• Smart Structures and Systems
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• 제14권2호
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• pp.71-83
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• 2014

The purpose of this paper is to investigate the flexible structure of parabolic shell using photostrictive actuators. The analysis is made to know its dynamic behavior and light-induced control forces for coupled parabolic shell. The effects of an actuator location as well as membrane and bending components under the control action have been analyzed considering the approximate spherical model. The parabolic membrane shell accuracy is being mathematically approximated and validated comparing the light induced control forces using approximate equivalent spherical shell model. The parabolic shell with kapton smart material and photostrictive actuators has been used to formulate the governing equation in the transverse direction. The Kirchhoff-Love assumptions are used to obtain the governing equation of shell with actuator. The mechanical membrane forces and bending moments for parabolic thin shell with actuator is used to analyze the dynamic effect. The results show that membrane control action is much more significant than bending control action. Photostrictive actuators oriented along circumferential direction (actuator-2) can give better control effect than actuators placed along longitudinal direction (actuator-1). The slight difference is observed between spherical and parabolic shell for a surface with focal length to the diameter ratio of 1.00 or more than unity. Space applications often have the shape of parabolical shells or shell of revolution, due to their required focusing, aiming, or reflecting performance. The present approach is focused that photostrictive actuators can effectively control the vibration of parabolical membrane shell. Also, the actuator's location plays an important role in defining the control force.

• Earthquakes and Structures
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• 제17권5호
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• pp.435-445
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• 2019

The collapses of curved bridges are mainly caused by the damaged columns, subjected to the combined loadings of axial load, shear force, flexural moment and torsional moment, under earthquakes. However, these combined loadings have not been fully investigated. This paper firstly investigated the mechanical characteristics of the bending-torsion coupling effects, based on the seismic response spectrum analysis of 24 curved bridge models. And then 9 reinforced concrete (RC) and circular column specimens were tested, by changing the bending-tortion ratio (M/T), axial compression ratio, longitudinal reinforcement ratio and spiral reinforcement ratio, respectively. The results show that the bending-torsion coupling effects of piers are more significant, along with the decrease of girder curvature and the increase of pier height. The M/T ratio ranges from 6 to 15 for common cases, and influences the crack distribution, plastic zone and hysteretic curve of piers. And these seismic characteristics are also influenced by the compression ratio, longitudinal reinforcement ratio and spiral reinforcement ratios of piers.

• Steel and Composite Structures
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• 제43권4호
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• pp.483-500
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• 2022

Cold-formed steel wall panels sheathed with gypsum plasterboard have shown superior thermal and structural performance in fire. Recent damage caused by fire events in Australia has increased the need for accurate fire resistance ratings of wall systems used in low- and mid-rise construction. Past fire research has mostly focused on light gauge steel framed (LSF) walls under uniform axial compression and LSF floors under pure bending. However, in reality, LSF wall studs may be subject to both compression and bending actions due to eccentric loading at the wall to-roof or wall-to-floor connections. In order to investigate the fire resistance of LSF walls under the effects of these loading eccentricities, four full-scale standard fire tests were conducted on 3 m × 3 m LSF wall specimens lined with two 16 mm gypsum plasterboards under different combinations of axial compression and lateral load ratios. The findings show that the loading eccentricity can adversely affect the fire resistance level of the LSF wall depending on the magnitude of the eccentricity, the resultant compressive stresses in the hot and cold flanges of the wall studs caused by combined loading and the temperatures of the hot and cold flanges of the studs. Structural fire designers should consider the effects of loading eccentricity in the design of LSF walls to eliminate their potential failures in fire.

• Structural Engineering and Mechanics
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• 제85권2호
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• pp.233-246
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• 2023

Bending and buckling analysis of multi-directional porous functionally graded sandwich plate has been performed for two cases namely: FG skin with homogeneous core and FG core with homogeneous skin. The principle of virtual displacements was employed and the solution was obtained using Navier's technique. This theory imposes traction-free boundary conditions on the surfaces and does not require shear correction factors. The validation of the present study has been performed with those available in the literature. The composition of metal-ceramic-based FGM changes in longitudinal and transverse directions according to the power law. Different porosity laws, such as uniform distribution, unevenly and logarithmically uneven distributions were used to mimic the imperfections in the functionally graded material that were introduced during the fabrication process. Several sandwich plates schemes were studied based on the plate's symmetry and the thickness of each layer. The effects of grading parameters and porosity laws on the bending and buckling of sandwich plates were examined.

• Wind and Structures
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• 제4권1호
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• pp.45-62
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• 2001

This paper is focused on the torsional effects that are induced on bridge piers by unbalanced wind buffeting on the deck during double cantilever erection stages. The case of decks with variable cross section is considered in particular as this characteristic is typical of most frame bridges that are built by the cantilever method. The procedure outlined in the paper is basically an application of the method that Dyrbye and Hansen (1996) have illustrated for decks with constant cross section. This format was chosen because it is suitable for design purposes and may easily be implemented in structural codes. As a complement, the correspondence with the format that is adopted in the Canadian code (NBCC 1990) for the gust factor is established, which might be useful to bridge designers used to the North-American approach to the gust effects on structures. Only alongwind turbulence and horizontal movements of the deck are considered. The combination of torsional and bending effects is also discussed and it is illustrated with an example of application.

• Advances in materials Research
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• 제8권2호
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• pp.137-154
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• 2019

In this study, thermal effects on the mechanical properties of cement mortars with some types of fibers is investigated. The replaced fibers were made of polypropylene (PP), aramid, glass and basalt. In other words, the main goal of this paper is to study the effects of different fibers on the mechanical properties of cement mortars after subjecting to normal and sub-elevated temperatures. The experimental tests used for investigating these effects were compressive, splitting tensile, and four-point bending tests at 20, 100 and $300^{\circ}C$, respectively. Moreover, the microstructures of the specimens in different temperatures were investigated using scanning electron microscope (SEM). Based on the experimental results, the negative effects of sub-elevated temperatures on four-point bending tests were much more than the others. Moreover, using the fibers with higher melting points could not improve the qualities of the samples in sub-elevated temperatures.

