• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 추계 학술발표회 2차
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• pp.122-130
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• 2010

In recent days, the foundations of huge structures in general and mega foundations of grand bridges in particular are required in geotechnical engineering. However, previous design method based on virtual fixed point theory cannot adequately predict Pile-Bent structure‘s physical behavior. Therefore, this paper describes a new analysis and design of Pile-Bent structure for grand bridges. A detailed analysis was performed for column-pile interactions using FB-Pier program and Midas program. As a result, the behavior of a column-pile is estimated and highlighted. Moreover, based on this study, it is found that the minimum reinforcement ratio(=0.4%) is applicable for plastic behavior of columns.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2001년도 사면안정 설계 및 시공 특별강연회
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• pp.78-97
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• 2001

• 한국구조물진단유지관리공학회 논문집
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• 제21권6호
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• pp.1-9
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• 2017

원형 기둥의 나선철근은 축방향 철근의 위치 고정 및 좌굴방지와 코어콘크리트의 충분한 횡구속으로 기둥의 연성거동에 효과적인 역할을 한다. 각국은 기둥에 요구되는 연성을 확보하기 위하여 나선철근의 최소철근비를 제시하고 있다. ACI 318-14와 국내 콘크리트 구조설계 기준에서 제시하는 나선철근 최소철근비는 Richart et al.(1928)의 이론에 기초하여 개발되었으며 현재까지 사용되고 있다. 그러나 Richart et al.(1928)의 이론은 현대의 고강도 콘크리트, 고강도철근 그리고 나선철근의 배근조건 등의 영향을 고려하지 못한다. 이 연구에서는 나선철근으로 구속된 철근콘크리트 원형 기둥의 내력회복 및 연성증진에 요구되는 나선철근에 대한 수정 최소철근비 산정식을 제시한다. 수정 최소철근비 산정식은 콘크리트 압축강도, 나선철근 항복강도, 기둥의 단면적, 나선철근 배근간격, 나선철근 직경의 영향을 고려하고 있다. 이 논문에서는 재료강도 및 나선철근 최적비를 변수로 한 실험체의 일축 압축실험을 통하여 ACI 318-14에 제시하는 나선철근 최소철근비 산정식의 타당성을 검토하고, 그 결과를 토대로 나선철근 최소철근비 산정식의 수정방안을 고찰하였다.

• 한국도로학회논문집
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• 제16권4호
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• pp.1-9
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• 2014

PURPOSES: The objective of this study is to evaluate construction issues and design for transverse steel in continuously reinforced concrete pavement(CRCP). METHODS : The first continuously reinforced concrete pavement(CRCP) design procedure appeared in the 1972 edition of the "AASHTO Interim Guide for Design of Pavement Structures", which was published in 1981 with Chapter 3 "Guide for the Design of Rigid Pavement" revised. A theory that was accepted at that time for the analysis of steel stress in concrete pavement, called subgrade drag theory(SGDT), was utilized for the design of reinforcement of CRCP - tie bar design and transverse steel design - in the aforementioned AASHTO Interim Guide. However SGDT has severe limitations due to simple assumptions made in the development of the theory. As a result, any design procedures for reinforcement utilizing SGDT may have intrinsic flaws and limitations. In this paper, CRCP design procedure for transverse steel was introduced and the limitations of assumptions for SGDT were evaluated based on various field testing. RESULTS: Various field tests were conducted to evaluate whether the assumptions of SGDT are reasonable or not. Test results show that 1) temperature variations exist along the concrete slab depth, 2) very little stress in transverse steel, and 3) warping and curling in concrete slab from the field test results. As a result, it is clearly revealed out that the assumptions of SGDT are not valid, and transverse steel and tie bar designs should be based on more reasonable theories. CONCLUSIONS : Since longitudinal joint is provided at 4.1-m spacing in Korea, as long as joint saw-cut is made in accordance with specification requirements, the probability of full-depth longitudinal cracking is extremely small. Hence, for transverse steel, the design should be based on the premise that its function is to keep the longitudinal steel at the correct locations. If longitudinal steel can be placed at the correct locations within tolerance limits, transverse steel is no longer needed.

• Steel and Composite Structures
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• 제30권6호
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• pp.567-576
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• 2019

Time-dependent creep analysis of a rotating functionally graded cantilever beam with trapezoidal longitudinal cross section subjected to thermal and inertia loading is investigated using first-order shear deformation theory (FSDT). The model described in this paper is a simple simulation of a turbine blade working under creep condition. The material is a metal based composite reinforced by a ceramic where the creep properties of which has been described by the Sherby's constitutive model. All mechanical and thermal properties except Poisson's ratio are assumed to be variable longitudinally based on the volume fraction of constituent. The principle of virtual work as well as first order shear deformation theory is used to derive governing equations. Longitudinal distribution of displacements and stresses are investigated for various volume fractions of reinforcement. Method of successive elastic solution is employed to obtain history of stresses and creep deformations. It is found that stresses and displacements approach their steady state values after 40000 hours. The results presented in this paper can be used for selection of appropriate longitudinal distribution of reinforcement to achieve the desired stresses and displacements.

