본 논문에서는 좌굴에 취약한 철도판형교의 전체좌굴 거동특성을 검토하였다. 우선 철도판형교의 전체좌굴에 영향을 미치는 영향인자를 파악하고 좌굴을 유발하는 모멘트를 전체좌굴에 대한 무차원좌굴계수 를 적용하여 이론적으로 산정하였 다. 다음으로는 개단면인 철도판형교의 하부를 브레이싱으로 보강한 단면을 보강단면과 등가인 두께를 가지는 얇은 판으로 치환하여 유사폐합단면을 형성하고 보강 형상별로 국부적인 항복 발생 여부를 검토한 후, 전체좌굴을 유발하는 모멘트를 산정 하고 효율적인 보강상세를 결정하였다. 유한요소 해석을 이용하여 표준열차하중이 재하되었을 때 보강모델별로 철도판형교에 발생하는 횡방향 변위를 비교하여 장대레일의 좌굴에 저항하기 위한 최적의 보강상세를 제안하였다.

이 논문에서는 내구성이 우수한 것으로 알려져 있는 펄트루젼 FRP의 습도 노출 및 동결 융해 영향을 검토하고, 이에 따른 국부좌굴강도 영향을 검토하기 위한 해석적 연구를 수행하였다. FRP는 일반적으로 내구성이 우수하다고 알려져 있기 때문 에, 해양 구조물 등 습윤환경에서 적용하기 위한 다양한 연구가 진행되고 있으며, 특히 구조용 부재로 제작되는 펄트루젼 FRP 부재는 하절기와 동절기의 온도변화에 노출되기 때문에 이에 대한 검토가 필요하다. 펄트루젼 FRP의 습도 노출 및 동결 융해 영향은 기존 연구의 실험 결과를 참고하였으며, 국부좌굴강도는 정밀해법을 통해 영향을 검토하였다. 검토 결과 펄트루젼 FRP 는 습도노출 및 동결융해의 영향으로 인해 최대 약 20%의 인장강도 및 탄성계수 변화를 나타내었으나, 국부좌굴강도는 약 3% 로 그 영향이 상대적으로 작은 것으로 나타났다. 따라서, 온도이력 및 습윤환경에서도 펄트루젼 FRP는 국부좌굴강도의 큰 변화 를 나타내지 않고 높은 내구성을 나타낼 수 있을 것으로 판단된다.

The high-temperature properties of mild steels were studied by comparing the test results of Kwon and the yield strength, tangent modulus predicted by the design provisions of ASCE and Eurocode(EC3). The column strengths for steel members at high temperatures were determined by the elastic and inelastic buckling strengths according to elevated temperatures. The material properties at high temperatures should be used in the strength evaluations of high temperature members. The buckling strengths obtained from the AISC, EC3 and approximate formula proposed by Takagi et al. were compared with ones calculated by the material nonlinear analysis using the EC3 material model. The newly simplified formulas for yield stress, tangent modulus, proportional limit and buckling strength which were proposed through a comparative study of the material properties and buckling strengths. The buckling strengths of proposed formulas were approximately equivalent to ones obtained from the formulas of Takagi et al. within 4% . They were corresponded to the lower bound values among the buckling strengths calculated by the design formulas and inelastic buckling analysis.

Beam bracing is applied to prevent the relative displacement of the top and bottom flanges or to effectively control the twisting of the section, and the lateral stability of the beams are provided by lateral bracing, torsional bracing or a combination of both. Modular steel I-girders are laterally interconnected by torsional bracings that are installed to increase the resistance to lateral torsional buckling. In this paper, numerical parametric study was carried out by varying the crossbeam web height to examine the effects of the web torsional stiffness. Three-dimensional finite-element analysis using the commercial finite element software ABAQUS was obtained for the parametric numerical analyses of a series of feasible two-girder models, and the failure mode, lateral-torsional buckling strength and the moment-displacement behavior of the main girders was determined.

곡률을 갖고 있는 쉘 부재들은 선박 및 육상구조 내에서 캠버와 선수, 선미, 파이프 및 저장용 탱크에 주로 사용되고 있다. 이러한 곡률 쉘 부재들은 기본적으로 원통형 실린더 부재의 일부라고 간주할 수 있다. 일반적으로 곡률의 존재는 압축하중 작용 시 좌굴강 도 및 최종강도를 증가시키는 것으로 알려져 있다. 본 논문에서는 이러한 영향을 확인하기 위하여 탄성대변형 시리즈해석을 수행하였으며, 매개변수의 영향을 분석하였다. 실린더의 최종강도 거동은 초기처짐과 해석모델링 방법에 큰 영향을 받는 것을 확인하였다.

