• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2006년도 춘계학술발표회 논문집(I)
• /
• pp.442-445
• /
• 2006

This paper presents an analytical prediction of nonlinear characteristics and behavior characteristics PSC structures with un-bonded tendon system. In this paper, a numerical model for un-bonded tendon is proposed based on the finite element method, which can represent straight or curved un-bonded tendon behavior. this model and time-dependent material model used to investigate the time-dependent behavior of un-bonded prestressed concrete structures. The accuracy and objectivity of the assessment process may be enhanced by the use of sophisticated nonlinear finite element analysis program. A computer program, named RCAHEST(Reinforced Concrete Analysis in Higher Evaluation System Technology), for the analysis of concrete structures and steel plate was used. The material nonlinearities are taken into account by comprising the tension, compression, and shear models of cracked concrete and models for reinforcements and tendons in the concrete. The smeared crack approach is incorporated. It accounts for the aging, creep and shrinkage of concrete and the stress relaxation of prestressed steel. The proposed un-bonded tendon model and numerical method of un-bonded prestressed concrete structures is verified by comparison with reliable experimental results.

• 비파괴검사학회지
• /
• 제36권2호
• /
• pp.121-129
• /
• 2016

As the lifespan of concrete structures increases, their load carrying capacity decreases owing to cyclic loads and long-term effects such as creep and shrinkage. For these reasons, there is a necessity for stress state monitoring of concrete members. Particularly, it is necessary to evaluate the concrete structures for behavioral changes by using a technique that can overcome the measuring limitations of usual ultrasonic nondestructive evaluation methods. This paper proposes the use of a nonlinear ultrasonic method, namely, nonlinear resonant ultrasonic spectroscopy (NRUS) for the measurement of nonlinearity parameters for stress monitoring. An experiment compared the use of NRUS method and a linear ultrasonic method, namely, ultrasonic pulse velocity (UPV) to study the effects of continuously increasing loads and cyclic loads on the nonlinearity parameter. Both NRUS and UPV methods found a similar direct relationship between load level and that parameter. The NRUS method showed a higher sensitivity to micro-structural changes of concrete than UPV method. Thus, the experiment confirms the possibility of using the nonlinear ultrasonic method for stress state monitoring of concrete members.

• 한국구조물진단유지관리공학회 논문집
• /
• 제6권2호
• /
• pp.183-194
• /
• 2002

A general procedure to evaluate the sensitivity of design variables to stresses and strains in PSC flexural members is proposed. To accomplish the purpose of this study, long-term losses including creep, shrinkage, and PS steel relaxation are formulated based on the equilibrium states of the deformed sectional geometry. Thereby, the formulation follows the basic steps which consider the fundamental formulas adopted by CEB-FIP, ACI, and KCI rather than the age adjusted effective modulus concept. Twenty-one design variable including the material and geometrical properties of concrete, nonprestressing steel and prestressing steel, and the geometry of the cross section are considered in the sensitivity analysis. The gradients of the stresses and strains needed for the sensitivity assessment are calculated in a closed format. The derived formulation is applied to the T-type section PSC beam with prestressing and nonprestressing steels for the sensitivity analysis. The analytically calculated sensitivity results are compared with those numerically calculated to ensure the validity of the proposed procedure.

• Structural Engineering and Mechanics
• /
• 제77권5호
• /
• pp.627-635
• /
• 2021

The speed of rail vehicles become higher and higher over two decades, and China has unveiled a prototype high-speed train in October 2020 that has been able to reach 400 km/h. At such high speeds, wheel-rail force items that had previously been ignored in common computational model should be reevaluated and reconsidered. Aiming at this problem, a new model for investigating the vehicle-bridge interaction at high moving speed is proposed. Comparing with the common model, the new model was more accurate and applicable, because it additionally considers the second-order pseudo-inertia forces effect and its modeling equilibrium position was based on the initial deformed curve of bridge, which could include the influences of temperature, pre-camber, shrinkage and creep deformation, and pier uneven settlement, etc. Taking 5 km/h as the speed interval, the dynamic responses of the classical vehicle-bridge system in the speed range of 5 km/h to 400 km/h are studied. The results show that ignoring the second-order pseudo-inertia force will underestimate the dynamic response of vehicle-bridge system and make the high-speed railway bridge structure design unsafe.

