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1、American Concrete Institute“ Advancing concrete knowlee io-Editors: N. J. Gardner and Jason Weiss SP-227 Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=Aramco HQ/9980755100 Not for Resale, 03/18/2007 06:52:13 MDTNo reproduction or networking permitted without l
2、icense from IHS -,-,- Shrinkage and Creep of Concrete Editors N. J. Gardner Jas on Weiss American Concrete Institute“ Advancing concrete knowlecige SP-227 Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=Aramco HQ/9980755100 Not for Resale, 03/18/2007 06:52:13 MD
3、TNo reproduction or networking permitted without license from IHS -,-,- First printing, April 2005 DISCUSSION of individual papers in this symposium may be submitted in accordance with general requirements of the AC1 Publication Policy to AC1 headquarters at the address given below. Closing date for
4、 submission of discussion is October 2005. All discussion approved by the Technical Activities Committee along with closing remarks by the authors will be published in the JanuaryFebruary 2005 issue of either AC1 Structural Journal o r a Materials Journal depending on the subject emphasis of the ind
5、ividual paper. The Institute is not responsible for the statements or opinions expressed in its publications. Institute publications are not able to, nor intended to, supplant individual training, responsibility, or judgment of the user, or the supplier, of the information presented. The papers in t
6、his volume have been reviewed under Institute publication procedures by individuals expert in the subject areas of the papers. Copyright O 2005 AMERICAN CONCRETE INSTITUTE P.O. Box 9094 Farmington Hills, Michigan 48333-9094 All rights reserved, including rights of reproduction and use in any form or
7、 by any means, including the making of copies by any photo process, or by any electronic or mechanical device, printed or written or oral, or recording for sound or visual reproduction or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyri
8、ght proprietors. Printed in the United States of America Editorial production: Lindsay K. Kennedy Library of Congress catalog card number: 2005922742 ISBN: 0-8703 1 - 178-6 Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=Aramco HQ/9980755100 Not for Resale, 03/1
9、8/2007 06:52:13 MDTNo reproduction or networking permitted without license from IHS -,-,- Preface Why should you be interested in the shrinkage and creep of concrete? To put this question into perspective, the load induced elastic (immediate) strains in concrete are of the order of 300 microstrain,
10、depending upon stress level. The ultimate drying shrinkage can range from 400 x 1 O“ to 900 x i O“. The creep strain can be 25% to 70% of the immediate strain after 24 hours and may be several multiples of the immediate strain after several years, depending on the relative humidity. If concrete is r
11、estrained against shrinkage it can crack. Structural engineers are concerned with the consequences of shrinkage, creep and cracking on the serviceability and durability of their structures. Creep increases deflections, reduces prestress in prestressed concrete elements, and causes redistribution of
12、internal force resultants in redundant structures. Shrinkage can cause warping of slabs on grade due to differential drying and increased deflections of non- symmetrically reinforced concrete elements. Materiais scientists are concerned with understanding the basic phenomena and assessing new materi
13、als and the effects of admixtures on the mechanical behavior of concrete. Concrete is an age stiffening material that has little tensile strength, shrinks, and exhibits creep in sealed conditions and additional drying creep in drying environments. Predicting the amount of shrinkage and deflection th
14、at may occur is not easy and is especially complicated in concrete that contains supplementary materials, chemical admixtures, and lightweight aggregates. Supplementary cementing materials and waste products are being used in increasing volumes in response to environmental concerns. Admixtures have
15、been developed to modifi the behavior of fresh and hardened concrete. Self consolidating concrete is being used in more applications. A recent development is the marketing of shrinkage reducing admixtures. This volume contains papers presented during four sessions sponsored by AC1 Committee 209, Cre
