• Structural Engineering and Mechanics
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• 제43권4호
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• pp.459-473
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• 2012

Post-tensioned concrete voided slab girders are widely used in highway bridge constructions. To obtain greater section hollow rate and reduce the self-weight, the plate thickness of slab girders are designed to be small with the adoption of flat anchorage system. Since large prestress is applied to the anchor end section, it was found that longitudinal shear cracks are easy to occur along the voided slab girder. The reason is the existence of great shearing effect at the junction area between web and bottom (top) plate in the anchor end section. This paper focuses on the longitudinal anti-cracking problem at the anchor end of post-tensioned concrete voided slab girders. Two possible models for longitudinal anticracking analysis are proposed. Differential element analysis method is adopted to derive the solving formula of the critical cracking state, and then the practical analysis method for longitudinal anti-cracking is established. The influence of some factors on the longitudinal anti-cracking ability is studied. Results show that the section dimensions (thickness of bottom, web and top plate) and prestress eccentricity on web plate are the main factors that influence the anti-cracking ability. Moreover, the proposed method is applied into three engineering examples to make longitudinal anti-cracking verification for the girders. According to the verification results, the design improvements for these girders are determined.

• Structural Engineering and Mechanics
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• 제71권2호
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• pp.153-163
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• 2019

Longitudinal fracture behavior of non-linear elastic beam configurations is studied in terms of the strain energy release rate. It is assumed that the beams exhibit continuous material inhomogeneity along the width as well as along the height of the crosssection. The Ramberg-Osgood stress-strain relation is used for describing the non-linear mechanical behavior of the inhomogeneous material. A solution to strain energy release rate is derived that holds for inhomogeneous beams of arbitrary cross-section under combination of axial force and bending moments. Besides, the solution may be applied at any law of continuous distribution of the modulus of elasticity in the beam cross-section. The longitudinal crack may be located arbitrary along the beam height. The solution is used to investigate a longitudinal crack in a beam configuration of rectangular cross-section under four-point bending. The crack is located symmetrically with respect to the beam mid-span. It is assumed that the modulus of elasticity varies continuously according a cosine law in the beam cross-section. The longitudinal fracture behavior of the inhomogeneous beam is studied also by applying the J-integral approach for verification of the non-linear solution to the strain energy release rate derived in the present paper. Effects of material inhomogeneity, crack location along the beam height and non-linear mechanical behavior of the material on the longitudinal fracture behavior are evaluated. Thus, the solution derived in the present paper can be used in engineering design of inhomogeneous non-linear elastic structural members to assess the influence of various material and geometrical parameters on longitudinal fracture.

• 한국도로학회논문집
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• 제17권1호
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• pp.105-118
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• 2015

PURPOSES : This study aims to evaluate the road safety of the super-elevation transition section of a left turn curve and suggest the minimum longitudinal grade of a super-elevation transition section to be used before and after a left curved section. METHODS : We evaluated the road condition by means of the safety-criterion-evaluation method involving side friction factors, and then solve the problem by introducing the minimum longitudinal grade criterion based on conditions described in the hydraulics literature. RESULTS : It was calculated that when a road satisfies hydroplaning conditions, the difference between side friction assumed and side friction demanded is less than -0.04. In this case, the safety criterion for the condition is unsatisfied. Conversely, when a road is in a normal state under either wet or dry conditions, it was calculated that the difference between side friction assumed and side friction demanded is more than 0.01. Thus, the safety criterion for this condition is found to be satisfied. After adjusting the minimum longitudinal grade applied to a super-elevation transition section, the hydroplaning condition can be eliminated and the safety criterion can be met for all sections. CONCLUSIONS : It is suggested that a minimum longitudinal grade should be provided on super-elevation transition sections in order to prevent hydroplaning.

• 한국강구조학회 논문집
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• 제16권5호통권72호
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• pp.653-660
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• 2004

도심지의 토지 이용률을 높이기 위하여 상대적으로 단면이 작은 원형 강교각의 건설이 요구되고 있다. 이때 줄어든 단면으로 인해 감소된 좌굴내하력을 높이는 방안으로 수직보강재의 적용을 고려할 수 있다. 그러나 수직보강재를 적용함으로써 얻어질 수 있는 좌굴내하력의 증가효과는 아직 명확하지 않다. 본 연구에서는 기하학적, 재료학적 비선형을 고려한 탄소성 유한요소해석을 수행하여 원형강교각의 반지름-두께비에 따른 수직보강재의 수가 좌굴내하력에 미치는 영향을 명확히 하였다. 또한, 수직보강재의 폭과 두께, 원형강교각의 세장비에 따른 좌굴해석을 수행하여 그 관계를 명확히 하였다.

• 한국정밀공학회지
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• 제17권6호
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• pp.83-88
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• 2000

In machining large screws such as those of extruders, it takes long time to machine them on conventional machines which usually use single-tipped fixed tools. And it is also difficult to use an existing CAD/CAM coftware when trying to get over the problems of conventional machines and making use of CNC machines. In this paper, generation of machining program using rotational tools for large screws defined by longitudinal-section profile is descrebed. Use of rotational tools in machining plays an important role in saving machining time. In the sort of extruder screws, it is easy to define a screw shape by longitudinal-section profile, and by which improvement of dimensional accuracy can be expected. The CAM software developed in this paper is based on user's and designer's friendliness.

