형상기억합금의 휨거동 및 교량변위제어장치적용 연구

최은수,박주남,김학수,이도형 한국지진공학회 2007 한국지진공학회논문집 Vol.11 No.5

본 논문은 형상기억합금 바의 휨 거동 특성 파악하기 위하여 여러 가지의 휨 거동 실험을 수행하였으며, 형상기억합금 바의 휨 거동분석을 통하여 지진 시에 적용 가능성을 규명하는데 목적이 있다. 이를 위해 단순 휨 및 이중 휨 실험을 재하속도 및 최대변위를 변수로 수행하였다. 힘-변위 곡선에서 추정한 재하 및 제하 시의 강성이 추정되었으며, 등가의 감쇠비도 각 실험결과에서 추정되었다. 단순 휨에서 형상기억합금 바는 32 mm 변위 이후에 강성증가현상을 나타냈으며, 이것은 SIM(Stress-Induced-Martensite) 현상에 의해서 발생하는 것으로 추정된다. 재하속도의 증가는 형상기억합금 휨 강성 증가에 영향을 주지 않는 것으로 나타났다. 이중 휨 거동에서 형상기억합금 바는 단순 휨에 비해 강성이 약 5배정도 크게 나타났으며, 감쇠비는 유사하게 나타났다. 휨 거동의 형상기억합금 바를 지진 변위 제어장치로 사용하여 3경간 단순지지 교량에 적용하여 지진해석을 수행하였다. 이러한 지진변위 제어장치는 매우 효과적인 것으로 나타났으며, 실용적인 것으로 판단된다. 본 논문의 의미는 형상기억합금 바의 휨 거동에 대한 기초 지식을 제공하는데 있다. The goal of this study is to perform several bending tests on a shape memory alloy bar and to analyze the characteristics of the bending behavior. The other goal is to verify the seismic performance of an SMA bar bending application. Single and double bending tests were conducted with varying loading speeds and maximum displacement. The loading and the unloading stiffness were estimated from the force-displacement curves and the equivalent damping ratio of each test was also assessed. In single bending, the SMA bar showed the stiffness hardening after the displacement of 32 mm. It is assumed that this phenomenon is due to the stress-induced-martensite hardening. The increasing loading speed did not influence on the stiffness of the single bending SMA bar. The stiffness of the double bending bar is about 5 times of that of the single bending. This study introduced a seismic application of SMA bending bars as seismic restrainers for bridges and showed its practicality. SMA bars in bending are used for seismic restrainers in a three-span-simply-supported bridge. They showed the effectiveness to reduce the responses of the bridge and the applicability for a seismic restrainer. The significance of this study is to provide basic knowledge of SMA bending and its seismic applications.

Seismic behavior of steel truss reinforced concrete L-shaped columns under combined loading

Fan Ning,Zongping Chen,Ji Zhou,Dingyi Xu 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.43 No.2

Steel-reinforced concrete (SRC) L-shaped column is the vertical load-bearing member with high spatial adaptability. The seismic behavior of SRC L-shaped column is complex because of their irregular cross sections. In this study, the hysteretic performance of six steel truss reinforced concrete L-shaped columns specimens under the combined loading of compression, bending, shear, and torsion was tested. There were two parameters, i.e., the moment ratio of torsion to bending (γ) and the aspect ratio (column length-to-depth ratio (φ)). The failure process, torsion-displacement hysteresis curves, and bending-displacement hysteresis curves of specimens were obtained, and the failure patterns, hysteresis curves, rigidity degradation, ductility, and energy dissipation were analyzed. The experimental research indicates that the failure mode of the specimen changes from bending failure to bending-shear failure and finally bendingtorsion failure with the increase of γ. The torsion-displacement hysteresis curves were pinched in the middle, formed a slip platform, and the phenomenon of “load drop” occurred after the peak load. The bending-displacement hysteresis curves were plump, which shows that the bending capacity of the specimen is better than torsion capacity. The results show that the steel truss reinforced concrete L-shaped columns have good collapse resistance, and the ultimate interstory drift ratio more than that of the Chinese Code of Seismic Design of Building (GB50011-2014), which is sufficient. The average value of displacement ductility coefficient is larger than rotation angle ductility coefficient, indicating that the specimen has a better bending deformation resistance. The specimen that has a more regular section with a small φ has better potential to bear bending moment and torsion evenly and consume more energy under a combined action.

