• 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.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.119-124
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• 2001

A general procedure to implement the sensitivity analysis of PSC flexural members is proposed based on the analytical calculation of the gradients of stresses and strains with respect to the 21 design variables in a closed format. The formulation covers the long term losses including concrete creep, shrinkage, and PS steel relaxation as well as load effects. The derived formulation is applied to the rectangular section PSC beam with prestressing and nonprestressing steels for the sensitivity analysis. The analytically calculated sensitivity results are compared with those numerically calculated.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.355-362
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• 2001

This study deals with cracking control of concrete deck in steel-concrete composite bridges according to the concrete slab casting sequences. In correlation studies between casting sequences, time dependent effects of concrete creep and shrinkage are implemented in the analytical model. Finally, the methods of cracking control in terms of concrete slump and relative humidity are suggested to prevent early transverse cracking of concrete slab.

• Proceedings of the KWS Conference
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• 2001.05a
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• pp.104-107
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• 2001

Creep-fatigue crack growth behavior at the heat affected zone of 1Cr-0.5Mo steel weldment has been experimentally studied. Load hold times of the tests for trapezoidal fatigue wave-shapes were varied among 0, 30, 300 and 3,600 seconds. Time-dependent crack growth rates were characterized by the $C_{t}$ estimated with the equation proposed by the previous finite element analysis work. It was concluded that the $C_{t}$ values calculated from the properties of parent metal were quite comparable to the accurate $C_{t}$ values calculated from both of weld and parent metals.etals.

• KCI Concrete Journal
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• v.11 no.3
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• pp.45-52
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• 1999

A Computer-based iterative method is provided for the calculation of minimum thickness values for one-way slabs to satisfy the maximum permissible limits given in the ACI Building Code. An algorithm includes the effects of cracking and time-dependent effects due to creep and shrinkage. Comparison of the calculated minimum thickness values with the current ACI limits is conducted to investigate limitations of the current tabulated minimum thickness. which are constant to a range of design conditions.

• Journal of the Korea Concrete Institute
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• v.18 no.1 s.91
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• pp.29-36
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• 2006

Steel reinforced concrete(SRC) columns, which have been widely employed in high-rise buildings, exhibit a time-dependent behavior because of creep and shrinkage of concrete. This long-term behavior may cause a serious serviceability problem in structural systems, so it is very important to predict the deformation due to creep and shrinkage of concrete. However, it was found from the previous experimental studies that the long-term deformation of SRC columns was quite dissimilar from that of RC columns. A new method is required to quantitatively predict the long-term deformation of SRC columns. In this study, the causes of the discrepancy between the behaviors of RC and SRC columns are investigated and discussed. SRC columns exhibit a time-dependent relative humidity distribution in a cross section differently from that of reinforced concrete(RC) columns owing to the presence of a inner steel plate, which interferes with the moisture diffusion of concrete. This relative humidity distribution may reduce the drying shrinkage and the drying creep in comparison with RC columns. Therefore it is suggested that the differential moisture distribution should be taken into account in order to reasonably predict column shortening of SRC columns.

• Proceedings of the Korean Geotechical Society Conference
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• 2003.03a
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• pp.257-264
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• 2003

Tunnelling in water bearing soils influences the ground water regime. It has been indicated in the literature that the existence of ground water above a tunnel influences tunnel stability and the settlement profile. Only limited research, however, has been done on ground water movements around tunnels and their influence on tunnel performance. Time dependent soil behaviour can be caused by the changes of pore water pressure and/or the viscous properties of soil(creep) under the stress change resulting from the advance of the tunnel face. De Moor(1989) demonstrated that the time dependent deformations due to tunnelling are mainly the results of pore pressure dissipation and should be interpreted in terms of effective stress changes. Drainage into tunnels is governed by the permeability of the soil, the length of the drainage path and the hydraulic boundary conditions. The potential effect of lime dependent settlement in a shallow tunnel is likely to occur rapidly due to the short drainage path and possibly high coefficient of consolidation. Existing 2D modelling methods are not applicable to these tunnelling problems, as it is difficult to define empirical parameters. In this paper the time-based 2D modelling method is adopted to account for the three dimensional effect and time dependent behaviour during tunnel construction. The effect of coupling between the unloading procedure and consolidation during excavation is profoundly investigated with the method. It is pointed out that realistic modelling can be achieved by defining a proper permeability at the excavation boundary and prescribing appropriate time for excavation Some guidelines for the numerical modelling of drained and undrained excavation has been suggested using characteristic time factor. It is highlighted that certain range of the factor shows combined effect between the unloading procedure due to excavation and consolidation during construction.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.191-200
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• 2003

