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This paper presents a simple design-office procedure for calculating the shrinkage and creep of concrete using the information available at design; namely the 28 day specified concrete strength, the concrete strength at end of curing or loading, element size and the relative humidity. The method includes strength development with age, relationship between modulus of elasticity and strength, and equations for predicting shrinkage and creep. The only arbitrary information are the factors appropriate to the cementitious material, which can be improved from measured strength age data. At the most basic level the proposed method requires only the information available to the design engi-neer. The prediction values can be improved by simply measuring concrete strength development with time and modulus of elasticity. Aggregate stiffness can be taken into account by back calculating a concrete pseudo strength from the measured modulus of elasticity. Measured short term shrinkage and creep values can be extrapolated to obtain long duration predictions for simi-lar sized elements. The predictions are compared with experimental results for seventy nine data sets for compliance and sixty three data sets for shrink-age. The comparisons indicate shrinkage and creep can be calculated within +/- 25%. The method can be used regardless of what chemical admixtures or mineral by-products are in the concrete, casting temperature or curing regime.

This paper discusses possible mechanisms of basic creep and autogenous shrinkage and their couplings. The starting point is a kinetics analysis of the basic creep of different types of concrete, a normal strength concrete and a high performance concrete. This approach reveals two domains: short term creep kinetics, active for some days after loading, and long term creep kinet-ics, characterized by a pronounced and non-asymptotic aging. Then, by ex-ploring the creep-shrinkage interaction under sealed conditions, we confirm that the long term autogenous skrinkage, which cannot be explained by pure hydration effects, can be associated with a matrix creep under internal pore pressure. This pressure seems to depend mainly on the water:cement ratio. Finally, we present some preliminary experimental results on the creep dila-tancy behavior of concrete. The results indicate that the short term creep is characterized by a viscous dilatant behavior (i.e., positive volume increase rate), while the long term creep is of rather non-dilatant nature occurring at constant volume.

This paper, supplementing the exposition of model B3 in this volume, examines various basic questions in formulating and evaluating a prediction model for creep and shrinkage of concrete. Verification by comparisons to a few subjectively selected data sets is no longer justifiable because computers have made statistical comparisons to the existing internationally accepted compre-hensive data bank very easy. The statistics based on the data bank alone, however, are insufficient. There are three further criteria: (1)After optimizing its coefficients, the prediction model should be capable of providing close fits of the individual test data covering a broad range of times, ages, humidities, thicknesses, etc.; (2) the model should have a rational, physically justified theoretical basis, and (3) should allow good and easy extrapolation of the short-time tests into long times, at high ages at loading, large thicknesses etc. The last criterion is paramount because good long-time predictions can be achieved only through updating based on short-time data for the given par-ticular concrete. Various aspects of the B3 model and the GZ model (also appearing in this volume), recently considered by ACI Committee 209, as well as some aspects of the CEF-FIP model, are briefly analyzed in the light of these criteria, clarifying their advantages and differences.

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.

This Symposium Publication contains 12 papers presented at the Adam Neville Symposium in Atlanta, Georgia, in 1997. Topics relating to creep and shrinkage include admixture and cementitious materials effects, special high-performance considerations, temperature and humidity influences, reinforced and prestressed concrete analysis and design procedures, and much more. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP194