• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1994년도 봄 학술발표회 논문집
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• pp.13-18
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• 1994

Most widened bridges have been constructed by the joining-construction method that makes new and existing bridge structurally single structure. However, joing-construction method has several problems in design and construction viewpoint. Therefore, this study is conducted in order to investigate structural behavior of widened RC slab and traffic-induced vibration of existing bridge during placing and curing of new concrete by the prototype flexural fatigue test. From the results of this study, it is shown that stress-concentration and slip occur between concrete and reinforcing rod at joint section but the reduction of load carrying capacity and of fatigue strength is negligible according to the traffic-induced vibration as well as the difference of construction method. A reasonable construction method for the bridge widening which takes into account the effects of the traffic-induced vibration and S-N curve for the widened bridge are also proposed.

• Structural Engineering and Mechanics
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• 제56권6호
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• pp.983-1001
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• 2015

This study focuses on the load carrying capacity and the force transfer mechanism of multi-hole perfobond shear connectors in steel-concrete composite structure. The behavior of multi-hole perfobond shear connector is more complicated than single-hole connector cases. 2 groups push-out tests were conducted. Based on the test results, behavior of the connection was analyzed and the failure mechanism was identified. Simplified iterative method and analytic solution were proposed based on force equilibrium for analyzing multi-hole perfobond shear connector performance. Finally, the sensitivity of design parameters of multi-hole perfobond shear connector was investigated. The results of this research showed that shear force distribution curve of multi-hole perfobond shear connector is near catenary. Shear forces distribution were determined by stiffness ratio of steel to concrete member, stiffness ratio of shear connector to steel member, and number of row. Efficiency coefficient was proposed to should be taking into account in different limit state.

• Steel and Composite Structures
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• 제37권2호
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• pp.193-209
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• 2020

In this paper, the efficiency of five Machine Learning (ML) methods consisting of Deep Learning (DL), Support Vector Machine (SVM), Random Forest (RF), Decision Tree (DT), and Gradient Tree Booting (GTB) for regression and classification of the Ultimate Load Factor (ULF) of nonlinear inelastic steel frames is compared. For this purpose, a two-story, a six-story, and a twenty-story space frame are considered. An advanced nonlinear inelastic analysis is carried out for the steel frames to generate datasets for the training of the considered ML methods. In each dataset, the input variables are the geometric features of W-sections and the output variable is the ULF of the frame. The comparison between the five ML methods is made in terms of the mean-squared-error (MSE) for the regression models and the accuracy for the classification models, respectively. Moreover, the ULF distribution curve is calculated for each frame and the strength failure probability is estimated. It is found that the GTB method has the best efficiency in both regression and classification of ULF regardless of the number of training samples and the space frames considered.

• Nuclear Engineering and Technology
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• 제44권7호
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• pp.791-798
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• 2012

Since standardized fracture test specimens cannot be easily extracted from in-service components, several alternative fracture toughness test methods have been proposed to characterize the deformation and fracture resistance of materials. One of the more promising alternatives is the local approach employing the SP(Small Punch) testing technique. However, this process has several limitations such as a lack of anisotropic yield potential and tediousness in the damage parameter calibration process. The present paper investigates estimation of ductile fracture resistance(J-R) curve by FE(Finite Element) analyses using an anisotropic damage model and enhanced calibration procedure. In this context, specific tensile tests to quantify plastic strain ratios were carried out and SP test data were obtained from the previous research. Also, damage parameters constituting the Gurson-Tvergaard-Needleman model in conjunction with Hill's 48 yield criterion were calibrated for a typical nuclear reactor material through a genetic algorithm. Finally, the J-R curve of a standard compact tension specimen was predicted by further detailed FE analyses employing the calibrated damage parameters. It showed a lower fracture resistance of the specimen material than that based on the isotropic yield criterion. Therefore, a more realistic J-R curve of a reactor material can be obtained effectively from the proposed methodology by taking into account a reduced load-carrying capacity due to anisotropy.

