• Structural Engineering and Mechanics
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• v.56 no.3
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• pp.473-490
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• 2015

This paper presents the analysis of intermediate crack-induced (IC) debonding failure loads for reinforced concrete (RC) beams strengthened with adhesively-bonded fiber-reinforced polymer (FRP) plates or sheets. The analysis consists of the energy release and simple ACI methods. In the energy release method, a fracture criterion is employed to predict the debonding loads. The interfacial fracture energy that indicates the resistance to debonding is related to the bond-slip relationships obtained from the shear test of FRP-to-concrete bonded joints. The section analysis that considers the effect of concrete's tension stiffening is employed to develop the moment-curvature relationships of the FRP-strengthened sections. In the ACI method, the onset of debonding is assumed when the FRP strain reaches the debonding strain limit. The tension stiffening effect is neglected in developing a moment-curvature relationship. For a comparison purpose, both methods are used to numerically investigate the effects of relevant parameters on the IC debonding failure loads. The results show that the debonding failure load generally increases as the concrete compressive strength, FRP reinforcement ratio, FRP elastic modulus and steel reinforcement ratio increase.

• Proceedings of the KSR Conference
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• 2006.11b
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• pp.552-557
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• 2006

Since the 20th century, the business of railway was invaded by the invention of airplanes and vehicles in the field of the transportation of passenger and commercial products, however, in the 21st century, the fervent development of a high-speed railway made possible the huge capacity of transporting passengers and commercial freight, so the railway industry is facing a new era of railway revolution. The 200 years old railway tradition includes the history of railway bridges built in areas of river, valley and metropolitan region and in that, the number of constructions of railway bridges that is composed of cable-stayed bridges is increasing as one of the most optimal bridges considering the quality of materials and the span of continuous-welded long rail. Thanks to the minimized effects of the fixed load on the stiffening girder section by delivering the fixed load which is applied to the pylon with the composition of elastic supporting-points by using cables and the effective structural system that can throughly resist extra loads in addition to fixed load, the long-extended span of a bridge becomes possible. In this structural system, the load that is applied to the stiffening girder section forms a flow pattern and in the process of these load delivery, there will be a necessity to examine the concentration of stress occurred in the cable-anchor system of the cable.

• Wind and Structures
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• v.31 no.6
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• pp.483-493
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• 2020

Large cylindrical floating-roof tanks, constructed as oil containers, are usually distributed regularly in open area and easily exposed to severe wind loads. However, wind pressures around these grouped squat tanks appear to have not been clearly given in design codes or thoroughly studied in existing researches. This paper conducts a detailed investigation on wind loads on the external wall of a four-tank group in square arrangement. To achieve that, wind tunnel tests are carried out on both empty and full tank groups, considering various wind angles and spacing. Results show that 3 regions in elevation can be identified on the tank shell according to the circumferential wind pressure distribution. The upper 2 regions cover a relatively small portion of the shell where excessive negative pressures are spotted, setting an alarm to the design of the top angle and stiffening rings. By comparing results on grouped tanks to those on an isolated tank, grouping effects concerning wind angle, tank position in group and spacing are discussed. Deviations on pressure distributions that will compromise structural safety are outlined, including the increase of negative pressures, the shift of maximum pressure locations as well as the change of positive pressure range. And, several potentially unfavourable wind pressure distributions are selected for further analyses.

• Journal of KSNVE
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• v.8 no.1
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• pp.99-111
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• 1998

An analytical method using the substructure synthesis and assumed modes method is developed to investigate the effect of flexibility of bladed disk assembly on vibrational modes of flexible rotor system. In modeling the system, Coriolis forces, gyroscopic moments, and centrifugal stiffening effects are taken into account. Then the coupled vibrations between the shaft and bladed disk are extensively investigated using simplistic models, as the shaft rotational speed and the pretwist and stagger angles of blade are varied.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.5
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• pp.99-107
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• 1993

In this study, material nonlinear finite element program is developed to analyze reinforced concrete shell of arbitrary geometry considering tension stiffening effects. This study is capable of tracing the load-deformation response and crack propagation, as well as determining the internal concrete and steel stresses through the elastic, inelastic and ultimate ranges in one continuous computer analysis. The cracked shear retention factor is introduced to estimate the effective shear modulus including aggregate interlock and dowel action. The concrete is assumed to be brittle in tension and elasto-plastic in compression. The Drucker-Prager yield criterion and the associated flow rule are adopted to govern the plastic behavior of the concrete. The reinforcing bars are considered as a steel layer of equivalent thickness. A layered isoparametric flat finite element considering the coupling effect between the in-plane and the bending action was developed. Mindlin plate theory taking account of transverse shear deformation was used. An incremental tangential stiffness method is used to obtain a numerical solution. Numerical examples about reinforced concrete shell are presented. Validity of this method is studied by comparing with the experimential results of Hedgren and the numerical analysis of Lin.