• Steel and Composite Structures
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• 제38권1호
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• pp.47-66
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• 2021

This work addresses the free vibration analysis of Functionally Graded Porous (FGP) nanocomposite truncated conical shells with Graphene PLatelet (GPL) reinforcement. In this study, three different distributions for porosity and three different dispersions for graphene platelets have been considered in the direction of the shell thickness. The Halpin-Tsai equations are used to find the effective material properties of the graphene platelet reinforced materials. The equations of motion are derived based on the higher-order shear deformation theory and Sanders's theory. The Fourier Differential Quadrature (FDQ) technique is implemented to solve the governing equations of the problem and to obtain the natural frequencies of the truncated conical shell. The combination of FDQ with higher-order shear deformation theory allows a very accurate prediction of the natural frequencies. The precision and reliability of the proposed method are verified by the results of literature. Moreover, a wide parametric study concerning the effect of some influential parameters, such as the geometrical parameters, porosity distribution, circumferential wave numbers, GPLs dispersion as well as boundary restraint conditions on free vibration response of FGP-GPL truncated conical shell is also carried out and investigated in detail.

• Advances in nano research
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• 제12권2호
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• pp.117-137
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• 2022

Effect of thickness stretching on free vibration, bending and buckling behavior of carbon nanotubes reinforced composite (CNTRC) laminated nanoplates rested on new variable elastic foundation is investigated in this paper using a developed four-unknown quasi-3D higher-order shear deformation theory (HSDT). The key feature of this theoretical formulation is that, in addition to considering the thickness stretching effect, the number of unknowns of the displacement field is reduced to four, and which is more than five in the other models. Two new forms of CNTs reinforcement distribution are proposed and analyzed based on cosine functions. By considering the higher-order nonlocal strain gradient theory, microstructure and length scale influences are included. Variational method is developed to derive the governing equation and Galerkin method is employed to derive an analytical solution of governing equilibrium equations. Two-dimensional variable Winkler elastic foundation is suggested in this study for the first time. A parametric study is executed to determine the impact of the reinforcement patterns, nonlocal parameter, length scale parameter, side-t-thickness ratio and aspect ratio, elastic foundation and various boundary conditions on bending, buckling and free vibration responses of the CNTRC plate.

• Advances in nano research
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• 제14권5호
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• pp.421-433
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• 2023

In the present paper, the influences of the variation of exponent of volume fraction of carbon nanotubes (CNTs) on the natural frequencies (NFs) of the carbon nanotube-reinforced composite (CNTRC) beams under four different boundary conditions (BCs) are investigated. The single-walled carbon nanotubes (SWCNTs) are assumed to be aligned and dispersed in a polymeric matrix with various reinforcing patterns, according to the variation of exponent of volume fraction of CNTs for functionally graded (FG) reinforcements. Besides, uniform distribution (UD) of reinforcement is also considered to analyze the influence of the non-linear (NL) variation of the reinforcement of CNTs. Using Hamilton's principle and third-order shear deformation theory (TSDT), the equations of motion of the CNTRC beam are derived. Under four different BCs, the resulting equations are solved analytically. To verify the present formulation, comparison investigations are conducted. To examine the impacts of several factors on the NFs of the CNTRC beams, numerical examples and some benchmark results are presented.

• Computers and Concrete
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• 제4권2호
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• pp.135-156
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• 2007

Three 3D nonlinear finite-element models are developed to study the behavior of concrete beams and plates with and without external reinforcement by fibre-reinforced plastic (FRP). All three models are formulated based upon the 3D theory of elasticity. The stress model is modified from the element developed by Ramtekkar, et al. (2002) to incorporate material nonlinearity in the formulation. Both transverse stress and displacement components are used as nodal degrees-of-freedom to ensure the continuity of both stress and displacement components between the elements. The displacement model uses only displacement components as nodal degrees-of-freedom. The transition model has both stress and displacement components as nodal degrees-of-freedom on one surface, and only displacement components as nodal degrees-of-freedom on the opposite surface. The transition model serves as a connector between the stress and the displacement models. The developed models are validated by comparing the results of the analyses with an existing experimental result. Parametric studies of the effects of the externally reinforced FRP on the load capacity of reinforced concrete (RC) beams and concrete plates are performed to demonstrate the practicality and the efficiency of the proposed models.

• 한국구조물진단유지관리공학회 논문집
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• 제17권6호
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• pp.31-39
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• 2013

고강도 콘크리트 보의 극한상태의 거동을 강도에 따라 연구하였다. 13개의 보를 해석하고 그 결과를 제시하였다. 변수는 콘크리트의 압축강도로 범위는 57~184 MPa이며, 횡방향 철근비로 범위는 0.35~1.49%이다. 실험에서 측정한 극한 비틀림 강도를 본 논문에서 제안한 값과 ACI 기준에 따른 값을 비교하였다. 그 결과 본 논문에서 제안한 이론에 의한 극한 비틀림 강도가 ACI 기준에 따른 값보다 더 좋은 결과를 보였다.