• 콘크리트학회논문집
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• 제26권3호
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• pp.267-275
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• 2014

최근 곡선교 사용이 증가함에 따라 기존 곡선 교량의 한계점을 극복하고자 PSC 곡선 주형을 이용한 곡선교에 대한 해석적 연구가 활발히 진행되고 있다. 그러나 기존의 프레임 요소를 이용한 격자해석방법으로는 PSC 곡선교에 대한 정밀해석이 어렵다. 이에 따라 이 연구에서는 PSC 곡선교의 정밀 유한 요소 해석을 실시하여 프리캐스트 PSC 곡선교의 설계를 위한 참고자료로 사용하고자 한다. 이를 위하여 3차원 솔리드 요소를 사용한 모델링을 실시하고, 거더 수, 하중 재하 위치, 단면 변화, 긴장력 변화 및 편긴장력 도입 여부와 같은 매개변수에 대한 거동을 평가하였다. 해석 결과 경간장 50 m 3주형 교량의 항복하중과 파괴 하중이 경간장 40 m 2주형 교량에 비해 200% 이상의 성능을 보였고, 외측거더에 하중을 가하였을 경우 도심의 위치에 따라 하중저항력 및 거더 간의 처짐 편차가 낮게 평가되는 것으로 나타났다. 또한 거더 단면을 변화시킨 경우 단면의 증가에 따라 구조성능이 향상되는 것으로 나타났으나 PS도입량의 변화에 의한 효과에 비해 경제성과 시공성에서 불리한 것으로 나타났다. PS 도입량 변화에 따른 영향을 분석한 결과 PS 도입량이 증가함에 따라 솟음량과 하중저항력이 비례하여 증가하였으며 거더 간 처짐 편차가 줄어드는 경향을 보였다. 또한, 편긴장력을 도입하였을 시 도입량 증가에 비례하여 내외측 거더 모두에서 하중저항력이 증가하며, 특히 외측거더에 편긴장력이 도입되었을 때 더 우수한 성능을 보이는 것으로 나타나, PSC 곡선교의 경제성 및 안정성을 확보하는데 효율적인 것으로 나타났다.

• 한국구조물진단유지관리공학회 논문집
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• 제26권6호
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• pp.73-81
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• 2022

최근 구조물의 사용연한이 증가함에 따라 다양한 요인에 의해 철근이 부식되어 구조물의 내하력이 감소하는 문제들이 발생하고 있다. 이를 해결하기 위하여 내식성, 경량성, 고인장강도를 갖는 FRP 보강근의 부착특성에 대한 연구가 활발히 진행중이나, 콘크리트에 매립된 격자형 CFRP 보강재의 부착특성에 관한 연구는 미흡한 실정이다. 따라서 격자형 CFRP 보강재를 철근의 대체재로 사용하고 사용성 측면에서 부착특성을 평가하기 위해, 격자형 CFRP 보강재의 종방향 부착길이와 횡방향 격자길이를 변수로 하여 직접인발시험을 수행하였다. 이를 통해 격자형 CFRP 보강재의 부착하중-슬립 곡선을 도출하였으며, 부착거동을 분석하였다. 총 부착하중 식은 종방향 부착길이의 부착력과 횡방향 격자의 전단력의 합으로 제안하였으며, 부착하중-슬립곡선의 면적을 전체 일로 표현하여 슬립량에 대한 에너지 소산량의 변화를 분석하여 횡방향 격자가 부착력에 미치는 영향에 대하여 검토하였다.

• Structural Engineering and Mechanics
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• 제32권2호
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• pp.251-267
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• 2009

Reinforced concrete (RC) structures consist of two different materials: concrete and steel bar. The stress transfer behaviour between the two materials through bond plays an important role in the load-carrying capacity of RC structures, especially when they subject to lateral load such as blast and seismic load. Therefore, bond and slip between concrete and reinforcement bar will affect the response of RC structures under such loads. However, in most numerical analyses of blast-induced structural responses, the perfect bond between concrete and steel bar is often assumed. The main reason is that it is very difficult to model bond slip in the commercial finite element software, especially in hydrodynamic codes. In the present study, a one-dimensional slide line contact model in LS-DYNA for modeling sliding of rebar along a string of concrete nodes is creatively used to model the bond slip between concrete and steel bars in RC structures. In order to model the bond slip accurately, a new approach to define the parameters of the one-dimensional slide line model from common pullout test data is proposed. Reliability and accuracy of the proposed approach and the one-dimensional slide line in modelling the bond slip between concrete and steel bar are demonstrated through comparison of numerical results and experimental data. A case study is then carried out to investigate the bond slip effect on numerical analysis of blast-induced responses of a RC column. Parametric studies are also conducted to investigate the effect of bond shear modulus, maximum elastic slip strain, and damage curve exponential coefficient on blast-induced response of RC columns. Finally, recommendations are given for modelling the bond slip in numerical analysis of blast-induced responses of RC columns.

