• 한국도로학회논문집
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• 제14권4호
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• pp.63-72
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• 2012

PURPOSES : Hot-mix asphalt(HMA) concretes show a trend of strength increase at low temperature due to binder stiffness increase, but strength decrease below a ceratin low temperature. This is due to the differential thermal contraction(DTC) which is induced by a significant difference in coefficients of thermal contraction between aggregate and asphalt which is coated around the aggregate. This DTC damage is well known to occur in HMA concrete, but is not yet investigated in warm-mix asphalt(WMA) concretes. METHODS : To evaluate DTC damage on WMA in this study, the flexural strength($S_f$) of WMA concretes, which were produced at $30{\sim}40^{\circ}C$ lower temperature, was evaluated in comparison with that of HMA at -5, -15 and $-25^{\circ}C$. RESULTS : Most of WMA and HMA mixtures showed flexural strength increase down to $-15^{\circ}C$ and decrease below $-15^{\circ}C$. this type of strength reduction below $-15^{\circ}C$ can e explained as the effect of differential thermal contraction that is a consequence of the large difference in coefficients of thermal contraction between aggregate and asphalt. the property reduction of WMA is similar the result of previous works dealt with HMA mixtures. CONCLUSIONS : Even though there is some differences by materials used, the WMA concretes showed a significantly lower DTC damage than HMA concrete at low temperature at ${\alpha}$=0.05 level.

• 한국건축시공학회지
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• 제24권2호
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• pp.193-202
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• 2024

본 연구에서는 초음파 속도법을 콘크리트의 초기동해 피해를 진단하기 위한 방법으로서의 적용 가능성을 평가하기 위해 모르타르 시험체를 대상으로 각각 동결 깊이에 따른 압축강도와 초음파 펄스 속도를 측정하여 미세구조와 그 상관관계를 분석하였다. 그 결과, 동결 피해를 입은 모르타르 시험체와 피해를 입지 않은 시험체 간의 압축강도와 초음파 펄스 속도 값의 차이가 확연하게 나타났으며, 미세구조 분석을 통해 동결 깊이가 증가할수록 초기동해 피해를 더 많이 받아 압축강도와 초음파 펄스 속도가 감소하였다고 판단할 수 있었다. 회귀분석을 통해 상관관계를 분석한 결과, 추정식과 실험값과의 관계성을 나타내는 결정계수( R²)가 0.87로 얻어져 초기동해 피해 깊이에 따른 압축강도와 초음파 펄스 속도 사이의 상호 연관성이 존재하는 것으로 분석된다. 이에 따라 초음파 속도법을 통한 콘크리트의 초기동해 피해 진단이 가능하며, 그 피해 깊이를 정량적으로 진단하기 위해서는 향후 추가적인 연구가 필요할 것으로 판단된다.

• 한국해양공학회지
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• 제25권3호
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• pp.1-10
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• 2011

This paper estimates the residual longitudinal strength of a damaged double hull VLCC (Very Large Crude Carrier) under combined vertical and horizontal bending moments using Smith's method. The damage estimated in this study occurred due to collision or grounding accidents. The effects of the randomness of the yield stress, plate thickness, extent of damage, and the combination of these three parameters on the ultimate hull girder strength were investigated. Random variables were generated by a Monte Carlo simulation and applied to the double hull VLCC described by the ISSC (International Ship and Offshore Structures Congress) 2000 report.

• Computers and Concrete
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• 제20권3호
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• pp.291-295
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• 2017

Tests on the fracture behavior of CFRP-concrete composite bonded interfaces have been extensively carried out. In this study, a progressive damage model is employed to simulate the fracture behaviors. The crack nucleation, propagation and more other details can be captured by these models. The numerical results indicate the fracture patterns seem to depend on the relative magnitudes of the interface cohesive strength and concrete tensile strength. The fracture pattern transits from the predominated adhesive-concrete interface debonding to the dominated concrete cohesive cracking as the interface cohesive strength changes from lower than concrete tensile strength to higher than that. The numerical results have an agreement with the experimental results.

