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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Showing 1-5 of 13 Abstracts search results
May 1, 2000
D. J. Carreira and R. G. Burg
This paper summarizes most of the aspects and details related to testing for creep and shrinkage in concrete. The experimental determination of con-crete creep and shrinkage is discussed in detail, analyzing each of the condi-tions likely to be encountered during planning, testing and reporting test data. The subjects discussed are: objectives of test programs, test concept, as-sumptions, designing a test program, standard test methods for creep and shrinkage, test specimens, equipment for measuring deformations, concrete-mixing, batching and preparation of test specimens, testing environments, tem-perature and humidity tolerances, deformation measurement schedule, docu-mentation and interpretation of test results. Test programs are presented in detail. Field studies are discussed and correlated to laboratory test programs for three types structures sensitive in varying degrees to effects of creep and shrinkage. That is, field studies of reinforced and prestressed concrete nuclear containments, the uneven long-term shortening of columns with respect to the shear walls in reinforced concrete high rise buildings with shear walls, and the determination of prestressing forces, cambers, deflections and prestress loss in prestressed members.
D. J. Carreira, M. Daye, and L. R. Greening
This paper presents a simplified, comprehensive and rational method to account for the effects of creep and shrinkage in reinforced concrete struc-tures. The analysis of the effects of creep and shrinkage on reinforced and prestressed concrete structure is a multifaceted problem. In general, creep and shrinkage are not common knowledge and concern of most structural engineers. The procedure includes (a) a simplified estimation of the creep and shrinkage strains in plain concrete, (b) the analysis of the effect of creep on reinforced concrete structures using the age-adjusted modulus of elasticity, (c) the analysis of the effects of shrinkage using an equivalent temperature drop. (d) the relaxation of stresses, internal forces and moments from imposed deformations, (e) the analysis of thermal changes on structures. An introductory approach of analysis of concrete structures creep and shrinkage should be satisfactory for structures not critically sensitive to the effects of creep and shrinkage. For structures sensitive to these effects, such as tall buildings or record span bridges, a more advanced analysis will be necessary, which is beyond the scope of this paper. The presented method includes most of the aspects affecting the effects of creep and shrinkage on concrete struc-tures, and it may be coupled with more advanced treatment of specifically related subjects.
M. A. Chiorino, L. Dezi, and A. M. Tarantino
Variation of statistical scheme of reinforced and prestressed concrete struc-tures is frequent in modern construction techniques. Construction sequences may include application of permanent loads and of prestressing in one or more steps, and connection of different portions of the structure, or introduction of additional restraints (sometime forcedly applied to correct the internal stress conditions), at different ages during or after the construction process. The resulting stress distribution is largely influenced by the time-dependent deformability of concrete. The paper presents a unified approach for its evalu-ation based on the linear theory of viscoelasticity for aging materials, which is normally adopted for modeling concrete creep, evidencing the important role played by the non-dimensional redistribution function (t, to, t1) describing the creep induced stress variation at time t for loading at t, and variation of re-straint conditions at t,. The obtained solutions are exact for all problems of variation of restraint conditions in homogeneous structures with rigid restraints, and normally suffkiently accurate for problems concerning structures charac-terized by heterogeneities in the properties of concrete along their structural configuration. Redistribution function may be computed from the creep function J characterizing the creep prediction model under consideration and made available in terms of design aids (graphs or tables). The computational procedure is illustrated and an example of application to a typical structural problem is presented.
K. Sakata and T. Ayano
The effect of ambient temperature and humidity to which concrete is exposed prior to or during loading should be taken into account; when creep and shrinkage are predicted. The purpose of this study is to clarify the effect of ambient temperature and humidity on the creep and shrinkage of concrete. In this study, we carried out creep and shrinkage tests under constant and varying histories of temperature and humidity. Creep and shrinkage tests sub-jected to ambient temperature and humidity were also carried out in the room where the effect of rain and wind were negligible. The effect of temperature on shrinkage is much bigger than that of changes in humidity. The shrinkage strain on concrete subjected to increase in temperature is much bigger than that measured under constant temperature. The magnitude of creep and shrinkage is highly influenced by the difference of the season in which concrete is cast. The effect or variance of humidity on creep seems to be small. The temperature of curing water before application of load significantly influenced creep of concrete.
Z. P. Bazant and S. Baweja
A simple model for the characterization of concrete creep and shrinkage in design of concrete structures is proposed. It represents a shortened form of model B3 which was presented in  (as and improvement of the original version ) and appears in this volume, and an update of a previous short form . The main simplification compared to model B3 comes from the use of the log-double-power law as the basic creep compliance function. The B3 formulae for predicting material parameters in the model are simplified by dropping the dependence of these parameters on the composition of concrete mix, leaving only dependence on the strength and the specific water content of the concrete mix. The model is justified by statistical comparisons with all the data in the internationally accepted RILEM data bank. The differences be-tween the present short-form and model B3 are discussed and limitations of the short form are compared to model B3 are noted. The model is suitable for design of concrete structures with the exception of highly creep-sensitive struc-tures for which the full model B3 is necessary
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