• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 가을 학술발표회 논문집
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• pp.577-580
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• 2003

Problem of repairing by boring is that it deteriorates stabelety and durability of structure by permeation of seawater from underneath after damage and repair of reinforcing rod regarding of spot. The purpose of this study is to improve the porblem by using the repair method of general boring to mend the of large mat basis. Direction of thes experiment is to apply the new repair material and the method to control the blazing fire factor caused by the crack from the foundation of large mat and also to estimate it's integrity. New method of construction is method of contruction that do speace scurity in vertical drilling and bottom useing water jet. New material used bantonite and rubberized asphalt. Test result existent repair method of construction large size mat basis perforation is difficult and reinforcing rod can be damaged coule there were a lot of problems with re-water leakage of crack repair region, but overcomes existent short coming by method that apply in this study.

• Computers and Concrete
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• 제20권6호
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• pp.689-704
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• 2017

The paper presents experimental and numerical investigations of prefabricated composite structural building reinforced concrete slabs with the insulating material for a residential building construction. The building slabs were composed of concrete and expanded polystyrene. In experiments, the slabs in the full-scale 1:1 were subjected to vertical concentrated loads and failed along a diagonal shear crack. The experiments were numerically evaluated using the finite element method based on two different constitutive continuum models for concrete. First, an elasto-plastic model with the Drucker-Prager criterion defined in compression and with the Rankine criterion defined in tension was used. Second, a coupled elasto-plastic-damage formulation based on the strain equivalence hypothesis was used. In order to describe strain localization in concrete, both models were enhanced in the softening regime by a characteristic length of micro-structure by means of a non-local theory. Attention was paid to the formation of critical diagonal shear crack which was a failure precursor.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2021년도 가을 학술논문 발표대회
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• pp.196-197
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• 2021

The underground method can be divided into Top-Down, Semi-Top-Down, Up-Up and Down-Up methods according to the construction order of the upper and lower structures. Among them, the Down-Up method proceeds with the construction of the first floor and its lower floors, and when the foundation is completed, the vertical members of the basement are sequentially completed from the foundation and the above-ground floor is constructed. In this paper, the crack reduction method around the open section of the Down-Up method affected by earth pressure was analyzed and divided into design and construction parts.

• 암석학회지
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• 제8권1호
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• pp.24-33
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• 1999

화강암에 대한 미세균열의 특성을 규명하기 위하여 노은리와 궁기리의 2개소 화강암을 대상으로 차분 변형율 분석(Differential Strain Analysis)을 실시하였다. 변형율은 압력을 처음 50MPa 까지는 5MPa씩, 50~100MPa에서는 10MPa씩, 250MPa 까지는 15MPa 씩 압력을 가하였다. 변형율 분석을 위하여 코아 시료의 수직바향과 수평방향에 각각 변형율 게이지를 부착하였다. 수직방향과 수평방향의 누적 균열 변형율은 매우 큰 편차를 보여주고 있어 미세균열의 발달에 이방성을 보임을 알수 있다. 수직방향의 누적 균열 변형율이 가장 큰 값을 보여 수평방향과 평행한 미세균열이 가장 잘 발달 해 있음을 지시하며, 이는 문경지역 화강암류 석제의 "결" 방향(rift plane)과 일치하고 있음을 알 수 있다. 240 MPa의 압력하에서 발생한 균열 변형율은 각각 N-1 : 174$\times$10-6~820$\times$10-6, N-2:190$\times$10-6~460$\times$10-6, G-1 : 329$\times$10-6~836$\times$10-6, G-1 : 833$\times$10-6~1,592$\times$10-6이다. 또한 250MPa의 압력에서 체적 균열 변형율은 궁기리지역 석재가 1,804$\times$10-6~3,936$\times$10-6, 노은리 지역의 석재가 1,125$\times$10-6~1,457$\times$10-6으로서 전자가 후자에 비해 훨씬 많은 미세균열들이 분포하고 있으며 "결" 의 발달상태가 더 양호한 것으로 나타났다. 화강암의 "결"과 미세균열의 방향성을 측정하기 위하여 최대 균열 변형율과 최소 균열 변형율의 비($\varepsilon$max/$\varepsilon$min)를 계산하였다. 그 비는 2.42에서 3.43까지의 높은 값을 가지는데, 이는 연구지역의 조립질 화강암류 석재에 발달되어 있는 미세균열은 대부분이 일정한 방향성을 보이는 입자내 균열임을 시사한다.분이 일정한 방향성을 보이는 입자내 균열임을 시사한다.

• 국제초고층학회논문집
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• 제4권4호
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• pp.283-290
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• 2015

Crack control remains a primary concern for mass concrete structures, where the majority of cracking is caused by temperature changes during the hydration process. One-time pouring is a useful construction method for mass concrete structures. The suitability of this method for constructingon of the Shanghai Tower's mass concrete foundation slab of Shanghai Tower is considered here by a numerical simulation method based on a 6- meter- thick slab. Some of the conclusions, which can be verified by monitoring results conducted during construction, are as follows. The temperature gradient is greater in the vertical direction than in the radial direction, therefore, the vertical temperature gradient should be carefully considered for the purpose of crack control. Moreover, owing to cooling conditions at the surfaces and the cement mortar content of the slab, the temperatures and temperature gradients with respect to time vary according to the position within the slab.

