• Steel and Composite Structures
• /
• v.49 no.4
• /
• pp.419-430
• /
• 2023

This paper is aimed at investigating the effect of multiple longitudinal stiffeners on the patch loading resistance of slender steel plate girders. Firstly, a numerical study is conducted through geometrically and materially nonlinear analysis with imperfections included (GMNIA), the model is validated with experimental results taken from the literature. The structural responses of girders with multiple longitudinal stiffeners are compared to the one of girders with a single longitudinal stiffener. Thereafter, a patch loading resistance model is developed through machine learning (ML) using symbolic regression (SR). An extensive numerical dataset covering a wide range of bridge girder geometries is employed to fit the resistance model using SR. Finally, the performance of the SR prediction model is evaluated by comparison of the resistances predicted using available formulae from the literature.

• Journal of the Korean Society of Safety
• /
• v.20 no.2 s.70
• /
• pp.38-43
• /
• 2005

Several nuclear power plants reported that they often found the combination cracks, which consist of longitudinal and circumferential cracks in the tubes. For the burst pressure of a tube with a single longitudinal or circumferential crack several experimental equations have been proposed in published literatures. But for the combination crack appropriate fracture criterion has not been proposed yet. In this study the burst pressures of a tube with a longitudinal crack or a T-type combination crack consisting of longitudinal and circumferential cracks were obtained experimentally and analytically. Fracture parameters such as crack opening angle (COA) were investigated by using elastic plastic analysis. Also the burst pressure far a T-type combination crack located near a tubesheet was considered to develop a length-based criterion. Because most of the axial, circumferential or combination cracks initiate in roll transition zone near the tubesheet.

• The Journal of Korean Association of Computer Education
• /
• v.23 no.1
• /
• pp.53-61
• /
• 2020

In the information society, the ability of learners to use computers to conduct self-directed learning is important. Indeed, the higher the computer's ability to use computers, the more the academic achievement needs to be analyzed. The purpose of this study was to identify longitudinal trajectories of student awareness of ICT literacy and frequency of computer use. We also examined the effects of the longitudinal patterns on academic achievement and college major choice. A non-parametric approach, K-means for longitudinal data(KML) algorithm, was conducted using 9-year longitudinal data from Seoul Education Longitudinal Study (2010-2018). Findings indicated that a pattern presenting a higher awareness of ICT literacy and frequency of computer use showed better academic achievements and was likely to prefer to choose engineering-related majors.

• International Journal of Highway Engineering
• /
• v.17 no.1
• /
• pp.105-118
• /
• 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.

• 제어로봇시스템학회:학술대회논문집
• /
• 1996.10b
• /
• pp.1300-1303
• /
• 1996

In this paper a typical problem is examined that a light, general aviation airplane, such as Cessna or Navion, in gliding turn flight shows helical-dive phenomenon when pilots try to stop the descent by using elevator only. It is known from pilot's experience that in a certain flight trim it is impossible to recover from helical-dive by using elevator only. From this study it is shown that helical-dive phenomenon is involved with longitudinal/lateral dynamics coupling to airplane's aerodynamics. Also this phenomenon consists of three parts of flight dynamics; first of all, fast longitudinal motion occurs, then is followed by a little slow lateral motion, and finally logitudinal/lateral coupled motion is fully developed.

• Korean Journal of Childcare and Education
• /
• v.15 no.5
• /
• pp.23-45
• /
• 2019

Objective: The purpose of this study is to identify the longitudinal reciprocal relationship between young children's vocabulary ability and physical aggression in young children. Methods: Two waves of panel data(2013/2015) from the Panel Study of Korean Children were analyzed in this study by using an adapted version of Autoregressive cross-lagged modeling. A total of 306 five-year-old and seven-year-old preschoolers, and their mothers participated in the study. Autoregressive cross-lagged modeling for multiple groups was conducted by using AMOS 24.0. Results: First, vocabulary ability and physical aggression showed stability over time. Second, young children's vocabulary ability(t) had a statistically significant effect on physical aggression(t+1). Conclusion/Implications: This study confirmed the interrelationships of young children's vocabulary ability and physical aggression by examining longitudinal data using the longitudinal analysis method. This study highlights the importance of developing interventions to support language development with aggressive children. The results of the present study can be used as a source in developing policies for aggressive children and their parents.

