Tension Stiffening in Reinforced Concrete Members with
Large Diameter Reinforcement

Abstract

Modern structural designs increasingly often call for the use of large diameter reinforcement as well as full de
ection calculations to be carried out in serviceability
limit state analysis. In order to achieve this effectively knowledge of the nature of time dependent eects such as tension stiffening is required. There is, however, virtually no experimental data available for reinforced concrete with bar diameters greater than 25 mm. This project aims to identify the behaviour of tension stiffening for reinforced concrete specimens with large diameter reinforcement under sustained loading. Four
tension specimens with single H25, H32, H40 and H50 strain gauged reinforcing bars were tested at multiple load stages. In addition, a finite element model was developed
in ABAQUS with the aim of evaluating various steel concrete interface models. The applicability of finite element models in the structural analysis of reinforced concrete
was also evaluated. The experimental results indicate that the existing conclusions for small diameter cases hold for the larger diameters. Tension stiffening, however, decays
at a much higher rate than previously believed and reached a constant value within a maximum of 10 days in each case. The suggestion that only the long-term calculation methods presented in the various building codes for tension stiffening should be used for serviceability limit state calculations is supported. Additionally, a trend is identified which indicates a decrease in tension stiffening decay time with increasing bar diameter.