• Structural Engineering and Mechanics
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• 제82권3호
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• pp.313-323
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• 2022

Steel laminated elastomeric bearings are commonly used in bridge structures to control displacements and rotations and transfer forces from the superstructure to the substructure. Proper knowledge of design, fabrication and erection procedures is important to ensure stability and adequate structural performance during the lifetime of the bridge. Difference in elevations sometimes leads to large size gaps between the bearing and the girder which makes the grout thickness that is commonly used for leveling deviate beyond standards. This paper investigates the structural response of High Strength Fiber Reinforced Cementitious (HSFRC) thin plinths that are used to close gaps between bearing pads and precast girders. An experimental program was developed for this purpose where HSFRC plinths of different size were cast and tested under vertical loads that simulate bridge loading in service. The structural performance of the plinths was closely monitored during testing, mainly crack propagation, vertical reaction and displacement. Analytically, the HSFRC plinth was analyzed using the beam on elastic foundation theory as the supporting elastomeric bearing pads are highly compressible. Closed form solutions were derived for induced displacement and forces and comparisons were made between analytical and experimental results. Finally, recommendations were made to facilitate the practical use of HSFRC plinths in bridge construction based on its enhanced load carrying capacity in shear and flexure.

• 콘크리트학회논문집
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• 제17권3호
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• pp.369-374
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• 2005

이 연구의 목적은 화상처리 기법과 신경회로망을 이용하여 다섯가지 균열 패턴 즉, 횡방향, 종방향, 대각선($-45^{\circ}$) 대각선($+45^{\circ}$) 그리고 비방향성 균열의 패턴을 인식할 수 있는 기법을 제안하는 것이다. 제안된 화상처리 알고리즘과 인공 신경회로망 모델은 MATLAB 언어를 이용하여 구현하였다. 인공 신경회로망의 입력층에 들어갈 패턴인자는 Total projection technique를 통해 구하였으며, 인공 신경회로망의 구조(은닉층의 수와 은닉노드의 수)와 가중치 값은 가상 균열 화상을 사용하여 학습을 통해 결정하였다. 인공 신경회로망의 학습은 Bayesian regularization 기법을 도입함으로써 과적합 문제가 발생하지 않도록 하였으며, 이 연구에서 제안한 기법의 적합성을 판정하기 위하여 총 38개의 실제 균열 화상을 사용하여 시험하였다. 검증 시험 결과내에서는 이 연구에서 제안한 기법이 사람의 균열 패턴 인식결과와 정확히 일치하는 결과것으로 나타났다.

• 한국지진공학회논문집
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• 제28권1호
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• pp.47-57
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• 2024

Recently, in newly constructed apartment buildings, the exterior wall structures have been characterized by thinness, having various openings, and a significantly low reinforcement ratio. In this study, a nonlinear finite element analysis was performed to investigate the crack damage characteristics of the exterior wall structure. The limited analysis models for a 10-story exterior wall were constructed based on the prototype apartment building, and nonlinear static analysis (push-over analysis) was performed. Based on the finite element (FE) analysis model, the parametric study was conducted to investigate the effects of various design parameters on the strength and crack width of the exterior walls. As the parameters, the vertical reinforcement ratio and horizontal reinforcement ratio of the wall, as well as the uniformly distributed longitudinal reinforcement ratio and shear reinforcement ratio of the connection beam, were addressed. The analysis results showed that the strength and deformation capacity of the prototype exterior walls were limited by the failure of the connection beam prior to the flexural yielding of the walls. Thus, the increase of wall reinforcement limitedly affected the failure modes, peak strengths, and crack damages. On the other hand, when the reinforcement ratio of the connection beams was increased, the peak strength was increased due to the increase in the load-carrying capacity of the connection beams. Further, the crack damage index decreased as the reinforcement ratio of the connection beam increased. In particular, it was more effective to increase the uniformly distributed longitudinal reinforcement ratio in the connection beams to decrease the crack damage of the coupling beams, regardless of the type of the prototype exterior walls.

• 동력기계공학회지
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• 제15권1호
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• pp.39-44
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• 2011

This study was to investigate the effects of stress ratio and anisotropy on Fatigue Crack Propagation(FCP) behavior of rolled magnesium alloy AZ31B. The experimental materials were a Mg-Al-Zn magnesium alloy. The FCP test was conducted on compact tension specimen by a servo-hydraulic fatigue testing machine in air at room temperature. Compact tension specimens were prepared from the extruded parallel and vertical rolling direction. The test condition was frequency of 10Hz and sinusoidal load stress ratios are 0.1 and 0.7. The FCP rates was automatically measured by a compliance method. In the case of the FCP of AZ31B, the FCP of both direction of LT and TL by anisotropy of specimens are almost same value. In lower stress ratio, the FCP of the LT, TL specimens are increased in lower ${\Delta}K$ region but higher ${\Delta}K$ regions are almost same value. Finally, the result of observed the surface crack, it expressed the quasi-cleavage fracture in lower ${\Delta}K$ region and straight mark on the aspect of the facet in high ${\Delta}K$ region.

• 한국정밀공학회지
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• 제27권11호
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• pp.30-36
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• 2010

Previous researches show that linearly integrated Hall sensor arrays (LIHaS) can detect cracks in the steel structure fast and effectively This paper proposes an algorithm that estimates the size and shape of cracks for the developed LIHaS. In most nondestructive testing (NDT), just crack existence and location are obtained by processing 1-dimensional data from the sensor that scans the object with relative speed in single direction. The proposed method is composed with two steps. The first step is constructing 2-dimensionally mapped data space by combining the converted position data from the time-based scan data with the position information of sensor arrays those are placed in the vertical direction to the scan direction. The second step is applying designed Laplacian filter and smoothing filter to estimate the size and shape of cracks. The experimental results of express train wheels show that the proposed algorithm is not only more reliable and accurate to detecting cracks but also effective to estimate the size and shape of cracks.