• Journal of Korean Academy of Nursing
• /
• v.35 no.2
• /
• pp.382-389
• /
• 2005

Purpose: This longitudinal study was done to investigate critical thinking dispositions and critical thinking skills of nursing students enrolled in a 4-year baccalaureate program at a university in Korea. Method: The study used a longitudinal design. A convenience sample of 32 nursing students who were completing their 1st, 2nd, 3rd, and 4th year in a baccalaureate program at a selected university was included. The subjects completed the California Critical Thinking Dispositions Inventory (CCTDI), the California Critical Thinking Skill Test (CCTST), and a demographic questionnaire. Data was analyzed by descriptive statistics, repeated ANOVA, adjusted p-values, and Pearson's correlation coefficient with SAS 8.12. Results: There was statistically significant improvement according to academic year in the CCTDI total mean score (F=7.54, p= .0001) and subscales of Open-mindedness, Self-confidence, and Maturity. Contrarily, no statistically significant difference was found in the CCTST total mean score and subscales' score except Analysis. Conclusion: There is no significant correlation between critical thinking dispositions and skills, so it will be necessary to repeat a study like this, and the translated instruments should be modified by considering Korean culture.

• Computers and Concrete
• /
• v.24 no.4
• /
• pp.313-327
• /
• 2019

The purpose of the present study is to present a new approach to designing and selecting the details of multidimensional continuous RC beam by applying all strength, serviceability, ductility and other constraints based on ACI318-14 using Teaching Learning Based Optimization (TLBO) algorithm. The optimum reinforcement detailing of longitudinal bars is done in two steps. in the first stage, only the dimensions of the beam in each span are considered as the variables of the optimization algorithm. in the second stage, the optimal design of the longitudinal bars of the beam is made according to the first step inputs. In the optimum shear reinforcement, using gradient-based methods, the most optimal possible mode is selected based on the existing assumptions. The objective function in this study is a cost function that includes the cost of concrete, formwork and reinforcing steel bars. The steel used in the objective function is the sum of longitudinal and shear bars. The use of a catalog list consisting of all existing patterns of longitudinal bars based on the minimum rules of the regulation in the second stage, leads to a sharp reduction in the volume of calculations and the achievement of the best solution. Three example with varying degrees of complexity, have been selected in order to investigate the optimal design of the longitudinal and shear reinforcement of continuous beam.

• Steel and Composite Structures
• /
• v.23 no.3
• /
• pp.351-362
• /
• 2017

This paper presents an experimental study on the behavior of composite floor slab comprised by a new steel sheet and concrete slab. The strength of composite slabs depends mainly on the strength of the connection between the steel sheet and concrete, which is denoted by longitudinal shear strength. The composite slabs have three main failures modes, failure by bending, vertical shear failure and longitudinal shear failure. These modes are based on the load versus deflection curves that are obtained in bending tests. The longitudinal shear failure is brittle due to the mechanical connection was not capable of transferring the shear force until the failure by bending occurs. The vertical shear failure is observed in slabs with short span, large heights and high concentrated loads subjected near the supports. In order to analyze the behavior of the composite slab with a new steel sheet, six bending tests were undertaken aiming to provide information on their longitudinal shear strength, and to assess the failure mechanisms of the proposed connections. Two groups of slabs were tested, one with 3000 mm in length and other with 1500 mm in length. The tested composite slabs showed satisfactory composite behavior and longitudinal shear resistance, as good as well, the analysis confirmed that the developed sheet is suitable for use in composite structures without damage to the global behavior.

• Bulletin of the Korean Space Science Society
• /
• 2004.10b
• /
• pp.325-327
• /
• 2004

The longitudinal instability (POGO) of the rocket should not be occurred during the whole flight time for the large class liquid propulsion system to complete a mission successfully. The longitudinal instability is caused by the resonance between the propulsion system and rocket structure in the low frequency range below 50Hz, ordinarily. Analysis on the low frequency dynamic characteristics on the liquid propulsion system with staged combustion cycle engine system was performed as a preliminary study on the longitudinal instability analysis.