This paper presents the rheological properties of bitumen for reducing negative skin friction. The bitumen has been widely used due to both the cost and construction effectiveness. Also, it is well known that the use of bitumen for reducing negative skin friction renders the best results among other available methods. Three different modified bitumens were used for the testing programs. The physical tests include the penetration, the softening point and penetration index. The rheological tests include phase angle, complex modulus, creep tests and flow tests. The tests were conducted at four different temperatures(15, 30, 45 and 6$0^{\circ}C$) in order to simulate the field condition. The test results were analyzed using the phase angle, G$^*$/sin $\delta$, creep compliance and shear viscosity. The result of tests showed that the phase angle increased and G$^*$/sin $\delta$ decreased with the increase of temperature. The creep compliance increased as the loading time increased. The difference of the creep compliance is detected as the time and temperature are varied, however, the difference of the shear viscosity is not significant among the samples tested in this study. The rheological properties of the bitumen also showed that the physical testing method and the temperature dependant testing method are somewhat limited to showing and expressing the full rheological properties of the modified bitumen. The introduction of the time and the temperature dependent testing method is necessary to find out the full rheological properties of the modified bitumen.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.6
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• pp.117-125
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• 1998

The paper attempts to estimate the incubation time of a cavity in the interface between a power law creep particle and an elastic matrix subjected to a uniaxial stress. Since the power law creep particle is time dependent, the stresses in the interface relax. The volume free energy associated with Helmholtz free energy includes strain energies caused by applied stress and dislocations piled up in interface(DPI). The energy due to DPI is found by modifying the result of Dundurs and Mura[4]. The volume free energies caused by both applied stress and DPI are a function of the cavity size(r) and elapsed time(t) and arise from stress relaxation in the interface. Critical radius $r^*$ and incubation time $t^*$ to maximise Helmholtz free energy is found in present analysis. Also, kinetics of cavity formation are investigated using the results obtained by Riede [7]. The incubation time is defined in the analysis as the time required to satisfy both the thermodynamic and kinetic conditions. Through the analysis it is found that 1) strain energy caused by the applied stress does not contribute significantly to the thermodynamic and kinetic conditions of a cavity formation, 2) in order to satisfy both thermodynamic and kinetic conditions, critical radius $r^*$ decreases or holds constant with increase of the time until the kinetic condition(eq. 2.3) is satisfied. there for the cavity may not grow right after it is formed, as postulated by Harris [15], and Ishida and Mclean [16], 3) the effects of strain rate exponent (m), material constant $\sigma$0, volume fraction of the particle to matrix(f)and particle size on the incubation time are estimated using material constants of the copper as matrix.

• Steel and Composite Structures
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• v.17 no.4
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• pp.405-429
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• 2014

In this paper, it is aimed to determine the structural behavior of suspension bridges considering construction stages and different soil conditions. Bosporus Suspension Bridge connecting the Europe and Asia in Istanbul is selected as an example. Finite element model of the bridge is constituted using SAP2000 program considering existing drawings. Geometric nonlinearities are taken into consideration in the analysis using P-Delta large displacement criterion. The time dependent material strength of steel and concrete and geometric variations is included in the analysis. Time dependent material properties are considered as compressive strength, aging, shrinkage and creep for concrete, and relaxation for steel. To emphases the soil condition effect on the structural behavior of suspension bridges, each of hard, medium and soft soils are considered in the analysis. The structural behavior of the bridge at different construction stages and different soil conditions has been examined. Two different finite element analyses with and without construction stages are carried out and results are compared with each other. At the end of the analyses, variation of the displacement and internal forces such as bending moment, axial forces and shear forces for bridge deck and towers are given in detail. Also, displacement and stresses for bridge foundation are given with detail. It can be seen from the analyses that there are some differences between both analyses (with and without construction stages) and the results obtained from the construction stages are bigger. It can be stated that the analysis without construction stages cannot give the reliable solutions. In addition, soil condition have effect on the structural behavior of the bridge. So, it is thought that construction stage analysis using time dependent material properties, geometric nonlinearity and soil conditions effects should be considered in order to obtain more realistic structural behavior of suspension bridges.