16、ep and Shrinkage in Concrete, and AC1 Committee 23 1, Properties of Concrete at Early Ages, held at the AC1 Spring 2005 Convention. The subjects addressed by the authors are diverse and cover many aspects of shrinkage and creep. Some papers pay special attention to the development, use, and evaluati
17、on of models to predict shrinkage, creep, and deflection, while other papers consider the behavior of early age concretes that are restrained from shrinking, resulting in the development of residual stresses and cracking. Papers are presented to evaluate models for predicting shrinkage and creep, wh
18、ich is especially crucial as AC1 Committee 209 attempts to refine the models that will are presented in the ACI Manual o f Concrete Practice. Several papers provide a field assessment of creep and shrinkage in concrete structures, thereby providing an explanation of how field data should be collecte
19、d and how this data can be used to refine predictive models. Other papers deal with an improved understanding of early-age tensile stress development, including demonstrating the measurement of creep and iii Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=Aramco
20、 HQ/9980755100 Not for Resale, 03/18/2007 06:52:13 MDTNo reproduction or networking permitted without license from IHS -,-,- stress development. One paper presents experimental results to quanti differential drying and thermal deflections in slabs. This volume also recognizes that modem concretes ar
21、e now no longer a simple mixture of water, cement, and aggregate. This volume discusses specific aspects of how the shrinkage of these modern concretes may differ from concrete made using conventional materials. Specifically, several papers deal with the shrinkage and curing of concrete containing s
22、upplementary cementing materials, which is especially important as the use of these materials is rapidly rising. The shrinkage and creep behaviour of high-strength, lightweight concrete is also evaluated and compared to existing models. One paper assesses the cracking behavior of self- consolidating
23、 concrete, a rapidly emerging material that is often suspected to be sensitive to shrinkage related concerns due to the higher paste volume that may exist in these mixtures. It is shown that self-consolidating concretes can be made to be resistant to cracking. Finally, this volume describes a study
24、that is focused on the development of an approach to describe the shrinkage and early age stress development in concrete containing shrinkage reducing admixtures. This volume includes significant contributions by many leading research and practicing engineers in the field of shrinkage and creep. The
25、 descriptions of field problems and the assessment of the accuracy of predictive models may assist practicing engineers. For researchers, the contents of this volume should be useful in the development and evaluation of future models and laboratory measurements. Finally, it should be noted that many
26、 people have contributed to the successful development of these proceedings, and the editors, and authors, thank all of the anonymous reviewers who assisted in reviewing the papers. Co-Editors N.J. Gardner Jason Weiss iv Copyright American Concrete Institute Provided by IHS under license with ACI Li
27、censee=Aramco HQ/9980755100 Not for Resale, 03/18/2007 06:52:13 MDTNo reproduction or networking permitted without license from IHS -,-,- TABLE OF CONTENTS . Preface 111 SP-227-1: Managing Deflection, Shortening and Crack Arising from Restrained Contraction . 1 by S. J. Alexander SP-227-2: AS3600 Cr
28、eep and Shrinkage Models for Normal and High Strength Concrete 2 1 by R. I. Gilbert SP-227-3: Sensitivty of the Models for Predicting Shrinkage of Concrete . 4 1 by A. Al-Manaseer and S. Ristanovic SP-227-4: Deviations from the Principle of Superposition and their Consequences on Structural Behavior
29、 . 67 by S. Staquet and B. Espion SP-227-5: Design Implication of Creep and Shrinkage in Integral Abutment Bridges . 85 by M. Arockiasamy and M. Sivakumar SP-227-6: A Rational Approach to the Analysis of Structural Effects due to Creep . 107 by M. A. Chiorino SP-227-7: Shrinkage and Creep Prediction
30、s Evaluated using 10-year Monitoring of the North Halawa Valley Viaduct 143 by I. N. Robertson and X. Li SP-227-8: Tension Cracking in Columns Under Compression Loads . 163 by D. J. Carreira SP-227-9: Estimating Time-Dependent Deformations of Prestressed Elements: Accuracy and Variability 195 by M.
