• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.3
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• pp.595-602
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• 1998

Specimens of 304 stainless steel were tested to failure at elevated temperatures under multiaxial stress states, uniaxial tension using smooth bar specimens, biaxial shearing using double shear bar specimens, and triaxial tension using notched bar specimens. Rupture times are compared for uniaxial, biaxial, and triaxial stress states with respect to the maximum principal stress, the von Mises effective stress, and the principal facet stress. The results indicate that the principal facet stress gives the best correlation for the material investigated, and this parameter can predict creep life data under multiaxial stress states with rupture data obtained with specimens under uniaxial stresses. The results also suggest that grain boundary cavitation, coupled with localized deformation processes such as grain boudary sliding, controls the lifetimes of the specimens.

• Magazine of the Korean Society of Agricultural Engineers
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• v.31 no.2
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• pp.125-134
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• 1989

This study was conducted to investigate the flexural behaviour of sandwich constructions with cement concrete core and polymer concrete facings. Six different cross-sectional shapes using epoxy based polymer concrete facings were investigated. Some of the results from the static tests are given including the load-deflection responses, load-strain relationships, ultimate moment, and mode of failure. From the. results the following conclusions can be made. 1. The various strengths of polymer concrete were very high compared to the strengths for portland cement concrete, while modulus of elasticity assumed an aspect of contrast. 2. The thickness of core and facing exerted a great influence on the deflection and ultimate strenght of polymer concrete sandwich constructions. 3. The variation shape of deflection and strain depend on loading were a very close approximation to the straight line. The ultimate strain of polymer concrete at the end of tensile side were ranged from 625x10-6 to 766x10-6 and these values increased in proportion to the decrease of thickness of core and facings. 4. The ultimate moments of polymer sandwich constructions were 3 to 4 times that of cement concrete constructions which was transformed same section. It should he noted that polymer concrete have an effect on the reinforcement of weak constructions. 5. Further tests are neede to investigate the shear strain of constructions, and thermal expansion, shrinkage and creep of cement and polymer concrete which were composite materials of sandwich constructions.

• Structural Engineering and Mechanics
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• v.36 no.2
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• pp.207-223
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• 2010

The aim of this study concerns with the construction stage analysis of highway bridges constructed with balanced cantilever method using time dependent material properties. K$\ddot{o}$m$\ddot{u}$rhan Highway Bridge constructed with balanced cantilever method and located on the 51st km of Elazi$\check{g}$-Malatya, Turkey, highway over Firat River is selected as an application. Finite element models of the bridge are modelled using SAP2000 program. Geometric nonlinearity is taken into consideration in the analysis using P-Delta plus large displacement criterion. The time dependent material strength variations and geometric variations are included in the analysis. Elasticity modulus, creep and shrinkage are computed for different stages of the construction process. The structural behaviour of the bridge at different construction stages has been examined. Two different finite element analyses with and without construction stages are carried out and results are compared with each other. As analyses result, variation of internal forces such as bending moment, axial forces and shear forces for bridge deck and column are given with detail. It is seen that construction stage analysis has remarkable effect on the structural behaviour of the bridge.

• Steel and Composite Structures
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• v.12 no.5
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• pp.413-426
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• 2012

In this paper, nonlinear static analysis of three-dimensional cable stayed bridges is performed for the time dependent materials properties such as creep, shrinkage and aging of concrete and relaxation of cable. Manavgat Cable-Stayed Bridge is selected as an application. The bridge located in Antalya, Turkey, was constructed with balanced cantilever construction method. Total length of the bridge is 202 m. The bridge consists of one $\ddot{e}$ shape steel tower. The tower is at the middle of the bridge span. The construction stages and 3D finite element model of bridge are modeled with SAP2000. Large displacement occurs in these types of bridges so geometric nonlinearity is taken into consideration in the analysis by using P-Delta plus large displacement criterion. The time dependent material strength and geometric variations are included in the analysis. Two different finite element analyses carried out which are evaluated with and without construction stages and results are compared with each other. As a result of these analyses, variation of internal forces such as bending moment, axial forces and shear forces for bridge tower and displacement and bending moment for bridge deck are given with detailed. It is seen that construction stage analysis has a remarkable effect on the structural behavior of the bridge.

• Journal of the Korean Society for Railway
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• v.17 no.1
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• pp.14-18
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• 2014

Wheel/rail contact is a significant problem in railway dynamics. In this paper, the wheel/rail contact is examined analytically and numerically as a contact problem between two cylinders where torque and friction have effect. Furthermore, the contact of a real wheel and rail is investigated numerically where the normal and shear force act. This study demonstrates that the wheel/rail contact is a process that generates traction force through creep where rolling and sliding occurs simultaneously depending on the shape of the wheel and rail, and the friction coefficient between them.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.442-445
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• 2006

