• 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.

• Computers and Concrete
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• v.9 no.5
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• pp.357-374
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• 2012

The aim of this paper is to develop a procedure able to calculate the long-term stress and strain patterns in modern prestressed composite structures which are largely influenced by creep and shrinkage and whose final static configuration is the result of many phases of loading and restraints conditions. The introduction of equivalent moduli, depending on the viscous and elastic features of materials, can guarantee a significant simplification of the problem presented above. The proposed calculation model has been used to design the "Quattroquercie Viaduct" located on the highway "A3" Salerno-Reggio Calabria, Italy.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2017.05a
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• pp.220-221
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• 2017

In this study, the thermal strain of high strength concrete with the compressive strength of 70, 80, 100MPa were measured under 33% of compressive strength loading condition. As results, it is considered that shrinkage strain of high strength concrete become grater at the elevated temperatures.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.6
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• pp.113-123
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• 2012

The technology developed for the decrease of applying loads and self-weight of a structure is to improve conventional Foam Cement Banking Method (FCB) by applying mixed slurry of bottom ash, cement and foams. Since the foam-mixed concrete, which is a major material of the Bottom ash-mixed Light weight concrete Banking method (BLB) developed, contains mineral admixture such as cement, the behavior shows time-dependent deformation and deterioration of durability due to environmental exposure. Thus, this study is subject to figure out the characteristics of long-termed behavior and durability of the developed method by carrying out experiments for schemed parameters, which are considered to be factors affecting mainly on concrete's characteristics from mechanical analysis. As results of tests, it was found that the developed concrete offers higher resistance than conventional foamed concrete in terms of long-termed behaviors associated with drying shrinkage and creep, and durability problems of freeze-thaw and carbonation processes, especially with addition of bottom ash.

• Steel and Composite Structures
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• v.10 no.1
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• pp.45-67
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• 2010

Composite steel-concrete structures are employed extensively in modern high rise buildings and bridges. This concept has achieved wide spread acceptance because it guarantees economic benefits attributable to reduced construction time and large improvements in stiffness. Even though the combination of steel and concrete enhances the strength and stiffness of composite beams, the time-dependent behaviour of concrete may weaken the strength of the shear connection. When the concrete loses its strength, it will transfer its stresses to the structural steel through the shear studs. This behaviour will reduce the strength of the composite member. This paper presents the development of an accurate finite element model using ABAQUS to study the behaviour of shear connectors in push tests incorporating the time-dependent behaviour of concrete. The structure is modelled using three-dimensional solid elements for the structural steel beam, shear connectors, concrete slab and profiled steel sheeting. Adequate care is taken in the modelling of the concrete behaviour when creep is taken into account owing to the change in the elastic modulus with respect to time. The finite element analyses indicated that the slip ductility, the strength and the stiffness of the composite member were all reduced with respect to time. The results of this paper will prove useful in the modelling of the overall composite beam behaviour. Further experiments to validate the models presented herein will be conducted and reported at a later stage.

• Structural Engineering and Mechanics
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• v.81 no.5
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• pp.617-631
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• 2022

In this paper the viscoelastic responses of four experimental steel-concrete composite beams subjected to highly variable environmental conditions are investigated by means of a finite element (FE) model. Concrete specimens submitted to stepped stress changes are also evaluated to validate the current formulations. Here, two well-known approaches commonly used to solve the viscoelastic constitutive relationship for concrete are employed. The first approach directly solves the integral-type form of the constitutive equation at the macroscopic level, in which aging is included by updating material properties. The second approach is postulated from a rate-type law based on an age-independent Generalized Kelvin rheological model together with Solidification Theory, using a micromechanical based approach. Thus, conceptually both approaches include concrete hardening in two different manners. The aim of this work is to compare and analyze the numerical prediction in terms of long-term deflections of the studied specimens according to both approaches. To accomplish this goal, the performance of several well-known model codes for concrete creep and shrinkage such as ACI 209, CEB-MC90, CEB-MC99, B3, GL 2000 and FIB-2010 are evaluated by means of statistical bias indicators. It is shown that both approaches with minor differences acceptably match the long-term experimental deflection and are able to capture complex oscillatory responses due to variable temperature and relative humidity. Nevertheless, the use of an age-independent scheme as proposed by Solidification Theory may be computationally more advantageous.

• Journal of the Korea Concrete Institute
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• v.18 no.6 s.96
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• pp.711-720
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• 2006

The structural behavior of concrete girder in bridges constructed by free cantilever method is time-dependent due to creep and shrinkage of concrete. The constraint effects of longitudinal movement of concrete girders can introduce unfavourable moment into piers. This study is aimed at proposing a method to reduce the moment of piers in bridge constructed by free cantilever method. The method are systematically composed of time-dependent structural analysis of bridges and loading of control force during construction of bridge. Numerical analyses are carried out depending on the parameters such as amount of control force and flexibility of pier. Time-dependent structural behavior shows that moment of pier increases according as pier height decreases. Also, moment of pier decreases when control method are applied. Numerical result of the study represents that time-dependent moment of piers can be controlled effectively by employing the proposed method.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.1
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• pp.125-132
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• 2010

In the recent construction industry, an external strengthening method using fiber reinforced polymers has been widely used. Since reinforced concrete structures strengthened with fiber reinforced polymers are always under sustained loads, influence of creep and shrinkage on the structures is inevitable. Due to the creep and shrinkage, behaviors of the structures, such as deflection, deformation, recovery capability, strength and so on are also under the influence of creep and shrinkage. Thus, in order to estimate efficacy, creep recovery and residual strength of FRP strengthened RC beams, long-term flexural experiments and static flexural experiments were carried out. As the result of the experiments, FRP strengthened RC beams were very effective in terms of deflection control. Furthermore, the strengthened beams had higher immediate deformation recovery than immediate deformation. Through the static flexural experiments, it was shown that the CFRP strengthened beam had high residual strength. It seems that the sustained loads did not affect bond and residual strength of the beams.

• Journal of the Korea Concrete Institute
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• v.21 no.3
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• pp.265-273
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• 2009

There have been numerous studies to develop eco-friendly concrete. The attempt to reduce the amount of cement used is suggested as one of the solutions for eco-friendly concrete. To decrease the usage of cement, the pozzolan reaction materials are used as a mineral admixture. Hwang-toh, which is broadly deposited in Korea is a well known environment friendly material and the activated hwang-toh, which has the property of pozzolan reaction, is alternatively used as a mineral admixture of concrete. The purpose of this study is to investigate the drying shrinkage of hwang-toh concrete mixed with recycled PET fiber. Therefore, drying shrinkage experiments are performed to analyze mechanical property of hwang-toh concrete mixed with recycled PET fiber. Test results showed that the drying shrinkage is controlled by hwang-toh admixture and PET fiber.

• Journal of the Korea Institute of Building Construction
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• v.19 no.2
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• pp.123-130
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• 2019

As a cold-weather-concrete construction technique for enhancing the sustainability and improving efficiency of cold-weather construction, the cracking timing, the starting point of deterioration for concrete, due to the shrinkage of the blast furnace slag cement concrete including accelerator was evaluated. As a result, by using blast furnace slag and accelerator, the cracking was developed faster with higher cracking potential under the restrained conditions at constant age and free-shrinkage strain. It can be considered that the results of decreased stress relaxation by creep or increased restraint with increased free-shrinkage strain causes the increased cracking development speed. Hence, it should be considered the necessary of cracking due to the shrinkage when blast furnace slag or accelerator was used for cold-weather construction.