• Structural Engineering and Mechanics
• /
• 제36권2호
• /
• pp.207-223
• /
• 2010

The aim of this study concerns with the construction stage analysis of highway bridges constructed with balanced cantilever method using time dependent material properties. K$\ddot{o}$m$\ddot{u}$rhan Highway Bridge constructed with balanced cantilever method and located on the 51st km of Elazi$\check{g}$-Malatya, Turkey, highway over Firat River is selected as an application. Finite element models of the bridge are modelled using SAP2000 program. Geometric nonlinearity is taken into consideration in the analysis using P-Delta plus large displacement criterion. The time dependent material strength variations and geometric variations are included in the analysis. Elasticity modulus, creep and shrinkage are computed for different stages of the construction process. The structural behaviour of the bridge at different construction stages has been examined. Two different finite element analyses with and without construction stages are carried out and results are compared with each other. As analyses result, variation of internal forces such as bending moment, axial forces and shear forces for bridge deck and column are given with detail. It is seen that construction stage analysis has remarkable effect on the structural behaviour of the bridge.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2000년도 가을 학술발표회 논문집(II)
• /
• pp.995-1000
• /
• 2000

Segmentally erected prestressed concrete box girder bridges have been widely used in Korean high speed railway. Segmental erection has been accomplished along the longitudinal direction and across the depth of cross section. The cross section is similar to a composite cross section, composed of old and new segments. Because these segments have different time-dependent creep and shrinkage properties, a stress redistribution takes place during the construction period. It is the main objective in this research to investigate this behavior. An actual bridge was instrumented with 96 vibrating wire embedded type strain gauges, 6 electronic type steel strain gauges, and 75 thermocouples. Two span continuous high speed railway bridge was selected. Two points of importance, such as the midpoint of the first span and the point of interior support, along the span of the girder were chosen to monitor the time dependent behaviors for an extended period of time. The data collection was starting just after concrete girder were cast and is still going on. According to the measured results, the strain distributions across the depth of the section at midspan and interior support were not continuous and the important redistribution of stresses takes place. Thus, rational design of prestressed concrete composite box girder bridges need.

• 대한토목학회논문집
• /
• 제14권1호
• /
• pp.49-62
• /
• 1994

본 논문에서는 평면 PC 사장교의 시장교의 각 단계를 고려할 뿐 아니라 재료의 비선형성은 물론 기하학적 비선형도 고려하는 해석방법을 제시했다. 재료의 시간의존적 특성들로는 콘크리트의 크리프, 건조수축, 강도증가와 PC 강재 및 케이블의 이완을 고려했다. 시공중의 각 단계를 표현하기 위해 시공명령어를 정의하여 임의의 해석단계마다 하중과 경계조건의 변화, 구조계의 변화와 가설장비의 이동을 고려했다. 본 해석방법을 실제적인 PC 사장교의 해석에 적용하여 시공의 진행에 따른 PC 사장교의 비선형거동 및 응력과 변형의 변화를 검토했고 또한 시공단계를 고려한 해석에 있어서 재료의 시간의존적 특성이 끼치는 영향을 검토했다.

• 콘크리트학회논문집
• /
• 제13권1호
• /
• pp.77-85
• /
• 2001

CFT 기둥은 뛰어난 구조적 성능으로 사용이 증가하고 있는 추세이다. 하지만 CFT 기둥을 사용하여 건설된 구조물도 내부콘크리트의 시간의존적 변형으로 사용상태에 이상 응력집중이나 과다 처짐 등의 구조적 문제를 초래할 수 있다. 따라서 이에 대한 연구가 필요하다. 본 논문에서는 CFT 기둥에 하중이 가해지는 시점에서의 해석법과 이를 기초로 한 장기거동 해석법을 제안하였다. 또한 이에 대한 실험을 실시하여 해석결과와 비교.분석하였다. 이를 통해 제안된 해석법을 검증하고 아울러 해석에 적용된 부착강도 모델식의 정확성 또한 평가하였다.

• 한국지반환경공학회 논문집
• /
• 제14권12호
• /
• pp.13-22
• /
• 2013

교량의 하부구조는 고정하중과 차량 활하중 등의 수직 방향 하중을 지지할 뿐만 아니라 횡방향 하중을 지지해야 하므로 교량의 안전성에 있어 매우 중요한 구조 요소임과 동시에 경제성에 영향을 미치는 요소이다. 따라서, 본 연구에서는 말뚝캡 직상부에 모멘트 집중을 피할 수 있는 말뚝형 기둥의 현장 적용성에 대한 기초적인 사례연구를 수행하였으며, 말뚝 본체의 구조성능보다는 지반의 지지력이 더 큰 영향을 미치는 것으로 분석되었다.

• 대한토목학회논문집
• /
• 제12권4호
• /
• pp.33-47
• /
• 1992

본 논문에서는 케이블로 지지된 프리스트레스트 콘크리트(PC) 뼈대의 시공중의 각 단계를 고려하고 콘크리트와 PC 강재, 케이블 재료의 시간의존적 특성 및 재료의 비선형성과 케이블의 색 및 구조물의 처짐에 의한 기하학적 비선형성도 고려하는 해석방법을 제시했다. 구조물의 비선형거동을 해석하기 위한 운동방정식은 Updated Lagrangian 방식을 이용하여 유도하고 시간의존적인 거동올 해석하기 위해서 시간영역을 시간단계로 나누어 순차적으로 적분했다. 시공중의 각 단계를 표현하기 위해 계속적인 구조계의 변화를 고려했다. 본 논문에서 제시한 해석방법에 근거하여 컴퓨터 프로그램 CFRAME을 개발하고 예제들을 통하여 해석방법의 정당성을 보였다.