Shrinkage, Cracking and Deflection-the Serviceability of Concrete Structures

Ian  Gilbert

doi:10.56748/ejse.1121

Authors

R.I. Gilbert UNSW Sydney https://orcid.org/0000-0001-8540-6517

DOI:

https://doi.org/10.56748/ejse.1121

Keywords:

Cracking, Deflection, Reinforced concrete, Serviceability, Shrinkage

Abstract

This paper addresses the effects of shrinkage on the serviceability of concrete structures. It outlines why shrinkage is important, its major influence on the final extent of cracking and the magnitude of deflection in structures, and what to do about it in design. A model is presented for predicting the shrinkage strain in normal and high strength concrete and the time-dependent behaviour of plain concrete and reinforced concrete, with and without external restraints, is explained. Analytical procedures are described for estimating the final width and spacing of both flexural cracks and direct tension cracks and a simplified procedure is presented for including the effects of shrinkage when calculating long-term deflection. The paper also contains an overview of the considerations currently being made by the working group established by Standards Australia to revise the serviceability provisions of AS3600-1994, particularly those clauses related to shrinkage.

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Author Biography

R.I. Gilbert, UNSW Sydney

Ian Gilbert is Professor of Civil Engineering and Head of the School of Civil and Environmental Engineering at the University of New South Wales. His main research interests have been in the area of serviceability and the time-dependent behaviour of concrete structures. His publications include three books and over one hundred refereed papers in the area of reinforced and prestressed concrete structures. He has served on Standards Australia’s Concrete Structures Code Committee BD/2 since 1981 and was actively involved in the development of AS3600. He is currently chairing two of the Working Groups (WG2 – Anchorage and WG7 – Serviceability) established to review AS3600. Professor Gilbert was awarded the Chapman Medal by the IEAust in 2000 and is the 2001 Eminent Speaker for the Structural College, IEAust.

References

AS3600-1994, Australian Standard for Concrete Structures, Standards Australia, Sydney, (1994).

ACI318-95, Building code requirements for reinforced concrete, American Concrete Institute, Committee 318, Detroit, 1995.

Base, G.D. and Murray, M.H., “New Look at Shrinkage Cracking”, Civil Engineering Transactions, IEAust, V.CE24, No.2, May 1982, 171pp.

Branson, D.E., “Instantaneous and Time-Dependent Deflection of Simple and Continuous RC Beams”, Alabama Highway Research Report, No.7, Bureau of Public Roads, 1963.

DD ENV-1992-1-1 Eurocode 2, Design of Concrete Structures, British Standards Institute, 1992.

Favre, R., et al., “Fissuration et Deformations”, Manual du Comite Ewo-International du Beton (CEB), Ecole Polytechnique Federale de Lausanne, Switzerland, 1983, 249 p.

Gilbert, R.I., “Time Effects in Concrete Structures”, Elsevier Science Publishers, Amsterdam, 1988, 321p.

Gilbert, R.I., “Shrinkage Cracking in Fully Restrained Concrete Members”, ACI Structural Journal, Vol. 89, No. 2, March-April 1992, pp 141-149 DOI: https://doi.org/10.14359/2917

Gilbert, R.I., “Serviceability Considerations and Requirements for High Performance Reinforced Concrete Slabs”, Proceedings International Conference On High-Performance High Strength Concrete, Curtin University of Technology, Perth, Western Australia, August 1998, pp 425-439.

Gilbert, R.I., "Deflection Calculations for Reinforced Concrete Structures - Why we sometimes get it Wrong", ACI Structural Journal, Vol. 96, No. 6, November-December 1999(a), pp 1027 - 1032. DOI: https://doi.org/10.14359/779

Gilbert, R.I., “Flexural Crack Control for Reinforced Concrete Beams and Slabs: An Evaluation of Design Procedures”, ACMSM 16, Proceedings of the 16th Conference on the Mechanics of Structures and Materials, Sydney, Balkema, Rotterdam, 1999(b), pp 175-180.

Gilbert, R.I. and Mickleborough, “Design of Prestressed Concrete”, E & FN Spon, London, 2nd Printing, 1997, 504p.

Gilbert, R.I., Patrick, M. and Adams, J.C., “Evaluation of Crack Control Design Rules for Reinforced Concrete Beams and Slabs”, Concrete 99, Bienniel Conference of the Concrete Institute of Australia, Sydney, 1999, pp 21-29.