• 대한토목학회논문집
• /
• 제34권2호
• /
• pp.403-413
• /
• 2014

스트럿-타이 모델 방법을 이용한 콘크리트 구조부재의 설계 시 가장 중요한 요소 중 하나는 콘크리트 스트럿의 유효강도를 정확하게 결정하는 것이다. 콘크리트 스트럿의 유효강도를 결정하기 위한 많은 연구가 진행되어 왔으며, 여러 종류의 스트럿의 유효강도 값 및 산정식이 제안되었다. 그러나 이들은 2차원 콘크리트 구조부재의 스트럿-타이 모델 설계를 위한 것으로, 그 값을 3차원 콘크리트 구조부재의 설계에 적용하는 것은 적절하지 않다. 이 연구에서는 콘크리트 스트럿이 위치한 곳의 3축 응력 상태, 콘크리트의 3차원 파괴기준, 스트럿 길이의 영향, 스트럿과 압축 주응력 흐름과의 불일치의 영향, 콘크리트 압축강도의 영향, 그리고 철근에 의한 콘크리트 스트럿의 구속의 정도 등을 고려하여 3차원 콘크리트 스트럿의 유효강도를 일관성 있게 결정할 수 있는 방법을 제안하였다. 제안한 방법의 타당성을 검증하기 위해 기존 연구자들에 의해 파괴실험이 수행된 115개의 철근콘크리트 파일캡 시험체의 극한강도를 평가하였으며, 그 결과를 실험결과 및 현행 설계기준에서 제안한 스트럿의 유효강도 값을 이용하여 평가한 결과와 비교분석하였다.

• Structural Engineering and Mechanics
• /
• 제28권4호
• /
• pp.387-410
• /
• 2008

The fatigue damage accumulation rates of horizontally curved thin walled box-girder bridge have been estimated from vehicle-induced dynamic stress history using rain flow cycle counting method in the time domain approach. The curved box-girder bridge has been numerically modeled using computationally efficient thin walled box-beam finite elements, which take into account the important structural actions like torsional warping, distortion and distortional warping in addition to the conventional displacement and rotational degrees of freedom. Vehicle model includes heave-pitch-roll degrees of freedom with longitudinal and transverse input to the wheels. The bridge deck unevenness, which is taken as inputs to the vehicle wheels, has been assumed to be a realization of homogeneous random process specified by a power spectral density (PSD) function. The linear damage accumulation theory has been applied to calculate fatigue life. The fatigue life estimated by cycle counting method in time domain has been compared with those found by estimating the PSD of response in frequency domain. The frequency domain method uses an analytical expression involving spectral moment characteristics of stress process. The effects of some of the important parameters on fatigue life of the curved box bridge have been studied.

• Structural Engineering and Mechanics
• /
• 제19권4호
• /
• pp.361-379
• /
• 2005

Reinforced concrete deep beams have useful applications in tall buildings and foundations. Over the past two decades, numerous design models for deep beams were suggested. However even the latest design manuals still offer little insight into the design of deep beams in particular when complexities exist in the beams like web openings. A method commonly suggested for the design of deep beams with openings is the strut-and-tie model which is primarily used to represent the actual load transfer mechanism in a structural concrete member under ultimate load. In the present study, the development of the strut-and-tie model is transformed to the topology optimization problem of continuum structures. During the optimization process, both the stress and displacement constraints are satisfied and the performance of progressive topologies is evaluated. The influences on the strut-and-tie model in relation to different size, location and number of openings, as well as different loading and support conditions in deep beams are examined in some detail. In all, eleven deep beams with web openings are optimized and compared in nine groups. The optimal strut-and-tie models achieved are also compared with published experimental crack patterns. Numerical results have shown to confirm the experimental observations and to efficiently represent the load transfer mechanism in concrete deep beams with openings under ultimate load.

• 한국보건간호학회지
• /
• 제37권2호
• /
• pp.275-289
• /
• 2023

Purpose: This study developed a structural model for explaining and predicting terminal care performance in long-term care hospital nurses. The model was based on the stress integration model of Ivancevich and Matteson(1980) and the results of previous studies. Method: Data was obtained from August to September 2022 from 267 nurses in 13 long-term care hospitals in G-do. Results: Results of model verification for this study, revealed that factors directly affecting the terminal care performance of long-term care hospital nurses were nursing work environment(β=0.43, p<0.001), death anxiety(β=-0.29, p<0.001), and terminal care stress(β=0.22, p=0.003). However, the attitude toward nursing care of dying(β=0.07, p=0.287) had no effect on the terminal care performance. Conclusion: The results of this study, confirmed the necessity of improving an individual's perceived nursing work environment, continuous education related to terminal care to reduce death anxiety, and an interventional approach for enhancing terminal care performance.

• Interaction and multiscale mechanics
• /
• 제3권3호
• /
• pp.213-234
• /
• 2010

A multiscale method is presented for analysis of thin slab structures in which the microstructures can not be reduced to two-dimensional plane stress models and thus three dimensional treatment of microstructures is necessary. This method is based on the classical asymptotic expansion multiscale approach but with consideration of the special geometric characteristics of the slab structures. This is achieved via a special form of multiscale asymptotic expansion of displacement field. The expanded three dimensional displacement field only exhibits in-plane periodicity and the thickness dimension is in the global scale. Consequently by employing the multiscale asymptotic expansion approach the global macroscopic structural problem and the local microscopic unit cell problem are rationally set up. It is noted that the unit cell is subjected to the in-plane periodic boundary conditions as well as the traction free conditions on the out of plane surfaces of the unit cell. The variational formulation and finite element implementation of the unit cell problem are discussed in details. Thereafter the in-plane material response is systematically characterized via homogenization analysis of the proposed special unit cell problem for different microstructures and the reasoning of the present method is justified. Moreover the present multiscale analysis procedure is illustrated through a plane stress beam example.

