• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.849-854
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• 2002

From the analysis results of some as-built drawings in national roadway bridges in Korea, many bridge piers are expected to show complex shear-flexural behaviour under earthquakes. But the previous research works about the seismic evaluation of bridges considered flexural behaviour RC piers only. In addition, the past bridge design specifications in Korea didn't include limitation on the amount of longitudinal lap splices in the plastic hinge zone of piers. Thus a large majority of non-seismically designed bridge piers in Korea may have lap splices in plastic hinge zone. In this study, prototype pier was selected among existent bridge piers whose failure mode is expected to be complex shear-flexural mode. And then, full scale and 1/2 reduced scale model RC piers with various longitudinal lap splice details were constructed. From the quasi static test results on these model RC piers, the effect of longitudinal lap splices on the seismic performance of bridges piers was analyzed. And the seismic capacity of the non-seismically designed shear-flexural RC piers was evaluated.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.145-150
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• 2003

The objective of this study is to investigate the effect of torsional eccentricity on the seismic response of high-rise RC bearing-wall structures with vertical irregularity. For this purpose, two 1:12 scale 17-story RC model structures, the one has concentric shear wall and the other has eccentric shear wall, were constructed and then subjected to a series of earthquake excitations. The test result shows the followings: 1) the layout of shear wall has the negligible effect on the natural period and the base shear coefficient, 2) the eccentric model behaves in the first and second mode while the concentric model has the first mode predominantly, 3) the stiff frame in the eccentric model resists most of overturning moment in the severe earthquake though both frames (the stiff and flexible frames) resist almost equally in the design earthquake.

• 한국안전학회지
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• 제13권1호
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• pp.40-46
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• 1998

This paper is presented that theoretical optimization design method in order to consider mass reduction for the structural safety In this paper, it described methods for reducing vibration in structural safety by the determination of the optimum sizes and locations of tunning masses through formal mathematical optimization techniques. The optimization procedure which employs the tunning masses and corresponding locations is developed. Design variables are systematically changed to achieve low values of shear without a large mass penalty. Three optimization methods ire developed and tested. The first is based on minimizing the modal shaping parameter which indirectly reduce the modal shear amplitudes corresponding to each harmonic of airload. The second method reduces these amplitudes directly and the third method reduces the shear as a function of time during a revolution of the blade. The first method works well for reducing the shear for one mode responding to a single harmonic of the airload but has been found in some bases to be ineffective for more than one mode.

• Steel and Composite Structures
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• 제34권2호
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• pp.241-260
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• 2020

This article presented a comprehensive model to study static buckling stability and associated mode-shapes of higher shear deformation theories of sandwich laminated composite beam under the compression of varying axial load function. Four higher order shear deformation beam theories are considered in formulation and analysis. So, the model can consider the influence of both thick and thin beams without needing to shear correction factor. The compression force can be described through axial direction by uniform constant, linear and parabolic distribution functions. The Hamilton's principle is exploited to derive equilibrium governing equations of unified sandwich laminated beams. The governing equilibrium differential equations are transformed to algebraic system of equations by using numerical differential quadrature method (DQM). The system of equations is solved as an eigenvalue problem to get critical buckling loads and their corresponding mode-shapes. The stability of DQM in determining of buckling loads of sandwich structure is performed. The validation studies are achieved and the obtained results are matched with those. Parametric studies are presented to figure out effects of in-plane load type, sandwich thickness, fiber orientation and boundary conditions on buckling loads and mode-shapes. The present model is important in designing process of aircraft, naval structural components, and naval structural when non-uniform in-plane compressive loading is dominated.

• Steel and Composite Structures
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• 제31권2호
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• pp.113-123
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• 2019

In this study, carbon fiber/epoxy (CF/EP) composites were interleaved with aramid nonwoven veils with an areal weight density of $8.5g/m^2$ to improve their Mode-I fracture toughness. The control and aramid interleaved CF/EP composite laminates were manufactured by VARTM in a [0]4 configuration. Tensile, three-point bending, compression, interlaminar shear, Charpy impact and Mode-I (DCB) fracture toughness values were determined to evaluate the effects of aramid nonwoven fabrics on the mechanical performance of the CF/EP composites. Thermomechanical behavior of the specimens was investigated by Dynamic Mechanical Analysis (DMA). The results showed that the propagation Mode-I fracture toughness values of CF/EP composites can be significantly improved (by about 72%) using aramid nonwoven fabrics. It was found that the main extrinsic toughening mechanism is aramid microfiber bridging acting behind the crack-tip. The incorporation of these nonwovens also increased interlaminar shear and Charpy impact strength by 10 and 16.5%, respectively. Moreover, it was revealed that the damping ability of the composites increased with the incorporation of aramid nonwoven fabrics in the interlaminar region of composites. On the other hand, they caused a reduction in in-plane mechanical properties due to the reduced carbon fiber volume fraction, increased thickness and void formation in the composites.

