• Structural Engineering and Mechanics
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• 제19권4호
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• pp.401-411
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• 2005

The influence of cracks on the elastic deflection and ultimate bearing capacity of eccentric thin-walled columns with both ends pinned was studied in this paper. First, a method was developed and applied to determine the elastic deflection of the eccentric thin-walled columns containing some model-I cracks. A trigonometric series solution of the elastic deflection equation was obtained by the Rayleigh-Ritz energy method. Compared with the solution presented in Okamura (1981), this solution meets the needs of compatibility of deformation and is useful for thin-walled columns. Second, a two-criteria approach to determine the stability factor ${\varphi}$ has been suggested and its analytical formula has been derived. Finally, as an example, box columns with a center through-wall crack were analyzed and calculated. The effects of cracks on both the maximum deflection and the stability coefficient ${\varphi}$ for various crack lengths or eccentricities were illustrated and discussed. The analytical and numerical results of tests on the columns show that the deflection increment caused by the cracks increases with increased crack length or eccentricity, and the critical transition crack length from yielding failure to fracture failure ${\xi}_c$ is found to decrease with an increase of the slenderness ratio or eccentricity.

• Advances in biomechanics and applications
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• 제1권1호
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• pp.1-14
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• 2014

In this paper, a simple and accurate finite element model coupled to quasi-brittle damage law able to describe the multiple cracks initiation and their progressive propagation is developed in order to predict the complete force-displacement curve and the fracture pattern of human proximal femur under quasi-static load. The motivation of this work was to propose a simple and practical FE model with a good compromise between complexity and accuracy of the simulation considering a limited number of model parameters that can predict proximal femur fracture more accurately and physically than the fracture criteria based models. Different damage laws for cortical and trabecular bone are proposed based on experimental results to describe the inelastic damage accumulation under the excessive load. When the damage parameter reaches its critical value inside an element of the mesh, its stiffness matrix is set to zero leading to the redistribution of the stress state in the vicinity of the fractured zone (crack initiation). Once a crack is initiated, the propagation direction is simulated by the propagation of the broken elements of the mesh. To illustrate the potential of the proposed approach, the left femur of a male (age 61) previously investigated by Keyak and Falkinstein, 2003 (Model B: male, age 61) was simulated till complete fracture under one-legged stance quasi-static load. The proposed finite element model leads to more realistic and precise results concerning the shape of the force-displacement curve (yielding and fracturing) and the profile of the fractured edge.

• Wind and Structures
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• 제37권1호
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• pp.57-78
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• 2023

In this study, a generalized three-degree-of-freedom (3-DoF) analytical model is formulated to predict linear aerodynamic instabilities of a prism under quasi-steady (QS) conditions. The prism is assumed to possess a generic cross-section exposed to turbulent wind flow. The 3-DoFs encompass two orthogonal horizontal directions and rotation about the prism body axis. Inertial coupling is considered to account for the non-coincidence of the mass center and the rotation center. The aerodynamic force coefficients-drag, lift, and moment-depend on the Reynolds number based on relative flow velocity, angle of attack, and the angle between the wind and the cable. Aerodynamic forces are linearized with respect to the static equilibrium configuration and mean wind velocity. Routh-Hurwitz and Liénard and Chipart criteria are used in the eigenvalue problem, yielding an analytical solution for instabilities in galloping and static divergence types. Additionally, the minimum structural damping and stiffness required to prevent these instabilities are numerically determined. The proposed 3-DoF instability model is subsequently applied to a conductor with ice accretion and a full-scale dry inclined cable. In comparison to existing models, the developed model demonstrates superior prediction accuracy for unstable regions compared with results in wind tunnel tests.

• 국제학술발표논문집
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• The 5th International Conference on Construction Engineering and Project Management
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• pp.592-595
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• 2013

Advent of Wireless Sensor Networks (WSN) has provided potentials to a variety of construction applications. It is well appreciated that WSNs have advantages over traditional wired system, such as ease of installation and maintenance with increased cost savings and efficiencies. However, the obstruction of wireless signal from physical objects in the heterogeneous construction environment often brings challenges to WSN measurement system. This paper analyzed the obstruction characteristic of construction environment where construction materials, equipment, and built structures obstruct the wireless signal yielding negative effect of measurement system. By adopting evaluation criteria, such as packet reception rate, field experiments have been implemented to quantitatively identify the interference of wireless signal from penetration, reflection, and network traffic under the construction environment. The results show that reliable performance of wireless sensor in construction environment depends on the optimal separation distance between a receiver and a transmitter, obstruction types, obstruction thickness, and transmission interval. In addition, the methodology and experimental results of this paper could be used in the practical design of network topology when hundreds of sensor nodes form a mesh network in the large scale construction applications.

