• Structural Engineering and Mechanics
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• 제27권6호
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• pp.651-670
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• 2007

An experimental study to evaluate a redundancy capacity in simple span two plate-girder bridges, which are generally classified as a non-redundant load path structure, has been performed under the condition that one of the two girders is seriously damaged. The bottom lateral bracing was selected as an experimental parameter and two 1/5-scale bridge specimens with and without bottom lateral bracing have been prepared. The loading tests were first performed on the intact specimens without cracked girder within elastic range. Thereafter, the ultimate loading tests were conducted on the damaged specimens with an induced crack at the center of a girder. The test results showed that the cross beams and concrete deck redistributed partly the applied load to the uncracked girder, but the lateral bracing system played a significant role of the load redistribution when a girder was damaged. The redundancy was evaluated based on the test results and an appropriate redundancy level was evaluated when the lateral bracing was provided in a seriously damaged simple span two-girder steel bridge.

• Steel and Composite Structures
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• 제3권4호
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• pp.261-275
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• 2003

Truss members built-up with double angles back-to-back have monosymmetric cross-section and twisting always accompanies flexion upon the onset of buckling about the axis of symmetry. Approximate formulae for calculating the buckling capacity are presented in this paper for routine design purpose. For a member susceptible only to flexural buckling, its optimal cross-section should consist of slender plate elements so as to get larger radius of gyration. But, occurrence of twisting changes the situation owing to the weakness of thin plates in resisting torsion. Criteria for limiting the leg slenderness are discussed herein. Truss web members in compression are usually considered as hinged at both ends for out-of-plane buckling. In case one (or both) end of member is not supported laterally by bracing member, its adjoining members have to provide an elastic support of adequate stiffness in order not to underdesign the member. The stiffness provided by either compression or tension chords in different cases is analyzed, and the effect of initial crookedness of compression chord is taken into account. Formulae are presented to compute the required stiffness of chord member and to determine the effective length factor for inadequately constrained compressive diagonals.

• Steel and Composite Structures
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• 제32권3호
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• pp.325-336
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• 2019

Concrete placement and temporary formwork of bridge deck overhangs result in unbalanced eccentric loads that cause exterior girders to rotate during construction. These construction loads affect the global and local stability of the girders and produce permanent girder rotation after construction. In addition to construction loads, the skew angle of the bridge also contributes to girder rotation. To prevent rotation (in both skewed and non-skewed bridges), a number of techniques have been suggested to temporarily brace the girders using transverse tie bars connecting the top flanges and embedded in the deck, temporary horizontal and diagonal steel pipes placed between the webs of the exterior and first interior girders, and permanent cross frames. This study includes a rigorous three-dimensional finite element analysis to evaluate the effectiveness of several bracing systems for non-skewed and several skewed bridges. In this paper, skew angles of $0^{\circ}$, $20^{\circ}$, $30^{\circ}$, and $45^{\circ}$ were considered for single- and three-span bridges. The results showed that permanent cross frames worked well for all bridges, whereas temporary measures have limited application depending on the skew angle of the bridge.

• Steel and Composite Structures
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• 제28권4호
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• pp.403-414
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• 2018

In this paper, the lateral-torsional buckling of axially-transversally functionally graded tapered beam is investigated. The structure cross-section is assumed to be symmetric I-section, and it is continuously laterally supported by torsional springs through the length. In addition, the height of cross-section varies linearly throughout the length of structure. The proposed formulation is obtained for the case that the elastic and shear modulus change as a power function along the beam length and section height. This structure carries two concentrated moments at the ends. In this study, the lateral displacement and twisting angle relation of the beam are defined by sinusoidal series. After establishing the eigenvalue equation of unknown constants, the beam critical bending moment is found. To validate the accuracy and correctness of results, several numerical examples are solved.

• Physical Therapy Rehabilitation Science
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• 제11권2호
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• pp.253-258
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• 2022

Objective: This study aimed to determine the effect of internal abdominis pressure(normal, hollowing and bracing) on trunk muscle activity during one leg bridge exercise. Design: Cross-sectional study. Methods: Thirteen healthy adults (9 men and 4 women) were instructed to perform Internal abdominal pressure(IAP) control(Normal, Hollowing, Bracing) during one leg bridge. Electromyography (EMG) data (% Maximum Voluntary Isometric Contraction, MVIC) were recorded three times on both sides of the participant's Internal Oblique(IO), Effector Spinae(ES), and Multifidus(MF) muscles and the average value was analyzed. Results: As a result, Abdominal bracing one leg bridge (BOLB) group and Abdominal hollowing one leg bridge (HOLB) group showed significantly increased muscle activation of bilateral internal oblique, erector spinae and multifidus activation compared to the Normal one leg bridge (NOLB) group (p<0.05). Abdominal hollowing one leg bridge (HOLB) group had a significant difference in bilateral Internal oblique muscle activation in compared to the NOLB group (p<0.05). Conclusions: Bilateral internal oblique, erector spinae, and multifidus muscles activation in healthy adults at one leg bridge exercise showed greater activation at abdominal bracing. Therefore, in this study, IAP control can be used as an indicator of choice to the dysfunction with trunk muscle weakness and corrective exercise subject's situation when the goal is to activate the trunk muscles by performing one leg bridge.