공무원의 재량과 규정변용(rule bending)의 관계에 대한 연구: 행정통제의 조절효과를 중심으로

권은주,김순은 서울행정학회 2018 한국사회와 행정연구 Vol.28 No.4

Although there have been many studies on the discretion and the exercise of discretion of public employees, Few empirical studies have tested the relationship between discretion and exercise of discretion or moderating effects on the relationship. This study aimed to examine the hypothesis that more discretion a public employee has, the more exercise of discretion(rule bending) occurs and investigated moderating effects of administrative control affecting the relationship. For this purpose, we performed hierarchical regression analysis on survey data from 2,885 local public employees nationwide. The result support the hypothesis that public employees with the high degree of discretion are likely to bend the rules. In addition, when public employees are highly alienated from decision-making, they are more likely to bend the rules. This implies that decentralization of decision-making rather be more effective control than centralization. Also, it is particularly interesting that the relationship between discretion and rule bending would be stronger for individuals under high formalization. Although it is known that high formalization means low discretionary behaviors, considering moderating effects, this relationship is only valid when one’s discretion is low. These findings lend greater support to the need of multidimensional research design for studies of discretion. 공무원의 재량과 재량행사에 대한 많은 연구가 축적되어 왔음에도 두 개념을 구분하여 그 관계를 살펴본 연구나 관계에 영향을 미치는 요인을 살펴보려는 실증 연구는 여전히 부족하다. 본 연구는 공무원의 재량이 클수록 더 많은 규정변용이 일어난다는 가설을 검증하고 해당 관계에 대한 통제의 조절효과를 살펴보고자 하였다. 이를 위해 전국의 2,885명의 지방공무원을 대상으로 한 ‘2014년 지방공무원 인식조사’ 자료를 대상으로 위계적 회귀분석을 실시하였다. 회귀분석 결과 공무원의 재량은 규정변용 행태에 정(+)의 영향을 미쳐 가설이 타당함을 밝혔다. 또한 공무원에 대한 통제방식 중 조직 의사결정과정에서 소외되는 정도가 크거나 규정과 절차에 대한 강제가 클 때, 공무원의 재량이 규정변용으로 이어지는 정(+)의 영향이 강화되는 조절효과를 확인하였다. 이를 통해 통념과는 달리 조직 의사결정의 집권화보다 분권화가 오히려 효과적인 통제방안이 될 수 있다는 정책적 시사점을 제공하였다. 또한 공식화를 강화하는 것은 규정변용 행위를 억제하는 효과적인 수단으로 알려져 왔으나, 이는 공무원의 재량이 낮은 경우에만 적용된다는 조건부(contingent) 관계를 발견하였다는 의의가 있다. 본 논문의 결과는 후속 연구에서 재량과 관련한 다차원적 모형을 설계해야 할 필요성을 시사한다.

수치해석을 이용한 말뚝이 결합된 블록식방파제의 수평저항력에 관한 연구

이원효,권순구,김태형 한국해안,해양공학회 2022 한국해안해양공학회 논문집 Vol.34 No.4

Three-dimensional FEM numerical analysis was performed to understand the behaviors of blocks and piles according to the horizontal load for the block breakwater combined with piles. The Modified Mohr-Coulomb model, the improved version of the Mohr-Coulomb model, was applied for the ground modeling. The cases when the pile is embedded only into the block, embedded to the riprap layer (H = 4.29 cm), and embedded to the ground down to 2H, 3H, and 4H were examined. The results of the laboratory model experiment and the numerical analysis showed similar horizontal resistance force-displacement behaviors. The pile showed rotational behavior up to the embedment depth of 1H~2H and bending behavior in the case of 3H~4H depth embedment. When the embedment depth of the pile is 3H or more, the pile shows a bending behavior, so it can be considered that the pile contributes significantly to the horizontal resistance of the block breakwater. The results of this study will be used for various numerical analyses for real-size structure design. 본 연구는 말뚝이 결합된 블록식방파제에 대하여 수평하중 재하에 따른 블록과 말뚝의 거동을 파악하기 위하여 FEM 3차원 수치해석을 실시하였다. 지반구성모델은 Mohr-Coulomb 모델을 향상시킨 Modified Mohr Coulomb 모델을 적용하였다. 말뚝이 블록에만 관입된 경우, 사석층(H = 4.29 cm)까지 근입된 경우, 원지반속에 근입된 2H, 3H, 4H의 경우에 검토하였다. 실내모형실험 결과와 수치해석를 비교한 결과, 수평저항력-변위가 서로 유사한 거동을보이는 것으로 나타났다. 말뚝의 근입깊이가 1 H~ 2H까지는 말뚝이 회전거동을 보이고, 3H~4H의 경우에는 휨거동양상을 보이는 것으로 해석되었다. 말뚝의 근입깊이가 3H 이상인 경우에는 말뚝이 휨거동을 보이므로 말뚝이 블록식방파제의 수평저항력에 크게 기여한다고 볼 수 있다. 본 연구 결과는 실제 크기 구조물 설계를 위한 다양한 수치해석 시 자료로 활용이 있을 것이다.

