• Steel and Composite Structures
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• v.42 no.5
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• pp.711-722
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• 2022

In this paper, hyperbolic shear deformation plate theory is developed for thermal buckling of functionally graded plates with porosity by dividing transverse displacement into bending and shear parts. The present theory is variationally consistent, and accounts for a quadratic variation of the transverse shearstrains across the thickness and satisfies the zero traction boundary conditions on the top and bottom surfaces of the plate without using shear correction factors. Three different patterns of porosity distributions (including even and uneven distribution patterns, and the logarithmic-uneven pattern) are considered. The logarithmic-uneven porosities for first time is mentioned. Equilibrium and stability equations are derived based on the present theory. The non-linear governing equations are solved for plates subjected to simply supported boundary conditions. The thermal loads are assumed to be uniform, linear and non-linear distribution through-the-thickness. A comprehensive parametric study is carried out to assess the effects of volume fraction index, porosity fraction index, aspect ratio and side-to-thickness ratio on the buckling temperature difference of imperfect FG plates.

• Journal of the Korea Concrete Institute
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• v.27 no.3
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• pp.207-214
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• 2015

This study examined the feasibility of wire ropes as lateral reinforcement at the boundary element of heavyweight concrete shear walls. The spacing of the wire ropes varied from 60 mm to 120 mm at an interval of 30 mm, which produces the volumetric index of the lateral reinforcement of 0.126~0.234. The wire ropes were applied as a external hoop and/or internal cross-tie. Five shear wall specimens were tested to failure under constant axial load and cyclic lateral loads. Test results showed that with the increase of the volumetric index of the lateral reinforcement, the ductility of shear walls tended to increase, whereas the variation of flexural capacity of walls was minimal. The flexural capacity of shear walls tested was slightly higher than predictions determined from ACI 318-11 procedure. The displacement ductility ratio of shear walls with wire ropes was higher than that of shear wall with the conventional mild bar at the same the volumetric index of the lateral reinforcement. In particular, the shear walls with wire rope index of 0.233 achieved the curvature ductility ratio of more than 16 required for high-ductility design.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.10
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• pp.123-130
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• 2007

Hypoplastic left heart syndrome is currently the most lethal cardiac malformation of the newborn infant. Survival following a Norwood operation depends on the balance between systemic and pulmonary blood flow, which is highly dependent on the fluid dynamics through the interposition shunt between the two circulations. The purpose of this study is an optimization of the systemic-to-pulmonary artery shunt. In this study, We used computational fluid dynamic(CFD) models to determine the velocity profile in a systemic-to-pulmonary artery shunt and suggested a simplified method of calculating the blood flow in the shunt based on Ultrasound systems. We analyzed the flow characteristic variations and oscillatory shear index(OSI) due to the anastomosis angle and shunt diameter changing. Four different CFD models were constructed with the shunt sizes ranging from 3 to 3.5mm. The angle between the brachiocephalic trunk(BCT) and the shunt were $30^{\circ}$ and $45^{\circ}$, respectively. When the diameter is 3.0 mm, the oscillatory shear index decreased by 1.2% at $30^{\circ}$ as opposed to at $45^{\circ}$. When the diameter is 3.5 mm, it increased by 18% more at $30^{\circ}$ as opposed to at $45^{\circ}$. When the joint angle is $30^{\circ}$ and the diameter is 3.0 mm, the oscillatory shear index decreased by 4.1% in comparison with the 3.5 mm diameter. When the angle is $45^{\circ}$ and the diameter is 3.0 mm, the index increased by 14.6% in comparison with the 3.5 mm diameter.

• Structural Engineering and Mechanics
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• v.58 no.3
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• pp.397-422
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• 2016

In the present work, a simple first-order shear deformation theory is developed and validated for a variety of numerical examples of the thermal buckling response of functionally graded sandwich plates with various boundary conditions. Contrary to the conventional first-order shear deformation theory, the present first-order shear deformation theory involves only four unknowns and has strong similarities with the classical plate theory in many aspects such as governing equations of motion, and stress resultant expressions. Material properties and thermal expansion coefficient of the sandwich plate faces are assumed to be graded in the thickness direction according to a simple power-law distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic material. The thermal loads are considered as uniform, linear and non-linear temperature rises within the thickness direction. The results reveal that the volume fraction index, loading type and functionally graded layers thickness have significant influence on the thermal buckling of functionally graded sandwich plates. Moreover, numerical results prove that the present simple first-order shear deformation theory can achieve the same accuracy of the existing conventional first-order shear deformation theory which has more number of unknowns.

• Smart Structures and Systems
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• v.26 no.2
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• pp.253-262
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• 2020

In this paper, a new higher order shear deformation model is developed for static analysis of functionally graded beams with considering porosities that may possibly occur inside the functionally graded materials (FGMs) during their fabrication. The model account for higher-order variation of transverse shear strain through the depth of the beam and satisfies the zero traction boundary conditions on the surfaces of the beam without using shear correction factors. The present work aims to study the effect of the distribution forms of porosity on the bending of simply supported FG beam. Based on the present higher-order shear deformation model, the equations of motion are derived by the principle of virtual works. Navier type solution method was used to obtain displacement and stresses, and the numerical results are compared with those available in the literature. A comprehensive parametric study is carried out to assess the effects of volume fraction index, porosity fraction index, and geometry on the bending of imperfect FG beams. It can be concluded that the proposed model is simple and precise for the resolution of the behavior of flexural FGM beams while taking into account the shape of distribution of the porosity.