• International Journal of Aeronautical and Space Sciences
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• 제8권1호
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• pp.21-31
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• 2007

Relaxed Static Stability (RSS) concept has been applied to improve aerodynamic performance of modern version supersonic jet fighter aircraft. The T-50 advanced supersonic trainer employs the RSS concept in order to improve the aerodynamic performance. And the flight control system stabilizes the unstable aircraft and provides adequate handling qualities. The T-50 longitudinal control laws employ a proportional-plus-integral type controller based on a dynamic inversion method. The longitudinal dynamic modes consist of short period with high frequency and phugoid mode with low frequency. The design goal of longitudinal control law is optimization of short period damping ratio and frequency using Lower Order Equivalent System (LOES) complying the requirement of MIL-F-8785C. This paper addresses phugoid mode characteristics such as damping ratio and natural frequency that is affected by the nonlinear control laws such as angle of attack limiter, auto pitch attitude command system and autopilot of pitch attitude hold.

• 대한토목학회논문집
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• 제30권6A호
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• pp.503-512
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• 2010

하중-저항계수 설계법에서 조밀단면은 휨모멘트에 의하여 특정단면이 소성모멘트에 도달하기 전에 복부판과 플랜지에 국부좌굴 및 거더의 횡비틈좌굴이 발생하지 않는 단면으로 정의하고 있다. AASHTO LRFD(2007)에서는 수평보강재를 갖지 않는 단면에 관해서만 조밀단면을 만족하는 복부판의 세장비 규정을 제시하고 있다. 복부판에 설치하는 수평보강재의 역할은 휨 좌굴강도를 증가시키는 것이다. 비록 비보강된 복부판이 조밀단면의 기준을 만족하지 못한다고 할지라도, 적당한 수평보강재를 설치한다면 복부판의 좌굴을 방지할 수 있을 것이다. 그러므로 복부판은 소성모멘트에 도달할 수 있을 것이다. 그러나 AASHTO LRFD(2007)에서는 수평보강재를 설치한 복부판이 조밀단면을 만족하지 못하는 이유에 관하여 분명하게 설명하고 있지 않다. 본 연구에서는 수평보강재를 설치한 복부판에서의 휨에 의한 좌굴과 극한강도거동을 선형과 비선형 유한요소법을 통하여 검토하였다. 비록 조밀단면의 세장비를 만족하지 못하는 복부판이라고 할지라도, 충분한 강성과 적절한 위치에 수평보강재로 보강하면 소성모멘트에 도달할 수 있다는 것을 알아냈다. 비선형해석의 분석을 통해 수평보강재를 갖는 복부판의 조밀단면을 만족하는 새로운 세장비 조건식을 제안하였다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1996년도 추계학술대회논문집
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• pp.7-13
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• 1996

The kinematically admissible velocity field is developed for the analysis of extruded products. The curving of product in extrusion is caused by the linearly distributed longitudinal velocity on the cross-section of the workpiece at the die exit. In the analysis, the longitudinal velocity in extrusion direction is divided into the uniform velocity and the deviated velocity. In order to satisfy the requrement of the kinematically admissible velocity field, the average value of the deviated velocity should be zero. At the same time, it should linearly change with the distance form the center of gravity of the cross-section of the workpiece. The results of the analysis show that the curvature of product increses with increses in eccentricity of gravity center of the cross-section of workpiece at die entrance form that of the cross-section at the die exit. In the analysis, the longitudinal velocity in extrusion direction is divided into the uniform velocity and the deviated velocity. In order to satisfy the requrement of the kinematically admissible velocity field, the average value of the deviated velocity should be zero. At the same time, it should linearly change with the distance from the center of gravity of the cross-section of the workpiece. The results of the analysis show that the curvature of product increses with increses in ecentricity of gravity center of the cross-section of workpiece at die entrance from that of the cross-section at the die exit.

• 한국조경학회지
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• 제27권5호
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• pp.138-149
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• 2000

The purpose of this study is to evaluate Suwon stream naturalness Index(S.N.I). and tofind out stats, problems and opportunities of the Suwon stream by assessment standard. Assessment standard is mainly based on physical structure of stream environment. the purpose evaluating sectors and elements are physical form and structure restoration of stream. To find out assessment standard of stream naturalness index, conceptual frame of assessment standard has been established, for which four sections, for example, longitudinal section, lateral section, stream bottom structure and water environment, have been selected. Overall stream naturalness index of the Suwon stream has been distributed at 3rd to 4th grade, and 3.3 of assessment index and mode were 3rd grade respectively. stream naturalness index of each section was as follows: Longitudinal section accounted for 3.7in average to be 4th grade, lateral section did 3.8 to be 4th grade, and water environment did 2.4 to be 2nd grade. Analysis of assessment outcome of stream naturalness index has checked status, problems and opportunities of corresponding stream. Assessment of stream naturalness index of the study provides useful information for restoration of close-to-nature stream, and furthermore has its meaning in checking problems and opportunities of Suwon stream.

• 한국분무공학회지
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• 제27권1호
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• pp.18-25
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• 2022

Hot-firing tests were performed to experimentally confirm the effect of the eigenmode in the fuel-air mixing section on combustion instability by changing mixing section length, inlet mean velocity, equivalence ratio, and swirler geometry. A premixed gas composed of air and ethylene was supplied to the combustion chamber through an mixing section and an axial swirler. As the mixing section length increased, the inlet velocity perturbation decreased, but the combustion instability increased more. It was found that the resonance frequency of the first longitudinal mode in the mixing section shifted to the third longitudinal mode as the length of the mixing section increased. The results implied that the transition of the resonace frquency by changing the length of the mixing section might cause combustion instability.