• Computers and Concrete
• /
• 제10권5호
• /
• pp.469-487
• /
• 2012

This paper presents a study on the behaviour of the joints of segmental concrete bridges with external prestressing, focusing on the structural response of dry non-epoxied joints with shear keys. A Finite Element joint model to study such structures is validated modelling eight concrete panel tests. The most important feature of this model is that it has been validated with experimental tests on concrete panels which were specifically designed to fail in shear. Interface elements are used to reproduce the non linear behaviour of the joint and parameters deduced from the tests are used to define the constitutive law of these elements. This joint model is of great importance because it will permit the development of a structural model that faithfully reproduces the behaviour of these structures under combined flexure and shear and the study of its global behaviour after the opening of the joints. Interesting conclusions about the behaviour of the dry joints, about the contribution of the different mechanisms transferring shear (friction and cohesion) and about the shear stress distribution in the joint have been reached.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2000년도 봄 학술발표회 논문집
• /
• pp.781-786
• /
• 2000

This paper presents the behavior and strenghening effect of reinforced concrete rectangular beams strengthened sing CFRP sheets with different strengthening level. In general, normally strengthened beams are failed by interfacial shear failure (delamination) within concrete, instead of by tensile failure of the CFRP sheets. The delamination occurred suddenly and the concrete cover cracked vertically by flexure was spalled off due to the release energy. The ultimate load considerably increased with an increase of strengthening level, while the ultimate deflection significantly decreased. The tensile force of CFRP sheets and average shear stress of concrete at delamination failure were curvilinearly proportional to the strengthening level. Therefore, the increment of ultimate load obtained by strengthening was curvilinearly proportional to th strengthening level.

• 대한토목학회논문집
• /
• 제14권6호
• /
• pp.1289-1298
• /
• 1994

휨거동을 받는 두꺼운 균열판의 응력확대계수를 산정할 수 있는 새로운 p-version 균열모델이 제시되었다. 제안된 모델에서는 고차이론과 전단변형을 고려할 수 있는 $C^{\circ}$-평판요소가 사용되었다. 임의의 변위장은 적분형 르장드르 다항식에 의해 정의되는데 이 다항식은 기본 모우드, 주변 모우드와 내부 모우드으로 구성되어 있다. 컴퓨터 프로그램에는 최고 10차까지의 적분형 르장드르 함수를 자유스럽게 사용할 수 있게 하였으며 응력확대계수는 가상균열전진법에 의해 계산되었다. 본 연구에서는 평판의 두께와 폭에 대한 균열진전길이의 변화와 경계조건의 변화에 따른 응력확대계수의 영향이 조사되었으며 모멘트 하중을 재하받는 균열판과 균열이 없는 평판의 해석이 기존의 문헌에 발표된 이론값과 유한요소해석 결과와 비교되어 높은 정확도를 보여주고 있다.

• Transactions on Electrical and Electronic Materials
• /
• 제9권4호
• /
• pp.147-150
• /
• 2008

Porcelain suspension insulators aged for 1, 5 and 10 years on Korean transmission lines and new insulators are tested for autoclave expansion. The compressive strength of the insulators aged in an autoclave with conditions of $250\;^{\circ}C$ and at 20 atm for 30 minutes, was about $7.6\;kgf/mm^2$, which is close to that measured on insulators aged for 10 years in the field. From simulation results, the cement displacement changed linearly with temperature. At a temperature of $200\;^{\circ}C$, the shear stress was approximately $7\;kgf/mm^2$; a stress that is brought about by a 0.07 % expansion of the cement. It is evident that the cement would fracture at a 0.07 % expansion, because the cement has about 7 to $9\;kgf/mm^2$ flexure strength. A turning point in the shear stress with mechanical load occurred at 0.02 % cement expansion. From an analysis of the porcelain body it is shown that there is sufficient margin of strength to guard against fracture of the porcelain body even for a cement expansion more than 0.12 %.

• Steel and Composite Structures
• /
• 제28권1호
• /
• pp.111-121
• /
• 2018

It has been argued that fracture energy of composite laminates depends on their thickness and number of layers. In this paper a modified direct energy balance approach (DEBA) has been developed to evaluate the mode-II shear fracture energy for E-glass/Epoxy laminates from finite element model at an arbitrary thickness. This approach considers friction and damage/plasticity deformations using cohesive zone modeling (CZM) and nonlinear finite element modeling. The presence of compressive stress and resulting friction was argued to be a possible cause for the thickness dependency of fracture energy. In the finite element modeling, CZM formulation has been developed with bilinear cohesive constitutive law combined with friction consideration. Also ply element have been developed with shear plastic damage model. Modified direct energy balance approach has been proposed for estimation of mode-II shear fracture energy. Experiments were performed on laminates of glass epoxy specimens for characterization of material parameters and determination of mode-II fracture energies for different thicknesses. Effect of laminate thickness on fracture energy of transverse crack tension (TCT) and end notched flexure (ENF) specimens has been numerically studied and comparison with experimental results has been made. It is shown that the developed numerical approach is capable of estimating increase in fracture energy due to size effect.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2000년도 봄 학술발표회 논문집
• /
• pp.745-750
• /
• 2000