• Journal of Pharmaceutical Investigation
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• v.25 no.3
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• pp.213-221
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• 1995

The steady shear flow properties of six kinds of commercial toothpastes were measured using a concentric cylinder type rheometer. In this paper, the shear rate and temperature dependencies of their flow behavior were investigated and the validity of the Casson and Herschel-Bulkley models was examined. Further, the flow properties over a wide temperature range were quantitatively evaluated by calculating the various material parameters. Main results obtained from this study can be summarized as follows: (1) Toothpastes are plastic fluids with a yield stress and their flow behavior shows shear-thinning characteristics. (2) With increasing temperature, the degree of shear-thinning becomes weaker and the Newtonian flow behavior occurs at a lower shear rate range. (3) The Herschel-Bulkley model is more effective than the Casson model in predicting their flow behavior. (4) As the temperature increases, the yield stress, plastic viscosity and consistency index become smaller, on the contrary, the flow behavior index becomes larger.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09b
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• pp.68-75
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• 2010

Around the Nakdong River which is one part of the repairing business of 4 Grand Rivers currently being constructed, sandy ground is distributed throughout the wide area. Many civil engineering structures such as small and medium sized dams, flood control basins, and redevelopment of reservoirs and retention reservoirs are scheduled to be constructed, so the prevention measures for liquefaction are surely needed. To identify such liquefaction, a lot of factor affecting the strength of liquefaction were studied through laboratory investigation. Most of the conducted study was about clean sands, but in the case of the real ground the sand can exist not in the clean conditions but in the conditions mostly including sand of fine grained soil. The sand of fine grained soil has become a significant factor to assess liquefaction because many cases of liquefaction happened in the silty and clayer soil. In this study, un-drained tests of plasticity index of fine grained particles were conducted with the sands from Nakdong River. In result, the study shows that dynamic shear strength characteristics differ according to the plasticity index.

• Structural Engineering and Mechanics
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• v.84 no.2
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• pp.143-154
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• 2022

Corrosion of steel reinforcement is considered as the main cause of concrete structures deterioration, especially those under humid environmental conditions. Hence, fiber reinforced polymer (FRP) bars are being increasingly used as a replacement for conventional steel owing to their non-corrodible characteristics. However, predicting the shear strength of beams reinforced with FRP bars still challenging due to the lack of robust shear theory. Thus, this paper aims to develop an explicit data driven based model to predict the shear strength of FRP reinforced beams using multi-objective evolutionary polynomial regression analysis (MOGA-EPR) as data driven models learn the behavior from the input data without the need to employee a theory that aid the derivation, and thus they have an enhanced accuracy. This study also evaluates the accuracy of predictive models of shear strength of FRP reinforced concrete beams employed by different design codes by calculating and comparing the values of the mean absolute error (MAE), root mean square error (RMSE), mean (𝜇), standard deviation of the mean (𝜎), coefficient of determination (R²), and percentage of prediction within error range of ±20% (a20-index). Experimental database has been developed and employed in the model learning, validation, and accuracy examination. The statistical analysis illustrated the robustness of the developed model with MAE, RMSE, 𝜇, 𝜎, R², and a20-index of 14.6, 20.8, 1.05, 0.27, 0.85, and 0.61, respectively for training data and 10.4, 14.1, 0.98, 0.25, 0.94, and 0.60, respectively for validation data. Furthermore, the developed model achieved much better predictions than the standard predictive models as it scored lower MAE, RMSE, and 𝜎, and higher R² and a20-index. The new model can be used in future with confidence in optimized designs as its accuracy is higher than standard predictive models.

• Steel and Composite Structures
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• v.15 no.4
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• pp.399-423
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• 2013

In the present study, the thermal buckling behavior of functionally graded sandwich plates is studied using a new hyperbolic displacement model. Unlike any other theory, the theory is variationally consistent and gives four governing equations. Number of unknown functions involved in displacement field is only four, as against five in case of other shear deformation theories. This present model takes into account the parabolic distribution of transverse shear stresses and satisfies the condition of zero shear stresses on the top and bottom surfaces without using shear correction factor. Material properties and thermal expansion coefficient of the sandwich plate faces are assumed to be graded in the thickness direction according to a simple power-law distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic material. The thermal loads are assumed as uniform, linear and non-linear temperature rises across the thickness direction. The results reveal that the volume fraction index, loading type and functionally graded layers thickness have significant influence on the thermal buckling of functionally graded sandwich plates.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.11a
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• pp.391-398
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• 2000

The index properties of cohesive soils play an important role to examine entire tendency of soil properties. Especially, the Atterberg limits have a good correlation with compression and shear strength of cohesive soils. However, these values strongly depend on their testing methods. In this study, for Pusan clays the Atterberg limits were peformed under different conditions; for example, four kinds of specimen preparation, two kinds of testing equipment, and four kinds of estimating method. And a laboratory vane test was peformed to compare the undrained shear strength with that of the fall cone test. As experimental results, the value of liquid limit performed for oven-dried sample, followed in ASTM D4318, underestimated by about 10% compared to those of another three methods, irrespective to the used equipments. But the value of plastic limit was not influenced by sample preparation methods and equipments. The liquid limits by one-point methods(Leroueil et al., 1996; Nagaraj et al., 1981) were agreed well with those of different methods. Finally, the undrained shear strength by laboratory vane test was relatively larger than that of fall cone test, and the relationship between both showed a bad trend.