Deflection Calculation and Control -Australian Code Amendments and Improvements


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Title: Deflection Calculation and Control -Australian Code Amendments and Improvements

Author(s): R. I. Gilbert

Publication: Special Publication

Volume: 203


Appears on pages(s): 45-78

Keywords: cracking; creep; deflection; design; prestressed concrete; reinforced concrete; serviceability; service loads; shrinkage; structural behavior; time-dependent behavior

Date: 8/1/2001

This paper describes the behavior of reinforced and prestressed concrete flexural members under sustained service loads and outlines recent developments in the design of concrete structures for the serviceability limit states, particularly with regard to deflection and crack control. The effects of concrete cracking, creep and shrinkage on cross-sectional stresses and deformation are demonstrated and discussed for a wide range of actions and reinforcement layouts. Recent amendments to the serviceability provisions of the Australian Standard for Concrete Structures AS3600 are presented and the background to, and reasons for, the proposed changes are explained. The paper also highlights the inadequacies of the existing deflection calculation procedure in AC1 3 I8M-99 and suggests ways to improve it. A method is proposed for calculating the time-dependent deflection of reinforced and prestressed concrete members taking into account the time-dependent effects of creep and shrinkage, including the loss of stiffness caused by shrinkage induced cracking and the breakdown of tension stiffening with time. The method is illustrated by several examples.