Steel plate bonding technique is most widely used in strengthening of existing concrete structures, but it has inherently a problem of the premature failure such as interface separation and rip off. So far, many studies have been arid out in the manner of laboratory tests for the reinforced concrete beams to find out he mechanism of the premature failure. However, in order to verify the characteristics of the premature failure, more reasonable local investigations are needed rather than such relatively global experimental works. In this study, therefore, the double lap test which simulate the pure shear loadings and the half beam tests which consider combined flexure-shear force have been done. There are, however, difficulties in getting the normal stress caused to premature failure, so that finite element analysis was performed, too. In numerical study, material nonlinearity was considered, and the interface element was applied to model the interface between steel plate and adhesive. From the results of experimental and numerical studies, a realistic failure criterion on the separation of steel plates has been derived.

• Smart Structures and Systems
• /
• 제1권4호
• /
• pp.385-404
• /
• 2005

The paper presents a model to calculate reinforcement strain using measured crack width in members under applied tension, flexure, and/or shear stress. Crack mapping using a new type of distributed coaxial cable sensors for health monitoring of large-scale civil engineering infrastructure was recently proposed and developed by the authors. This paper shows the results and performance of such sensors mounted on near surface of two flexural beams and a large scale reinforced concrete box girder that was subjected to cyclic combined shear and torsion. The main objectives of this health monitoring study was to correlate the sensor's response to strain in the member, and show that magnitude of the signal's reflection coefficient is related to increases in applied load, repeated cycles, cracking, and reinforcement yielding. The effect of multiple adjacent cracks, and signal loss was also investigated. The results shown in this paper are an important step in using the sensors for crack mapping and determining reinforcement strain for in-situ structures.

• 대한건축학회논문집:구조계
• /
• 제36권2호
• /
• pp.145-153
• /
• 2020

The purpose of this study is to investigate the effects of composition of underground structural wall and H-pile in soil cement. The results of previous experimental studies are re-analyzed and the nonlinear cross-sectional analyses of composite basement walls are performed to verify their nonlinear flexural behavior. Based on the study, it is explained how the gap deformation between H-Pile and RC wall should be considered in the design of flexure of composite underground walls. The nonlinear cross-sectional analysis shows that the load-displacement curves of composite basement wall specimens exhibiting flexural behavior exist between the results of the analysis of the complete and non-composite cases. When predicting the behavior of the composite basement wall by nonlinear cross-sectional analysis, the flexural behavior of the composite basement wall could be suitably predicted by considering the reduction of the composite ratio due to tensile stress acting on shear connectors.

• 한국건축시공학회지
• /
• 제12권1호
• /
• pp.115-121
• /
• 2012

클링커 대신 고로슬래그, 폐인산석고, 폐석회 등의 산업 부산물을 이용하여 비소성시멘트를 제조하면 산업부산물 재활용, 클링커 제조를 위한 에너지 감소, $CO_2$저감으로 인한 환경오염문제 및 생산원가 저감 등의 장점이 있다. 이러한 이유로 본 연구에서는 비소성 시멘트 콘크리트의 역학적 거동실험을 수행하여 비소성 시멘트 콘크리트의 탄성계수, 응력-변형률 관계를 제안하였다. 또한 철근비, 압축강도를 변수로 9개의 구조 시험체를 제작하였으며, 그 실험 결과 비소성 시멘트 콘크리트의 휨 및 전단 거동 경향은 일반 콘크리트 부재와 크게 차이나지 않는 것으로 나타났다.

• 콘크리트학회논문집
• /
• 제26권6호
• /
• pp.687-694
• /
• 2014

이 연구에서는 철근콘크리트 전단벽의 경계요소의 연성설계를 위한 변위연성비모델을 제시하였다. 부재의 길이에 따른 곡률과 자유단에서의 변위를 산정하기 위한 전단벽의 단면의 변형률 및 내부힘들의 분포는 베르누이(Bernoulli)의 정리, 변형률 적합조건 및 힘의 평형조건을 이용하여 이상화하였다. 경계요소내의 횡보강근에 의한 구속효과는 Razvi and Saatcioglu에 의해 제시된 콘크리트의 응력-변형률 관계를 이용하여 고려하였다. 항복시 및 최대내력 이후 최대모멘트 80%에서의 곡률은 등가소성 힌지길이 개념을 도입하여 변위값으로 환산하였다. 일반화된 변위연성비의 모델은 다양한 범위에서 수행된 변수연구로부터 얻어진 데이터들의 회귀분석을 통하여 단순식으로 정립되었다. 제시된 단순모델은 실험결과 대비 평균, 표준편차 및 변동계수가 각각 1.05, 0.19 및 0.18로 대부분의 실험결과의 경향을 잘 예측하였다. 따라서 제시된 모델은 경계요소에서 소요연성비에 따른 횡보강근의 상세를 결정하는데 쉽게 이용될 수 있을 것으로 기대된다.