• 대한조선학회논문집
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• 제54권6호
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• pp.476-484
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• 2017

The purpose of this paper is to verify the structural integrity of a region with numerous penetration-holes in offshore structures such as semi-submersible rig and FPSO. In order to effectively check the yielding and buckling strength of plate members with penetration-holes, a screening analysis program was developed with the FE analysis tool to generate fine meshed model using the theoretical and analysis methods. When a hole is appeared in the plate structure members, the flow of stress is altered such that concentrations of stress form near the hole. Stress concentrations are of concern during both preliminary and detail design and need to be addressed from the perspectives of strength. To configure the geometrical shape, very fine meshed FE analysis is needed as the most accurate method. However, this method is practically impossible to apply for the strength verifications for all perforated plates. In this paper, screening analysis method was introduced to reduce analysis tasks prior to detailed FE analysis. This method is applied to not only the peak stress calculation combined stress concentration factor with nominal stress but also nominal equivalent stress calculation considering cutout effects. The areas investigated by very fine meshed analysis were to be chosen through screening analysis without any reinforcements for penetration-holes. If screening analysis results did not satisfy the acceptance criteria, direct FE analysis method as the 2nd step approach were applied with one of the coarse meshed model considering hole or with the very fine meshed model considering the hole shape and size. In order to effectively perform the local fine meshed analysis, automatic model generating program was developed based on the MSC/PATRAN which is pre-post FE analysis program. Buckling strength was also evaluated by Common Structure Rule (CSR) adopted by IACS as the stress obtained from very fine meshed FE analysis. Due to development of the screening analysis program and automatic FE modeling program, it was able to reduce the design periods and structural analysis costs.

• 한국작물학회:학술대회논문집
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• 한국작물학회 1998년도 21세기 한반도 농업전망과 대책(한국작물학회.한국육종학회 공동주관 심포지움 회보)
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• pp.266-287
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• 1998

Environmental conditions and expected profit are the major criteria to select crops to be cultivated in any region. Traditionally, miscellaneous crops have been cultivated as alternative crop in case of unfavorable climate or supplementary crop in marginal lands. Since the successful breeding of high yielding varieties of staple crops and development of cultural techniques in 1970s in Korea, production of miscellaneous crops decreased markedly due to the rapid commercialization of agriculture and increased productions of horticultural crops, although yields have been doubled during the last $2\~3$ decades. On the other hand, animal husbandry has been developing remarkably parallel with national economic development and the increased consumption of animal products. As a result, imports of feed grains such as corn have increased rapidly, while roughage production became lower than demand. Among miscellaneous crops, corn production increased markedly through the development of hybrids and due to its importance as silage crops. Acreage of corn production including grains, fresh corns and feeding is about 120,000 ha, while acreage of buckwheat is about 5,000 ha and those of other miscellaneous crops decreased to a level of about 1,000 ha. Although miscellaneous crops have low yield potential and are unprofitable due to low price and imports of cheap foreign products, they should be kept to cultivate. Miscellaneous crops are important components that maintain diversity among upland crops as well as alternative crops in case of unfavorable climate. The low yield potential of miscellaneous crops might be due to lack of efforts to breed high yielding varieties and to develope cultural techniques. Continuous investment in research, exploitation of new utilization for miscellaneous crops as sustainable crop, honey crop and sightseeing crop, and development of healthy and special foods will promote their cultivation. Animal feeding in Korea depends mainly on formula feeds. As the number of animals increases to meet demand of animal products, there is no alternative way but to import grains to feed them. But roughage production, which is necessary for normal growth of ruminant animals, should be increased. However, lack of arable land and pasture land limits the production of good roughages. It is estimated that number of course for meat and milk production will be $2.5{\~}2.6$ million and total of $6.2{\~}7.5$ million tons of roughages should be produced. This implies that more than 1 million tons of roughage are needed, although pasture land, upland for forage crops, forage crops after rice cultivation and rice straw are utilized. Therefore, new reclamation of pasture land, increased roughage production in cultivating land, increased cultivation of forage crops after rice, more utilization of rice straw and active exploration of indigenous plant species as roughage resources should be promoted

• 대한토목학회논문집
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• 제29권6C호
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• pp.267-275
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• 2009

강관합성말뚝은 외부 강관의 합성 구속효과에 의해 말뚝강도가 커지고, 연성파괴 거동이 발생한다. 본 연구에서는 해상 지반에 근입된 말뚝에 대하여 말뚝재료의 항복거동 및 지반의 탄소성 거동을 함께 고려할 수 있는 3차원 수치해석을 수행하여 하중-변위 거동 및 강관합성말뚝의 보강효과를 분석하였다. 이를 위하여 강관, 콘크리트, 강관합성말뚝에 대하여 각각 말뚝직경과 재하방향에 따른 변수연구를 수행하였다. 그 결과, 수직방향 극한지지력의 경우 강관합성말뚝은 강관말뚝과 비교하여 평균 1.90배, 콘크리트 말뚝에 대하여는 평균적으로 동일한 지지력을 보여주었다. 허용변위 기준에서의 수평방향 지지력의 경우 강관합성말뚝은 강관말뚝에 비하여 평균 1.46배, 콘크리트 말뚝에 비하여 평균 1.25배 큰 것으로 나타났다. 그리고, 허용변위 기준에서의 강관합성말뚝의 말뚝두부 변위는 평균적으로 강관말뚝의 약 78%, 콘크리트 말뚝의 약 53%로 나타나 강관합성말뚝의 변위억제 효과가 큰 것으로 나타났다. 본 해석조건에서 강관합성말뚝의 수직방향 극한지지력 증가효과는 작았지만 수평방향 재하시의 강관합성말뚝의 변위억제 효과에 의해 현장타설말뚝의 경제적인 설계가 가능할 것으로 판단된다.