• 한국강구조학회 논문집
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• 제19권4호
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• pp.425-434
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• 2007

SC 합성기둥은 기존의 합성기둥들이 가지는 내력상승, 방청효과, 공사기간 단축이 가능하고, 충전상태의 육안확인도 용이하여 이와 관련된 연구가 활발히 진행되고 있지만 SC합성기둥의 내화성능에 관한 연구는 미흡한 실정이다. 이에 본 논문에서는 SC합성기둥의 내화성능평가를 위해 하중비, 콘크리트 면적비, 피복유무를 변수로 두어 실험을 수행하였다. 또한 온도증가에 따른 실험체의 강도감소를 단순 수치해석으로 산출하여 내화성능시간을 유추하였고, 실험결과와 비교분석 하였다. 이 실험을 통하여 하중비가 작을수록 내화성능은 향상되었다. 그러나 콘크리트 면적비는 SC합성기둥의 내화성능 향상에 큰 영향을 미치지 못하였다.

• Tribology and Lubricants
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• 제31권2호
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• pp.50-55
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• 2015

This study investigates the effects of a pattern of 200 μm dimples in a hexagonal array on tribological characteristics. A textured surface might reduce the friction coefficient and wear caused by third-body abrasion and thus improve the tribological performance. There are three friction conditions based on the Stribeck curve: boundary friction, mixed friction, and fluid friction conditions. In this experiment, we investigate the friction characteristics by carrying out the friction tests at sliding speeds ranging from 0.06 to 0.34 m/s and normal load ranging from 10 to 100 N. We create dimple surfaces for texturing by using the photolithography method. There are three kinds of specimens with different dimple densities ranging from 10% to 30%. The dimple density on the surface area is the one of the important factors affecting friction characteristics. Friction coefficient generally decreases with an increase in the velocity and load, indicating that the lubrication regime changes depending on the load and velocity. The fluid friction regime is fully developed, as indicated by the duty number graph. Fluid friction occurs at a velocity of 0.14-0.26 m/s. The best performance is seen at 10% dimple density and 200 μm dimple circle in the hexagonal array.

• 대한토목학회논문집
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• 제35권4호
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• pp.863-874
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• 2015

본 연구에서는 보강날개로 보강된 수중잠제 지지말뚝의 보강효과를 분석하기 위하여 하중전이거동을 분석하였다. 먼저 3차원 유한요소해석을 통해 말뚝의 변위 및 하중전이곡선(지반반력) 결과로부터 보강효과를 확인하고, 하중전이곡선에서 극한저항력 비율로 보강말뚝의 수평 및 인발하중에 대한 보강계수를 산정함으로써 보강효과를 정량화 하였다. 산정된 보강계수를 쌍곡선 하중전이함수의 극한저항력 $p_u$와 $t_{max}$에 곱해서 보정상수(fitting parameter)로 적용하여 보강효과를 고려한 하중전이함수를 제안하였다. 제안된 하중전이함수가 수치해석 결과를 잘 반영하고 있는지 확인하기 위해 3차원 유한요소해석을 비교하여 보강말뚝의 하중전이거동을 분석하였다. 제안된 하중전이함수를 하중전이법 해석에 적용하여, 실제 수중잠제를 해석한 결과 보강말뚝의 전단력, 휨 모멘트, 변위가 무보강말뚝보다 작게 발생하고, 지반반력은 더 크게 발생하여 비교적 경제적인 설계가 가능할 것으로 판단된다.