Ferroelectric and Antiferroelectric Behavior in Chiral Bent-shaped Molecules with an Asymmetric Central Naphthalene Core

Seng Kue Lee*,Masatoshi Tokita,Yoshio Shimbo,Kyung-Tae Kang,Hideo Takezoe,Junji Watanabe 대한화학회 2007 Bulletin of the Korean Chemical Society Vol.28 No.12

A new series of chiral bent-shaped liquid crystals with an asymmetric central core based on 1,6-dihydroxynaphthalene and chiral terminal chain prepared from (S)-(-)-2-methyl-1-butanol, 1,6-naphthalene bis[4-(4-alkoxyphenyliminomethyl)]benzoates [N(1,6)-n-O-PIMB(n-2)*-(n-4)O (n = 8-11)] were synthesized. Their mesomorphic properties and phase structures were investigated by means of electro-optical, polarization reversal current, and second harmonic generation measurements in order to confirm the relationship between the molecular structure and phase structure. All odd n (n = 9 and 11) compounds, N(1,6)-9-O-PIMB7*-5O and N(1,6)-11-O-PIMB9*-7O exhibit antiferroelectric phase, whereas even n (n = 8 and 10) compounds was flexible, N(1,6)-10-O-PIMB8*-6O exhibits the ferroelectric phase but N(1,6)-8-O-PIMB6*-4O exhibits the antiferroelectric phase. These results come from the decrease of the closed packing efficiency within a layer and the lack of uniform interlayer interaction between adjacent layers, which were caused by the asymmetrical naphthalene central core. Thus, we concluded that the structure of central core as well as the terminal chain plays an important role for the emergence of particular polar ordering in phase structures.

Properties controlling the bend-assisted fracture of AHSS

Lee, J.,Kim, J.H.,Lee, M.G.,Barlat, F.,Zhou, C.,Chen, Z.,Wagoner, R.H. Pergamon Press ; Elsevier Science Ltd 2015 International journal of plasticity Vol.75 No.-

Bend-assisted fracture, also commonly called shear fracture, is the splitting of metal sheets during forming in tight-bending regions. It has been shown to be predominantly a result of plastic localization for most advanced high strength steels (AHSS). Such fractures are poorly predicted by typical industrial methods involving finite element modeling (FEM) and forming limit diagrams (FLDs). In order to understand the source of the problem, the sensitivity of simulated shear-fracture formability to material and process parameters was determined using FEM in conjunction with a realistic range of constitutive models, element sizes, and friction coefficients. Two types of shear fracture process were simulated. (1) Draw-bend fracture (DBF) tests are laboratory analogs of industrial forming conditions producing shear fracture; they offer the opportunity of experimental validation but introduce complexity because of varying strain state and unavoidable transitions between shear fracture and tensile fracture. (2) Plane-strain (PS) draw-bend fracture simulations correspond more closely to industrial forming conditions; they simplify the modeling (fixed strain state, no transitions) but no corresponding full-scale laboratory experiments currently exist. The DBF test was found to be sensitive to every material and process parameter tested, with the largest factors being the form of 1-D hardening law and the yield function. Varying these quantities in ranges representing what practical measurements would produce showed variations in predicted formability of up to 80%. The PS simulations, which represent industrial practice more closely, showed large variations in predicted formability only for two variables: 1-D hardening law and friction coefficient. All other parameters were insignificant, except for thermo-mechanical effects, which were important for high-rate tests only. These results show why it is difficult or impossible to predict shear fracture using standard industrial techniques designed for traditional steels. They suggest ways to modify such techniques to accommodate advanced high strength steels. The results also give guidance to alloy designers in terms of which constitutive parameters are most important in inhibiting shear fracture, and which are relatively insignificant.