• Earthquakes and Structures
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• 제19권1호
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• pp.29-44
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• 2020

The effectiveness and the sensitivity of a Wireless impedance/Admittance Monitoring System (WiAMS) for the prompt damage diagnosis of two single-storey single-span Reinforced Concrete (RC) frames under cyclic loading is experimentally investigated. The geometrical and the reinforcement characteristics of the RC structural members of the frames represent typical old RC frame structure without consideration of seismic design criteria. The columns of the frames are vulnerable to shear failure under lateral load due to their low height-to-depth ratio and insufficient transverse reinforcement. The proposed Structural Health Monitoring (SHM) system comprises of specially manufactured autonomous portable devices that acquire the in-situ voltage frequency responses of a network of twenty piezoelectric transducers mounted to the RC frames. Measurements of external and internal small-sized piezoelectric patches are utilized for damage localization and assessment at various and increased damage levels as the magnitude of the imposed lateral cycle deformations increases. A bare RC frame and a strengthened one using a pair of steel crossed tension-ties (X-bracing) have been tested in order to check the sensitivity of the developed WiAMS in different structural conditions since crack propagation, damage locations and failure mode of the examined frames vary. Indeed, the imposed loading caused brittle shear failure to the column of the bare frame and the formation of plastic hinges at the beam ends of the X-braced frame. Test results highlighted the ability of the proposed SHM to identify incipient damages due to concrete cracking and steel yielding since promising early indication of the forthcoming critical failures before any visible sign has been obtained.

• 콘크리트학회논문집
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• 제23권2호
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• pp.159-168
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• 2011

이 연구에서는 뚫림 전단을 재하받는 전단 보강/전단 무보강 슬래브-기둥 내부 접합부와 기초판에 대하여 개선된 설계 방법을 개발하였다. 슬래브-기둥 접합부와 기초판의 다양한 파괴 메커니즘(경사 인장 균열 파괴, 전단 보강근의 항복, 콘크리트 압축대/스트럿의 압축 파괴)을 고려하여 뚫림 전단강도를 산정하였다. 콘크리트 위험 단면에 작용하는 뚫림 전단은 대부분 콘크리트 압축대에 의하여 지지된다고 가정하였으며, 콘크리트 압축대의 뚫림 전단강도는 압축 수직 및 전단의 조합 응력을 재하받는 콘크리트 재료 파괴 기준에 근거하여 산정하였다. 제안된 강도 모델은 실험 결과 와의 비교를 통하여 검증하였다. 검증 결과, 제안된 설계 방법은 전단 보강 및 전단 무보강 경우에 대하여 현행 KCI 설계기준 보다 우수한 강도 추정 능력을 가지고 있다는 점이 밝혀졌다.

• 대한토목학회논문집
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• 제7권1호
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• pp.75-82
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• 1987

본(本) 연구(硏究)는 소규모강복범위(小規模降伏範圍)를 벗어나는 대규모강복조건하(大規模降伏條件下)에서 구조안정성(構造安定性)에 관(關)한 중요(重要)한 문제(問題)인 불안정연성파괴(不安定延性破壞)를 평가(評價)할 수 있는 파괴역학인자(破壞力學因子)로서의 J 적분(積分)을 수치해(數値解)로서 구하는데 그 목적(目的)을 두었다. 이를 위해 균열재(龜裂材)의 균열선단요소(龜裂先端要素)로 8절점등방특이요소(節點等方特異要素)를 사용(使用)하고, 균열발생(發生)은 파괴인성(破壞靭性) $J_{IC}$를 초과할 때 일어나도록 하였으며, 그리고 균열성장(成長)의 취급(取級)은 균열개구각(龜裂開口角)을 이용(利用)했다. 본(本) 연구(硏究)에 의해 해석(解析)된 J 적분치(積分値)를 사용(使用)하여 균열재의 균열발생 과 안정성장(安定成長), 불안정(不安定) 발생점(發生點)을 찾은 결과(結果) 다른 연구결과(硏究結果)와 잘 일치(一致)하고 있어 탄소성(彈塑性)을 고려(考慮)한 J 적분치(積分値)가 균열의 안정성장(安定成長) 및 불안정연성파괴(不安定延性破壞) 문제(問題)를 다루는 파괴역학인자(破壞力學因子)로서 직접(直接) 이용(利用)될 수 있음을 보였다.