• Fire Science and Engineering
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• v.24 no.4
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• pp.33-40
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• 2010

A numerical model considering the vapor pressure and the creep models, in the form of a analytical program, for tracing the behavior of high strength concrete (HSC) members exposed to fire is presented. The two stages, i.e., spalling procedure and fire resistance time, associated with the thermal, moisture flow, creep and structural analysis, for the prediction of fire resistance behavior are explained. The use of the analytical program for tracing the response of HSC member from the initial pre-loading stage to collapse, due to fire, is demonstrated. The validity of the numerical model used in this program is established by comparing the predictions from this program with results from others fire resistance tests. The analytical program can be used to predict the fire resistance of HSC members for any value of the significant parameters, such as load, sectional dimensions, member length, and concrete strength.

• Advances in concrete construction
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• v.5 no.2
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• pp.155-171
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• 2017

The phenomenon of concrete column shortening has been widely acknowledged since it first became apparent in the 1960s. Axial column shortening is due to the combined effect of elastic and inelastic deformations, shrinkage and creep. This study aims to investigate the effects of ambient temperature, relative humidity, cement hardening speed and aggregate type on concrete column shortening. The investigation was conducted using a column shortening prediction model which is underpinned by the Eurocode 2. Critical analysis and evaluation of the results showed that the concrete aggregate types used in the concrete have significant impact on column shortening. Generally, aggregates with higher moduli of elasticity hold the best results in terms of shortening. Cement type used is another significant factor, as using slow hardening cement gives better results compared to rapid hardening cement. This study also showed that environmental factors, namely, ambient temperature and relative humidity have less impact on column shortening.

• Proceedings of the Korea Concrete Institute Conference
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• 1996.04a
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• pp.141-145
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• 1996

The primary purpose of this study is to investigate reusal techniques of by-product produced the combined heat power plant in the construction field, which may contribute to the savings of construction materials and the conservation of enviornment. This study is compared and evaluated by testing the chemical resistance, adiabatic temperature rising test, creep and drying shrinkage. As the result of the study, the following conclusions are derived : (1) hydration heat of the fly ash concrete is less than the plain concrete in adiabatic temperature rising test, (2) the fly axh concrete (FA 30%) is similar to the plain concrete in the chemical resistamce, (3) the fly ash concrete (FA 10, 30%) is similar to the plain concrete in drying shrinkage, but the fly ash concrete (FA 50%) is highly increased, (4) the fly ash concrete (FA 30%) is less than the plain concrete in creep test.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.4
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• pp.771-781
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• 1994

The heat generation of cement causes the internal temperature rise and volume change at early age, particulary in massive concrete structures. As the results of the temperature rise and restraint conditions, the thermal stress may induce cracks in concrete. Therefore, the prediction of the thermal stress is very important in the design and construction in order to control the cracks developed in mass concrete. In case of young concrete, creep effect by the temperature load is larger than that of old concrete. Thus, the effect of creep must be considered for checking the cracks, serviceability, durability and leakage. This paper is concentrated on the development of a finite element program which is capable of simulating the temperature history and the thermal stress considering creep and the modified elastic modulus due to inner temperature change and maturity. The analytical results in the inner parts highest important to control cracks are in good agreement with experimental data. Therefore this study may provide available method to control the cracks.

• Journal of the Korea Concrete Institute
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• v.17 no.1 s.85
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• pp.11-18
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• 2005

In order to accurately assess the stresses occurring in the early-age concrete, a compliance function which can consider the characteristics of early-age concrete is required. Existing compliance functions, however, have the limit that they have been deduced from the data of hardened concrete and therefore, do not take into account the fast development of material properties in early-age concrete. Furthermore, the distinction between instantaneous compliance and creep compliance is not clear in the existing experimental method. The purpose of present study is to propose a compliance function which can describe the rapid change of hardening processes in early-age concrete. To this end, a test method which can estimate the instantaneous compliance without creep effects in the early-age concrete was suggested first. Based on the suggested experimental method, tests on the instantaneous as well as creep compliance were performed using MTS automatic servo-loop test machine. The test results showed that both instantaneous and aging viscoelastic compliance, which are constants in B3 model, were functions in terms of age of concrete especially at early ages. Therefore, the modified compliance function based on B3 model was proposed to provide more realistic prediction on the behavior of early-age concrete. It is expected that the present model allows more realistic evaluation of varying stresses in concrete structures at early ages.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.555-560
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• 2003

