【正文】 tory, providing the designer satisfies certain detailing requirements. These involve maximum limits on the centretocentre spacing of bars and on the distance from the side or soffit of the beam to the nearest longitudinal bar. These limits do not depend on the stress in the tensile steel under service loads and have been found to be unreliable when the steel stress exceeds about 240 MPa. The provisions of AS36001994 oversimplify the problem and do not always ensure adequate control of cracking. With the current move to higher strength reinforcing steels (characteristic strengths of 500 MPa and above), there is an urgent need to review the crackcontrol design rules in AS3600 for reinforced concrete beams and slabs. The existing design rules for reinforced concrete flexural elements are intended for use in the design of elements containing 400 MPa bars and are sometimes unconservative. They are unlikely to be satisfactory for members in which higher strength steels are used, where steel stresses at service loads are likely to be higher due to the reduced steel area required for strength. 6. Conclusions The effects of shrinkage on the behaviour of reinforced and prestressed concrete members under sustained service loads has been discussed. In particular, the mechanisms of shrinkage warping in unsymmetrically reinforced elements and shrinkage cracking in restrained direct tension members has been described. Recent amendments to the serviceability provisions of AS3600 have been outlined and techniques for the control of deflection and cracking are presented. Reliable procedures for the prediction of longterm deflections and final crack widths in flexural members have also been proposed and illustrated by examples. Electronic Journal of Structural Engineering, 1 ( 2021) 21 收縮，開裂和 變形 – 混凝土結(jié)構(gòu) 使用的可靠性 里吉爾伯特 土木及環(huán)境工程學(xué)校 校長兼 教授 新南威爾士大學(xué)，悉尼，新南威爾士州 2052 號 電子郵件： 摘要 本文 討 論收縮對混凝土結(jié)構(gòu) 可靠性的影響 ，它概述了為什么收縮是重要的，它的主要 影響，即 對 結(jié)構(gòu)最終 的開裂程度和 撓度大小的影響，以及在設(shè)計中應(yīng)該注意什么？有一種模型可以預(yù)測在普通混凝土、高強(qiáng)度不穩(wěn)定性普和鋼筋混凝土中的收縮應(yīng)變 ， 無論有 沒有外部約束 的情況下 ， 都可以用這種模型來 解釋。 Serviceability。 Deflection。Electronic Journal of Structural Engineering, 1 ( 2021) 15 Shrinkage, Cracking and Deflection the Serviceability of Concrete Structures . Gilbert Professor and Head, School of Civil and Environmental Engineering The University of New South Wales, Sydney, NSW, 2052 Email: 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 th e 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 timedependent 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 longterm 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。 Reinforced concrete。 Shrinkage. 1. Introduction For a concrete structure to be serviceable, cracking must be controlled and deflections must not be excessive. It must also not vibrate excessively. Concrete shrinkage plays a major role in each of these aspects of the service load behaviour of concrete structures. The design for serviceability is possibility the most difficult and least well understood aspect of the design of concrete structures. Service load behaviour depends primarily on the properties of the concrete and these are often not known reliably at the design stage. Moreover, concrete behaves in a nonlinear and inelastic manner at service loads. The nonlinear behaviour that plicates serviceability calculations is due to cracking, tension stiffening, creep, and shrinkage. Of these, shrinkage is the most problematic. Restraint to shrinkage causes timedependent cracking and gradually reduces the beneficial effects of tension stiffening. It results in a gradual widening of existing cracks and, in flexural members, a significant increase in deflections with time. The control of cracking in a reinforced or prestressed concrete structure is usually achieved by limiting the stress increment in the bonded reinforcement to some appropriately low value and ensuring that the bonded reinforcement is suitably distributed. Many codes of practice specify maximum steel stress increments after cracking and maximum spacing requirements for the bonded reinforcement. However, few existing code procedures, if any, account adequately for the gradual increase in existing crack widths with time, due primarily to shrinkage, or the timedependent development of new cracks resulting from tensile stresses caused by restraint to shrinkage. For deflection control, the structural designer should select maximum deflection limits that are appropriate to the structure and its intended use. The calculated deflection (or camber) must not exceed these limits. Codes of practice give general guidance for both the selection of the maximum deflection limits and the calculation of deflection. However, the simplified procedures for calculating deflection in eJSE International Electronic Journal of Structural Engineering, 1 ( 2021) 16 most codes were developed from tests on simplysupported reinforced concrete beams and often produce grossly inaccurate pr