• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.1
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• pp.25-31
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• 2024

This paper introduces a numerical analysis model capable of evaluating CFT (Concrete-Filled Tube) columns across all time stages, incorporating creep behavior analysis and inelastic analysis to account for time-dependent behavior. The proposed model is compared with experimental results, revealing that the numerical model presented in this paper demonstrates more accurate trends than existing design criteria. Following verification, a numerical analysis is conducted for each slenderness ratio, determining the ultimate load capacity and examining the short-term and long-term sustained load behavior of the overall CFT column members.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.1
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• pp.81-90
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• 2012

The indentation test, which is one of the testing methods for evaluating the mechanical properties of materials, can be applied to the evaluation of creep properties. Many studies related to the indentation creep test, however, have just focused on the characteristics of the steady-state creep, so there are wide discrepancies between the uniaxial test and the indentation test. To obtain accurate creep properties, it is therefore important to consider the effects of transient creep. In the present work, the Ogbonna et al.'s work on the spherical indentation test including the transient creep was expanded and applied to the conical indentation creep test. The characteristics of the transient creep were analyzed via finite element simulations and compared with those obtained through spherical indentation. Other effects, such as elastic strain, indenter shape, contact area, and representative strain, which have not been considered properly in prior studies on the creep test, are also discussed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2A
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• pp.243-247
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• 2008

An analytical approach to calculate time-dependent stresses and strains in initially cracked reinforced concrete section with biaxial bending was proposed. The method utilized the aging coefficient approach of Bazant and the linear creep theory. The position of neutral axis and strain and stress distributions of cracked section after creep and shrinkage were determined from the requirements of strain compatibility and equilibrium of a section. With this proposed algorithm, examples were given for rectangular section and a comparative analysis for stress and strain was also made.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.4D
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• pp.387-393
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• 2010

This paper studies static crack growth of asphalt pavement using the extended finite element method (XFEM). To consider nonlinear characteristics of asphalt concrete, a viscoelastic constitutive equation using the Maxwell chain is used. And a linear cohesive crack model is used to regularize the crack. Instead of constructing the viscoelastic constitutive law from the Prony approximation of compliance and retardation time measured experimentally, we use a smooth log-power function which optimally fits experimental data and is infinitely differentiable. The partial moduli of the Maxwell chain from the log-power function make analysis easy because they change more smoothly in a more stable way than the ordinary method such as the least square method. Using the developed method, we can simulates the static crack growth test results satisfactorily.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.742-745
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• 2010

본 논문은 초고층구조물의 해석방법으로 탄성변형과 아울러 시간의존성을 가진 크리프와 건조수축에 의한 비탄성변형을 고려한 비선형 시공단계 해석법을 제시한다. 기존의 초고층구조물 해석에서 주로 행하는 기둥 축소량 해석은 실무자의 경험과 프로그램을 통한 간략화에 맞추어져 있다. 이는 실제 시공 시 발생하는 구조해석 요소들을 충분히 반영하지 못하여 계산 값과 실제 값 사이에 오차가 발생된다. 비선형 시공단계 해석은 실제 시공 때 발생되는 해석변수들을 고려한 단계별 해석의 수행이 가능하며, 시간의 의존성을 가진 creep과 shrinkage의 효과를 함께 고려하여 일괄해석의 문제점을 구조해석 단계에서 실제상황에 가까운 해석을 가능하게 할 수 있다. 이를 위해 시공단계해석이 가능한 범용 프로그램을 이용한 50층 규모의 3차원 골조 프레임 모델 예제 해석을 통하여 기존 해석법들과의 비교, 분석으로 시간의 의존성을 고려한 시공단계해석의 필요성을 제시한다. 본 논문에는 범용프로그램인 SAP2000(ver.14)와 CEB-FIP모델 코드를 사용 하였다.

• Journal of the KSME
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• v.33 no.2
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• pp.145-151
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• 1993

전자산업이 고도화되어감에 따라 전자기술은 소재 . 기계분야와 복합된 기술의 발전이 가속화 되어 가고 있다. 특히 이 글에서는 응력해석 CAE 기술이 전자부품산업에 적용되는 사례를 소 개하고자 한다. 그 중 하나는 하드디스크의 정밀부품 중의 하나인 스핀들 모터용 Hub의 절삭 가공시 고려하여야 하는 탄성 변형량을 해석하고 이를 적용하는 사례이고 또 하나는 Audio Deck의 Capatan Shaft를 지지하는 플리스틱 Base가 신뢰성 시험도중 또는 고온 부하시 발생하는 크리프현상을 해석하여 적용하는 사례이다. 이 글에서 소개하는 두 가지 사례는 전자부품산업에 응력해석 CAE를 적용할 수 있는 예들 중 빙산의 일각에 불과할 뿐이고, 이와 유사한 전자부품에 응력해석 CAE를 적용할 수 있다.