Mechanical behavior and buckling failure of sharp-notched circular tubes under cyclic bending

Kuo-Long Lee 국제구조공학회 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.34 No.3

In this paper, an experimental investigation of the mechanical behavior and buckling failure of sharp-notched circular tubes subjected to cyclic bending is discussed. The unnotched and sharp-notched circular tubes of SUS 304 stainless steel were tested under symmetric curvature-controlled cyclic bending. It was found from moment-curvature curves that the loops show cyclic hardening and gradually steady after a few cycles for all tested tubes. The ovalization-curvature curves show an unsymmetric, ratcheting and increasing manner with the number of cycles. In addition, it was found that six almost parallel lines corresponding to unnotched and five different notch-depth (0.2, 0.4, 0.6, 0.8 and 1.0 mm) tubes were noted from the experimental relationship between the cyclic controlled curvature and the number of cycles necessary to produce buckling on a log-log scale. An empirical formulation was proposed so that it could be used for simulating the aforementioned relationship. By comparing with the experimental finding, the simulation was in good agreement with the experimental data.

Mechanical behavior and buckling failure of sharp-notched circular tubes under cyclic bending

Lee, Kuo-Long Techno-Press 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.34 No.3

In this paper, an experimental investigation of the mechanical behavior and buckling failure of sharp-notched circular tubes subjected to cyclic bending is discussed. The unnotched and sharp-notched circular tubes of SUS 304 stainless steel were tested under symmetric curvature-controlled cyclic bending. It was found from moment-curvature curves that the loops show cyclic hardening and gradually steady after a few cycles for all tested tubes. The ovalization-curvature curves show an unsymmetric, ratcheting and increasing manner with the number of cycles. In addition, it was found that six almost parallel lines corresponding to unnotched and five different notch-depth (0.2, 0.4, 0.6, 0.8 and 1.0 mm) tubes were noted from the experimental relationship between the cyclic controlled curvature and the number of cycles necessary to produce buckling on a log-log scale. An empirical formulation was proposed so that it could be used for simulating the aforementioned relationship. By comparing with the experimental finding, the simulation was in good agreement with the experimental data.

소성거동이 고려된 원주방향 균열 열림에 미치는 압력유기굽힘의 구속효과 평가 모델

김진원(Jin Weon Kim) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11

This paper presents the evaluation model for restraint effect of pressure induced bending (PIB) on the circumferential through-wall crack opening displacement(COD), which is governed by plastic crack opening behavior. This study performed 3-D elastic-plastic finite element (FE) analyses under various crack angles, restraint conditions, pipe geometries, stress levels, and materials, and investigated the influence of each parameter on the restraint effect. Based on the investigations and additional elastic-perfectly plastic FE analysis results, a closed form model that can evaluate the restraint effect on the plastic crack opening of circumferential through-wall crack, was proposed as function of crack angle, restraint length, radius to thickness ratio, applied axial stress corresponding to an internal pressure, and normalized COD evaluated under linear-elastic crack opening condition.

Tension Chord Model and Flexural Stiff ness for Circular CFST in Bending

Carlos Zanuy 한국강구조학회 2019 International Journal of Steel Structures Vol.19 No.1

The fl exural behavior of circular concrete-fi lled steel tubes (CFST) is addressed in the present paper, with the aim of understanding the contribution of the concrete infi ll and the steel tube to the fl exural stiff ness under in-service loads. The provisions given by current codes of practice are oversimplifi ed and they result in a very diff erent contribution of the concrete infi ll from one code to another. In the present paper, a mechanical approach is proposed by taking into account the stress transfer mechanism from the steel to the concrete through bond stresses. The paper fi rstly addresses the response of the cracked section in pure bending. Secondly, a tension chord model for CFST is proposed, so that the contribution of concrete in tension between cracks (tension stiff ening) can be evaluated. The model capabilities are compared with experimental results from the scientifi c literature and with own experimental results of the author, showing that the proposed approach can predict the fl exural stiff ness of CFST very satisfactorily. For the fi rst time, a model with sound mechanical background is introduced to calculate the bending stiff ness of CFST.