Fatigue strength of concrete is ususlly presented by the Wohler Curve. But, new dimension T(time) from the view point of cyclic creep concept should be considerd. This paper presented four variable F-N-T-R relationship, this four variable relationship simultaneously accounts for the time effect and the effect of load rate. And analytical models are presented to predict fatigue strength of R/C beam strengthened with steel plate and carbon fiber sheet. Also, the correlation between the ratio of stress and the fatigue life was investigated.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.1A
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• pp.85-93
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• 2009

The primary objective of this study is to construct more simple and reasonable rheological model and propose a methodology for predicting a phenomenon of concrete creep. Deformations of concrete under sustained stress can be expressed by the sum of immediately elastic deformation, time-dependent and time-independent short-term creep, and long-term creep according to the mechanism and time-dependency. To simulate these deformations, a rheological model having six parameters was constructed. In the composing of each parameter, the microprestress-solidification theory and design model code were incorporated together with the numerical approach for the components which can not be theoretically approached. Finally, actual test data were applied in the verification of the proposed model, and suitability of the model was confirmed by comparisons with existing predicting models and design codes.

• Advances in concrete construction
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• v.9 no.3
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• pp.289-299
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• 2020

To investigate the long-term behavior of eccentrically loaded RC columns, which are more realistic in practice than concentrically loaded RC columns, long-term eccentric loading tests were conducted for 10 RC columns. Test parameters included concrete compressive strength, reinforcement ratio, bar yield strength, eccentricity ratio, slenderness ratio, and loading pattern. Test results showed that the strain and curvature of the columns increased with time, and concrete forces were gradually transferred to longitudinal bars due to the creep and shrinkage of concrete. The long-term behavior of the columns varied with the test parameters, and long-term effects were more pronounced in the case of using the lower strength concrete, lower strength steel, lower bar ratio, fewer loading-step, higher eccentricity ratio, and higher slenderness ratio. However, in all the columns, no longitudinal bars were yielded under service loads at the final measuring day. Meanwhile, the numerical analysis modeling using the ultimate creep coefficient and ultimate shrinkage strain measured from cylinder tests gave quite good predictions for the behavior of the columns.

• International Journal of Concrete Structures and Materials
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• v.1 no.1
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• pp.3-9
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• 2007

Fiber-reinforced self-compacting concrete (FRSCC) is a new type of concrete mix that can mitigate two opposing weaknesses: poor workability in fiber-reinforced concrete and cracking resistance in plain SCC concrete. This study focused on early-age cracking of FRSCC due to restrained drying shrinkage, one of the most common causes of cracking. In order to investigate the effect of fiber on shrinkage cracking of FRSCC, ring shrinkage tests were performed for polypropylene and steel fiber-reinforced SCC. In addition, finite element analyses for those specimens were carried out considering drying shrinkage based on moisture diffusion, creep, cracking resistance of concrete, and the effect of fiber. The analysis results were verified via a comparison between the measured and calculated crack width. From the test and analysis results, the effectiveness of fiber with respect to reducing cracking was confirmed and some salient features on the shrinkage cracking of FRSCC were obtained.

• Structural Engineering and Mechanics
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• v.60 no.2
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• pp.301-312
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• 2016

In a concrete member under pure tension, the stress in concrete is uniformly distributed over the whole concrete section. It is supposed that a local bond failure occurs at each crack, and there is a relative slip between steel and surrounding concrete. The compatibility of deformation between the concrete and reinforcement is thus not maintained. The bond transfer length is a length of reinforcement adjacent to the crack where the compatibility of strain between the steel and concrete is not maintained because of partially bond breakdown and slip. It is an empirical measure of the bond characteristics of the reinforcement, incorporating bar diameter and surface characteristics such as texture. Based on results from a series of previously conducted long-term tests on eight restrained reinforced concrete slab specimens and material properties including creep and shrinkage of two concrete batches, the ratio of final bond transfer length after all shrinkage cracking, to THE initial bond transfer length is presented.