본 연구에서는 쌍동형 카페리에 다수 존재하는 유공판의 좌굴강도 설계 수행 결과 및 개선사항을 논의하고 있다. 카페리와 같이 길이가 50미터 이상이고, 길이/폭의 비가 12보다 큰 중/소형 고속선박은 상대적으로 두께가 얇고 연강을 사용함으로서 좌굴강도가 취약해질 가능성이 농후하다. 특히, 작업자의 접근 및 통로로 활용되는 유공판에서 좌굴강도가 취약해질 가능성이 있다. 안전한 구조설계를 위해서는 유공주위의 면내 하중 재 분포에 의한 좌굴강도 및 최종강도에 대한 명확한 검토가 필요하다. 본 연구에서는 유공판의 좌굴 및 최종강도 특성에 영향을 미치는 매개변수의 영향을 종합적으로 고려하기 위하여 유한요소해석 프로그램인 ANSYS를 활용한 비선형시리즈 해석을 수행하였으며, 주요 변수(종횡비, 유공비, 유공형상)들에 대한 영향을 검토하였다. 이 결과를 바탕으로 하여, 유공판의 좌굴강도를 결정짓는 가장 큰 인자는 유공비였으며, 종횡비와 유공의 형상은 그 영향이 미비하였다.

Recent studies have revealed that plates stiffened by closed-section ribs can be designed to have greater strength. Thus, this study is about the increasing effect on local plate buckling strength of isotropic plates when longitudinally stiffened with closed-section ribs, which is mainly due to the rotational restraint of the closed-section ribs. The effects on buckling strengths of the stiffened plates are examined by numerical analyses. Three-dimensional finite element models were obtained using a general structural analysis program ABAQUS and a series of eigenvalue analyses were conducted. Through this study, the increasing effect on the local buckling strength due to the rotational stiffness is numerically verified. From the parametric studies, there is an obvious tendency that the local buckling strength of the stiffened plate would converge to the buckling strength of plate with fixed boundary condition. The findings of this study would contribute in improving the optimum design of longitudinally stiffened isotropic plates.

All structures can not be perfect due to geometric or material initial imperfections. Initial imperfections are an important factor in determining the buckling mode and are known to be important factors in evaluating the actual buckling strength. The DNV-RP-C202 design standard limits the longitudinal stiffener spacing. However, the criteria for the stiffener spacing presented in DNV-RP-C202 is a guideline derived from the curved panel theory of perfect cross-sectional shape without initial imperfections. In this study, considering geometric initial imperfections, the transition point of stiffener spacing where longitudinal stiffeners affect the buckling strength of reinforced steel wind turbine tower is analyzed using finite element analysis program. The results of finite element analysis compared with theoretical results based on the perfect shape. As a result, a more reasonable stiffener spacing considering the initial imperfections was suggested.

The initial production scale of wind tower is very few. But recently, the production scale of wind tower structure has increased gradually because it maximizes the efficiency in green energy. Many researchers are studying the wind tower, but there is no study about the difference of allowable buckling stress of the wind tower with and without opening. Guideline of codes and standards are very limited when designing a wind tower with an opening. It is also rarely that a study considers the design of the wind tower to be a tubular shell with or without an opening. ABAQUS, a general purpose finite element program, which provides safety evaluation and economical standards for the design and behavior of the wind tower considering the effect of opening was used in the study. Finally, results from this study can serve as reference for structural engineers, manufacturers and further studies of wind turbine when designing a tubular shell wind tower with an opening.

Pultruded fiber reinforced polymeric plastic (PFRP) has many advantages such as high corrosion resistance, high specific stength/stiffness, light weight, etc. Pultrusion is a manufacturing process for producing continuous lengths of reinforced polymeric structural shapes with constant cross-section. The mechanical property of PFRP is usually regarded as an orthotropic material. The pultruded structural shapes are usually composed of thin-walled plate element. Because the composite material has relatively low elastic moduli, the design of pultruded compression members may not be governed by the material strength limit state but by the stability limit state such as the local buckling. Therefore, the stability limit state must be checked to design pultruded thin-walled compression members. In this paper, we present the analytical study results of elastic buckling strength of PFRP orthotropic plates with different fiber volume ratios. The local buckling analysis of pultruded compression members was conducted for various composite materials using the closed-form solution. From the study it was found that if E11/E22 is increased then the plate buckling coefficient, hence the plate buckling strength, is decreased.