31、W. Pauken, S. D. B. Alexander, and D. M. Rogowsky SP-227-10: Shrinkage of Virginia Transportation Concrete Mixtures 2 17 by D. W. Mokarem, R. E. Weyers, and M. M. Sprinkel SP-227-11: Design Aids for the Evaluation of Creep Induced Structural Effects . 239 by M. Sassone and M. A. Chionno V Copyright
32、American Concrete Institute Provided by IHS under license with ACI Licensee=Aramco HQ/9980755100 Not for Resale, 03/18/2007 06:52:13 MDTNo reproduction or networking permitted without license from IHS -,-,- SP-227-12: Effect of Modulus of Elasticity on Creep Prediction of High Strength Concrete Cont
33、aining Pozzoans 261 by N. Suksawang and H. H. Nassif SP-227-13: Shrinkage Behavior and Residual Stress Development in Mortar Containing Shrinkage Reducing Admixtures (SRAS) 285 by B. Pease, H. Shah, and J. Weiss SP-227-14: Performance of Self-Consolidating Concrete Under Restrained Shrinkage 303 by
34、H. T. See and E. K. Attiogbe SP-227-15: Long-Term Creep and Shrinkage in High-Strength Lightweight Concrete . 3 i 7 by M. Lopez, L. Kahn, K. Kurtis, and B. Buchberg SP-227-16: Stress Relaxation of Concrete Under Autogenous Early-Age Restrained Shrinkage 337 by M. Pigeon, B. Bissonnette, J. Marchand,
35、 D. Boily, and L. Barcelo SP-227-17: Modeling Early Age Tension Creep and Shrinkage of Concrete . 349 by M. D. DAmbrosia and D. A. Lange SP-227-18: Evaluation of Thermal Warping in Pavements . 367 by M. A. Miltenberger, E. K. Attiogbe, and A. R. Stoddard . vi Copyright American Concrete Institute Pr
36、ovided by IHS under license with ACI Licensee=Aramco HQ/9980755100 Not for Resale, 03/18/2007 06:52:13 MDTNo reproduction or networking permitted without license from IHS -,-,- Managing eflection, Shortening and Cracking Arising from Restrained Contraction by S. J. Alexander SvnoDsis: Concrete shrin
37、ks. Steel doesn?t, and the resistance of reinforcement to shrinkage causes deflection of slabs and beams and shortening of columns and walls. A simple visualization is given, and used to derive formulae for analysis. Current methods of calculating shrinkage curvature and deflection in reinforced sec
38、tions are examined and compared, concluding that the AC1 method appears realistic while the UK and European methods significantly over-estimate the deflection. Restraint by differential contraction between an insitu concrete overlay and an older substrate produces tension in the overlay and curvatur
39、e and deflection of the composite unit. A method for calculating this is given, and the resulting effects are found - to be significant in certain circumstances. The method is extended to consider shrinkage in insitu slabs in steel-concrete composite construction. The deflection from shrinkage is fo
40、und to be approaching spani750, and cracking in the slabs is predicted in some cases. External restraint to contraction induces tensile stresses, and a rational approach to providing sufficient reinforcement to control cracking in direct tension is given. It is particularly relevant to elements whic
41、h need to be water-resisting, and a case study of a basement is presented. The reinforcement needed to control cracking reliably is found to exceed most current US, UK and European recommendations. bywords: composite beams; cracking; creep; deflection; design; early age contractions; overlays; reinf
42、orced concrete; restraint; serviceability; shortening; shrinkage; structural analysis 1 Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=Aramco HQ/9980755100 Not for Resale, 03/18/2007 06:52:13 MDTNo reproduction or networking permitted without license from IHS -
43、,-,- 2 Alexander AC1 member Stuart Alexander is UK-based Group Technical Coordinator for world-wide engineering consultancy WSP Group. This involves publishing material on the intranet- based technical library, preparing and delivering seminars, and giving expert advice. He is also a regular contrib
44、utor to technical journals, particularly on movements in building structures. INTRODUCTION Concrete contracts and shrinks. The main effects to be considered in design are early age contraction, temperature drop and long-term drying shrinkage. Restraint arises in a number of ways. Embedded reinforcem
45、ent causes deflection of slabs and beams and contributes to shortening of columns and walls. Casting concrete against a previous pour or as an overlay on top of an older substrate induces tensile stresses that can cause cracking. So do metal decking and supporting beams in steel-concrete composite c
46、onstruction. Similarly, external restraint from rigid elements such as in-plane walls, piles and pile caps, and even friction from the underlying soil, can cause cracking. Shrinkage is also significant in concrete roads and industrial ground floors, but the paper is limited to typical structural ele
47、ments in buildings. The paper considers how to quanti these effects, and makes recommendations for managing them. LIFE CYCLE OF CONCRETE Concrete typically goes through the following life cycle: Early age contractions. In the first three to six days, the hydration process first causes the concrete t
48、o heat up - from a casting temperature that is usually already a few degrees above ambient. During this period, it behaves in a plastic manner so the only result is an increase in volume. However, when it cools to ambient temperature (Figure i) it has hardened enough to go into tension and may crack if it is restrained. At the same time, shrinkage (a complex combination of actions, see Altoubat and Lange (1) also occurs, adding to the contractions. Strength gain. In the following three to four weeks (longer in mixtures with flyash or slag),