• Journal of the Korea Concrete Institute
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• v.13 no.3
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• pp.268-276
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• 2001

A numerical model for the thermal response analysis of concrete structures is suggested. The model includes the stress-strain relationship, constitutive relationship, and multiaxial failure criteria at elevated temperature conditions. Modified Saenz's model was used to describe the stress-strain relationship at high temperatures. Concrete subjected to elevated temperatures undergoes rapid strain increase and dimensional instability. In order to explain those changes in mechanical properties, a constitutive model of concrete subjected to elevated temperature is proposed. The model consists of four strain components; free thermal creep strain, stress-induced (mechanical) strain, thermal creep strain, and transient strain due to moisture effects. The failure model employs modified Drucker-Prager model in order to describe the temperature dependent multiaxial failure criteria. Some numerical analyses are performed and compared with the experimental results to verify the proposed model. According to the comparison, the suggested material model gives reliable analytical results.

• Journal of the Korea Concrete Institute
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• v.16 no.2 s.80
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• pp.155-162
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• 2004

An analytical method to predict the time dependent flexural behavior of composite girder is presented based on sectional analysis. The time dependent constitutive relation accounting for the early-age concrete properties including maturing of elastic modulus, creep and shrinkage is derived in an incremental format by the first order Taylor series expansion. The sectional analysis calculates the axial and curvature strains based on the force and moment equilibriums. The deflection curve of the girder approximated by the quadratic polynomial function is calculated by applying to the proper boundary conditions in the consecutive segments. Numerical applications are made for the 3-span double composite steel box girder which is a composite bridge girder filled with concrete at the bottom of the steel box in the negative moment region. The calculated results are compared with those by finite element analysis results. Close agreement is observed between the two approaches.

• Journal of the Korea Concrete Institute
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• v.13 no.5
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• pp.457-465
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• 2001

Shrinkage strains of concrete slab in multi-story building are restrained by structural members such as columns or walls, then can induce cracks due to excessive shrinkage stress over tensile strength of member. In this study, a shrinkage stress analysis method of concrete slab in multi-story building considering not only material properties such as shrinkage, creep and reinforcement effect but also construction sequence is proposed. Tensile stresses of slab due to shrinkage are calculated by converting shrinkage strains into equivalent temperature gradients, creep that can release shrinkage stress can be considered by replacing the modulus of elasticity of concrete, Ec , to the effective secant modulus of elasticity of concrete, E$\_$eff/ Reinforcements are also considered by modeling them as equivalent beam elements in FEM program. Results of step by step analysis reflecting construction sequence summed up to calculate stresses of the whole building considering that shrinkage stresses of the building come from the difference of shrinkage between i-th floor and (i-1)-th floor, named as effecitive shrinkage, and it can be varied by construction sequence. The results of 10-story example building show that shrinkage stresses of lower floors are greater than those of upper floors, that is, stresses of lower floors(1∼2FI.) exceed modulus of rupture of concrete, but stress ratios of higher floors are in the range of 27.9∼92.8%.

• Journal of the Korea Concrete Institute
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• v.23 no.1
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• pp.77-86
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• 2011

The concrete creep deformation of a hybrid composite section can cause additional deformation of the composite section and the stress relaxation of pre-compressive stress on the concrete section due to partial restraint of the deformation. In this study, the stress relaxation coefficient method (SRCM) is derived for simple analysis of complicate hybrid or composite sections for engineering purpose. Also, an equation of the stress relaxation coefficient (SRC) required for the SRCM is proposed. The SRCM is derived with the parameters of a creep coefficient, section and loading properties using the same method as the constant-creep step-by-step method (CC-SSM). The errors of the SRCM is improved by using the proposed SRC equation than the average SRC's which were estimated from the CC-SSM. The root mean square error (RMSE) of the SRCM with the proposed SRC equation for concrete with creep coefficient less than 3 was less than 1.2% to the creep deformation at the free condition and was 3.3% for the 99% reliability. The proposed SRC equation reflects the internal restraint of composite sections, and the effective modulus of elasticity computed with the proposed SRC can be used effectively to estimate the rigidity of a composite section in a numerical analysis which can be applied in analysis of the external restrain effect of boundary conditions.