• Structural Engineering and Mechanics
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• 제77권1호
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• pp.1-17
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• 2021

The influence of prestress force on the fundamental frequency and static deflection shape of uncracked Prestressed Concrete (PC) beams with a parabolic bonded tendon was examined in this paper. Due to the conflicts among existing theories, the analytical solutions for properly considering the dynamic and static behavior of these members is not straightforward. A series of experiments were conducted for a total period of approximately 2.5 months on a PC beam made with high strength concrete, subsequently and closely to the 28 days of age of concrete. Specifically, the simply supported PC member was short term subjected to free transverse vibration and three-point bending tests during its early-age. Subsequently, the experimental data were compared with a model that describes the dynamic behavior of PC girders as a combination of two substructures interconnected, i.e., a compressed Euler-Bernoulli beam and a tensioned parabolic cable. It was established that the fundamental frequency of uncracked PC beams with a parabolic bonded tendon is sensitive to the variation of the initial elastic modulus of concrete in the early-age curing. Furthermore, the small variation in experimental frequency with time makes doubtful its use in inverse problem identifications. Conversely, the relationship between prestress force and static deflection shape is well described by the magnification factor formula of the "compression-softening" theory by assuming the variation of the chord elastic modulus of concrete with time.

• Steel and Composite Structures
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• 제19권1호
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• pp.43-58
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• 2015

There are many studies on the optimization of steel trusses in literature; and, a large number of them include a shape optimization. However, only a few of these studies are focused on the prestressed steel trusses. Therefore, this paper aims to determine the amounts of the material and cost savings in steel plane trusses in the case of prestressing. A parallel-chord simply supported steel truss is handled as an example to evaluate the used approach. It is considered that prestressing tendon is settled under the bottom bar, between two end supports, using deviators. Cross-sections of the truss members and height of the truss are taken as the design variables. The prestress losses are calculated in two steps as instantaneous losses and time-dependent losses. Tension increment in prestressing tendon due to the external loads is also considered. A computer program based on genetic algorithm is developed to solve the optimization problem. The handled truss is optimized for different span lengths and different tendon eccentricities using the coded program. The effects of span length and eccentricity of tendon on prestressed truss optimization are investigated. The results of different solutions are compared with each other and those of the non-prestressed solution. It is concluded that the amounts of the material and the cost of a steel plane truss can be reduced up to 19.9% and 14.6%, respectively, by applying prestressing.

• 한국산업융합학회 논문집
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• 제27권3호
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• pp.555-561
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• 2024

This paper derives material properties of steel bars that simulate the distribution of stress and strain of prestressed tendons used in Prestressed concrete(PSC) girders and presents an optimal material model. ABAQUS software was used to establish the 3D solid model of the PSC girder and strand wire rope for a PS(Prestressed) tendon. Then the model of steel wire rope was imported into the Isight interface plugin directly through the ABAQUS and the Data Matching. In ABAQUS, the contact pairs were established, the models were meshed, the constraints were applied to solve the finite element model and an axial tension of 0.5m/s was loaded to analyze the stress and deformation distributions in the normal working range of the PS strand wire rope. In Data Matching, classical experimental data is fitted to the optimal material properties through finite element analysis and multi-objective optimization. The results show that the steel bar with optimal material properties presents a similar linear area and stress distribution with the PS tendon.

• Structural Engineering and Mechanics
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• 제62권5호
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• pp.595-606
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• 2017

During their life span, post-tensioned concrete structures may be exposed to thermal loads. Therefore, there has been a growing interest in research on the advanced analysis and design of post-tensioned concrete slabs subjected to thermal loads. This paper investigates the structural behaviour of post-tensioned one-way spanning concrete slabs. A nonlinear finite element model for the analysis of post- tensioned unbonded and bonded concrete slabs at elevated temperatures was developed. The interface between the tendon and surrounding concrete was also modelled, allowing the tendon to retain its profile shape during the deformation of the slab. The load-deflection behaviour, load-force behaviour in the tendon, and the failure modes are presented. The numerical analysis was conducted by the finite element ANSYS software and was carried out on two different one-way concrete slabs chosen from literature. A parametric study was conducted to investigate the effect of several selected parameters on the overall behavior of post-tensioned one-way concrete slab. These parameters include the effect of tendon bonding, the effect of thermal loading and the effect of tendon profile. Comparison between uniform thermal loading and nonuniform thermal loading showed that restrained post tensioned slab with bottom surface hotter has smaller failure load capacity.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.93-98
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• 2001

This study is to develop the end anchorage of external steel reinforcement of RC slab bridges. External prestress method using the existing steel is that When the anchorage is installed in slab end, a plenty of anchor bolts were required because the only tangential stress of anchor bolt received a tendon force. Then, for this reason, the wide end anchorage was required and the shape was complicate. But this reinforcement method using method that inserts anchor key at concrete surface cut a groove gets big internal force comparing to the anchorage using existing anchor bolt. Furthermore, the number of anchor bolt for installing apparently will be reduced, and the operation will be convenient because a small anchorage of a simple shape will be received a great tendon force