• Journal of the Korean Wood Science and Technology
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• 제34권2호
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• pp.46-57
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• 2006

To estimate nondestructively strength performances of laminated woods, 3-ply parallel- and cross-laminated wood specimens exposed under atmosphere conditions after bending creep test were prepared for this study. The effects of density of species, arrangement of laminae and lamination types on dynamic MOE obtained by flexural vibration were investigated, and regression analyses were conducted in order to estimate static bending strength and bending creep performances. Dynamic MOE of parallel-laminated woods showed 1.0~1.2 times higher values than static bending MOE, and those of cross-laminated woods showed 1.0~1.4 times higher values than static bending MOE. The degree of anisotropy of dynamic MOE perpendicular to the grain of face laminae versus that parallel to the grain of face laminae was markedly decreased by cross-laminating. There were strong correlations between dynamic MOE by flexural vibration and static bending MOE (correlation coefficient r = 0.919~0.972) or bending MOR (correlation coefficient r = 0.811~0.947) of 3-ply laminated woods, and the correlation coefficient were higher in parallel-laminated woods than in cross-laminated woods. It indicated that static bending strength performances were able to be estimated from dynamic MOE by flexural vibration. Also, close correlations between the reciprocal of dynamic MOE by flexural vibration and initial compliance at 0.008 h of 3-ply laminated woods were found (correlation coefficient r = 0.873~0.991). However, the correlation coefficient between the reciprocal of dynamic MOE and creep compliance at 168 h of 3-ply laminated woods was considerably lower than those between dynamic MOE and initial compliance, and it was hard to estimate creep compliance with a high accuracy from dynamic MOE due to the variation of creep deformation.

• Corrosion Science and Technology
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• 제14권3호
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• pp.120-126
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• 2015

The usage of bending products recently have increased since many industries such as automobile, aerospace, shipbuilding, and chemical plants need the application of pipings. Bending process is one of the inevitable steps to fabricate the facilities. Induction heat bending is composed of compressive bending process by local heating and cooling. This work focused on the effect of induction heat bending process on the properties of ASME SA312 Gr. TP304 stainless steel pipes. Tests were performed for base metal and bended area including extrados, intrados, crown up, and down parts. Microstructure was analyzed using an optical microscope and SEM. In order to determine intergranular corrosion resistance, Double Loop Electrochemical Potentiokinetic Reactivation (DL-EPR) test and ASTM A262 practice A and C tests were done. Every specimen revealed non-metallic inclusion free under the criteria of 1.5i of the standard and the induction heat bending process did not affect the non-metallic inclusion in the alloys. Also, all the bended specimens had finer grain size than ASTM grain size number 5 corresponding to the grain sizes of the base metal and thus the grain size of the pipe bended by induction heat bending process is acceptable. Hardness of transition start, bend, and transition end areas of ASME SA312 TP304 stainless steel was a little higher than that of base metal. Intergranular corrosion behavior was determined by ASTM A262 practice A and C and DL-EPR test, and respectively step structure, corrosion rate under 0.3 mm/y, and Degree of Sensitization (DOS) of 0.001~0.075% were obtained. That is, the induction heat bending process didn't affect the intergranular corrosion behavior of ASME SA312 TP304 stainless steel.

• 대한토목학회논문집
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• 제43권5호
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• pp.567-576
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• 2023

일반적으로 RC 보 부재는 휨 부재로서 휨 하중에 대해서만 고려하여 설계된다. 하지만, 실제 건축물에서는 부재 간의 연속성으로 인해 축력과 휨 하중을 동시에 받게 된다. 이로 인해 RC 보 부재의 휨 강도는 증가하지만, 변위는 감소하며, 균열은 주로 보의 중앙부에 집중되게 된다. 따라서 본 연구에서는 축력과 휨 하중을 동시에 받는 RC 보 부재에 탄소섬유시트를 이용한 보강에 따른 휨 성능을 실험적으로 평가하였다. 탄소섬유시트는 부재의 중앙부에 감싸 보강을 하였으며, 축력과 휨 하중을 부재에 가력하였다. 축력의 크기와 탄소섬유시트 보강에 따른 철근콘크리트 부재의 파괴 형태, 휨 강도, 처짐 및 연성을 분석하였다. 그 결과, 축력의 증가에 따라 최대 휨 강도의 상승이 발생하였지만, 연성은 최대 64%까지 감소하였다. 탄소섬유시트 보강을 통해 휨 강도는 최대 27% 증가하였으며, 휨에 의한 보의 최대 처짐은 8% 감소하였으며 연성은 최대 43% 증가하였다.

• 대한토목학회논문집
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• 제36권4호
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• pp.595-604
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• 2016

본 연구에서는 현행 도로교설계기준의 KL-510 하중을 적용하여 장지간 바닥판의 내측 지간에 따른 캔틸레버 바닥판의 설계휨모멘트를 제안하였다. 장지간 바닥판의 내측 지간은 6.0~12.0m 범위를 대상으로 하였고, 캔틸레버 바닥판의 길이는 내측 지간의 30~50%를 적용하였다. 설계휨모멘트의 결정을 위해 바닥판의 직교이방성, 거더의 강성, 그리고 다차로재하계수의 영향을 반영하였으며, 이를 기존의 DB-24 하중에 대한 설계휨모멘트와 비교하였다.