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Behavior of circular CFT columns subject to axial force and bending moment
곽지현,곽효경,김진국 국제구조공학회 2013 Steel and Composite Structures, An International J Vol.14 No.2
The major objective of this paper is to evaluate the behavior and ultimate resisting capacity of circular CFT columns. To consider the confinement effect, proper material models with respect to the confinement pressure are selected. A fiber section approach is adopted to simulate the nonlinear stress distribution along the section depth. Material nonlinearity due to the cracking of concrete and the yielding of the surrounding steel tube, as well as geometric nonlinearity due to the P-Δ effect, are taken into account. The validity of the proposed numerical analysis model is established by comparing the analytical predictions with the results from previous experimental studies about pure bending and eccentric axial loading. Numerical predictions using an unconfined material model were also compared to investigate the confinement effects on various loading combinations. The ultimate resisting capacities predicted by the proposed numerical model and the design guidelines in Eurocode 4 are compared to evaluate the existing design recommendation.
스프링클러 신축배관의 굽힘횟수 및 굽힘각도가 마찰압력손실에 미치는 영향
곽지현,박정화 한국위험물학회 2019 한국위험물학회지 Vol.7 No.2
A sprinkler system is the most frequently used among fire extinguishing systems and sprinklers are usually installed irregularly on the ceiling according to the structure and condition of protected area. Consequently, flexible hoses are used for the connection between horizontal pipes and sprinklers because they are easily bended. As common flexible hoses have a structure of spiral wrinkles, so they have big friction loss in contrast to straight pipes. In particular, discharge pressure is able to decrease under the minimum working pressure(0.1MPa) if the whole pipe length becomes too long, which affects fire control performance because of the flow rate deficiency in a cabinet type simplified sprinkler system. In this study, the friction loss characteristics of 5 common sprinkler flexible hoses was experimently considered in accordance with the type approval standard. That is, it was quantitatively examined according to the bending time and angle and how the bending condition affects the friction loss was investigated. In the experiment, the friction loss increased in accordance with the bending time and its difference between bending time also increased with the flow rate. The friction loss in case of 4 times bending in contrast to 1 time bending increased for 17%∽36% according to each hose at the flow rate of 50L/min. Furthermore, the increase of the bending angle from 30 degree to 90 degree resulted in the increase of friction loss for 16%∽22% in the condition of 2 times bending which is the most frequent case. As things turned out, the bending time and angle of sprinkler flexible hoses need to be minimized to decrease their friction loss.