• 대한토목학회논문집
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• 제9권4호
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• pp.63-71
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• 1989

고강도(高強度) 콘크리트 보의 전단균열강도와 극한전단강도를 조사하기 위하여 4개의 Series로 철근콘크리트 보를 실험(實驗)하였다. 모든 보는 전단보강철근(剪斷補強鐵筋)이 없는 단철근 보로 하였으며, 주변수는 콘크리트 강도로써 공시체 압축강도를 $247kg/cm^2$(3500 psi)에서 $708kg/cm^2$(10000 psi)까지 변화(變化)시켰다. 각 Series는 콘크리트 강도를 일정(一定)하게 하고서, 보의 전단지간(剪斷支間) 대(對) 유효(有效)깊이의 비(比)(a/d)를 2에서 5까지 변화(變化)시켰다. 실험결과(實險結果)에 따르면, 전단지지력(剪斷支持力)에 대한 콘크리트 강도(強度)의 영향은 보의 a/d에 따라 각기 달랐을 뿐만 아니라 현행(現行) 시방서의 전단설계규정은 철근콘크리트 보의 전단지지력을 산정하는데 일정성이 없음을 보였다. 본 연구에서는 전단지간(剪斷支間) 대 유효(有效)깊이의 비(比)의 변화(變化)에 따른 전단강도(剪斷強度)에 대(對)한 콘크리트 압축강도(壓縮強度)의 영향을 고려하기 위하여 shear failure mode index를 사용한 극한전단강도식(極限剪斷強度式)을 제안(提案)하여 타당성을 검토하였다.

• 대한금속재료학회지
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• 제49권8호
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• pp.635-641
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• 2011

The effect of high shear speed on shear force, shear energy and fracture surface was investigated for the solder joint of a $Sn-_{3.0}Ag-_{0.5}Cu$ ball. For both ENIG and OSP pads, the shear force increased with an increase in shearing speed to 0.3 m/s. However, for an ENEPIG pad, the shear force increased with an increase in shear speed to 0.6 m/s and kept almost constant afterward. The shear energy decreased with an increase in shearing speed for ENIG and OSP pads. For the ENEPIG pad, however, the shear energy almost remained constant in a shearing speed range 0.3-3.0 m/s. The fracture mode analysis revealed that the amount of brittle fracture for the ENIG and the OSP pads increased with shearing speed, and a complete brittle fracture appeared at 1.0 m/s for ENIG and 2.0 m/s for OSP. However, the ENEPIG pad showed only a ductile fracture until 0.25 m/s, and a full brittle fracture didn't occur up to 3.0 m/s. The fracture mode matched well with the shear energy. The results from the high speed shear test of SAC305 were similar to those of SAC105.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.69-72
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• 2006

The objective of this study is to find out the shear capacity of URM wall and the variables that affect the shear capacity of URM wall such as the opening and the aspect ratio, considering four kinds of failure modes, sliding shear failure, toe crushing failure, and diagonal shear failure. The main varialble is the shape of opening of URM walls. First URM has one door, second has one window, third hase one door and one window, the last has two windows. The test results of URM with openings show that the specimens are governed by rocking failure mode.

• 대한기계학회논문집
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• 제13권5호
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• pp.911-920
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• 1989

본 연구에서는 층간균열면에서의 보 두께비를 달리함에 따라 다양한 혼합 모우드 층간파괴인성을 평가할 수 있는 Fig.1과 같은 층간균열 시편에 대해 3점 굽힘하중 하중이 작용될 때의 전체어너지방출률을 전단변형을 고려한 보이론에 의해 유도하고 이를 층간균열면에서의 보 두께비에 따라 모우드I 성분과 모우드II 성분의 분리된 형태로 나타내었다. 또 한 여러가지 시편두께에 대해 전체에너지방출률을 구해 전단변형에 의한 에너지방출률이 전체에너지방출률에 미치는 영향도 조사하였다. 그리고 층간 균열면에서의 보 두께비가 0.3, 0.5, 0.6, 0.7, 그리고 0.9인 경우의 층간균열시편에 대해 실험적으로 혼합모우드 층간 파괴인성을 평가하고 혼합 모우드 변형을 받을 때의 층간파괴 거동도 조사하였다.

• Korean Journal of Radiology
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• 제21권9호
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• pp.1045-1054
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• 2020

Objective: This study aimed to evaluate the diagnostic value of combining the quantitative parameters of shear wave elastography (SWE) and superb microvascular imaging (SMI) to breast ultrasound (US) to differentiate between benign and malignant breast masses. Materials and Methods: A total of 200 pathologically confirmed breast lesions in 192 patients were retrospectively reviewed using breast US with B-mode imaging, SWE, and SMI. Breast masses were assessed based on the breast imaging reporting and data system (BI-RADS) and quantitative parameters using the maximum elasticity (Emax) and ratio (Eratio) in SWE and the vascular index in SMI (SMI_VI). The area under the receiver operating characteristic curve (AUC) value, sensitivity, specificity, accuracy, negative predictive value, and positive predictive value of B-mode alone versus the combination of B-mode US with SWE or SMI of both parameters in differentiating between benign and malignant breast masses was compared, respectively. Hypothetical performances of selective downgrading of BI-RADS category 4a (set 1) and both upgrading of category 3 and downgrading of category 4a (set 2) were calculated. Results: Emax with a cutoff value of 86.45 kPa had the highest AUC value compared to Eratio of 3.57 or SMI_VI of 3.35%. In set 1, the combination of B-mode with Emax or SMI_VI had a significantly higher AUC value (0.829 and 0.778, respectively) than B-mode alone (0.719) (p < 0.001 and p = 0.047, respectively). B-mode US with the addition of Emax, Eratio, and SMI_VI had the best diagnostic performance of AUC value (0.849). The accuracy and specificity increased significantly from 68.0% to 84.0% (p < 0.001) and from 46.1% to 79.1% (p < 0.001), respectively, and the sensitivity decreased from 97.6% to 90.6% without statistical loss (p = 0.199). Conclusion: Combining all quantitative values of SWE and SMI with B-mode US improved the diagnostic performance in differentiating between benign and malignant breast lesions.