This paper presents an analytical prediction of nonlinear characteristics and behavior characteristics PSC structures with un-bonded tendon system. In this paper, a numerical model for un-bonded tendon is proposed based on the finite element method, which can represent straight or curved un-bonded tendon behavior. this model and time-dependent material model used to investigate the time-dependent behavior of un-bonded prestressed concrete structures. The accuracy and objectivity of the assessment process may be enhanced by the use of sophisticated nonlinear finite element analysis program. A computer program, named RCAHEST(Reinforced Concrete Analysis in Higher Evaluation System Technology), for the analysis of concrete structures and steel plate was used. The material nonlinearities are taken into account by comprising the tension, compression, and shear models of cracked concrete and models for reinforcements and tendons in the concrete. The smeared crack approach is incorporated. It accounts for the aging, creep and shrinkage of concrete and the stress relaxation of prestressed steel. The proposed un-bonded tendon model and numerical method of un-bonded prestressed concrete structures is verified by comparison with reliable experimental results.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.2
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• pp.49-58
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• 1990

A numerical procedure is developed to analyze the time-dependent deflections of prestressed concrete bridges constructed by the segmental cantilever method. The developed computer program accounts for the time-dependent properties of prestressed concrete materials due to the varying modulus of elasticity, creep and shrinkage of concrete and the stress relaxation of prestressing steel. It also accounts for the stiffness increase due to the presence of the steel reinforcements and the effects of the shear deformation of the prestressed concrete bridge girders. The program is applied to a multi-span continuous segmental prestressed concrete bridge to demonstrate its capabilities and to explore the behavior characteristics of the segmental bridges.

• Tunnel and Underground Space
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• v.22 no.2
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• pp.77-85
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• 2012

In a material, micro-cracks can be progressively occurred, propagated and finally lead to failure when it is subjected to cyclic or periodic loading less than its ultimate strength. This phenomenon, fatigue, is usually considered in a metal, alloy and structures under repeated loading conditions. In underground structures, a static creep behavior rather than a dynamic fatigue behavior is mostly considered. However, when compressed air is stored in a rock cavern, an inner pressure is periodically changed due to repeated in- and-out process of compressed air. Therefore mechanical properties of surrounding rock mass and an inner lining system under cyclic loading/unloading conditions should be investigated. In this study, considering an underground lined rock cavern for compressed air energy storage (CAES), the mechanical properties of a lining system, that is, concrete lining and plug under periodic loading/unloading conditions were characterized through cyclic bending tests and shear tests. From these tests, the stability of the plug was evaluated and the S-N line of the concrete lining was obtained.

• International Journal of Highway Engineering
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• v.2 no.3
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• pp.129-144
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• 2000

This paper presents the characteristics of viscoelastic properties and fatigue performance of SBS modified asphalt mixtures depending on the aggregate gradation. Dynamic shear rheometer (DSR) and uniaxial tensile creep tests are performed to analyze the thermomechanical behavior of asphalt binders and mixtures, respectively. Uniaxial tensile fatigue tests for seven different asphalt mixtures are conducted to evaluate the effects of aggregate gradations and SBS modifier on the fatigue performance of the mixtures. DSR and uniaxial tensile creep tests results show that the SBS modified asphalt mixtures have better rutting resistance than the unmodified mixtures at high temperatures regardless of the aggregate gradations used. Fatigue factor $G^*sin\delta$ in Superpave binder specification may not be adequate for evaluating the fatigue Performance of asphalt mixtures. It is observed from uniaxial tensile fatigue tests that SBS modified asphalt mixtures compared to unmodified mixtures have ten times longer fatigue lives regardless of the aggregate gradations(dense, SMA, and Superpave gradations) used in the mixtures. The better fatigue performance of the SBS modified mixtures is observed even after long-term aging process. The effect of aggregate gradations on the fatigue performance is not as significant as the SBS modifier. The cellulose fiber added in the SMA mixture has negligible effects on the viscoelastic Properties and fatigue performance of the mixture, but is effective in reducing draindown. Although the SBS modified asphalt binder is used, it may be necessary to add the cellulose fiber into the SMA mixture to prevent the draindown.

• Journal of the Korea Concrete Institute
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• v.28 no.5
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• pp.535-544
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• 2016

This paper aims at examining the effects of sustained load and elevated temperature on the time-dependent deformation of a carbon fiber reinforced polymer (CFRP) sheets bonded to concrete as well as the pull-off strength of single-lap shear specimens after the sustained loading period using digital images. Elevated temperature during the sustained loading period resulted in increased slip of the CFRP composites, whereas increased curing time of the polymer resin prior to the sustained loading period resulted in reduced slip. Pull-off tests conducted after sustained loading period showed that the presence of sustained load resulted in increased pull-off strength and interfacial fracture energy. This beneficial effect decreased with increased creep duration. Based on analysis of digital images, results on strain distributions and fracture surfaces indicated that stress relaxation of the epoxy occurred in the 30 mm closest to the loaded end of the CFRP composites during sustained loading, which increased the pull-off strength provided the failure locus remained mostly in the concrete. For longer sustained loading duration, the failure mode of concrete-CFRP bond region can change from a cohesive failure in the concrete to an interfacial failure along the concrete/epoxy interface, which diminished part of the strength increase due to the stress relaxation of the adhesive.