• Proceedings of the Computational Structural Engineering Institute Conference
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• 2000.04b
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• pp.141-149
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• 2000

This study performs the elastic and viscoelastic analysis of composite continuous beams with flexible shear connectors. Due to creep and shrinkage of the concrete part, the stress redistribution between the concrete slab and steel beam, and the evolution of the redundant restraint reaction occur with time. Using the equation of equilibrium, internal and external compatibility condition, and constitutive relationships, mathematical formulations are formulated. The solution is obtained by means of numerical step-by-step techniques and the finite difference method. Numerical parametric studies are performed to evaluate the stress redistribution, and the evolution of the redundant restraint reaction. The parameters include the stiffness and spacing of shear connectors, the age of concrete at loading, and the relative humidity.

• Korea-Australia Rheology Journal
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• v.14 no.1
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• pp.33-45
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• 2002

Recent results obtained for the port-pom model and the constitutive equations with time-strain separability are examined. The time-strain separability in viscoelastic systems Is not a rule derived from fundamental principles but merely a hypothesis based on experimental phenomena, stress relaxation at long times. The violation of separability in the short-time response just after a step strain is also well understood (Archer, 1999). In constitutive modeling, time-strain separability has been extensively employed because of its theoretical simplicity and practical convenience. Here we present a simple analysis that verifies this hypothesis inevitably incurs mathematical inconsistency in the viewpoint of stability. Employing an asymptotic analysis, we show that both differential and integral constitutive equations based on time-strain separability are either Hadamard-type unstable or dissipative unstable. The conclusion drawn in this study is shown to be applicable to the Doi-Edwards model (with independent alignment approximation). Hence, the Hadamardtype instability of the Doi-Edwards model results from the time-strain separability in its formulation, and its remedy may lie in the transition mechanism from Rouse to reptational relaxation supposed by Doi and Edwards. Recently in order to describe the complex rheological behavior of polymer melts with long side branches like low density polyethylene, new constitutive equations called the port-pom equations have been derived in the integral/differential form and also in the simplifled differential type by McLeish and carson on the basis of the reptation dynamics with simplifled branch structure taken into account. In this study mathematical stability analysis under short and high frequency wave disturbances has been performed for these constitutive equations. It is proved that the differential model is globally Hadamard stable, and the integral model seems stable, as long as the orientation tensor remains positive definite or the smooth strain history in the flow is previously given. However cautious attention has to be paid when one employs the simplified version of the constitutive equations without arm withdrawal, since neglecting the arm withdrawal immediately yields Hadamard instability. In the flow regime of creep shear flow where the applied constant shear stress exceeds the maximum achievable value in the steady flow curves, the constitutive equations exhibit severe instability that the solution possesses strong discontinuity at the moment of change of chain dynamics mechanisms.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.4
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• pp.87-96
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• 2004

As a special concrete, which is a mixture of soil, cement and water, has strength like regular concrete for pavement, soil cement has been used in various field such as pavement and soft soil improvement. The objective of this study was to investigate the characteristic of unconfined compressive strength and time dependent behavior of soil cement that is made from decomposed granite soil or coluvial and inorganic solidification liquid. The results showed that the unconfined compressive strength appears to increase as the amount of cement and curing time increase In addition, the strength seems to decrease with increase of the potion of fine particles(No 200 sieve). The result of XRD indicated that there is Vermiculite, the product of reaction, in the soil cement. The dynamic properties of material, such as shear complex compliance, shear complex modulus, and phase angle could be calculated from the hysteresis loop obtained from the Haversine Creep Tests. Finally, creep behavior was able to be predicted from these dynamic properties.

• Korean Journal of Materials Research
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• v.25 no.11
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• pp.630-635
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• 2015

The fatigue strength of a nickel-base superalloy was studied. Stress-controlled fatigue tests were carried out at $700^{\circ}C$ and 5 Hz using triangular wave forms. In this study, two kinds of testing procedures were adopted. One is the conventional tension-zero fatigue test(R = 0). The other was a procedure in which the maximum stress was held at 1000 MPa and the minimum stress was diverse from zero to 1000 MPa at 24 and $700^{\circ}C$. The results of the fatigue tests at $700^{\circ}C$ indicate that the fracture mechanism changed according to both the mean stress and the stress range. At a higher stress range, ${\gamma}^{\prime}$ precipitates are sheared by a/2<110> dislocation pairs coupled by APB. Therefore, in a large stress range, the deformation occurred by shearing of ${\gamma}^{\prime}$ by a/2<110> dislocations, which brought about crystallographic shear fracture. As the stress range was decreased, the fracture mode gradually changed from crystallographic shear fracture to gradual growth of fatigue cracks. At an intermediate stress range, as it became more difficult for a/2<110> dislocation pairs to shear ${\gamma}^{\prime}$ particles, cracks started to propagate in the matrix, avoiding the harder ${\gamma}^{\prime}$ particles. High mean stress induced creep deformation, that is, ${\gamma}^{\prime}$ particles were sheared by {111}<112> slip systems, which led to the formation of stacking faults in the precipitates. Thus, the change in fracture mechanism brought about the inversion of the S-N curves.