• 한국해양공학회지
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• 제9권1호
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• pp.47-56
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• 1995

This study is aimed to have a database of system development for the prediction, monitoring, analyzing, and evaluation of tensile strength and damage characteristics through AE technique for CFRP. Therefore the correlations between impact characteristics (such as impact velocity, impact energy, delamination area etc) and AE signals for CFRP laminates were investigated. And also it were accomplished the evaluation of tensile strength and the investigation on correlation with AE signals for impact damaged specimen of CFRP laminates.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 봄 학술발표회 논문집
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• pp.411-416
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• 2000

The behavior of high strength reinforced concrete columns subjected to uniaxal reversal loading and biaxial reversal circle path loading was investigated. Four full scale test specimens were tested. All specimens were adopted cantilever type, in order that the critical region is to locate only at the bottom of column. The parameters studied were transverse reinforcement ratio, uniaxial lateral loading and biaxial lateral loading. The damage features of columns by the biaxial loading are different from those of the uniaxial loading, However, the maximum strength and the draft angle at maximum strength were almost the same under uniaxial and biaxial loading. The transverse reinforcement under biaxial loading was very effective for increasing ductility of specimens.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.1580-1587
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• 2005

To calculate the long-term allowable strength of geosynthetic reinforcement, replacement method was recommended. The isochronous creep curve by S. Turner was used to define the relation between creep strain and allowable strength. In isochronous curve at given time, one can read the allowable strength at allowable creep strain. The allowable strain gets from specification by directors or manufacturers according to the allowable displacement of reinforced structures. The allowable strength can be determined in relation to the allowable horizontal displacement each structures case by case. The effect of install damage on isochronous behaviors of geosynthetic reinforcement was little. In previous study, install damage increase the creep strain slightly. And the degradation was not identified. But it is supposed that degradation increase the creep strain. In conclusion, The recommended model to determine long-term allowable strength of geosynthetic reinforcements considering tensile deformation of reinforcement and soil is fit for proper, correct and economic design for reinforced earth walls.

• Steel and Composite Structures
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• 제33권3호
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• pp.433-444
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• 2019

Fatigue failure of a grid structure using bolt-sphere joints is liable to occur in a high-strength bolt due to the alternating and reciprocal actions of a suspension crane. In this study, variable amplitude fatigue tests were carried out on 20 40 Cr steel alloy M30 high-strength bolts using an MTS fatigue testing machine, and four cyclic stress amplitude loading patterns, Low-High, High-Low, Low-High-Low, and High-Low-High, were tested. The scanning electron microscope images of bolt fatigue failure due to variable amplitude stress were obtained, and the fractographic analysis of fatigue fractures was performed to investigate the fatigue failure mechanisms. Based on the available data from the constant amplitude fatigue tests, the variable amplitude fatigue life of an M30 high-strength bolt in a bolt-sphere joint was estimated using both Miner's rule and the Corten-Dolan model. Since both cumulative damage models gave similar predictions, Miner's rule is suggested for estimating the variable-amplitude fatigue life of M30 high-strength bolts in a grid structure with bolt-sphere joints; the S-N fatigue curve of the M30 high-strength bolts under variable amplitude loading was derived using equivalent stress amplitude as a design parameter.

• Journal of Advanced Research in Ocean Engineering
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• 제1권4호
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• pp.198-210
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• 2015

This paper presents the damage assessment of a free-fall dropped object on the seabed. The damage to a dropped object totally depends on the relationship between the impact energy and the soil strength at the mudline. In this study, unexpected dropping scenarios were first assumed by varying the relevant range of the impact velocity, structure geometry at the moment of impact, and soil strength profile along the penetration depth. Theoretical damage assessments were then undertaken for a free-fall dropping event with a fixed final embedment depth for the structure. This paper also describes the results of a three-dimensional large deformation finite element analysis undertaken for the purpose of validation. The analyses were carried out using the coupled Eulerian-Lagrangian approach, modifying the simple elastic-perfectly plastic Tresca soil model. The validation exercises for each dropping scenario showed good agreement, and the present numerical approach was capable of predicting the behavior of a free-fall dropped object.

• 대한기계학회논문집A
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• 제25권8호
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• pp.1189-1196
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• 2001

The objective of this paper is to investigate the applicability of acoustic emission(AE) technique to monitor the progress of the thermal shock damage on alumina ceramic. For this purpose, alumina ceramic specimen was heated in the furnace and then was quenched in the water tank. When the specimen was quenched in the water tank, complex AE signals due to the initiation of micro-cracks and boiling effect were generated by the progress of thermal shock damage. These mixed AE signals have to be classified for monitoring the degree of the thermal shock damage of alumina ceramics. In this paper, the mixed AE signals generated from both the boiling effect and the crack initiation under thermal shock test was analyzed. The characteristics of AE signals were also discussed by considering the variation of bending strength and Yongs modulus of specimens.