In curved I-girder systems, stability is mainly provided by interconnecting cross-frames or diaphragms. These members act as primary load carrying component thus proper design and analysis must be made. This study proposes improvement on the existing cross-frame spacing limit for horizontally curved girder systems utilizing buckling capacities. Eigenvalue analysis was conducted using the finite element program, ABAQUS. Maximum cross-frames spacing (Smax) was computed with varying degree of curvature, flange width-to-depth ratio ( ) and span length-to-depth ratio (L/d). Models were then generated and their buckling modes and critical buckling capacity ratios were obtained. Lastly, a suggestion was developed based on the results of the finite element analysis to provide a better guide on the design of cross-frame spacing limit. The suggested limit was then compared to the existing cross-frame limit to verify the improvement on the cross-frame spacing.

This study analyzes buckling in the lower segment of a tubular steel shell that exhibits the characteristics of a 3MW wind tower with opening and reinforcement. Analytical method using parametric equations based on Eurocode 3 - Design of Steel Structures and numerical method of finite element are used to analyze the critical meridional buckling stress. ABAQUS, a finite element program, is used for the numerical method analysis. Four different cases of tubular steel tower is modeled: without door opening and without reinforcement; with door opening and without reinforcement; without door opening and with reinforcement; and with door opening and with reinforcement. Using the ABAQUS, a linear buckling analysis is done for all cases to recognize five of its buckling mode shapes and its corresponding eigenvalues. Mode shapes from the previous analysis are considered in performing the non-linear analysis using Static Riks. Buckling capacity and its trends in the localized area near the opening is investigated, tabulated and shown in illustrative charts. Moreover, comparison is made between the parametric and finite element analyses.

In this paper we present the result of investigations pertaining to the buckling strength of Zelkova Serrata (Elm-like) tree column with entasis at the Muryangsujeon in Buseoksa-Temple, Korea. Wooden columns with entasis had been used in the construction of ancient architectural buildings in Korea. It was not known why did they design columns with entasis of the buildings. It is just presumed that the reason may be the compensation of optical illusion, aesthetics, and/or structural safety. The question is not answered even today and it may not be possible to answer clearly and easily. In the paper, the buckling analyses are conducted on both of the wooden column with entasis and the prismatic wooden column by the successive approximations technique and the finite element methods, respectively. The results of analyses are compared and discussed.

Fiber reinforced polymeric plastic (FRP) materials have many advantages over conventional structural materials, i.e., high specific strength and stiffness, high corrosion resistance, right weight, etc. Among the various manufacturing methods, pultrusion process is one of the best choices for the mass production of structural plastic members. Since the major reinforcing fibers are placed along the axial direction of the member, this material is usually considered as an orthotropic material. However, pultruded FRP (PFRP) structural members have low modulus of elasticity and are composed of orthotropic thin plate components the members are prone to buckle. Therefore, stability is an important issue in the design of the pultruded FRP structural members. Many researchers have conducted related studies to publish the design method of FRP structures and recently, referred to the previous researches, pre-standard for LRFD of pultruded FRP structures is presented. In this paper, the accuracy and suitability of design equation for the local buckling strength of pultruded FRP I-shape compression members presented by ASCE are estimated. In the estimation, we compared the results obtained by design equation, closed-form solution, and experiments conducted by previous researches.

Pultruded FRP can be regarded as an orthotropic material due to its manufacturing process that pull-out fibers impregnated with polymeric resin, which is suitable to produce structural member with unlimited lengths of reinforced polymer structural shapes with a various shape of cross-section. However, fiber distribution in the cross-section is not uniform because of the characteristics of pultrusion process. Therefore, random fiber distribution causes the difference of the modulus of elasticity throughout the cross-section. In this paper, closed-form local buckling analysis is conducted on the pultruded FRP I-shape compression members. The mechanical properties used to analytical investigations are obtained from the coupon test. The coupon test specimens are taken from the pultruded FRP I-shape member. Moreover, the local buckling tests of pultruded FRP I-shape members are conducted and test results are compared with the analytical results.

This study is aimed to examine the influence of the rotational stiffness of U-shaped ribs on the local buckling behaviors of laminated composite plates. Applying the orthotropic plates with eight layers of the layup [(0°)4]s and [(0°/90°)2]s, 3-dimensional finite element models for the U-rib stiffened plates were setup by using ABAQUS and then a series of eigenvalue analyses were conducted. There is a need to develope a simple design equation to establish the rotational stiffness effect, which could be easily quantified by comparing the theoretical critical stress equation for laminated composite plates with elastic restraints based on the Classical laminated plate theory. Through the parametric numerical studies, it is confirmed that there should clearly exist an increasing effect of local plate buckling strength due to the rotational stiffness by closed-section ribs. An applicable coefficient for practical design should be verified and proposed for future study. This study will contribute to the future study for establishing an increasing coefficient for the design strength and optimum design of U-rib stiffened plates.