• Structural Engineering and Mechanics
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• v.83 no.2
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• pp.207-227
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• 2022

In general, the interaction conditions between the discrete stones are not taken into account by structural engineers during the modeling and analyzing of historical stone bridges. However, many structural damages in the stone bridges occur due to ignoring the interaction conditions between discrete stones. In this study, it is aimed to examine the seismic behavior of a historical stone bridge by considering the interaction stiffness parameters between stone elements. For this purpose, Tokatli historical stone arch bridge was built in 1179 in Karabük-Turkey, is chosen for three-dimensional (3D) seismic analyses. Firstly, the 3D finite-difference model of the Tokatli stone bridge is created using the FLAC3D software. During the modeling processes, the Burger-Creep material model which was not used to examine the seismic behavior of historical stone bridges in the past is utilized. Furthermore, the free-field and quiet non-reflecting boundary conditions are defined to the lateral and bottom boundaries of the bridge. Thanks to these boundary conditions, earthquake waves do not reflect in the 3D model. After each stone element is modeled separately, stiffness elements are defined between the stone elements. Three situations of the stiffness elements are considered in the seismic analyses; a) for only normal direction b) for only shear direction c) for both normal and shear directions. The earthquake analyses of the bridge are performed for these three different situations of the bridge. The far-fault and near-fault conditions of 1989 Loma Prieta earthquake are taken into account during the earthquake analyses. According to the seismic analysis results, the directions of the stiffness parameters seriously changed the earthquake behavior of the Tokatli bridge. Moreover, the most critical stiffness parameter is determined for seismic analyses of historical stone arch bridges.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.516-521
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• 2004

In unmanned aerial vehicles (UAV), the high temperature results from friction among the air, combustion of fuel in engine and combustion gas of a nozzle. The high temperature may cause serious damages in UAV structure. The Functionally Graded Material (FGM) is chosen as a material of thc engine duct structure. Thermal stress analysis of FGM is performed in this paper. FGM is composed of two constituent materials that are mixed up according to the specific volume fraction distribution in order to withstand high temperature. Therefore, hoop stress, axial stress and shear stress of duct with 2 layers, 4 layers and 8 layers FGM are compared and analyzed respectively. In addition, the creep behavior of FGM used in duct structure of an engine is analyzed for better understanding of FGM characteristics.

• International Journal of Highway Engineering
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• v.14 no.5
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• pp.47-55
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• 2012

PURPOSES: SUPERPAVE binder grade tests including Multiple Stress Creep and Recovery(MSCR) test are applied to evaluate rheological properties of four polymer modified binders. METHODS: To evaluate grade of four modified binders, PG testing protocols, such as DSR, BBR and MSCR are employed. RESULTS: It is observed that MSCR test shows different performance grades especially on modified binders. Both DMP and EG binder show similar high temperature performance to SBS 5% modified binder. CONCLUSIONS: Binder Grading system in Korea need to be reviewed to properly reflect the performnace of modified binders. The binders modified with DMP and EG can be possible alternatives SBS 5% modified binder considering its performance and cost.

• Structural Engineering and Mechanics
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• v.71 no.4
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• pp.433-444
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• 2019

Shear studs are often used to connect steel girders and concrete deck to form a composite bridge system. The application of precast concrete deck to steel-concrete composite bridges can improve the strength of decks and reduce the shrinkage and creep effect on the long-term behavior of structures. How to ensure the connection between steel girders and concrete deck directly influences the composite behavior between steel girder and precast concrete deck as well as the behavior of the structure system. Compared with traditional multi-I girder systems, a twin-I girder composite bridge system is more simplified but may lead to additional requirements on the shear studs connecting steel girders and decks due to the larger girder spacing. Up to date, only very limited quantity of researches has been conducted regarding the behavior of shear studs on twin-I girder bridge systems. One convenient way for steel composite bridge system is to cast concrete deck in place with shear studs uniformly-distributed along the span direction. For steel composite bridge system using precast concrete deck, voids are included in the precast concrete deck segments, and they are casted with cast-in-place concrete after the concrete segments are erected. In this paper, several sets of push-out tests are conducted, which are used to investigate the heavier of shear studs within the voids in the precast concrete deck. The test data are analyzed and compared with those from finite element models. A simplified shear stud model is proposed using a beam element instead of solid elements. It is used in the finite element model analyses of the twin-I girder composite bridge system to relieve the computational efforts of the shear studs. Additionally, a parametric study is developed to find the effects of void size, void spacing, and shear stud diameter and spacing. Finally, the recommendations are given for the design of precast deck using void for twin I-girder bridge systems.

• Steel and Composite Structures
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• v.6 no.3
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• pp.237-255
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• 2006

This paper presents a novel analytical formulation for the analysis of composite beams with partial shear interaction stiffened by a bolted longitudinal plate accounting for time effects, such as creep and shrinkage. The model is derived by means of the principle of virtual work using a displacement-based formulation. The particularity of this approach is that the partial interaction behaviour is assumed to exist between the top slab and the joist as well as between the joist and the bolted longitudinal stiffening plate, therefore leading to a three-layered structural representation. For this purpose, a novel finite element is derived and presented. Its accuracy is validated based on short-and long-term analyses for the particular cases of full shear interaction and partial shear interaction of two layers for which solutions in closed form are available in the literature. A parametric study is carried out considering different stiffening arrangements to investigate the influence on the short-and long-term behaviour of the composite beam of the shear connection stiffness between the concrete slab and the steel joist, the stiffness of the plate-to-beam connection, the properties of the longitudinal plate and the concrete properties. The values of the deflection obtained from the finite element simulations are compared against those calculated using the effective flexural rigidity in accordance with EC5 guidelines for the behaviour of elastic multi-layered beams with flexible connection and it is shown how the latter well predicts the structural response. The proposed numerical examples highlight the ease of use of the proposed approach in determining the effectiveness of different retrofitting solutions at service conditions.

• Proceedings of the Korea Concrete Institute Conference
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• 1989.10a
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• pp.73-76
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• 1989

A numerical procedure is developed to analyze the time-dependent behavior 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 varing 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.