Shrinkage, Cracking and Deflection-the Serviceability of Concrete Structures

 

R.I. Gilbert

Professor and Head, School of Civil and Environmental Engineering
The University of New South Wales

Sydney, NSW, 2052

Email: i.gilbert@unsw.edu.au


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.

 

Keywords

 

Creep; Cracking; Deflection; Reinforced concrete; Serviceability; Shrinkage.