• Structural Engineering and Mechanics
• /
• 제63권5호
• /
• pp.585-595
• /
• 2017

This study aimed to presents a simple analytical approach to investigate the thermal buckling behavior of thick functionally graded sandwich by employing both the sinusoidal shear deformation theory and stress function. The material properties of the sandwich plate faces are continuously varied within the plate thickness according to a simple power-law distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic material. The thermal loads are considered as uniform, linear and non-linear temperature rises across the thickness direction. Numerical examples are presented to prove the effect of power law index, loading type and functionally graded layers thickness on the thermal buckling response of thick functionally graded sandwich.

• Structural Engineering and Mechanics
• /
• 제72권2호
• /
• pp.141-153
• /
• 2019

The effect of galleries on the earthquake behavior of dams should be investigated to obtain more realistic results. Therefore, a roller compacted concrete (RCC) dam with and without galleries are examined under ground motion effects. For this purpose, Cine RCC dam constructed in Aydın, Turkey, is selected in applications. The optimal mesh around galleries is investigated to obtain the most realistic results. Two-dimensional finite element models of Cine RCC dam with and without galleries are prepared by using ANSYS software. Empty and full reservoir conditions were taken into account in the time-history analyses. Hydrodynamic effect of the reservoir water was taken into account considering two-dimensional fluid finite elements based on the Lagrangian approach. It is examined that how principle stresses and displacements change by height and during earthquake. The dam-foundation-reservoir interaction was taken into consideration with contact-target element pairs. The displacements and principle stress components obtained from the linear analyses are compared each other for various cases of reservoir water and galleries. According to numerical analyses, the effect of galleries is clear on the response of RCC dam. Besides, hydrodynamic water effect obviously increases the principle stress components and horizontal displacements of the dam.

• Structural Engineering and Mechanics
• /
• 제1권1호
• /
• pp.75-86
• /
• 1993

The punching shear strength of concrete flat plates is one of the topics of intensive research in recent years by various concrete structures researchers. This paper reviews four current methods of analysing the punching shear strength at the corner-and edge-column positions of reinforced concrete flat plates. They include those recommended in the Australian Standard AS3600-1988, the American Concrete Institute ACI318-89 and the British Standard on Concrete Practices (BS8110) as well as the approach developed at the University of Wollongong, Australia. Based on half-scale model test results, a comparative study of these four analysis methods is made with regard to their limitation, accuracy and reliability. It is found that the Wollongong approach in general gives the best performance in predicting the punching shear strength of flat plates with torsion strips and those with spandrel beams. The Australian Standard procedure performs just as satisfactorily for flat plates with torsion strips but tends to be unsafe for those with spandrel beams. Both the ACI and the British methods are applicable only to flat plates with torsion strips; they also tend to give unsafe predictions for the punching shear strength.

• Structural Engineering and Mechanics
• /
• 제57권3호
• /
• pp.543-567
• /
• 2016

This study attempts to address the buckling and free vibration characteristics of an isotropic cylindrical panel subjected to non-uniform temperature rise using numerical approach. Finite element analysis has been used in the present study. The approach involves three parts, in the first part non-uniform temperature field is obtained using heat transfer analysis, in the second part, the stress field is computed under the thermal load using static condition and, the last part, the buckling and pre-stressed modal analysis are carried out to compute critical buckling temperature as well as natural frequencies and associated mode shapes. In the present study, the effect of non-uniform temperature field, heat sink temperatures and in-plane boundary constraints are considered. The relation between buckling temperature under uniform and non-uniform temperature fields has been established. Results revealed that decrease (Case (ii)) type temperature variation field influences the fundamental buckling mode shape significantly. Further, it is observed that natural frequencies under free vibration state, decreases as temperature increases. However, the reduction is significantly higher for the lowest natural frequency. It is also found that, with an increase in temperature, nodal and anti-nodal positions of free vibration mode shapes is shifting towards the location where the intensity of the heat source is high and structural stiffness is low.

• 대한조선학회지
• /
• 제25권4호
• /
• pp.47-57
• /
• 1988

A new discrete method using idealized rigid body-spring model is introduced. This rigid element method is known to be more efficient and accurate than the finite element method in the inelastic range of structural analysis owing to simplified stress-strain and strain-displacement relations This kind of physical concept using idealized rigid model has been already applied among structural engineers to some problems such as rigid-plastic analysis or plastic design considering rigid bodies and plastic hinges. However the most rigorous and systematic research has been recently performed by T. Kawai et al.[1]. In this paper, an attempt is made to analyze the collapse behavior of stiffened plates under lateral loading by some modification and expansion of Kawai's rigid element approach to the collapse of plates without stiffener. Stiffened plates are treated as orthotropic plates which have equivalent bending rigidities. By employing Morley's plate element resubdivision technique, variety is given to mesh-division styles which have greate effect on the accuracy of numerical results. Some examples are shown to verify the validity of applying rigid element method to the ultimate strength analysis of stiffened plates. It is clarified that lateral deflections and detailed collapse patterns up to the ultimate state of stiffened plates can be easily obtained by the present approach.