• Steel and Composite Structures
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• 제4권5호
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• pp.385-402
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• 2004

Nearly 400 composite railway bridge decks of a new kind belonging to the trough type with U-shaped cross section have been constructed in Belgium over the last fifteen years. The construction of these bridge decks is rather complex with the preflexion of precambered steel girders, the prestressing of a concrete slab and the addition of a 2nd phase concrete. Until now, they have been designed with a classical computation method using a pseudo-elastic analysis with modular ratios. Globally, they perform according to the expectations but variability has been observed between the measured and the computed camber of these bridge decks just after the transfer of prestressing and also at long-term. A statistical analysis of the variability of the relative difference between the measured camber and the computed camber is made for a sample of 36 bridge decks using no less than 10 variables. The most significant variables to explain this variability at prestressing are the ratio between the maximum tensile stress reached in the steel girders during the preflexion and the yield strength and the type of steel girder. For the same sample, the long-term camber under permanent loading is computed by two methods and compared with measurements taken one or two years after the construction. The camber computed by the step-by-step method shows a better agreement with the measured camber than the camber computed by the classical method. The purpose of the paper is to report on the statistical analysis which was used to determine the most significant parameters to consider in the modeling in order to improve the prediction of the behaviour of these composite railway bridge decks.

• 한국응용과학기술학회지
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• 제34권1호
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• pp.125-131
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• 2017

콘크리트 혼화제의 무수축 그라우트에서 산란체와 흡수체의 영향은 빛산란에 의해 파장에 대한 산란세기로 설명된다. New Austria Tunnel Method의 수지에 대한 산란의 분자특성들은 연구하기 위해 Monte Carlo Simulation하였다. 이는 산란매질에서 광학적 파라미터들(${\mu}_s$, ${\mu}_a$, ${\mu}_t$)에 의해 조사되어 그들의 영향을 알 수 있었다. 산란매질에서 광자에 대한 빛 분포에 의한 결과는 광원에서 검출기까지 거리가 가까우면 무수축혼화제의 산란이 증가하여 산란세기가 크게 나타나는데 혼화제가 첨가함에 따라 무수축 성질이 크게 나타났다. 이는 강구조물의 내구성을 위한 코팅과 부식에서 좋은 모델을 디자인하는데 도움이 될 것이다.

• 콘크리트학회지
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• 제7권3호
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• pp.175-186
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• 1995

매시브 콘크리트 구조물의 균열선단의 응력확대계수를 구하는 데 표면적분법을도입하였다. 표면적분법은 경로적분인 J-적분법을 근저로 하여 유도가 된다. J-적분법에서는 균열면의 압력고 구조물의 물체력을 고려할 수가 없는 반면에 본 이론은 이러한 일반 하중조건을 고려할 수가 있으므로 보다 정확한 균열선단부의 응력상태를 고찰하는데 유용하다. 또한 균열선단부의 특이성을 표현하기 위해 특이요소를 사용하거나 균열선단부의 세밀한 요소분할을 요하는 등의 불편함을 제거할 수 있는 기법이다. 본 이론을 바탕으로 응력확대계수$K_I$, $K_{II}$를 구하는 프로그램을 작성하였으며 8절점 등매개 변수요소를 사용하여 $K_I$, $K_{II}$를 검증하였으며 실제 댐 구조물에 적용시켜 응력확대계수의 변화를 살펴보았다.

• Computers and Concrete
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• 제17권5호
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• pp.673-692
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• 2016

In the standards, minimum reinforcement ratios are presented as the least reinforcement ratios that bearing elements should have in a way to include all systems and in general. However, naturally these general minimum ratios might be presented as being lower than the normally required reinforcement ratios by criteria such as system size, bearing system arrangement, section situation and distributions of the elements and earthquake effect. In this case, minimum reinforcement ratios may remain as meaningless restrictions. Then grouping the criterion that might affect reinforcement ratios according to certain parameters and creating minimum reinforcement ratios regarding preliminary design will provide ease and safety during the project designing. Moreover, it will enable fast and simple examinations in the beginning of project control and evaluation process. By means of the data which could be defined as "preliminary design & minimum reinforcement ratios", a more realistic and safe restriction compared to general minimum reinforcement ratios could be presented. As a result of numerous comprehensive studies, reinforcement ratios to include all certain systems might be obtained. Today, thanks to the development level of finite elements programs which can make reinforced concrete modelling, with the studies that are impossible to carry out beforehand, this deficiency in the minimum reinforcement ratios in the standarts may at least be partially made up with the advisory regulation of preliminary design & minimum reinforcement ratios. As the structure of the system to be examined and the diversity of the parameters range from the specific to the general, preliminary design & minimum reinforcement ratios will approximate to general minimum reinforcement ratios in real terms. By focusing on a more specific system structure and diversity of the parameters, preliminary design and even design reinforcement ratios will be approximated. In this preliminary study, a route between these two extremes was attempted to be followed. Today, it is possible to determine suggested practical ratios for project designs through carrying out numerous studies.

