• 제73권3호
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• pp.239-257
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• 2020

In the present study, an innovative steel bracket and haunch hybrid scheme is devised, for retrofitting of earthquake damaged deficient beam-column sub-assemblages. Formulations are presented for evaluating haunch force factor under combined load case of lateral and gravity loads for the design of double haunch retrofit. The strength hierarchies of control and retrofitted beam-column sub-assemblages are established to showcase the efficacy of the retrofit in reversing the undesirable strength hierarchy. Further, the efficacy of the proposed retrofit scheme is demonstrated through experimental investigations carried out on gravity load designed (GLD), non-ductile and ductile detailed beam-column sub-assemblages which were damaged under reverse cyclic loading. The maximum load carried by repaired and retrofitted GLD specimen in positive and negative cycle is 12% and 28% respectively higher than that of the control GLD specimen. Further, the retrofitted GLD specimen sustained load up to drift ratio of 5.88% compared with 2.94% drift sustained by control GLD specimen. Repaired and retrofitted non-ductile specimen, could attain the displacement ductility of three during positive cycle of loading and showed improved ductility well above the expected displacement ductility of three during negative cycle. The hybrid haunch retrofit restored the load carrying capacity of damaged ductile specimen to the original level of control specimen and improved the ductility closer to the expected displacement ductility of five. The total cumulative energy dissipated by repaired and retrofitted GLD, non-ductile and ductile specimens are respectively 6.5 times, 2.31 times, 1.21 times that of the corresponding undamaged control specimens. Further, the damage indices of the repaired and retrofitted specimens are found to be lower than that of the corresponding control specimens. The novel and innovative steel bracket and haunch hybrid retrofit scheme proposed in the present study demonstrated its effectiveness by attaining the required displacement ductility and load carrying capacity and would be an excellent candidate for post-earthquake retrofit of damaged existing RC structures designed according to different design evolutions.