Revised code provisions for long-term deflection calculations

Abstract

It is well established that tension stiffening, the contribution of the concrete in tension to the stiffness of a reinforced concrete member, is a significant parameter in deflection calculations and this is recognised by design codes such as BS 8110 and Eurocode 2. These codes make provision for tension stiffening effects and also distinguish between short- and long-term behaviour. What is not known, however, is how rapidly tension stiffening decays with time or how significant this rate of decay might be for deflection calculations. This paper reviews the current approaches to tension stiffening in BS 8110 and Eurocode 2 and then summarises a major experimental investigation which was undertaken to explore time dependent aspects. Revisions to BS 8110 and Eurocode 2 are proposed as a result of this work. Further refinements for modelling tension stiffening effects in reinforced concrete members are also described.