• Earthquakes and Structures
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• 제15권3호
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• pp.335-350
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• 2018

This paper presents numerical modelling, modal testing, finite element model updating, linear and nonlinear earthquake behavior of a reinforced concrete building model. A 1/2 geometrically scale, two-storey, reinforced concrete frame model with raft base were constructed, tested and analyzed. Modal testing on the model using ambient vibrations is performed to illustrate the dynamic characteristics experimentally. Finite element model of the structure is developed by ANSYS software and dynamic characteristics such as natural frequencies, mode shapes and damping ratios are calculated numerically. The enhanced frequency domain decomposition method and the stochastic subspace identification method are used for identifying dynamic characteristics experimentally and such values are used to update the finite element models. Different parameters of the model are calibrated using manual tuning process to minimize the differences between the numerically calculated and experimentally measured dynamic characteristics. The maximum difference between the measured and numerically calculated frequencies is reduced from 28.47% to 4.75% with the model updating. To determine the effects of the finite element model updating on the earthquake behavior, linear and nonlinear earthquake analyses are performed using 1992 Erzincan earthquake record, before and after model updating. After model updating, the maximum differences in the displacements and stresses were obtained as 29% and 25% for the linear earthquake analysis and 28% and 47% for the nonlinear earthquake analysis compared with that obtained from initial earthquake results before model updating. These differences state that finite element model updating provides a significant influence on linear and especially nonlinear earthquake behavior of buildings.

• Computers and Concrete
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• 제20권5호
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• pp.605-616
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• 2017

Concrete filled steel tubular (CFST) composite girder is a new type of structures for bridge constructions. The existing design codes cannot be used to predict the thermal stress in the CFST truss girder structures under solar radiation. This study is to develop the temperature gradient curves for predicting thermal stress of the structure based on field and laboratory monitoring data. An in-field testing had been carried out on Ganhaizi Bridge for over two months. Thermal couples were installed at the cross section of the CFST truss girder and the continuous data was collected every 30 minutes. A typical temperature gradient mode was then extracted by comparing temperature distributions at different times. To further verify the temperature gradient mode and investigate the evolution of temperature fields, an outdoor experiment was conducted on a 1:8 scale bridge model, which was installed with both thermal couples and strain gauges. The main factors including solar radiation and ambient temperature on the different positions were studied. Laboratory results were consistent with that from the in-field data and temperature gradient curves were obtained from the in-field and laboratory data. The relationship between the strain difference at top and bottom surfaces of the concrete deck and its corresponding temperature change was also obtained and a method based on curve fitting was proposed to predict the thermal strain under elevated temperature. The thermal stress model for CFST composite girder was derived. By the proposed model, the thermal stress was obtained from the temperature gradient curves. The results using the proposed model were agreed well with that by finite element modelling.

• Advances in concrete construction
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• 제11권5호
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• pp.429-445
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• 2021

With regard to economic efficiency, composite fix beams are widely used to pass longitudinal shear forces across the interface. The current knowledge of the composite beam load-slip activity and shear capability are restricted to data from measurements of push-off. Modelling and analysis of the composite beams based on Euro-code 4 regarding to shear, bending, and deflection under differing loads were carried out using Finite Element through an efficient computer simulation and the final loading and sections capacity based on the failure modes was analysed. In bending, the section potential was increased by an improvement of the strength in both steel and concrete, but the flexural and compressive resistance growth is very weak (3.2% 3.1% and 3.0%), while the strength of the concrete has increased respectively from 25 N/mm² to 30, 35, and 40 N/mm² compared to the increment of steel strength by 27% and 21% when it was raised from 275 to 355 and 460 N/mm², respectively. It was found that the final flexural load capacity of fix beams was declined with increase in the fix beam span for both three steel strength. The shear capacity of sections was remained unchanged at constant steel strength and different length, but raised with final yield strength increment of steel sections by 29%, and 67% when it was raised from 275 N/mm² to 355 N/mm² and 460 N/mm², respectively.

