• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.700-703
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• 2010

일반적으로 구조부재의 안전성 평가는 계측된 센서의 변형률로부터 부재의 최대응력 또는 부재력 수준을 결정하고 설계기준에 의한 부재의 허용응력 또는 설계 강도와의 비교에 의해서 이루어진다. 그러나 이러한 설계기준은 건물의 설계단계에서 미리 가정된 하중 및 부재의 강도에 대한 여러 확률분포 또는 안전율을 반영하여 작성된 것으로 실질적으로 센서로부터 측정한 데이터를 직접 설계기준에 반영하는 것은 합리적이지 못하다. 본 연구에서는 실제 센서로부터 측정되는 변형률을 이용하여 합리적으로 구조부재의 안전성 평가를 수행하기 위한 방법을 모색하고자 한다. 설계기준을 고려한 변형률 제한치, 저감계수가 도입되었으며 이에 추가적으로 센서와 관련한 계수를 도입하여 구조부재의 안전성 평가를 위한 방향을 제시한다.

• Journal of Korean Society of Steel Construction
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• v.12 no.6
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• pp.701-713
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• 2000

In this study, the 4-point bending test been performed in order to estimate effect of grinding on fatigue characteristics quantitatively for as-welded specimen, grinding specimen & TIG-dressing specimen for non load-carrying fillet welded joints subjected to pure bending. As a result of fatigue tests, fatigue strength at $2{\times}106$cycles of grinding specimen and TIG-dressing specimen has been increased compared with as-welded specimen and satisfied the grade of fatigue strength prescribed in specifications of domestics and AASHTO & JSSC. As a result of beachmark test, fatigue cracks on all specimens have occurred at several points where stress

• The Journal of Engineering Geology
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• v.11 no.3
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• pp.315-325
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• 2001

A series of laboratory tests was conducted to observe damage process by stress and to understand characteristics of permeability related with rock damage. Rock specimens which were composed of the Cretaceous medium grained granites were experienced of damage stress between 65% and 95% of the compressive strength. Rock deformation by damage process was identified with the elastic wave velocity test. Relationship between rock damage and permeability change was also analyzed by water injection test in the laboratory. According to the results of the tests, damage tends to be occurred from stress level of 80% of the compressive strength and it reduces elastic wave velocity. The damaged specimens with stress more than 80% of the compressive strength showed crack density more than 0.6 and persistent length with good connectivity of cracks. They also have higher permeability than that of specimens with crack density less than 0.6. Considered with the above results, the rock specimens used in this study were fully damaged from stress level of 80% of the compressive strength. Crack initiation and propagation by damage caused good connectivity of cracks through rock specimen. These damage process, therefore, brought high permeability coefficient through water flow conduit in the rock specimen.

• Journal of the Korean Wood Science and Technology
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• v.43 no.4
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• pp.456-462
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• 2015

365 pieces of domestic $38{\times}140{\times}3600mm$ Red pine structural lumber were machine graded conforming to a softwood structural lumber standard (KS F 3020). The allowable bending stresses calculated for each grade were compared with the values currently tabulated in the standard. Four calculation methods for lower $5^{th}$ percentile bending stress were non-parametric estimation with 75% confidence level, 2-parameter and 3-parameter Weibull distribution fit, and bending modulus of rupture (MOR)-modulus of elasticity (MOE) regression based method. Only the data set of Grades E8, E9, and E10 were statistically eligible for the $5^{th}$ percentile calculation. The MOR-MOE regression based method only was able to estimate the lower $5^{th}$ percentile values theoretically for the full range of grades. The results showed that all allowable bending stresses calculated were lower than the design values tabulated in the standard. This implies that the current machine grading system has the pitfall of structural safety. Improvement in current machine grading system could be achieved by introducing the bending strength and stiffness combination grade system.

• Tunnel and Underground Space
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• v.13 no.3
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• pp.180-186
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• 2003

The fracture processes under dynamic loading in tension were simulated using a proposed numerical approach and analyzed to determine dynamic tensile strength. The dynamic tensile strength and the scatter of the strength data decreased with increasing uniformity coefficients. The differences of static and dynamic tensile strength were due to the stress concentrations and redistribution mechanisms in the rock specimen. Although there were different mechanisms for the static and dynamic fracture processes, the static and dynamic tensile strengths were close to the mean microscopic tensile strength at high values of the uniformity coefficient. This paper shows that the rock inhomogeneity has an effect on dynamic tensile strength and is a factor that contributes to the different specimen strengths under dynamic and static loading conditions.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.1
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• pp.80-90
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• 2001

The aim of this study is to develop the methodology which enables to identify the mechanical properties of element such as stress intensity factor by using the AE parameters. Considering the multivariate and nonlinear properties of AE parameters such as ringdown count, rise time, energy, event duration and peak amplitude from fatigue cracks of machine element the principal component regression(PCR) and artificial neural network(ANN) models for the estimation of stress intensity factor were developed and validated. The AE parameters were found to be very significant to estimate the stress intensity factor. Since the statistical values including correlation coefficients, standard mr of calibration, standard error of prediction and bias were stable, the PCR and ANN models for stress intensity factor were very robust. The performance of ANN model for unknown data of stress intensity factor was better than that of PCR model.

• Proceedings of the KWS Conference
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• 1990.11a
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• pp.124-127
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• 1990

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.3
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• pp.202-208
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• 2014

For evaluating basic structural behavior of HVFA (High Volume Fly Ash) concrete, several tests are performed considering different ratios of fly ash replacement and structural evaluation regarding compressive strength, elasticity modulus, stress-strain relationship, and bond strength is also performed. Test results show that elasticity modulus of HVFA concrete has close relationships with compressive strength and fly ash replacement ratio. The ultimate strain shows slight difference from domestic design code. On the other hand, there are no differences between general concrete and HVFA concrete for elasticity modulus and bond strength.

• Journal of the Korean Geotechnical Society
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• v.21 no.9
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• pp.53-64
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• 2005

For geotechnical design in practice, soils are, in general, assumed to behave as a linear elastic or perfect plastic material. More realistic geotechnical design, however, should take into account various factors that affect soil behavior in the field, such as non-linearity of stress-strain response, stress history, and water content. In this study, a series of laboratory tests including triaxial and resonant column tests were peformed with sands of various silt contents, relative densities, stress states, OCR and water contents. This aims at investigating effects of various factors that affect strength and stiffness of sands. From the results in this study, it is found that the effect of OCR is significant for the intermediate stress-strain range from the initial to failure, while it may be ignored for the initial stiffness and peak strength. For the effect of water content, it is observed that the initial elastic modulus decreases with increasing water content at lower confining stress and relative density At higher confining stresses, the effect of water content Is found to become small.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.3
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• pp.194-200
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• 2013

In this paper, the results of composite laminate mechanical joints test(ASTM D5961) are compared with the theoretical strength calculations and FEM analysis results. To calculate the S.C.F.(stress concentration factor) on joint strength, equations on metallic and composite materials in ASM Handbook used and compared with experimental results. The difference of joint strength are compared by geometrical parameters and joining types(single/double lap joint). In FEM analysis, to find efficient FEM model on composite laminate mechanical joint, several FEM models are compared with experimental test results.