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
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• pp.1009-1014
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• 2001

This study is to develop the end anchorage of external steel reinforcement of RC slab bridges. External prestress method using the existing steel is that When the anchorage is installed in slab end, a plenty of anchor bolts were required because the only tangential stress of anchor bolt received a tendon force. Then, for this reason, the wide end anchorage was required and the shape was complicate. But this reinforcement method using method that inserts anchor key at concrete surface cut a groove gets big internal force comparing to the anchorage using existing anchor bolt. Furthermore, the number of anchor bolt for installing apparently will be reduced, and the operation will be convenient because a small anchorage of a simple shape will be received a great tendon force.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1997년도 한국자동제어학술회의논문집; 한국전력공사 서울연수원; 17-18 Oct. 1997
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• pp.1285-1288
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• 1997

The basic technology of virtual reality can be described as the cognition of the condition change in virtual world by stimulating the visual, auditory, kinesthetic and tactile sensation. Among these, the kinesthetic and tactile sensation is one of the most important things to recognize the interaction. In this paper, it is addressed the haptic device which help the human feel the sense of the operator, and is designed in modular type to expand for five fingers later. the haptic device is driven by tendon and ultrasonic motors located in the wrist part. Each joint is actuated by coupled tendons and adopts more actrator by one than the number of the joints, called 'N+1 type'. The haptic device adopts metamorphic 4-bar linkage structure and the length of linkages, shape and the location of joint displacement sensor are optimized through the analysis.

• 한국구조물진단유지관리공학회 논문집
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• 제12권6호
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• pp.63-70
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• 2008

외부 긴장재를 이용한 보강공법은 효과적인 보강기술의 하나로써 연구되고 있으며 그 적용사례가 증가하고 있다. 본 논문에서는 실험적 연구를 수행하여 외부긴장재로 보강된 강합성교량의 항복하중 및 극한하중에 대한 효과를 살펴보았다. 또한 긴장력, 편향부, 편심거리와 긴장재의 배치형상 등의 다양한 실험변수를 설정하여 외부긴장재를 이용한 공법의 보강효과를 정량적으로 분석하였다.

• 대한족부족관절학회지
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• 제13권2호
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• pp.193-196
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• 2009

The first metatarsophalangeal joint injury is common in professional soldiers and athletes. But this was rarely reported. A professional soldier has varus instability in the first metatarsophalangeal joint due to hyperextension. In the MR Imaging, weavy appearance in lateral collateral ligament and high signal change in plantar plate was shown. So he has surgical treatment using reconstructive procedure. At first, $4^{th}$ extensor digitorum longus tendon was splitted longitudinally and harvested, second triangular shape reconstruction on lateral joint line was done using harvested tendon. One year later, fifteen degrees was limited compared with intact side. Reconstruction using $4^{th}$ extensor digitorum longus tendon in traumatic dynamic hallux varus was good method.

• 환경생물
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• 제37권3호
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• pp.343-350
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• 2019

도토리거위벌레는 큰턱을 이용하여 도토리에 구멍을 뚫고 가지를 자르는 독특한 행동을 한다. 이러한 행동을 이해하기 위해 다양한 현미경을 이용하여 구기의 해부학적 특징을 관찰하였다. 실체현미경을 이용한 연구에서는 도토리거위벌레 수컷의 평균 내전건과 외전건의 두께는 각각 32.87 ㎛, 53.83 ㎛이었고, 암컷의 평균 내전건과 외전건의 두께는 각각 40.81 ㎛, 75.55 ㎛이었다. 내전건과 외전건의 유의한 두께 차이로 인해 큰턱을 닫는 힘보다 벌리는 힘이 더 강하다는 것을 유추할 수 있다. 광학현미경을 이용한 관찰에서는 주둥이 안쪽에 위치한 내전건과 외전건의 너비 차이와 큰턱 쪽에서는 원형으로 위치하며 두부로 갈수록 납작해져 두부 외피 안쪽에 근육으로 연결된다는 것을 확인할 수 있었고, 내전건의 위치와 모양의 변화에 대한 관찰을 수행하였다. 전자현미경을 통한 연구에서는 외전건이 내전건보다 더 굵으며 이로 인해 큰턱을 안쪽으로 당기는 힘보다 바깥쪽으로 밀어내는 힘이 더 크다는 것을 확인하였다. 관찰 결과를 바탕으로, 도토리거위벌레, 밤바구미, 왕거위벌레의 큰턱의 형태와 이빨의 위치 그리고 큰턱의 움직임에 대해 비교 분석하였고, 도토리거위벌레가 보여주는 특징적인 행동은 해부학적/형태적 특징과 연관되어 있음을 확인할 수 있었다.