• 대한토목학회논문집
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• 제41권3호
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• pp.201-208
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• 2021

본 논문에서는 하부수평브레이싱 설치에 따른 무도상 철도판형교의 횡방향 및 비틀림거동에 관한 영향을 검토하였다. 우선 하부브레이싱의 부재 배치 형태가 다른 해석모델을 대상으로 하여 열차하중에 의한 횡방향변위를 비교 검토하여 가장 효율적인 하부 브레이싱의 배치에 대하여 검토하였다. 다음으로는 하부브레이싱을 설치한 2주형 철도판형교의 비틀림거동에 대해 검토를 수행하였다. 또한, FEM 해석결과로부터 구한 비틀림상수와 상부와 하부수평브레이싱을 등가두께로 치환하여 폐합단면으로 하는 철도판형교의 비틀림상수를 비교하였고, 교량의 지간길이와 하부브레이싱의 단면적의 영향을 검토하였다. 이와같은 해석결과를 기초로 본 연구에서는 횡좌굴모멘트와 비틀림상수비와의 관계곡선을 제시하였고 비틀림보강이 필요한 철도판형교의 범위를 제안하였다.

• 한국강구조학회 논문집
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• 제19권3호
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• pp.271-280
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• 2007

본 연구에서는 단재하경로 구조로 인식되는 2-거더교에서 한 개 거더의 손상 시 여유도를 평가하기 위한 실험적 연구를 수행하였다. 실험변수는 하부 수평브레이싱으로 하여 하부 수평브레이싱이 설치된 경우와 설치되지 않은 경우의 단경간 1/5 모형 시험체 2개를 제작하였다. 먼저 균열이 없는 정상상태 시험체에 대해서 탄성범위 내에서 재하실험을 수행하였으며, 이후 지간 중앙부의 한 개 거더에 인위적인 손상을 가한 후 종국상태에 이르기까지 재하 실험을 수행하였다. 실험으로부터 정상상태의 교량에서도 수평브레이싱은 하중 재분배 역할을 수행하였으며, 한 개 거더에 심각한 손상이 발생한 경우에는 가로보와 바닥판이 비균열 거더 측으로 하중 재분배 기능을 일부 수행하였으나, 특히 하부 수평브레이싱은 2-거더교의 손상 시 여유도 향상에 매우 중요한 기능을 하는 것으로 나타났다.

• 대한토목학회논문집
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• 제26권4A호
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• pp.611-620
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• 2006

강합성 플레이트 2-거더교는 피로균열에 의해 한 개의 거더에 심각한 손상이 발생되는 경우 교량의 붕괴가 유발되는 단재 하경로 구조로 인식되고 있다. 본 논문에서는 강합성 2-거더교의 거더 손상시 교량의 여유도를 평가하기 위한 해석적 연구를 수행하였다. 여유도 평가는 단경간 및 3경간 연속교를 대상으로 하였으며, 수직브레이싱은 I-단면 가로보로 적용하고 하부 수평브레이싱이 설치되는 경우와 설치되지 않는 경우를 고려하였다. 정상 상태 및 손상 상태의 교량에 대해 하부 수평브레이싱의 유 무에 따른 내하 성능을 재료 및 기하비선형 해석으로 구하고 각 경우의 여유도를 비교 평가하였다. 해석 결과에 따르면 정상 상태의 2-거더 교량은 단순교와 연속교 모두 수평브레이싱이 없어도 여유도가 충분하며, 손상 상태의 교량에서는 수평브레이싱이 여유도 향상에 중요한 역할을 하는 것으로 분석되었다.

• 한국강구조학회 논문집
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• 제18권2호
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• pp.137-146
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• 2006

본 연구에서는 단재하경로 구조로 인식되는 강합성 2-거더교에서 가로보의 제원 및 배치 간격에 따른 여유도 평가를 위한 해석적인 연구를 수행하였다. 이를 위해 수평브레이싱은 생략하고 수직브레이싱은 I-단면 가로보로 적용한 40+50+40m의 2차로 연속교를 대상으로 하였다. 본 교량에 대해 정상 상태 및 한 개 거더에 심각한 균열을 가정한 손상 상태로 구분하고 가로보의 제원과 배치 간격을 변수로 하여 재료 및 기하비선형 해석을 수행하였다. 해석으로부터 구해진 각 경우에 대한 내하력을 토대로 정상 상태 및 손상 상태 교량의 여유도를 평가하였다. 평가 결과, 정상 상태 및 손상 상태 모두 가로보의 제원과 배치 간격에 따른 여유도 차이는 거의 없었다.

• Structural Engineering and Mechanics
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• 제5권4호
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• pp.415-431
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• 1997

Stability equations that evaluate the elastic critical axial load of stepped columns under extreme and intermediate concentrated axial loads in any type of construction with sidesway totally inhibited, partially inhibited and uninhibited are derived in a classical manner. These equations can be utilized in the stability analysis of framed structures (totally braced, partially braced, and unbraced) with stepped columns with rigid, semirigid, and simple connetions. The proposed column classification and the corresponding stability equations overcome the limitations of current methods which are based on a classification of braced and unbraced columns. The proposed stability equations include the effects of: 1) semirigid connections; 2) step variation in the column cross section at the point of application of the intermediate axial load; and 3) lateral and rotational restraints at the intermediate connection and at the column ends. The proposed method consists in determining the eigenvalue of a $2{\times}2$ matrix for a braced column at the two ends and of a $3{\times}3$ matrix for a partially braced or unbraced column. The stability analysis can be carried out directly with the help of a pocket calculator. The proposed method is general and can be extended to multi-stepped columns. Various examples are include to demonstrate the effectiveness of the proposed method and to verify that the calculated results are exact. Definite minimum bracing criteria for single stepped columns is also presented.