• Journal of KSNVE
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• v.8 no.3
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• pp.477-484
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• 1998

An analytical procedure on the base of the substructure synthesis and assumed modes method is developed to investigate the flexibility effect of bladed disk assembly on vibrational modes of flexible rotor system. In modeling the system, Coriolis forces, gyroscopic moments, and centrifugal stiffening effects are taken into account. The coupled vibrations between the shaft and bladed disk are then extensively investigated through the numerical simulation of simplified models, with varying the shaft rotational speed and the prewist and stagger angles of the blade. It is found that the Coriolis and inertia forces and the inertia torque, which are induced by the one nodal diameter modes of the bladed disk and vary depending upon the stagger and prewist angles, lead to the coupled motions of the shaft and the bladed disk.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.10a
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• pp.101-109
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• 1997

An analytical procedure on the base of the substructure synthesis and assumed modes method is developed to investigate the flexibility effect of bladed disk assembly on vibrational modes of flexible rotor system. In modeling the system, Coriolis forces, gyroscopic moments, and centrifugal stiffening effects are taken into account. The coupled vibrations between the shaft and bladed disk are then extensively investigated through the numerical simulation of simplified models, with varying the shaft rotational speed and the pretwist and stagger angles of the blade. It is found that the Coriolis and inertia forces and the inertia torque, which are induced by the one nodal diameter modes of the bladed disk and vary depending upon the stagger and pretwist angles, lead to the coupled motions of the shaft and the bladed disk.

• Journal of Photoscience
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• v.3 no.3
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• pp.167-169
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• 1996

Absorption of UV light induces photocleavage of polymer chains to produce free radicals which initiate photodegradation of the polymer molecules. Discoloration, cracking of surface, stiffening, and decreasing of mechanical properties of polymeric products occur as a result of photodegradation of the polymers. Photostabilizers are added to the polymer systems in order to minimize the unwanted effects of UV light. It is well known that Hindered Amine Light Stabilizers (HALS) are one of the most effective photostabilizer for polymers.' HALS have been used in a large number of commercial polymers and predominantly used in styrenic and engineering plastics. They are efficient and cost-effective in many applications despite their high prices. However, low molecular weight HALS vaporize easily, emitting harmful amines, and have poor extraction resistance, decreasing their photostabilization effect. They also decompose during processing and migrate within the polymers resulting in deposition on the polymer surfaces called 'blooming". These drawbacks of low molecular HALS can be overcome by use of the polymeric HALS. We have been studying photochemical reactions of the polymer systems. The present paper reports the preparation of a new polymeric photostabilizer containing HALS groups and their stabilization effects on photooxidation of polystyrene. The synthetic scheme for the preparation of polymeric photostabilizers containing HALS groups were shown at Scheme 1. N-[(Chloroformyl) phenyl]maleimide (CPMI) and N-[4-(chlorocarbonyl) phenyl]maleimide (CPMIC) were prepared by the known procedure. N[4-N'-(2,2,6,6-tetramethyl-4-piperidinyl)aminocarbonyl-phenyl] maleimide (TMPI) was prepared by the reaction of CPMI with 4-amino-2,2,6,6-tetramethylpiperidine (ATMP).

• Structural Engineering and Mechanics
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• v.50 no.5
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• pp.617-633
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• 2014

Because the elevated temperature degrades the mechanical properties of materials used in containments, the global behavior of containments subjected to the internal pressure under high temperature is remarkably different from that subjected to the internal pressure only. This paper concentrates on the nonlinear finite element analyses of the nuclear power plant containment structures, and the importance for the consideration of the elevated temperature effect has been emphasized because severe accident usually accompanies internal high pressure together with a high temperature increase. In addition to the consideration of nonlinear effects in the containment structure such as the tension stiffening and bond-slip effects, the change in material properties under elevated temperature is also taken into account. This paper, accordingly, focuses on the three-dimensional nonlinear analyses with thermal effects. Upon the comparison of experiment data with numerical results for the SNL 1/4 PCCV tested by internal pressure only, three-dimensional analyses for the same structure have been performed by considering internal pressure and temperature loadings designed for two kinds of severe accidents of Saturated Station Condition (SSC) and Station Black-out Scenario (SBO). Through the difference in the structural behavior of containment structures according to the addition of temperature loading, the importance of elevated temperature effect on the ultimate resisting capacity of PCCV has been emphasized.

• Journal of Mechanical Science and Technology
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• v.20 no.1
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• pp.66-75
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• 2006

A modeling method for the modal analysis of rotating beam structures having complex configurations employing multi-reference frames is presented in the present study. In most structural analysis methods, single reference frame is employed for the modal analysis. For simple structures such as single beam or single plate, the method of employing single reference frame usually provides rapidly converging accurate results. However, for general structures having complex configurations, such a method provides slowly converging, and often erroneous, results. In the present study, the effects of employing multi-reference frames on the convergence and the accuracy of the modal analysis of rotating beam structures having complex configurations are investigated.