• Coupled systems mechanics
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• 제11권5호
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• pp.439-458
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• 2022

Over-coating is one of the most popular engineering practices to strengthen Reinforced Concrete (RC) structures, due to the relative quickness and ease of construction. It consists of an external coat bonded to the outer surface of the structural RC element, either by the use of chemical adhesives, mechanical anchor bolts or simply mortar injection. In contrast to these constructive advantages, the numerical estimation of the bearing capacity of the strengthened reinforced concrete element is still complicated, not only for the complexity of modelling a flexible membrane or plate attached to a quasi-rigid solid, but also for the difficulties that raise of simulating any potential delamination between both materials. For these reasons, the standard engineering calculations used in the practice remain very approximated and clumsy. In this work, we propose the formulation of a new 2D solid-layer finite element capable to link a solid body with a flexible thin layer, as it were the "skin" of the body, allowing the potential delamination between both materials. In numerical terms, this "skin" element is intended to work as a transitional region between a solid body (modelled with a classical formulation of a standard quadrilateral four-nodes element) and a flexible coat layer (modelled with cubic beam element), dealing with the incompatibility of Degrees-Of-Freedom between them (two DOF for the solid and three DOF for the beam). The aim of the solid-layer element is to simplify the mesh construction of the strengthened RC element being aware of two aspects: a) to prevent the inappropriate use of very small solid elements to simulate the coat; b) to improve the numerical estimation of the real bearing capacity of the strengthened element when the coat is attached or detached from the solid body.

• Coupled systems mechanics
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• 제12권6호
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• pp.481-501
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• 2023

Over-coating is one of the most popular engineering practices to strengthen Reinforced Concrete (RC) structures, due to the relative quickness and ease of construction. It consists of an external coat bonded to the outer surface of the structural RC element, either by the use of chemical adhesives, mechanical anchor bolts or simply mortar injection. In contrast to these constructive advantages, the numerical estimation of the bearing capacity of the strengthened reinforced concrete element is still complicated, not only for the complexity of modelling a flexible membrane or plate attached to a quasi-rigid solid, but also for the difficulties that raise of simulating any potential delamination between both materials. For these reasons, the standard engineering calculations used in the practice remain very approximated and clumsy. In this work, we propose the formulation of a new 2D solid-layer finite element capable to link a solid body with a flexible thin layer, as it were the "skin" of the body, allowing the potential delamination between both materials. In numerical terms, this "skin" element is intended to work as a transitional region between a solid body (modelled with a classical formulation of a standard quadrilateral four-nodes element) and a flexible coat layer (modelled with cubic beam element), dealing with the incompatibility of Degrees-OfFreedom between them (two DOF for the solid and three DOF for the beam). The aim of the solid-layer element is to simplify the mesh construction of the strengthened RC element being aware of two aspects: a) to prevent the inappropriate use of very small solid elements to simulate the coat; b) to improve the numerical estimation of the real bearing capacity of the strengthened element when the coat is attached or detached from the solid body.

• 한국구조물진단유지관리공학회 논문집
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• 제12권3호
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• pp.155-166
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• 2008

연구대상댐의 우안부는 콘크리트구조물로 축조된 콘크리트 중력식댐으로 이루어져 있고, 좌안부는 사력재료로 이루어진 사력댐으로 구성되어 있는 복합댐이다. 이련 형식의 댐 거동에 대한 연구에 있어서 국내는 물론 선진외국의 참고자료도 희소한 실정이다. 국내의 경우 약 17,000의 저수시설물중 복합댐 형식은 지자체나 기타 기관에서 관리하는 생 공 용수댐의 경우 거의 존재하지 않으며, 설혹 존재하더라도 시설물의 관리자료가 전무한 실정으로, 국내 다목적댐 중 유일한 복합댐을 선정하여 중력식댐과 사력댐 접합부의 거동특성을 분석하였다. 본 연구에서는 해석적 방법에 의하여 복합댐의 동적 상호거동특성을 분석하기 위하여 댐 축을 기준으로 모델링하여 정적(유사정적법, 수정진도법) 및 동적해석을 수행하여, 지진시 콘크리트댐과 사력댐 접합부의 지진 응답해석을 분석하였다.